Impact of obstructive sleep apnea on clinical outcomes in patients hospitalized with COVID-19.

PURPOSE: Data from large patient registry studies suggested an increased incidence and increased mortality in coronavirus disease-2019 (COVID-19) in patients with a history of obstructive sleep apnea (OSA). This study aimed to compare the prevalence of OSA in patients with and without COVID-19 among patients admitted to the same hospital in the same time period. In addition, the impact of OSA on clinical outcomes of COVID-19 infection was investigated. METHODS: Observational cohort study. Clinical data were collected retrospectively from the complete medical records for each patient individually from March 1st 2020 to May 16th 2020. RESULTS: A total of 723 patients were diagnosed with COVID-19 and 1161 with non-COVID-19 disease. The prevalence of OSA did not differ between these groups (n = 49; 6.8% versus n = 66; 5.7%; p = 0.230). In patients with COVID-19, mortality was increased in the group of 49 patients with OSA (n = 17; 34.7%) compared to 674 COVID-19 patients without OSA (n = 143; 21.2%; p = 0.028). This increased risk of mortality in COVID-19 patients with OSA (OR = 2.590; 95%CI 1.218-5.507) was independent from Body Mass Index (BMI), male gender, age, diabetes, cardiovascular disease, and obstructive lung disease. Presence of OSA in COVID-19 disease was further associated with an increased length of hospital stay (12.6 ± 15.7 days versus 9.6 ± 9.9 days; p = 0.049). CONCLUSION: The prevalence of OSA did not differ between patients with or without COVID-19, but mortality and hospital length of stay were increased in patients with OSA and comorbid COVID-19. Hence, OSA should be included in COVID-19 risk factor analyses, Clinicians should be aware of the association and the mechanism should be further explored.

CHRM3 rs2165870 polymorphism is independently associated with postoperative nausea and vomiting, but combined prophylaxis is effective.

BACKGROUND: Clinical risk factors for postoperative nausea and vomiting (PONV) are evaluated with the Apfel score, however patients with low Apfel scores still experience PONV suggesting a genetic predisposition. PONV risk associates with specific M3 muscarinic acetylcholine receptor (CHRM3) rs 2165870 polymorphism. We investigated whether the Apfel score and this genetic variation independently contribute to PONV risk and whether prophylaxis reduces PONV in patients with low Apfel score but at high genetic risk. METHODS: In a prospective, controlled study, 454 subjects undergoing elective surgery were genotyped for rs2165870 and its association with PONV was investigated with log-binomial regression analysis. Subjects were randomised to receive acustimulation/dexamethasone, acustimulation/vehicle, sham acustimulation/dexamethasone, or sham acustimulation/vehicle to investigate their effects on PONV risk. RESULTS: Early PONV occurred in 37% of subjects. The rs2165870 genotype distribution was GG in 191, GA in 207, and AA in 56 subjects. The CHRM3 polymorphism was associated with a relative risk (RR) of 1.5 for GA vs GG [95% confidence interval (CI): 1.1-1.9; P=0.003] and 1.6 for AA vs GG (95% CI: 1.1-2.2; P=0.009) genotypes to develop PONV, and this was independent from the Apfel score (RR per Apfel point: 1.3, 95% CI: 1.2-1.5; P<0.0001). While dexamethasone and acustimulation each reduced the PONV risk by 30% in AA genotype carriers with low Apfel score, combined therapy reduced the risk by 86% (P=0.015). CONCLUSIONS: The CHRM3 polymorphism and the Apfel score independently predict PONV susceptibility. Dexamethasone/acustimulation should be considered in patients with low Apfel score but at high genetic risk. CLINICAL TRIAL REGISTRATION: DRKS00005664.

Vasopressin regulates social recognition in juvenile and adult rats of both sexes, but in sex- and age-specific ways.

