Suprachiasmatic vasopressin and the circadian regulation of voluntary locomotor behavior

Neural substrates for regulating self-grooming behavior in rodents

Grooming, as an evolutionarily conserved repetitive behavior, is common in various animals, including humans, and serves essential functions including, but not limited to, hygiene maintenance, thermoregulation, de-arousal, stress reduction, and social behaviors. In rodents, grooming involves a patterned and sequenced structure, known as the syntactic chain with four phases that comprise repeated stereotyped movements happening in a cephalocaudal progression style, beginning from the nose to the face, to the head, and finally ending with body licking. The context-dependent occurrence of grooming behavior indicates its adaptive significance. This review briefly summarizes the neural substrates responsible for rodent grooming behavior and explores its relevance in rodent models of neuropsychiatric disorders and neurodegenerative diseases with aberrant grooming phenotypes. We further emphasize the utility of rodent grooming as a reliable measure of repetitive behavior in neuropsychiatric models, holding promise for translational psychiatry. Herein, we mainly focus on rodent self-grooming. Allogrooming (grooming being applied on one animal by its conspecifics via licking or carefully nibbling) and heterogrooming (a form of grooming behavior directing towards another animal, which occurs in other contexts, such as maternal, sexual, aggressive, or social behaviors) are not covered due to space constraints.

Blood flows from the SCN toward the OVLT within a new brain vascular portal pathway

The suprachiasmatic nucleus (SCN) sets the phase of oscillation throughout the brain and body. Anatomical evidence reveals a portal system linking the SCN and the organum vasculosum of the lamina terminalis (OVLT), begging the question of the direction of blood flow and the nature of diffusible signals that flow in this specialized vasculature. Using a combination of anatomical and in vivo two-photon imaging approaches, we unequivocally show that blood flows unidirectionally from the SCN to the OVLT, that blood flow rate displays daily oscillations with a higher rate at night than in the day, and that circulating vasopressin can access portal vessels. These findings highlight a previously unknown central nervous system communication pathway, which, like that of the pituitary portal system, could allow neurosecretions to reach nearby target sites in OVLT, avoiding dilution in the systemic blood. In both of these brain portal pathways, the target sites relay signals broadly to both the brain and the rest of the body.

Vasopressin as Possible Treatment Option in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is rather common, presenting with prevalent early problems in social communication and accompanied by repetitive behavior. As vasopressin was implicated not only in salt-water homeostasis and stress-axis regulation, but also in social behavior, its role in the development of ASD might be suggested. In this review, we summarized a wide range of problems associated with ASD to which vasopressin might contribute, from social skills to communication, motor function problems, autonomous nervous system alterations as well as sleep disturbances, and altered sensory information processing. Beside functional connections between vasopressin and ASD, we draw attention to the anatomical background, highlighting several brain areas, including the paraventricular nucleus of the hypothalamus, medial preoptic area, lateral septum, bed nucleus of stria terminalis, amygdala, hippocampus, olfactory bulb and even the cerebellum, either producing vasopressin or containing vasopressinergic receptors (presumably V1a). Sex differences in the vasopressinergic system might underline the male prevalence of ASD. Moreover, vasopressin might contribute to the effectiveness of available off-label therapies as well as serve as a possible target for intervention. In this sense, vasopressin, but paradoxically also V1a receptor antagonist, were found to be effective in some clinical trials. We concluded that although vasopressin might be an effective candidate for ASD treatment, we might assume that only a subgroup (e.g., with stress-axis disturbances), a certain sex (most probably males) and a certain brain area (targeting by means of virus vectors) would benefit from this therapy.

Adult Neurogenesis under Control of the Circadian System

The mammalian circadian system is a hierarchically organized system, which controls a 24-h periodicity in a wide variety of body and brain functions and physiological processes. There is increasing evidence that the circadian system modulates the complex multistep process of adult neurogenesis, which is crucial for brain plasticity. This modulatory effect may be exercised via rhythmic systemic factors including neurotransmitters, hormones and neurotrophic factors as well as rhythmic behavior and physiology or via intrinsic factors within the neural progenitor cells such as the redox state and clock genes/molecular clockwork. In this review, we discuss the role of the circadian system for adult neurogenesis at both the systemic and the cellular levels. Better understanding of the role of the circadian system in modulation of adult neurogenesis can help develop new treatment strategies to improve the cognitive deterioration associated with chronodisruption due to detrimental light regimes or neurodegenerative diseases.

