Calbindin and Fos within the suprachiasmatic nucleus and the adjacent hypothalamus of Arvicanthis niloticus and Rattus norvegicus

The suprachiasmatic nucleus is the site of the primary circadian pacemaker in mammals. The lower sub paraventricular zone that is dorsal to and receives input from the suprachiasmatic nucleus may also play a role in the regulation of circadian rhythms. Calbindin has been described in the suprachiasmatic nucleus of some mammals, and may be important in the control of endogenous rhythms. In the first study we characterized calbindin-expressing cells in the suprachiasmatic nucleus and lower sub-paraventricular zone of nocturnal and diurnal rodents. Specifically, Rattus norvegicus was compared to Arvicanthis niloticus, a primarily diurnal species within which some individuals exhibit nocturnal patterns of wheel running. Calbindin-immunoreactive cells were present in the suprachiasmatic nucleus of Arvicanthis and were most concentrated within its central region but were relatively sparse in the suprachiasmatic nucleus of Rattus. Calbindin-expressing cells were present in the lower sub-paraventricular zone of both species. In the second study we evaluated Fos expression within calbindin-immunoreactive cells in nocturnal Rattus and in Arvicanthis that were either diurnal or nocturnal with respect to wheel-running. All animals were kept on a 12:12 light/dark cycle and perfused at either 4h after lights-on or 4h after lights-off. In the suprachiasmatic nucleus in both species, Fos expression was elevated during the day relative to the night but less than 1% of calbindin cells contained Fos in Arvicanthis, compared with 13-17% in Rattus. In the lower sub-paraventricular zone of both species, 9-14% of calbindin cells expressed Fos, and this proportion did not change as a function of time. Among Arvicanthis, the number of calbindin expressing neurons in the lower sub-paraventricular zone was influenced by an interaction between the wheel running patterns (nocturnal vs diurnal) and time of day. Thus, the number of calbindin-positive cells within the suprachiasmatic nucleus differed in Arvicanthis and Rattus, whereas the number of calbindin-positive cells within the lower sub-paraventricular zone differed in nocturnal and diurnal Arvicanthis.Our examination of R. norvegicus and A. niloticus suggests potentially important relationships between calbindin-containing neurons and whether animals are nocturnal or diurnal. Specifically, rats had more Fos expression in calbindin containing cells in the suprachiasmatic nucleus than Arvicanthis. In contrast, Arvicanthis exhibiting diurnal and nocturnal patterns of wheel-running differed in the number of calbindin-containing cells in the lower sub-paraventricular zone, dorsal to the suprachiasmatic nucleus.     

Tyrosine hydroxylase positive neurons and their contacts with vasoactive intestinal polypeptide-containing fibers in the hypothalamus of the diurnal murid rodent, Arvicanthis niloticus

Diurnal and nocturnal animals differ with respect to the timing of a host of behavioral and physiological events including those associated with neuroendocrine functions, but the neural bases of these differences are poorly understood. In nocturnal species, rhythms in tyrosine hydroxylase-containing (TH+) neurons in the hypothalamus appear to be responsible for rhythms in prolactin secretion. Here we investigated TH+ cells in a diurnal rodent (Arvicanthis niloticus, the unstriped Nile grass rat), and comparing them with those of a nocturnal rodent (Rattus norvegicus, Sprague-Dawley rat). We also examined relationships between TH+ cells and fibers containing vasoactive intestinal polypeptide (VIP) that are thought to originate from cells in the suprachiasmatic nucleus (SCN), the site of the primary circadian clock in mammals. The distribution of TH+ neurons was very similar in the two species except for a population of cells in the basal forebrain that was only present in grass rats. Fibers containing VIP appeared to contact neuroendocrine TH+ cells in both species. These data suggest that, though there may be subtle species differences, temporal information is likely to be carried along the same direct pathways from the SCN to the TH+ neurons in day- and night-active species.     

