Social buffering in rats reduces fear by oxytocin triggering sustained changes in central amygdala neuronal activity

The presence of a companion can reduce fear, but the neural mechanisms underlying this social buffering of fear are incompletely known. We studied social buffering of fear in male and female, and its encoding in the amygdala of male, auditory fear-conditioned rats. Pharmacological, opto,- and/or chemogenetic interventions showed that oxytocin signaling from hypothalamus-to-central amygdala projections underlied fear reduction acutely with a companion and social buffering retention 24 h later without a companion. Single-unit recordings with optetrodes in the central amygdala revealed fear-encoding neurons (showing increased conditioned stimulus-responses after fear conditioning) inhibited by social buffering and blue light-stimulated oxytocinergic hypothalamic projections. Other central amygdala neurons showed baseline activity enhanced by blue light and companion exposure, with increased conditioned stimulus responses that persisted without the companion. Social buffering of fear thus switches the conditioned stimulus from encoding "fear" to "safety" by oxytocin-mediated recruitment of a distinct group of central amygdala "buffer neurons".

Selective oxytocin receptor activation prevents prefrontal circuit dysfunction and social behavioral alterations in response to chronic prefrontal cortex activation in male rats

Introduction

Social behavioral changes are a hallmark of several neurodevelopmental and neuropsychiatric conditions, nevertheless the underlying neural substrates of such dysfunction remain poorly understood. Building evidence points to the prefrontal cortex (PFC) as one of the key brain regions that orchestrates social behavior. We used this concept with the aim to develop a translational rat model of social-circuit dysfunction, the chronic PFC activation model (CPA).

Methods

Chemogenetic designer receptor hM3Dq was used to induce chronic activation of the PFC over 10 days, and the behavioral and electrophysiological signatures of prolonged PFC hyperactivity were evaluated. To test the sensitivity of this model to pharmacological interventions on longer timescales, and validate its translational potential, the rats were treated with our novel highly selective oxytocin receptor (OXTR) agonist RO6958375, which is not activating the related vasopressin V1a receptor.

Results

CPA rats showed reduced sociability in the three-chamber sociability test, and a concomitant decrease in neuronal excitability and synaptic transmission within the PFC as measured by electrophysiological recordings in acute slice preparation. Sub-chronic treatment with a low dose of the novel OXTR agonist following CPA interferes with the emergence of PFC circuit dysfunction, abnormal social behavior and specific transcriptomic changes.

Discussion

These results demonstrate that sustained PFC hyperactivity modifies circuit characteristics and social behaviors in ways that can be modulated by selective OXTR activation and that this model may be used to understand the circuit recruitment of prosocial therapies in drug discovery.

Discovery of Balovaptan, a Vasopressin 1a Receptor Antagonist for the Treatment of Autism Spectrum Disorder

We recently reported the discovery of a potent, selective, and brain-penetrant V1a receptor antagonist, which was not suitable for full development. Nevertheless, this compound was found to improve surrogates of social behavior in adults with autism spectrum disorder in an exploratory proof-of-mechanism study. Here we describe scaffold hopping that gave rise to triazolobenzodiazepines with improved pharmacokinetic properties. The key to balancing potency and selectivity while minimizing P-gp mediated efflux was fine-tuning of hydrogen bond acceptor basicity. Ascertaining a V1a antagonist specific brain activity pattern by pharmacological magnetic resonance imaging in the rat played a seminal role in guiding optimization efforts, culminating in the discovery of balovaptan (RG7314, RO5285119) 1. In a 12-week clinical phase 2 study in adults with autism spectrum disorder balovaptan demonstrated improvements in Vineland-II Adaptive Behavior Scales, a secondary end point comprising communication, socialization, and daily living skills. Balovaptan entered phase 3 clinical development in August 2018.

High-yielding 18F radiosynthesis of a novel oxytocin receptor tracer, a probe for nose-to-brain oxytocin uptake in vivo

A novel Al18F labelled peptide tracer for PET imaging of oxytocin receptor has been accessed through a high radiochemical yield approach. This tracer showed comparable affinity and higher selectivity and stability compared to oxytocin, and was used to demonstrate direct nose-to-brain uptake following intranasal administration, a common yet controversial delivery route for oxytocin-based therapeutics.

