The impact of COVID-19 on clinical cancer care: An individual-patient level analysis

1533

Background: At the outset of the COVID-19 pandemic, concerns for the safety of patients receiving anti-cancer treatment coupled with pressures on healthcare services prompted review of standard clinical care pathways in the UK. Revised consensus treatment guidelines were generated. Individual patient-level data regarding actual treatment modifications implemented in clinical practice are lacking. Methods: All anti-cancer treatment plans of patients with breast, lung, renal, hepatopancreatobiliary, CNS cancers and melanoma attending a single academic cancer centre in the UK between 16 March and 31 May 2020 were reviewed and any modifications to standard practice were documented. The effect of patient (age, ECOG performance status [PS], sex) and cancer (site, stage, treatment intent) characteristics on likelihood of treatment modifications were analysed using univariable and multivariable models. Results: Treatment plans for 925 patients were reviewed: median patient age was 63 (range 19-97); 66% were female; 73% were PS 0-1; 45% were on a curative pathway. Overall, 47% of all patients had one or more modifications made to their treatment plans: 53% of surgeries (primarily being delayed); 41% of radiotherapy (primarily reduced fractions delivered); 39% of systemic therapy prescriptions. 96-100% of all systemic therapy modifications resulted in treatment de-escalation, excluding endocrine therapy used as a bridge to defer primary breast cancer surgery. Biological therapy was predominantly interrupted (49%), immunotherapy was mostly omitted entirely (36%), and chemotherapy varied between interruptions (39%) or omissions (31%). Relative to the likelihood of modification to chemotherapy, surgery was significantly more likely to be modified (OR 1.69 95%CI 1.20-2.38). Chemotherapy, radiotherapy, biological therapy and immunotherapy were all modified to a similar degree. Multivariate analysis identified PS ≥2 (OR 1.79, 95% CI 1.18–2.75), but not patient age, as a predictor of treatment modification. Some tumour types were less likely to undergo any modification: stage 1-3 lung (OR 0.13, 95%CI 0.04-0.37), stage 4 lung (OR 0.26 95%CI 0.24–0.60) and stage 4 renal cancer (OR 0.22 95%CI 0.09-0.52). Conclusions: This single centre analysis demonstrated almost half of cancer patients had their treatment modified, the overwhelming majority resulting in treatment de-escalation. The impact of the treatment modifications on overall cancer patient outcomes remains to be determined.

Characterization of GDF2 Mutations and Levels of BMP9 and BMP10 in Pulmonary Arterial Hypertension

Rationale: Recently, rare heterozygous mutations in GDF2 were identified in patients with pulmonary arterial hypertension (PAH). GDF2 encodes the circulating BMP (bone morphogenetic protein) type 9, which is a ligand for the BMP2 receptor.Objectives: Here we determined the functional impact of GDF2 mutations and characterized plasma BMP9 and BMP10 levels in patients with idiopathic PAH.Methods: Missense BMP9 mutant proteins were expressed in vitro and the impact on BMP9 protein processing and secretion, endothelial signaling, and functional activity was assessed. Plasma BMP9 and BMP10 levels and activity were assayed in patients with PAH with GDF2 variants and in control subjects. Levels were also measured in a larger cohort of control subjects (n = 120) and patients with idiopathic PAH (n = 260).Measurements and Main Results: We identified a novel rare variation at the GDF2 and BMP10 loci, including copy number variation. In vitro, BMP9 missense proteins demonstrated impaired cellular processing and secretion. Patients with PAH who carried these mutations exhibited reduced plasma levels of BMP9 and reduced BMP activity. Unexpectedly, plasma BMP10 levels were also markedly reduced in these individuals. Although overall BMP9 and BMP10 levels did not differ between patients with PAH and control subjects, BMP10 levels were lower in PAH females. A subset of patients with PAH had markedly reduced plasma levels of BMP9 and BMP10 in the absence of GDF2 mutations.Conclusions: Our findings demonstrate that GDF2 mutations result in BMP9 loss of function and are likely causal. These mutations lead to reduced circulating levels of both BMP9 and BMP10. These findings support therapeutic strategies to enhance BMP9 or BMP10 signaling in PAH.