Fos expression in arousal and reward areas of the brain in grass rats following induced wakefulness

In the diurnal grass rat nocturnal voluntary wakefulness induces Fos expression in specific cellular populations of arousal and reward areas of the brain. Here, we evaluated whether involuntary wakefulness would result in similar patterns of Fos expression. We assessed this question using male grass rats that were sleep deprived for 6h by gentle stimulation (SD group), starting 2h before lights off (12:12 LD cycle). Then, we examined expression of Fos in cholinergic cells of the basal forebrain (BF), as well as in dopaminergic cells of the reward system, and compared these results to those obtained from an undisturbed control group. Different from previous results with grass rats that were voluntary awake, the BF of SD animals only showed a significant increase in Fos expression in non-cholinergic neurons of the medial septum (MS). These observations differ from reports for nocturnal rodents that are sleep deprived. Thus, our results show that voluntary and induced wakefulness have different effects on neural systems involved in wakefulness and reward, and that the effects of sleep deprivation are different across species. We also investigated whether other arousal promoting regions and circadian and stress related areas responded to sleep deprivation by changing the level of Fos expression. Among these areas, only the lateral hypothalamus (LH) and the ventro lateral preoptic area showed significant effects of sleep deprivation that dissipated after a 2h period of sleep recovery, as it was also the case for the non-cholinergic MS. In addition, we found that Fos expression in the LH was robustly associated with Fos expression in other arousal and reward areas of the brain. This is consistent with the view that the arousal system of the LH modulates neural activity of other arousal regions of the brain, as described for nocturnal rodents.     

PER2 rhythms in the amygdala and bed nucleus of the stria terminalis of the diurnal grass rat (Arvicanthis niloticus)

The suprachiasmatic nucleus (SCN) of the hypothalamus is the central pacemaker that controls circadian rhythms in mammals. In diurnal grass rats (Arvicanthis niloticus), many functional aspects of the SCN are similar to those of nocturnal rodents, making it likely that the difference in the circadian system of diurnal and nocturnal animals lies downstream from the SCN. Rhythms in clock genes expression occur in several brain regions outside the SCN that may function as extra-SCN oscillators. In male grass rats PER1 is expressed in the oval nucleus of the bed nucleus of the stria terminalis (BNST-ov) and in the central and basolateral amygdala (CEA and BLA, respectively); several features of PER1 expression in these regions of the grass rat brain differ substantially from those of nocturnal species. Here we describe PER2 rhythms in the same three brain regions of the grass rat. In the BNST-ov and CEA PER2 expression peaked early in the light period Zeitgeber time (ZT) 2 and was low during the early night, which is the reverse of the pattern of nocturnal rodents. In the BLA, PER2 expression was relatively low for most of the 24-h cycle, but showed an acute elevation late in the light period (ZT10). This pattern is also different from that of nocturnal rodents that show elevated PER2 expression in the mid to late night and into the early day. These results are consistent with the hypothesis that diurnal behavior is associated with a phase change between the SCN and extra-SCN oscillators.     

Secretion of DJ-1 into the serum of patients with Parkinson's disease

In the diurnal rodent Arvicanthis niloticus (grass rats) the pattern of expression of the clock genes and their proteins in the suprachiasmatic nucleus (SCN) is very similar to that seen in nocturnal rodents. Rhythms in clock gene expression have been also documented in several forebrain regions outside the SCN in nocturnal Ratus norvegicus (lab rats). To investigate the neural basis for differences in the circadian systems of diurnal and nocturnal mammals, we examined PER1 expression in the oval nucleus of the bed nucleus of the stria terminalis (BNST-OV), and in the basolateral (BLA) and the central (CEA) amygdala of male grass rats kept in a 12:12 light/dark cycle. In the BNST-OV, peak levels of PER1 expression were seen early in the light phase of the cycle, 12h out of phase with what has been reported for nocturnal lab rats. In the BLA the pattern of PER1 expression featured sustained high levels during the day and low levels at night. PER1 expression in the CEA was also at its highest early in the light phase, but the effect of sampling time was not statistically significant (p<0.06). The results are consistent with the hypothesis that differences between nocturnal and diurnal species are due to differences in neural systems downstream from the SCN.     

