Cellular and serotonergic correlates of habituated neuroendocrine responses in male and female rats

Differential cortical aspartate uptake across the oestrous cycle is associated with changes in gut microbiota in Wistar-Kyoto rats

Pain and psychological stress are intricately linked, with sex differences evident in disorders associated with both systems. Glutamatergic signalling in the central nervous system is influenced by gonadal hormones via the hypothalamic-pituitary-adrenal axis and is central in pain research. Emerging evidence supports an important role for the gut microbiota in influencing pain signalling. Here, the functional activity of excitatory amino acid transporters (EAATs) in the anterior cingulate cortex (ACC) and lumbosacral spinal cord of male and female Wistar-Kyoto rats, an animal model of comorbid visceral hypersensitivity and enhanced stress responsivity, was investigated across the oestrous cycle. Correlations between the gut microbiota and changes in the functional activity of the central glutamatergic system were also investigated. EAAT function in the lumbosacral spinal cord was similar between males and females across the oestrous cycle. EAAT function was higher in the ACC of dioestrus females compared to proestrus and oestrus females. In males, aspartate uptake in the ACC positively correlated with Bacteroides, while aspartate uptake in the spinal cord positively correlated with the relative abundance of Lachnospiraceae NK4A136. Positive associations with aspartate uptake in the spinal cord were also observed for Alistipes and Bifidobacterium during oestrus, and Eubacterium coprostanoligenes during proestrus. Clostridium sensu stricto1 was negatively associated with aspartate uptake in the ACC in males and dioestrus females. These data indicate that glutamate metabolism in the ACC is oestrous stage-dependent and that short-chain fatty acid-producing bacteria are positively correlated with aspartate uptake in males and during specific oestrous stages in females.

Sexual dimorphism of hypothalamic serotonin release during systemic inflammation: Role of endothelin-1

The hypothalamus receives serotonergic projections from the raphe nucleus in a sex-specific manner. During systemic inflammation, hypothalamic levels of serotonin (5-hydroxytryptamine [5-HT]) decrease in male rats. The present study evaluated the involvement of endothelin-1 (ET-1) in the febrile response, hypolocomotion, and changes in hypothalamic 5-HT levels during systemic inflammation in male and female rats. An intraperitoneal injection of lipopolysaccharide (LPS) induced a febrile response and hypolocomotion in both male and female rats. However, although LPS reduced hypothalamic levels of 5-HT and its metabolite 5-hydroxyindol acetic acid (5-HIAA) in male rats, it increased these levels in female rats. An intracerebroventricular injection of the endothelin-B receptor antagonist BQ788 significantly reduced LPS-induced fever and hypolocomotion and changes in hypothalamic 5-HT and 5-HIAA levels in both male and female rats. The i.c.v. administration of ET-1 induced a significant fever and hypolocomotion, but reduced the hypothalamic levels of 5-HT and 5-HIAA in both males and females. These results suggest an important sexual dimorphism during systemic inflammation regarding the release of 5-HT in the hypothalamus. Moreover, ET-1 arises as an important mediator involved in the changes in hypothalamic 5-HT levels in both male and female rats.

Analysis of lumateperone data for patients with schizophrenia using related adverse events from the FDA adverse reporting system

BACKGROUND

Our study utilized the U.S. Food and Drug Administration's Adverse Event Reporting System (FAERS) to analyze and study the adverse event (AEs) signals of second-generation antipsychotic drug lumateperone, providing a reference for clinical safety monitoring in the treatment of schizophrenia.

METHODS

The International Dictionary of Medical Terminology (version 26.0) was used to standardize the preferred system organ category (SOC) and preferred terminology (PT) for adverse drug events (ADE) data related to lumateperone. ADE signals were classified and described using four algorithms: reporting odds ratios (ROR), proportional reporting ratios (PRR), Bayesian confidence-propagation neural network (BCPNN) and Multinomial gamma-poisson shrinkage (MGPS).

RESULT

Among the 2542 case reports collected from the FAERS database, 1762 reports with lumateperone as a 'principal suspect(PS)' AEs were identified. Lumateperone-induced AEs occurred in 26 system organ categories (SOC). A total of 118 significant disproportionate preferred terms (PTs) meeting the requirements of 4 algorithms were retained, and unexpected major events, such as burning sensation, tremor, migraine etc. may also occur. The median time to onset of lumateperone-related adverse events was 9 days (interquartile range [IQR] 2-31.25 days), and most AEs occurred within the first 10 days and 1 month after initiation of lumateperone therapy.

CONCLUSION

Our research may provide a better understanding of the potential adverse events that may be caused by lumateperone and those not recorded in the drug instructions, providing valuable signals for clinical use.

