Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the 'WIN' site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small-molecule WINi, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anticancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in human MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anticancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

Lactate Utilization Enables Metabolic Escape to Confer Resistance to BET Inhibition in Acute Myeloid Leukemia

Impairing the BET family coactivator BRD4 with small-molecule inhibitors (BETi) showed encouraging preclinical activity in treating acute myeloid leukemia (AML). However, dose-limiting toxicities and limited clinical activity dampened the enthusiasm for BETi as a single agent. BETi resistance in AML myeloblasts was found to correlate with maintaining mitochondrial respiration, suggesting that identifying the metabolic pathway sustaining mitochondrial integrity could help develop approaches to improve BETi efficacy. Herein, we demonstrated that mitochondria-associated lactate dehydrogenase allows AML myeloblasts to utilize lactate as a metabolic bypass to fuel mitochondrial respiration and maintain cellular viability. Pharmacologically and genetically impairing lactate utilization rendered resistant myeloblasts susceptible to BET inhibition. Low-dose combinations of BETi and oxamate, a lactate dehydrogenase inhibitor, reduced in vivo expansion of BETi-resistant AML in cell line and patient-derived murine models. These results elucidate how AML myeloblasts metabolically adapt to BETi by consuming lactate and demonstrate that combining BETi with inhibitors of lactate utilization may be useful in AML treatment.

SIGNIFICANCE

Lactate utilization allows AML myeloblasts to maintain metabolic integrity and circumvent antileukemic therapy, which supports testing of lactate utilization inhibitors in clinical settings to overcome BET inhibitor resistance in AML. See related commentary by Boët and Sarry, p. 950.

Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the "WIN" site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small molecule WIN site inhibitors, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anti-cancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anti-cancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

TLR3 agonism augments CD47 inhibition in acute myeloid leukemia

CD47-SIRPa is a myeloid check point pathway that inhibits phagocytosis of cells lacking markers for self-recognition. Tumor cells can overexpress CD47 and bind to SIRPa on macrophages, preventing phagocytosis. CD47 expression is enhanced and correlated with a negative prognosis in Acute Myeloid Leukemia (AML), with its blockade leading to cell clearance. ALX90 is an engineered fusion protein with high-affinity for CD47. Composed of the N-terminal D1 domain of SIRPα genetically linked to an inactive Fc domain from human IgG, ALX90 is designed to avoid potential toxicity of CD47-expressing red blood cells. Venetoclax (VEN) is a specific B-cell lymphoma-2 (BCL-2) inhibitor that can restore apoptosis in malignant cells. In AML VEN is combined with azanucleosides to induce superior remission rates, however treatment for refractory/relapse is an unmet need. We questioned whether the anti-tumor activity of a VEN based regimen can be augmented through CD47 inhibition (CD47i) in AML. Human AML cell lines were sensitive to ALX90 and its addition increased efficacy of a VEN+AZA regimen in vivo. However, CD47i failed to clear bone marrow tumor burden in PDX models. We hypothesized that in cases of high medullary tumor burden, loss of resident macrophages reduced ALX efficiency. Therefore, we attempted to enhance this medullary macrophage population with agonism of TLR3 via Poly(I:C), which led to expansion and activation of medullary macrophages in in vivo AML PDX models and potentiated CD47i. In summary, the addition of Poly(I:C) can enhance medullary macrophage populations to potentiate the phagocytosis merited by therapeutic inhibition of CD47.

Selective inhibition of MCL1 overcomes venetoclax resistance in a murine model of myelodysplastic syndromes

Treatment for myelodysplastic syndromes (MDS) remains insufficient due to clonal heterogeneity and lack of effective clinical therapies. Dysregulation of apoptosis is observed across MDS subtypes regardless of mutations and represents an attractive therapeutic opportunity. Venetoclax (VEN), a selective inhibitor of anti-apoptotic protein B-cell lymphoma- 2 (BCL2), has yielded impressive responses in older patients with acute myeloid leukemia (AML) and high risk MDS. BCL2 family anti-apoptotic proteins BCL-XL and induced myeloid cell leukemia 1 (MCL1) are implicated in leukemia survival, and upregulation of MCL1 is seen in VEN-resistant AML and MDS. We determined in vitro sensitivity of MDS patient samples to selective inhibitors of BCL2, BCL-XL and MCL1. While VEN response positively correlated with MDS with excess blasts, all MDS subtypes responded to MCL1 inhibition. Treatment with combined VEN + MCL1 inhibtion was synergistic in all MDS subtypes without significant injury to normal hematopoiesis and reduced MDS engraftment in MISTRG6 mice, supporting the pursuit of clinical trials with combined BCL2 + MCL1 inhibition in MDS.

Pevonedistat and azacitidine upregulate NOXA (PMAIP1) to increase sensitivity to venetoclax in preclinical models of acute myeloid leukemia

Dysregulation of apoptotic machinery is one mechanism by which acute myeloid leukemia (AML) acquires a clonal survival advantage. B-cell lymphoma protein-2 (BCL2) overexpression is a common feature in hematologic malignancies. The selective BCL2 inhibitor, venetoclax (VEN) is used in combination with azacitidine (AZA), a DNAmethyltransferase inhibitor (DNMTi), to treat patients with AML. Despite promising response rates to VEN/AZA, resistance to the agent is common. One identified mechanism of resistance is the upregulation of myeloid cell leukemia-1 protein (MCL1). Pevonedistat (PEV), a novel agent that inhibits NEDD8-activating enzyme, and AZA both upregulate NOXA (PMAIP1), a BCL2 family protein that competes with effector molecules at the BH3 binding site of MCL1. We demonstrate that PEV/AZA combination induces NOXA to a greater degree than either PEV or AZA alone, which enhances VEN-mediated apoptosis. Herein, using AML cell lines and primary AML patient samples ex vivo, including in cells with genetic alterations linked to treatment resistance, we demonstrate robust activity of the PEV/VEN/AZA triplet. These findings were corroborated in preclinical systemic engrafted models of AML. Collectively, these results provide rational for combining PEV/VEN/AZA as a novel therapeutic approach in overcoming AML resistance in current therapies.

Dietary supplementation with anti-IL-10 antibody during a severe Eimeria challenge in broiler chickens

Attenuation of host IL-10 activity during Eimeria infection may elicit a robust Th1 response to eliminate the parasite from the gut epithelium. An experiment was conducted to study the effects of feeding IL-10 neutralizing antibody delivered via a dried egg product (DEP) on growth performance, immune responsivity, and gut health outcomes during a severe challenge with either Eimeria acervulina (study 1) or Eimeria tenella (study 2) following FDA CVM #217 protocol to test anticoccidial products. A total of 720 male Ross 308 chicks were used in each study, with 15 replicate cages of 12 birds and the following 4 treatments: sham-inoculated (uninfected) control diet (UCON), Eimeria-infected control diet (ICON), and Eimeria-infected control diet supplemented with DEP at 2 levels (165 [I-165] or 287 [I-287] U/tonne in study 1 and 143 [I-143] or 287 [I-287] U/tonne in study 2). Individual birds assigned to infected treatment groups received a single oral dose of either 200,000 E. acervulina (study 1) or 80,000 E. tenella (study 2) oocysts at 12 d of age (i.e., d post inoculation [DPI] 0), whereas uninfected birds were sham-inoculated with tap water. A one-way ANOVA was performed on outcomes including growth performance, hematology, serum chemistry profiles, immunophenotyping profiles, and intestinal lesion scores. In both studies, DPI 0 to 7 weight gain, feed intake, and feed conversion ratio were worse (P < 0.05) in all infected groups compared with the UCON group. Compared with ICON, DEP supplementation elicited no differences on overall growth performance. Histopathology and lesion scores revealed severe damage to the gut epithelium owing to the Eimeria challenge, yet DEP supplementation did not improve these outcomes or oocyst shedding, hematological measurements, or serum chemistry. However, DEP supplementation improved (P < 0.05) the percentage of circulating CD3⁺ cells at 6 DPI in study 2. These results indicate that DEP does not appear to elicit a coccidiostatic effect during a severe infection with E. acervulina or E. tenella.

