Hamster Wheel-running Activity Research Articles

Illuminating serotonergic gateways for strong resetting of the mammalian circadian clock

circadian clocks regulate animal behavior and physiology by generating daily rhythms and coordinating these with local time. If you sleep well and abstain from flying around the globe or working rotating shift schedules, this pervasive influence is easy to take for granted, a background rhythm of

MDMA alters the response of the mammalian circadian clock in hamsters: Effects on re-entrainment and triazolam-induced phase shifts

Serotonin (5-hydroxytryptamine or 5-HT) is a neurotransmitter that is involved in a wide range of behavioural and physiological processes. Previous work has indicated that serotonin is important in the regulation of the circadian clock, which is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. 3,4-methylenedioxymethamphetamine (MDMA or ‘Ecstasy’), which is widely used as a recreational drug of abuse, is a serotonin neurotoxin in animals and non-human primates. Previous work has shown that MDMA exposure can alter circadian clock function both in vitro and in vivo. Evidence shows that 5-HT may have a modulatory role in the regulation of the circadian clock by non-photic stimuli, such as the benzodiazepine triazolam (TRZ). Triazolam is a short-acting benzodiazepine that results in phase advances of the wheel running activity in hamsters when administered during the mid-subjective day. In the present study, male Syrian hamsters treated with TRZ (5 mg/kg) at ZT6 significantly phase advanced their clock. Treatment with MDMA significantly diminished the TRZ induced phase shift in hamsters. Previous evidence shows the involvement of 5-HT in the re-synchronisation of the endogenous clock to a new shifted light–dark cycle. Untreated animals were successfully entrained to a new, 6 h advanced light–dark cycle within an average of 4.5 ± 0.1 days. Following treatment with MDMA, these animals took an average of 8.3 ± 0.1 days to re-entrain to a shifted environmental cycle. Immunohistochemical analysis revealed that animals treated with MDMA showed reduced serotonin staining, as evidenced by a decrease in innervation density in the SCN. No significant differences were found in cell counts within the raphe nuclei. These results demonstrate the importance of the serotonergic system in the modulation of photic and non-photic responses of the circadian pacemaker.

Effects of the 5HT1A agonist/antagonist BMY 7378 on light-induced phase advances in hamster circadian activity rhythms during aging.

The entrainment of some circadian rhythms in rodents and humans to the environmental light-dark cycle deteriorates during aging. Recent evidence suggests that the time-keeping ability of the circadian pacemaker maintains its endogenous period in both hamsters and humans. This suggests that any changes in the coupling between environmental cues and the circadian pacemaker are not due to changes in "clock speed," but rather due to a weakened coupling between the afferent systems relaying environmental information and the circadian pacemaker located in the suprachiasmatic nucleus. The suprachiasmatic nucleus receives serotonergic input from the raphe nuclei, and serotonergic 5HT1A,7 agonists have been reported to lose their circadian phase-adjusting efficacy during aging in hamsters. In the present study, the authors report the effects of a novel serotonergic agonist BMY 7378 on light-induced phase advances during aging in the hamster. The present report demonstrates that BMY 7378 is a highly efficacious chronobiotic that more than doubles the magnitude of light-induced phase shifts in hamster wheel-running activity rhythms. Light-induced phase advances in hamster wheel-running activity of at least 6 h following a single systemic dose of BMY 7378 are routinely observed. Furthermore, BMY 7378 potentiation of phase shifts is maintained in old hamsters, suggesting that BMY 7378 has a different site of activity than previously reported 5HT1A,7 agonists that have a diminished effect on circadian phase during aging.

Opioid induced non-photic phase shifts of hamster circadian activity rhythms

The phase of the circadian pacemaker in hamsters can be shifted by the application of certain non-photic stimuli late in the subjective day. A projection from the intergeniculate leaflet of the thalamus to the circadian pacemaker in the suprachiasmatic nucleus is believed to mediate some types of non-photic phase-shifting stimuli. In hamsters, this projection is immunoreactive to both Neuropeptide Y and enkephalin. Previous work in other laboratories has shown that Neuropeptide Y administration is capable of phase shifting circadian rhythms without the application of light. The present study was undertaken to determine if enkephalinergic compounds likewise have the ability to non-photically phase shift hamster activity rhythms. Hamsters were maintained under conditions of constant darkness and circadian wheel running activity was recorded. Agonists and antagonists selective for κ, μ, and δ opioid receptors were systemically applied without light to hamsters at circadian times 8 and 10 to determine if they were able to elicit phase shifts in wheel running activity rhythms. Of the compounds tested, only the delta opioid agonist BW373U86 significantly affected circadian phase. BW373U86 phase advanced hamster wheel running activity rhythms by approximately 45 min, although total activity levels following drug application were not significantly affected. Changes in the amount of wheel running activity were detected after administration of some μ and κ opioids, although the circadian phase was not altered. These results indicate that enkephalin-mimetic δ opioid agonists are capable of producing non-photic phase shifts in hamster activity rhythms, and that opioids can independently affect circadian phase and activity levels in hamsters.