Large-Scale Whole-Genome Sequencing Reveals the Genetic Architecture of Primary Membranoproliferative GN and C3 Glomerulopathy

BACKGROUND

Primary membranoproliferative GN, including complement 3 (C3) glomerulopathy, is a rare, untreatable kidney disease characterized by glomerular complement deposition. Complement gene mutations can cause familial C3 glomerulopathy, and studies have reported rare variants in complement genes in nonfamilial primary membranoproliferative GN.

METHODS

We analyzed whole-genome sequence data from 165 primary membranoproliferative GN cases and 10,250 individuals without the condition (controls) as part of the National Institutes of Health Research BioResource-Rare Diseases Study. We examined copy number, rare, and common variants.

RESULTS

Our analysis included 146 primary membranoproliferative GN cases and 6442 controls who were unrelated and of European ancestry. We observed no significant enrichment of rare variants in candidate genes (genes encoding components of the complement alternative pathway and other genes associated with the related disease atypical hemolytic uremic syndrome; 6.8% in cases versus 5.9% in controls) or exome-wide. However, a significant common variant locus was identified at 6p21.32 (rs35406322) (P=3.29×10^-8; odds ratio [OR], 1.93; 95% confidence interval [95% CI], 1.53 to 2.44), overlapping the HLA locus. Imputation of HLA types mapped this signal to a haplotype incorporating DQA1*05:01, DQB1*02:01, and DRB1*03:01 (P=1.21×10^-8; OR, 2.19; 95% CI, 1.66 to 2.89). This finding was replicated by analysis of HLA serotypes in 338 individuals with membranoproliferative GN and 15,614 individuals with nonimmune renal failure.

CONCLUSIONS

We found that HLA type, but not rare complement gene variation, is associated with primary membranoproliferative GN. These findings challenge the paradigm of complement gene mutations typically causing primary membranoproliferative GN and implicate an underlying autoimmune mechanism in most cases.

Bi-allelic Loss-of-Function CACNA1B Mutations in Progressive Epilepsy-Dyskinesia

The occurrence of non-epileptic hyperkinetic movements in the context of developmental epileptic encephalopathies is an increasingly recognized phenomenon. Identification of causative mutations provides an important insight into common pathogenic mechanisms that cause both seizures and abnormal motor control. We report bi-allelic loss-of-function CACNA1B variants in six children from three unrelated families whose affected members present with a complex and progressive neurological syndrome. All affected individuals presented with epileptic encephalopathy, severe neurodevelopmental delay (often with regression), and a hyperkinetic movement disorder. Additional neurological features included postnatal microcephaly and hypotonia. Five children died in childhood or adolescence (mean age of death: 9 years), mainly as a result of secondary respiratory complications. CACNA1B encodes the pore-forming subunit of the pre-synaptic neuronal voltage-gated calcium channel Ca_v2.2/N-type, crucial for SNARE-mediated neurotransmission, particularly in the early postnatal period. Bi-allelic loss-of-function variants in CACNA1B are predicted to cause disruption of Ca²⁺ influx, leading to impaired synaptic neurotransmission. The resultant effect on neuronal function is likely to be important in the development of involuntary movements and epilepsy. Overall, our findings provide further evidence for the key role of Ca_v2.2 in normal human neurodevelopment.

Sphingolipid dysregulation due to lack of functional KDSR impairs proplatelet formation causing thrombocytopenia

Sphingolipids are fundamental to membrane trafficking, apoptosis, and cell differentiation and proliferation. KDSR or 3-keto-dihydrosphingosine reductase is an essential enzyme for de novo sphingolipid synthesis, and pathogenic mutations in KDSR result in the severe skin disorder erythrokeratodermia variabilis et progressiva-4. Four of the eight reported cases also had thrombocytopenia but the underlying mechanism has remained unexplored. Here we expand upon the phenotypic spectrum of KDSR deficiency with studies in two siblings with novel compound heterozygous variants associated with thrombocytopenia, anemia, and minimal skin involvement. We report a novel phenotype of progressive juvenile myelofibrosis in the propositus, with spontaneous recovery of anemia and thrombocytopenia in the first decade of life. Examination of bone marrow biopsies showed megakaryocyte hyperproliferation and dysplasia. Megakaryocytes obtained by culture of CD34⁺ stem cells confirmed hyperproliferation and showed reduced proplatelet formation. The effect of KDSR insufficiency on the sphingolipid profile was unknown, and was explored in vivo and in vitro by a broad metabolomics screen that indicated activation of an in vivo compensatory pathway that leads to normalization of downstream metabolites such as ceramide. Differentiation of propositus-derived induced pluripotent stem cells to megakaryocytes followed by expression of functional KDSR showed correction of the aberrant cellular and biochemical phenotypes, corroborating the critical role of KDSR in proplatelet formation. Finally, Kdsr depletion in zebrafish recapitulated the thrombocytopenia and showed biochemical changes similar to those observed in the affected siblings. These studies support an important role for sphingolipids as regulators of cytoskeletal organization during megakaryopoiesis and proplatelet formation.