The development of hypocretin (orexin) deficiency in hypocretin/ataxin-3 transgenic rats

Narcolepsy is linked to a widespread loss of neurons containing the neuropeptide hypocretin (HCRT), also named orexin. A transgenic (TG) rat model has been developed to mimic the neuronal loss found in narcoleptic humans. In these rats, HCRT neurons gradually die as a result of the expression of a poly-glutamine repeat under the control of the HCRT promoter. To better characterize the changes in HCRT-1 levels in response to the gradual HCRT neuronal loss cerebrospinal fluid (CSF) HCRT-1 levels were measured in various age groups (2-82 weeks) of wild-type (WT) and TG Sprague-Dawley rats. TG rats showed a sharp decline in CSF HCRT-1 level at week 4 with levels remaining consistently low (26%+/-9%, mean+/-S.D.) thereafter compared with WT rats. In TG rats, HCRT-1 levels were dramatically lower in target regions such as the cortex and brainstem (100-fold), indicating decreased HCRT-1 levels at terminals. In TG rats, CSF HCRT-1 levels significantly increased in response to 6 h of prolonged waking, indicating that the remaining HCRT neurons can be stimulated to release more neuropeptide. Rapid eye movement (REM) sleep in TG rats (n=5) was consistent with a HCRT deficiency. In TG rats HCRT immunoreactive (HCRT-ir) neurons were present in the lateral hypothalamus (LH), even in old rats (24 months) but some HCRT-ir somata were in various stages of disintegration. The low output of these neurons is consistent with a widespread dysfunction of these neurons, and establishes this model as a tool to investigate the consequences of partial hypocretin deficiency.     

Circadian phase alteration by GABA and light differs in diurnal and nocturnal rodents during the day

These studies investigated the circadian effects of light and gamma aminobutyric acid-A (GABAA) receptor activation in the suprachiasmatic nucleus (SCN) of the diurnal unstriped Nile grass rat (Arvicanthis niloticus). Microinjection of the GABAA agonist muscimol into the SCN during the day produced phase shifts that were opposite in direction to those previously reported in nocturnal rodents. In addition, light had no significant effect on the magnitude of muscimol-induced phase delays during the daytime. Injection of muscimol during the night, however, significantly inhibited light-induced phase delays and advances in a manner similar to that previously reported in nocturnal rodents. Therefore, the circadian effects of GABAA receptor activation are similar in diurnal and nocturnal species during the night but differ significantly during the day.     

Sleep-waking discharge patterns of neurons recorded in the rat perifornical lateral hypothalamic area

The perifornical lateral hypothalamic area (PF-LHA) has been implicated in the control of several waking behaviours, including feeding, motor activity and arousal. Several cell types are located in the PF-LHA, including projection neurons that contain the hypocretin peptides (also known as orexins). Recent findings suggest that hypocretin neurons are involved in sleep-wake regulation. Loss of hypocretin neurons in the human disorder narcolepsy is associated with excessive somnolence, cataplexy and increased propensity for rapid eye movement (REM) sleep. However, the relationship of PF-LHA neuronal activity to different arousal states is unknown. We recorded neuronal activity in the PF-LHA of rats during natural sleep and waking. Neuronal discharge rates were calculated during active waking (waking accompanied by movement), quiet waking, non-REM sleep and REM sleep. Fifty-six of 106 neurons (53 %) were classified as wake/REM-related. These neurons exhibited peak discharge rates during waking and REM sleep and reduced discharge rates during non-REM sleep. Wake-related neurons (38 %) exhibited reduced discharge rates during both non-REM and REM sleep when compared to that during waking. Wake-related neurons exhibited significantly higher discharge rates during active waking than during quiet waking. The discharge of wake-related neurons was positively correlated with muscle activity across all sleep-waking states. Recording sites were located within the hypocretin-immunoreactive neuronal field of the PF-LHA. Although the neurotransmitter phenotype of recorded cells was not determined, the prevalence of neurons with wake-related discharge patterns is consistent with the hypothesis that the PF-LHA participates in the regulation of arousal, muscle activity and sleep-waking states.     

