Effects of enhanced cerebrospinal fluid levels of vasopressin, vasopressin antagonist or vasoactive intestinal polypeptide on circadian sleep-wake rhythm in the rat

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Roles of Neuropeptides in Sleep-Wake Regulation

Sleep and wakefulness are basic behavioral states that require coordination between several brain regions, and they involve multiple neurochemical systems, including neuropeptides. Neuropeptides are a group of peptides produced by neurons and neuroendocrine cells of the central nervous system. Like traditional neurotransmitters, neuropeptides can bind to specific surface receptors and subsequently regulate neuronal activities. For example, orexin is a crucial component for the maintenance of wakefulness and the suppression of rapid eye movement (REM) sleep. In addition to orexin, melanin-concentrating hormone, and galanin may promote REM sleep. These results suggest that neuropeptides play an important role in sleep–wake regulation. These neuropeptides can be divided into three categories according to their effects on sleep–wake behaviors in rodents and humans. (i) Galanin, melanin-concentrating hormone, and vasoactive intestinal polypeptide are sleep-promoting peptides. It is also noticeable that vasoactive intestinal polypeptide particularly increases REM sleep. (ii) Orexin and neuropeptide S have been shown to induce wakefulness. (iii) Neuropeptide Y and substance P may have a bidirectional function as they can produce both arousal and sleep-inducing effects. This review will introduce the distribution of various neuropeptides in the brain and summarize the roles of different neuropeptides in sleep–wake regulation. We aim to lay the foundation for future studies to uncover the mechanisms that underlie the initiation, maintenance, and end of sleep–wake states.

Sleep Disturbance and Alzheimer's Disease: The Glial Connection

Poor quality and quantity of sleep are very common in elderly people throughout the world. Growing evidence has suggested that sleep disturbances could accelerate the process of neurodegeneration. Recent reports have shown a positive correlation between sleep deprivation and amyloid-β (Aβ)/tau aggregation in the brain of Alzheimer's patients. Glial cells have long been implicated in the progression of Alzheimer's disease (AD) and recent findings have also suggested their role in regulating sleep homeostasis. However, how glial cells control the sleep-wake balance and exactly how disturbed sleep may act as a trigger for Alzheimer's or other neurological disorders have recently gotten attention. In an attempt to connect the dots, the present review has highlighted the role of glia-derived sleep regulatory molecules in AD pathogenesis. Role of glia in sleep disturbance and Alzheimer's progression.

Decreased REM sleep and altered circadian sleep regulation in mice lacking vasoactive intestinal polypeptide

OBJECTIVES

Vasoactive intestinal polypeptide (VIP) has been implicated in sleep regulation as a promoter of rapid eye movement (REM) sleep. Previous work has shown that the amount of time spent in REM sleep is increased by intracerebroventricular administration of VIP, and reduced by treatment with VIP antagonists or antibodies against VIP. A variety of evidence suggests that VIP is critical for normal expression of circadian rhythmicity of diverse physiological and behavioral parameters. In the present study, we investigated the role of this peptide in sleep regulation using VIP-deficient (VIP-/-) mice.

METHODS

EEG/EMG sleep-wake patterns were recorded in VIP-/- mice and their wild-type littermate controls under normal light-dark (LD), constant darkness (DD) and sleep deprivation conditions.

RESULTS

VIP-/- mice exhibited reduced REM sleep time over the 24-h cycle while total daily amounts of NREM sleep and wakefulness were not altered significantly. The reduced REM sleep time in VIP-/- mice occurred entirely during the day due to a reduction in the duration, but not the frequency, of REM sleep bouts. In response to sleep deprivation, compensatory rebounds in NREM sleep and REM sleep were also attenuated in VIP-/- mice. Finally, the loss of VIP altered the temporal distribution of sleep in that the VIP -/- mice exhibited smaller amplitude rhythms in total sleep, NREM sleep, and REM sleep under both LD and DD.

CONCLUSIONS

These results indicate that VIP regulates the duration of REM sleep, sleep homeostatic mechanisms as well as the temporal patterning of sleep.

Vasopressin and the output of the hypothalamic biological clock

The physiological effects of vasopressin as a peripheral hormone were first reported more than 100 years ago. However, it was not until the first immunocytochemical studies were carried out in the early 1970s, using vasopressin antibodies, and the discovery of an extensive distribution of vasopressin-containing fibres outside the hypothalamus, that a neurotransmitter role for vasopressin could be hypothesised. These studies revealed four additional vasopressin systems next to the classical magnocellular vasopressin system in the paraventricular and supraoptic nuclei: a sexually dimorphic system originating from the bed nucleus of the stria terminalis and the medial amygdala, an autonomic and endocrine system originating from the medial part of the paraventricular nucleus, and the circadian system originating from the hypothalamic suprachiasmatic nuclei (SCN). At about the same time as the discovery of the neurotransmitter function of vasopressin, it also became clear that the SCN contain the main component of the mammalian biological clock system (i.e. the endogenous pacemaker). This review will concentrate on the significance of the vasopressin neurones in the SCN for the functional output of the biological clock that is contained within it. The vasopressin-containing subpopulation is a characteristic feature of the SCN in many species, including humans. The activity of the vasopressin neurones in the SCN shows a pronounced daily variation in its activity that has also been demonstrated in human post-mortem brains. Animal experiments show an important role for SCN-derived vasopressin in the control of neuroendocrine day/night rhythms such as that of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes. The remarkable correlation between a diminished presence of vasopressin in the SCN and a deterioration of sleep-wake rhythms during ageing and depression make it likely that, also in humans, the vasopressin neurones contribute considerably to the rhythmic output of the SCN.

SCN outputs and the hypothalamic balance of life

The circadian clock in the suprachiasmatic nucleus (SCN) is composed of thousands of oscillator neurons, each dependent on the cell-autonomous action of a defined set of circadian clock genes. Still, the major question remains how these individual oscillators are organized into a biological clock producing a coherent output able to time all the different daily changes in behavior and physiology. In the present review, the authors discuss the anatomical connections and neurotransmitters used by the SCN to control the daily rhythms in hormone release. The efferent SCN projections mainly target neurons in the medial hypothalamus surrounding the SCN. The activity of these preautonomic and neuroendocrine target neurons is controlled by differentially timed waves of, among others, vasopressin, GABA, and glutamate release from SCN terminals. Together, the data on the SCN control of neuroendocrine rhythms provide clear evidence not only that the SCN consists of phenotypically (i.e., according to neurotransmitter content) different subpopulations of neurons but also that subpopulations should be distinguished (within phenotypically similar groups of neurons) based on the acrophase of their (electrical) activity. Moreover, the specialization of the SCN may go as far as a single body structure, that is, the SCN seems to contain neurons that specifically target the liver, pineal, and adrenal.

It's all in the timing: many clocks, many outputs

It is thought that circadian regulation of physiology and behavior imparts survival advantages to organisms that use clocks. In mammals, a master clock resident in the SCN synchronizes other central and peripheral oscillators to evoke this regulation. This master oscillator consists of interlocking transcriptional-translational feedback loops, and it regulates both core clock genes necessary for oscillator maintenance as well as specific output genes that directly or indirectly mediate physiology under circadian control. It is now clear that both neuroanatomic and molecular outputs of the clock are necessary for proper circadian clock function. Recent technology has improved our understanding of these processes, elucidating the anatomic outputs of the SCN, as well as the molecular outputs of both central and peripheral oscillators that mediate observed physiological changes.