Building bridges for highly selective, potent and stable oxytocin and vasopressin analogs

Oxytocin (OT) is an exciting potential therapeutic agent, but it is highly sensitive to modification and suffers extensive degradation at elevated temperature and in vivo. Here we report studies towards OT analogs with favorable selectivity, affinity and potency towards the oxytocin receptor (OTR), in addition to improving stability of the peptide by bridging the disulfide region with substituted dibromo-xylene analogs. We found a sensitive structure-activity relationship in which meta-cyclized analogs (dOT_meta) gave highest affinity (50 nM K_i), selectivity (34-fold), and agonist potency (34 nM EC₅₀, 87-fold selectivity) towards OTR. Surprisingly, ortho-cyclized analogs demonstrated OTR and vasopressin V_1a receptor subtype affinity (220 nM and 69 nM, respectively) and pharmacological activity (294 nM and 35 nM, respectively). V_1a binding and selectivity for ortho-cyclized peptides could be improved 6-fold by substituting a neutral residue at position 8 with a basic amino acid, providing potent antagonists (14 nM IC₅₀) that displayed no activation of the OTR. Furthermore, xylene-bridged analogs demonstrated increased stability compared to OT at elevated temperature, demonstrating promising therapeutic potential for these analogs which warrants further study.

Imaging trait anxiety in high anxiety F344 rats: Focus on the dorsomedial prefrontal cortex

Functional magnetic resonance imaging (fMRI) has become an important method in clinical psychiatry research whereas there are still only few comparable preclinical investigations. Herein, we report that fMRI in rats can provide key information regarding brain areas underlying anxiety behavior. Perfusion as surrogate for neuronal activity was measured by means of arterial spin labeling-based fMRI in various brain areas of high anxiety F344 rats and control Sprague-Dawley rats. In one of these areas, the dorsomedial prefrontal cortex (dmPFC), c-Fos labeling was compared between these two strains with immunolabeling. The effects of a neurotoxic ibotenic acid lesion of the dmPFC in F344 rats were examined in a social approach-avoidance anxiety procedure and fMRI. Regional brain activity of high anxiety F344 rats was different in selective cortical and subcortical areas as compared to that of low anxiety Sprague-Dawley rats; the largest difference (i.e. hyperactivity) was measured in the dmPFC. Independently, c-Fos labeling confirmed that F344 rats show increased dmPFC activity. The functional role was confirmed by neurotoxic lesion of the dmPFC that reversed the high anxiety-like behavior and partially normalized the brain activity pattern of F344 rats. The current findings may have translational value as increased activity is reported in an equivalent cortical area in patients with social anxiety, suggesting that pharmacological or functional inhibition of activity in this brain area should be explored to alleviate social anxiety in patients.

Dimorphic effects of leptin on the circadian and hypocretinergic systems of mice

The hormone leptin controls food intake and body weight through its receptor in the hypothalamus, and may modulate physiological functions such as reproduction, sleep or circadian timing. In the present study, the effects of leptin on the resetting of the circadian clock, the hypothalamic suprachiasmatic nucleus (SCN) and on the activity of the hypocretinergic system were examined in vivo, with comparative analysis between male and female mice. A single leptin injection (5 mg/kg) at both the onset and offset of the activity period did not alter locomotion of mice housed under a 12 : 12 h light/dark cycle and did not shift the circadian behavioral rhythm of mice housed in constant darkness. By contrast, leptin potentiated the phase-shifting effect of a 30-min light-pulse on behavioural rhythms during the late subjective night, although only in females. This was accompanied by a higher induction of the clock genes Per1 and Per2 in the SCN. A 2-week chronic exposure to a physiological dose of leptin (100 μg/kg per day) decreased locomotor activity, expression of hypocretin receptor 1 and 2, as well as the number of hypocretin-immunoreactive neurones only in female mice, whereas the number of c-fos-positive hypocretinergic neurones was reduced in both genders. These results highlight a dimorphic effect of leptin on the hypocretinergic system and on the response of the circadian clock to light. Leptin may thus modulate the sleep/wake cycle and circadian system beside its well-established action on food intake and regulation of body weight.