In adult male rats, vasopressin (AVP) facilitates social recognition via activation of V1a receptors within the lateral septum. Much less is known about how AVP affects social recognition in adult females or in juvenile animals of either sex. We found that administration of the specific V1a receptor antagonist d(CH(2))(5)[Tyr(Me)(2)]AVP into the lateral septum of adult rats impaired, whereas AVP extended, social discrimination in both sexes. In juveniles, however, we detected a sex difference, such that males but not females showed social discrimination. Interestingly, administration of the V1a receptor antagonist to juveniles (either intracerebroventricularly or locally in the lateral septum) did not prevent social discrimination, but instead significantly decreased the investigation of a novel as opposed to a familiar animal in both sexes, with stronger effects in males. V1a receptors were found to be abundantly expressed in the lateral septum with higher binding density in females than in males. These findings demonstrate that activation of V1a receptors in the lateral septum is important for social recognition in both sexes, and that the roles of septal V1a receptors in social recognition change during development.

Absence of progestin receptors alters distribution of vasopressin fibers but not sexual differentiation of vasopressin system in mice.

Perinatal estrogens increase the number of vasopressin-expressing cells and the density of vasopressin-immunoreactive fibers observed in adult male rodents. The mechanism of action of estrogens on sexual differentiation of the extra-hypothalamic vasopressin system is unknown. We hypothesized that the sexually dimorphic expression of progestin receptors (PRs) during development would masculinize vasopressin expression in mice. We compared the number of vasopressin-expressing cells in the bed nucleus of the stria terminalis (BNST) and medial amygdala and the density of vasopressin-immunoreactive fibers in several brain regions of male and female wild type and PRKO mice using in situ hybridization and immunohistochemistry. As expected, sex differences in vasopressin cell number were observed in the BNST and medial amygdaloid nucleus. Vasopressin-immunoreactive fiber density was sexually dimorphic in the lateral septum, lateral habenular nucleus, medial amygdaloid nucleus, and mediodorsal thalamus. Sex differences were also observed in the principal nucleus of the BNST and medial preoptic area but not in the dorsomedial hypothalamus, which are thought to receive vasopressin innervation from the suprachiasmatic nucleus. Deletion of PRs did not alter the sex difference in vasopressin mRNA expression and vasopressin fiber immunoreactivity in any area examined. However, deletion of PRs increased the density of vasopressin fiber immunoreactivity in the lateral habenular nucleus. Our data suggest that PRs modulate vasopressin levels, but not sexual differentiation of vasopressin innervation in mice.

Distribution of oxytocin in the brain of a eusocial rodent.

Naked mole-rats are highly social rodents that live in large colonies characterized by a rigid social and reproductive hierarchy. Only one female, the queen, breeds. Most colony members are non-reproductive subordinates that work cooperatively to rear the young and maintain an underground burrow system. Little is known about the neurobiological basis of the complex sociality exhibited by this species. The neuropeptide oxytocin (Oxt) modulates social bonding and other social behaviors in many vertebrates. Here we examined the distribution of Oxt immunoreactivity in the brains of male and female naked mole-rats. As in other species, the majority of Oxt-immunoreactive (Oxt-ir) cells were found in the paraventricular and supraoptic nuclei, with additional labeled cells scattered throughout the preoptic and anterior hypothalamic areas. Oxt-ir fibers were found traveling toward and through the median eminence, as well as in the tenia tecta, septum, and nucleus of the diagonal band of Broca. A moderate network of fibers covered the bed nucleus of the stria terminalis and preoptic area, and a particularly dense fiber innervation of the nucleus accumbens and substantia innominata was observed. In the brainstem, Oxt-ir fibers were found in the periaqueductal gray, locus coeruleus, parabrachial nucleus, nucleus of the solitary tract, and nucleus ambiguus. The high levels of Oxt immunoreactivity in the nucleus accumbens and preoptic area are intriguing, given the link in other rodents between Oxt signaling in these regions and maternal behavior. Although only the queen gives birth or nurses pups in a naked mole-rat colony, most individuals actively participate in pup care.

