Swim stress triggers the release of vasopressin within the suprachiasmatic nucleus of male rats

Chronobiology of Exercise: Evaluating the Best Time to Exercise for Greater Cardiovascular and Metabolic Benefits

Physiological function fluctuates across 24 h due to ongoing daily patterns of behaviors and environmental changes, including the sleep/wake, rest/activity, light/dark, and daily temperature cycles. The internal circadian system prepares the body for these anticipated behavioral and environmental changes, helping to orchestrate optimal cardiovascular and metabolic responses to these daily changes. In addition, circadian disruption, caused principally by exposure to artificial light at night (e.g., as occurs with night-shift work), increases the risk for both cardiovascular and metabolic morbidity and mortality. Regular exercise is a countermeasure against cardiovascular and metabolic risk, and recent findings suggest that the cardiovascular benefits on blood pressure and autonomic control are greater with evening exercise compared to morning exercise. Moreover, exercise can also reset the timing of the circadian system, which raises the possibility that appropriate timing of exercise could be used to counteract circadian disruption. This article introduces the overall functional relevance of the human circadian system and presents the evidence surrounding the concepts that the time of day that exercise is performed can modulate the cardiovascular and metabolic benefits. Further work is needed to establish exercise as a tool to appropriately reset the circadian system following circadian misalignment to preserve cardiovascular and metabolic health. © 2022 American Physiological Society. Compr Physiol 12:3621-3639, 2022.

Central and peripheral neuropeptide RFRP-3: A bridge linking reproduction, nutrition, and stress response

This article is an amalgamation of the current status of RFRP-3 (GnIH) in reproduction and its association with the nutrition and stress-mediated changes in the reproductive activities. GnIH has been demonstrated in the hypothalamus of all the vertebrates studied so far and is a well-known inhibitor of GnRH mediated reproduction. The RFRP-3 neurons interact with the other hypothalamic neurons and the hormonal signals from peripheral organs for coordinating the nutritional, stress, and environmental associated changes to regulate reproduction. RFRP-3 has also been shown to regulate puberty, reproductive cyclicity and senescence depending upon the nutritional status. A favourable nutritional status and the environmental cues which are permissive for the successful breeding and pregnancy outcome keep RFRP-3 level low, whereas unfavourable nutritional status and stressful conditions increase the expression of RFRP-3 which impairs the reproduction. Still our knowledge about RFRP-3 is incomplete regarding its therapeutic application for nutritional or stress-related reproductive disorders.

The impact of stress and stress hormones on endogenous clocks and circadian rhythms

In mammals, daily rhythms in physiology and behavior are under control of a circadian pacemaker situated in the suprachiasmatic nucleus (SCN). This master clock receives photic input from the retina and coordinates peripheral oscillators present in other tissues, maintaining all rhythms in the body synchronized to the environmental light-dark cycle. In line with its function as a master clock, the SCN appears to be well protected against unpredictable stressful stimuli. However, available data indicate that stress and stress hormones at certain times of day are capable of shifting peripheral oscillators in, e.g., liver, kidney and heart, which are normally under control of the SCN. Such shifts of peripheral oscillators may represent a temporary change in circadian organization that facilitates adaptation to repeated stress. Alternatively, these shifts of internal rhythms may represent an imbalance between precisely orchestrated physiological and behavioral processes that may have severe consequences for health and well-being.

Traumatic stress and the circadian system: neurobiology, timing and treatment of posttraumatic chronodisruption

Background: Humans have an evolutionary need for a well-preserved internal 'clock', adjusted to the 24-hour rotation period of our planet. This intrinsic circadian timing system enables the temporal organization of numerous physiologic processes, from gene expression to behaviour. The human circadian system is tightly and bidirectionally interconnected to the human stress system, as both systems regulate each other's activity along the anticipated diurnal challenges. The understanding of the temporal relationship between stressors and stress responses is critical in the molecular pathophysiology of stress-and trauma-related diseases, such as posttraumatic stress disorder (PTSD). Objectives/Methods: In this narrative review, we present the functional components of the stress and circadian system and their multilevel interactions and discuss how traumatic stress can affect the harmonious interplay between the two systems. Results: Circadian dysregulation after trauma exposure (posttraumatic chronodisruption) may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of traumatic stress through a loss of the temporal order at different organizational levels. Posttraumatic chronodisruption may, thus, affect fundamental properties of neuroendocrine, immune and autonomic systems, leading to a breakdown of biobehavioral adaptive mechanisms with increased stress sensitivity and vulnerability. Given that many traumatic events occur in the late evening or night hours, we also describe how the time of day of trauma exposure can differentially affect the stress system and, finally, discuss potential chronotherapeutic interventions. Conclusion: Understanding the stress-related mechanisms susceptible to chronodisruption and their role in PTSD could deliver new insights into stress pathophysiology, provide better psychochronobiological treatment alternatives and enhance preventive strategies in stress-exposed populations.