Suprachiasmatic nuclei grafts restore the circadian rhythm in the paraventricular nucleus of the hypothalamus

The mammalian suprachiasmatic nucleus (SCN) controls the circadian rhythm of many physiological and behavioral events by an orchestrated output of the electrical activity of SCN neurons. We examined the propagation of output signals from the SCN into the hypothalamus, especially into the region of the paraventricular nucleus, through multimicroelectrode recordings using acute and organotypic brain slices. Circadian rhythms in spontaneous firing rate with a period close to 24 hr were demonstrated in the SCN, in directly adjacent hypothalamic regions, and in the region of the paraventricular nucleus of the hypothalamus, an important center for the integration of neuroendocrine, homeostatic, and autonomic functions. The activity rhythms recorded from structures outside of the SCN were in phase with the rhythms in the SCN. Cyclic information in the hypothalamus was lost after ablation of the SCN but could be restored by SCN grafts, indicating that a humoral factor is responsible for the restoration of circadian rhythmicity in the absence of neural connections. Periodic application of arginine-vasopressin (AVP) provided evidence that AVP can induce rhythmicity in the hypothalamus. These data indicate that the SCN uses a dual (neuronal and humoral) mechanism for communication with its targets in the brain.

Increases in amino-cupric-silver staining of the supraoptic nucleus after sleep deprivation

Sleep deprived rats undergo a predictable sequence of physiological changes, including changes in skin condition, increased energy expenditure, and altered thermoregulation. Amino-cupric-silver staining was used to identify sleep deprivation related changes in the brain. A significant increase in staining was observed in the supraoptic nucleus (SON) of the hypothalamus of rats with high sleep loss (>45 h) vs. their yoked controls. Follow-up experiments showed that staining was not significantly different in rats sleep deprived for less than 45 h, suggesting that injurious sleep deprivation-related processes occur above a threshold quantity of sleep loss. These anatomical changes suggest that the effects of sleep deprivation may be related to protein metabolism in certain brain regions.

Vasopressin into the preoptic area increases grooming behavior in mice

In mice, the neuropeptide arginine-8-vasopressin (AVP) induces excessive grooming, scratching, and hyperactivity when administered intracerebroventricularly. In hamsters, AVP infusion into the medial preoptic area/anterior hypothalamus (MPOA/AH) increases flank marking and flank mark grooming. We measured the behavioral effects of administration of AVP (0, 1, and 10 ng/250 nl) into the preoptic area (POA) of male C57BL/6 mice. Administration of AVP into the POA induced robust effects on grooming, including increased hindleg scratching and face washing. Rearing and olfactory investigation were inhibited by AVP into the POA. These findings indicate that the POA is one site in which AVP induces grooming behavior in mice.

Manipulating neuropeptidergic pathways in humans: a novel approach to neuropharmacology?

Given the tremendous number of neuropeptides, which are synthesized in the central nervous system, the brain can be viewed as one of the most prominent endocrine organs. Elucidation of the functions of these peptides is hampered by the facts that after intravenous administration access to brain receptors is prevented or impaired by the blood-brain barrier. Here, we provide evidence that intranasal administration can be a way to circumvent the blood-brain barrier. Selected experiments will be reported indicating that peptides after intranasal administration in humans can specifically alter a great variety of brain functions. For vasopressin, we demonstrated improving effects of long-term intranasal treatment on sleep in elderly people. Insulin showed improving effects of short-term memory functions. For adrenocorticotropin/melanocyte stimulating hormone, ACTH/MSH-(4-10), a twofold action was isolated: The melanocortin fragment diminished selective attention and, with subchronic administration, reduced body fat. These results could provide the basis for developing a new, specific, and "soft" neuropharmacology.

The suprachiasmatic nucleus and the circadian time-keeping system revisited

Many physiological and behavioral processes show circadian rhythms which are generated by an internal time-keeping system, the biological clock. In rodents, evidence from a variety of studies has shown the suprachiasmatic nucleus (SCN) to be the site of the master pacemaker controlling circadian rhythms. The clock of the SCN oscillates with a near 24-h period but is entrained to solar day/night rhythm by light. Much progress has been made recently in understanding the mechanisms of the circadian system of the SCN, its inputs for entrainment and its outputs for transfer of the rhythm to the rest of the brain. The present review summarizes these new developments concerning the properties of the SCN and the mechanisms of circadian time-keeping. First, we will summarize data concerning the anatomical and physiological organization of the SCN, including the roles of SCN neuropeptide/neurotransmitter systems, and our current knowledge of SCN input and output pathways. Second, we will discuss SCN transplantation studies and how they have contributed to knowledge of the intrinsic properties of the SCN, communication between the SCN and its targets, and age-related changes in the circadian system. Third, recent findings concerning the genes and molecules involved in the intrinsic pacemaker mechanisms of insect and mammalian clocks will be reviewed. Finally, we will discuss exciting new possibilities concerning the use of viral vector-mediated gene transfer as an approach to investigate mechanisms of circadian time-keeping.

Neuropsychological effects of vasopressin in healthy humans

Animal research indicated that vasopressin (VP) exerts its principle behavioral influence, the improvement of memory formation, through an action on septo-hippocampal and connected limbic structures. Here human research is reviewed with the notion of a comparable effect of VP in healthy humans. Although the human studies yielded less consistent results than those in rats, they indicate that VP is able to improve declarative memory formation which is the type of memory essentially relying on hippocampal function. The effect appears to center on the encoding process for memory. In examinations of event-related brain potentials (ERPs) VP was consistently found to increase the 'mismatch negativity' (MMN) and the P3 components which are ERP potentials closely linked to the hippocampal processing of novel, unexpected and salient events. Enhanced processing of these stimulus aspects is considered to precipitate memory encoding. The regulation of voluntary selective attention and arousal do not appear to be primary targets of VP effects in humans. A mediation of effects by peripheral changes can be excluded since the central nervous effects were observed in studies using intranasal VP administration providing a direct access to brain functions.

The human hypothalamo-neurohypophysial system in health and disease

The present paper reviews the changes observed in the human supraoptic (SON) and paraventricular (PVN) nuclei, and their projections to the neurohypophysis, median eminence and to other brain areas in health and disease.