Loss-of-function nuclear factor κB subunit 1 (NFKB1) variants are the most common monogenic cause of common variable immunodeficiency in Europeans

BACKGROUND

The genetic cause of primary immunodeficiency disease (PID) carries prognostic information.

OBJECTIVE

We conducted a whole-genome sequencing study assessing a large proportion of the NIHR BioResource-Rare Diseases cohort.

METHODS

In the predominantly European study population of principally sporadic unrelated PID cases (n = 846), a novel Bayesian method identified nuclear factor κB subunit 1 (NFKB1) as one of the genes most strongly associated with PID, and the association was explained by 16 novel heterozygous truncating, missense, and gene deletion variants. This accounted for 4% of common variable immunodeficiency (CVID) cases (n = 390) in the cohort. Amino acid substitutions predicted to be pathogenic were assessed by means of analysis of structural protein data. Immunophenotyping, immunoblotting, and ex vivo stimulation of lymphocytes determined the functional effects of these variants. Detailed clinical and pedigree information was collected for genotype-phenotype cosegregation analyses.

RESULTS

Both sporadic and familial cases demonstrated evidence of the noninfective complications of CVID, including massive lymphadenopathy (24%), unexplained splenomegaly (48%), and autoimmune disease (48%), features prior studies correlated with worse clinical prognosis. Although partial penetrance of clinical symptoms was noted in certain pedigrees, all carriers have a deficiency in B-lymphocyte differentiation. Detailed assessment of B-lymphocyte numbers, phenotype, and function identifies the presence of an increased CD21low B-cell population. Combined with identification of the disease-causing variant, this distinguishes between healthy subjects, asymptomatic carriers, and clinically affected cases.

CONCLUSION

We show that heterozygous loss-of-function variants in NFKB1 are the most common known monogenic cause of CVID, which results in a temporally progressive defect in the formation of immunoglobulin-producing B cells.

Comprehensive Cancer-Predisposition Gene Testing in an Adult Multiple Primary Tumor Series Shows a Broad Range of Deleterious Variants and Atypical Tumor Phenotypes

Multiple primary tumors (MPTs) affect a substantial proportion of cancer survivors and can result from various causes, including inherited predisposition. Currently, germline genetic testing of MPT-affected individuals for variants in cancer-predisposition genes (CPGs) is mostly targeted by tumor type. We ascertained pre-assessed MPT individuals (with at least two primary tumors by age 60 years or at least three by 70 years) from genetics centers and performed whole-genome sequencing (WGS) on 460 individuals from 440 families. Despite previous negative genetic assessment and molecular investigations, pathogenic variants in moderate- and high-risk CPGs were detected in 67/440 (15.2%) probands. WGS detected variants that would not be (or were not) detected by targeted resequencing strategies, including low-frequency structural variants (6/440 [1.4%] probands). In most individuals with a germline variant assessed as pathogenic or likely pathogenic (P/LP), at least one of their tumor types was characteristic of variants in the relevant CPG. However, in 29 probands (42.2% of those with a P/LP variant), the tumor phenotype appeared discordant. The frequency of individuals with truncating or splice-site CPG variants and at least one discordant tumor type was significantly higher than in a control population (χ2 = 43.642; p ≤ 0.0001). 2/67 (3%) probands with P/LP variants had evidence of multiple inherited neoplasia allele syndrome (MINAS) with deleterious variants in two CPGs. Together with variant detection rates from a previous series of similarly ascertained MPT-affected individuals, the present results suggest that first-line comprehensive CPG analysis in an MPT cohort referred to clinical genetics services would detect a deleterious variant in about a third of individuals.