Ventrolateral preoptic nucleus contains sleep-active,galaninergic neurons in multiple mammalian species

The ventrolateral preoptic nucleus (VLPO) is a group of sleep-active neurons that has been identified in the hypothalamus of rats and is thought to inhibit the major ascending monoaminergic arousal systems during sleep; lesions of the VLPO cause insomnia. Identification of the VLPO in other species has been complicated by the lack of a marker for this cell population, other than the expression of Fos during sleep. We now report that a high percentage of the sleep-active (Fos-expressing) VLPO neurons express mRNA for the inhibitory neuropeptide, galanin, in nocturnal rodents (mice and rats), diurnal rodents (degus), and cats. A homologous (i.e. galanin mRNA-containing cell group) is clearly distinguishable in the ventrolateral region of the preoptic area in diurnal and nocturnal monkeys, as well as in humans. Galanin expression may serve to identify sleep-active neurons in the ventrolateral preoptic area of the mammalian brain.The VLPO appears to be a critical component of sleep circuitry across multiple species, and we hypothesize that shrinkage of the VLPO with advancing age may explain sleep deficits in elderly humans.     

Diurnal variation in continuous measures of the rat EEG power spectra.

EEG measures that vary on a continuous scale, without separating behavior into discrete states, may complement sleep staging as a means of characterizing diurnal variation in level of arousal. The object of the present study was to evaluate diurnal variation in the EEG power spectrum averaged independently of sleep state, and to determine which parameters best reflect this variation. The EEG from rats maintained with chronic cortical electrodes was continuously digitized at 256 Hz, and power spectra computed by fast Fourier transformation every four seconds. Artifact-free spectra occurring over one-hour periods were averaged. Spectral edge, calculated from 66 percent of the area of spectra, and relative power in delta and theta band-widths derived from averaged spectra vary in a consistent and highly significant diurnal pattern. The trend of relative delta power over the daytime, inactive period (when sleep occurs in nocturnal rodents) resembles that seen in human subjects during sleep, with peak levels occurring at the onset, followed by a steady decline during remaining hours of the daytime rest period.     

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.     

Survival rates through time of hypocretin grafted neurons within their projection site

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness, inadvertent transitions from wakefulness to rapid eye movement sleep (so called "sleep-onset REMS period") and cataplexy (sudden bilateral skeletal muscle weakness during waking without impairment of consciousness). This disorder has been recently linked to a loss of hypocretin (HCRT) neurons making narcolepsy a neurodegenerative disease. Neuronal replacement could be used to reverse the symptoms of narcolepsy. Towards this end, we have recently reported that HCRT neurons from rat pups can survive when grafted into the pons of adult rats. Here, we investigate the time-course of survival of grafted HCRT neurons into the pons of adult rats. The HCRT neurons are present only in the lateral hypothalamus, and therefore suspension of cells from this region was derived from 8- to 10-day-old rat pups (donor), and grafted into the pons of adult (60 days old) host rats. Control rats received a transplant that consisted of cells from the cerebellum where no HCRT neurons are present. All adult host rats were sacrificed 1, 3, 6, 9, 12, 24, or 36 days after grafting. Immunohistochemistry was used to identify and count the presence of the HCRT grafted neurons in the target area. The tally of HCRT neurons present in the graft zone 1 day post-grafting was considered to be the baseline. From day 3 to 36 post-transplant there was a steady decline in the number of HCRT neurons. We also noted that on day 36, the HCRT neurons that survived in the pons had morphological features that were similar to mature HCRT neurons in the adult lateral hypothalamus, suggesting that these neurons might be functionally active. Control rats that received grafts of cerebellar tissue did not show HCRT neurons in the target area. These results demonstrate that there is a progressive decline in the number of transplanted neurons, but a significant percentage of HCRT neurons do survive until day 36. This study highlights the potential use of transplants as a therapeutical tool in order to treat narcolepsy.     