Vasopressin neurotransmission and the control of circadian rhythms in the suprachiasmatic nucleus

Vasopressin (VP) is one of the principal transmitters in the suprachiasmatic nucleus (SCN). Approximately 20% of neurones in the dorsomedial division of the SCN synthesize the peptide and a high proportion of SCN neurones (> 40%) are excited by VP acting through the V1 receptor. This suggests that VP may act as a feedback regulator of electrical activity within the nucleus. Such an intrinsic excitatory signal can be demonstrated by perifusion with a V1 antagonist which reduces spontaneous neural activity. As the synthesis and release of VP occurs in a circadian manner, this leads to a variable feedback excitation which may contribute to the circadian pattern of activity of the neural clock. This role in amplifying rhythmicity is supported by observations that animals deficient in VP show a reduced circadian amplitude of behavioural rhythms (e.g. locomotor and cortical electroencephalographic rhythms). VP expression declines during ageing and although aged animals show no change in the proportion of SCN neurones excited by VP, the rhythm of spontaneous electrical activity shows a progressive decline, consistent with the reduced endogenous excitatory feedback. However, the homozygous Brattleboro rat which lacks any VP expression still maintains rhythms of electrical activity, indicating that VP is not the sole factor generating circadian activity. The generation of this rhythmicity may depend upon the interaction of VP with other transmitter systems, such as the inhibitory transmitters somatostatin and GABA which show a circadian variation in efficacy. In addition to its role in feedback amplification of the endogenous rhythm of electrical activity, VP also functions as part of the efferent signal to the rest of the CNS where it potentially regulates a number of behavioural and physiological rhythms, including the circadian activity of the hypothalamo-pituitary-adrenal axis. Thus, the combined amplification and signalling functions makes VP an important component of the neuronal clock function in mammals.

Vasopressin-deficient suprachiasmatic nucleus grafts re-instate circadian rhythmicity in suprachiasmatic nucleus-lesioned arrhythmic rats

It was investigated whether grafts of the suprachiasmatic nucleus could re-instate circadian rhythmicity in the absence of its endogenous vasopressin production and whether the restored rhythm would have the long period length of the donor. Grafts of 17-days-old vasopressin-deficient homozygous Brattleboro rat fetuses, homotopically placed in arrhythmic suprachiasmatic nucleus-lesioned Wistar rats, re-instated circadian drinking rhythm within 20-50 days similar as seen for grafts of heterozygous control fetuses. Period length of the recovered rhythm revealed a similar difference (average 24.3 vs. 23.8 h) as reported for the rhythm between the adult Brattleboro genotypes. In all transplants, also those of the two-third non-recovery rats, a surviving suprachiasmatic nucleus was visible as a vasoactive intestinal polypeptide-positive neuronal cell cluster, whereas heterozygous transplants also revealed the complementary vasopressinergic cell part. Explanation of the absence of recovery failed since no undisputable correlation emerged between recovery of rhythm and vasoactive intestinal polypeptide, vasopressin and/or somatostatin immunocytochemical characteristics of the suprachiasmatic nucleus of the transplant. Special focus on the somatostatinergic neurons revealed their presence only occasionally near or in between the vasoactive intestinal polypeptidergic and (in the case of heterozygous grafts) vasopressinergic cell cluster. However their aberrant cytoarchitectural position appeared not to have affected the possibility to restore drinking rhythm of the suprachiasmatic nucleus-lesioned arrhythmic rat. It was concluded that grafted Brattleboro fetal suprachiasmatic nucleus develop their intrinsic rhythm conform their genotype and that vasopressin is not a crucial component in the maintenance nor in the transfer of circadian activity of the biological clock for drinking activity. Vasopressin of the suprachiasmatic nucleus may instead serve modulation within the circadian system.

Circadian rhythmicity of vasopressin levels in the cerebrospinal fluid of suprachiasmatic nucleus-lesioned and -grafted rats

Transplantation of the fetal suprachiasmatic nucleus (SCN) in arrhythmic SCN-lesioned rats can reinstate circadian drinking rhythms in 40% to 50% of the cases. In the current article, it was investigated whether the failure in the other rats could be due to the absence of a circadian rhythm in the grafted SCN, using a circadian vasopressin (VP) rhythm in the cerebrospinal fluid (CSF) as the indicator for a rhythmic SCN. CSF was sampled in continuous darkness from-intact control rats and SCN-lesioned and -grafted rats. VP could be detected in all samples, with concentrations of 15 to 30 pg/ml in the control rats and 5 to 15 pg/ml in the grafted rats. A circadian VP rhythm with a two- to threefold difference between peak and nadir values was found in all 7 control rats but in only 4 of 13 experimental rats, despite the presence of a VP-positive SCN in all grafts. A circadian VP rhythm was present in 2 drinking rhythm-recovered rats (6 of 13) and in 2 nonrecovery rats. Apparently, in these latter rats, the failure of the grafted SCN to restore a circadian drinking rhythm cannot be attributed to a lack of rhythmicity in the SCN itself. Thus, the presence of a rhythmic grafted SCN, as is deduced from a circadian CSF VP rhythm, appears not to be sufficient for restoration of a circadian drinking rhythm in SCN-lesioned arrhythmic rats.

Severe loss of vasopressin-immunoreactive cells in the suprachiasmatic nucleus of aging voles coincides with reduced circadian organization of running wheel activity

Aging leads to a decrease in circadian organization of behavior. Whether this general observation is related to the finding that in older subjects the arginine-vasopressin (AVP) system in the suprachiasmatic nucleus (SCN) has deteriorated is an unsolved question. Here we assessed circadian organization of running wheel behavior and numbers of AVP cells in the SCN of old voles (n=12, 11. 5 months of age) and compared the results with data from young voles (n=16, 4.5 months of age). A third of the young voles, but three-quarter of the old voles lost circadian rhythmicity. Analysis of daily onset to onset periodicity of running wheel activity at the age of 5 and 10 months in individual voles revealed a significant loss of precision of circadian rhythmicity at the higher age. The number of AVP cells in the SCN of old voles decreased substantially, over 78% compared to young voles in general. AVP cell numbers, however, cannot be directly correlated with the state of rhythmicity in old voles; in one of the three circadian rhythmic old voles the SCN contained the least AVP cells. This study does not support the idea of a causal relationship between aging induced reduction in AVP cells in the SCN and the presence of circadian rhythmicity in behavior.

Cellular requirements of suprachiasmatic nucleus transplants for restoration of circadian rhythm

Fetal neurografts containing the suprachiasmatic nucleus (SCN) can restore the circadian locomotor and drinking rhythm of SCN-lesioned (SCNX) rat and hamster. This functional outcome finally proves that the endogenous biological clock autonomously resides in the SCN. Observations on the cellular requirements of the "new" SCN for restoration of the arrhythmic SCNX animals have led to some new insights and confirmed findings from other studies. A critical mass of SCN neurons appeared necessary for functional effects, whereas the temporal profile of reinstatement of rhythm correlated with the delayed maturation of the grafted SCN. Cytoarchitectonically, the grafted SCN does not seem to develop normally for all anatomical aspects. Complementary clusters of vasoactive intestinal polypeptide(VIP)- and vasopressin(VP)ergic neurons are formed, but somatostatin(SOM)ergic neurons do not always "join" this group, as is normally seen in situ. Nevertheless, these new SCNs can restore the ablated functions. As the period length of restored rhythms tends to vary, it might be that the grafted SCN underwent an altered or impaired maturation that resulted in a different setting of its clock mechanism. A prominent role of VIPergic neurons seems indicated by their presence in all functional grafts, but, although they may be required, these cells do not appear to be a sufficient condition for restoration of rhythm. Many grafts exhibit the presence of VIPergic cells without counteracting the arrhythmia, whereas VP- and SOMergic SCN neurons are usually present as well. Findings with VP-deficient Brattleboro rat grafts indicated that VP is not the primary obligatory signal of circadian activity. It is argued that perhaps the role of SOMergic neurons in the clock function of the (grafted) SCN has been insufficiently considered. However, one should keep in mind that the peptides of the various types of SCN neurons may function only as cofactors, mutually modulating molecular or bioelectrical cellular activities within the nucleus or the message of the main transmitter gamma-aminobutyric acid.