Identification of rare sequence variation underlying heritable pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder with a poor prognosis. Deleterious variation within components of the transforming growth factor-β pathway, particularly the bone morphogenetic protein type 2 receptor (BMPR2), underlies most heritable forms of PAH. To identify the missing heritability we perform whole-genome sequencing in 1038 PAH index cases and 6385 PAH-negative control subjects. Case-control analyses reveal significant overrepresentation of rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of a critical role for GDF2 in PAH. We demonstrate familial segregation of mutations in SOX17 and AQP1 with PAH. Mutations in GDF2, encoding a BMPR2 ligand, lead to reduced secretion from transfected cells. In addition, we identify pathogenic mutations in the majority of previously reported PAH genes, and provide evidence for further putative genes. Taken together these findings contribute new insights into the molecular basis of PAH and indicate unexplored pathways for therapeutic intervention.

Improvement in cognitive functioning in patients with first-episode psychosis during treatment with quetiapine: An interim analysis

Background

The efficacies of second-generation antipsychotic medications in reducing symptoms are reasonably well-documented, but their effects on cognition are less clearly understood.

Aims

To undertake an interim analysis of an open label, 2-year study examining the effects of quetiapine on cognition in patients with a first episode of schizophrenia and related disorders.

Method

Cognitive testing was performed before quetiapine was initiated and repeated after 3, 6 and 12 months of treatment. To date, 13 patients have been fully assessed (mean dose 517.9 mg/day; s.d.=225.8).

Results

Statistically significant improvement was noted on measures of attention (Continuous Performance Test; CPT), verbal productivity (Verbal Fluency Test) and executive function (Object Alternation Test) after 6 and 12 months of treatment. For the CPT, improvement was also noted after 3 months of treatment.

Conclusions

During treatment for 1 year with quetiapine, cognitive performance was improved in young patients with psychosis. Continued controlled investigations of the effects of quetiapine on cognition are desirable.

A dominant gain-of-function mutation in universal tyrosine kinase SRC causes thrombocytopenia, myelofibrosis, bleeding, and bone pathologies

The Src family kinase (SFK) member SRC is a major target in drug development because it is activated in many human cancers, yet deleterious SRC germline mutations have not been reported. We used genome sequencing and Human Phenotype Ontology patient coding to identify a gain-of-function mutation in SRC causing thrombocytopenia, myelofibrosis, bleeding, and bone pathologies in nine cases. Modeling of the E527K substitution predicts loss of SRC's self-inhibitory capacity, which we confirmed with in vitro studies showing increased SRC kinase activity and enhanced Tyr(419) phosphorylation in COS-7 cells overexpressing E527K SRC. The active form of SRC predominates in patients' platelets, resulting in enhanced overall tyrosine phosphorylation. Patients with myelofibrosis have hypercellular bone marrow with trilineage dysplasia, and their stem cells grown in vitro form more myeloid and megakaryocyte (MK) colonies than control cells. These MKs generate platelets that are dysmorphic, low in number, highly variable in size, and have a paucity of α-granules. Overactive SRC in patient-derived MKs causes a reduction in proplatelet formation, which can be rescued by SRC kinase inhibition. Stem cells transduced with lentiviral E527K SRC form MKs with a similar defect and enhanced tyrosine phosphorylation levels. Patient-derived and E527K-transduced MKs show Y419 SRC-positive stained podosomes that induce altered actin organization. Expression of mutated src in zebrafish recapitulates patients' blood and bone phenotypes. Similar studies of platelets and MKs may reveal the mechanism underlying the severe bleeding frequently observed in cancer patients treated with next-generation SFK inhibitors.