Somato-dendritic vasopressin and oxytocin secretion in endocrine and autonomic regulation

Somato-dendritic secretion was first demonstrated over 30 years ago. However, although its existence has become widely accepted, the function of somato-dendritic secretion is still not completely understood. Hypothalamic magnocellular neurosecretory cells were among the first neuronal phenotypes in which somato-dendritic secretion was demonstrated and are among the neurones for which the functions of somato-dendritic secretion are best characterised. These neurones secrete the neuropeptides, vasopressin and oxytocin, in an orthograde manner from their axons in the posterior pituitary gland into the blood circulation to regulate body fluid balance and reproductive physiology. Retrograde somato-dendritic secretion of vasopressin and oxytocin modulates the activity of the neurones from which they are secreted, as well as the activity of neighbouring populations of neurones, to provide intra- and inter-population signals that coordinate the endocrine and autonomic responses for the control of peripheral physiology. Somato-dendritic vasopressin and oxytocin have also been proposed to act as hormone-like signals in the brain. There is some evidence that somato-dendritic secretion from magnocellular neurosecretory cells modulates the activity of neurones beyond their local environment where there are no vasopressin- or oxytocin-containing axons but, to date, there is no conclusive evidence for, or against, hormone-like signalling throughout the brain, although it is difficult to imagine that the levels of vasopressin found throughout the brain could be underpinned by release from relatively sparse axon terminal fields. The generation of data to resolve this issue remains a priority for the field.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal "clock," adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other's activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

Seasonal loss and resumption of circadian rhythms in hibernating arctic ground squirrels

Circadian clocks are near universal among organisms and play a key role in coordinating physiological and metabolic functions to anticipate or coincide with predictable daily changes in the physical and social environment. However, whether circadian rhythms persist and are functionally important during hibernation in all mammals is currently unclear. We examined whether circadian rhythms of body temperature (T _b) persist during multi-day, steady-state torpor and investigated the association between timing of animal emergence, exposure to light, and resumption of activity and T _b rhythms in free-living and captive male arctic ground squirrels. High-resolution (0.02 °C) temperature loggers revealed that circadian rhythms of T _b were not present during deep torpor in free-living arctic ground squirrels. Significant circadian rhythms of T _b resumed, however, following the resumption of euthermia, but prior to emergence, though rhythms became much more robust coincident with aboveground emergence. Additionally, squirrels maintained in captivity under conditions of constant darkness spontaneously developed significant circadian rhythms of T _b and activity soon after ending torpor. Exposing animals to a 5-s pulse of light within a week when they ended torpor increased the strength of rhythms. Our results are consistent with the hypothesis that circadian clock function is inhibited during hibernation in arctic ground squirrels, and we postulate that exposure to external stimuli, such as light in free-living animals, and meals or acute disturbance for captive squirrels, may enhance T _b rhythmicity by synchronizing loosely coupled circadian oscillators within the suprachiasmatic nucleus.

Cognitive dysfunction, elevated anxiety, and reduced cocaine response in circadian clock-deficient cryptochrome knockout mice