Steroids, stress and the gut microbiome-brain axis.

It is becoming well established that the gut microbiome has a profound impact on human health and disease. In this review, we explore how steroids can influence the gut microbiota and, in turn, how the gut microbiota can influence hormone levels. Within the context of the gut microbiome-brain axis, we discuss how perturbations in the gut microbiota can alter the stress axis and behaviour. In addition, human studies on the possible role of gut microbiota in depression and anxiety are examined. Finally, we present some of the challenges and important questions that need to be addressed by future research in this exciting new area at the intersection of steroids, stress, gut-brain axis and human health.

Sexual differentiation of central vasopressin and vasotocin systems in vertebrates: different mechanisms, similar endpoints.

Vasopressin neurons in the bed nucleus of the stria terminalis and amygdala and vasotocin neurons in homologous areas in non-mammalian vertebrates show some of the most consistently found neural sex differences, with males having more cells and denser projections than females. These projections have been implicated in social and reproductive behaviors but also in autonomic functions. The sex differences in these projections may cause as well as prevent sex differences in these functions. This paper discusses the anatomy, steroid dependency, and sexual differentiation of these neurons. Although the final steps in sexual differentiation of vasopressin/vasotocin expression may be similar across vertebrate species, what triggers differentiation may vary dramatically. For example, during development, estrogen masculinizes vasopressin expression in rats but feminizes its counterpart in Japanese quail. Apparently, nature consistently finds a way of maintaining sex differences in vasopressin and vasotocin pathways, suggesting that the function of these differences is important enough that it was conserved during evolution.

Cirrhosis related chylous ascites successfully treated with TIPS.

We describe a patient with chylous ascites, who was extensively investigated for the cause. No malignant or lymphatic disease could be found, but a liver biopsy revealed liver cirrhosis. The chylous ascites was unsuccessfully treated with a sodium restriction diet, diuretics and a medium chain triglyceride diet. After the placement of a transjugular intrahepatic portosystemic shunt the ascites disappeared.

Risk factors for mortality in patients with pulmonary infections with non-tuberculous mycobacteria: a retrospective cohort study.

BACKGROUND: Infections with non-tuberculous mycobacteria (NTM) represent an increasing problem. Their clinical relevance is still largely unknown as well as predictors for mortality in affected patients. The objective was to describe prevalence and clinical relevance of different NTM and to identify risk factors for mortality. METHODS: Retrospective cohort study of 124 patients with NTM detection between January 2001 and December 2011. Clinical characteristics like symptoms and radiological appearance were assessed at presentation. The primary outcome was all cause mortality during the follow-up period. Univariate and multivariate survival analyses using Cox proportional hazard models were employed for statistical analysis. RESULTS: Over the study period, the frequency of NTM isolation varied from 4 to 12 patients per year. Twenty-nine out of 124 patients (23%) had a clinically relevant infection, according to the criteria of the American Thoracic Society (ATS). Mycobacterium avium was isolated most frequently, but Mycobacterium kansasii, Mycobacterium malmoense and Mycobacterium xenopi had the highest clinical relevance. Symptoms were mostly diverse and non-specific. On radiology, cavities were observed more frequently than a nodular-bronchiectatic variant or consolidation. In 75% of all patients, follow up time was more than two years. Median survival was 6.5 years (95%CI = 2.7-10.3). Factors significantly influencing survival time were haemoptysis (HR = 0.2, 95%CI = 0.1-0.6) and a consolidation on imaging (HR = 5.1, 95%CI 1.4-18.2). CONCLUSIONS: The presentation of an infection with NTM can be diverse and depends mainly on the causative NTM pathogen. The most important predictor for increased mortality is the radiological appearance of a consolidation.

Sex differences in the parental behavior of rodents.

