Serum chemistry profiling and prognostication in systemic mastocytosis: a registry-based study of the ECNM and GREM

Certain laboratory abnormalities correlate with subvariants of systemic mastocytosis (SM) and are often prognostically relevant. To assess the diagnostic and prognostic value of individual serum chemistry parameters in SM, 2607 patients enrolled within the European Competence Network on Mastocytosis (ECNM) and 575 patients enrolled within the German Registry on Eosinophils and Mast Cells (GREM) were analyzed. For screening and diagnosis of SM, tryptase was identified as the most specific serum parameter. For differentiation between indolent and advanced SM (AdvSM), the following serum parameters were most relevant: tryptase, alkaline phosphatase (AP), ß2-microglobulin, lactate dehydrogenase (LDH), albumin, vitamin B12, and C-reactive protein (P<0.001). With regard to subvariants of AdvSM, an elevated LDH ≥260U/L was associated with multi-lineage expansion (leukocytosis, r=0.37, P<0.001; monocytosis, r=0.26, P<0.001) and the presence of an associated myeloid neoplasm (P<0.001), whereas tryptase levels were highest in mast cell leukemia (MCL vs. non-MCL, 308 µg/L vs. 146 µg/L, P=0.003). Based on multivariable analysis, the hazard-risk weighted assignment of 1 point to lactate dehydrogenase (HR 2.1 [95% CI 1.1-4.0], P=0.018) and 1.5 points each to ß2-microglobulin (HR 2.7 [95% CI 1.4-5.4], P=0.004) and albumin (HR 3.3 [95% CI 1.7-6.5], P=0.001) delineated a highly predictive three-tier risk classification system (0 points, 8.1 years vs. 1 point, 2.5 years, ≥1.5 points, 1.7 years; P<0.001). Moreover, serum chemistry parameters enabled further stratification of IPSM-AdvSM1/2 risk-score classified patients (P=0.027). In conclusion, serum chemistry profiling is a crucial tool in the clinical practice supporting diagnosis and prognostication of SM and its subvariants.

Allogeneic Hematopoietic Cell Transplantation in Advanced Systemic Mastocytosis: A retrospective analysis of the DRST and GREM registries

We identified 71 patients with AdvSM (aggressive SM [ASM], SM with an associated hematologic neoplasm [SM-AHN, e.g., acute myeloid leukemia, SM-AML], mast cell leukemia [MCL]) in two national registries (DRST/GREM) who received an allogeneic hematopoietic cell transplantation (alloHCT) performed in Germany from 1999-2021. Median overall survival (OS) of ASM/SM-AHN (n = 30, 45%), SM-AML (n = 28, 39%) and MCL ± AHN (n = 13, 19%) was 9.0, 3.3 and 0.9 years (P = 0.007). Improved median OS was associated with response of SM (17/41, 41%; HR 0.4 [0.2-0.9], P = 0.035) and/or of AHN (26/43, 60%, HR 0.3 [0.1-0.7], P = 0.004) prior to alloHCT. Adverse predictors for OS included absence of KIT D816V (10/61, 16%, HR 2.9 [1.2-6.5], P < 0.001) and a complex karyotype (9/60, 15%, HR 4.2 [1.8-10.0], P = 0.016). HLA-match, conditioning type or transplantation at centers reporting above-average alloHCTs (≥7) had no impact on OS. Taking into account competing events at years 1, 3 and 5, relapse-related mortality and non-relapse mortality rate were 15%/23%, 20%/30% and 23%/35%, respectively. Irrespective of subtype, subsequent treatment response was achieved in 13/30 (43%) patients and was highest on midostaurin/avapritinib (7/9, 78%). We conclude that outcome of alloHCT in AdvSM is more affected by disease phenotype and treatment response prior to transplant than by transplant characteristics.

Poor Applicability of Currently Available Prognostic Scoring Systems for Prediction of Outcome in KIT D816V-Negative Advanced Systemic Mastocytosis

Within our nationwide registry, we identified a KIT D816V mutation (KIT D816Vpos.) in 280/299 (94%) patients with advanced systemic mastocytosis (AdvSM). Age, cytopenias and the presence of additional somatic mutations confer inferior overall survival (OS). However, little is known about the characteristics of KIT D816V-negative (D816Vneg.) AdvSM. In 19 D816Vneg. patients, a combination of clinical, morphological and genetic features revealed three subgroups: (a) KIT D816H- or Y-positive SM (KIT D816H/Ypos., n = 7), predominantly presenting as mast cell leukemia (MCL; 6/7 patients), (b) MCL with negative KIT sequencing (KITneg. MCL, n = 7) and (c) KITneg. SM with associated hematologic neoplasm (KITneg. SM-AHN, n = 5). Although >70% of patients in the two MCL cohorts (KIT D816H/Ypos. and KITneg.) were classified as low/intermediate risk according to prognostic scoring systems (PSS), treatment response was poor and median OS was shorter than in a KIT D816Vpos. MCL control cohort (n = 29; 1.7 vs. 0.9 vs. 2.6 years; p < 0.04). The KITneg. SM-AHN phenotype was dominated by the heterogeneous AHN (low mast cell burden, presence of additional mutations) with a better median OS of 4.5 years. We conclude that (i) in MCL, negativity for D816V is a relevant prognostic factor and (ii) PSS fail to correctly classify D816Vneg. patients.

A clinical, morphological and molecular study of 70 patients with gastrointestinal involvement in systemic mastocytosis

In 70 patients with KIT D816V positive systemic mastocytosis (SM) including 36 patients with advanced SM (AdvSM), we correlated the extent of reported mucosal mast cell ([m]MC) infiltration of the upper and/or lower gastrointestinal tract (UGIT, n = 63; LGIT, n = 64; both, n = 57) with symptoms and markers of MC burden/subtype. GI symptoms were reported by all patients (mean 2.1 number of symptoms). A strong mMC infiltration was identified in 24 patients (UGIT, 17/63, 27%; LGIT, 19/64, 30%). Concurrent involvement of UGIT and LGIT (n = 12) correlated with female gender (75%) and a higher symptom burden (mean 2.7) but not with MC burden or subtype. Significant differences between non-AdvSM and AdvSM were reported regarding food intolerance (54% vs. 17%), cramping (54% vs. 22%) and weight loss (0% vs. 64%). KIT D816V was identified in 54/56 (96%) available biopsies. In 46 patients, digital PCR revealed a correlation with low albumin levels (r =  - 0.270, P = 0.069) and the KIT D816V VAF in peripheral blood (r = 0.317, P = 0.036) but not with the extent of mMC infiltration or markers of MC burden/subtype. Although MC mediator triggered GI symptoms have a substantial impact on the quality of life, correlation to objective disease parameters is lacking thus making its systematic assessment challenging.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions: reevaluation of the defining characteristics in a registry-based cohort

In a registry-based analysis of 135 patients with "myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions" (MLN-TK; FIP1L1::PDGFRA, n = 78; PDGFRB, diverse fusions, n = 26; FGFR1, diverse, n = 9; JAK2, diverse, n = 11; ETV6::ABL1, n = 11), we sought to evaluate the disease-defining characteristics. In 81/135 (60%) evaluable patients, hypereosinophilia (>1.5 × 109/l) was observed in 40/44 (91%) FIP1L1::PDGFRA and 7/7 (100%) ETV6::ABL1 positive patients but only in 13/30 (43%) patients with PDGFRB, FGFR1, and JAK2 fusion genes while 9/30 (30%) patients had no eosinophilia. Monocytosis >1 × 109/l was identified in 27/81 (33%) patients, most frequently in association with hypereosinophilia (23/27, 85%). Overall, a blast phase (BP) was diagnosed in 38/135 (28%) patients (myeloid, 61%; lymphoid, 39%), which was at extramedullary sites in 18 (47%) patients. The comparison between patients with PDGFRA/PDGFRB vs. FGFR1, JAK2, and ETV6::ABL1 fusion genes revealed a similar occurrence of primary BP (17/104, 16% vs. 8/31 26%, p = 0.32), a lower frequency (5/87, 6% vs. 8/23, 35%, p = 0.003) of and a later progression (median 87 vs. 19 months, p = 0.053) into secondary BP, and a better overall survival from diagnosis of BP (17.1 vs. 1.7 years, p < 0.0008). We conclude that hypereosinophilia with or without monocytosis and various phenotypes of BP occur at variable frequencies in MLN-TK.

[Photodynamic therapy in Germany-Quo vadis?]

BACKGROUND

Photodynamic therapy (PDT) was originally approved for the treatment of neovascular age-related macular degeneration (nAMD) and secondary choroidal neovascularization in myopia (mCNV). In addition, it is used as an off-label treatment in patients with choroidal hemangioma, polypoidal choroidal vasculopathy (PCV), and central serous chorioretinopathy (CSC).

OBJECTIVE

To track the development of PDT treatment numbers in Germany between 2006 and 2021 and to investigate the composition of the therapeutic indications.

METHODS

In this retrospective study the quality reports of German hospitals were evaluated in the period from 2006 to 2019 and the number of PDTs performed was recorded. In addition, the range of indications for PDT was determined exemplarily for the Eye Center at Medical Center, University of Freiburg and the Eye Center at St. Franziskus Hospital in Münster between 2006 and 2021. Finally, the estimated prevalence of CSC and an estimate of cases requiring treatment were used to calculate the number of patients in need of PDT treatment in Germany.

RESULTS

The number of PDTs performed in Germany decreased from 1072 in 2006 to 202 in 2019. While PDT was used in 86% of cases in patients with nAMD and in 7% of cases with mCNV in 2006, it was mainly performed in patients with CSC (70%) and choroidal hemangiomas (21%) from 2016 to 2021. With an estimated incidence of CSC of 1:10,000 and assuming that 16% of patients develop chronic CCS requiring treatment, approximately 1330 PDTs would need to be performed per year in Germany for patients with newly diagnosed chronic CSC alone.