The circadian clock comprises a set of genes involved in cell-autonomous transcriptional feedback loops that orchestrate the expression of a range of downstream genes, driving circadian patterns of behavior. Cognitive dysfunction, mood disorders, anxiety disorders, and substance abuse disorders have been associated with disruptions in circadian rhythm and circadian clock genes, but the causal relationship of these associations is still poorly understood. In the present study, we investigate the effect of genetic disruption of the circadian clock, through deletion of both paralogs of the core gene cryptochrome (Cry1 and Cry2). Mice lacking Cry1 and Cry2 (Cry1(-/-)Cry2(-/-) ) displayed attenuated dark phase and novelty-induced locomotor activity. Moreover, they showed impaired recognition memory but intact fear memory. Depression-related behaviors in the forced swim test or sucrose preference tests were unaffected but Cry1(-/-)Cry2(-/-) mice displayed increased anxiety in the open field and elevated plus maze tests. Finally, hyperlocomotion and striatal phosphorylation of extracellular signal-regulated kinase (ERK) induced by a single cocaine administration are strongly reduced in Cry1(-/-)Cry2(-/-) mice. Interestingly, only some behavioral measures were affected in mice lacking either Cry1 or Cry2. Notably, recognition memory was impaired in both Cry1(-/-)Cry2(+/+) and Cry1(+/+)Cry2(-/-) mice. Moreover, we further observed elevated anxiety in Cry1(-/-)Cry2(+/+) and Cry1(+/+)Cry2(-/-) mice. Our data indicate that beyond their role in the control of circadian rhythm, cryptochrome genes have a direct influence in cognitive function, anxiety-related behaviors and sensitivity to psychostimulant drugs.

Circadian genes Period 1 and Period 2 in the nucleus accumbens regulate anxiety-related behavior

It has been suggested for some time that circadian rhythm abnormalities underlie the development of multiple psychiatric disorders. However, it is unclear how disruptions in individual circadian genes might regulate mood and anxiety. Here we found that mice lacking functional mPeriod 1 (mPer1) or mPeriod 2 (mPer2) individually did not have consistent behavioral abnormalities in measures of anxiety-related behavior. However, mice deficient in both mPer1 and mPer2 had an increase in levels of anxiety-like behavior in multiple measures. Moreover, we found that mPer1 and mPer2 expression was reduced in the nucleus accumbens (NAc) after exposure to chronic social defeat stress, a paradigm that led to increased anxiety-related behavior. Following social defeat, chronic treatment with fluoxetine normalized Per gene expression towards wild-type levels. Knockdown of both mPer1 and mPer2 expression via RNA interference specifically in the NAc led to a similar increase in anxiety-like behavior as seen in the mutant animals. Taken together, these results implicate the Per genes in the NAc in response to stress and the development of anxiety.

Anti-depression effects of Danggui-Shaoyao-San, a fixed combination of Traditional Chinese Medicine, on depression model in mice and rats

Anti-depression effects of Danggui-Shaoyao-San (DSS, 1.8-7.2g/kg, orally), a famous Chinese compound prescription with a fixed combination, on forced swimming test (FST) and chronic unpredictable mild stress (CUMS) model were investigated. DSS (7.2g/kg, orally, 7 days) shortened immobility time in FST model and DSS (3.6 or 7.2g/kg, orally, 21 days) increased the open-field activities and the percentage of sugar preference in CUMS model. DSS (7.2g/kg, orally, 21 days) also decreased the content of arginine vasopressin (AVP) in the pituitary and the expression of AVP mRNA in hypothalamus compared with the stress control group. These results demonstrated for the first time DSS has anti-depression effect and it may be influencing the central AVP system.

Dissociation of the anxiolytic-like effects of Avpr1a and Avpr1b receptor antagonists in the dorsal and ventral hippocampus

Arginine-vasopressin (AVP) is synthesized and released centrally in several brain structures. AVP is thought to mediate anxiety-related behavior through two central receptor subtypes, Avpr1a and Avpr1b. Although these AVP receptor subtypes are expressed in several brain regions, including the hippocampus, little is known about their explicit role in unconditioned fear or anxiety. This experiment assessed the anxiety-related effects of a selective Avpr1a antagonist ([beta-Mercapto-beta,beta-cyclopentamethylenepropionyl1, O-me-Tyr2, Arg8]-AVP) and a selective Avpr1b antagonist ((2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide; SSR 149415) microinfused into either the dorsal or ventral sub-regions of the rat hippocampus. Avpr1a antagonism in the ventral, but not the dorsal hippocampus reduced rats' anxiety-like behavior in the elevated plus-maze test. Conversely, Avpr1b antagonism in the dorsal, but not the ventral, hippocampus reduced anxiety in the plus-maze test. Neither antagonist reduced anxiety-like behavior in the shock-probe burying test. Overall, the results show that both receptor subtypes of AVP are involved in anxiety-related responses, but their specific contributions depend on three variables: (1) the anxiety-related response (shock-probe avoidance versus open-arm avoidance), (2) the receptor subtype antagonized (Avpr1a versus Avpr1b), and (3) the area of hippocampus (dorsal versus ventral) into which these antagonists are infused. These dissociations suggest that different fear responses are under the control of specific AVP receptor systems within discrete parts of the hippocampus.