The reproductive strategy of many mammalian species that give birth to altricial young involves intense and prolonged care of their offspring. In most cases, the mother provides all nurturance, but in some cases fathers, older siblings, or unrelated conspecifics participate in parental care. The display of these behaviors by animals other than mothers is affected by numerous factors, including their sex. We herein review the literature on similarities and/or differences between male and female laboratory rodents (rats, mice, voles, gerbils, and hamsters) in their parental responsiveness and discuss how the parental behavior of males and females is influenced by hormones, developmental processes, and prior social experiences. Understanding the mechanisms that generate sex differences in the parental responsiveness of rodents may indicate how similar sex differences in parental care are generated in other mammals.

Distribution of androgen receptor immunoreactivity in vasopressin- and oxytocin-immunoreactive neurons in the male rat brain.

Arginine vasopressin-immunoreactive (AVP-ir) neurons in the bed nucleus of stria terminalis (BST) and medial amygdaloid nucleus are very responsive to gonadal hormones. After gonadectomy, these neurons lose their AVP immunoreactivity and stop expressing AVP mRNA. Testosterone treatment reverses these changes, acting via androgen as well as estrogen receptor-mediated mechanisms. Although AVP-ir neurons contain estrogen receptor immunoreactivity, it is not known whether they also contain androgen receptor immunoreactivity. To answer this question, brains of male rats were stained immunocytochemically for AVP as well as for androgen receptors. In the BST and medial amygdaloid nucleus, respectively, 90.5% and 91.2% of the AVP-ir neurons contained androgen receptor immunoreactivity. In contrast, in the suprachiasmatic nucleus, the supraoptic nucleus, and the magnocellular portion of the paraventricular nucleus (PVN), none of the AVP-ir neurons contained androgen receptor immunoreactivity. In the ventral zone of the medial parvocellular part of the PVN (mpvPVN), 4.3% of the scattered AVP-ir neurons contained androgen receptor immunoreactivity. One of the control experiments, i.e. staining sections for oxytocin (OT) rather than AVP, revealed that although OT-ir neurons in the supraoptic and magnocellular portion of the PVN did not contain androgen receptor immunoreactivity, 52.5% of the OT-ir neurons in the mpvPVN did. The results suggest that androgens can bind to androgen receptors in AVP-ir neurons in the BST and medial amygdaloid nucleus, possibly to influence AVP expression. The results also suggest that androgens can bind to androgen receptors in AVP-ir and OT-ir neurons in the mpvPVN. The function of the latter interaction, however, is unclear.

Potential role of maternal progesterone in the sexual differentiation of the brain.

In rats, fetal testosterone directs sexual differentiation of the brain. However, fetuses are also exposed to maternal progesterone. Here we report that progestin receptor immunoreactivity in the medial preoptic nucleus (MPN) of fetal and neonatal rats is high in males but virtually absent in females. The MPN is one of the most sexually dimorphic structures in the rat brain and mediates several sexually differentiated behaviors. This suggests that progesterone may play a previously overlooked role in the development of sex differences in the brain and behavior. Henceforth, a novel function of the mother in the sexual differentiation of the CNS must be considered.

Sexual differentiation of vasopressin projections of the bed nucleus of the stria terminals and medial amygdaloid nucleus in rats.