Plasma arginine vasopressin and motor activity in major depression

BACKGROUND

Previously, we found that mean plasma concentrations of arginine vasopressin (AVP), but not of oxytocin (OT), were higher in depressed patients than in healthy controls. Plasma AVP concentrations were positively correlated to clinically rated psychomotor retardation. To further explore this previously reported relation we studied psychomotor retardation by means of an activity monitor, which is a more fine-focused and more objective instrument to analyze motor retardation than a clinical rating scale.

METHODS

Plasma AVP and OT concentrations, and day- and nighttime wrist activity were measured in 48 in- and outpatients with major depression and 30 healthy controls during a period of 5 consecutive days and nights.

RESULTS

Principal components analysis revealed three components of motor activity: motor activity during wakefulness, motor activity during sleep, and the awake/sleep time ratio. In patients and controls an inverse relationship between plasma AVP concentrations and motor activity during wakefulness was found. Patients with elevated AVP plasma levels showed increased motor activity during sleep.

CONCLUSIONS

These results suggest that high plasma AVP levels are related to the clinical picture of daytime psychomotor retardation and nighttime motor activity in major depression. Mean plasma OT concentrations were not related to measures of motor activity.

The effects of 'sleep promoting agents' on behavioural state in the ovine fetus

Fetal behavioural states, with similarities to adult sleep states, exist in both the human and ovine fetus near term. The purpose of the present study was to determine the effects of intracerebral administration of pharmacologic agents, known to affect sleep states in the adult, on fetal behavioural states and physiologic correlates using the chronically catheterized ovine fetus near term. Each drug was infused into either the cisterna magna or lateral ventricle for 90 min in one of two doses. Carbachol (1.35 x 10(-5) and 4.25 x 10(-6) M) led to an increase in low-voltage ECOG, eye movement and FBM activities, while scopolamine (4.68 x 10(-4) and 1.56 x 10(-4) M) led to a decrease in low-voltage ECOG and eye movement activity with an increase in high-voltage ECOG activity. L-5-Hydroxytryptophan (5-HTP) (2.04 x 10(-3) and 6.81 x 10(-4) M) infusion led to an increase in FBM, while VIP (3.00 x 10(-7) and 1.00 x 10(-7) M) infusion had no effect on fetal behavioural state parameters. Study results indicate that fetal behavioural states can be altered pharmacologically and in a manner similar to that seen in the adult but with notable differences that may relate to species, developmental or dose-response issues.

Vasoactive intestinal polypeptide microinjections into the oral pontine tegmentum enhance rapid eye movement sleep in the rat

Rapid eye movement sleep can be elicited in the rat by microinjection of the cholinergic agonist carbachol into the oral pontine reticular nucleus. Intracerebroventricular administration, during the light period, of vasoactive intestinal peptide enhances rapid eye movement sleep in several species. Since this peptide is co-localized with acetylcholine in many neurons in the central nervous system, it was assumed that the oral pontine tegmentum could also be one target for vasoactive intestinal peptide to induce rapid eye movement sleep. This hypothesis was tested by recording the sleep-wakefulness cycle in freely-moving rats injected with vasoactive intestinal peptide or its fragments (1-12 and 10-28) directly into the oral pontine reticular nucleus. when administered into the posterior part of this nucleus, vasoactive intestinal peptide at 1 and 10 ng (in 0.1 microliter of saline), but not its fragments, induced a 2-fold enhancement of rapid eye movement sleep during 4 h, at the expense of wakefulness. At the dose of 10 ng, a significant increase in rapid eye movement sleep persisted for up to 8 h. Moreover, when the peptide was injected into the centre of the positive zone, rapid eye movement sleep was enhanced during three to eight consecutive days. These data provide the first evidence that rapid eye movement sleep can be elicited at both short- and long-term by a single intracerebral microinjection of vasoactive intestinal peptide. Peptidergic mechanisms, possibly in association with cholinergic mechanisms, within the caudal part of the oral pontine reticular nucleus may play a critical role in the long-term regulation of rapid eye movement sleep in rats.

Effects of the CLIP fragment ACTH 20-24 on the duration of REM sleep episodes

Substances acting upon rapid eye movement (REM) sleep or paradoxical sleep (PS) can affect the number and/or the duration of PS episodes. In the present study, we investigated the effects of the proopiomelanocortin-derived peptide CLIP (corticotropin-like intermediate lobe peptide, ACTH 18-39) and its N-terminal fragments ACTH 18-24 and ACTH 20-24 on the duration of PS episodes in rats. Intracerebroventricular injection of ACTH 20-24 caused a pronounced prolongation of PS episodes (up to 7 min duration, never seen under baseline conditions), whereas ACTH 18-24 acted in a similar way but without reaching statistical significance. We suggest that short N-terminal CLIP fragment(s) may represent endogenous hypnogenic factor(s) involved in the regulation of paradoxical sleep.

Circadian rhythm of neuronal activity in suprachiasmatic nucleus slices from the vasopressin-deficient Brattleboro rat

In vitro extracellular recordings were made from tissue slices of suprachiasmatic nucleus from homozygous Brattleboro rats which are deficient in vasopressin. A high proportion (56%) of neurons were excited by application of exogenous vasopressin, indicating that the V1 receptors expressed by these neurons were functional. Basal activity of these vasopressin-sensitive neurons showed a marked circadian variation (higher during the subjective light phase) while vasopressin-insensitive neurons showed no significant variation, suggesting the presence of the V1 receptor identifies a population of highly circadian neurons. Suprachiasmatic neurons from both homozygous rats and their heterozygous (vasopressin-containing) litter mates displayed a circadian rhythm of spontaneous (basal) activity, with firing rates declining during the subjective dark phase, indicating that the endogenous pacemaker driving the circadian rhythm was not dependent upon the presence of vasopressin. However, the peak of spontaneous activity displayed during the subjective light phase was significantly lower in the vasopressin-deficient animals. These data show that the presence of endogenous vasopressin within the suprachiasmatic nucleus is not necessary for the generation of the circadian pattern of activity. However, vasopressin does function to amplify the rhythm by its excitatory effect during the light phase.