Distribution of hypocretin-(orexin) immunoreactivity in the central nervous system of Syrian hamsters (Mesocricetus auratus)

The hypocretins are peptides synthesized in neurons of the hypothalamus. Recent studies have suggested a role for these peptides in the regulation of sleep, feeding, and endocrine regulation. The distribution of hypocretin-immunoreactive cell bodies and fibers has been extensively described in rats, but not in other species. This study was designed to examine the distribution of hypocretin immunoreactivity in Syrian hamsters, as important differences in neuropeptide distribution between rats and hamsters have previously been demonstrated. Immunoreactive cell bodies were found primarily in the lateral hypothalamic area and the perifornical area, although a few hypocretin-positive cells were also located in the dorsomedial hypothalamus and the retrochiasmatic area. Fibers were distributed throughout the brain in a pattern similar to that seen in rats. The densest projections were found in the paraventricular nucleus of the thalamus, locus coeruleus, dorsal raphe, and lateroanterior hypothalamus. The innervation of the anterior hypothalamus may be of particular interest as similar cluster of immunoreactivity does not appear to be present in rats. Moderate levels of immunoreactivity could be seen throughout the hypothalamus, the lateral septum, bed nucleus of the stria terminalis, A5 noradrenergic area, and the midline thalamic nuclei. Hypocretin-immunoreactive fibers are present in all lamina of the spinal cord, with the greatest axon densities in lamina 1 and 10. The widespread distribution of hypocretin suggests its involvement in a wide variety of physiological and behavioral processes. Our results in hamsters indicate that the organization of the hypocretin system is strongly conserved across species, suggesting an important role for the peptide and its projections.     

Fos immunoreactivity in hypocretin-synthesizing and hypocretin-1 receptor-expressing neurons: effects of diurnal and nocturnal spontaneous waking,stress and hypocretin-1 administration

Hypocretin/orexin modulates sleep-wake state via actions across multiple terminal fields. Within waking, hypocretin may also participate in high-arousal processes, including those associated with stress. The current studies examined the extent to which alterations in neuronal activity, as measured by Fos immunoreactivity, occur within both hypocretin-synthesizing and hypocretin-1 receptor-expressing neurons across varying behavioral state/environmental conditions associated with varying levels of waking and arousal. Double-label immunohistochemistry was used to visualize Fos and either prepro-hypocretin in the lateral hypothalamus or hypocretin-1 receptors in the locus coeruleus and select basal forebrain regions involved in the regulation of behavioral state/arousal. Animals were tested under the following conditions: 1). diurnal sleeping; 2). diurnal spontaneous waking; 3). nocturnal spontaneous waking; and 4). high-arousal waking (diurnal novelty-stress). Additionally, the effects of hypocretin-1 administration (0.07 and 0.7 nmol) on levels of Fos were examined within these two neuronal populations. Time spent awake, scored for the 90-min preceding perfusion, was largely comparable in diurnal spontaneous waking, nocturnal spontaneous waking and high-arousal waking. Nocturnal spontaneous waking and high-arousal waking, but not diurnal spontaneous waking, were associated with increased levels of Fos within hypocretin-synthesizing neurons, relative to diurnal sleeping. Within hypocretin-1 receptor-expressing neurons, only high-arousal waking was associated with increased levels of Fos. Hypocretin-1 administration dose-dependently increased levels of Fos within hypocretin-1 receptor-expressing neurons to levels comparable to, or exceeding, levels observed in high-arousal waking. Combined, these observations support the hypothesis that hypocretin neuronal activity varies across the circadian cycle. Additionally, these data suggest that waking per se may not be associated with increased hypocretin neurotransmission. In contrast, high-arousal states, including stress, appear to be associated with substantially higher rates of hypocretin neurotransmission. Finally, these studies provide further evidence indicating coordinated actions of hypocretin across a variety of arousal-related basal forebrain and brainstem regions in the behavioral state modulatory actions of this peptide system.     