CONCLUSION

The decreasing numbers of PDT treatment performed in Germany is mainly due to a change to intravitreal injections as the preferred treatment for nAMD and mCNV. As PDT is currently the recommended treatment of choice for chronic CSC, an underprovision of PDT in Germany can be assumed. To enable an appropriate treatment for patients, a reliable verteporfin production, a simplified approval process by health insurance companies and a close cooperation between ophthalmologists in private practice and larger centers are urgently needed.

Mast cell leukemia: clinical and molecular features and survival outcomes of patients in the ECNM Registry

Mast cell leukemia (MCL) is a rare subtype of systemic mastocytosis defined by ≥20% mast cells (MC) on a bone marrow aspirate. We evaluated 92 patients with MCL from the European Competence Network on Mastocytosis registry. Thirty-one (34%) patients had a diagnosis of MCL with an associated hematologic neoplasm (MCL-AHN). Chronic MCL (lack of C-findings) comprised 14% of patients, and only 4.5% had "leukemic MCL" (≥10% circulating MCs). KIT D816V was found in 62/85 (73%) evaluable patients; 9 (11%) individuals exhibited alternative KIT mutations, and no KIT variants were detected in 14 (17%) subjects. Ten evaluable patients (17%) had an abnormal karyotype and the poor-risk SRSF2, ASXL1, and RUNX1 (S/A/R) mutations were identified in 16/36 (44%) patients who underwent next-generation sequencing. Midostaurin was the most common therapy administered to 65% of patients and 45% as first-line therapy. The median overall survival (OS) was 1.6 years. In multivariate analysis (S/A/R mutations excluded owing to low event rates), a diagnosis of MCL-AHN (hazard ratio [HR], 4.7; 95% confidence interval [CI], 1.7-13.0; P = .001) and abnormal karyotype (HR, 5.6; 95% CI, 1.4-13.3; P = .02) were associated with inferior OS; KIT D816V positivity (HR, 0.33; 95% CI, 0.11-0.98; P = .04) and midostaurin treatment (HR, 0.32; 95% CI, 0.08-0.72; P = .008) were associated with superior OS. These data provide the most comprehensive snapshot of the clinicopathologic, molecular, and treatment landscape of MCL to date, and should help further inform subtyping and prognostication of MCL.

Response and resistance to cladribine in patients with advanced systemic mastocytosis: a registry-based analysis

We sought to evaluate the efficacy of the purine analogue cladribine in 79 patients with advanced systemic mastocytosis (AdvSM) using data from the 'German Registry on Disorders of Eosinophils and Mast Cells (GREM)'. The overall response rate according to modified Valent criteria (46 evaluable patients) for first- (1L) and second-line (2L) cladribine treatment was 41% (12/29) and 35% (6/17, P = 0.690), respectively, and the median overall survival (OS, all patients evaluable) was 1.9 years (n = 48) and 1.2 years (n = 31; P = 0.311). Univariate and multivariable analyses of baseline and on-treatment parameters identified diagnosis of mast cell leukemia (hazard ratio [HR] 3.5, 95% confidence interval [CI, 1.3-9.1], P = 0.012), eosinophilia ≥ 1.5 × 10⁹/L (HR 2.9 [CI 1.4-6.2], P = 0.006) and < 3 cycles of cladribine (HR 0.4 [CI 0.2-0.8], P = 0.008) as independent adverse prognostic parameters for OS. There was no impact of other laboratory (anemia, thrombocytopenia, serum tryptase) or genetic markers (mutations in SRSF2, ASXL1 or RUNX1) on OS. In consequence, none of the recently established prognostic scoring systems (MARS, IPSM, MAPS or GPSM) was predictive for OS. Modified Valent criteria were superior to a single factor-based response assessment (HR 2.9 [CI 1.3-6.6], P = 0.026). In conclusion, cladribine is effective in 1L and 2L treatment of AdvSM. Mast cell leukemia, eosinophilia, application of < 3 cycles and a lack of response are adverse prognostic markers.

Fibrinogen reflects severity and predicts outcomes in patients with sepsis and septic shock

The study investigates the diagnostic and prognostic value of fibrinogen and the albumin-to-fibrinogen-ratio (AFR) in patients with sepsis and septic shock. Limited data regarding the prognostic value of fibrinogen and AFR during the course of sepsis or septic shock are available. Consecutive patients with sepsis and septic shock from 2019 to 2021 were included monocentrically. Blood samples were retrieved from the day of disease onset (day 1), as well as on day 2 and 3. Firstly, the diagnostic value of fibrinogen and the AFR for the diagnosis of a septic shock was tested. Secondly, the prognostic value of fibrinogen and AFR was tested with regard to the 30-day all-cause mortality. Statistical analyses included univariable t-tests, Spearman's correlations, C-statistics, Kaplan-Meier and multivariable Cox regression analyses. Ninety-one patients with sepsis and septic shock were included. With an area under the curve (AUC) of 0.653-0.801, fibrinogen discriminated patients with septic shock from those with sepsis. In the septic shock group, fibrinogen levels were shown to decrease from day 1 to 3 (median decrease 41%). In line, fibrinogen was a reliable predictor for 30-day all-cause mortality (AUC 0.661-0.744), whereas fibrinogen levels less than 3.6 g/l were associated with an increased risk of 30-day all-cause mortality (78 vs. 53%; log rank P  = 0.004; hazard ratio = 2.073; 95% confidence interval 1.233-3.486; P  = 0.006), which was still observed after multivariable adjustment. In contrast, the AFR was no longer associated with the risk of mortality after multivariable adjustment. Fibrinogen was a reliable diagnostic and prognostic tool for the diagnosis of septic shock as well as for 30-day all-cause mortality and superior compared with the AFR in patients admitted with sepsis or septic shock.

Prognostic Impact of Organomegaly in Mastocytosis: An Analysis of the European Competence Network on Mastocytosis

BACKGROUND

Organomegaly, including splenomegaly, hepatomegaly, and/or lymphadenopathy, are important diagnostic and prognostic features in patients with cutaneous mastocytosis (CM) or systemic mastocytosis (SM).

OBJECTIVES

To investigate the prevalence and prognostic impact of 1 or more organomegalies on clinical course and survival in patients with CM/SM.

METHODS

Therefore, 3155 patients with CM (n = 1002 [32%]) or SM (n = 2153 [68%]) enrolled within the registry of the European Competence Network on Mastocytosis were analyzed.

RESULTS

Overall survival (OS) was adversely affected by the number of organomegalies (OS: #0 vs #1 hazard ratio [HR], 4.9; 95% CI, 3.4-7.1, P < .001; #1 vs #2 HR, 2.1, 95% CI, 1.4-3.1, P < .001; #2 vs #3 HR, 1.7, 95% CI, 1.2-2.5, P = .004). Lymphadenopathy was frequently detected in patients with smoldering SM (SSM, 18 of 60 [30%]) or advanced SM (AdvSM, 137 of 344 [40%]). Its presence confered an inferior outcome in patients with AdvSM compared with patients with AdvSM without lymphadenopathy (median OS, 3.8 vs 2.6 years; HR, 1.6; 95% CI, 1.2-2.2; P = .003). OS was not different between patients having organomegaly with either ISM or SSM (median, 25.5 years vs not reached; P = .435). At time of disease progression, a new occurrence of any organomegaly was observed in 17 of 40 (43%) patients with ISM, 4 of 10 (40%) patients with SSM, and 33 of 86 (38%) patients with AdvSM, respectively.

CONCLUSIONS

Organomegalies including lymphadenopathy are often found in SSM and AdvSM. ISM with organomegaly has a similar course and prognosis compared with SSM. The number of organomegalies is adversely associated with OS. A new occurrence of organomegaly in all variants of SM may indicate disease progression.

MPN-435 Overall Survival in Patients With Systemic Mastocytosis With Associated Hematologic Neoplasm Treated With Avapritinib Versus Best Available Therapy

CONTEXT

Avapritinib, a selective KIT D816V inhibitor, was approved by the FDA and EMA (by EMA only after prior systemic therapy) for treating adults with advanced systemic mastocytosis (AdvSM) based on the single-arm phase 1 EXPLORER (NCT02561988) and phase 2 PATHFINDER (NCT03580655) studies. SM-AHN is the most common AdvSM subtype, however, there is no randomized controlled trial that compares the efficacy of avapritinib versus best available therapy (BAT) in this population.

OBJECTIVE

This study (NCT04695431) compared overall survival (OS) in patients with SM-AHN treated with avapritinib in EXPLORER and PATHFINDER versus patients treated with BAT in standard clinical practice.

DESIGN

A global, observational, retrospective chart review study was conducted at 6 sites to collect data on SM-AHN patients treated with BAT. These data were pooled with those from EXPLORER and PATHFINDER.

PATIENTS

Patients with SM-AHN receiving BAT were identified using inclusion/ exclusion criteria similar to EXPLORER and PATHFINDER and could contribute data on multiple lines of therapy (LOTs).

METHODS

OS, defined as time from avapritinib or BAT initiation to death from any cause, was descriptively analyzed using the Kaplan-Meier method. Inverse probability of treatment weighting (IPTW) was used to adjust for differences in key covariates between the treatment cohorts. OS was compared between cohorts using an IPTW-weighted Cox proportional hazards model.

RESULTS

119 avapritinib (median age 70 years; 61% male) and 83 BAT patients (median age 71 years; 76% male) were included; 58% of avapritinib and 44% of BAT patients had received prior systemic therapy. BAT patients contributed 121 LOTs, most commonly tyrosine kinase inhibitors (60%) or cytoreductive therapies (38%). Median OS for avapritinib patients was 46.9 months (95% confidence interval [CI]: 44.9-not estimable) and 18.0 months (95% CI: 13.0-26.8) for BAT. Weighted Cox analyses showed that OS was significantly improved for patients treated with avapritinib versus BAT (hazard ratio [95% CI]: 0.42 [0.24-0.74]; P<0.001), after adjustment for key covariates.