SNC 80, a delta-opioid agonist, elicits phase advances in hamster circadian activity rhythms.

Non-photic stimuli administered to hamsters during the subjective day can cause phase advances in circadian wheel running activity. It is believed that afferent projections from the intergeniculate leaflet of the thalamus to circadian pacemaker cells within the suprachiasmatic nucleus mediate the phase shifting effects of some non-photic stimuli. In hamsters, many of the intergeniculate leaflet afferents contain enkephalin, yet the role of opioids in producing non-photic phase shifts in hamsters has not been reported. In the present study, we show that SNC 80, an agonist for the delta opioid receptor subtype, will phase advance hamster wheel running activity rhythms when administered late in the subjective day. These results indicate that opioids may be involved in modulating the circadian pacemaker in hamsters.

Pituitary adenylyl cyclase-activating peptide: a pivotal modulator of glutamatergic regulation of the suprachiasmatic circadian clock.

The circadian clock in the suprachiasmatic nucleus (SCN) of the hypothalamus organizes behavioral rhythms, such as the sleep-wake cycle, on a near 24-h time base and synchronizes them to environmental day and night. Light information is transmitted to the SCN by direct retinal projections via the retinohypothalamic tract (RHT). Both glutamate (Glu) and pituitary adenylyl cyclase-activating peptide (PACAP) are localized within the RHT. Whereas Glu is an established mediator of light entrainment, the role of PACAP is unknown. To understand the functional significance of this colocalization, we assessed the effects of nocturnal Glu and PACAP on phasing of the circadian rhythm of neuronal firing in slices of rat SCN. When coadministered, PACAP blocked the phase advance normally induced by Glu during late night. Surprisingly, blocking PACAP neurotransmission, with either PACAP6-38, a specific PACAP receptor antagonist, or anti-PACAP antibodies, augmented the Glu-induced phase advance. Blocking PACAP in vivo also potentiated the light-induced phase advance of the rhythm of hamster wheel-running activity. Conversely, PACAP enhanced the Glu-induced delay in the early night, whereas PACAP6-38 inhibited it. These results reveal that PACAP is a significant component of the Glu-mediated light-entrainment pathway. When Glu activates the system, PACAP receptor-mediated processes can provide gain control that generates graded phase shifts. The relative strengths of the Glu and PACAP signals together may encode the amplitude of adaptive circadian behavioral responses to the natural range of intensities of nocturnal light.

Quantitative analysis of the age-related fragmentation of hamster 24-h activity rhythms.

The continuous monitoring of spontaneous locomotor activity has emerged as one of the most widely used metrics in rodent circadian research. This behavioral measure is also extremely useful for the description of the effects of aging on circadian rhythms. The present study describes the successful use of a log-survivorship approach to identify discrete bouts of hamster wheel-running activity and provides a detailed description of the age-related fragmentation in the 24-h profile of this behavioral variable. In addition, stepwise discriminant analysis identified the most important quantitative measures for distinguishing between the individual patterns of wheel-running activity of young (3 mo) and old (17-18 mo) golden hamsters. The results suggest that this method of bout analysis can be a valuable tool for the study of genetic, developmental, neurochemical, physiological, and environmental factors involved in the temporal control of rodent locomotor behavior.

Effect of a nitric oxide synthase inhibitor, N-nitro- l-arginine methylester, on light-induced phase delay of circadian rhythm of wheel-running activity in golden hamsters

Under constant darkness hamsters demonstrate free-running activity rhythms and light exposure during the early subjective night results in permanent phase delays of the activity rhythm. Recently, we reported that application of glutamate receptor agonists such as N-methyl- d-aspartate could reset the phase of the circadian rhythm of suprachiasmatic nucleus firing activity in vitro via nitric oxide production. In order to confirm this result by in vivo experiment, we examined the effect of nitric oxide synthesis inhibitor on the light-induced phase delay of circadian rhythms of wheel-running activity in hamsters. In vehicle-treated animals, light stimulation at circadian time 13.5 resulted in stable phase delays (1.3 ± 0.63 h), whereas pre-treatment with 150 mg/kg of N-nitro- l-arginine methylester ( l-NAME) significantly attenuated light-induced phase delays (0.72 ± 0.18 h). l-NAME administration alone without light exposure, did not cause phase changes. The l-NAME-induced attenuating effect was reversed by co-administration of l-arginine (300 mg/kg). The present results suggest that nitric oxide production is involved in the light-induced phase delay of the hamster's circadian system.

Effects of the 5-HT 1a receptor agonist 8-OH-DPAT and other non-photic stimuli on the circadian rhythm of wheel-running activity in hamsters under different constant conditions

Our findings show that administration of the 5-HT 1A receptor agonist 8-OH-DPAT (8-hydroxy-2[di- n-propylamino] tetralin) was able to induce significant phase-advances 4 h before onset of hamster locomotor activity under constant darkness. All other non-photic treatments applied such as melatonin, dimethyl sulphoxide, Ringer, saline or enforced wheel-running failed to induce any significant phase-advances. Similar results were obtained in pinealectomized animals. In constant light (LL), all treatments produced phase-advances. These results show that: (1) LL seems to be an inappropriate constant condition to study the chronobiological effect of drugs or other non-photic stimuli; (2) the endogenous circadian pacemaker (SCN) can be affected specifically by 8-OH-DPAT.