Detection of High Fructose Corn Syrup in Apple Juice by Mass Spectrometric 13C/12C Analysis: Collaborative Study

The addition of high fructose corn syrups (HFCSs) to apple juice can be detected by mass spectrometric determination of 13C/12C ratios. Forty-one pure apple juice samples, representing 18 varieties, gave a mean value for δ13C of −25.3‰ (parts per thousand), while 4 HFCSs averaged −9.7‰. In a collaborative study, 1 pure apple juice and 4 apple juice-HFCS mixtures containing from 25 to 70% apple juice were properly classified by 6 laboratories. Samples with δ13C values less negative than −20.2‰, 4 standard deviations from the mean of pure juices, can, with a high degree of confidence, be classified as adulterated. Because of the range of values for pure apple juices, other interpretations of δ13C data on suspect samples are meaningless (i.e., samples with values more negative than −20.2‰ must be considered unadulterated with HFCS). The 13C/12C mass spectrometric method for corn syrup products, 31.150-31.153, has been adopted official first action for detecting HFCS in apple juice.

Dietary methylsulfonylmethane supplementation and oxidative stress in broiler chickens

Methylsulfonylmethane (MSM) is an organic, sulfur-containing compound widely used as a dietary supplement to improve joint health and treat arthritic pain. An experiment was conducted to study the effects of feeding 0.05% MSM to broilers exposed to diet-induced oxidative stress on tissue MSM distribution, growth performance, oxidative stress biomarkers, and immune responsivity. A total of 528 birds were allocated to 4 dietary treatments (fresh oil-no MSM, fresh oil-MSM, oxidized oil-no MSM, oxidized oil-MSM) as provided ad libitum to 11 replicate cages of 12 birds per treatment. Blood and tissue samples were collected to analyze MSM concentrations, and oxidative stress biomarkers including concentrations of thiobarbituric acid reactive substances (TBARS), total antioxidant capacity (TAC), total glutathione, and glutathione peroxidase (GPx) and reductase (GR) activities. Additionally, blood samples collected at day 25 were used to quantify T-cell (TC) populations using flow cytometry. Overall, MSM was quantified in all tissues and plasma samples of MSM-treated groups at all time points. Oxidized oil reduced (P = 0.006) feed intake over the 21-d feeding period, but MSM did not affect growth equally across time points. No effects (P > 0.2) of MSM or oil type were observed on TC populations. In the presence of oxidized oil, MSM reduced (P = 0.013) plasma TBARS and increased (P = 0.02) liver GPx at day 21, and increased (P = 0.06) liver GR at day 7. Irrespective of dietary oil type, groups supplemented with MSM showed higher plasma TAC at day 7 (P = 0.023), liver GPx activity at day 21 (P = 0.003), and liver GR activity at day 7 (P = 0.004) compared with groups not receiving MSM. In conclusion, 0.05% dietary MSM supplementation partially protected birds from oxidative stress but did not affect immune cell profiles.

Toxicity and tissue distribution of methylsulfonylmethane following oral gavage in broilers

An experiment was conducted to investigate the toxicity and tissue distribution of methylsulfonylmethane (MSM) following oral gavage in broilers. A total of four hundred and thirty-two 15-day-old Ross 308 male broilers were allotted to 6 treatments with 6 replicates of 12 birds per replicate and administered a single oral dose of MSM at 0, 50, 100, 300, 1,000, or 2,000 mg/kg BW (Study 1). Another one hundred and sixty-eight 3-day-old chicks were allotted to either control or test group (Study 2) and administered a daily oral gavage of either 0 or 1, 500 mg/kg BW of MSM for 21 D consecutively. Blood and tissue samples were collected over a 48 h (Study 1) or 21 D (Study 2) period and analyzed for MSM concentrations. Toxicity was assessed through changes in hematology and clinical blood chemistry. In Study 1, plasma MSM concentrations were below 167 μg/mL at all time-points in birds receiving up to 300 mg/kg BW, and were significantly higher (P < 0.05) in birds receiving 1,000 or 2,000 mg/kg BW. Similarly, only the highest 2 MSM dosages elicited increased lymphocyte and decreased heterophil counts at 8 h (P < 0.003) and decreased hematocrit at 48 h (P = 0.015). Growth performance variables were unaffected by MSM in Study 2, and plasma and tissue MSM concentrations were highest on study day 21, with MSM-dosed birds always exhibiting higher (P < 0.03) concentrations compared with the control. Birds in Study 2 that were dosed with MSM had decreased liver enzyme concentrations at day 7 and 21 and decreased glucose and phosphorus at day 7. Importantly, MSM was detected in plasma and all tissues of control groups, confirming that MSM is synthesized de novo in chickens. In conclusion, oral MSM at either acute (single dose at 1,000 to 2,000 mg/kg BW) or sub-chronic (1,500 mg/kg BW daily for 21 D) concentrations did not cause any adverse effects on growth or clinical outcomes and appeared to be absorbed and distributed throughout the body.

Effects of Yucca schidigera-derived saponin supplementation during a mixed Eimeria challenge in broilers

An experiment was conducted to determine if dietary Yucca-derived saponin supplementation could ameliorate the immune and growth responses of broilers during a mixed coccidian challenge. A total of 576 two-day-old male Ross 308 broiler chicks were housed in galvanized starter batteries and randomly assigned to 1 of 4 dietary treatment groups (12 replicate cages of 12 birds). Dietary treatments were corn-soybean meal-based and included 1) control diet + sham-inoculated (Ucon), 2) control diet + Eimeria oocyst challenge (Icon), 3) control diet with 250 mg/kg Yucca-derived saponin product + Eimeria oocyst challenge (ISap250), and 4) control diet with 500 mg/kg of Yucca-derived saponin product + Eimeria oocyst challenge (ISap500). On study day 14, birds were orally inoculated with 1.5 mL of tap water containing Eimeria acervulina, E. maxima, and E. tenella (100,000, 40,000, and 30,000 oocysts/dose, respectively), or sham-inoculated with 1.5 mL of tap water. Eimeria-challenged birds exhibited a reduction in growth compared with uninfected birds (P < 0.001); however, there were no detectable differences due to dietary treatment among Eimeria-challenged groups. Mucosal thickness in the jejunum was increased (P < 0.042) in all infected groups and there were no differences among infected groups; however, saponin supplementation included at 250 mg/kg was not significantly different from the uninfected birds. Lymphocytes as a percentage of total white blood cells were increased (P < 0.014) in all Eimeria-challenged groups at 7 D post-inoculation compared with uninfected birds, but birds supplemented at 250 mg/kg were not different from uninfected birds. Cecal and duodenal IFN-γ expression increased with infection when compared with sham-inoculated birds. Cecal and duodenal IL-1β expression increased (P < 0.008 and P < 0.039) due to infection, and ISap250 and ISap500 treatments ameliorated IL-1β expression to levels not different from sham-inoculated birds. These results suggest that saponin supplementation may provide some immunomodulatory effects during a mixed coccidian challenge as evidenced by lymphocyte responses, changes in intestinal structure, and alterations in cecal and duodenal inflammatory cytokine mRNA expression.

Challenges in Myelodysplastic/Myeloproliferative Neoplasms (MDS/MPN)

Myelodysplastic/myeloproliferative neoplasms (MDS/MPN) are hybrid group of chronic myeloid neoplasms combining features of both MDS and MPN. The World Health Organization classification coined this group designation in 2008 to include chronic myelomonocytic leukemia, atypical chronic myeloid leukemia, juvenile myelomoncoytic leukemia, refractory anemia with ring sideroblasts and thrombocytosis as a provisional entity, and MDS/MPN unclassified. In this review, we highlight the challenges in diagnosing this group of the diseases, summarize the updates in classification, and discuss recent evolving understanding of the genetic landscape. We review risk-stratification models and overview the current management largely adapted from current MDS or MPN therapies. We define clinical benefit of therapy based on new proposed response criteria developed specifically for these groups of neoplasms. Finally, we introduce future opportunities including the planned international ABN MARRO (A Novel therapy combinations in untreated MDS/MPN And Relapsed/Refractory Overlap Syndromes) clinical study led by the MDS/MPN International Working Group.

A Review of Studies on the System-Wide Implementation of Evidence-Based Psychotherapies for Posttraumatic Stress Disorder in the Veterans Health Administration

Since 2006, the Veterans Health Administration (VHA) has instituted policy changes and training programs to support system-wide implementation of two evidence-based psychotherapies (EBPs) for posttraumatic stress disorder (PTSD). To assess lessons learned from this unprecedented effort, we used PubMed and the PILOTS databases and networking with researchers to identify 32 reports on contextual influences on implementation or sustainment of EBPs for PTSD in VHA settings. Findings were initially organized using the exploration, planning, implementation, and sustainment framework (EPIS; Aarons et al. in Adm Policy Ment Health Health Serv Res 38:4-23, 2011). Results that could not be adequately captured within the EPIS framework, such as implementation outcomes and adopter beliefs about the innovation, were coded using constructs from the reach, effectiveness, adoption, implementation, maintenance (RE-AIM) framework (Glasgow et al. in Am J Public Health 89:1322-1327, 1999) and Consolidated Framework for Implementation Research (CFIR; Damschroder et al. in Implement Sci 4(1):50, 2009). We highlight key areas of progress in implementation, identify continuing challenges and research questions, and discuss implications for future efforts to promote EBPs in large health care systems.