Duration of untreated psychosis predicts treatment outcome in an early psychosis program

For patients first presenting with a non-affective psychotic disorder, the duration of untreated psychosis (DUP; the time between the onset of positive psychotic symptoms and the initiation of appropriate treatment) varies widely, from a few weeks to several years. A number of studies report that a longer DUP is associated with poorer clinical outcomes. We studied DUP and its association with clinical outcomes in a group of patients with schizophrenia and related psychotic disorders treated in the naturalistic clinical setting of an early psychosis program. DUP was determined for 19 patients with a non-affective psychotic disorder (schizophrenia, schizoaffective disorder or schizophreniform disorder) and no previous treatment for psychosis, by use of the IRAOS, a retrospective structured interview carried out with patients and their families. Positive and Negative Syndrome Scale (PANSS) and Global Assessment of Function (GAF) ratings were available at baseline and 6month follow-up. For analysis, patients were categorized into a short DUP (n=9) or long DUP (n=10) group. The median DUP (57weeks) was used as the dividing point. At baseline, the two groups did not differ significantly on positive symptoms or total PANSS ratings. However, negative symptoms were more severe in the long DUP group at baseline (P=0.029), and the long DUP group had a significantly higher mean rating for the passive/apathetic social withdrawal item of the PANSS (P=0.024). At 6month follow-up, the long DUP group had significantly higher ratings for positive symptoms (P=0.028) and had lower GAF scores (P=0.044). Significantly more (P=0.033) long DUP patients had enduring positive psychotic symptoms. The results confirm both the wide range of DUP among patients first presenting with schizophrenia and related psychotic disorders and the association of long DUP, defined as greater than approximately 1year, with a poorer clinical outcome. This study highlights the importance of collecting data regarding DUP and supports the view that patients with a long DUP are likely to be less responsive to treatment in general and will require greater resources and more intensive interventions.

Towards an aggression-free health care environment

Over the past few years, nurses across Canada have participated in surveys that have exposed the previously unspoken issue of nurse abuse. Reports from the registered nurses' associations in Manitoba and Ontario reveal that more than half of all RNs have been physically assaulted in the workplace. In a study of 600 nurses in the Toronto area, fully one-third had experienced some form of abuse at work in the five days prior to the study. A recent Nova Scotia study of more than 400 nurses found that 63 percent had experienced verbal abuse at work in the past year, while 35 per cent had experienced attempts of physical harm and 21 percent had been the victims of a physical attack.

Age, sex and strain differences in activity and habituation in SHR and WKY rats

The highly inbred strain of Wistar-Kyoto spontaneously hypertensive rat (SHR) and its normotensive, genetic control (WKY) were examined with respect to strain differences in spontaneous activity scores in a novel environment (small activity cage) and in ability to habituate to that environment. These behaviors were examined in experimentally naive rats, 197 SHR and WKY, males and females, at varying ages from 4 to 56 weeks, in order to determine whether there are sex and age differences in addition to the well-known strain differences in these behaviors. Total activity scores, determined in a 15 min test in the activity cage, were higher in SHR than WKY rats; females were significantly more active than males in either strain, and activity scores varied significantly with age both within strains and between strains. Ability to habituate to the test cage was determined by repeating the 15 min activity test at hourly intervals for three additional trials on the same day. The results indicate that the SHR, males and females and at all ages tested, habituate poorly if at all to the test cage as compared with WKY rats. Moreover, despite the variability of baseline activity scores (first trial) observed across ages, sexes and strains, the habituation patterns of either strain remained relatively fixed throughout the first year of life.

Alterations of evoked potentials in the medial lemniscus of the rat due to acute and chronic elevations in blood pressure

The influence of elevated blood pressure on evoked field potentials in the medial lemniscus induced by peripheral stimulation was studied in the rat. Acute hypertension as a result of phenylephrine infusions reduced the size of this response in individual Wistar Kyoto rats. Chronic renal hypertension in Sprague-Dawley rats also caused a reduction in the dorsal column-medial lemniscal evoked response. These results confirm an inhibitory action of elevated blood pressure on transmission through the dorsal column nuclei.

Genetically related rats with differences in hippocampal uptake of norepinephrine and maze performance

The spontaneously hypertensive rat (SHR) and its progenitor strain, the Wistar-Kyoto (WKY) display marked differences in brain catecholamines and behavior. The behavioral differences are suggestive of alterations in hippocampal function and, in particular, the noradrenergic input to the hippocampus. To test these hypotheses we have analyzed the performance of the SHR and WKY in a spatial memory maze task that is specific to hippocampal function and determined the kinetics of norepinephrine (NE) uptake in synaptosomal preparations of the hippocampus. We have found that WKYs exhibit an abnormally strong bias tendency in T-maze arm preference that influences the rate of acquisition and the final level of maze performance. We have also found differences in noradrenergic uptake in hippocampal synaptosomes. WKYs exhibit higher NE uptake rates and higher kinetic constants for NE uptake when compared with SHRs, suggesting that strain differences in noradrenergic function may contribute to the observed behavioral differences.

