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Long-term (>48 h) sleep deprivation (SD) reduces adult rat hippocampal cell proliferation and neurogenesis, yet reported effects of short-term (<24 h) SD are inconsistent. We systematically assessed the effects of various durations of SD on adult rat hippocampal cell proliferation. Rats were sleep-deprived for 6, 12, 24, 36 or 48 h and injected with 5-bromo-2'-deoxyuridine (BrdU) 2 h before the end of SD. Immunolabeling for BrdU in the hippocampal subgranular zone increased significantly after 12 h SD but tended to decrease after 48 h SD relative to respective Controls. Surprisingly, SD did not alter immunolabeling for Ki67 protein (Ki67) or proliferating cell nuclear antigen (PCNA), two intrinsic cell proliferation markers. SD did not affect BrdU or Ki67 labeling in the subventricular zone, nor did it affect serum corticosterone levels. Because immunoreactivity for Ki67 and PCNA can identify cells in all phases of the ∼25 h cell cycle in adult rat hippocampus, whereas BrdU labels only cells in S-phase (∼9.5 h), this discrepancy suggests that 12 h SD might have affected cell cycle dynamics. A separate group of rats were injected with BrdU 10 h before the end of 12 h SD, which would allow some time for labeled cells to divide; the results were consistent with an acceleration of the timing of hippocampal progenitor cell division during 12 h SD. These results suggest that short-term (12 h) SD transiently produces more hippocampal progenitor cells via cell cycle acceleration, and confirm the importance of using multiple cell cycle markers or BrdU injection paradigms to assess potential changes in cell proliferation., (Copyright © 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Sleep restriction alters hormone patterns and appetite in men, but less is known about effects on women. We assessed effects of overnight sleep restriction on cortisol and leptin levels and on appetite in young women. Participants' baseline sleep duration and eating habits were monitored for a week before the study. Salivary cortisol and leptin were sampled from fifteen healthy women (aged 18-25) during two consecutive days: first after a 10h overnight sleep opportunity (Baseline day) and then after a night including only 3h sleep (Post sleep-restriction day). Participants also completed appetite questionnaires on both days. Sleep restriction significantly reduced morning cortisol levels (p=0.02), elevated morning leptin levels (p=0.04), elevated afternoon/evening cortisol area under the curve values (p=0.008), and slowed the decline in cortisol concentration during the day (p=0.04). Hunger and craving scores did not differ significantly between days. A single night of restricted sleep affected cortisol rhythms and morning leptin levels in young women., ((c) 2010 Elsevier Inc. All rights reserved.)

Women recover from sleep deprivation more efficiently than men, but the mechanism for this difference is unknown. Effects of estrogen on sleep suggest that it could play a role, but the brain targets on which estrogen may act to have this effect have not been identified. Sleep deprivation increases levels of the immediate-early gene protein c-Fos in selected brain regions, but it is unknown whether estrogen modulates this response. We investigated the influence of different levels of exogenous estradiol on the c-Fos response to sleep deprivation in ovariectomized female rats. Female rats were treated with low or high levels of estradiol (mimicking diestrous and proestrous levels, respectively) delivered via subcutaneous silastic tubes. Control ovariectomized females and sham-operated males were implanted with tubes filled with cholesterol. One week after surgery, half of the rats underwent a 3 h period of sleep deprivation during the light phase in a motorized Wahmann activity wheel that rotated constantly at a slow speed, while half were confined to fixed wheels. Immediately after sleep deprivation, animals were killed and their brains processed to detect c-Fos using immunohistochemistry. Sleep deprivation increased the number of c-Fos positive cells in a number of brain areas, including the caudate putamen, medial preoptic area, perifornical hypothalamus, and anterior paraventricular thalamic nucleus. Other areas, including the suprachiasmatic nucleus, posterior paraventricular hypothalamic nucleus, posterior paraventricular thalamic nucleus, arcuate nucleus, and central amygdala, did not respond to 3 h sleep deprivation with a significant increase in c-Fos levels. Levels of c-Fos induced in the selected brain regions by sleep deprivation were not modulated by estrogen levels, nor by sex.