The Pituitary-Adrenal Response to Paradoxical Sleep Deprivation Is Similar to a Psychological Stressor, Whereas the Hypothalamic Response Is Unique

Stressors of different natures induce activation of the hypothalamic-pituitary-adrenal (HPA) axis at different magnitudes. Moreover, the HPA axis response to repeated exposure is usually distinct from that elicited by a single session. Paradoxical sleep deprivation (PSD) augments ACTH and corticosterone (CORT) levels, but the nature of this stimulus is not yet defined. The purpose of the present study was to qualitatively compare the stress response of animals submitted to PSD to that of rats exposed once or four times to cold, as a physiological stress, movement restraint (RST) as a mixed stressor and predator odour (PRED) as the psychological stressor, whilst animals were submitted for 1 or 4 days to PSD and respective control groups. None of the stressors altered corticotropin releasing factor immunoreactivity in the paraventricular nucleus of the hypothalamus (PVN), median eminence (ME) or central amygdala, compared to control groups, whereas vasopressin immunoreactivity in PSD animals was decreased in the PVN and increased in the ME, indicating augmented activity of this system. ACTH levels were higher after repeated stress or prolonged PSD than after single- or 1 day-exposure and control groups, whereas the CORT response was habituated by repeated stress, but not by 4-days PSD. This dissociation resulted in changes in the CORT : ACTH ratio, with repeated cold and RST decreasing the ratio compared to single exposure, but no change was seen in PRED and PSD groups. Comparing the magnitude and pattern of pituitary-adrenal response to the different stressors, PSD-induced responses were closer to that shown by PRED-exposed rats. In contrast, the hypothalamic response of PSD-exposed rats was unique, inasmuch as this was the only stressor which increased the activity of the vasopressin system. In conclusion, we propose that the pituitary-adrenal response to PSD is similar to that induced by a psychological stressor.

Targeted modification of the Per2 clock gene alters circadian function in mPer2luciferase (mPer2Luc) mice

Modification of the Per2 clock gene in mPer2Luc reporter mice significantly alters circadian function. Behavioral period in constant dark is lengthened, and dissociates into two distinct components in constant light. Rhythms exhibit increased bimodality, enhanced phase resetting to light pulses, and altered entrainment to scheduled feeding. Mechanistic mathematical modelling predicts that enhanced protein interactions with the modified mPER2 C-terminus, combined with differential clock regulation among SCN subregions, can account for effects on circadian behavior via increased Per2 transcript and protein stability. PER2::LUC produces greater suppression of CLOCK:BMAL1 E-box activity than PER2. mPer2Luc carries a 72 bp deletion in exon 23 of Per2, and retains a neomycin resistance cassette that affects rhythm amplitude but not period. The results show that mPer2Luc acts as a circadian clock mutation illustrating a need for detailed assessment of potential impacts of c-terminal tags in genetically modified animal models.

Antagonism for NPY signaling reverses cognitive behavior defects induced by activity-based anorexia in mice

Patients with AN often express psychological symptoms such as body image distortion, cognitive biases, abnormal facial recognition, and deficits in working memory. However, the molecular mechanisms underlying the impairment of cognitive behaviors in AN remain unknown. In the present study, we measured cognitive behavior using novel object recognition (NOR) tasks and mRNA expressions in hypothalamic neuropeptides in female C57BL/6J mice with activity-based anorexia (ABA). Additionally, we evaluated the effects of antagonists with intracerebroventricular (icv) administration on the impairment of cognitive behavior in NOR tasks. Our results showed that NOR indices were lowered, subsequently increasing mRNA levels of agouti-related peptide (AgRP) and neuropeptide Y (NPY), and c-Fos- and AgRP- or NPY-positive cells in the hypothalamic arcuate nucleus in ABA mice. We also observed that icv administration of anti-NPY antiserum (2 µl), anti-AgRP antibody (0.1 μg), and Y5 receptor antagonist CPG71683 (15 nmol) significantly reversed the decreased NOR indices. Therefore, our results suggest that increased NPY and AgRP signaling in the brain might contribute to the impairment of cognitive behavior in AN.