Enhanced preganglionic sympathetic nerve responses in spontaneously hypertensive rats

Sympathetic nerve responses to posterior hypothalamic stimulation were recorded from the preceliac splanchnic nerve in spontaneously hypertensive rats (SHR) and normotensive, Wistar-Kyoto rats (WKY) following interruption of the baroreceptor reflex. Responses to identical stimulation were then recorded following ganglionic blockade with hexamethonium. The enhanced preganglionic sympathetic nerve responses measured in SHR indicate that the sympathetic hyperresponsiveness strain occurs, at least in part, at a site within the central nervous system.

Differences in transmission through the dorsal column nuclei in spontaneously hypertensive and Wistar Kyoto rats

The medical lemniscal evoked potential in response to a range of footshock intensities was recorded in spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY). Input-output (I-O) relationships were constructed as the percent of maximum response at each intensity. The SHR had a steeper I-O relationship than did the WKY. This difference was also evident when SHR maintained normotensive from weaning with hydralazine were compared with identically treated WKY. The treatment itself steepened the I-O relationship of the SHR while leaving that of the WKY unchanged. These results indicate an inherent hyperresponsiveness in the SHR dorsal column nuclei and an inhibitory effect of elevated blood pressure on transmission through these nuclei.

Locomotor activity, auditory startle and shock thresholds in spontaneously hypertensive rats

A group of SHRs and a group of WKY normotensive controls were compared sequentially on open-field behavior, Y-maze activity, responsiveness and habituation of the auditory startle response, and shock thresholds. In the open field and Y maze the SHRs were more active than the WKYs, but the locomotor activity of the SHRs decreased more within sessions. However, the SHRs could be described as showing more, less or the same between-session habituation depending upon the apparatus and the portion of the session analyzed. The SHRs were less responsive than controls on the auditory startle response measure, and they did not differ from controls on startle-response habituation. The SHRs were less responsive than controls at low shock levels but more responsive at high shock levels. The relationship between SHRs and WKYs on the responsiveness dimension depended upon the modality and intensity of the stimulus, the response characteristics of the test situation, and the time sample of behavior taken.

Field-potential evidence for extrasynaptic alterations in the hippocampal CA1 pyramidal cell population during paired-pulse potentiation

The mechanisms of paired-pulse potentiation of the CA1 pyramidal cell population were examined by determining input-output relations for control and potentiated responses originating from the activation of radiatum fibers in the hippocampal slice preparation. Two types of potentiation for synchronously discharging pyramidal cells (population spike) were observed. In the first type, the potentiation of the population spike was found to be a combination of synaptic and extrasynaptic factors. This form of potentiation was observed in 16 of 28 slices. In the second type, the potentiation of the population spike was attributed entirely to the potentiation of summated dendritic depolarizations (population EPSP). This synaptic process of potentiation was observed in 12 of 28 slices. The involvement of only extrasynaptic mechanisms in the paired-pulse potentiation of the population spike was not observed. For the potentiation originating from a combination of synaptic and extrasynaptic mechanisms, 60% of the potentiation of the population spike was a result of synaptic factors and 40% could be attributed to extrasynaptic factors. These results support the concept that alterations in the excitability of postsynaptic neurons serve as a component of the mechanisms of paired-pulse potentiation in the radiatum fiber-CA1 pyramidal cell system.

Independence of blood pressure and locomotor hyperactivity in normotensive and genetically hypertensive rat

The spontaneously hypertensive rat (SHR) exhibits locomotor hyperactivity in comparison to its normotensive progenitor Wistar-Kyoto (WKY) strain. We asked whether the hyperactive behavior was a direct consequence of elevated blood pressure in the hypertensive rat. Three experimental protocols were used to chronically alter blood pressure. In the first protocol, a group of adult SHRs was given hydralazine (20 mg/kg/day) in their drinking water to lower blood pressure. These animals exhibited a significant decrease in blood pressure, but no change in locomotor activity. In the second protocol, young SHRs (4 weeks of age) were treated with the same dosage of hydralazine until 16 weeks of age. Blood pressure was significantly decreased in these animals with no change in locomotor activity. In the third protocol, normotensive WKY and Sprague-Dawley (SD) rats were made hypertensive with unilateral renal clips. The resulting increase in blood pressure in these animals did not alter locomotor activity. These results suggest that locomotor hyperactivity is an inherent property of the SHR and is independent of blood pressure.