Molecular and functional changes in glucokinase expression in the brainstem dorsal vagal complex in a murine model of type 1 diabetes

Glucose concentration changes in the nucleus tractus solitarius (NTS) affect visceral function and metabolism by influencing central vagal circuits, especially inhibitory, GABAergic NTS neurons. Acutely elevated glucose can alter NTS neuron activity, and prolonged hyperglycemia and hypoinsulemia in animal models of type 1 diabetes results in plasticity of neural responses in the NTS. NTS neurons contributing to metabolic regulation therefore act as central glucose sensors and are functionally altered in type 1 diabetes. Glucokinase (GCK) mediates cellular utilization of glucose, linking increased glucose concentration to excitability changes mediated by ATP-sensitive K(+) channels (KATP). Using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, and in vitro electrophysiology, we tested the hypothesis that changes in GCK expression in the NTS accompany the development of diabetes symptoms in the streptozotocin (STZ)-treated mouse model of type 1 diabetes. After several days of hyperglycemia in STZ-treated mice, RNA expression of GCK, but not Kir6.2 or SUR1, was decreased versus controls in the dorsal vagal complex. Electrophysiological recordings in vitro indicated that neural responses to acute hyperglycemia, and synaptic responsiveness to blockade of GCK with glucosamine, were attenuated in GABAergic NTS neurons from STZ-treated mice, consistent with reduced molecular and functional expression of GCK in the vagal complex of hyperglycemic, STZ-treated mice. Altered autonomic responses to glucose in type 1 diabetes may therefore involve reduced functional GCK expression in the dorsal vagal complex.

Diabetes induces GABA receptor plasticity in murine vagal motor neurons

Autonomic dysregulation accompanies type-1 diabetes, and synaptic regulation of parasympathetic preganglionic motor neurons in the dorsal motor nucleus of the vagus (DMV) is altered after chronic hyperglycemia/hypoinsulinemia. Tonic gamma-aminobutyric acid A (GABAA) inhibition prominently regulates DMV neuron activity, which contributes to autonomic control of energy homeostasis. This study investigated persistent effects of chronic hyperglycemia/hypoinsulinemia on GABAA receptor-mediated inhibition in the DMV after streptozotocin-induced type-1 diabetes using electrophysiological recordings in vitro, quantitative (q)RT-PCR, and immunohistochemistry. Application of the nonspecific GABAA receptor agonist muscimol evoked an outward current of significantly larger amplitude in DMV neurons from diabetic mice than controls. Results from application of 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol hydrochloride (THIP), a δ-subunit agonist, suggested that GABAA receptors containing δ-subunits contributed to the enhanced inducible tonic GABA current in diabetic mice. Sensitivity to THIP of inhibitory postsynaptic currents in DMV neurons from diabetic mice was also increased. Results from qRT-PCR and immunohistochemical analyses indicated that the altered GABAergic inhibition may be related to increased trafficking of GABAA receptors that contain the δ-subunit, rather than an expression change. Overall these findings suggest increased sensitivity of δ-subunit containing GABAA receptors after several days of hyperglycemia/hypoinsulinemia, which dramatically alters GABAergic inhibition of DMV neurons and could contribute to diabetic autonomic dysregulation.

The effect of the Rim Cutter on cement pressurization and penetration on cemented acetabular fixation in total hip arthroplasty: an in vitro study

The Rim Cutter (Stryker Orthopedics, Mahwah, New Jersey) is a tool designed to cut a ledge inside the rim of the acetabulum, onto which a precisely trimmed, cemented, flanged cup can be fitted. The aim was to investigate the effect of the Rim Cutter on the intra-acetabular cement mantle pressure and the depth of cement penetration during cup insertion. The study had two parts. In the first part, hemi-pelvis models were fitted with pressure sensors. Pressure in the acetabulum was measured on insertion of a conventional cemented flanged cup with and without the use of a Rim Cutter to prepare the rim of the acetabulum. The second part assessed cement penetration when the same cups were inserted into a foam shell model. The shell was mounted in a jig and had holes drilled in it; the distance that cement penetrated into the holes was measured. A significant increase in cement pressure at the apex (p = 0.04) and the rim (p = 0.004) is seen when the Rim Cutter is used. Cement penetration in the Rim Cutter group was significantly increased at the rim of the acetabulum (p = 0.003). Insertion of a flanged cup after the acetabulum is prepared with the Rim Cutter leads to a significant increase in cement pressure and penetration during cup insertion in vitro when compared with conventional flanged cups.

Rapid inhibition of neurons in the dorsal motor nucleus of the vagus by leptin

The peptide leptin conveys the availability of adipose energy stores to the brain. Increasing evidence implicates a significant role for extrahypothalamic sites of leptin action, including the dorsal vagal complex, a region critical for regulating visceral parasympathetic function. The hypothesis that leptin suppresses cellular activity in the dorsal motor nucleus of the vagus nerve (DMV) was tested using whole-cell patch-clamp recordings in brainstem slices. Leptin caused a rapid membrane hyperpolarization in 50% of rat DMV neurons. Leptin also hyperpolarized a subset of gastric-related neurons (62%), identified after gastric inoculation with a transneuronal retrograde viral tracer. The hyperpolarization was associated with a decrease in input resistance and cellular responsiveness and displayed characteristics consistent with an increased K+ conductance. Perfusion of tolbutamide (200 microM) reversed the leptin-induced hyperpolarization, and tolbutamide or wortmannin (10-100 nM) prevented the hyperpolarization, indicating that leptin activated an ATP-sensitive K+ channel via a phosphoinositide-3-kinase-dependent mechanism. Leptin reduced the frequency of spontaneous and miniature excitatory postsynaptic currents (EPSCs), whereas inhibitory postsynaptic currents (IPSCs) were largely unaffected. Electrical stimulation of the nucleus tractus solitarii (NTS) resulted in constant-latency EPSCs, which were decreased in amplitude by leptin. The paired-pulse ratio was increased, suggesting leptin effects involved activation of receptors presynaptic to the recorded neuron. A leptin-induced suppression of EPSCs, but not IPSCs, evoked by focal photolytic uncaging of glutamate within the NTS was also observed, supportive of leptin effects on the glutamatergic NTS projection to the DMV. Therefore, leptin directly hyperpolarized and indirectly suppressed excitatory synaptic activity to DMV neurons involved in visceral regulation, including gastric-related neurons.

Rapid inhibition of neural excitability in the nucleus tractus solitarii by leptin: implications for ingestive behaviour

The fat-derived peptide leptin regulates cellular activity in areas of the CNS related to feeding, and application of leptin to the fourth ventricle or the nucleus tractus solitarii (NTS) inhibits food intake and weight gain. The hypothesis that leptin modulates cellular activity in the NTS was tested using whole-cell patch-clamp recordings in brainstem slices. Leptin caused a rapid membrane hyperpolarization in 58% of rat NTS neurones, including neurones receiving tractus solitarius input (i.e. viscerosensory) and those involved in regulating output to the stomach, identified after gastric inoculation with a transneuronal retrograde viral label. The hyperpolarization was accompanied by a decrease in input resistance and cellular responsiveness, reversed near the K(+) equilibrium potential, and was prevented by intracellular Cs(+). Perfusion of tolbutamide (200 microm) or wortmannin (100-200 nm) prevented the hyperpolarization, indicating activation of an ATP-sensitive K(+) channel via a PI3 kinase-dependent mechanism. Constant latency tractus solitarius-evoked EPSCs were decreased in amplitude by leptin, and the paired-pulse ratio was increased, suggesting effects on evoked EPSCs involved activation of receptors on vagal afferent terminals. Leptin reduced the frequency of spontaneous and miniature EPSCs, whereas IPSCs were largely unaffected. Leptin's effects were observed in neurones from lean, but not obese, Zucker rats. Neurones that expressed enhanced green fluorescent protein (EGFP) in a subpopulation of putative GABAergic neurones in transgenic mice did not respond to leptin, whereas unlabelled murine neurones responded similarly to rat neurones. Leptin therefore directly and rapidly suppresses activity of excitatory NTS neurones likely to be involved in viscerosensory integration and/or premotor control of the stomach.