The vasopressin-immunoreactive (AVP-ir) projections of the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) are much denser in males than in females even if males and females are treated with similar amounts of testosterone. Previous studies have established that testosterone influences AVP-ir projections during development, but not whether these effects of testosterone were permanent. This study tested the effects of various hormonal manipulations during development on the ability of testosterone to influence the AVP immunostaining in cells of the BST and MA and of fibers in the lateral septum of adult rats. In the first experiment, male rats that were castrated at 3 months of age (control males) had more AVP-ir cells in the BST and a higher density of AVP-ir fibers in the lateral septum than neonatally castrated male rats, whose cell numbers and fiber density did not differ from female rats that were ovariectomized neonatally or at 3 months of age (control females). This suggested that testicular secretions influence sexual differentiation of AVP-ir fiber pathways after birth. The second experiment showed that males castrated at the day of birth or at 1 week after birth had less AVP-ir cells in the BST and MA and a lower AVP-ir fiber density in the lateral septum than male rats castrated at the third week after birth or control males. This indicated that testicular secretions influenced the differentiation of AVP-ir pathways around postnatal day 7. This was further confirmed in the third experiment, in which testosterone propionate treatment at the seventh postnatal day significantly raised AVP-ir fiber density in the lateral septum of neonatally gonadectomized male and female rats and fully restored the number of AVP-ir cells in the BST of neonatally castrated males. Combined, these data suggest that testosterone levels around the seventh postnatal day determine the sexual differentiation of AVP-ir projections to the lateral septum.

Androstenedione effects on the vasopressin innervation of the rat brain.

The steroid hormone androstenedione profoundly influences the development and expression of sexual and aggressive behavior. The neural basis of these effects are, however, poorly understood. In this study we evaluated androstenedione's ability to maintain vasopressin peptide levels in the gonadal steroid-responsive vasopressin cells of the bed nucleus of the stria terminalis and the centromedial amygdala, and their projections. Adult male rats were castrated and given testosterone, androstenedione or no hormonal treatment for five weeks. Their brains were then processed for vasopressin immunoreactivity. Androstenedione and testosterone treatment were equally effective in preventing the reduction of vasopressin immunoreactivity associated with castration. Androstenedione may therefore be able to mimic the effects of testosterone on testosterone-responsive neural systems.

Afferent connections of the sexually dimorphic area of the hypothalamus of male and female gerbils.

We studied neural inputs to the sexually dimorphic area (SDA) of the gerbil hypothalamus by injecting wheat-germ agglutinin-horseradish peroxidase into its medial or lateral components in males and females. To confirm the topography of SDA afferents, we injected Phaseolus vulgaris-leucoagglutinin into areas where retrograde labeling from the medial and lateral SDA differed. Both methods indicated that the medial SDA received stronger inputs from the medial part of the bed nucleus of the stria terminalis, the ventral part of the lateral septal nucleus, the medial amygdaloid nucleus, and the amygdalohippocampal area, than the lateral SDA does. In contrast, the rostrodorsal part of the lateral septum, the lateral part of the bed nucleus of the stria terminalis, the anterior and posterior hypothalamic areas, and the dorsomedial hypothalamic nucleus project more heavily to the lateral than to the medial SDA. In addition, retrograde labeling suggested that the ventral part of the premammillary nucleus projects more strongly to the medial than to the lateral SDA, whereas the infralimbic area of the cortex and the lateral preoptic area project more strongly to the lateral than to the medial SDA. The densities of cells in the bed nucleus of the stria terminalis and medial amygdaloid nucleus that could be retrogradely labeled from the medial SDA were greater in males than in females. This was not true of labeling in the arcuate nucleus or in the ventral part of the lateral septal nucleus. Since the medial SDA receives strong inputs from areas with many steroid-accumulating cells, it could respond to steroids directly and via these afferents. In contrast, hormonal effects on the lateral SDA are more likely to occur locally.

Evidence for a functional and anatomical relationship between the lateral septum and the hypothalamus in the control of flank marking behavior in Golden hamsters.