Behavioral despair is differentially affected by the length and timing of photic stimulation in the dark phase of an L/D cycle

The effect of varying the length and timing of photic stimulation in the dark phase of an L/D lighting cycle on behavioral despair was investigated in female Wistar rats. Animals were kept in a vivarium on an L/D 12 h:12 h light cycle (lights on at 0700 h) except for a single day of light exposure in an insulated chamber in the dark phase of the L/D schedule. Light pulses provided by an incandescent lamp (15- and 25-W, for Exps. 1 and 2, respectively) either 2-h (Exp. 1) or 30-min in length (Exp. 2) were administered to independent groups of rats (n=8 each) either in the early, middle or late hours of the dark phase of the L/D cycle in the insulated chamber. Light pulses were delivered beginning 2 1/2, 5 1/2 or 7 1/2 h (Exp. 1) or 3 1/4, 6 1/4 and 8 1/4 h (Exp. 2) after dark onset. Control animals were treated similarly except for photic stimulation. In each experiment, an additional group received a light pulse of the appropriate length both in the early and late portion of the dark phase (double double-pulse groups): beginning 2 1/2 and 7 1/2 h (Exp. 1) or 3 1/4 and 8 1/4 h (Exp. 2) after dark onset. All animals then underwent two forced swim tests separated by 24 h with the first test occurring in the light (starting at 1500 h) following the dark phase when photic stimulation was administered. Total duration of immobility in the second swim test was measured to gauge behavioral despair. In Exp. 1, the 2-h double double-pulse group showed significantly shorter immobility compared to controls (p<0.05). In Exp. 2, 30-min light pulse delivered late in the dark phase reduced immobility significantly compared to controls and all the other light-treated groups (p<0.01). Results indicate that photic stimulation may have antidepressant effect on behavioral despair depending on the timing and the duration of photic stimulation.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

Changes in vasoactive intestinal peptide and arginine vasopressin expression in the suprachiasmatic nucleus of the rat brain following footshock stress

The neuropeptides, arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are synthesized by neurons of the suprachiasmatic nucleus (SCN) of the hypothalamus and are important regulators of SCN function. Previous studies have demonstrated that acute exposure to stressors can disrupt circadian activity rhythms, suggesting the possibility of stress-related alterations in the expression of these neuropeptides within SCN neurons. In this study, we examined the effect of intermittent footshock stress on AVP mRNA and heterogeneous nuclear RNA (hnRNA) and VIP mRNA expression in neurons of the SCN. Young adult male Sprague/Dawley rats were subjected to 15 s of scrambled intermittent footshock (0.50 mA pulses, 1 pulse/s, 300 ms duration) every 5 min for 30 min. Animals were sacrificed 75 or 135 min after the onset of stress and brains examined for AVP mRNA and hnRNA, and VIP mRNA using in situ hybridization. Footshock stress increased AVP hnRNA levels at the 75 min time point whereas AVP mRNA was elevated at both the 75 and 135 min time points. In contrast, footshock stress decreased the number of cells expressing VIP mRNA in the SCN without changing hybridization level per cell. These data indicate that the disruptive effect of stress on activity rhythms correlate with alterations in the expression of regulatory peptides within the SCN.

Signs of attenuated depression-like behavior in vasopressin deficient Brattleboro rats

Vasopressin, a peptide hormone functioning also as a neurotransmitter, neuromodulator and regulator of the stress response is considered to be one of the factors related to the development and course of depression. In the present study, we have tested the hypothesis that congenital deficit of vasopressin in Brattleboro rats leads to attenuated depression-like behavior in tests modeling different symptoms of depression. In addition, hypothalamic-pituitary-adrenocortical axis activity was investigated. Vasopressin deficient rats showed signs of attenuated depression-like behavior in forced swimming and sucrose preference tests, while their behavior on elevated plus maze was unchanged. Vasopressin deficiency had no influence on basal levels of ACTH and corticosterone and had only mild impact on hormonal activation in response to forced swimming and plus-maze exposure. However, vasopressin deficient animals showed higher level of dexamethasone induced suppression of corticosterone response to restraint stress and higher basal levels of corticotropin-releasing hormone mRNA in the hypothalamic paraventricular nucleus. In conclusion, present data obtained in vasopressin deficient rats show that vasopressin is involved in the development of depression-like behavior, in particular of the coping style and anhedonia. Moreover, behavioral and endocrine responses were found to be dissociated. We suggest that brain vasopressinergic circuits distinct from those regulating the HPA axis are involved in generating depression-like behavior.