The suprachiasmatic nuclei of the anterior hypothalamus serve as the principal pacemaker of the mammalian circadian system. Among its efferent targets are the habenular nucleus (Hb), especially the lateral Hb (LHb), which plays an important role in conveying input from the limbic forebrain to midbrain structures. We recorded extracellularly from single neurons in the LHb and medial Hb (MHb), both in vivo and using an in vitro slice preparation, to assess their responses to retinal illumination and the rhythmicity of their firing rates. Of cells recorded in the LHb, 42% were tonically activated or suppressed by retinal illumination, while significantly fewer cells recorded in the MHb responded to retinal illumination (19%). Of photically responsive cells, 68% in the LHb were activated and the remainder suppressed, while only 25% of those recorded in the MHb were activated. Cells in both the LHb and MHb showed higher baseline firing rates during the day than during the night in vivo, while photic responses were of significantly larger amplitude among LHb cells during the projected night than during the projected day. LHb cells recorded in vitro maintained their rhythmicity for two circadian cycles, but MHb cells did not show a rhythm in vitro. The habenula may play a role in linking circadian and motivational systems and may contribute to photic regulation of these systems, as well as to the rhythmicity of their function.

The walls of the third ventricle have been proposed to serve as a bidirectional conduit for exchanges between the neural parenchyma and the cerebrospinal fluid. In immunohistochemical studies of mice, we observed that light exposure and circadian phase affected peptide staining surrounding the third ventricle at the level of the suprachiasmatic nuclei. Under high magnification, we observed robust staining for the neurohormone oxytocin and the calcium-binding protein parvalbumin associated with cilia extending into the third ventricle from the surrounding ventricular wall; no similar staining was observed for vasopressin or calbindin. Retinal illumination had opposite effects on levels of parvalbumin and oxytocin in the cilia: light exposure during late subjective night increased oxytocin staining, but decreased parvalbumin staining in the cilia. Preventing cellular transport with colchicine eliminated immunohistochemical staining for oxytocin in the cilia. There was also a significant daily rhythm of oxytocin immunostaining in the third ventricle wall, and in magnocellular neurons in the anterior hypothalamus. The results suggest that environmental lighting and circadian rhythms regulate levels of oxytocin in the cerebrospinal fluid, possibly by regulating movement of oxytocin through the third ventricle wall.

If food is presented for a limited duration once every 24 h, rats will gradually develop increased activity in the hours preceding mealtime, even if this is during a time of day when they are normally inactive. This food-anticipatory activity (FAA) is mediated by the entrainment of an endogenous self-sustaining circadian pacemaker. Mice are increasingly being used for the molecular analysis of behavior because of the large number of genetically manipulated mouse models available, but little is known about food entrainment in this species. This study assessed the impact of different housing conditions on the expression of FAA in a temporally restricted feeding paradigm. Wheel-running activity rhythms were recorded from mice (Mus musculus) undergoing food restriction while housed under one of two conditions. The results demonstrated that mice housed on open shelves showed robust FAA while those housed in isolation boxes did not. These results indicate that differences in susceptibility to food entrainment among mice (e.g., those with different genotypes) should be interpreted cautiously, since at least one strain is strongly affected by a relatively minor procedural difference that was not anticipated to have a significant impact.

Several immediate-early genes have been shown to be induced in the rodent circadian pacemaker, the suprachiasmatic nucleus, by retinal illumination at night. We compared spontaneous and light-evoked levels of the immediate-early gene protein ZIF268 (NGFI-A) in the Syrian hamster and C57BL/6J mouse suprachiasmatic nucleus. Exposure of both hamsters and mice to light pulses early and late in the subjective night caused increased ZIF268 immunoreactivity in the region of the suprachiasmatic nucleus that receives retinal innervation. In contrast to hamsters, mice also showed spontaneous increases in ZIF268 at both subjective night phases at the lateral edges of the suprachiasmatic nucleus. Light also evoked a significant increase in ZIF268 levels during the subjective day in the lateral suprachiasmatic nucleus, with few labeled cells in the ventral and dorsal suprachiasmatic nucleus. These results demonstrate a novel circadian pattern and regional differentiation of ZIF268 immunoreactivity in the suprachiasmatic nucleus of mice that differ from those in other rodents. There are pronounced species differences in both spontaneous and light-evoked expression of ZIF268 immunoreactivity.