Golden hamsters with established dominant/subordinate relationships communicate their social status by rubbing pheromone-producing flank glands against objects in the environment. This behavior, called flank marking, is controlled by vasopressin-sensitive neurons localized to the anterior hypothalamus. Vasopressinergic magnocellular neurons in the nucleus circularis and medial aspect of the supraoptic nucleus are thought to be a source of neurotransmitter for the initiation of flank marking. The present study was undertaken to examine the extrahypothalamic control of flank marking. The anatomical and functional connections between the lateral septum and the vasopressin-containing nuclear groups in and around the anterior hypothalamus were examined by: (1) tracing afferent and efferent connections following microinjection of horseradish peroxidase and Phaseolus vulgaris-leucoagglutinin into the lateral septum, and (2) recording odor-induced flank marking prior to and following ibotenate lesions in the septum. The greatest number of perikarya retrogradely labeled with horseradish peroxidase were found lateral to the anterior hypothalamus and ventral to the fornix in the area of the lateral hypothalamus. The vasopressin-containing nuclear groups, e.g., paraventricular, supraoptic, suprachiasmatic nuclei, and the nucleus circularis, were devoid of labeled perikarya. Nerve terminals anterogradely labeled with Phaseolus vulgaris-leucoagglutinin were primarily localized to the anterior hypothalamus, in and around the nucleus circularis, and the medial aspect of the supraoptic nucleus. The lateral aspect of the supraoptic nucleus was devoid of nerve terminals as were the paraventricular and suprachiasmatic nuclei. The anatomical connections between the lateral septum and the hypothalamus appear to be necessary for the control of flank marking, since the microinjection of ibotenate into this limbic site significantly reduced odor-induced flank marking as compared to control microinjections of 0.9% NaCl.

Sexual dimorphism in the vasotocin system of the bullfrog (Rana catesbeiana).

Arginine vasotocin (AVT) is widespread in amphibian brains, where its levels have been correlated with reproductive behaviors. To better understand which neural systems are involved in central actions of AVT, we used immunocytochemistry to compare the distribution of AVT in the brains of male and female bullfrogs (Rana catesbeiana). AVT-immunoreactive cells were observed in the septal nucleus, amygdala pars lateralis, magnocellular preoptic area, suprachiasmatic nucleus, and hypothalamus. AVT-immunoreactive cells were also found in the pretrigeminal nucleus, but only in animals killed in the fall. Immunoreactive fibers were broadly distributed in hypothalamic and extrahypothalamic areas. The most obvious sex differences were found in the amygdala pars lateralis, where the density of immunoreactive cells and fibers was significantly greater in male than in female bullfrogs. In addition, in the habenular nucleus, males had a denser distribution of AVT-immunoreactive fibers than females. In the suprachiasmatic nucleus, AVT-immunoreactive cells were larger in females than in males but did not differ in number. Since the areas that showed sex differences in AVT distribution have also been implicated in control of reproductive behaviors, they may form the neural substrates for the effects of AVT on sexually dimorphic behaviors in amphibians.

Efferent projections of the sexually dimorphic area of the gerbil hypothalamus: anterograde identification and retrograde verification in males and females.

Outputs of the sexually dimorphic area (SDA) of the gerbil hypothalamus were identified by injecting Phaseolus vulgaris-leucoagglutinin into the medial or lateral SDA (mSDA, lSDA) in males and females. They were verified by injecting Fluoro-Gold or rhodamine-labeled beads into over half the areas that contained labeled fibers. Both anterograde and retrograde tracing showed that the mSDA and lSDA project to many of the same sites but often to differing degrees. The mSDA projects more heavily than the lSDA to many of their forebrain targets including the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the medial tuberal area, and the anteroventral periventricular, arcuate, ventromedial and ventral premammillary nuclei of the hypothalamus. The lSDA projects more heavily than the mSDA to many of their mid- and hindbrain targets including the caudal, ventrolateral part of the periaqueductal gray, the retrorubral field, the pedunculopontine tegmental nucleus, and the locus coeruleus. In many other areas of the brain, the projections of the mSDA and lSDA are similar in size. These areas include the substantia innominata, the vascular organ of the lamina terminalis, the anterior amygdala, the posterior hypothalamus, the reuniens and paraventricular nuclei of the thalamus, and the pontine periaqueductal gray lateral to the fourth ventricle. The SDA pars compacta (SDApc), a small cell group embedded in the mSDA of males, projects to many fewer areas than the surrounding mSDA. It was strongly labeled when retrograde tracers were injected into the encapsulated part of the bed nucleus of the stria terminalis, the anteroventral periventricular nucleus, or the mSDA. It was also labeled from the vascular organ of the lamina terminalis, the caudal part of the lateral bed nucleus of the stria terminalis, the lSDA, the area lateral to the mSDA, the arcuate nucleus, the ventral premammillary nucleus, and the ventrolateral part of the ventromedial nucleus of the hypothalamus. Nothing resembling an SDApc was identified during retrograde tracing in females.