Phase-resetting efect of 8-OH-DPAT, a serotonin 1A receptor agonist, on the circadian rhythm of firing rate in the rat suprachiasmatic nuclei in vitro

The 5-HTergic neurons in the mesencephalic raphe nuclei provide a robust projection to the hypothalamic suprachiasmatic nucleus (SCN), the site of a putative neuronal circadian pacemaker. Although it has been suggested that 5-HT neurons may play a role in the circadian timing system, this role has not yet been specified. Prosser et al. ( Brain Res., 534 (1990) 336–339) reported that 1 h treatments with quipazine induce robust phase shifts in vitro, and that this effect depends upon the circadian time of treatment. However, quipazine is a non-specific 5-HT agonist. Besides, it is reported that the 5-HT 1A agonist,8-hydroxy-2-(di- n-propylamino)tetraline hydrobromide (8-OH-DPAT) affected a circadian rhythm of hamster wheel-running activity. In the present study we investigated whether the 5-HT 1A agonist 8-OH-DPAT can reset the phase of the SCN clock when it is isolated in vitro. The present results show that 1 h treatments with 8-OH-DPAT induce robust phase advances in vitro when it was administered during the subjective day. This result suggests that 5HT 1A receptor functioning may play a role in modulating the phase of SCN clock, especially during the subjective day.

Effects of 5-HT 1A receptor agonists on the circadian rhythm of wheel-running activity in hamsters

The effects of 5-HT 1A receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), buspirone and ipsapirone on wheel-running activity in hamsters were investigated in comparison with those of GABA A receptor agonist muscimol and benzodiazepine triazolam. Intraperitoneal administration of 8-OH-DPAT, buspirone, ipsapirone, muscimol and triazolam at circadian time (CT) 8 (CT 12; onset of activity) induced a significant phase advance of wheel-running activity under constant light conditions. However, administration of these drugs at other CT points did not induce phase changes. The administration of trifluoromethylphenylpiperazine (TFMPP), a 5-HT 1B receptor agonist, at CT8 produced a small phase advance. The phase advance induced by 8-OH-DPAT was blocked by pretreatment with (−)-pindolol, a 5-HT 1A receptor antagonist. In addition, 8-OH-DPAT, buspirone and SM3997 accelerated the rate of re-entrainment to an 8-h phase advance in the light-dark cycle. These observations suggest that 5-HT 1A receptors in the brain participate in the regulation of the circadian rhythm of wheel-running activity in hamsters.

Olfactory bulbectomy lengthens circadian period of locomotor activity in golden hamsters

Removal of the olfactory bulbs (BX) of rats or mice lengthens the circadian period of locomotor activity. In golden hamsters, BX elevates serum gonadotropin levels of hamsters maintained in long or short photoperiod and prevents the testicular regression associated with short days without altering the secretion or action of pineal melatonin. The present study examined the influence of BX on circadian wheel-running activity in hamsters and tested whether this effect was related to changes in serum testosterone levels. BX lengthened the free-running period of locomotor activity in gonadally intact hamsters by a mean of 21.0 min, and BX had a similar effect in orchidectomized animals with or without testosterone replacement. These results suggest that the olfactory bulbs normally tend to increase the frequency of the hamster's circadian oscillator and that this effect is unrelated to altering gonadal steroid levels.

Phase shifting the circadian clock with cycloheximide: response of hamster with an intact or a split rhythm of locomotor activity

Systematic administration of the protein synthesis inhibitor, cycloheximide, induced both phase advances and phase delays in the circadian rhythm of wheel-running activity in hamsters ( Mesocricetus auratus) maintained in constant darkness or constant light. The magnitude and direction of the phase shifts were dependent on the circadian time (CT) of drug treatment. The phase response curves in constant darkness and constant light were of similar general shape, but they differed in the overall mean amplitude of the phase shifts. Maximal phase advances were observed after injections around CT 6–8, maximal delays at CT 0–2. Injections of various doses of cycloheximide at CT 0 induced a dose-dependent phase delay in the rhythm with a maximum delay induced by 10 mg cycloheximide. Injections of cycloheximide in animals with a split activity rhythm caused phase shifts of both components in the same direction (20/39) and in different directions (10/39). The results support the hypothesis that 80S ribosomal protein synthesis plays an important role in the biochemical mechanisms of circadian systems.

Entrainment of the circadian rhythm of wheel-running activity is phase shifted by ablation of the intergeniculate leaflet

The phase angle of entrainment of golden hamster wheel-running activity was determined before and after bilateral destruction of the intergeniculate leaflet (IGL). Animals were maintained under continuous dim light which rhythmically varied in intensity (10-5 lux) in the form of a sine wave with a 24 h period. The phase angle of entrainment changed significantly following IGL ablation suggesting a role for the IGL in entrainment.