CONCLUSIONS

The results of this observational, retrospective analysis indicate that patients with SM-AHN who were treated with avapritinib had significantly longer OS than patients treated with BAT. This study was sponsored by Blueprint Medicines Corporation.

Proposed European Competence Network on Mastocytosis-American Initiative in Mast Cell Diseases (ECNM-AIM) Response Criteria in Advanced Systemic Mastocytosis

Advanced systemic mastocytosis (AdvSM) is characterized by the presence of KIT D816V and other somatic mutations (eg, in SRSF2, ASXL1, and RUNX1) in 95% and 60% to 70% of patients, respectively. The biological and clinical consequences of AdvSM include multilineage involvement (eg, associated hematologic neoplasm) in 60% to 80% of patients, variable infiltration and damage (C-findings) of predominantly bone marrow and visceral organs through affected mast cell (MC) and non-MC lineages, and elevated levels of serum tryptase. Recently, the treatment landscape has substantially changed with the introduction of the multikinase/KIT inhibitor midostaurin and the selective KIT D816V inhibitor avapritinib. In this review, we discuss the evolution of AdvSM response criteria that have been developed to better capture clinical benefit (eg, improved responses and progression-free and overall survival). We propose refined response criteria from European Competence Network on Mastocytosis and American Initiative in Mast Cell Diseases investigators that use a tiered approach to segregate the effects of histopathologic (eg, bone marrow MC burden, tryptase), molecular (eg, KIT D816V variant allele frequency), clinical (eg, C-findings), and symptom response on long-term outcomes. These response criteria require evaluation in future prospective clinical trials of selective KIT inhibitors and other novel agents.

Superior Efficacy of Midostaurin Over Cladribine in Advanced Systemic Mastocytosis: A Registry-Based Analysis

PURPOSE

On the basis of data from the German Registry on Disorders of Eosinophils and Mast Cells, we compared the efficacy of midostaurin and cladribine in patients with advanced systemic mastocytosis (AdvSM).

PATIENTS AND METHODS

Patients with AdvSM (n = 139) were treated with midostaurin only (n = 63, 45%), cladribine only (n = 23, 17%), or sequentially (midostaurin-cladribine, n = 30, 57%; cladribine-midostaurin, n = 23, 43%). Prognosis was assessed through the Mutation-Adjusted Risk Score (MARS). Besides the comparison of efficacy between midostaurin and cladribine on response (eg, organ dysfunction, bone marrow mast cell [MC] infiltration, and tryptase), overall survival (OS), and leukemia-free survival, we focused on the impact of treatment on involved non-MC lineages, for example, monocytes or eosinophils, and the KIT D816V expressed allele burden.

RESULTS

Midostaurin only was superior to cladribine only with effects from responses on MC and non-MC lineages conferring on a significantly improved OS (median 4.2 v 1.9 years, P = .033) and leukemia-free survival (2.7 v 1.3 years, P = .044) on the basis of a propensity score-weighted analysis of parameters included in MARS. Midostaurin compensated the inferior efficacy of cladribine in first- and second-line treatment. On midostaurin in any line, response of eosinophilia did not improve its baseline adverse prognostic impact, whereas response of monocytosis proved to be a positive on-treatment parameter. Multivariable analysis allowed to establish three risk categories (low/intermediate/high) through the combination of MARS and the reduction of the KIT D816V expressed allele burden of ≥ 25% at month 6 (median OS not reached v 3.0 years v 1.0 year; P < .001).

CONCLUSION

In this registry-based analysis, midostaurin revealed superior efficacy over cladribine in patients with AdvSM. In midostaurin-treated patients, the combination of baseline MARS and molecular response provided a compelling three-tier risk categorization (MARSv2.0) for OS.

Clinical and histopathological features of myeloid neoplasms with concurrent Janus kinase 2 (JAK2) V617F and KIT proto-oncogene, receptor tyrosine kinase (KIT) D816V mutations

We report on 45 patients with myeloid neoplasms and concurrent Janus kinase 2 (JAK2) V617F and KIT proto-oncogene, receptor tyrosine kinase (KIT) D816V (JAK2^{pos .} /KIT^{pos .} ) mutations, which are individually identified in >60% of patients with classical myeloproliferative neoplasms (MPN) and >90% of patients with systemic mastocytosis (SM) respectively. In SM, the concurrent presence of a clonal non-mast cell neoplasm [SM with associated haematological neoplasm (SM-AHN)] usually constitutes a distinct subtype associated with poor survival. All 45 patients presented with a heterogeneous combination of clinical/morphological features typical of the individual disorders (e.g. leuco-/erythro-/thrombocytosis and elevated lactate dehydrogenase for MPN; elevated serum tryptase and alkaline phosphatase for SM). Overlapping features identified in 70% of patients included splenomegaly, cytopenia(s), bone marrow fibrosis and additional somatic mutations. Molecular dissection revealed discordant development of variant allele frequency for both mutations and absence of concurrently positive single-cell derived colonies, indicating disease evolution in two independent clones rather than monoclonal disease in >60% of patients examined. Overall survival of JAK2^{pos .} /KIT^{pos .} patients without additional somatic high-risk mutations [HRM, e.g. in serine and arginine-rich splicing factor 2 (SRSF2), additional sex combs like-1 (ASXL1) or Runt-related transcription factor 1 (RUNX1)] at 5 years was 77%, indicating that the mutual impact of JAK2 V617F and KIT D816V on prognosis is fundamentally different from the adverse impact of additional HRM in the individual disorders.

Long-term follow-up of intraocular pressure and pressure-lowering medication in patients following Excimer laser trabeculotomy

BACKGROUND

Excimer laser trabeculotomy (ELT) is a minimally invasive procedure to lower the intraocular pressure (IOP) via a photo-ablative laser that is applied to the trabecular meshwork. With this procedure, it is possible to improve the outflow of the aqueous humor. Until now, a limited number of studies examining mostly relatively small sample sizes with midterm follow-up exist. We therefore present the analysis of a large ELT cohort in a long-term follow-up.

METHODS

We recorded data from 580 patients who underwent ELT or combined ELT with cataract surgery at our institution from November 2000 until March 2011. A total of 512 patients with primary open angle glaucoma (POAG), pseudoexfoliation glaucoma (PEX), and ocular hypertension (OHT) were included in the analysis. At every follow-up examination, the usage of IOP-lowering medication and the IOP were recorded. Failure criteria were defined as the need for another surgical glaucoma procedure, when the IOP was not 21 mmHg or less and a reduction of 20% from the baseline was not achieved with (qualified success) or without (absolute success) additional medication. Statistical analysis was done using Kaplan-Meier analysis and Cox regression.

RESULTS

Four hundred twenty-eight patients underwent combined cataract and ELT surgery, and 84 underwent solitary ELT surgery. After a median follow-up time of 656 days, 87% (combined surgery) and 66% (ELT) of the patients did not have to undergo another IOP-lowering intervention; 47/31% were classified as a qualified success and 31/11% as a complete success. The IOP-lowering medication, however, could not be significantly reduced within that time period.

CONCLUSION

Especially when combined with cataract surgery, ELT is a feasible minimally invasive procedure to lower the IOP on a mid- to long-term basis. Over the long term, however, IOP-lowering medication could not be reduced.

Importance of Adequate Diagnostic Workup for Correct Diagnosis of Advanced Systemic Mastocytosis

BACKGROUND

Little is known about the epidemiology of advanced systemic mastocytosis (advSM).

OBJECTIVES

To investigate epidemiologic features and diagnostic pitfalls of advSM in Germany.

METHODS

Therefore, 140 patients from a single German reference center of the European Competence Network on Mastocytosis between 2003 and 2018 were analyzed.

RESULTS

The patients' median age was 68 years (range, 26-86 years), and male versus female ratio was 2:1. An elevated serum tryptase, a KIT D816 mutation, and additional somatic mutations, for example, in SRSF2, ASXL1, or RUNX1, were identified in 95%, 91%, and 74% of patients, respectively. Median overall survival was 3.5 years (range, 0.03-14.3 years; male vs female 2.6 vs 4.2 years; P = .02). Two categories of misdiagnoses were identified in 51 of 140 (36%) patients: First, systemic mastocytosis (SM) was overlooked in 28 of 140 (20%) patients primarily diagnosed with various subtypes of myeloid neoplasms. Second, 23 of 140 (16%) patients were diagnosed with supposed progression from indolent SM to advSM; however, combination of an elevated KIT D816V variant allele frequency in peripheral blood (n = 22), monocytosis (n = 9), eosinophilia (n = 6), and/or mutations in SRSF2, ASXL1, or RUNX1 (n = 10) suggest that distinct signs of potential advSM were overlooked in virtually all patients. Based on locally diagnosed patients in an area of 2.5 million inhabitants, but obviously without considering more, yet unrecognized cases, the incidence and prevalence of advSM is at least 0.8 and 5.2, respectively, per 1 million inhabitants.

CONCLUSIONS

Adequate analyses of tryptase levels, bone marrow morphology, and genetics in patients with myeloid neoplasms or SM would help to prevent the significant underdiagnosis of advSM.

MARS: Mutation-Adjusted Risk Score for Advanced Systemic Mastocytosis

PURPOSE

To develop a risk score for patients with advanced systemic mastocytosis (AdvSM) that integrates clinical and mutation characteristics.

PATIENTS AND METHODS

The study included 383 patients with AdvSM from the German Registry on Disorders of Eosinophils and Mast Cells (training set; n = 231) and several centers for mastocytosis in the United States and Europe, all within the European Competence Network on Mastocytosis (validation set; n = 152). A Cox multivariable model was used to select variables that were predictive of overall survival (OS).