Vasopressin innervation of sexually dimorphic structures of the gerbil forebrain under various hormonal conditions.

The distribution of vasopressin-immunoreactive fibers in the forebrain of male and female gerbils was studied, focusing on the lateral septum and the sexually dimorphic area (SDA) found at the border between the medial preoptic area and the anterior hypothalamus. To study hormonal influences on the densities of these fibers, some animals of each sex were gonadectomized or gonadectomized and given testosterone. Others were given sham operations. High densities of vasopressin-immunoreactive fibers were found in the lateral septum. In the SDA, the densities of these fibers varied considerably. Many were found in the medial half of the medial SDA, but few in the lateral SDA. Vasopressin-immunoreactive fibers were also sparse in the lateral half of the medial SDA, except for a dense cluster in the SDA pars compacta of males. Similar but smaller clusters were seen in the same location in females although the SDA pars compacta could not be detected in Nissl-stained sections from the female brains. Fiber densities in two areas, the lateral septum and the lateral SDA, were sensitive to gonadal steroids. In both cases, castration reduced fiber density and testosterone enhanced it. In addition, fiber densities in two areas, the lateral septum and the medial SDA, were sexually dimorphic. In each case, fiber density was greater in males. There was no hormonal effect, however, on the fiber densities in the medial SDA. The fact that the fiber plexuses in the lateral septum and the medial SDA respond differently to gonadal steroids suggests that they arise from different cells and possibly from different areas of the brain. The vasopressin-immunoreactive fibers in the lateral septum probably come from steroid-sensitive vasopressin neurons in the bed nucleus of the stria terminalis. Those in the medial SDA may originate in the dorsal aspect of the suprachiasmatic nucleus where vasopressin-immunoreactive cell bodies were seen.

Distribution of small vasopressinergic neurons in golden hamsters.

In rats, small (diameter: ca. 10 micrograms) vasopressinergic neurons have been localized in the forebrain, including extrahypothalamic sites, such as the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). In golden hamsters, no such neurons have ever been described in extrahypothalamic sites, while their presence in some hypothalamic sites, such as the paraventricular nucleus (PVN), remains controversial. The present studies were carried out to confirm the existence of small vasopressinergic neurons in the forebrain of golden hamsters, using rats as a positive control. The presence of small vasopressinergic neurons in these sites was first tested by immunocytochemistry in colchicine-treated animals. The resulting distribution was corroborated by in situ hybridization for vasopressin (AVP) mRNA. While a large number of small AVP-immunoreactive (AVP-ir) neurons was found in the BST and MeA of colchicine-treated rats, none was found in the same locations in hamsters. Interestingly, as a few large (diameter: 20-25 micrograms) AVP-ir neurons were found in the BST just medial to the small neurons in rats, the same area contained a few large and small AVP-ir neurons in hamsters. In the PVN, large and small AVP-ir neurons were found in rats and hamsters. However, three to four times more neurons were counted in rats. These data were confirmed by in situ hybridization. Indeed, in hamsters, no labelling for AVP mRNA was detected in small neurons within the BST and MeA. Furthermore, the PVN of rats contained more labelling for AVP mRNA, as compared to hamsters. These results confirm that the distribution of vasopressinergic neurons in rats cannot be generalized to other species without a detailed analysis.