Selective enhancement of excitatory synaptic activity in the rat nucleus tractus solitarius by hypocretin 2

Hypocretin 2 (orexin B) is a hypothalamic neuropeptide thought to be involved in regulating energy homeostasis, autonomic function, arousal, and sensory processing. Neural circuits in the caudal nucleus tractus solitarius (NTS) integrate viscerosensory inputs, and are therefore implicated in aspects of all these functions. We tested the hypothesis that hypocretin 2 modulates fast synaptic activity in caudal NTS areas that are generally associated with visceral sensation from cardiorespiratory and gastrointestinal systems. Hypocretin 2-immunoreactive fibers were observed throughout the caudal NTS. In whole-cell recordings from neurons in acute slices, hypocretin 2 depolarized 48% and hyperpolarized 10% of caudal NTS neurons, effects that were not observed when Cs(+) was used as the primary cation carrier. Hypocretin 2 also increased the amplitude of tractus solitarius-evoked excitatory postsynaptic currents (EPSCs) in 36% of neurons and significantly enhanced the frequency of spontaneous EPSCs in most (59%) neurons. Spontaneous inhibitory postsynaptic currents (IPSCs) were relatively unaffected by the peptide. The increase in EPSC frequency persisted in the presence of tetrodotoxin, suggesting a role for the peptide in regulating glutamate release in the NTS by acting at presynaptic terminals. These data suggest that hypocretin 2 modulates excitatory, but not inhibitory, synapses in caudal NTS neurons, including viscerosensory inputs. The selective nature of the effect supports the hypothesis that hypocretin 2 plays a role in modulating autonomic sensory signaling in the NTS.

Serotonergic modulation of retinal input to the mouse suprachiasmatic nucleus mediated by 5-HT1B and 5-HT7 receptors

Serotonin (5-HT) and 5-HT receptor agonists can modify the response of the mammalian suprachiasmatic nucleus (SCN) to light. It remains uncertain which 5-HT receptor subtypes mediate these effects. The effects of 5-HT receptor activation on optic nerve-mediated input to SCN neurons were examined using whole-cell patch-clamp recordings in horizontal slices of ventral hypothalamus from the male mouse. The hypothesis that 5-HT reduces the effect of retinohypothalamic tract (RHT) input to the SCN by acting at 5-HT1B receptors was tested first. As previously described in the hamster, a mixed 5-HT(1A/1B) receptor agonist, 1-[3-(trifluoromethyl)phenyl]-piperazine hydrochloride (TFMPP), reduced the amplitude of glutamatergic excitatory postsynaptic currents (EPSCs) evoked by selectively stimulating the optic nerve of wild-type mice. The agonist was negligibly effective in a 5-HT1B receptor knockout mouse, suggesting minimal contribution of 5-HT1A receptors to the TFMPP-induced reduction in the amplitude of the optic nerve-evoked EPSC. We next tested the hypothesis that 5-HT also reduces RHT input to the SCN via activation of 5-HT7 receptors. The mixed 5-HT(1A/7) receptor agonist, R(+)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT), reduced the evoked EPSC amplitude in both wild-type and 5-HT1B receptor knockout mice. This effect of 8-OH-DPAT was minimally attenuated by the selective 5-HT1A receptor antagonist WAY 100635 but was reversibly and significantly reduced in the presence of ritanserin, a mixed 5-HT(2/7) receptor antagonist. Taken together with the authors' previous ultrastructural studies of 5-HT1B receptors in the mouse SCN, these results indicate that in the mouse, 5-HT reduces RHT input to the SCN by acting at 5-HT1B receptors located on RHT terminals. Moreover, activation of 5-HT7 receptors in the mouse SCN, but not 5-HT1A receptors, also results in a reduction in the amplitude of the optic nerve-evoked EPSC. The findings indicate that 5-HT may modulate RHT glutamatergic input to the SCN through 2 or more 5-HT receptors. The likely mechanism of altered RHT glutamatergic input to SCN neurons is an alteration of photic effects on the SCN circadian oscillator.

Short- and long-term changes in CA1 network excitability after kainate treatment in rats

Neuron loss, axon sprouting, and the formation of new synaptic circuits have been hypothesized to contribute to seizures in temporal lobe epilepsy (TLE). Using the kainate-treated rat, we examined how alterations in the density of CA1 pyramidal cells and interneurons, and subsequent sprouting of CA1 pyramidal cell axons, were temporally associated with functional changes in the network properties of the CA1 area. Control rats were compared with animals during the first week after kainate treatment versus several weeks after treatment. The density of CA1 pyramidal cells and putative inhibitory neurons in stratum oriens was reduced within 8 days after kainate treatment. Axon branching of CA1 pyramidal cells was similar between controls and animals examined in the first week after kainate treatment but was increased several weeks after kainate treatment. Stimulation of afferent fibers in brain slices containing the isolated CA1 region produced graded responses in slices from controls and kainate-treated rats tested <8 days after treatment. In contrast, synchronous all-or-none bursts of spikes at low stimulus intensity (i.e., "network bursts") were only observed in the CA1 several weeks after kainate treatment. In the presence of bicuculline, the duration of evoked bursts was significantly longer in CA1 pyramidal cells weeks after kainate treatment than from controls or those examined in the first week posttreatment. Spontaneous network bursts were also observed in the isolated CA1 several weeks after kainate treatment in bicuculline-treated slices. The data suggest that the early loss of neurons directly associated with kainate-induced status epilepticus is followed by increased axon sprouting and new recurrent excitatory circuits in CA1 pyramidal cells. These changes characterize the transition from the initial acute effects of the kainate-induced insult to the eventual development of all-or-none epileptiform discharges in the CA1 area.

Whole-cell recordings from preoptic/hypothalamic slices reveal burst firing in gonadotropin-releasing hormone neurons identified with green fluorescent protein in transgenic mice

Central control of reproduction is governed by a neuronal pulse generator that underlies the activity of hypothalamic neuroendocrine cells that secrete GnRH. Bursts and prolonged episodes of repetitive action potentials have been associated with hormone secretion in this and other neuroendocrine systems. To begin to investigate the cellular mechanisms responsible for the GnRH pulse generator, we used transgenic mice in which green fluorescent protein was genetically targeted to GnRH neurons. Whole-cell recordings were obtained from 21 GnRH neurons, visually identified in 200-microm preoptic/hypothalamic slices, to determine whether they exhibit high frequency bursts of action potentials and are electrically coupled at or near the somata. All GnRH neurons fired spontaneous action potentials, and in 15 of 21 GnRH neurons, the action potentials occurred in single bursts or episodes of repetitive bursts of high frequency spikes (9.77 +/- 0.87 Hz) lasting 3-120 sec. Extended periods of quiescence of up to 30 min preceded and followed these periods of repetitive firing. Examination of 92 GnRH neurons (including 32 neurons that were located near another green fluorescent protein-positive neuron) revealed evidence for coupling in only 1 pair of GnRH neurons. The evidence for minimal coupling between these neuroendocrine cells suggests that direct soma to soma transfer of information, through either cytoplasmic bridges or gap junctions, has a minor role in synchronization of GnRH neurons. The pattern of electrical activity observed in single GnRH neurons within slices is temporally consistent with observations of GnRH release and multiple unit electrophysiological correlates of LH release. Episodes of burst firing of individual GnRH neurons may represent a component of the GnRH pulse generator.

Ribotype diversity of porcine Pasteurella multocida from Australia

OBJECTIVE

To use the technique of ribotyping to investigate the genetic diversity of Australian isolates of Pasteurella multocida associated with outbreaks of clinical disease in Australian pigs.

DESIGN

One hundred and seven porcine P multocida isolates were analysed by ribotyping using the restriction enzymes HpaII and HindIII. The genetic population structure of the Australian porcine P multocida isolates was determined through statistical analysis of the joint ribotype patterns, and this was then compared with biochemical and epidemiological data available for the population.

RESULTS

A total of 25 combined ribotypes were recognised, which were grouped into five ribotype clusters. Despite the deliberate selection of diverse isolates, the study revealed only a limited degree of genetic diversity. Fourteen of the ribotypes contained multiple isolates, and 12 of these ribotypes were present on more than one farm. Three of the seven biovars analysed in the study showed very limited diversity. All fifteen biovar 2 isolates (subsp multocida) were found in a single cluster (III), while all four biovar 8 isolates, which correspond to P multocida subsp gallicida, were allocated by themselves to a single cluster (IV). All nine of the biovar 12 isolates (lactose-positive subsp multocida) were assigned to a single cluster (I), together with the single biovar 14 isolate, which was the only other lactose-positive isolate in the population (ODC-negative).