Restraint stress delays reentrainment in male and female diurnal and nocturnal rodents

A temporary loss of normal circadian entrainment, such as that associated with shift work and transmeridian travel, can result in an array of detrimental symptoms, making rapid reentrainment of rhythmicity essential. While there is a wealth of literature examining the effects of stress on the entrained circadian system, less is known about the influence of stress on circadian function following a phase shift of the light: dark (LD) cycle. The authors find that recovery of locomotor activity synchronization is altered by restraint stress in the diurnal rodent Octodon degus (degu) and the nocturnal rat. In the first experiment, degus were subjected to a 6-h phase advance of the LD cycle. Sixty minutes after the new lights-on, animals underwent 60 min of restraint stress. The number of days it took each animal to reentrain its activity rhythms to the new LD cycle was recorded and compared to the number of days it took the animal to reentrain under control conditions. When subjected to restraint stress, degus took 30% longer to reentrain their activity rhythms (p < 0.01). In a second experiment, rats underwent a similar experimental paradigm. As with the degus, stress significantly delayed the reentrainment of rats' activity rhythms (p < 0.01). There was no interaction between sex and stress on the rate of reentrainment for either rats or degus. Furthermore, there was no effect of stress on the free-running activity rhythm of degus, suggesting that the effect of stress on reentrainment rate is not secondary to alterations of period length. Together, these data point to a detrimental effect of stress on recovery of entrainment of circadian rhythms, which is independent of activity niche and sex.

A single day of constant light (L/L) provides immunity to behavioral despair in female rats maintained on an L/D cycle

The present experiment investigated the potentially ameliorative effect of exposure to light in the dark phase of an 12:12 h daily lighting schedule (12L/12D cycle) on behavioral despair, an animal model of depression based on two forced swim tests separated by 24 h. Experimental groups of female Wistar rats were maintained on the 12L/12D cycle except for a single exposure to 12 h of light treatment in the dark phase of the 12L/12D cycle. Control animals were treated similarly except for light treatment. Animals then underwent one of two sets of behavioral tests starting on either the day light (or control) treatment ended (No Delay groups) or 24 h thereafter (Delay groups). The treatment for subgroups of light-treated and control animals tested with or without delay consisted of either two forced swim tests separated by 24 h or testing in the open field and elevated plus maze. Results indicated that a single exposure to a 12-h light treatment has protective effect on behavioral despair in groups tested with or without delay as measured by shorter duration of immobility in the second swim test compared to the controls. Light-treated and control animals behaved similarly in the open field and elevated plus-maze tests.

Inhibiting cortisol response accelerates recovery from a photic phase shift

Jetlag results when a temporary loss of circadian entrainment alters phase relationships among internal rhythms and between an organism and the outside world. After a large shift in the light-dark (LD) cycle, rapid recovery of entrainment minimizes the negative effects of internal circadian disorganization. There is evidence in the existing literature for an activation of the hypothalamic-pituitary-adrenal (HPA) axis after a photic phase shift, and it is possible that the degree of HPA-axis response is a determining factor of reentrainment time. This study utilized a diurnal rodent, Octodon degus, to test the prediction that the alteration of cortisol levels would affect the reentrainment rate of circadian locomotor rhythms. In experiment 1, we examined the effects of decreased cortisol (using metyrapone, an 11beta-hydroxylase inhibitor) on the rate of running-wheel rhythm recovery after a 6-h photic phase advance. Metyrapone treatment significantly shortened the length of time it took animals to entrain to the new LD cycle (11.5% acceleration). In experiment 2, we examined the effects of increased cortisol on the rate of reentrainment after a 6-h photic phase advance. Increasing plasma cortisol levels increased the number of days (8%) animals took to reentrain running-wheel activity rhythms, but this effect did not reach significance. A third experiment replicated the results of experiment 1 and also demonstrated that suppression of HPA activity via dexamethasone injection is capable of accelerating reentrainment rates by approximately 33%. These studies provide support for an interaction between the stress axis and circadian rhythms in determining the rate of recovery from a phase shift of the LD cycle.