RESULTS

In multivariable analysis, the following risk factors were identified as being associated with OS: age greater than 60 years, anemia (hemoglobin < 10 g/dL), thrombocytopenia (platelets < 100 × 10⁹/L), presence of one high molecular risk gene mutation (ie, in SRSF2, ASXL1, and/or RUNX1), and presence of two or more high molecular risk gene mutations. By assigning hazard ratio–weighted points to these variables, the following three risk categories were defined: low risk (median OS, not reached), intermediate risk (median OS, 3.9 years; 95% CI, 2.1 to 5.7 years), and high risk (median OS, 1.9 years; 95% CI, 1.3 to 2.6 years; P < .001). The mutation-adjusted risk score (MARS) was independent of the WHO classification and was confirmed in the independent validation set. During a median follow-up time of 2.2 years (range, 0 to 23 years), 63 (16%) of 383 patients experienced a leukemic transformation to secondary mast cell leukemia (32%) or secondary acute myeloid leukemia (68%). The MARS was also predictive for leukemia-free survival (P < .001).

CONCLUSION

The MARS is a validated, five-parameter, WHO-independent prognostic score that defines three risk groups among patients with AdvSM and may improve up-front treatment stratification for these rare hematologic neoplasms.

Inhibitory effects of midostaurin and avapritinib on myeloid progenitors derived from patients with KIT D816V positive advanced systemic mastocytosis

Advanced systemic mastocytosis (advSM) is characterized by the presence of an acquired KIT D816V mutation in >90% of patients. In the majority of patients, KIT D816V is not only detected in mast cells but also in other hematopoietic lineages. We sought to investigate the effects of the KIT-inhibitors midostaurin and avapritinib on single-cell-derived myeloid progenitor cells using granulocyte-macrophage colony-forming-units of patients with KIT D816V positive advSM. Colonies obtained prior to treatment were incubated in vitro with midostaurin (n = 10) or avapritinib (n = 11) and showed a marked reduction (≥50%) of KIT D816V positive colonies in 3/10 (30%) and 7/11 (64%) patient samples, respectively. Three of those 7 (43%) avapritinib responders were resistant to midostaurin in both, in vitro and in vivo. Colonies from four patients with high-risk molecular profile and aggressive clinical course were resistant to both drugs. The in vitro activity of midostaurin strongly correlated with clinical and molecular responses, e.g., relative reduction of KIT D816V allele burden and the proportion of KIT D816V positive colonies obtained after six months midostaurin-treatment in vivo. We conclude that the colony inhibition assay provides useful information for prediction of responses on midostaurin and that avapritinib has a superior in vitro activity compared to midostaurin.

Recurrent activating STAT5B N642H mutation in myeloid neoplasms with eosinophilia

Determining the underlying cause of persistent eosinophilia is important for effective clinical management but remains a diagnostic challenge in many cases. We identified STAT5B N642H, an established oncogenic mutation, in 27/1715 (1.6%) cases referred for investigation of eosinophilia. Of the 27 mutated cases, a working diagnosis of hypereosinophilic syndrome (HES; n = 7) or a myeloid neoplasm with eosinophilia (n = 20) had been made prior to the detection of STAT5B N642H. Myeloid panel analysis identified a median of 2 additional mutated genes (range 0–4) with 4 cases having STAT5B N642H as a sole abnormality. STAT5B N642H was absent in cultured T cells of 4/4 positive cases. Individuals with SF3B1 mutations (9/27; 33%) or STAT5B N642H as a sole abnormality had a markedly better overall survival compared to cases with other additional mutations (median 65 months vs. 14 months; hazard ratio = 8.1; P < 0.001). The overall survival of STAT5B-mutated HES cases was only 30 months, suggesting that these cases should be reclassified as chronic eosinophilic leukemia, not otherwise specified (CEL-NOS). The finding of STAT5B N642H as a recurrent mutation in myeloid neoplasia with eosinophilia provides a new diagnostic and prognostic marker as well as a potential target for therapy.

Incidence and prognostic impact of cytogenetic aberrations in patients with systemic mastocytosis

The clinical behavior of systemic mastocytosis (SM) is strongly associated with activating mutations in KIT (D816V in >80% of cases), with the severity of the phenotype influenced by additional somatic mutations, for example, in SRSF2, ASXL1, or RUNX1. Complex molecular profiles are frequently associated with the presence of an associated hematologic neoplasm (AHN) and an unfavorable clinical outcome. However, little is known about the incidence and prognostic impact of cytogenetic aberrations. We analyzed cytogenetic and molecular characteristics of 109 patients (KIT D816V+, n = 102, 94%) with indolent (ISM, n = 26) and advanced SM (n = 83) with (n = 73, 88%) or without AHN. An aberrant karyotype was identified in SM-AHN (16/73, 22%) patients only. In patients with an aberrant karyotype, additional somatic mutations were identified in 12/16 (75%) patients. Seven of 10 (70%) patients with a poor-risk karyotype, for example, monosomy 7 or complex karyotype, and 1/6 (17%) patients with a good-risk karyotype progressed to secondary acute myeloid leukemia (n = 7) or mast cell leukemia (n = 1) within a median of 40 months (range 2-190, P = .04). In advanced SM, the median overall survival (OS) of poor-risk karyotype patients was significantly shorter than in good-risk/normal karyotype patients (4 vs 39 months; hazard ratio 11.7, 95% CI 5.0-27.3; P < .0001). Additionally, the shortened OS in patients with poor-risk karyotype was independent from the mutation status. In summary, a poor-risk karyotype is an independent prognostic variable in advanced SM. Cytogenetic and molecular analyses should be routinely performed in all patients with advanced SM ± AHN because these investigations greatly support prognostication and treatment decisions.

[Individualization of exercise load control for inpatient cardiac rehabilitation. Development and evaluation of a HRV-based intervention program for patients with ischemic heart failure]

BACKGROUND

The effective use of rehabilitation programs is of primary importance in order to improve the physical performance of cardiac disease patients. A modular program has been developed which is intended to structure and individualize conventional, exercise-based rehabilitation programs according to the individual needs and physical condition of each patient. The individualization of the program is based on detailed diagnostics before patients enter the program and daily measurements of heart rate variability (HRV) during cardiac rehabilitation.

METHODS

A total of 30 patients with ischemic heart disease were randomly assigned either to the intervention group (IG), completing the modular individualized rehabilitation program [n=15, mean age 54.4±4.2 years and mean left ventricular ejection fraction (LVEF) 28.53±6.25%) or to the control group (CG) taking part in the conventional rehabilitation program (n=15, mean age 56.4±4.4 years and mean LVEF 27.63±5.62). Before and after the intervention, cardiorespiratory fitness was assessed by measurement of maximal oxygen consumption (relative VO2max) during bicycle ergometry and the 6-minute walk test (6-MWT). Pre-post comparisons of cardiorespiratory fitness indicators were used to evaluate the effectiveness of the rehabilitation program. In addition to the results of the basic clinical investigations and the cardiorespiratory testing, results of standardized HRV measurements of 10 min at morning rest served as criteria for program individualization.

RESULTS

The relative VO2max increased significantly (p<0.05) in the IG whereas no change was found in the CG. Similar results were found for maximum power output during bicycle ergometry (p<0.01) and for 6-MWT distance (p<0.001). Although patients in the IG completed less aerobic exercise sessions than those in the CG (p<0.001) the physical performance of the IG improved significantly.

DISCUSSION

The results prove the effectiveness and efficacy of the modular individualized rehabilitation program. They further suggest the need for an individual program matrix instead of a maximum performance matrix in cardiac rehabilitation. Individualization should be based on clinical and performance diagnostics before and accompanying assessments of training condition, e.g. by HRV measurements, during rehabilitation programs. Each patient should only perform those intervention programs which match the results of the basic clinical investigation and additional analyses during rehabilitation.

Fuctional outcome after open and arthroscopic bankart repair for traumatic shoulder instability

Purpose

Both open and arthroscopic Bankart repair are established procedures in the treatment of anterior shoulder instability. While the open procedure is still considered as the "golden standard" functional outcome is supposed to be better in the arthroscopic procedure. The aim of this retrospective study was to compare the functional outcome between open and arthroscopic Bankart repair.

Materials and methods

In 199 patients a Bankart procedure with suture anchors was performed, either arthroscopically in presence of an detached, but not elongated capsulolabral complex (40) or open (159). After a median time of 31 months (12 to 67 months) 174 patients were contacted and agreed to follow-up, 135 after open and 39 after arthroscopic Bankart procedure.

Results

Re-dislocations occurred in 8% after open and 15% after arthroscopic Bankart procedure. After open surgery 4 of the 11 re-dislocations occurred after a new adequate trauma and 1 of the 6 re-dislocations after arthroscopic surgery. Re-dislocations after arthroscopic procedure occured earlier than after open Bankart repair. An external rotation lag of 20° or more was observed more often (16%) after open than after arthroscopic surgery (3%). The Rowe score demonstrated "good" or "excellent" functional results in 87% after open and in 80% patients after arthroscopic treatment.

Conclusion

In this retrospective investigation the open Bankart procedure demonstrated good functional results. The arthroscopic treatment without capsular shift resulted in a better range of motion, but showed a tendency towards more frequently and earlier recurrence of instability. Sensitive patient selection for arthroscopic Bankart repair is recommended especially in patients with more than five dislocations.