CONCLUSION

A limited number of ribotypes of P multocida are associated with Australian pigs. The majority of these ribotypes are widely distributed across multiple farms, and across multiple states. Individual farms can possess multiple ribotypes of P multocida. Some of the unusual biochemical variants of P multocida present in Australian pigs have a very limited genetic diversity. The nature of pig production in Australia, primarily involving continuous flow systems with few closed herds, has possibly contributed to the widespread distribution of a limited number ribotypes.

Pseudorabies virus expressing enhanced green fluorescent protein: A tool for in vitro electrophysiological analysis of transsynaptically labeled neurons in identified central nervous system circuits

Physiological properties of central nervous system neurons infected with a pseudorabies virus were examined in vitro by using whole-cell patch-clamp techniques. A strain of pseudorabies virus (PRV 152) isogenic with the Bartha strain of PRV was constructed to express an enhanced green fluorescent protein (EGFP) from the human cytomegalovirus immediate early promoter. Unilateral PRV 152 injections into the vitreous body of the hamster eye transsynaptically infected a restricted set of retinorecipient neurons including neurons in the hypothalamic suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) of the thalamus. Retinorecipient SCN neurons were identified in tissue slices prepared for in vitro electrophysiological analysis by their expression of EGFP. At longer postinjection times, retinal ganglion cells in the contralateral eye also expressed EGFP, becoming infected after transsynaptic uptake and retrograde transport from infected retinorecipient neurons. Retinal ganglion cells that expressed EGFP were easily identified in retinal whole mounts viewed under epifluorescence. Whole-cell patch-clamp recordings revealed that the physiological properties of PRV 152-infected SCN neurons were within the range of properties observed in noninfected SCN neurons. Physiological properties of retinal ganglion cells also appeared normal. The results suggest that PRV 152 is a powerful tool for the transsynaptic labeling of neurons in defined central nervous system circuits that allows neurons to be identified in vitro by their expression of EGFP, analyzed electrophysiologically, and described in morphological detail.

Electrophysiological responses in vivo of hippocampal CA1 pyramidal neurons in an animal model of neuronal migration disorders

Cortical dysgenesis arising from neuronal migration disorders is closely associated with intractable epilepsy in humans. We used extracellular field potential and conventional intracellular recordings from the dorsal hippocampus of intact adult rats to determine if the excitability of CA1 pyramidal cells was enhanced in rats with experimentally induced hippocampal dysplasia. Electrical stimulation of afferent fibers resulted in more robust population responses in the CA1 region of irradiated rats versus controls. Synaptic inhibition of pyramidal cells was also reduced in these animals. These results suggest that the excitability of the CA1 region in rats with hippocampal dysplasia is greater than in control animals.

Synaptic responses of neurons in heterotopic gray matter in an animal model of cortical dysgenesis

Neuronal heterotopia is a malformation of cortical development that is closely associated with epilepsy in humans. Despite emerging interest in the structure and function of the heterotopic cortex, little is known about the membrane properties and synaptic connections of these displaced neurons. We used whole-cell patch-clamp and extracellular field potential recordings from heterotopic neurons in slices from young adult rats with experimentally induced cortical dysgenesis to determine if local synaptic connections were present in nodular heterotopia. Complex synaptic responses were observed after electrical stimulation of adjacent white matter. The results suggest that neurons in nodular heterotopic gray matter can form local excitatory and inhibitory synaptic connections and may participate in epileptiform events.

Alpha-tocopherol dietary supplement decreases titers of antibody against 5-hydroxymethyl-2'-deoxyuridine (HMdU)

This study evaluated the effects of vitamin E (alpha-tocopherol) on oxidative DNA damage in a randomized double-blind Phase II chemoprevention trial. Oxidative DNA damage was measured by the level of auto-antibody (Ab) against 5-hydroxymethyl-2'-deoxyuridine (HMdU) in plasma. After the baseline screening, eligible subjects (n = 31; plasma samples from 28 subjects were available for this study) were randomized to receive 15, 60, or 200 mg of alpha-tocopherol per day for 28 days. Biomarkers were measured twice at baseline--on day 1 (visit 1) and day 3 (visit 2)--and twice after intervention--on day 17 (visit 3) and day 31 (visit 4). At baseline, there was a highly significant inverse correlation between anti-HMdU Ab titer and plasma vitamin E level (r = -0.53; P = 0.004; n = 28). Smoking did not affect baseline anti-HMdU Ab titer; however, anti-HMdU Ab titer levels at baseline were significantly lower in subjects with above-median (0.75 ounce/day) alcohol consumption (P = 0.008). No significant change in anti-HMdU Ab level occurred at either visit 3 or visit 4 for subjects on the lowest dose, 15 mg alpha-tocopherol per day. Subjects receiving 60 mg of alpha-tocopherol per day had a significant decrease in anti-HMdU Ab level at visits 3 and 4 compared with baseline (P = 0.049 and P = 0.02, respectively). However, subjects receiving the highest dose, 200 mg/day, had less consistent results: a significant decrease in anti-HMdU Ab level was seen at visit 4 (P = 0.04) but not at visit 3. Our results demonstrate an inverse relationship between alpha-tocopherol and anti-HMdU Abs in plasma; oxidative DNA damage can be modulated by short-term dietary supplementation of alpha-tocopherol in some subjects.

Electrophysiological recording from brain slices

This article discusses several of the currently used methodologies for recording from brain slices. Aspects of slice preparation as well as appropriate uses for the various slice models (i.e., thin or thick slices) are considered. The merits of extracellular and intracellular electrophysiological recording and their uses are discussed. In addition, mechanisms of neuronal circuit activation and stimulation are presented.

5-HT1B receptor-mediated presynaptic inhibition of retinal input to the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) receives glutamatergic afferents from the retina and serotonergic afferents from the midbrain, and serotonin (5-HT) can modify the response of the SCN circadian oscillator to light. 5-HT1B receptor-mediated presynaptic inhibition has been proposed as one mechanism by which 5-HT modifies retinal input to the SCN (Pickard et al., 1996). This hypothesis was tested by examining the subcellular localization of 5-HT1B receptors in the mouse SCN using electron microscopic immunocytochemical analysis with 5-HT1B receptor antibodies and whole-cell patch-clamp recordings from SCN neurons in hamster hypothalamic slices. 5-HT1B receptor immunostaining was observed associated with the plasma membrane of retinal terminals in the SCN. 1-[3-(Trifluoromethyl)phenyl]-piperazine HCl (TFMPP), a 5-HT1B receptor agonist, reduced in a dose-related manner the amplitude of glutamatergic EPSCs evoked by stimulating selectively the optic nerve. Selective 5-HT1A or 5-HT7 receptor antagonists did not block this effect. Moreover, in cells demonstrating an evoked EPSC in response to optic nerve stimulation, TFMPP had no effect on the amplitude of inward currents generated by local application of glutamate. The effect of TFMPP on light-induced phase shifts was also examined using 5-HT1B receptor knock-out mice. TFMPP inhibited behavioral responses to light in wild-type mice but was ineffective in inhibiting light-induced phase shifts in 5-HT1B receptor knock-out mice. The results indicate that 5-HT can reduce retinal input to the circadian system by acting at presynaptic 5-HT1B receptors located on retinal axons in the SCN.

Serological characterisation of Actinobacillus pleuropneumoniae isolated from pigs in 1993 to 1996

OBJECTIVES

To clarify the serological identity of the prototype strain of a group of Actinobacillus pleuropneumoniae isolates that could not be serotyped in previous studies and to establish the serovar of 378 isolates of A pleuropneumoniae obtained from pigs in Australia over the period 1993 to 1996.

DESIGN

After initial validation, QGD and IHA tests were used to characterise the prototype isolate (HS143) selected to represent the cross-reacting isolates that were found in a previous study. Next, 378 recent field isolates of A pleuropneumoniae were characterised using the existing gel diffusion serotyping technique and/or the IHA or QGD tests.

RESULTS

The indirect haemagglutination test was shown to be capable of correctly recognising the reference strain for all serovars except serovar 11. While the quantitative gel diffusion test was not as effective as indirect haemagglutination, it could recognise serovar 11. When the two tests were used to examine the prototype strain (HS143) of the cross-reactive isolates, the results indicated that HS143 is serologically distinct from all 12 of the recognised serovars of A pleuropneumoniae. However, as HS143 was subsequently identified as serovar 12 by one of the leading international reference laboratories, the antiserum to isolate HS143 was used as the serovar 12 antiserum. A total of 346 of the 378 A pleuropneumoniae field isolates examined could be confidently serotyped with almost 90% of the isolates being either serovar 1 (104 isolates); serovar 7 (83 isolates) or serovar 12 (142 isolates). A range of other serovars and some cross-reactive isolates made up the remainder of the isolates.