Distribution of orexin-A immunoreactive neurons and their terminal networks in the brain of the rock hyrax, Procavia capensis

The present study describes the distribution of orexin-A immunoreactive neurons and terminal networks in relation to the previously described catecholaminergic, cholinergic and serotonergic systems within the brain of the rock hyrax, Procavia capensis. Adult female rock hyrax brains were sectioned and immunohistochemically stained with an antibody to orexin-A. The staining revealed that the neurons were mainly located within the hypothalamus as with other mammals. The orexinergic terminal network distribution also resembled the typical mammalian plan. High-density orexinergic terminal networks were located within regions of the diencephalon (e.g. paraventricular nuclei), midbrain (e.g. serotonergic nuclei) and pons (locus coeruleus), while medium density orexinergic terminal networks were evident in the telencephalic (e.g. basal forebrain), diencephalic (e.g. hypothalamus), midbrain (e.g. periaqueductal gray matter), pontine (e.g. serotonergic nuclei) and medullary regions (e.g. serotonergic and catecholaminergic nuclei). Although the distribution of the orexinergic terminal networks was typically mammalian, the rock hyrax did show one atypical feature, the presence of a high-density orexinergic terminal network within the anterodorsal nucleus of the dorsal thalamus (AD). The dense orexinergic innervation of the AD nucleus has only been reported previously in the Nile grass rat, Arvicanthis niloticus and Syrian hamster, Mesocricetus auratus, both diurnal mammals. It is possible that orexinergic innervation of the AD nucleus might be a unique feature associated with diurnal mammals. It was also noted that the dense orexinergic innervation of the AD nucleus coincided with previously identified cholinergic neurons and terminal networks in this particular nucleus of the rock hyrax brain. It is possible that this dense orexinergic innervation of the AD nucleus in the brain of the rock hyrax may act in concert with the cholinergic neurons and/or the cholinergic axonal terminals, which in turn may influence arousal states and motivational processing.     

Efferent projections of the suprachiasmatic nucleus based on the distribution of vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) immunoreactive fibers in the hypothalamus of Sapajus apella

The suprachiasmatic nucleus (SCN), which is considered to be the master circadian clock in mammals, establishes biological rhythms of approximately 24 h that several organs exhibit. One aspect relevant to the study of the neurofunctional features of biological rhythmicity is the identification of communication pathways between the SCN and other brain areas. As a result, SCN efferent projections have been investigated in several species, including rodents and a few primates. The fibers originating from the two main intrinsic fiber subpopulations, one producing vasoactive intestinal peptide (VIP) and the other producing arginine vasopressin (AVP), exhibit morphological traits that distinguish them from fibers that originate from other brain areas. This distinction provides a parameter to study SCN efferent projections. In this study, we mapped VIP (VIP-ir) and AVP (AVP-ir) immunoreactive (ir) fibers and endings in the hypothalamus of the primate Sapajus apella via immunohistochemical and morphologic study. Regarding the fiber distribution pattern, AVP-ir and VIP-ir fibers were identified in regions of the tuberal hypothalamic area, retrochiasmatic area, lateral hypothalamic area, and anterior hypothalamic area. VIP-ir and AVP-ir fibers coexisted in several hypothalamic areas; however, AVP-ir fibers were predominant over VIP-ir fibers in the posterior hypothalamus and medial periventricular area. This distribution pattern and the receiving hypothalamic areas of the VIP-ir and AVP-ir fibers, which shared similar morphological features with those found in SCN, were similar to the patterns observed in diurnal and nocturnal animals. This finding supports the conservative nature of this feature among different species. Morphometric analysis of SCN intrinsic neurons indicated homogeneity in the size of VIP-ir neurons in the SCN ventral portion and heterogeneity in the size of two subpopulations of AVP-ir neurons in the SCN dorsal portion. The distribution of fibers and morphometric features of these neuronal populations are described and compared with those of other species in the present study.     

Effects of medial preoptic area lesions on sleep and wakefulness in unrestrained rats

Bilateral radiofrequency lesions of the medial preoptic area (MPOA) in unrestrained male rats resulted in a significant decrease in slow wave sleep (SWS) in the light period throughout two postoperative weeks, although the night-active pattern of circadian rhythms was little affected. Both diurnal and nocturnal paradoxical sleep (PS) gradually increased after the lesions. Within one week, however, the daily amount of total sleep (SWS + PS) was recovered to the normal level, since the loss of diurnal SWS was compensated by an increase in nocturnal sleep at the expense of wakefulness. The MPOA lesions brought about a transient elevation of brain temperature, which lasted only for the diurnal period of the day of lesioning. It is speculated that the MPOA plays a definite role in the passage of sleep-regulatory information, especially concerning the circadian distribution of sleep.     