Dissociation of genetic hyperactivity and hypertension in SHR

The Wistar Kyoto strain of spontaneously hypertensive rat (SHR) has been characterized as behaviorally hyperactive as well as hypertensive. The relationship between these two inbred traits remains uncertain, and their coexistence in the SHR has complicated studies of central nervous system mechanisms underlying the hypertensive process. A breeding program was initiated to examine the possible genetic linkage of these two traits which, if separable, would allow us to develop substrains of SHR that are hypertensive without being hyperactive, or hyperactive without being hypertensive. We crossed SHR males with Wistar Kyoto, normotensive (WKY) female rats and produced F1 hybrids which were then randomly inbred to produce an F2 population. When tested at 12 weeks of age, F2 rats exhibited the expected wide range of mean systolic blood pressures (BP), from 111 to 174 mm Hg, as determined using indirect tail plethysmography. The BP in the parental rats at the time of breeding (16 weeks) was 187 +/- 4.5 mm Hg (SHR males, n = 7) and 111 +/- 2.4 (WKY females, n = 7). Locomotor activity was determined in an automated activity cage in F1 and F2 rats at 12 weeks of age. These strains exhibited a wide range of phenotypic distribution of locomotor activity scores, and the mean scores were intermediary between those of SHR rats and WKY rats of the same age. Among individual rats of both the F1 and F2 hybrid strains, there was no correlation between the activity score and the level of the BP at 12 weeks of age. These findings indicated that the genes responsible for the hypertensive trait and those responsible for the hyperactivity trait were not tightly linked in the hybrid populations, suggesting that different genetic factors were involved in the transmission of each of these traits. Accordingly, it should be possible to separate the two traits by further selective, recombinant inbreeding procedures.

Baroreceptor reflex gain is not diminished in spontaneous hypertension

The magnitudes of both spontaneous and hypothalamically evoked sympathetic nerve activity are greater in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto rats (WKY). Because the baroreceptor reflex influences the magnitude and time course of the sympathetic response to hypothalamic stimulation, we evaluated the role of the baroreceptor reflex in this sympathetic hyperresponsiveness. Changes in spontaneous nerve activity following comparable shifts in mean blood pressure (static reflex gain) were not different between the two strains. The effect of alterations in prestimulation blood pressure on the size of the evoked sympathetic response (response gain) was greater in SHR. Baroreceptor reflex inhibition resulting from the evoked blood pressure rise during hypothalamic stimulation (dynamic gain) was also greater in SHR. Expressing response magnitudes and gains as a percent of the spontaneous activity eliminated these strain differences. Interruption of the baroreceptor reflex resulted in equivalent percent increases in spontaneous and evoked activity in the two strains. Postdenervation levels of spontaneous and evoked nerve activity were greater in SHR. The results show that sympathetic hyperreactivity in SHR is not due to deficient baroreceptor reflex function.

Cardiovascular responses elicited by electrical stimulation of the amygdala central nucleus in the rabbit

Recent behavioral and anatomical evidence suggests the involvement of the amygdala central nucleus projection to medullary cardioregulatory nuclei in the expression of conditioned bradycardia during aversive Pavlovian conditioning in the rabbit 6,7,11,15. The present study sought to determine the extent to which electrical stimulation of the central nucleus produces bradycardia in the rabbit, and the extent to which any bradycardia elicited varies with stimulation at sites within as opposed to adjacent to the medial component of the central nucleus, the component from which the projection to cardioregulatory nuclei originates. Over 900 sites in 30 rabbits anesthetized with alpha-chloralose were explored. Monopolar stimulation (30-100 Hz; 0.5 ms pulse duration; 5.0 s train duration; 100-500 microamperemeter) at sites within the central nucleus produced bradycardia and depressor responses. Maximum bradycardia was produced from sites within the anterior, medial component of the nucleus. This response usually began within one second of stimulus onset, reached peak magnitude within two seconds of stimulus onset and in many instances was followed by a slight tachycardia following stimulus termination. The accompanying depressor responses occurred at longer latencies than the bradycardia responses. The responses persisted following artificial ventilation and immobilization by Flaxedil and were attenuated by i.v. injections of atropine methylnitrate. While bradycardia and depressor responses were elicited from sites immediately dorsal, ventral and lateral to the medial central nucleus, component. The results are consistent with previous evidence which suggests a contribution for the central nucleus in the expression of cardiovascular responding during aversive Pavlovian conditioning in the rabbit.