Connectome of the Suprachiasmatic Nucleus: New Evidence of the Core-Shell Relationship

A brain clock, constituted of ∼20,000 peptidergically heterogeneous neurons, is located in the hypothalamic suprachiasmatic nucleus (SCN). While many peptidergic cell types have been identified, little is known about the connections among these neurons in mice. We first sought to identify contacts among major peptidergic cell types in the SCN using triple-label fluorescent immunocytochemistry (ICC). To this end, contacts among vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and calretinin (CALR) cells of the core, and arginine vasopressin (AVP) and met-enkephalin (ENK) cells of the shell were analyzed. Some core-to-shell and shell-to-core communications are specialized. We found that in wild-type (WT) mice, AVP fibers make extremely sparse contacts onto VIP neurons but contacts in the reverse direction are numerous. In contrast, AVP fibers make more contacts onto GRP neurons than conversely. For the other cell types tested, largely reciprocal connections are made. These results point to peptidergic cell type-specific communications between core and shell SCN neurons. To further understand the impact of VIP-to-AVP communication, we next explored the SCN in VIP-deficient mice (VIP-KO). In these animals, AVP expression is markedly reduced in the SCN, but it is not altered in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Surprisingly, in VIP-KO mice, the number of AVP appositions onto other peptidergic cell types is not different from controls. Colchicine administration, which blocks AVP transport, restored the numbers of AVP neurons in VIP-KO to that of WT littermates. The results indicate that VIP has an important role in modulating AVP expression levels in the SCN in this mouse.

Neonatal exposure to monosodium glutamate induces morphological alterations in suprachiasmatic nucleus of adult rat

Neonatal exposure to monosodium glutamate (MSG) induces circadian disorders in several physiological and behavioural processes regulated by the suprachiasmatic nucleus (SCN). The objective of this study was to evaluate the effects of neonatal exposure to MSG on locomotor activity, and on morphology, cellular density and expression of proteins, as evaluated by optical density (OD), of vasopressin (VP)-, vasoactive intestinal polypeptide (VIP)- and glial fibrillary acidic protein (GFAP)-immunoreactive cells in the SCN. Male Wistar rats were used: the MSG group was subcutaneously treated from 3 to 10 days of age with 3.5 mg/g/day. Locomotor activity was evaluated at 90 days of age using 'open-field' test, and the brains were processed for immunohistochemical studies. MSG exposure induced a significant decrease in locomotor activity. VP- and VIP-immunoreactive neuronal densities showed a significant decrease, while the somatic OD showed an increase. Major axes and somatic area were significantly increased in VIP neurons. The cellular and optical densities of GFAP-immunoreactive sections of SCN were significantly increased. These results demonstrated that newborn exposure to MSG induced morphological alterations in SCN cells, an alteration that could be the basis for behavioural disorders observed in the animals.

Nasal oxytocin administration reduces food intake without affecting locomotor activity and glycemia with c-Fos induction in limited brain areas

Recent studies have considered oxytocin (Oxt) as a possible medicine to treat obesity and hyperphagia. To find the effective and safe route for Oxt treatment, we compared the effects of its nasal and intraperitoneal (IP) administration on food intake, locomotor activity, and glucose tolerance in mice. Nasal Oxt administration decreased food intake without altering locomotor activity and increased the number of c-Fos-immunoreactive (ir) neurons in the paraventricular nucleus (PVN) of the hypothalamus, the area postrema (AP), and the dorsal motor nucleus of vagus (DMNV) of the medulla. IP Oxt administration decreased food intake and locomotor activity and increased the number of c-Fos-ir neurons not only in the PVN, AP, and DMNV but also in the nucleus of solitary tract of the medulla and in the arcuate nucleus of the hypothalamus. In IP glucose tolerance tests, IP Oxt injection attenuated the rise of blood glucose, whereas neither nasal nor intracerebroventricular Oxt affected blood glucose. In isolated islets, Oxt administration potentiated glucose-induced insulin secretion. These results indicate that both nasal and IP Oxt injections reduce food intake to a similar extent and increase the number of c-Fos-ir neurons in common brain regions. IP Oxt administration, in addition, activates broader brain regions, reduces locomotor activity, and affects glucose tolerance possibly by promoting insulin secretion from pancreatic islets. In comparison with IP administration, the nasal route of Oxt administration could exert a similar anorexigenic effect with a lesser effect on peripheral organs.