CONCLUSION

The serovar 12 antiserum produced against the international reference strain (1096) does not recognise Australian serovar 12 isolates. The antiserum raised against isolate HS143 does recognise the Australian serovar 12 isolates. The dominant serovars of A pleuropneumoniae infecting Australian pigs are (in decreasing order) serovars 12, 1 and 7.

Vagally evoked synaptic currents in the immature rat nucleus tractus solitarii in an intact in vitro preparation

1. Whole-cell voltage-clamp recordings in an in vitro brainstem-cranial nerve explant preparation were used to assess the local circuitry activated by vagal input to nucleus tractus solitarii (NTS) neurones in immature rats. 2. All neurones that responded to vagal stimulation displayed EPSCs of relatively constant latency. Approximately 50 % of these also demonstrated variable-latency IPSCs, and approximately 31 % also displayed variable-latency EPSCs to vagal stimulation. All neurones also had spontaneous EPSCs and IPSCs. 3. Evoked and spontaneous EPSCs reversed near 0 mV and were blocked by the glutamate AMPA/kainate receptor antagonists 6,7-nitroquinoxaline-2,3-dione (DNQX) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) at rest. Evoked EPSCs had rapid rise times (< 1 s) and decayed monoexponentially (tau = 2. 04 +/- 0.03 ms) at potentials near rest. 4. At holding potentials positive to approximately -50 mV, a slow EPSC could be evoked in the presence of DNQX or CNQX. This current peaked at holding potentials near -25 mV and was blocked by the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP5). It was therefore probably due to activation of NMDA receptors by vagal afferent fibres. 5. Fast IPSCs reversed near -70 mV and were blocked by the GABAA receptor antagonist bicuculline. In addition, bicuculline enhanced excitatory responses to vagal stimulation and increased spontaneous EPSC frequency. Antagonists to AMPA/kainate receptors reversibly blocked stimulus-associated IPSCs and also decreased the frequency of spontaneous IPSCs. 6. These findings suggest that glutamate mediates synaptic transmission from the vagus nerve to neurones in the immature NTS by acting at non-NMDA and NMDA receptors. NTS neurones may also receive glutamatergic and GABAergic synaptic input from local neurones that can be activated by vagal input and/or regulated by amino acid inputs from other brainstem neurones.1. Whole-cell voltage-clamp recordings in an in vitro brainstem-cranial nerve explant preparation were used to assess the local circuitry activated by vagal input to nucleus tractus solitarii (NTS) neurones in immature rats.

Prevalence of hereditary hemochromatosis in a Massachusetts corporation: is Celtic origin a risk factor?

The prevalence of homozygous hereditary hemochromatosis (HHC) is estimated at 1:250 in Caucasian adults. Little is known about ethnic subpopulations that might be at increased risk for this disease. HLA data have suggested a Celtic origin for HHC. Screening for HHC was offered to all employees of the Massachusetts Polaroid Corporation. Participants with a transferrin saturation of >55% or >45% and an elevated serum ferritin concentration on two screenings were referred for liver biopsy. The diagnosis of HHC was based on histological criteria, quantitative hepatic iron determination, hepatic iron index, and the phlebotomy requirement for iron depletion. Participants completed a questionnaire regarding their ethnic background. Two thousand two hundred ninety-four employees were screened, and 5 cases of HHC were detected. All 5 cases involved Caucasian men, yielding a prevalence of 1:395 for the Caucasian population. Four of the 5 cases were of 100% British-Irish ancestry based on the country of origin of their grandparents. Additional analysis revealed that the majority of grandparents of all 4 individuals came from Ireland or Wales. The exact two-tailed trend test showed a significant association of HHC with Celtic background (P = .012). The estimated cost of screening per patient identified was $18,041. Polaroid Corporation has a high representation of employees of British-Irish ancestry. Our data suggest that they are at high risk for developing HHC. A significant association of HHC with Celtic ancestry was found in this subpopulation, supporting the concept of a Celtic origin for this disease.

Enhanced population responses in the basolateral amygdala of kainate-treated, epileptic rats in vitro

Several lines of evidence suggest that the amygdala is altered functionally in humans with temporal lobe epilepsy, but little is known about neuronal interactions in the amygdala of humans or animals with chronic epilepsy. Using extracellular and intracellular recordings in horizontal slices, we tested the hypothesis that changes in local circuitry in the basolateral amygdala (BLA) permanently enhance neuronal responsiveness in kainate-treated, epileptic rats. Population responses in the BLA to orthodromic stimulation were significantly enhanced, which was at least partly due to a decrease in local inhibition. In the presence of GABA receptor antagonists, population responses were about twice as robust in epileptic versus control rats. We conclude that the enhanced neuronal responsiveness of the BLA in this model of temporal lobe epilepsy involves decreased inhibition, but may also include increased excitation.

Long latency ankle responses to dynamic perturbation in older fallers and non-fallers

OBJECTIVE

The purpose of this study was to examine the effects of falling history and aging on the latency and magnitude of long latency responses in the lateral gastrocnemius (LG) and tibialis anterior (TA) muscles of older adults.

DESIGN

Single observation study.

SETTING

Emory University School of Medicine, Center for Rehabilitation Medicine, serving the greater Atlanta, Georgia, area.

PARTICIPANTS

There were 62 community-dwelling adults aged 60 or older, 32 with a history of two or more unexplained falls in the past year and 30 with no history of falls in the past year.

MEASUREMENTS

The electromyographic activity of the gastrocnemius and tibialis anterior muscles was recorded bilaterally during repeated 10 degree dorsiflexion perturbations to standing subjects at the acceleration of gravity and a velocity of approximately 100 deg/sec. The latency and magnitude of the long latency EMG responses (LLR) of both muscles were determined and compared between individuals by falls history and by decades of age.

MAIN RESULTS

No significant differences between falls status groups existed for mean LLR latencies or magnitudes of either LG or TA. Attenuation of the LLR throughout the trials was significantly different between groups. Non-fallers demonstrated attenuation of the LG magnitude over the first five stretches. Fallers showed maladaptation of the LG response, with the latency becoming shorter over 25 trials. More than half of the subjects in both groups had one or more instances of temporal reversal of the response latencies, with the TA response occurring earlier than the LG response during the first five stretches. No differences existed in the LLR between age decades within faller or non-faller groups. A timed measure of mobility (Up & Go) showed a significant difference between falls status, but not between age decades in either group.

CONCLUSIONS

Lack of differences between falls status and age decade groups over all trials suggests that LLRs remain intact between older fallers and non-fallers and between older age groups. The mechanism of perturbation is a distinguishing feature of this study and probably contributes to our findings. The appearance of an atypical response strategy in both groups, where the TA response often occurs before the LG response, has raised the question of whether there is always a stereotypical pattern of LLRs during postural perturbations outside the experimental setting.

The ionic dependence of the histamine-induced depolarization of vasopressin neurones in the rat supraoptic nucleus

1. The ionic basis of the histamine-induced depolarization of immunohistochemically identified neurones in the supraoptic nucleus (SON) was investigated in the hypothalamo-neurohypophysial explant of male rats. Histamine (0.1-100 microM) caused an H1 receptor-mediated, dose-dependent depolarization of fifty of sixty-two vasopressin neurones in the SON. In contrast, twenty-three oxytocin neurones were either depolarized (n = 6), hyperpolarized (n = 4), or unaffected (n = 13) by histamine. Due to the low percentage of responding cells, oxytocin neurones were not further investigated. 2. Chelation of intracellular Ca2+ with 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA; 100-500 mM) blocked the depolarization, whereas blocking Ca2+ influx and synaptic transmission with equimolar Co2+ or elevated (5-20 mM) Mg2+ in nominally Ca(2+)-free solutions was without effect. 3. The amplitude of the histamine-induced depolarization was relatively independent of membrane potential. The input resistance was unaltered by histamine in nine neurones, but in nine other neurones it was decreased and in two neurones it was increased by more than 5%. Neither elevating extracellular K+ nor addition of the K+ channel blockers, apamin, d-tubocurarine, tetraethylammonium (TEA), or intracellular Cs+ decreased the histamine effect. Indeed, broadly blocking K+ currents with TEA and Cs+ significantly increased the depolarization to histamine. 4. Tetrodotoxin (2-3 microM) did not inhibit the histamine-induced depolarization. However, equimolar replacement of approximately 50% of extracellular Na+ with Tris+ or N-methyl-D-glucamine reduced or eliminated the response. 5. The depolarization of vasopressin neurones by histamine thus requires extracellular Na+ and intracellular Ca2+. Activation of a Ca(2+)-activated non-specific cation current or a Ca(2+)-Na+ pump are possible mechanisms for this effect.