Examining face and construct validity of a noninvasive model of panic disorder in Lister-hooded rats

RATIONALE

Increasing evidence suggests that defensive escape behavior in Lister-hooded (LH) rats induced by ultrasound application may be an animal model of panic disorder.

OBJECTIVE

The objectives of this study were to further explore the face and construct validity of ultrasound-induced escape behavior by characterizing the autonomic and neuroendocrine response to ultrasound, and to examine the underlying neuronal structures by comparing the effects of the anxiolytic with panicolytic properties, diazepam, with a preclinical anxiolytic without panicolytic-like activity, the NOP agonist Ro 64-6198.

MATERIALS AND METHODS

LH rats were implanted with telemetry transmitters to monitor heart rate and core body temperature before, during, and after ultrasound application. Blood samples were taken after ultrasound application for corticosterone analysis. Ultrasound-induced c-Fos expression was measured in different periaqueductal gray (PAG) and amygdala subregions after treatment with diazepam or Ro 64-6198.

RESULTS

Ultrasound application increased heart rate and body temperature, but did not alter plasma corticosterone levels. Ultrasound application increased c-Fos expression in the dorsal and dorsolateral PAG (dPAG, dlPAG) and amygdaloid subregions. Diazepam, but not Ro 64-6198, reduced c-Fos expression in the dPAG/dlPAG, while Ro 64-6198, but not diazepam, reduced c-Fos expression in the central amygdala.

CONCLUSIONS

Similar to human panic attacks, ultrasound application to LH rats activated the autonomic, but not the neuroendocrine, stress system. Also, like in humans, the current data confirm and extend that the dPAG/dlPAG plays a key role in ultrasound-induced escape behavior. These observations suggest that ultrasound-induced escape behaviors in LH rats have face and construct validity for panic disorders.

Neurosecretion competence. A comprehensive gene expression program identified in PC12 cells

The phenotype of neurosecretory cells is characterized by clear vesicles and dense granules, both discharged by regulated exocytosis. However, these organelles are lacking completely in a few neurosecretion-incompetent clones of the pheochromocytoma PC12 line, in which other specific features are maintained (incompetent clones). In view of the heterogeneity of PC12 cells, a differential characterization of the incompetent phenotype based on the comparison of a single incompetent and a single wild-type clone would have been inconclusive. Therefore, we have compared two pairs of PC12 clones, studying in parallel the transcript levels of 4,200 genes and 19,000 express sequence tags (ESTs) by high density oligonucleotide arrays. After accurate data processing for quality control and filtration, a total of 755 transcripts, corresponding to 448 genes and 307 ESTs, was found consistently changed, with 46% up-regulated and 54% down-regulated in incompetent versus wild-type clones. Many but not all neurosecretion genes were profoundly down-regulated in incompetent cells. Expression of endocytosis genes was normal, whereas that of many nuclear and transcription factors, including some previously shown to play key roles in neurogenesis, was profoundly changed. Additional differences appeared in genes involved in signaling and metabolism. Taken together these results demonstrate for the first time that expression of neurosecretory vesicles and granules is part of a complex gene expression program that includes many other features that so far have not been recognized.

Circadian regulation of diverse gene products revealed by mRNA expression profiling of synchronized fibroblasts

Genes under a 24-h regulation period may represent drug targets relevant to diseases involving circadian dysfunctions. As a testing model of the circadian clock system, we have used synchronized rat fibroblasts that are known to express at least six genes in a circadian fashion. We have determined the expression patterns of 9957 transcripts every 4 h over a total period of 76 h using high density oligonucleotide microarrays. The spectral analysis of our mRNA profiling data indicated that approximately 2% (85 genes) of all expressed genes followed a robust circadian pattern. We have confirmed the circadian expression of previously known clock or clock-driven genes, and we identified 81 novel circadian genes. The majority of the circadian-regulated gene products are known and are involved in diverse cellular functions. We have classified these circadian genes in seven clusters according to their phase of cycling. Our pathway analysis of the mRNA profiling data strongly suggests a direct link between circadian rhythm and cell cycle.