Columnar organization of dendrites and axons of single and synaptically coupled excitatory spiny neurons in layer 4 of the rat barrel cortex

Cortical columns are the functional units of the neocortex that are particularly prominent in the "barrel" field of the somatosensory cortex. Here we describe the morphology of two classes of synaptically coupled excitatory neurons in layer 4 of the barrel cortex, spiny stellate, and star pyramidal cells, respectively. Within a single barrel, their somata tend to be organized in clusters. The dendritic arbors are largely confined to layer 4, except for the distal part of the apical dendrite of star pyramidal neurons that extends into layer 2/3. In contrast, the axon of both types of neurons spans the cortex from layer 1 to layer 6. The most prominent axonal projections are those to layers 4 and 2/3 where they are largely restricted to a single cortical column. In layers 5 and 6, a small fraction of axon collaterals projects also across cortical columns. Consistent with the dense axonal projection to layers 4 and 2/3, the total number and density of boutons per unit axonal length was also highest there. Electron microscopy combined with GABA postimmunogold labeling revealed that most (>90%) of the synaptic contacts were established on dendritic spines and shafts of excitatory neurons in layers 4 and 2/3. The largely columnar organization of dendrites and axons of both cell types, combined with the preferential and dense projections within cortical layers 4 and 2/3, suggests that spiny stellate and star pyramidal neurons of layer 4 serve to amplify thalamic input and relay excitation vertically within a single cortical column.

Hippocampal Cajal-Retzius cells project to the entorhinal cortex: retrograde tracing and intracellular labelling studies

Cajal-Retzius (CR) cells are characteristic horizontally orientated, early-generated transient neurons in the marginal zones of the neocortex and hippocampus that synthesize the extracellular matrix protein reelin. They have been implicated in the pathfinding of entorhino-hippocampal axons, but their role in this process remained unclear. Here we have studied the axonal projection of hippocampal CR cells. Following injection of the carbocyanine dye DiI into the entorhinal cortex of aldehyde-fixed rat embryos and young postnatal rats, neurons in the outer molecular layer of the dentate gyrus and stratum lacunosum-moleculare of the hippocampus proper with morphological characteristics of CR cells were retrogradely labelled. In a time course analysis, the first retrogradely labelled CR cells were observed on embryonic day 17. This projection of hippocampal CR cells to the entorhinal cortex was confirmed by retrograde tracing with Fast Blue in new-born rats and by intracellular biocytin filling of CR cells in acute slices from young postnatal rat hippocampus/entorhinal cortex and in entorhino-hippocampal slice cocultures using infrared videomicroscopy in combination with the patch-clamp technique. In double-labelling experiments CR cells were identified by their immunocytochemical staining for reelin or calretinin, and their interaction with entorhino-hippocampal axons labelled by anterograde tracers was analysed. Future studies need to investigate whether this early transient projection of hippocampal CR cells to the entorhinal cortex is used as a template by the entorhinal axons growing to their target layers in the hippocampus.

Importance of AMPA receptors for hippocampal synaptic plasticity but not for spatial learning

Gene-targeted mice lacking the L-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit GluR-A exhibited normal development, life expectancy, and fine structure of neuronal dendrites and synapses. In hippocampal CA1 pyramidal neurons, GluR-A-/- mice showed a reduction in functional AMPA receptors, with the remaining receptors preferentially targeted to synapses. Thus, the CA1 soma-patch currents were strongly reduced, but glutamatergic synaptic currents were unaltered; and evoked dendritic and spinous Ca2+ transients, Ca2+-dependent gene activation, and hippocampal field potentials were as in the wild type. In adult GluR-A-/- mice, associative long-term potentiation (LTP) was absent in CA3 to CA1 synapses, but spatial learning in the water maze was not impaired. The results suggest that CA1 hippocampal LTP is controlled by the number or subunit composition of AMPA receptors and show a dichotomy between LTP in CA1 and acquisition of spatial memory.

Specialized electrophysiological properties of anatomically identified neurons in the hilar region of the rat fascia dentata

Because of their strategic position between the granule cell and pyramidal cell layers, neurons of the hilar region of the hippocampal formation are likely to play an important role in the information processing between the entorhinal cortex and the hippocampus proper. Here we present an electrophysiological characterization of anatomically identified neurons in the fascia dentata as studied using patch-pipette recordings and subsequent biocytin-staining of neurons in slices. The resting potential, input resistance (RN), membrane time constant (taum), "sag" in hyperpolarizing responses, maximum firing rate during a 1-s current pulse, spike width, and fast and slow afterhyperpolarizations (AHPs) were determined for several different types of hilar neurons. Basket cells had a dense axonal plexus almost exclusively within the granule cell layer and were distinguishable by their low RN, short taum, lack of sag, and rapid firing rates. Dentate granule cells also lacked sag and were identifiable by their higher RN, longer taum, and lower firing rates than basket cells. Mossy cells had extensive axon collaterals within the hilus and a few long-range collaterals to the inner molecular layer and CA3c and were characterized physiologically by small fast and slow AHPs. Spiny and aspiny hilar interneurons projected primarily either to the inner or outer segment of the molecular layer and had a dense intrahilar axonal plexus, terminating onto somata within the hilus and CA3c. Physiologically, spiny hilar interneurons generally had higher RN values than mossy cells and a smaller slow AHP than aspiny interneurons. The specialized physiological properties of different classes of hilar neurons are likely to be important determinants of their functional operation within the hippocampal circuitry.

Interneurons in the stratum lucidum of the rat hippocampus: an anatomical and electrophysiological characterization

The anatomical and electrophysiological properties of neurons in the stratum lucidum of the CA3 subfield of the hippocampus were examined by using patch-pipette recordings combined with biocytin staining. This method facilitated the analysis of the morphological features and passive and active properties of a recently described class of spiny neurons in the stratum lucidum, as well as aspiny neurons in this region. Some, but not all, synaptic inputs of both types of neurons were found to arise from the mossy fiber system. The axons of spiny neurons in the stratum lucidum were heavily collateralized, terminating primarily in the stratum lucidum and stratum radiatum of CA3, and to a lesser extent in the stratum pyramidale and stratum oriens. Only a few axonal projections were found that extended beyond the CA3 region into CA1 and the hilus. Aspiny neurons fell into two classes: those projecting axons to the stratum lucidum and stratum radiatum of CA3 and those with axon terminations mainly in the stratum pyramidale and stratum oriens. The electrophysiological properties of spiny and aspiny neurons in the stratum lucidum were similar, but on average, the aspiny neurons had significantly higher maximal firing rates and narrower action potential half-widths. The results demonstrate that a diverse population of neurons exists in the region of mossy fiber termination in area CA3. These neurons may be involved in local-circuit feedback, or feed-forward systems controlling the flow of information through the hippocampus.

A novel type of GABAergic interneuron connecting the input and the output regions of the hippocampus

The main excitatory pathway of the hippocampal formation is controlled by a network of morphologically distinct populations of GABAergic interneurons. Here we describe a novel type of GABAergic interneuron located in the outer molecular layer (OML) of the rat dentate gyrus with a long-range forward projection from the dentate gyrus to the subiculum across the hippocampal fissure. OML interneurons were recorded in hippocampal slices by using the whole-cell patch-clamp configuration. During recording, cells were filled with biocytin for subsequent light and electron microscopic analysis. Neurons projecting to the subiculum were distributed throughout the entire OML. They had round or ovoid somata and a multipolar dendritic morphology. Two axonal domains could be distinguished: an extensive, tangential distribution within the OML and a long-range vertical and tangential projection to layer 1 and stratum pyramidale of the subiculum. Symmetric synaptic contacts were established by these interneurons on dendritic shafts in the OML and subiculum. OML interneurons were characterized physiologically by short action potential duration and marked afterhyperpolarization that followed the spike. On sustained current injection, they generated high-frequency (up to 130 Hz, 34 degrees C) trains of action potentials with only little adaptation. In situ hybridization and single-cell RT-PCR analysis for GAD67 mRNA confirmed the GABAergic nature of OML interneurons. GABAergic interneurons in the OML projecting to the subiculum connect the input and output regions of the hippocampus. Hence, they could mediate long-range feed-forward inhibition and may participate in an oscillating cross-regional interneuron network that may synchronize the activity of spatially distributed principal neurons in the dentate gyrus and the subiculum.

Submillisecond AMPA receptor-mediated signaling at a principal neuron-interneuron synapse

Glutamatergic transmission at a principal neuron-interneuron synapse was investigated by dual whole-cell patch-clamp recording in rat hippocampal slices combined with morphological analysis. Evoked EPSPs with rapid time course (half duration = 4 ms; 34 degrees C) were generated at multiple synaptic contacts established on the interneuron dendrites close to the soma. The underlying postsynaptic conductance change showed a submillisecond rise and decay, due to the precise timing of glutamate release and the rapid deactivation of the postsynaptic AMPA receptors. Simulations based on a compartmental model of the interneuron indicated that the rapid postsynaptic conductance change determines the shape and the somatodendritic integration of EPSPs, thus enabling interneurons to detect synchronous principal neuron activity.

Septal innervation of mossy cells in the hilus of the rat dentate gyrus: an anterograde tracing and intracellular labeling study

Mossy cells in the hilus of the rat dentate gyrus are the main cells of origin of the dentate commissural and associational projections. They project along the septotemporal axis of the dentate gyrus and may thus influence the hippocampal signal flow in a longitudinal direction. To analyze the septal innervation of these hilar neurons, anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHAL) was used in combination with intracellular labeling of mossy cells (Lucifer yellow). Anterogradely labeled septal fibers impinge on proximal and distal dendrites of hilar mossy cells but spare the cell body. In contrast, numerous aspiny hilar neurons, presumably GABAergic interneurons, receive a septal innervation on their somata and proximal primary dendrites. These data demonstrate that septal fibers show a specificity for the dendritic segments of hilar mossy cells. Since mossy cells project predominantly to adjacent hippocampal lamellae, the activity of adjacent portions of the dentate gyrus may be influenced by the septal input onto these neurons.