Quantitative differences in the circadian rhythm of locomotor activity and vasopressin and vasoactive intestinal peptide gene expression in the suprachiasmatic nucleus of tau mutant compared to wildtype hamsters

The activity profiles of homozygous tau mutant hamsters bred in our colony exhibit several differences when compared to wildtype golden hamsters. In addition, tau mutant hamsters respond to saturating white light pulses presented between circadian time (CT) 11 and CT 16 with extremely large phase shifts (type 0 resetting) after prolonged time in constant darkness. We measured five parameters of the activity rhythm early during exposure to constant darkness (DD) (cycles 5-9), and after 44-48 cycles in DD, and we confirmed the tau mutants' unusual phase shifting response to light. Next we determined whether neurotransmitter peptide mRNA levels in the SCN differed between wildtype and tau mutant hamsters exhibiting these divergent activity patterns and responses to light. After 49 circadian cycles in DD, tau mutant hamsters responded to a 1 h light pulse at CT 15 with phase shifts averaging 10.19 +/- 0.35 h. Among wildtype hamsters the mean phase shift was 1.22 +/- 0.34 h and the largest phase shift observed was 3.67 h. Total wheel revolutions/circadian cycle were significantly lower in tau mutants (4022 +/- 1103) vs. wildtypes (7528 +/- 458) and there was a significant decrease in wheel-running activity after prolonged exposure to DD, particularly among the wildtype hamsters (tau = 3045 +/- 972, wildtype = 4362 +/- 388 rev/circadian cycle). When analyzed by 5 min segments throughout the circadian cycle, the highest intensity wheel-running activity did not differ between groups and there was no significant effect of length of time in DD on this measure (tau = 38.5 +/- 6.3 and 38.4 +/- 4.7 rev/min, wildtype = 46.8 +/- 1.7 and 41.4 +/- 2.7 rev/min early or late in DD, respectively). The precision of activity onset differed greatly between groups with tau mutants exhibiting a much higher daily deviation from mean tau (1.00 +/- 0.24 h) than wildtypes (0.14 +/- .02 h). Activity onset became significantly less precise with increased time in DD: tau = 1.66 +/- 0.21 h, wildtype = 0.45 +/- 0.14 h after 44-48 circadian cycles. The length of the active period, alpha, was significantly shorter in tau mutants than in wildtypes (7.2 +/- 0.2 h vs. 8.0 +/- 0.2 h) but alpha was a similar percentage of tau in the two groups (tau mutant = 36%, wildtype = 33%). After 48 circadian cycles in DD, alpha measured 7.2 +/- 0.5 h in tau mutants and 8.9 +/- 0.6 h in wildtypes, thus there was no significant effect of time in DD on this parameter. Activity records of tau mutant animals appear more fragmented to the eye and we quantitated this with a computer-aided analysis of the number of bouts of wheel-running per active period. Wildtype hamsters exhibited 2.8 +/- 0.2 bouts of wheel-running activity early in DD and 3.1 +/- 0.2 bouts per circadian cycle later in DD. The activity records of tau mutant hamsters were significantly more fragmented but this group actually showed some consolidation of bouts per circadian cycle after prolonged time in DD (4.7 +/- 0.3 vs. 3.9 +/- 0.3 bouts per cycle). Wildtype and tau mutant hamsters were killed after 66-71 cycles in DD at either CT 4 or CT 16 and in situ hybridization was performed for vasopressin (AVP) and vasoactive intestinal peptide (VIP). Levels of AVP and VIP mRNA were significantly lower in tau mutant than wildtype hamsters at CT 16. We conclude that the tau mutation causes these differences in gene expression and we speculate that differences in the peptidergic output of the clock may have some relevance for the differences in the quantitative aspects of the activity rhythm and the response to light pulses exhibited by these animals.

Desmopressin and vasopressin increase locomotor activity in the rat via a central mechanism: implications for nocturnal enuresis

PURPOSE

Nocturnal enuresis is characterized by nocturnal urine volumes exceeding bladder capacity and by inability to wake up to the stimulus of a full bladder. Desmopressin (DDAVP) is believed to be efficient in treating nocturnal enuresis by reducing nocturnal urine production. However, clinical observations indicate an additional mode of action since the drug appears to modify sleep architecture, apparently improving the patient's ability to awaken to the stimulus of a full bladder. Because of this, a possible arousing effect of DDAVP was studied.

MATERIALS AND METHODS

The tentative ability of DDAVP and the endogenous hormone vasopressin (AVP) to produce locomotor stimulation in resting rats after both intracerebroventricular and subcutaneous administration was used as an animal model of arousal. In addition brain monoamine biochemistry was analyzed.

RESULTS

The intracerebroventricular injection of AVP (0.1 and 1 microgram.) and the intracerebroventricular (0.1, 1, 10 and 100 microgram.) and subcutaneous (90 and 180 microgram.) injections of DDAVP were both associated with a significant increase in the locomotor activity of the animals compared with controls. The biochemical analysis of cerebral monoamines indicated that DDAVP lowers brain dopamine levels after both types of administration.

CONCLUSIONS

These results suggest that DDAVP exerts a stimulatory effect in the CNS, which is also observed after peripheral administration. There are also indications for an increase in central dopamine turnover which could explain the registered increase in locomotor activity.

Light perception in the vertebrate brain: an ultrastructural analysis of opsin- and vasoactive intestinal polypeptide-immunoreactive neurons in iguanid lizards

Recent biochemical and immunocytochemical evidence indicates that a population of circadian and reproductive rhythm-entraining photoreceptors lies in the basal diencephalon of iguanid lizards. Here, we report the results of correlated light and electron microscopy of opsin-immunoreactive cells in the basal brain, and we discuss their ultrastructural relationship to known photoreceptors. Cerebrospinal fluid (CSF)-contacting bipolar neurons in the lizards Anolis carolinensis and Iguana iguana were immunolabeled with antisera generated against vertebrate retinal opsins and vasoactive intestinal polypeptide (VIP). Within the brain, opsin-immunoreactive cells were found exclusively in the ependyma of the basal region of the lateral ventricles (adjacent to nucleus paraolfactorius/nucleus ventromedialis and neostriatum/paleostriatum). Cells in the same anatomical location and with the same morphology were labeled with anti-VIP antisera. These cells possessed a dendritic process that extended toward the lateral ventricle, ending in a bulbous terminal that protruded into the ventricle. Axonal processes travelled ventrally and caudally. The entire cell, including the axonal process, exhibited opsin-like and VIP-like immunoreactivity. By light microscopy, opsin-like immunostaining appeared punctate, with immunoreactivity greatest in the bulbous terminal. Opsin- and VIP-immunostained thick sections were resectioned, and individual cells observed by light microscopy were then characterized using electron microscopy. We found that all immunostained cells were morphologically similar and that they were morphologically distinct from neighboring nonimmunoreactive cells. CSF-contacting opsin- and VIP-immunoreactive cells lacked the membranous stacks characteristic of retinal photoreceptors but were ciliated and contained numerous large electron-dense vesicles. Multiple synaptic contacts were made on the soma and putative dendritic processes of opsin- and VIP-immunoreactive CSF-contacting neurons. Our results provide the first ultrastructural characterization of opsin-immunostained encephalic CSF-contacting neurons in a vertebrate animal, and they indicate that these putative photoreceptors share structural features with pineal photoreceptors and with certain invertebrate extraretinal photoreceptors, but they are morphologically and biochemically distinct from visual photoreceptors of the retina.

Towards a molecular biology of the circadian clock and sleep of mammals

Behavioral states of rest and activity are temporally organized. Since the beginning of life on Earth, plants and animals have been forced to adapt to the daily rhythm of the planet's rotation about its axis. In complex vertebrates (birds and mammals), rest and activity have evolved into the electrophysiologically and behaviorally distinct states of sleep and wakefulness. The evolutionary emergence of bouts of rapid eye movement (REM) sleep may be even more recent; the echidna, one of the earliest mammals, lacks this sleep stage (Siegel et al., 1994), The cycling of these behavioral states is under neural control, and much is known about their cellular basis, but the underlying events at the molecular level are virtually unknown. Here each of us highlights some of the new approaches for investigating the molecular substrate for behavioral state control of circadian rhythmicity (WJS) and sleep (PJS) in mammals.