The molecular determination of HLA-Cw alleles in the Mandenka (West Africa) reveals a close genetic relationship between Africans and Europeans

HLA-Cw alleles were determined by high-resolution polymerase chain reaction-sequence-specific oligonucleotide probe (PCR-SSOP) oligotyping in a sample of 165 Mandenka, a population from Eastern Senegal previously analysed for A/B and DRB/DQB polymorphisms. A total of 18 Cw alleles were identified, with Cw*0401/5 and 1601 accounting for a combined frequency of 36%. A comparison of Cw allele frequencies among several populations of different origins, Mandenka, Swiss, English, Ashkenazi Jews from the UK and Japanese, reveals a high genetic heterogeneity among them, but also a much closer relationship between Mandenka, Europeans and Ashkenazi than between any of these populations and Japanese. Cw*0501, Cw*0701 and Cw*1601, among others, appear to be restricted to the European and African populations. Many B-Cw haplotypes exhibit a significant linkage disequilibrium in the Mandenka, among which B*3501-Cw*0401 and B*7801-Cw*1601, formed by the most frequent B and Cw alleles, and B*5201-Cw*1601, B*5702-Cw*18 and B*4410-Cw*0401, not yet observed in other populations. B*3501-Cw*0401 is found with similar frequencies in Europeans. The results possibly support a close historical relationship between Africans and Europeans as compared to East Asiatics. However, the HLA-Cw frequency distributions are characterised by an excess of heterozygotes, indicating that balancing selection may have played a role in the evolution of this polymorphism.

Sequence of four new HLA-Cw alleles: a possible role of interallelic recombination

In order to extend our current understanding of HLA-C polymorphism, four new alleles have been cloned and sequenced: Cw*1801 in a donor of mixed origin, Cw*02024 in a Senegalese individual, Cw*1205 and Cw*1604 in European Caucasoid blood donors. HLA-Cw*1801, which most likely results from an interallelic recombination between Cw*0704 and 0401 alleles, was not associated with B*8101, but with either B*4403 or B18. The Cw*02024 allele differs from Cw*02022 by a silent mutation in exon 3. Both Cw*1801 and Cw*02024 appear to be rather frequent in populations of African origin but have not yet been detected in Caucasoids. HLA-Cw*1604 differs from Cw*1601 by two nucleotides at codon 156 leading to a Gln to Trp substitution. This new Cw16 subtype was subsequently identified in three additional unrelated families, all of South-European origin, and presented an unusual association with B*4402 in all cases. HLA-Cw*1205 is a composite allele with the alpha1 domain of Cw*1602 and the alpha2 domain of Cw*1203. It appears to be rare, at least in European Caucasoids. Three of these four alleles may have resulted from gene conversion-like or interallelic recombination events.

Molecular characterization of HLA-C incompatibilities in HLA-ABDR-matched unrelated bone marrow donor-recipient pairs. Sequence of two new Cw alleles (Cw*02023 and Cw*0707) and recognition by cytotoxic T lymphocytes

While the influence of HLA-AB and -DRB1 matching on the outcome of bone marrow transplantation (BMT) with unrelated donors is clear, the evaluation of HLA-C has been hampered by its poor serological definition. Because the low resolution of standard HLA-C typing could explain the significant number of positive cytotoxic T lymphocyte precursor frequency (CTLpf) tests found among HLA-AB-subtype, DRB1/B3/B5-subtype matched patient/donor pairs, we have identified by sequencing the incompatibilities recognized by CD8+ CTL clones obtained from such positive CTLpf tests. In most cases the target molecules were HLA-C antigens that had escaped detection by serology (e.g. Cw*1601, 1502 or 0702). Direct recognition of HLA-C by a CTL clone was demonstrated by lysis of the HLA class I-negative 721.221 cell line transfected with Cw*1601 cDNA. Because of the functional importance of Cw polymorphism, a PCR-SSO oligotyping procedure was set up allowing the resolution of 29 Cw alleles. Oligotyping of a panel of 382 individuals (including 101 patients and their 272 potential unrelated donors, 5 related donors and 4 platelet donors) allowed to determine HLA-C and HLA A-B-Cw-DRB1 allelic frequencies, as well as a number of A-Cw, B-Cw, and DRB1-Cw associations. Two new HLA-Cw alleles (Cw*02023 and Cw*0707) were identified by DNA sequencing of PCR-amplified exon 2-intron 2-exon 3 amplicons. Furthermore, we determined the degree of HLA-C compatibility in 287 matched pairs that could be formed from 73 patients and their 184 potential unrelated donors compatible for HLA-AB by serology and for HLA-DRB1/ B3/B5 by oligotyping. Cw mismatches were identified in 42.1% of these pairs, and AB-subtype oligotyping showed that 30% of these Cw-incompatible pairs were also mismatched for A or B-locus subtype. The degree of HLA-C incompatibility was strongly influenced by the linkage with B alleles and by the ABDR haplotypes. Cw alleles linked with B*4403, B*5101, B18, and B62 haplotypes were frequently mismatched. Apparently high resolution DNA typing for HLA-AB does not result in full matching at locus C. Since HLA-C polymorphism is recognized by alloreactive CTLs, such incompatibilities might be as relevant as AB-subtype mismatches in clinical transplantation.