Extracellular and whole-cell patch-clamp recordings were made from neurons in the ventromedial preoptic area in rat horizontal brain slices. Responses to single-pulse electrical stimulation of the ipsilateral suprachiasmatic nucleus were characterized using peristimulus time histograms or postsynaptic current recordings, and bath application of neurotransmitter receptor antagonists. Extracellular recordings showed that suprachiasmatic nucleus stimulation (50-150 microA) elicited a short-latency suppression in 35 of 64 neurons (55%), with the majority (29/35, 83%) showing a biphasic response consisting of a short-latency suppression followed by a long-duration activation. In addition, 14 cells (22%) showed activation only, while 15 (23%) were unresponsive. The GABA(A) receptor antagonist bicuculline (5-10 microM) reversibly blocked suppressions evoked by suprachiasmatic nucleus stimulation (20/20 cells). In the majority of these neurons (13/20), bicuculline also unmasked an activation in response to stimulation. Activations elicited by suprachiasmatic nucleus stimulation, either in the presence or absence of bicuculline, were blocked by the non-N-methyl-D-aspartate and N-methyl-D-aspartate glutamate receptor antagonists 6,7-dinitroquinoxaline-2,3-dione and (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (10/10 cells). 6,7-Dinitroquinoxaline-2,3-dione (10 microM) selectively and reversibly blocked the initial, short-duration (<50 ms) activation, but had no effect on the longer-duration activation. In contrast, (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (10 microM) appeared to inhibit the long-duration activation selectively without affecting the initial rapid activation. Combined applications of the two ionotropic glutamate receptor antagonists blocked stimulation-induced activations completely. All the pharmacological effects were concentration dependent. Whole-cell patch-clamp recordings showed that suprachiasmatic nucleus stimulation elicited inhibitory postsynaptic currents or a combination of inhibitory and excitatory postsynaptic currents in 25 of 33 neurons tested. The inhibitory postsynaptic currents had short onset latencies (4.9+/-0.3 ms) and a reversal potential of -56.0+/-3.8 mV (n=5), and were reversibly blocked by bicuculline (5-10 microM, 4/4 cells). In the presence of bicuculline (5-10 microM), excitatory postsynaptic currents had short onset latencies (4.7+/-0.5 ms), and had a fast and a slow component. (+/-) 3-(2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid blocked the slow, but not the fast, component, whereas 6,7-dinitroquinoxaline-2, 3-dione blocked the fast, but not the slow, component (n=7). These results suggest that the projection from the suprachiasmatic nucleus conveys both inhibitory (GABA) and excitatory (glutamate) inputs to the ventromedial preoptic area. GABA(A) receptor and both non-N-methyl-D-aspartate and N-methyl-D-aspartate glutamate receptors mediate these influences. These inputs may be responsible for conveying information related to circadian phase from the suprachiasmatic nucleus to regions of the preoptic area known to be involved in regulation of sleep/waking and other physiological functions.

The hypothalamic suprachiasmatic nucleus is the site of an endogenous circadian clock synchronized by daily light-dark cycles. At some daily phases, light exposure both shifts the clock and alters the expression of several immediate-early genes in cells of the suprachiasmatic nucleus. We have studied both spontaneous circadian and light-induced expression of several immediate-early gene messenger RNAs and proteins in hamsters in constant darkness or in response to brief light exposure. There was no detectable spontaneous expression of NGFI-A messenger RNA in suprachiasmatic nucleus cells at any circadian phase, but light pulses induced its expression selectively during the subjective night, with highest levels of expression 6 h into the night. We also found that there are two independent rhythms of expression of junB messenger RNA and JunB protein, as well as c-fos messenger RNA and c-Fos protein, in the suprachiasmatic nucleus of hamsters: a rhythm of photic sensitivity expressed throughout the night and a spontaneous rhythm of expression triggered around dawn. Induction of NGFI-A messenger RNA and c-fos messenger RNA and c-Fos protein in response to a light pulse were found throughout the suprachiasmatic nucleus, with the highest levels of expression in the ventrolateral subdivision; however, the spontaneous expression of JunB and c-Fos proteins was confined mainly to the dorsomedial suprachiasmatic nucleus. The temporal and anatomical differences in the expression of these immediate-early genes in the mammalian suprachiasmatic nucleus suggest that their protein products may be involved in different signaling mechanisms mediating either photic entrainment or endogenous oscillations within distinct subpopulations of suprachiasmatic nucleus cells.