Effect of lesioning the suprachiasmatic nuclei on behavioral despair in rats

The suprachiasmatic nucleus (SCN) is involved in regulating many biological rhythms. Several lines of research implicate the SCN in affective behavior. The SCN is directly involved in regulating the daily rhythms of the hypothalamo-pituitary-adrenal (HPA) axis hormones involved in stress. Bilateral lesions of the SCN disrupt both the rhythms and the basal levels of the HPA axis hormones involved in coping with stress. Moreover, stress can affect the biological rhythms regulated by the SCN, and disruption of biological rhythms in turn can cause stress. The present study assessed the effect of bilateral destruction of the SCN on behavioral despair, an animal model of depression sensitive to antidepressant treatment. The results indicate that bilateral destruction of the SCN results in reduced immobility in the second forced swimming test (FST) compared to sham controls and animals with incomplete lesions. These results indicate that bilateral destruction of the SCN has a protective effect in the induction of behavioral despair which may arise out of disruption of the secretion of the HPA axis hormones and/or of the neural connections between the SCN and the limbic structures that modulate the response to swim stress.

Effect of inescapable tones on behavioral despair in Wistar rats

The present experiment investigated the potentially differential effects of presenting inescapable tones with progressively increasing or decreasing durations on performance in behavioral despair, an animal model of depression based on two forced swim tests. Groups of female Wistar rats (n=8 each) were exposed to 60 inescapable tones (2000 Hz, 120 dB) either in a series of increasing or decreasing durations. Duration of tone exposure was incrementally increased (from 1 to 10 s) or decreased (from 10 to 1 s) by 1 s every six trials. A third group (n=8) was kept in the experimental chamber for a similar period but not exposed to tones. Animals were exposed to a 15 min forced swim test a day after tone (or control) treatment, followed by a 5 min swim test 24 h later. Analyses were done on diving, jumping, head shakes, duration and time of onset of immobility for the two swim tests. Compared to controls, animals that received tone exposure displayed greater immobility in the second swim test, indicating aggravation of behavioral despair due to inescapable tones.

Fear and power-dominance motivation: proposed contributions of peptide hormones present in cerebrospinal fluid and plasma

We propose that fear and power-dominance drive motivation are generated by the presence of elevated plasma and cerebrospinal fluid (CSF) levels of certain peptide hormones. For the fear drive, the controlling hormone is corticotropin releasing factor, and we argue that elevated CSF and plasma levels of this peptide which occur as a result of fear-evoking and other stressful experiences in the recent past are detected and transduced into neuronal activities by neurons in the vicinity of the third ventricle, primarily in the periventricular and arcuate hypothalamic nuclei. For the power-dominance drive, we propose that the primary signal is the CSF concentration of vasopressin, which is detected in two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis. We suggest that the peptide-generated signals detected in periventricular structures are transmitted to four areas in which neuronal activities represent fear and power-dominance: one in the medial hypothalamus, one in the dorsolateral quadrant of the periaqueductal gray matter, a third in the midline thalamic nuclei, and the fourth within medial prefrontal cortex. The probable purpose of this system is to maintain a state of fear or anger and consequent vigilant or aggressive behavior after the initial fear- or anger-inducing stimulus is no longer perceptible. We further propose that all the motivational drives, including thirst, hunger and sexual desire are generated in part by non-steroidal hormonal signals, and that the unstimulated motivational status of an individual is determined by the relative CSF and plasma levels of several peptide hormones.

Age-dependent effects of conditioning on cholinergic and vasopressin systems in the rat suprachiasmatic nucleus

Active shock avoidance was used to explore the impact of behavioural stimulation on the neurochemistry of the suprachiasmatic nucleus. We have found previously that the expression of muscarinic acetylcholine receptors in the suprachiasmatic nucleus of young rats was significantly enhanced 24 hours after fear conditioning. Here, we investigated whether this observation is age-dependent. We used 26 month-old Wistar rats with a deteriorated circadian system, and compared them with young rats (4 months of age) with an intact circadian system. Vasopressin, representing a major output system of the suprachiasmatic nucleus, was studied in addition to muscarinic receptors. Young rats showed a significant increase in immunostaining for muscarinic acetylcholine receptors 24 h after training, corroborating earlier observations. Aged rats did not show such an increase. In contrast, aged rats did show an increase in vasopressin immunoreactivity 24 h after fear conditioning, both at the level of content and cell number, while young rats did not reveal a significant rise. Thus, it seems that these two neurochemical systems in the suprachiasmatic nucleus are regulated independently. The results further demonstrate that the circadian pacemaker is influenced by fear conditioning in an age-dependent manner.