Amino acid-mediated regulation of spontaneous synaptic activity patterns in the rat basolateral amygdala

1. Spontaneous postsynaptic currents (PSCs) were examined in the basolateral amygdala using whole cell patch-clamp recordings in coronal slices (400 microns) from young rats (postnatal day 6-25). In most cells, Cs+ was used in the electrode to block putative voltage-activated K(+)-currents. Both inward and outward spontaneous PSCs were examined. 2. The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonist, 6,7-nitroquinoxaline-2,3-dione (DNQX) blocked all inward PSCs, which reversed near 0 mV. They therefore were considered to be glutamate-mediated excitatory postsynaptic currents (EPSCs). Averaged EPSCs had a rapid 10-90% rise time (1.0 +/- 0.04 ms; mean +/- SD) and monoexponential decay (tau = 3.6 +/- 0.18 ms) at potentials negative to about -50 mV. Above this potential, a second, slower time constant (tau 1 = 41 +/- 4.5 ms at -30 mV), accounting for 10-30% of the total EPSC amplitude was resolved in 8 of 10 cells examined. The slower decay time constant was sensitive to the N-methyl-D-aspartate (NMDA)-receptor antagonist, DL-2-amino-5-phosphonovaleric acid (AP5) and therefore probably was due to activation of NMDA receptors. 3. The gamma-aminobutyric acid-A (GABAA) antagonist, bicuculline, blocked all outward PSCs, which reversed near -70 mV. They therefore were considered to be GABA-mediated inhibitory postsynaptic currents (IPSCs). Averaged IPSCs displayed rapid 10-90% rise times (1.0 +/- 0.03 ms) and monoexponential decay time constants (tau = 5.16 +/- 0.14 ms). 4. Tetrodotoxin (TTX) reduced the frequency of synaptic activity and eliminated the largest PSCs, thus reducing slightly the mean EPSC and IPSC amplitude. Most cells received bursts of spontaneous IPSCs and/or EPSCs (30-68 Hz lasting 0.5-6 s), which were also TTX sensitive. The TTX data suggest that the somata of the cells responsible for the largest PSCs and the PSC bursts were contained within the slice. 5. In addition to blocking EPSCs, DNQX blocked the bursts of IPSCs, but not all individual IPSCs. DNQX had similar effects as TTX on the bursts and frequency of the IPSCs. 6. Bicuculline enhanced spontaneous EPSC frequency (231 +/- 90%). Much of this increase was due to an increase in the bursts of EPSCs. 7. Neurons in the basolateral amygdala therefore appear to receive both excitatory (glutamatergic) and inhibitory (GABAergic) synaptic input from local neurons. The activity of the neurons responsible for these inputs are themselves largely regulated by glutamatergic and GABAergic inputs. The relevance of this local circuitry to seizures and epilepsy is discussed briefly.

Age-related epileptogenic effects of corticotropin-releasing hormone in the isolated CA1 region of rat hippocampal slices

1. The effects of corticotropin-releasing hormone (CRH) on synaptically evoked population and intracellular responses in the isolated rat CA1 region of hippocampal slices were studied to evaluate possible differences between adult and juvenile rats. 2. The amplitude of orthodromically evoked (stratum radiatum stimulation) population spikes was reversibly enhanced by 0.2-0.6 microM CRH to a greater extent in slices from juvenile rats than from adult rats. In no case, however, did CRH cause seizure-like activity to develop under normal recording conditions. 3. In the presence of 10-30 microM bicuculline, interictal-like bursts of population spikes and corresponding intracellularly recorded action potentials could be evoked starting at postnatal day 8. The number of spikes and the duration of the evoked bursts in the CA1 region were reversibly increased by CRH (0.2-0.6 microM) to a greater extent in slices from juvenile than from adult rats. 4. The amplitude of the afterhyperpolarization following intracellularly evoked bursts of action potentials in CA1 pyramidal cells was reduced by 0.2 microM CRH to a similar degree in both young and adult rats. No consistent changes in input resistance or membrane potential were observed. 5. No correlation was found between the magnitude of the CRH-induced increase in responsiveness and the initial excitability in controls, suggesting that the CRH-induced changes were independent of any age-dependent differences in general slice excitability. 6. Our results indicate that, in the CA1 region, CRH augments bicuculline-induced bursts to a greater extent in slices from young versus adult rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological characteristics of immunochemically identified rat oxytocin and vasopressin neurones in vitro

1. Intracellular recordings were made from supraoptic neurones in vitro from hypothalamic explants prepared from adult male rats. Neurones were injected with biotinylated markers, and of thirty-nine labelled neurones, nineteen were identified immunocytochemically as containing oxytocin-neurophysin and twenty as containing vasopressin-neurophysin. 2. Vasopressin and oxytocin neurones did not differ in their resting membrane potential, input resistance, membrane time constant, action potential height from threshold, action potential width at half-amplitude, and spike hyperpolarizing after-potential amplitude. Both cell types exhibited spike broadening during brief, evoked spike trains (6-8 spikes), but the degree of broadening was slightly greater for vasopressin neurones. When hyperpolarized below -75 mV, all but one neurone exhibited a transient outward rectification to depolarizing pulses, which delayed the occurrence of the first spike. 3. Both cell types exhibited a long after-hyperpolarizing potential (AHP) following brief spike trains evoked either with a square wave pulse or using 5 ms pulses in a train. There were no significant differences between cell types in the size of the AHP evoked with nine spikes, or in the time constant of its decay. The maximal AHP evoked by a 180 ms pulse was elicited by an average of twelve to thirteen spikes, and neither the size of this maximal AHP nor its time constant of decay were different for the two cell types. 4. In most oxytocin and vasopressin neurones the AHP, and concomitantly spike frequency adaptation, were markedly reduced by the bee venom apamin and by d-tubocurarine, known blockers of a Ca(2+)-mediated K+ conductance. However, a minority of neurones, of both cell types, were relatively resistant to both agents. 5. In untreated neurones, 55% of vasopressin neurones and 32% of oxytocin neurones exhibited a depolarizing after-potential (DAP) after individual spikes or, more commonly, after brief trains of spikes evoked with current pulses. For each neurone with a DAP, bursts of spikes could be evoked if the membrane potential was sufficiently depolarized such that the DAP reached spike threshold. In four out of five vasopressin neurones a DAP became evident only after pharmacological blockade of the AHP, whereas in six oxytocin neurones tested no such masking was found. 6. The firing patterns of neurones were examined at rest and after varying the membrane potential with continuous current injection. No identifying pattern was strictly associated with either cell type, and a substantial number of neurones were silent at rest.(ABSTRACT TRUNCATED AT 400 WORDS)

Histamine enhances the depolarizing afterpotential of immunohistochemically identified vasopressin neurons in the rat supraoptic nucleus via H1-receptor activation

Previous studies have demonstrated that histamine primarily excites unidentified neurons in the rat supraoptic nucleus. We investigated the neuromodulatory effects of histamine on immunohistochemically identified vasopressin neurons in the rat supraoptic nucleus using intracellular recording techniques from the hypothalamo-neurohypophysial explant. Exogenous application of histamine (0.1-100 microM) to vasopressinergic neurons produced a small membrane depolarization accompanied by an increase of up to 100% in the amplitude of the depolarizing afterpotential that follows current-evoked trains of action potentials. The enhancement of the depolarizing afterpotential by histamine did not depend upon the depolarization. Further, histamine enhanced the amplitude of the depolarizing afterpotential when blocking the afterhyperpolarizing potential with d-tubocurarine or apamin, and in the presence of tetrodotoxin and d-tubocurarine or apamin, indicating a postsynaptic action of histamine on the depolarizing afterpotential that is not simply a reflection of a decrease in the afterhyperpolarizing potential. These toxins also had no effect on the histamine-induced depolarization. The enhancement of the depolarizing afterpotential by histamine was mimicked by the histamine H1-receptor agonist 2-thiazolylethylamine and was reduced or blocked by the H1-receptor antagonist promethazine, but was not blocked or reduced in the presence of the histamine H2-receptor antagonist, cimetidine. In summary, these results show that the excitatory effect of histamine on immunohistochemically identified vasopressin neurons in the supraoptic nucleus is due in part to the H1-receptor-mediated enhancement of the depolarizing afterpotential independent of any change in the afterhyperpolarizing potential or membrane potential.