Previous studies have demonstrated that melatonin and a novel melatonin receptor agonist, S20098 (N-[2-(7-methoxy-1-naphthyl) ethyl] acetamide), regulate neuronal firing activity of photically responsive cells in the suprachiasmatic nucleus in vivo. In the present study, we used several different methods to investigate the effects of chronic daily treatment with melatonin, S20098 (1.0 mg/kg, s.c.) or control vehicle for 14 d on responsiveness of suprachiasmatic nucleus cells to these agonists. Both chronic and acute application of drugs were carried out during the day-night transition period. We confirmed that suprachiasmatic nucleus cells from control animals were most sensitive at this circadian phase. Chronic drug treatments did not alter sensitivity of photically responsive suprachiasmatic nucleus cells to S20098 or melatonin given intraperitoneally (i.p.) or iontophoretically in vivo. Suprachiasmatic nucleus cells studied in brain slice preparations also responded similarly to micropressure ejections of melatonin receptor agonists regardless of drug pretreatment. These results indicate that chronic melatonin receptor agonist pretreatment does not result in desensitization of suprachiasmatic nucleus neuronal responses to these agonists during the daily phase of maximum melatonin sensitivity.

In mammals, the suprachiasmatic nucleus is critical for the generation of circadian rhythms and their entrainment to environmental cues. In the rat, the ventrolateral aspect of the suprachiasmatic nucleus receives a robust retinal input. This region also exhibits the most intense immunolabeling for the low-affinity nerve growth factor receptor in the forebrain. Our study was aimed at identifying the sources of this low-affinity nerve growth factor receptor immunoreactivity using immunohistochemistry combined with retrograde tract-tracing, and orbital enucleation. To determine the origin of the low-affinity nerve growth factor receptor immunoreactivity from sources extrinsic to the suprachiasmatic nucleus, unilateral injections of the retrograde tracer, Fluorogold, were made into the suprachiasmatic nucleus. Retrogradely labeled neurons that were also immunopositive for the low-affinity nerve growth factor receptor were found in both the basal forebrain and the retina. In the basal forebrain, such cells were found throughout its rostrocaudal extent, with the majority also being immunoreactive for the cholinergic marker, choline acetyltransferase. In the retina, cells retrogradely labeled with Fluorogold that were immunoreactive for low-affinity nerve growth factor receptor were located in the ganglion cell layer. Orbital enucleations were performed to confirm the findings observed following retrograde labeling in the retina. Unilateral orbital enucleations resulted in a significant reduction in low-affinity nerve growth factor receptor immunoreactivity in the contralateral suprachiasmatic nucleus compared to that seen on the ipsilateral side when examined one week post-surgery. Bilateral enucleations resulted in an equal decrease on both sides of the suprachiasmatic nucleus. Similar low-affinity nerve growth factor-like immunoreactivity was seen in the suprachiasmatic nucleus even two to four weeks after bilateral enucleations. Taken together, these findings suggest that low-affinity nerve growth factor receptors in the suprachiasmatic nucleus derive from multiple sources. While some receptors may be intrinsic to suprachiasmatic nucleus neurons, most appear to be of extrinsic origin and are located on axon terminals of basal forebrain cholinergic neurons and retinal ganglion cells.