Increase of prolactin mRNA in the rat hypothalamus after intracerebroventricular injection of VIP or PACAP

Vasoactive intestinal peptide (VIP), the structurally homologous pituitary adenylate cyclase-activating peptide (PACAP) and the pituitary hormone, prolactin (PRL) enhance rapid eye movement sleep (REMS). VIP and PACAP are both inducers of PRL gene expression and release in the pituitary gland. Little is known about PRL regulation in the brain although it is hypothesized that the REMS-promoting activity of i.c.v. administered VIP may be mediated via the activation of cerebral PRL. To test whether VIP or PACAP in fact increase intracerebral mRNA, the peptides (VIP: 30 or 300 pmol; PACAP: 220 pmol) were injected i.c.v. into rats at dark onset. 1 h later, cDNA was synthesized from purified hypothalamic mRNA. Standardized amounts were analysed for PRL using the polymerase chain reaction followed by Southern blotting and hybridization. Compared with beta-actin mRNA levels, both VIP and PACAP increased PRL mRNA levels in a dose-dependent fashion though VIP was more effective on a molar basis. The previously reported alternatively spliced PRL mRNA (lacking exon 4) was not detected. The data support the hypothesis that the REMS-promoting activity of central VIP and PACAP might be mediated by cerebral PRL.

The effects of [Arg8]vasopressin and [Arg8]vasotocin on the firing rate of suprachiasmatic neurons in vitro

The excitatory effect of [Arg8]-vasopressin and its potential contribution to the circadian cycle of electrical activity in the suprachiasmatic nucleus of the rat was investigated using extracellular recordings from hypothalamic slices from virgin female rats. The majority of neurons tested for their responses to vasopressin and [Arg8]-vasotocin displayed coincident, dose-dependent excitation by both peptides, although the relative efficacy varied between neurons, with some showing a highly preferential excitation by vasotocin. Perifusion with the vasopressin receptor antagonist d(CH2)5[Tyr(OEt)2,Val4,Cit8]-vasopressin was able to block the majority of responses to vasopressin or vasotocin (20/25), and similar excitation could be induced by the selective agonist [Phe2,Orn8]-vasotocin, indicating a mainly V1 receptor-mediated effect. Few neurons (3/27; 11%) responded to the oxytocin-specific agonist, [Thr4,Gly7]-oxytocin, suggesting a low occurrence of oxytocin receptors. In addition to blocking the action of exogenous vasopressin, the V1 antagonist caused a reversible suppression of spontaneous basal activity in 7/25 cases, consistent with the presence of an endogenous excitatory vasopressin tone. In agreement with previous reports, the activity of suprachiasmatic nucleus neurons showed a significant correlation between spontaneous activity and the light-dark cycle, with activity decreasing during the subjective dark phase. When neurons were divided on the basis of their response to vasopressin and/or vasotocin, the peptide-sensitive neurons continued to show a strong correlation (r = 0.513, P < 0.01) while the insensitive neurons showed no correlation (r = 0.136, P > 0.05). These data confirm the presence of V1 type receptors in the suprachiasmatic nucleus and also indicate a small number of neurons possessing additional classes of receptor selective for either oxytocin or vasotocin. Contrary to previous reports, they also demonstrate that endogenous vasopressin tonically excites suprachiasmatic nucleus neurons. The fact that vasopressin-sensitive (but not vasopressin-insensitive) neurons show a level of basal activity correlated with time, suggests that this tone may contribute to the circadian cycle of electrical activity in the suprachiasmatic nucleus.

Suppression of suprachiasmatic nucleus neurone activity with a vasopressin receptor antagonist: possible role for endogenous vasopressin in circadian activity cycles in vitro

Neurones of the rat suprachiasmatic nucleus (SCN) were tested with [Arg8]vasopressin (AVP) and the AVP receptor antagonist, [d(CH2)5,d-Tyr(OEt)2,Val4,Cit8]-vasopressin in vitro. 52% of AVP-responsive neurones showed an antagonist-induced decrease in activity, indicative of the presence of an endogenous excitatory tone. The magnitude of this effect declined significantly between subjective light and dark phases, consistent with the possibility that circadian fluctuations in endogenous AVP excitation contribute to the cycle of electrical activity within the SCN. However, similar fluctuations in basal activity between the light and dark phases was observed for both antagonist-sensitive and -insensitive neurones, indicating that endogenous AVP was not the only factor determining the circadian cycle.

Neurochemical organization of circadian rhythm in the suprachiasmatic nucleus

The circadian rhythm in mammals is under control of the pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. This tiny nucleus contains a number of neurochemicals, including peptides, amines and amino acids. Heterogeneous distribution of these neurochemicals defines the substructures of the SCN. In the present review, functional significance of such neurochemical heterogeneity in the SCN is discussed in the light of circadian patterns of the concentrations of these neurochemicals in the SCN and their effects on SCN neurons in in vitro slice preparation. In particular, the hypothesis that the dorsomedial SCN is involved in maintaining the circadian rhythm, while the ventrolateral SCN is involved in adjusting the phase of the rhythm, is critically discussed. These considerations suggest that distinct sub-components of the SCN as marked by neurochemicals, interact with each other and this organizational architecture could be the basis of the proper operation of the circadian time keeping system in this nucleus.

Involvement of prolactin in the REM sleep-promoting activity of systemic vasoactive intestinal peptide (VIP)

The involvement of pituitary prolactin (PRL) in systemic vasoactive intestinal peptide (VIP)-induced sleep was studied. Male rats were implanted with electrodes for EEG-recording, with brain thermistors to record cortical temperature (Tcrt) and with chronic intracardial catheters to obtain blood samples and to deliver substances. One group of rats (n = 8) received normal rabbit serum (NS)+physiological saline (SAL) on the baseline day and was injected with NS+VIP on the experimental day. In the other group of rats (n = 6), the baseline day was followed by administration of PRL-antiserum (PRL-AS) + VIP on the experimental day. The sera and VIP or SAL were injected 30 min before and at light onset, respectively. Sleep-wake activity was then recorded for the next 12-h light period. Systemic VIP-stimulated PRL secretion as measured by RIA in serial samples obtained hour 1 postinjection. VIP also elicited selective increases in REM sleep (REMS) in the rats pretreated with NS. Tcrt was not affected by VIP. Administration of PRL-AS blocked the increase in circulating levels of free (non-IgG-bound) PRL and prevented VIP-enhanced REMS. Comparisons of the sleep effects of PRL-AS+VIP with the previously reported changes in sleep after PRL-AS alone indicate that PRL has a major role in the mediation of the REMS-promoting activity of systemic VIP. The results suggest that an increased release of endogenous pituitary PRL modulates REMS.