Hypothalamic Hypocretinergic/Orexinergic Neurons Projecting to the Oral Pontine Rapid Eye Movement Sleep Inducing Site in the Cat

The cat ventral oral pontine reticular nucleus (vRPO) is responsible for the generation and maintenance of rapid eye movement (REM) sleep. Hypothalamic neurons containing the peptide hypocretin‐1 (also called orexin‐A) which will be herewith defined as orexinergic (Orx) neurons, occupy a pre‐eminent place in the integration and stabilization of arousal networks as well as in the physiopathology of narcolepsy/cataplexy. In the previous investigations, low‐volume and dose microinjections of hypocretin‐1 in cat vRPO produced a specific and significant suppression of REM sleep. The aim of this study is to map the hypothalamic Orx neurons that project to the vRPO and suppress REM sleep generation in the cat. Five adult cats received microinjections of the retrograde tracer cholera toxin (CTb) into the vRPO. Brains were processed employing both CTb staining and antiorexin‐A immunocytochemistry techniques. A large number of double‐labeled neurons (Orx–CTb) intermingled with the single CTb‐positive and single Orx neurons were detected in the ipsilateral lateral, perifornical, dorsal, anterior, perimammillothalamic, and posterior hypothalamic areas but were very scarce in the paraventricular, dorsomedial, ventromedial, and periventricular hypothalamic nuclei. A considerable number of double‐labeled neurons were also observed in both the dorsal and the lateral hypothalamic areas in the contralateral hypothalamus. Our results suggest that the widely distributed Orx neuronal hypothalamic groups could physiologically inhibit REM sleep generation in vRPO. Anat Rec, 296:815–821, 2013. © 2013 Wiley Periodicals, Inc.     

Effects of Night Duty on Sleep Patterns of Nurses

The diurnal sleep patterns of female nurses working night duty were compared to their nocturnal sleep patterns while they were working regular hours during the day. Continuous EEG, EOG, and EMG recordings were made at the end of 2 month periods of night and day duty respectively. Day and night sleep differed with respect to both duration and pattern. Despite an earlier onset, the major sleep period was shorter during the day than the night and seemed to be more interrupted later in the session. This finding is in keeping with the increased amount of Stage 1 and decreased amount of slow wave sleep during the day than the night. Although no differences were evident with respect to overall percent REM, differences in the distribution of REM did occur. REM sleep occurred sooner during day than night sleep and there was more of it during the first part of day sleep. Thus night duty seemed to affect the pattern of sleep stage distribution as well as the absolute amount of, not only total sleep, but also some sleep stages, such as Stage SS. It is an open question how the naps of extended duration taken while on night duty influence the pattern of sleep during the day.     

Individual differences in wheel-running rhythms are related to temporal and spatial patterns of activation of orexin A and B cells in a diurnal rodent (Arvicanthis niloticus)

This study investigated the relationship between the orexins and patterns of activity in the diurnal Nile grass rat, Arvicanthis niloticus. Some individuals of this species switch to a more nocturnal pattern when given access to a running wheel, while others continue to be most active during the day. In both day- and night-active grass rats, the percentages of orexin A (OXA) and orexin B (OXB) cells expressing Fos were highest when animals were actively running in wheels. In night-active animals, removal of the running wheel significantly decreased OXA and OXB cell Fos expression. Additionally, in night-active animals, clear regional differences were apparent. In these animals the presence of a wheel induced higher percentages of Fos in both OXA and OXB cells in medial regions of the lateral hypothalamus than in lateral regions. In night-active animals without access to wheels, this medial-lateral gradient was present only in OXA cells. No regional differences were observed in day-active animals. This study demonstrates that individual differences in the patterns of activation of OXA and OXB cell populations are related to differences in the temporal pattern of wheel running. We also present evidence that orexin cells have projections to the intergeniculate leaflet that appear to make contact with neuropeptide-Y cells. We discuss the possibility that these fibers may be involved in relaying feedback regarding the activity state of the animal to the circadian system through these projections.