Physiology and anatomy of synaptic connections between thick tufted pyramidal neurones in the developing rat neocortex

1. Dual voltage recordings were made from pairs of adjacent, synaptically connected thick tufted layer 5 pyramidal neurones in brain slices of young rat (14-16 days) somatosensory cortex to examine the physiological properties of unitary EPSPs. Pre- and postsynaptic neurones were filled with biocytin and examined in the light and electron microscope to quantify the morphology of axonal and dendritic arbors and the number and location of synaptic contacts on the target neurone. 2. In 138 synaptic connections between pairs of pyramidal neurones 96 (70%) were unidirectional and 42 (30%) were bidirectional. The probability of finding a synaptic connection in dual recordings was 0.1. Unitary EPSPs evoked by a single presynaptic action potential (AP) had a mean peak amplitude ranging from 0.15 to 5.5 mV in different connections with a mean of 1.3 +/- 1.1 mV, a latency of 1.7 +/- 0.9 ms, a 20-80% rise time of 2.9 +/- 2.3 ms and a decay time constant of 40 +/- 18 ms at 32-24 degrees C and -60 +/- 2 mV membrane potential. 3. Peak amplitudes of unitary EPSPs fluctuated randomly from trial to trial. The coefficient of variation (c.v.) of the unitary EPSP amplitudes ranged from 0.13 to 2.8 in different synaptic connections (mean, 0.52; median, 0.41). The percentage of failures of single APs to evoke a unitary EPSP ranged from 0 to 73% (mean, 14%; median, 7%). Both c.v. and percentage of failures decreased with increasing mean EPSP amplitude. 4. Postsynaptic glutamate receptors which mediate unitary EPSPs at -60 mV were predominantly of the L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor type. Receptors of the N-methyl-D-aspartate (NMDA) type contributed only a small fraction (< 20%) to the voltage-time integral of the unitary EPSP at -60 mV, but their contribution increased at more positive membrane potentials. 5. Branching patterns of dendrites and axon collaterals of forty-five synaptically connected neurones, when examined in the light microscope, indicated that the axonal and dendritic anatomy of both projecting and target neurones and of uni- and bidirectionally connected neurones was uniform. 6. The number of potential synaptic contacts formed by a presynaptic neurone on a target neurone varied between four and eight (mean, 5.5 +/- 1.1 contacts; n = 19 connections). Synaptic contacts were preferentially located on basal dendrites (63%, 82 +/- 35 microns from the soma, n = 67) and apical oblique dendrites (27%, 145 +/- 59 microns, n = 29), and 35% of all contacts were located on tertiary basal dendritic branches. The mean geometric distances (from the soma) of the contacts of a connection varied between 80 and 585 microns (mean, 147 microns; median, 105 microns). The correlation between EPSP amplitude and the number of morphologically determined synaptic contacts or the mean geometric distances from the soma was only weak (correlation coefficients were 0.2 and 0.26, respectively). 7. Compartmental models constructed from camera lucida drawings of eight target neurones showed that synaptic contacts were located at mean electrotonic distances between 0.07 and 0.33 from the soma (mean, 0.13). Simulations of unitary EPSPs, assuming quantal conductance changes with fast rise time and short duration, indicated that amplitudes of quantal EPSPs at the soma were attenuated, on average, to < 10% of dendritic EPSPs and varied in amplitude up to 10-fold depending on the dendritic location of synaptic contacts. The inferred quantal peak conductance increase varied between 1.5 and 5.5 nS (mean, 3 nS). 8. The combined physiological and morphological measurements in conjunction with EPSP simulations indicated that the 20-fold range in efficacy of the synaptic connections between thick tufted pyramidal neurones, which have their synaptic contacts preferentially located on basal and apical oblique dendrites, was due to differences in transmitter release probability of the projecting neurones and, to a lesser extent, to differenc

Regulation of synaptic efficacy by coincidence of postsynaptic APs and EPSPs

Activity-driven modifications in synaptic connections between neurons in the neocortex may occur during development and learning. In dual whole-cell voltage recordings from pyramidal neurons, the coincidence of postsynaptic action potentials (APs) and unitary excitatory postsynaptic potentials (EPSPs) was found to induce changes in EPSPs. Their average amplitudes were differentially up- or down-regulated, depending on the precise timing of postsynaptic APs relative to EPSPs. These observations suggest that APs propagating back into dendrites serve to modify single active synaptic connections, depending on the pattern of electrical activity in the pre- and postsynaptic neurons.

Functional properties of AMPA and NMDA receptors expressed in identified types of basal ganglia neurons

AMPA- and NMDA-type glutamate receptors (AMPARs and NMDARs) mediate excitatory synaptic transmission in the basal ganglia and may contribute to excitotoxic injury. We investigated the functional properties of AMPARs and NMDARs expressed by six main types of basal ganglia neurons in acute rat brain slices (principal neurons and cholinergic interneurons of striatum, GABAergic and dopaminergic neurons of substantia nigra, globus pallidus neurons, and subthalamic nucleus neurons) using fast application of glutamate to nucleated and outside-out membrane patches. AMPARs in different types of basal ganglia neurons were functionally distinct. Those expressed in striatal principal neurons exhibited the slowest gating (desensitization time constant tau = 11.5 msec, 1 mM glutamate, 22 degrees C), whereas those in striatal cholinergic interneurons showed the fastest gating (desensitization time constant tau = 3.6 msec). The lowest Ca2+ permeability of AMPARs was observed in nigral dopaminergic neurons (PCa/PNa = 0.10), whereas the highest Ca2+ permeability was found in subthalamic nucleus neurons (PCa/PNa = 1.17). NMDARs of different types of basal ganglia neurons were less variable in their functional properties; those expressed in nigral dopaminergic neurons exhibited the slowest gating (deactivation time constant of predominant fast component tau1 = 150 msec, 100 microM glutamate), and those of globus pallidus neurons showed the fastest gating (tau1 = 67 msec). The Mg2+ block of NMDARs was similar; the average chord conductance ratio g-60mV/g+40mV was 0.18-0.22 in 100 microM external Mg2+. Hence, AMPARs expressed in different types of basal ganglia neurons are markedly diverse, whereas NMDARs are less variable in functional properties that are relevant for excitatory synaptic transmission and neuronal vulnerability.

Regional variability and postsynaptic targets of chandelier cells in the hippocampal formation of the rat

Chandelier cells are specialized cortical GABAergic neurons that establish synaptic contacts exclusively with the axon initial segments of principal neurons. They are found in all regions of the hippocampal formation. Here we describe their morphological features in the hilus and in regions CA1 and CA3 by using Golgi/electron microscopy. Attempts were also made to identify the target neurons of chandelier cells in the hilus and entorhinal cortex. Golgi-impregnated chandelier cells display a complex axonal arbor in CA1, with many collaterals forming strings of boutons. The axon plexuses of such cells are less developed in CA3, whereas those in the hilus cover the entire region, although single collaterals are rather simple, with only a few boutons. The dendrites of chandelier cells in CA1 and CA3 have an orientation similar to that of pyramidal cell dendrites and are thus likely to be activated by the same afferent fiber systems. The hilar chandelier cells do not give rise to dendrites invading the molecular layer. Thus, these cells may not receive a dense input from the entorhinal cortex but may be driven by the abundant mossy fiber collaterals in the hilar region. In the CA1 and CA3 regions, the axons of chandelier cells contact the axon initial segments of pyramidal cells. In the hilar region, gold-toned boutons were found to impinge on the initial segments of neurons displaying characteristics of mossy cells. This notion was substantiated by electron microscopic analysis of mossy cells identified by intracellular injection of Lucifer yellow. Those cells regularly showed numerous symmetric synapses on their axon initial segments. Entorhinohippocampal projection cells, identified by injection of horseradish peroxidase into the hippocampus, were found to be preferential targets of chandelier cells in the entorhinal cortex. Our data point to regional variations in chandelier cell morphology and connectivity and indicate that chandelier cells are a principal component of inhibitory mechanisms in all stations of the main excitatory pathway of the hippocampal formation.

Frequency and dendritic distribution of autapses established by layer 5 pyramidal neurons in the developing rat neocortex: comparison with synaptic innervation of adjacent neurons of the same class

Synaptic contacts formed by the axon of a neuron on its own dendrites are known as autapses. Autaptic contacts occur frequently in cultured neurons and have been considered to be aberrant structures. We examined the regular occurrence, dendritic distribution, and fine structure of autapses established on layer 5 pyramidal neurons in the developing rat neocortex. Whole-cell recordings were made from single neurons and synaptically coupled pairs of pyramidal cells, which were filled with biocytin, morphologically reconstructed, and quantitatively analyzed. Autapses were found in most neurons (in 80% of all cells analyzed; n = 41). On average, 2.3 +/- 0.9 autapses per neuron were found, located primarily on basal dendrites (64%; 50-70 microns from the soma), to a lesser extent on apical oblique dendrites (31%; 130-200 microns from the soma), and rarely on the main apical dendrite (5% 480-540 microns from the soma). About three times more synaptic than autaptic contacts (ratio 2.4:1) were formed by a single adjacent synaptically coupled neuron of the same type. The dendritic locations of these synapses were remarkably similar to those of autapses. Electron microscopic examination of serial ultrathin sections confirmed the formation of autapses and synapses, respectively, and showed that both types of contacts were located either on dendritic spines or shafts. The similarities between autapses and synapses suggest that autaptic and synaptic circuits are governed by some common principles of synapse formation.