Periodic fluctations in synaptic transmission and enhancement of transmission in hippocampal slices

The properties of the synchronously activated radiatum fiber-CA1 synaptic population were examined with the in vitro hippocampal slice preparation. Periodic fluctuations in synaptic transmission and in the enhancement of synaptic transmission were observed with periods ranging from 8 to 20 s. Such periodic fluctuations did not arise from fluctuations in afferent radiatum fiber activity. The period and amplitude of the cyclic variations in the enhancement of synaptic transmission were found to be altered with repeated electrical stimulation of the radiatum fibers. These results reflect cooperative synaptic actions which must be taken into consideration in the delineation of the mechanisms of potentiation.

Effect of hypothalamic stimulation in spontaneously hypertensive and Wistar-Kyoto rats

This study was undertaken to determine if central nervous system differences in blood pressure regulation exist between spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls. Central control mechanisms were examined by observing the effects of posterior hypothalamic (PH) stimulation upon preganglionic sympathetic activity in 14--18 week old SHR and WKY rats. A bipolar, concentric electrode was stereotaxically placed in the PH. Stimulation was delivered at 20, 60 and 100 Hz (3-sec duration, 0.1 msec pulse width) at a voltage twice that producing an increase in blood pressure (less than 5 mm Hg) at 60 Hz. Sympathetic activity was recorded from a portion of the splanchnic nerve just distal to the diaphragm. Blood pressure was measured from a femoral artery catheter. SHR responded with greater increases in sympathetic activity than WKY; the differences were statistically significant at 60 and 100 Hz. SHR also responded with significantly greater increases in blood pressure at all frequencies of stimulation. To determine if the enhanced sympathetic response to PH stimulation seen in adult SHR is an intrinsic difference rather than secondary to sustained hypertension, we maintained SHR normotensive from four weeks of age with antihypertensive drug therapy (clonidine or hydralazine). Chronically treated animals were then tested at 14--18 weeks of age while on antihypertensives or four days after drug discontinuance. Sympathetic and blood pressure responses to PH stimulation were significantly greater in SHR maintained normotensive than untreated or chronically treated WKY. These data support the concept that a central factor is involved in the etiology of hypertension in the SHR.

Ascending collaterals of cutaneous neurons in the fasciculus gracilis of the cat

Primary sensory neurons with myelinated axons in the sural nerve of the cat were found to be divisible into 3 systems on the basis of the length of their central collaterals in the dorsal columns. The short system consists of neurons that ascend only a segment or two in the fasciculus gracilis above their level of entry into the spinal cord. It is composed of all neurons with peripheral conduction velocities in the Adelta range and thus includes both D hair and nociceptive neurons. Approximately 35% of the Aalpha neurons join the intermediate system and ascend 4-12 segments before leaving the forsal columns. This system is composed of all sural type I neurons, as well as about 40% of the G2 hair, 40% of the intermediate field, and 50% of the F2 field neurons in the nerve. Those nociceptive neurons conducting at Aalpha velocities also contribute to the intermediate system. The remaining G2 hair, intermediate field, and F2 field neurons, together with almost all the sural type II, G1 hair, intermediate hair and F1 field neurons, join the long system and ascend to the nucleus gracilis. Fibers in the intermediate system showed a relatively abrupt decrease in conduction velocity usually of 50% or more (median 71%) a few millimeters rostral to their entry into the spinal cord. Members of the long system also decreased in conduction velocity at this point, but the magnitude of the changes was typically less than 50% of the peripheral velocity (median 36%). In addition, the ascending collaterals of the long system underwent a second reduction in conduction velocity near the cervical enlargement.