Effects of CLIP (corticotropin-like intermediate lobe peptide) and CLIP fragments on paradoxical sleep in rats

The effects of the POMC-derived peptide CLIP [corticotropin-like intermediate lobe peptide; ACTH(18-39)] and its shorter fragments ACTH(25-39), ACTH(18-24), and ACTH(20-24) on sleep were investigated in rats housed under normal 12-h light/12-h dark conditions (0600 light on). CLIP (10 ng) or equimolar doses of CLIP fragments, respectively, were injected intracerebroventricularly immediately before the 8-h recording period (0800-1600). It was found that paradoxical sleep (PS) was increased by CLIP (+20%) as well as by the N-terminal CLIP fragment ACTH(18-24) (+18%) and by the pentapeptide ACTH(20-24) (+25%), whereas the C-terminal fragment ACTH(25-39) was ineffective. Slow-wave sleep (SWS) was not influenced. These results clearly demonstrate that CLIP and its N-terminal fragments have selective PS-enhancing effects. CLIP and/or CLIP partial sequences are possible candidates for endogenous PS-inducing peptides involved in the physiological regulation of paradoxical sleep.

Mild sustained effects of neonatal vasopressin and oxytocin treatment on brain growth and behavior of the rat

The lasting effects of a 9-day neonatal exposure to vasopressin and oxytocin were examined in the rat to discover if peptide administration results in organizational effects. When tested in young adulthood, brain growth, not body growth, appeared to be impaired. Basal and challenge tests of urine production, carried out to see the development of the hormonal antidiuretic function of vasopressin, revealed no lasting changes, and therefore did not confirm earlier findings of an induced mild polyurea. Behavioral testing of learning by making use of a one-trail step-through paradigm with a 24-h retention trial--a test that is sensitive to vasopressin--did not show impairments. Open field tests, however, showed enhanced emotionality in the vasopressin-treated females, as well as an initially increased ambulation in the males, and increased grooming in both sexes, the latter also having been reported to be induced by vasopressin administration in the septal areas. Oxytocin treatment did not produce lasting changes. Our conclusion, therefore, is that peripherally circulating vasopressin can affect the organizational development of the rat brain. It remains to be established whether this is an effect obtained through changes in the general peripheral physiology or a reflection of plasticity phenomena at the level of central vasopressin neurotransmission.

Antiserum to prolactin decreases rapid eye movement sleep (REM sleep) in the male rat

Previous reports suggest that blood-born prolactin (PRL) may selectively promote rapid eye movement sleep (REMS). To study the possible involvement of endogenous PRL in sleep regulation, rats were systemically injected with either antiserum to PRL or normal rabbit serum, and the sleep-wake activity was determined during the subsequent 12-h light cycle. The administration of normal rabbit serum in physiological saline did not alter sleep-wake activity compared to control recordings, whereas the PRL antiserum caused a modest and selective suppression in REMS. Immunoreactive PRL was eliminated from the serial plasma samples obtained between 6 to 11 h after the injection of the antiserum. Brain temperature was not affected by the antiserum. The results indicate that physiological pituitary PRL secretion has a slight REMS-promoting activity in the male rat. It is speculated that an increased release of pituitary PRL or the PRL-like substance previously demonstrated in the brain may significantly stimulate REMS.

Chronic intracerebral infusions of vasopressin and vasopressin antagonist modulate behavioral effects of interleukin-1 in rat

To assess the role of sex dependent brain vasopressinergic transmission in the modulation of the neural effects of interleukin-1, castrated male rats that are deficient in vasopressin were implanted intracerebroventricularly with an Accurel collodion mini device containing 10 micrograms AVP whereas intact male rats were implanted with a similar device containing 50 micrograms of dPTyr(Me)AVP, a specific antagonist of the vasopressor-like receptors of vasopressin. Control rats in each sex group were implanted with an Accurel device containing distilled water. Acute intracerebroventricular injection of 1.25-2.50 ng recombinant human interleukin-1 beta decreased in a dose and time-dependent manner social investigation of a juvenile conspecific. This effect was more intense in intact rats chronically infused with dPTyr(Me)AVP and less intense in castrates infused with AVP. These results confirm the modulatory role of sex-dependent vasopressinergic neurotransmission on the neural effects of interleukin-1.

Effect of paradoxical sleep deprivation on vasoactive intestinal peptide-like immunoreactivity in discrete brain areas and anterior pituitary of the rat

To determine whether vasoactive intestinal peptide (VIP) is involved in paradoxical sleep (PS) homeostasis, VIP-like immunoreactivity (VIP-LI) of discrete brain areas was determined by radioimmunoassay after 24 and 48 h of PS deprivation by the watertank technique followed or not by 5 h of sleep rebound. This study was carried out with an environmental control (placed in dry watertank: DWC) and a nonstressed control. Such PS deprivation induced a decrease of VIP content in PS-deprived rats restricted to cortex and anterior pituitary. In the cortex, the decrease in VIP-LI was of the same magnitude after 24 and 48 h of PS deprivation and VIP-LI was normal by 5 h of sleep rebound; as such a decrease was also observed after 48 h in DWC, it could be due to the stress related to the experiment rather than lack of sleep. In the anterior pituitary, the decrease was related to the duration of deprivation with a greater decrease in VIP-LI after 48 than after 24 h of PS deprivation and specifically related to PS deprivation since it was not observed in DWC rats. After 5 h of sleep rebound, recovery of VIP-LI was total in the 24-h experiment and partial in the 48-h one. In all eight other structures studied, VIP was unchanged after experimentation. These results strongly suggest that VIP is not involved in PS homeostasis but as indicated by other experiments more probably in circadian organization of sleep.

Vasopressin regulates human sleep by reducing rapid-eye-movement sleep

In two double-blind experiments, effects of intravenous infusion of arginine vasopressin (AVP) on sleep were evaluated in 2 groups of 10 men (20-35 yr). In experiment I, subjects were tested on two occasions, during which they received either placebo or 0.33 IU/h AVP. In experiment II, on three different occasions, subjects received either placebo or 0.66 or 0.99 IU/h AVP. Infusions were administered between 2200 and 0700 h. Nocturnal plasma AVP concentrations were close to the upper limit of the normal physiological range during 0.66 IU/h AVP (16.6 +/- 2.2 pg/ml) but markedly exceeded this range during 0.99 IU/h AVP (25.0 +/- 1.6 pg/ml). Results indicate primary effects of AVP on rapid-eye-movement (REM) sleep, with moderate reductions in REM sleep during 0.33 IU/h AVP (averaging -10.5%) and with substantial reductions in REM sleep (-24.0%) during 0.66 IU/h AVP. During 0.99 IU/h AVP the effect did not further increase (-24.4%). Less consistent effects of AVP were an increase in stage 2 sleep and in time awake. Effects of AVP were not mediated by changes in cortisol or blood pressure. Results suggest AVP to participate in REM sleep regulation under normal physiological conditions.

Chronic intracerebral infusions of vasopressin and vasopressin antagonist modulate social recognition in rat

To assess the role of androgen-dependent brain vasopressinergic transmission in the modulation of social recognition, castrated male rats which are deficient in vasopressin were implanted intracerebroventricularly with an Accurel collodion mini-device containing 10 micrograms vasopressin (AVP) whereas intact male rats were implanted with a similar device containing 50 micrograms of 1-deaminopenicillamine 2-O-methyltyrosine arginine vasopressin (dPTyr(Me)AVP), a specific antagonist of the vasopressor like receptors of vasopressin. Control rats in each experimental group were implanted with an Accurel device containing water. Castrated rats treated with AVP explored familiar juvenile conspecifics in the same manner as intact male rats. Conversely, intact male rats treated with dPTyr(Me)AVP explored familiar juveniles in the same manner as castrated male rats. These results confirm the role of androgen-dependent vasopressinergic neurotransmission in social recognition.