The suprachiasmatic nucleus (SCN) receives a direct retinal projection, which in rats includes substance P (SP)-immunoreactive retinal ganglion cells. While SP has been shown to have neurophysiological effects on SCN cells in Syrian hamsters and rats, it is not known what effects SP in the SCN has on circadian rhythms in hamsters. We examined this question using male Syrian hamsters that were implanted with cannulas aimed at the SCN region and maintained in constant dim red lighting conditions. Hamsters received 0.5 microl microinjections of saline or SP (500 pmol in saline) at a variety of circadian times (CT). Saline injections had little or no phase-shifting effects at any phase tested. SP had no significant effects at CT4-8, 16-20, or 20-24, but did cause small phase delays of -23.7 +/- 7 min (mean +/- sem) at CT12-16. In order to examine the dose-response relations of this effect, hamsters were also microinjected with 50 and 2500 pmol of SP at CT12-16. Both the 50 and 2500 pmol doses induced very small phase delays (-14.2 +/- 7 min and -18.2 +/- 5 min, respectively), indicating no obvious dose dependence within this range. These results do not suggest that SP alone in the SCN mimics light effects on circadian rhythms or is a key neurotransmitter involved in photic entrainment. It remains to be determined whether SP interacts with other transmitters in the SCN to modulate their effects on rhythm phase.

The neurophysiological effects of ionophoretic application of the metabotropic glutamate receptor agonist (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid on the firing rate of single suprachiasmatic nucleus cells was studied in a hypothalamic slice preparation. In addition, the effects of the phenylglycine derivative (RS)-alpha-methyl-4-carboxyphenylglycine, a selective metabotropic glutamate receptor antagonist, on responses evoked by (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid and N-methyl-D-aspartate were assessed. (1S,3R)-1-Amino-1,3-cyclopentanedicarboxylic acid elicited current-dependent increases in neuronal activity in 65% of all suprachiasmatic nucleus cells studied, while N-methyl-D-aspartate activated 93% of the same cells. Cells in the ventrolateral suprachiasmatic nucleus were more sensitive to (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid application (82% of cells activated) than those in the dorsomedial suprachiasmatic nucleus (28% of cells activated). In addition, responses evoked by (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid in the ventrolateral suprachiasmatic nucleus had a rapid onset and a prolonged recovery from agonist application, whereas responses elicited in the dorsomedial suprachiasmatic nucleus were slower in onset and recovered more quickly from agonist application. Co-application of (RS)-alpha-methyl-4-carboxyphenylglycine selectivity attenuated (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid-evoked responses but had no effect on N-methyl-D-aspartate-evoked activity in the same cells. These results indicate that (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid application activates single cells in the hamster suprachiasmatic nucleus and these responses are selectively attenuated by (RS)-alpha-methyl-4-carboxyphenylglycine. Cells in the ventrolateral suprachiasmatic nucleus are more sensitive to (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid application than those in the dorsomedial suprachiasmatic nucleus. These results are the first demonstration that metabotropic glutamate receptors can modulate spontaneous neuronal activity within the suprachiasmatic nucleus, the predominant mammalian circadian pacemaker.

We studied the effects of drugs related to melatonin on neuronal firing activity in the suprachiasmatic nucleus, intergeniculate leaflet and other brain areas in urethane-anesthetized Syrian hamsters. We tested melatonin and two naphthalenic derivatives of melatonin, a putative agonist (S20098: N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide), and a putative antagonist (S20928: N-[2-(1-naphthyl)ethyl]cyclobutyl carboxamide). Both melatonin and S20098 given intraperitoneally (i.p.) were able to suppress firing rates of cells in a similar dose-dependent manner, but the effects of S20098 were longer lasting. Iontophoresis of melatonin dose dependently depressed spontaneous and light-evoked activity of cells in the suprachiasmatic nucleus and intergeniculate leaflet, while iontophoresis of S20098 was relatively ineffective, probably because it is a poorly charged compound. S20928 (2.0-10 mg/kg, i.p.) alone decreased firing rates of light-sensitive cells by 25-50% for 5-30 min in the suprachiasmatic nucleus and intergeniculate leaflet; however, low doses (< 2.0 mg/kg) of S20928 partially blocked the effects of melatonin agonists on most cells. The non-selective serotonin antagonist metergoline did not block the effects of either melatonin agonist. Both melatonin agonists and antagonists were less effective when applied to cells in the hippocampus and dorsal lateral geniculate nucleus. These results indicate that S20098 is an agonist acting probably on melatonin receptors in the Syrian hamster brain. S20928 may have mixed agonist/antagonist properties, but at low doses appears to function as an antagonist at melatonin receptors in the suprachiasmatic nucleus and intergeniculate leaflet.