FM1-43 dye ultrastructural localization in and release from frog motor nerve terminals

Previous work has shown that the fluorescent styryl dye FM1-43 stains nerve terminals in an activity-dependent fashion. This dye appears to label the membranes of recycled synaptic vesicles by being trapped during endocytosis. Stained terminals can subsequently be destained by repeating nerve stimulation in the absence of dye; the destaining evidently reflects escape of dye into the bathing medium from membranes of exocytosing synaptic vesicles. In the present study we tested two key aspects of this interpretation of FM1-43 behavior, namely: (i) that the dye is localized in synaptic vesicles, and (ii) that it is actually released into the bathing medium during destaining. To accomplish this, we first photolyzed the internalized dye in the presence of diaminobenzidine. This created an electron-dense reaction product that could be visualized in the electron microscope. Reaction product was confined to synaptic vesicles, as predicted. Second, using spectrofluorometry, we quantified the release of dye liberated into the medium from tubocurarine-treated nerve-muscle preparations. Nerve stimulation increased the amount of FM1-43 released, and we estimate that normally a stained synaptic vesicle contains a few hundred molecules of the dye. The key to the successful detection of released FM1-43 was to add the micelle-forming detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), which increased FM1-43 quantum yield by more than two orders of magnitude.

Inverted pyramidal neurons and interneurons in cat cortical subplate zone are labelled by monoclonal antibody SP1

During development, the subplate zone of the cat neocortex contains neuronal populations with distinct morphological and neurochemical phenotypes. A subset of those are specifically recognized by a mouse monoclonal antibody termed SUBPLATE-1 (SP1), which was generated against tissue homogenates of kitten cortical white matter. SP1 stains cell bodies and proximal dendrites, but rarely distal dendrites, axonal arbors or spines. In order to characterize morphologically the SP1 immunoreactive subplate cell types, we combined SP1 immunohistochemistry with intracellular iontophoretic injections of Lucifer yellow. The majority of double-labelled neurons were inverted pyramids with a single thicker spine-covered dendrite that descended into the white matter and a tuft of thinner spinous dendrites that ascended from the upper somatic pole, but generally remained confined to the white matter. Other double-labelled neurons were multipolar to bitufted, although often equipped with one thicker descending dendrite. In inverted pyramidal cells, the axons originated from the descending dendrite or, more rarely, from the lower portion of the soma, and descended into the white matter. They formed collaterals recurring toward the grey matter. The presence of dendritic spines on double-labelled pyramidal cells and the axonal arborization patterns were two novel features not revealed previously by SP1 immunohistochemistry alone. The inverted pyramidal morphology was typical for double-labelled neurons located in the subplate zone below the apices of the gyri, whereas those located below the flanks or sulci or deep in the white matter often displayed a bitufted or multipolar spinous morphology. A minority of the double-labelled neurons were multipolar with smooth dendrites and locally branching axons. These results suggest that in the cat subplate zone, a majority of the cells expressing the SP1 antigen are spinous, and we termed the spinous subplate cells 'subplate pyramidal neurons'.

Morphological assessment of grafted rat and mouse cortical neurons: a light and electron microscopic study

The morphology of cortical neurons grafted into (or near) the rat striatum was studied by means of intracellular Lucifer yellow injections in fixed slices. Rat donor syngeneic cortical tissue (from postnatal day 1 old rats; AO strain) as well as mouse donor xenogeneic cortical tissue (prenatal day 19; C3H/HE strain) were grafted as solid pieces into 8-12 week-old rats (AO strain). Recipients of mouse xenografts were immunosuppressed with a monoclonal antibody against the interleukin-2 receptor. After perfusion and sectioning of the graft-containing areas, individual slices were incubated in the DNA stain 4.6-diamidino-2-phenylindole (DAPI) to visualize the cell nuclei. Grafts could be easily identified by a surrounding rim of astrocytes which outline the border between grafted and host tissue. Grafted cortical neurons were intracellularly filled with Lucifer yellow, DAB-photoconverted, and further processed for light and electron microscopy. In general, no cortical lamination could be observed in the grafted rat and mouse cortical tissue, but neurons were loosely packed throughout the graft. Two major cell types could be identified in all grafts investigated so far. The majority resembled those described as spiny neurons (85%), which could be further classified into pyramid-like, spiny stellate-like or fusiform spiny neurons, with somata ranging between 15 and 25 microns in diameter. The remaining 15% resembled non-spiny neurons with either a multipolar basket-like or fusiform morphology. Dendrites of spiny and non-spiny neurons, which could extend to distances up to 400 microns, were never seen to cross the astrocytic border, but some main axon and axonal collaterals of spiny neurons were found to leave the graft. On the basis of light microscopic observations no difference was found between mouse and rat grafted cortical neurons. The results of this study show that grafted cortical neurons retain some of the characteristic features of neurons in the intact adult cerebral cortex, although there appears to be a greater preponderance of spiny neurons in grafted tissue. This may reflect an immaturity of the grafted tissue or a response to the striatal environment.

Pyramidal neurons in layer 5 of the rat visual cortex. III. Differential maturation of axon targeting, dendritic morphology, and electrophysiological properties

This paper describes the early morphological and physiological development of pyramidal neurons in layer 5 of the rat visual cortex in relation to the targets chosen by their axons. Cells were prelabeled by retrograde transport from the superior colliculus or the contralateral visual cortex and intracellularly injected either in fixed slices or after recording in living slices. In the adult, corticotectal cells have thick apical dendrites with an extensive terminal arborization extending into layer 1, and fire characteristic bursts of action potentials when injected with a depolarizing current; interhemispheric cells have slender apical dendrites that terminate without a terminal tuft, usually in layer 2/3, and they display a more regular firing pattern (Kasper et al.: J Comp Neurol, this issue, 339:459-474). At embryonic day E18 (when axons of the two classes of cells are already taking different routes towards their targets) and E21, pyramidal-like cells throughout the cortical plate all have similar soma-dendritic morphology, with spindle-shaped cell bodies and few, short basal dendrites but apical dendrites that all end in distinct tufts in the marginal zone. At postnatal day P3, after the axons of both cell classes have reached their targets, all pyramidal neurons in layer 5 still have distinct terminal arborizations in layer 1, though they vary in complexity and extent. The somata are now more mature (round to ovoid in shape), and the basal dendritic tree has extended. As early as P5, all cells studied could be clearly classified as tufted or untufted (considerably earlier than previously reported; Koester and O'Leary: J Neurosci 12:1382, '92), and these features correlated precisely with the projection target, as in the adult. Measurement showed that although interhemispheric cells lose their terminal tufts, in general the trunks of their apical dendrites do not withdraw but continue to grow, at roughly the same rate as those of corticotectal cells. The two classes of layer 5 pyramidal neurons differentiate from each other in three distinct phases: pathway selection by axons precedes the loss of the apical tuft by interhemispheric cells, and these morphological characteristics are established 10 days before the onset of burst-firing in corticotectal cells. These three steps may be guided by different molecular signals.

Pyramidal neurons in layer 5 of the rat visual cortex. II. Development of electrophysiological properties

Two major classes of pyramidal neurons can be distinguished in layer 5 of the adult rat visual cortex. Cells of the "thick/tufted" type have stout apical dendrites with terminal tufts, and most of them project to the superior colliculus (Larkman and Mason: J Neurosci 10:407, '90; Kasper et al.: J Comp Neurol, this issue, 339:459-474). "Slender/untufted" cells have thinner apical trunks with no obvious terminal tufts, and a substantial proportion of them project to the contralateral visual cortex. These two types also differ in their intrinsic electrophysiological features. In this study we describe the postnatal maturation of the electrophysiological and synaptic properties of layer 5 pyramidal neurons and relate these findings to the morphological development and divergence of the two cell types. Living slices were prepared from the visual cortex of rats aged between postnatal day 3 (P3) and young adults and maintained in vitro. Stable intracellular impalements were obtained from a total of 63 pyramidal cells of layer 5 at various ages, which were injected with biocytin so that morphological and electrophysiological data could be obtained from the same cell. Before P15, injection of a single cell sometimes stained a cluster of neurons of similar morphology, probably as a result of dye coupling. The incidence of such clustering and the number of neurons within each cluster decreased with age. There was no obvious difference in electrophysiological properties between cells in clusters and age-matched, noncoupled neurons. From P5, the apical dendrites of neurons could easily be classified as "thick/tufted" or "slender/untufted." On average, the resting potential became more negative, and membrane time constant and input resistance decreased with age. Electrophysiological differences between the "thick/tufted" and "slender/untufted" cell types did not become apparent until the third postnatal week, after which the "thick/tufted" cells on average had lower input resistances and slightly faster time constants than "slender/untufted" cells. The current-voltage relations of the neurons became progressively more nonlinear during maturation, with both rapid inward rectification and time-dependent rectification or "sag" becoming more prominent. There were also changes in the amplitude and waveform of action potentials, which generally approached adult values by 3 weeks of age. Action potential threshold became more negative, both in absolute terms and relative to the resting membrane potential. Action potentials became larger in peak amplitude and of shorter duration, with both rise and fall times decreasing progressively during development.(ABSTRACT TRUNCATED AT 400 WORDS)

Pyramidal neurons in layer 5 of the rat visual cortex. I. Correlation among cell morphology, intrinsic electrophysiological properties, and axon targets