Evidence for subdivisions in the human suprachiasmatic nucleus

The human suprachiasmatic nucleus was analysed by immunohistochemical demonstration of various substances in combination with 3-dimensional computerized reconstruction and video overlay facilities. In the human, the suprachiasmatic nucleus is not as compact as in the rodent. Its boundaries are not easily delineated using conventional stains, and it shows no obvious cytoarchitectonic structure. However, based on its chemoarchitecture, the human suprachiasmatic nucleus can be apportioned into five major subdivisions: Dorsal, comprising a crescent shaped mass of densely packed neurophysin/vasopressin-neurons as well as neurotensin-neurons, and also containing 3-fucosyl-N-acetyl-lactosamine (FAL)-positive neurons in its medial part. Central, occupying the core of the nucleus and consisting precisely of a region devoid of neurophysin/vasopressin neurons but demarcated by calbindin, synaptophysin, and a circumscribed cluster of vasoactive intestinal polypeptide-neurons and containing neurotensin neurons as well. Anteroventrally this division also contains some intermingled neurons positive for neurotensin, neuropeptide Y, somatostatin, and FAL. Ventral, extending from the anterior extreme of the preoptic recess caudolaterally to a field between the optic chiasm and the anteroventral margin of the supraoptic nucleus. This subdivision is specified by synaptophysin, calbindin, and substance P immunoreactivity and is almost free of glial fibrillary acidic protein. From its rostral portion, fibers immunoreactive for calbindin, vasoactive intestinal polypeptide, synaptophysin, and substance P protrude deeply into the optic chiasm. Medial, comprising a thin band between the subependymal zone and the dorsal subdivision, containing scattered somatostatin neurons. External, extending as a band around the dorsal and lateral borders of the nucleus, containing astrocytes expressing the FAL-epitope and scattered neurophysin/vasopressin and neurotensin neurons. These findings indicate that the human suprachiasmatic nucleus contains well-defined subdivisions with different, chemically specific, connections and provides a basis for comparing these subdivisions with the structure and function of subdivisions previously described for the suprachiasmatic nucleus in experimental animals. In addition, the findings strengthen the concept that the human suprachiasmatic nucleus generates and expresses circadian rhythms in a manner similar to that documented for the suprachiasmatic nucleus in experimental animals, and suggest that different subdivisions may subserve specific functional roles.

Daily variations in concentration of vasoactive intestinal polypeptide immunoreactivity in discrete brain areas of the rat

The concentration of VIP-like immunoreactivity (VIP-LI) was determined by radioimmunoassay at various times of the day in 11 discrete brain areas and in the antehypophysis of rats maintained on a regular 12 h/12 h light-dark cycle. In the suprachiasmatic and periventricular nuclei the VIP-LI increased during the dark period and decreased during the subsequent light period. In addition, the VIP-LI exhibited complex variations in the locus coeruleus, the periaqueductal gray matter and the paraventricular nucleus, but did not change in the other areas investigated.

Vasopressinergic innervation of the mouse suprachiasmatic nucleus: an immuno-electron microscopic analysis

Attempts are being made to unravel the local circuitry of the suprachiasmatic nucleus, with a view toward eventually correlating specific neuronal systems with circadian events. Hence, the vasopressinergic innervation of this nucleus in the laboratory mouse has been analyzed immunocytochemically at the light and electron microscopical levels. Monoclonal antineurophysin and polyclonal antivasopressin were used on aldehyde-fixed brains. Serial vibratome sections of the appropriate forebrain region were prepared for pre-embedding immunoperoxidase staining and/or postembedding immunogold labeling. Immunoreactive somata, processes, varicosities, and synaptic terminals were found throughout the suprachiasmatic nucleus, their ratio and density varying at different locations. The predominant type of vasopressinergic soma was ovoid to rounded (7-10 microns), containing secretory granules (85-120 nm), a large proportion of which were immunoreactive. Axon terminals, both nonimmunoreactive and immunoreactive, impinged upon vasopressinergic somata and processes, often displaying synaptic specializations. Vasopressinergic terminals, containing secretory granules and microvesicles, were found throughout the nucleus, particularly within the dorsomedial neuropil. These labeled terminals varied in size (0.4-3.4 microns 2) and shape, ranging from compact boutons to pleomorphic profiles, some deeply indented by postsynaptic spines, either dendritic or somatic. Approximately 65% of the vasopressin-containing terminals were axodendritic and 30% axosomatic; about 5% appeared to be axoaxonic. At least a quarter of all vasopressinergic synaptic terminals were axospinous. Other forms of interneuronal contact involving vasopressinergic elements (somata, dendrites) included extensive membrane to membrane appositional sites, and multiple puncta adhaerentia. The versatility of interconnections between vasopressin-containing neurons in the mouse suprachiasmatic nucleus suggests a highly active and coordinated network, which contributes substantially to local intranuclear circuitry. In addition, a dense efferent vasopressinergic output is directed dorsally towards the periventricular hypothalamus, where direct associations may be established with diverse hypothalamic neuroendocrine systems.

Vasopressin-deficient rats show a reduced amplitude of the circadian sleep rhythm

The hypothalamic suprachiasmatic nuclei are responsible for the generation of many circadian rhythms, including the rhythm of arginine vasopressin (AVP) in the cerebrospinal fluid (CSF). We used cortical EEG recordings taken from AVP-deficient (Brattleboro strain) rats to investigate the possible role of AVP in the generation of circadian sleep/arousal rhythms. When housed either in a light-dark cycle or in constant light, Brattleboro rats showed circadian rhythms of arousal, slow-wave sleep, and paradoxical sleep. However, the amplitudes of the slow-wave and paradoxical sleep (but not arousal) rhythms in these animals were significantly lower than in controls. The results indicate that hypothalamic synthesis of AVP is not necessary for the generation of circadian sleep rhythms, but the amplitude of the rhythms may be modulated by the circadian release of AVP into CSF.

Vasoactive intestinal peptide: behavioral effects in the rat and hamster

The behavioral effects of intracerebroventricular (ICV) injection of the brain-gut peptide vasoactive intestinal peptide (VIP) were quantified with a behavioral sampling technique in home-caged, nondeprived, male and female albino rats and golden hamsters. ICV VIP sex-dependently decreased observed resting behavior during 1 hr after injections in both rats and hamsters at 0.1-10.0 micrograms. Grooming behavior was increased in hamsters, and rearing and standing behaviors were increased in rats, sex-dependently at VIP doses that decreased resting. Drinking behavior was suppressed in rats by VIP at 10.0 micrograms. Intraperitoneal (IP) VIP (100.0 micrograms/kg) increased 5% ethanol intake and decreased eating behavior in fluid-deprived male rats. The increase in ethanol intake produced by IP VIP was prevented by IP cholecystokinin octapeptide (CCK, 4.0 micrograms/kg). VIP potently controls resting and ingestive behaviors, suggesting a role for this neuropeptide, along with CCK, in the feedback regulation of rodent behavior.