ionophoretic ejection of substance P (SP) activated 31% and suppressed 9% of hamster suprachiasmatic nucleus (SCN) cells in vitro. Hamster SCN cells did not demonstrate variation in sensitivity to SP across the circadian phases tested. SP modulated the response of 47% of hamster SCN cells to the excitatory amino acid (EAA) agonists glutamate and N-methyl-D-aspartate (NMDA). The results indicate that SP can alter both the spontaneous and EAA-evoked firing rate characteristics of hamster SCN neurons.

Ionophoresis of the smaller bombesin-like peptides (gastrin releasing peptide [GRP]-(18-27), neuromedin B, and bombesin) evoked responses from 30-60% of hamster suprachiasmatic nucleus cells recorded in a hypothalamic slice preparation, depending on the circadian phase. We also demonstrated for the first time that the putative bombesin-like peptide receptor antagonists [D-F5,D-Phe6,D-Ala11]bombesin-(6-13)methyl ester (BIM 26226) and [D-Phe6,Des-Met14]bombesin-(6-14)ethyl amide can be applied ionophoretically to block physiological responses to bombesin-like peptides. Together with earlier findings, these results show that bombesin-like peptides administered by several methods can potently alter the firing rates of hamster suprachiasmatic nucleus neurons in vitro. These results indicate that bombesin-like peptides affect suprachiasmatic nucleus cells and could play a role in modulating suprachiasmatic nucleus-mediated circadian rhythm entrainment.

We previously reported that systemic treatment with a noncompetitive antagonist affecting the NMDA subtype of excitatory amino acid (EAA) receptor, MK-801, inhibits photic induction of Fos-like immunoreactivity (Fos-lir) in the hamster suprachiasmatic nucleus (SCN). Because MK-801 blocks the Ca2+ channel associated with the NMDA receptor, it may also influence the activity of other transmitters acting through Ca2+ channels. To assess the specificity of these effects, we compared the effects on photic induction of Fos-lir of several treatments: central injection of a competitive NMDA antagonist, CPP; central injection of a non-NMDA antagonist, DNQX; and systemic injection of the non-competitive NMDA antagonist, ketamine. Fos-lir was induced in SCN cells of vehicle-injected hamsters exposed to a light pulse 4-5 h after dark onset. Pretreatment with CPP (greater than 2 nmoles) or ketamine (greater than 100 mg/kg) caused a dose-related inhibition of photic induction of Fos-lir in portions of the SCN. These treatments reduced Fos-lir mainly in the rostral SCN and ventrolateral, but not dorsolateral, portions of the caudal SCN. Pretreatment with DNQX (greater than 20 nmoles) also inhibited photic induction of Fos-lir in the same regions of the SCN. These results indicate that photic induction of Fos protein in a portion of the hamster SCN is regulated by both NMDA and non-NMDA types of EAA receptor.

Constant light exposure (LL) can result in "splitting" of circadian rhythms into two components coupled about 12 hr apart. Splitting has been interpreted as evidence for the presence of two main oscillators or groups of oscillators underlying circadian rhythms. Abolition of splitting after unilateral suprachiasmatic nucleus ablation suggested that each suprachiasmatic nucleus could correspond to one of these component oscillators. We examined whether lesions outside the suprachiasmatic nuclei (SCN) would abolish split activity rhythms of hamsters in LL. Wheel-running activity was recorded for 3 months after surgery. Tissue damage was assessed by Klüver-Barrera staining. Damage to areas dorso-caudal to the SCN was able to abolish the split condition. Bilateral damage to the anterior SCN, partial unilateral SCN ablation or unilateral periventricular damage also abolished the split pattern. These results indicate that destruction of one SCN is not essential for the elimination of split rhythms since lesions dorsal to the SCN or partial bilateral SCN damage are also effective. Indirect lesion effects on SCN function or damage to extra-SCN oscillators may account for the loss of the split condition.