Forced swimming stimulates the expression of vasopressin and oxytocin in magnocellular neurons of the rat hypothalamic paraventricular nucleus

Previous studies have shown that a 10-min forced swimming session triggers the release of both vasopressin and oxytocin into the extracellular fluid of the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON) in rats. At the same time oxytocin, but not vasopressin, was released from the axon terminals into the blood. Here we combined forced swimming with in situ hybridization to investigate whether (i) the stressor-induced release of vasopressin and oxytocin within the PVN originates from parvo- or magnocellular neurons of the nucleus, and (ii) central release with or without concomitant peripheral secretion is followed by changes in the synthesis of vasopressin and/or oxytocin. Adult male Wistar rats were killed 2, 4 or 8 h after a 10-min forced swimming session and their brains processed for in situ hybridization using 35S-labelled oligonucleotide probes. As measured on photo-emulsion-coated slides, cellular vasopressin mRNA concentration increased in magnocellular PVN neurons 2 and 4 h after swimming (P < 0.05). Similarly, oxytocin mRNA concentration was significantly increased in magnocellular neurons of the PVN at 2 and 8 h (P < 0.05). We failed to observe significant effects on vasopressin and oxytocin mRNA levels in the parvocellular PVN and in the SON. Taken together with results from previous studies, our data suggest that magnocellular neurons are the predominant source of vasopressin and oxytocin released within PVN in response to forced swimming. Furthermore, in the case of vasopressin, central release in the absence of peripheral secretion is followed by increased mRNA levels, implying a refill of depleted somato-dendritic vasopressin stores. Within the SON, however, mRNA levels are poor indicators of the secretory activity of magnocellular neurons during stress.

In vivo microdialysis for nonapeptides in rat brain--a practical guide

Microdialysis provides a direct approach to monitor changes in interneuronal communication by monitoring the fluctuation of local, extracellular concentrations of potential neurotransmitters/neuromodulators. The present article is based on more than 10 years experience in performing microdialysis experiments in freely moving animals with inexpensive self-made microdialysis probes and accessories for monitoring of intracerebral neuropeptide release. On the basis of this experience, we provide a guide for the construction of different types of microdialysis probes and their application. Furthermore, we give information about organizing and performing a microdialysis experiment that can easily be adapted to fit individual applications needs. Finally, on the basis of theoretical background information advantages as well as limitations of the microdialysis technique are discussed with the intent to provide help to potential users for designing an appropriate microdialysis experiment.

Vasopressin released within the septal brain area during swim stress modulates the behavioural stress response in rats

The aim of the present study was to investigate the physiological significance of the neuropeptide arginine vasopressin (AVP) released within the septum, in the behavioural response of rats to stress. In the first experiment, rats were chronically implanted with a microdialysis probe aimed at the mediolateral or ventral septum to monitor the local release of AVP in response to 10 min of forced swimming in 20 degrees C warm water. Exposure to this stressor caused a significant increase in AVP release in both the mediolateral (174 +/- 21%, P < 0.01) and ventral septum (220 +/- 33%, P < 0.01). In contrast, microdialysates collected outside the mediolateral septum or in the lateral ventricle remained at prestress levels throughout the dialysis period. Furthermore, unstressed control animals failed to show significant alterations in vasopressin release in the mediolateral septum. In a second experiment, the introduction of the V1 receptor antagonist d(CH2)5Tyr(Me)AVP into the mediolateral septum via inverse microdialysis concomitant with stressor exposure caused the rats to spend an increased time floating and a reduced time swimming compared to vehicle-treated rats. This effect was acute and also detected 24 h after antagonist administration. Taken together, these findings demonstrate a significant activation of the septal vasopressinergic system in response to swim stress. Furthermore, our data support the view that AVP released within this brain area is involved in the generation of active behavioural strategies aimed at coping with new and challenging situations.