Sex-specific expression of distinct serotonin receptors mediates stress vulnerability of adult hippocampal neural stem cells in mice

Women are more vulnerable to stress and have a higher likelihood of developing mood disorders. The serotonin (5HT) system has been highly implicated in stress response and mood regulation. However, sex-dependent mechanisms underlying serotonergic regulation of stress vulnerability remain poorly understood. Here, we report that adult hippocampal neural stem cells (NSCs) of the Ascl1 lineage (Ascl1-NSCs) in female mice express functional 5HT1A receptors (5HT1ARs), and selective deletion of 5HT1ARs in Ascl1-NSCs decreases the Ascl1-NSC pool only in females. Mechanistically, 5HT1AR deletion in Ascl1-NSCs of females leads to 5HT-induced depolarization mediated by upregulation of 5HT7Rs. Furthermore, repeated restraint stress (RRS) impairs Ascl1-NSC maintenance through a 5HT1AR-mediated mechanism. By contrast, Ascl1-NSCs in males express 5HT7R receptors (5HT7Rs) that are downregulated by RRS, thus maintaining the Ascl1-NSC pool. These findings suggest that sex-specific expression of distinct 5HTRs and their differential interactions with stress may underlie sex differences in stress vulnerability.

Anti-angiogenic mechanisms and serotonergic dysfunction in the Rgs2 knockout model for the study of psycho-obstetric risk

Psychiatric and obstetric diseases are growing threats to public health and share high rates of co-morbidity. G protein-coupled receptor signaling (e.g., vasopressin, serotonin) may be a convergent psycho-obstetric risk mechanism. Regulator of G Protein Signaling 2 (RGS2) mutations increase risk for both the gestational disease preeclampsia and for depression. We previously found preeclampsia-like, anti-angiogenic obstetric phenotypes with reduced placental Rgs2 expression in mice. Here, we extend this to test whether conserved cerebrovascular and serotonergic mechanisms are also associated with risk for neurobiological phenotypes in the Rgs2 KO mouse. Rgs2 KO exhibited anxiety-, depression-, and hedonic-like behaviors. Cortical vascular density and vessel length decreased in Rgs2 KO; cortical and white matter thickness and cell densities were unchanged. In Rgs2 KO, serotonergic gene expression was sex-specifically changed (e.g., cortical Htr2a, Maoa increased in females but all serotonin targets unchanged or decreased in males); redox-related expression increased in paraventricular nucleus and aorta; and angiogenic gene expression was changed in male but not female cortex. Whole-cell recordings from dorsal raphe serotonin neurons revealed altered 5-HT1A receptor-dependent inhibitory postsynaptic currents (5-HT1A-IPSCs) in female but not male KO neurons. Additionally, serotonin transporter blockade by the SSRI sertraline increased the amplitude and time-to-peak of 5-HT1A-IPSCs in KO neurons to a greater extent than in WT neurons in females only. These results demonstrate behavioral, cerebrovascular, and sertraline hypersensitivity phenotypes in Rgs2 KOs, some of which are sex-specific. Disruptions may be driven by vascular and cell stress mechanisms linking the shared pathogenesis of psychiatric and obstetric disease to reveal future targets.

Restraint or immobilization: a comparison of methodologies for restricting free movement in rodents and their potential impact on physiology and behavior

Restriction of free movement has historically been used as a model for inducing acute and chronic stress in laboratory animals. This paradigm is one of the most widely employed experimental procedures for basic research studies of stress-related disorders. It is easy to implement, and it rarely involves any physical harm to the animal. Many different restraint methods have been developed with variations in the apparatuses used and the degree of limitation of movement. Unfortunately, very few studies directly compare the differential impact of the distinct protocols. Additionally, restraint and immobilization terms are not differentiated and are sometimes used interchangeably in the literature. This review offers evidence of great physiological differences in the impact of distinct restraint procedures in rats and mice and emphasizes the need for a standardized language on this topic. Moreover, it illustrates the necessity of additional systematic studies that compare the effects of the distinct restraint methodologies, which would help to decide better which procedure should be used depending on the objectives of each particular study.

Analysis of a genetic region affecting mouse body weight

Genetic factors affect an individual's risk of developing obesity, but in most cases each genetic variant has a small effect. Discovery of genes that regulate obesity may provide clues about its underlying biological processes and point to new ways the disease can be treated. Preclinical animal models facilitate genetic discovery in obesity because environmental factors can be better controlled compared with the human population. We studied inbred mouse strains to identify novel genes affecting obesity and glucose metabolism. BTBR T+ Itpr3^tf/J (BTBR) mice are fatter and more glucose intolerant than C57BL/6J (B6) mice. Prior genetic studies of these strains identified an obesity locus on chromosome 2. Using congenic mice, we found that obesity was affected by a ∼316 kb region, with only two known genes, pyruvate dehydrogenase kinase 1 (Pdk1) and integrin α 6 (Itga6). Both genes had mutations affecting their amino acid sequence and reducing mRNA levels. Both genes have known functions that could modulate obesity, lipid metabolism, insulin secretion, and/or glucose homeostasis. We hypothesized that genetic variation in or near Pdk1 or Itga6 causing reduced Pdk1 and Itga6 expression would promote obesity and impaired glucose tolerance. We used knockout mice lacking Pdk1 or Itga6 fed an obesigenic diet to test this hypothesis. Under the conditions we studied, we were unable to detect an individual contribution of either Pdk1 or Itga6 to body weight. During our studies, with conditions outside our control, we were unable to reproduce some of our previous body weight data. However, we identified a previously unknown role for Pdk1 in cardiac cholesterol metabolism providing the basis for future investigations. The studies described in this paper highlight the importance and the challenge using physiological outcomes to study obesity genes in mice.