Previous work has established two structure/function correlations for pyramidal neurons of layer 5 of the primary visual cortex of the rat. First, cells projecting to the superior colliculus have thick apical dendrites with a florid terminal arborization in layer 1, whereas those projecting to the visual cortex of the opposite hemisphere have thinner apical dendrites that terminate below layer 1, without a terminal tuft (e.g., Hallman et al.: J Comp Neurol 272:149, '90). Second, intracellular recording combined with dye injection has revealed two classes of cells: the first has a thick, tufted apical dendrite and fires a distinctive initial burst of two or more impulses, of virtually fixed, short interspike interval, in response to current injection; and the other, with a slender apical dendrite lacking a terminal tuft, tends to have a longer membrane time constant and higher input resistance, and does not fire characteristic bursts (e.g., Larkman and Mason: J Neurosci 10:1407, '90). The present study combined intracellular recording in isolated slices of rat visual cortex and injection of carboxyfluorescein, to reveal soma-dendritic morphology, with prior injection of rhodamine-conjugated microspheres into the superior colliculus or contralateral visual cortex to label neurons according to the target of their axons. This permitted a complete correlation of morphology, intrinsic electrophysiological properties, and identity of the projection target for individual pyramidal cells. Neurons retrogradely labeled from the opposite visual cortex were found in all layers except layer 1 while those labeled from the superior colliculus lay exclusively in layer 5. Within layer 5 interhemispheric cells were more concentrated in the lower half of the layer but extensively overlapped the distribution of corticotectal cells. Every cell studied that projected to the superior colliculus was of the bursting type and had a thick apical dendrite with a terminal tuft. Every cell in this study projecting to the opposite visual cortex was a "nonburster" and had a slender apical dendrite with fewer oblique branches that ended without a terminal tuft, usually in the upper part of layer 2/3. Interhemispheric cells also had rounder, less conical somata and generally had fewer basal dendrites than corticotectal neurons. Many cells with the physiological and morphological characteristics of interhemispheric cells were not back-labeled from the opposite visual cortex, implying that pyramidal cells of this type can have other projection targets (e.g., other cortical sites in the ipsilateral hemisphere).(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology of neurons in the thalamic reticular nucleus (TRN) of mammals as revealed by intracellular injections into fixed brain slices

I have investigated the morphology of neurons in the thalamic reticular nucleus (TRN) by means of intracellular injections in fixed tissue in order to study whether neurons in visual (dorsocaudal part), somatosensory (intermediate part), or limbic/motor (rostral part) sectors in the rat, rabbit, and cat differ morphologically in relation to their different sensory cortical or thalamic inputs. In addition, I have compared the different mammalian species to ask whether there is a morphological difference of TRN neurons according to reported differences in the intrinsic thalamic organisation, for example, due to the presence of GABAergic local circuit neurons in the majority of thalamic nuclei in the cat and the lack of those neurons in most of the rat thalamic nuclei, and presynaptic dendrites in the cat but not in the rat. In all animals investigated so far, neurons in the caudal (visual) and intermediate (somatosensory) part of the TRN have an elongated dendritic morphology in all three species, but some neurons in the rostral part, in particular in dorsal sections, have a distinctive multipolar morphology. Neurons have round, ovoid, or elongated somata ranging in area between 150 and 860 microns 2. In general, 4-8 first order dendrites emerge directly from the two poles of the soma or from a thick stem segment. Most of the dendrites then run parallel to the borders of the nucleus extending for relatively long distances, up to 450 microns, but remain inside the border of the nucleus. Only a few (1-3) dendrites could be observed to run perpendicular to the border of the nucleus and generally only for a short distance (20-70 microns). Some of the smooth first order dendrites give rise to second order dendrites (up to 200 microns in length), which then branch into short (15-70 microns) third order dendrites. Dendritic spines and varicosities, spine-like protusions and/or hair-like processes are mainly found on second and third order dendrites. Surprisingly, the shape, arrangement, and the size of the dendritic field are not strictly related to the shape and size of the nucleus. In mammalian species with a comparatively narrow TRN (rat and cat) the dendritic field size was similar to that in the rabbit with a broad TRN. There was considerable variability in dendritic morphology in the caudal and intermediate parts of TRN. However, in contrast to two recent studies in the rat TRN I have found no obvious basis for classification of neurons in the mammalian TRN according to dendritic morphology.(ABSTRACT TRUNCATED AT 400 WORDS)

Photoconversion of diaminobenzidine with different fluorescent neuronal markers into a light and electron microscopic dense reaction product

This article describes methods for photoconverting diaminobenzidine (DAB) into a stable, light and electron microscopically visible dark reaction product in neurons which contain a fluorescent dye. Photoconversion of DAB has been achieved so far with the following fluorescent dyes: rhodamine labeled latex microspheres (RLM), 4,6-diamidino-2-phenylindole (DAPI), 5,7-dihydroxytryptamine (5,7-DHT), Fast Blue (FB), Nuclear Yellow (NY), Diamidino Yellow (DY), Evans Blue (EB), acridine orange (AO), ethidium bromide (EBR),1,1'-dioctadecyl- 3,3,3',3'-tetramethylindolcarbocyanine perchlorate, D-282 (DiI), propidium iodide (PI), and intracellularly injected Lucifer Yellow (LY). The dye is introduced into the neurons by tinctorial staining, retrograde transport, or intracellular injection. Photoconversion is conducted by incubating the tissue with the fluorescent substance-containing cells in a DAB solution under simultaneous strong illumination with ultraviolet (UV) light. During the formation of the reaction product, the fluorescence disappears from the cell. In all cases, photoconversion provided a stable, nonfading DAB reaction product for light microscopy. In addition, at the electron microscopic level, it appeared that the photoconversion results in a homogeneously distributed, fine granular, dark, intracellularly located reaction product. With most of the retrograde tracers tested, photoconversion led only to staining of the cell bodies and the proximal portions of primary dendrites. Following photoconversion with intracellularly LY-filled neurons and cells labeled retrogradely with DiI, DiO, and 5,7-DHT, the reaction product was present throughout the cells, extending from the cell bodies into dendrites and dendritic appendices, and into axons. The high selectivity and methodological simplicity of photoconversion of DAB with fluorescent dyes into a stable, light and electron microscopical dense reaction product provide a promising alternative to classical neuroanatomical techniques and a new useful application of fluorescent neuronal tracers to light and electron microscopy.

Rapid rearrangement of intrinsic tangential connections in the striate cortex of normal and dark-reared kittens: lack of exuberance beyond the second postnatal week

Clustered intrinsic connections in the kitten striate cortex originate from an unclustered, diffusely organized pattern prevailing during the first postnatal week. We have studied the progress of this reorganization and its dependence on visual input by determining the topographies of the intrinsic tangential connections at various postnatal ages by means of axonal tracing methods. Neurons were labeled either by diffusion of the carbocyanin dye DiI in animals ranging in age between 1 day and 30 days, or by retrograde transport of fluorescent microspheres in animals ranging in age between 7 days and 11 months. Quantitative evaluation of retrogradely labeled neurons revealed that during the first postnatal week, intrinsic tangential connections are organized in an unclustered fashion. During the second postnatal week a rapid rearrangement of connections occurs and is complete around postnatal day 11. The main events taking place during the course of this rearrangement are a decrease in the density of tangential connections and an arrangement of them in a clustered fashion. Once the clusters have been formed, the periodicity of the clustered pattern of connections and the size and distinctness of the clusters do not change. This means that the system of clustered tangential connections is adult-like at the end of the second postnatal week. Dark rearing affects neither the rapid rearrangement of horizontal connections into an adult-like system of clusters, nor the integrity of this clustered topography until the end of the first postnatal month. The overall distribution and the lateral extent of the tangential connections remain about the same during the postnatal period and are not affected by dark rearing until the end of the first postnatal month. We conclude that the clustered system of tangential connections in the cat's striate cortex is determined innately.

Widespread lateral processes of glial cells in the immature striate cortex of the cat

The topographies of intrinsic tangential connections of cells in the striate cortex of cats were determined in animals ranging in age between 1 day and 30 days. Implants of the carbocyanin dye, DiI, were found to label cellular elements which are classified by morphological criteria as astrocytes, in addition to neurons. Labeled astrocytes are seen in all cortical layers and in the superficial and deep white matter. Most labeled astrocytes occur underneath the DiI implant, but a number of them are also located horizontally at various distances from the implant. The horizontal span of the glial processes is the same as that for neuronal processes; in contrast to neurons however, the laterally distributed astrocytes assume a flat and unclustered distribution in the horizontal plane. Our observations suggest that the program for determining the span of laterally directed projections in the cat striate cortex is likely to be the same for neurons and astrocyte-like neuroglia.

Olfactory bulb granule cell aggregates: morphological evidence for interperikaryal electrotonic coupling via gap junctions

Anaxonic interneurons of the granule cell type in the mammalian main olfactory bulb (MOB) are characterized by prominent membrane specializations, which include reciprocal, interdendritic chemical and electrical synapses; however, the latter are thought to be restricted to the external plexiform layer (EPL) and connect granule-mitral- and granule-tufted-cell dendrites (Landis et al., 1974). The present study focuses on interperikaryal membrane specializations between tangentially oriented aggregates of granule microneurons in the lamina granularis interna (IGL). Both infraprimate (Rattus norvegicus, Gerbillus perpallidus) and primate species (Callithrix jacchus) were studied using the following methods: (1) transmission electron microscopy (TEM), (2) freeze-fracture analysis, (3) light and TEM immunohistochemistry using affinity-purified antibodies directed against the connexin-32 or connexin-43 carboxy tail fragment of the gap-junction protein (GJP), and (4) intracellular Lucifer yellow injections in fixed tissue (LYF technique). Freeze-fracture replicas of the MOB-IGL showed that adjacent granule cell perikarya have numerous particle aggregates on the cytoplasmic membrane; in terms of their structure and arrangement, such particles are characteristic of gap junctions. The existence of junctional membranes was substantiated by application of antibodies against GJP demonstrating punctate immunoreactivity, frequently confined to the interperikaryal plasmalemmae of granule cells in the IGL and their dendritic processes in the EPL. Upon TEM analysis, GJP-like immunoreactivity was additionally found in membranous organelles, including Golgi apparati and associated vesicular components. In order to test the permeability of identified membrane specializations, the LYF technique was used, which resulted in bright fluorescence of the perikaryal and dendritic components of the transsomatically injected neuron and staining of neighboring neurons with similar morphology. These findings imply that small molecules can diffuse across the interperikaryal membrane specializations. The existence of gap junctions between granule cell perikarya suggests that there is a significant, low-resistance electrical transmission between aggregated granule cells. This coupling might permit synchronization of neural discharge among small aggregates of these neurons. Gap junctions between granule cells may also serve signaling functions associated with the protracted period of granule cell development.