Relationships between sensory responsiveness and premovement activity of quickly adapting neurons in areas 3b and 1 of monkey primary somatosensory cortex

When monkeys make wrist movements in response to vibration of their hands, primary somatosensory (SI) cortical neurons that adapt quickly to the vibratory stimulus often exhibit two temporally separate types of activity. Initially, these neurons respond to the stimulus. They then cease discharging, only to resume firing prior to the movement. This activation, cessation and reactivation occurs even though the sensory stimulus remains on until after the movement is begun. The first change in activity is most likely related to sensory input. The second, which has been called premovement activity, may have a sensory component as well as one related to the upcoming movement. We wanted to test the hypothesis that the premovement activity exhibited when vibration is present represents both a reactivation of a neuron's vibratory response and the premovement activity that normally occurs when vibration is absent. We also wanted to determine if area 3b and 1 quickly adapting (QA) neurons show similar or different activity patterns during the initiation and execution of sensory triggered wrist movements. Four monkeys were trained to make wrist flexion and extension movements in response to vibratory stimuli delivered to the handle which the animals used to control the behavioral paradigm. Two fo the four monkeys also made similar wrist movements following visual cues. We found that the premovement activity of QA neurons located in area 1 (but not area 3b) is comprised of a sensory-related component as well as a movement-related component. The magnitude of these individual components differs in relationship to a neuron's receptive field type, the movement direction and the external force imposed on the stimulated forelimb. Premovement activity of area 3b and area 1 QA neurons occurs at the same time prior to movement, regardless of whether visual or vibratory cues are used to trigger wrist movements. This activity occurs at about the same time as others have observed elevations in the threshold for tactile perception, suggesting that premovement activity and changes in sensory responsiveness before movement may be related. These and previous findings are used to construct a model which may predict the firing patterns of SI QA neurons during behavioral tasks. These findings also suggest that areas 3b and 1 may have different roles in processing task-related somatosensory information.

Tuberal supraoptic neurons--II. Electrotonic properties

The electrotonic properties of tuberal supraoptic neurons were studied from conventional intracellular recordings made in the hypothalamo-neurohypophysial explant in vitro. The cable parameters electrotonic dendritic length, and the dendritic to somatic conductance ratio, were estimated using the slopes and intercepts of the first two peeled exponentials of the voltage transients generated by current steps. The estimations were made assuming an equivalent cylinder model consisting of a soma and an attached, lumped dendrite of finite length. An equalizing time constant was resolved in 12 of 17 neurons, allowing calculation of both cable parameters. In only one of these 12 was it necessary to assume a somatic shunt to account for the data. The average value of the dendritic electrotonic length was 1.02, and that of the dendritic to somatic conductance ratio, 4.11. In the remaining five neurons, an equalizing time constant could not be peeled and consequently the dendritic cable parameters could not be estimated. The average input resistance of these 12 neurons was 162 M omega and the average membrane time constant was 11.86 ms. Principal Components Analysis revealed that the variance of input resistance and time constant was largely explained by one factor, while that of dendritic electrotonic length and the dendritic to somatic conductance ratio was explained by a separate, independent factor, suggesting a separation of electrical and morphological parameters, respectively. In addition, the variability of the data indicates that considerable differences in the morphology and specific membrane resistivity exist across supraoptic neurons. An analysis of spontaneously occurring postsynaptic potentials revealed that the shapes of these potentials could not be explained simply by assuming that they were determined by their passive decay from some point along the equivalent cable to the soma. In conclusion, dendrites make a significant and previously unappreciated contribution to the electrotonic behavior of supraoptic neurons. These electrotonic properties are similar to those of many other, morphologically diverse, central nervous system neurons.

Tuberal supraoptic neurons--I. Morphological and electrophysiological characteristics observed with intracellular recording and biocytin filling in vitro

Previous studies of the tuberal, or retrochiasmatic, portion of the supraoptic nucleus suggest its functional similarity to the more densely populated anterior supraoptic nucleus, but the basic electrophysiological and morphological features of tuberal supraoptic nucleus neurons have not been described. Using the hypothalamo-neurohypophysial explant preparation in the rat, intracellular recordings and biocytin injections were made in tuberal supraoptic nucleus neurons and the results indicate that the two parts of the nucleus are similar. The generally oval-shaped somata of tuberal supraoptic nucleus neurons exhibited short, irregularly shaped appendages, and possessed 2-5 varicose, sparsely branching dendrites oriented in the horizontal plane. Many tuberal supraoptic nucleus neurons could be antidromically stimulated (mean latency = 6.4 ms). Filled neurons had varicose axons which were traced to the median eminence and even as far as the neural stalk, but which did not bifurcate. Both axons and dendrites were sparsely invested with short, hair-like appendages. The input resistance of the recorded neurons (mean = 177.7 M omega) was positively correlated with the membrane time constant (mean = 13.1 ms; r = 0.83). Tuberal supraoptic nucleus neurons displayed a prominent afterhyperpolarization following individual spikes or bursts of spikes, as well as firing frequency adaptation in response to positive current pulses. Although numbering far fewer than those of the anterior supraoptic nucleus, tuberal supraoptic nucleus neurons have axons which are more often intact in this preparation, and a dendritic tree which radiates within the plane of the explant. Thus these neurons should provide a useful model for further study of the electrophysiological and morphological characteristics of mammalian neurosecretory neurons.

Influence of 2-(3,4 dichlorophenoxy)-triethylamine on photosynthesis of Phaseolus vulgaris L

The effect of foliar sprays of the growth regulator 2-(3,4 dichlorophenoxy)-triethylamine (DCPTA) on net photosynthesis (Pn) by intact bean plants depended upon concentration and the stage of development of the leaves. A single foliar spray of 2.0 mM DCPTA reduced Pn when applied to young expanding leaves but had little effect on fully expanded leaves. Lower DCPTA concentrations (0.2 to 0.8 mM) had no effect on Pn, unless applied more than once which resulted in reduced Pn. The DCPTA-induced inhibition of Pn was associated with chlorosis and aberrations in chloroplast ultrastructure. DCPTA did not affect stomatal resistance. When applied to detached leaf disks in the dark, DCPTA retarded the normal loss of chlorophyll suggesting that DCPTA may have anti-seneseent properties.

Mass spectrometric 13C/12C determinations to detect high fructose corn syrup in orange juice: collaborative study

The 13C/12C ratios in orange juice are sufficiently uniform and different from those in high fructose corn syrup (HFCS) so that the addition of HFCS to orange juice can be detected. HFCS averages -9.7% (parts per thousand) delta 13C, orange juice averages -24.5%, and mixtures of HFCS and orange juice possess intermediate values. One pure orange juice and 4 orange juice -HFCS mixtures containing from 25 to 70% orange juice were properly classified by 7 collaborators. Samples with delta 13C values less negative than -22.1%, 4 standard deviations from the mean of pure juices, can, with a high degree of confidence, be classified as adulterated. Samples with values more negative than -22.1% must be considered unadulterated with HFCS, because pure orange juices possess a range of delta 13C values. The 13C/12C mass spectrometric method was adopted official first action for detecting HFCS in orange juice.

Mass Spectrometric 13C/12C Determinations to Detect High Fructose Corn Syrup in Orange Juice: Collaborative Study

The 13C/12C ratios in orange juice are sufficiently uniform and different from those in high fructose corn syrup (HFCS) so that the addition of HFCS to orange juice can be detected. HFCS averages –9.7‰ (parts per thousand) δ13C, orange juice averages —24.5‰, and mixtures of HFCS and orange juice possess intermediate values. One pure orange juice and 4 orange juice-HFCS mixtures containing from 25 to 70% orange juice were properly classified by 7 collaborators. Samples with δ13C values less negative than — 22.1‰, 4 standard deviations from the mean of pure juices, can, with a high degree of confidence, be classified as adulterated. Samples with values more negative than —22.1‰ must be considered unadulterated with HFCS, because pure orange juices possess a range of δ13C values. The 13C/12C mass spectrometric method was adopted official first action for detecting HFCS in orange juice.

Localization of ribulose bisphosphate carboxylase in the guard cells by an indirect, immunofluorescence technique

Ribulose bisphosphate carboxylase, a key enzyme in the photosynthetic carboxylation process, has been localized through an indirect immunofluorescent technique in the guard cells of some of the 41 species of plants examined. This sample includes 17 families of both dicotyledons and monocotyledons, one gymnosperm, and one pteridophyte. Plants were selected to represent all of the three major photosynthetic categories, namely C(3), C(4), and Crassulacean acid metabolism. Antibodies raised against tobacco (Nicotiana tabacum L.) ribulose bisphosphate carboxylase were used for this immunofluorescent study. A good degree of fluorescence was observed in the guard cells of seven out of 21 species exhibiting Crassulacean acid metabolism. C(3) plants exhibited a very low degree (almost negligible) of fluorescence, while the C(4) species did not exhibit any fluorescence.