Restraint Stress and Repeated Corticosterone Administration Differentially Affect Neuronal Excitability, Synaptic Transmission and 5-HT7 Receptor Reactivity in the Dorsal Raphe Nucleus of Young Adult Male Rats

Exogenous corticosterone administration reduces GABAergic transmission and impairs its 5-HT₇ receptor-dependent modulation in the rat dorsal raphe nucleus (DRN), but it is largely unknown how neuronal functions of the DRN are affected by repeated physical and psychological stress. This study compared the effects of repeated restraint stress and corticosterone injections on DRN neuronal excitability, spontaneous synaptic transmission, and its 5-HT₇ receptor-dependent modulation. Male Wistar rats received corticosterone injections for 7 or 14 days or were restrained for 10 min twice daily for 3 days. Repeated restraint stress and repeated corticosterone administration evoked similar changes in performance in the forced swim test. They increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from DRN neurons. In contrast to the treatment with corticosterone, restraint stress-induced changes in sEPSC kinetics and decreased intrinsic excitability of DRN neurons did not modify inhibitory transmission. Repeated injections of the 5-HT₇ receptor antagonist SB 269970 ameliorated the effects of restraint on excitability and sEPSC frequency but did not restore the altered kinetics of sEPSCs. Thus, repeated restraint stress and repeated corticosterone administration differ in consequences for the intrinsic excitability of DRN projection neurons and their excitatory and inhibitory synaptic inputs. Effects of repeated restraint stress on DRN neurons can be partially abrogated by blocking the 5-HT₇ receptor.

Sex Differences in Serotonin 5-HT 1A Receptor Responses to Repeated Restraint Stress in Adult Male and Female Rats

BACKGROUND

Male and female rats were exposed to repeated restraint to determine how changes in serotonin (5-hydroxytryptamine; 5-HT) 1A receptors associate with stress hypothalamic-pituitary-adrenal (HPA) axis habituation.

METHODS

In response to 2-hour episodes of restraint, repeated daily for 5 consecutive days, males and females displayed reliable declines in HPA output, indicated by diminished adrenocorticotropin and corticosterone secretory responses. Using the 5-HT 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) as a pharmacological challenge for inducing hypothermia and elevations in plasma corticosterone, males displayed sensitized hypothermal responses after repeated restraint, whereas corticosterone responses to 8-OH-DPAT were enhanced in both sexes following single or repeated exposure.

RESULTS

Only males showed elevations in 5-HT 1A receptor G-protein coupling responses in the dorsal raphe after repeated restraint, whereas only females showed an increase in 5-HT 1A receptor responses in the hippocampus following single or repeated exposure. G-protein coupling responses within both regions correlated positively with 5-HT 1A receptor binding capacity. Thus, despite expressing similar capacities for stress HPA axis habituation, males and females emerged from repeated restraint to show region-specific changes in 5-HT 1A receptor function that may be explained, at least in part, by changes in receptor availability.

CONCLUSIONS

Based on the hypothermal and corticosteroid responses to 8-OH-DPAT, the present data suggest that stress habituation is met by an increase in the sensitivity of presynaptic 5-HT 1A receptors in males and by an increase in the sensitivity of a population of postsynaptic receptors in both sexes.

Pubertal changes in the pituitary and adrenal glands of male and female rats: Relevance to stress reactivity

The hormonal stress response mediated by the hypothalamic-pituitary-adrenal (HPA) axis changes significantly during puberty in a variety of species, including humans. For example, stress-induced adrenocorticotropic hormone (ACTH) and corticosterone responses are greater in prepubertal compared to adult rats, yet the mechanisms that mediate these age-related differences are unclear. It is possible that the pituitary and adrenal glands have higher hormonal concentrations prior to puberty, thus enabling a greater hormonal response if a stressor were to occur. Thus, we tested the hypothesis that resting levels of ACTH, and its precursor, proopiomelanocortin (POMC), are higher in the pituitary, and corticosterone levels are higher in the adrenals, of prepubertal compared to adult rats. Furthermore, to investigate any potential sex differences in these parameters, both males and females were assessed. Here we report that despite similar circulating plasma ACTH and corticosterone levels, prepubertal males and females have greater ACTH levels in the pituitary and greater corticosterone concentrations in the adrenals compared to adult males and females. Moreover, we show that POMC protein levels are significantly greater in the pituitary gland of prepubertal than adult rats, particularly in prepubertal females. These data suggest that increased glandular production of ACTH and corticosterone during puberty in part mediate pubertal differences in hormonal stress reactivity and highlight how each node of the HPA axis may contribute to these developmental changes. Given the dramatic increase in stress-related dysfunctions during puberty, continued study of all parts of the HPA axis will be imperative.