Circadian wheel-running rhythms were monitored continuously in 3 groups of female Sprague-Dawley rats under different palatable food availability schedules. All rats had free access to standard rat chow and water throughout the study. In addition, Group 1 rats received a palatable nutrient-rich mash for 2 hr each day for 28 days, beginning 3 hr after light onset of a 12:12 LD cycle. Group 2 rats received the same mash but were limited to 4 g daily. Group 3 rats received a palatable non-nutritive mash. Ten of 13 Group 1 rats, 2 of 13 Group 2 rats, and 0 of 13 Group 3 rats showed anticipatory running prior to the daily palatable meal. Palatable mash intake was generally lower among Group 3 rats than among Group 1 rats. However, several Group 3 rats consumed non-nutritive mash in amounts which equalled or exceeded the nutritive mash intake of Group 1 rats showing anticipatory running. The results indicate that temporally limited daily access to a palatable food can entrain anticipatory wheel-running in rats that are not food-deprived. They also indicate that entrainment to periodic food availability depends on stimuli associated with the concentrated intake of nutrients rather than on the absolute size or palatability of a meal.

The distributions of neuropeptide Y (NPY) and avian pancreatic polypeptide (APP) immunoreactivity were examined in the suprachiasmatic nucleus and the geniculate area of male golden hamster brains. In some cases, colchicine was injected intraventricularly to aid in visualization of immunoreactive cell bodies. A group of hamsters were given bilateral or unilateral radiofrequency lesions of the geniculate area and neuropeptide Y immunoreactivity was examined in the suprachiasmatic nucleus after survival times varying between 8 and 300 days. Another group of hamsters received unilateral intraocular injections of anterograde tracers and the overlap of NPY-immunoreactive cells in the geniculate area and labeled retinal afferents was assessed. It was found that NPY- and APP-immunoreactive fibers formed a dense plexus in the ventro-lateral suprachiasmatic nucleus. NPY-immunoreactive cell bodies were observed in the intergeniculate leaflet as well as in the external lamina of the anterior portion of the ventral lateral geniculate nucleus. Unilateral lesions of the geniculate produced a relative reduction in neuropeptide Y immunoreactivity in the ipsilateral suprachiasmatic nucleus whereas bilateral lesions produced a reduction of neuropeptide Y immunoreactivity in both suprachiasmatic nuclei. All NPY-immunoreactive cells in the intergeniculate leaflet were overlapped by bilateral retinal afferents. In the ventral lateral geniculate nucleus, all NPY-immunoreactive cells were overlapped by contralateral retinal afferents; however, not all such cells were in areas receiving ipsilateral retinal afferents. These results indicate that the hamster geniculo-suprachiasmatic tract originates in part from NPY-immunoreactive cell bodies and that these cells lie in areas receiving direct retinal afferents.

Retino-recipient cells in the hamster lateral geniculate nucleus project to the suprachiasmatic nucleus via the geniculo-hypothalamic tract (GHT). GHT-ablation alters phase advance shifts to light pulses in a hamster's late subjective night. In this study, the effects of GHT-ablation on wheel-running rhythms of hamsters housed under continuous illumination (LL) were assessed. In the first experiment, hamsters received GHT-ablation or sham surgery while under a light:dark schedule and were subsequently exposed to 250 days of LL. GHT-ablated hamsters showed rhythms with shorter periods and were less likely to show split activity rhythms than sham-operated or partial-lesion controls. In the second experiment, hamsters were housed under LL until rhythms split into two components; hamsters then received either GHT-ablation or sham surgery. Four of seven GHT-ablated hamsters showed re-fusion of their activity pattern into one component, while none of the eight sham-operated animals showed such re-fusion. The results of these two experiments indicate that GHT-ablation alters the responsiveness of the activity rhythm pacemaker to LL exposure.