High resolution HLA matching associated with decreased mortality after unrelated bone marrow transplantation

As compared with related HLA-identical sibling donors, bone marrow transplantation (BMT) with phenotypically HLA ABDR-compatible unrelated donors is associated with increased mortality. This may be due to hidden HLA incompatibilities not detected by conventional typing. We have analyzed 44 unrelated patient-donor pairs who were matched for HLA-A, -B, and -DR by routine tissue typing. Our comprehensive HLA typing approach consisted of serology, cytotoxic T-cell precursor (CTLp) tests, T-cell cloning, oligotyping, and DNA sequencing. Using these techniques, we identified numerous HLA allele mismatches not detected by the previously applied routine typing. Twenty-four patient-donor pairs were highly matched and had a low CTLp frequency, whereas the remaining 20 pairs were allele-mismatched for HLA-A, -B, -C, -DR, -DQ antigens and/or had a positive result of the CTLp test. Patient and donor age, diagnosis, and treatment did not differ significantly between the matched and mismatched transplants. The probability for severe acute graft-versus-host disease grades III-IV was 21% in the matched and 47% in the mismatched patients (P = .0464). Transplant-related mortality was 21% and 57% (P = .0072) and actuarial patient survival rates at 3 years were 61% and 13% (P = .0005). We conclude that both HLA class I and class II allele mismatches between unrelated phenotypically ABDR-compatible patient-donor pairs are frequent and associated with increased incidence of posttransplant complications.

HLA-DPB1 DNA polymorphism in the Swiss population: linkage disequilibrium with other HLA loci and population genetic affinities

Allelic diversity at the HLA-DPB1 locus was determined by PCR-oligotyping in a sample of 125 healthy Swiss individuals. A total of 17 alleles were detected among which four main alleles (DPB1*0401, *0201, *0301, *0402) reached a cumulative frequency of 74.8%. HLA-A and -B (by serology) and HLA-DRB1 (by oligotyping) allelic polymorphisms were analysed also. HLA-B and HLA-DRB1 loci were highly polymorphic with 25 and 28 alleles respectively and similar heterozygosity levels of 0.93 and 0.92. These two loci were found to be more polymorphic than expected under neutrality, while lower heterozygosity levels were found for HLA-A (0.87) and DPB1 (0.81) loci. This paper presents also a global comparison of DPB1 allelic frequencies among 15 populations from four continents. As opposed to the DRB1 locus, overall DPB1 is shown to have a lower level of polymorphism and may be considered as neutral in all tested populations. DPB1 genetic diversity is correlated significantly with geography also, as found previously for DRB1. Two- and four-locus haplotype frequencies were determined and the significance of their linkage disequilibrium tested by an original non-parametric method. A significant positive linkage disequilibrium was found for 11 A-B, 16 B-DRB1, 7 DRB1-DPB1 and 3 A-B-DRB1-DPB1 haplotypes. The overall linkage disequilibrium between DRB1 and DPB1 was much lower than expected from the physical distance and lower than for A-B and B-DRB1 pairs. The implications of these results for bone marrow transplantation and for the evolution of HLA loci are discussed.