Phase Shifts Of Activity Rhythms Research Articles

Scheduled feeding improves behavioral outcomes and reduces inflammation in a mouse model of Fragile X syndrome.

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by the abnormal expansion of CGG repeats in the fragile X mental retardation 1 (FMR1) gene. Many FXS patients experience sleep disruptions, and we sought to explore these symptoms along with the possible benefits of a scheduled feeding intervention using the Fmr1 knockout (KO) mouse model. These mutants displayed clear evidence for sleep and circadian disturbances including delay in the onset of sleep and fragmented activity rhythms with increases in cycle-to-cycle variability. Importantly, the Fmr1 KO mice exhibited deficits in their circadian behavioral response to light with reduced masking, longer time to resetting to shifts in the Light-Dark cycle, altered synchronization to a skeleton photoperiod and lower magnitude light-induced phase shifts of activity rhythms. Investigation of the retinal input to the surprachiasmatic nucleus (SCN) with the neurotracer cholera toxin (β subunit) and quantification of the light-evoked cFos expression in the SCN revealed an abnormal retinal innervation of the SCN in the Fmr1 KO, providing a possible mechanistic explanation for the observed behavioral deficits. Interestingly, disruptions in social and repetitive behaviors correlated with sleep duration and fragmentation. Understanding the nature of the deficits, we decided to apply a scheduled feeding regimen (6-hr/18-hr feed/fast cycle) as a circadian-based strategy to boast circadian rhythms independently of light. This intervention significantly improved the activity rhythms and sleep in the mutants. Strikingly, the scheduled feeding ameliorated social interactions and reduced repetitive behaviors as well as the levels of Interferon-gamma and Interleukin-12 in the Fmr1 KO mutants, suggesting that timed eating may be an effective way to lessen inflammation. Collectively, this work adds support to efforts to develop circadian based interventions to help with symptoms of neurodevelopmental disorders.

Circadian Rhythm and Leptin Hormone Responses to Nutritional Restriction in Gerbils (Meriones unguiculatus) with Suprachiasmatic Nucleus Lesions

Rhythmically-regulated feeding behavior is in harmony with physiologic and metabolic activities in mammals. This rhythmic regulation is orchestrated by Suprachiasmatic Nucleus (SCN). However, it is not entirely clear how the SCN, which generates endogenous (internal) rhythms, influences body weight and serum leptin profile with activity rhythms in relation to feeding timing. In this study, animals in long photoperiod (14L:10D) were divided into two groups as control (sham-SCNx) and SCN lesions (SCNx). Then, these groups were split into four separate subgroups: a) ad libitum feeding; b) feeding only during the dark phase; c) feeding only during the light phase; and d) feeding during a specific period of the day (11:00-14:00 h). Locomotor activity and leptin hormone changes were observed in animals fed in cages attached to activity wheels for one month. Under the conditions of food restriction, the locomotor activities of the groups with SCNx and sham-SCNx demonstrated a phase shift toward the time of feeding. Serum leptin level did not change with feeding conditions but decreased in lesioned groups (SCNx). In conclusion, nutritional restriction caused phase shifts in activity rhythms and it was found that the SCN in gerbils was in charge of these rhythmic changes in the presence and absence of nutrients.

Phase-resetting response to (+)8-OH-DPAT, a serotonin 1A/7 receptor agonist, in the mouse in vivo

Several lines of evidence indicate that 5-HT neuronal systems may play a critical role for the non-photic entrainment of the rodent circadian clock. Although it is well established that (+)8-hydroxy-2-(di- n-propylamino)tetralin [(+)8-OH-DPAT], a 5-HT 1A/7 receptor agonist, causes a phase-advance of behavioral rhythm in hamsters, little is known whether this agent produces phase shifts of activity rhythm in mice. Therefore, we examined the effect of (+)8-OH-DPAT on the mouse locomotor activity rhythm. Systemic administration of this chemical at mid-subjective daytime induced a clear and dose-dependent phase advance, while there were no significant phase shifts at other times (early-subjective day, late-subjective day, or subjective night). Additionally, (+)8-OH-DPAT accelerated the re-entrainment of mouse behavioral rhythm to a 6-h advanced light–dark cycle. These results suggest that we can use mice for understanding the molecular mechanism of (+)8-OH-DPAT-induced phase shift because of availability of clock gene targeted mice.

Differential effects of glutamatergic blockade on circadian and photic regulation of gene expression in the hamster suprachiasmatic nucleus

Nocturnal light exposure induces immediate-early gene (IEG) expression in the hypothalamic suprachiasmatic nucleus (SCN) and causes phase shifts of activity rhythms in mammals. Some IEGs also show a circadian rhythm of expression in the SCN. While excitatory amino acids (EAAs) are known to be involved in mediating photic regulation of entrainment and gene expression, their involvement in spontaneous rhythms of gene expression has not been studied. We assessed the role of NMDA receptors in the expression of NGFI-A, junB and fosB mRNAs induced by light pulses of different intensities late in the night (Zeitgeber Time [ZT] 18). We also examined the spontaneous expression of junB mRNA near subjective dawn (ZT 0). Both dim (5 lx) and bright (100 lx) light pulses induced similar levels of expression of NGFI-A and junB in the SCN late in the night. fosB mRNA was strongly induced by bright light but was less sensitive to dim light. At ZT 18, dizocilpine (MK-801) (3 mg/kg, i.p.), a non-competitive NMDA receptor antagonist, almost completely blocked light-evoked expression of IEG mRNAs in the ventral SCN but not in the dorsolateral region at a mid-caudal level using either light intensity. At ZT 0, MK-801 strongly reduced light-evoked expression of junB mRNA in both SCN subdivisions, but inhibited spontaneous expression significantly only in the dorsal region. NMDA receptors appear to play an important role in mediating photic input regulating IEG expression only in the ventral SCN at night. At dawn, however, NMDA receptors are involved in mediating photic effects in both parts of the SCN, as well as being involved in spontaneous activation of junB expression selectively in the dorsal SCN. These findings support the idea that the effects in the dorsolateral SCN of nocturnal light exposure are mediated by different mechanisms than those in other portions of the nucleus.

Distribution of ionotropic glutamate receptor subunit immunoreactivity in the suprachiasmatic nucleus and intergeniculate leaflet of the hamster

Glutamate is thought to mediate the effects of light on the circadian pacemaker contained in the suprachiasmatic nucleus. Glutamate can reset this pacemaker both in vivo and in vitro while glutamate antagonists can reduce photically induced phase shifts in activity rhythms and c-fos expression in the suprachiasmatic nucleus. Most behavioural and gene expression experiments investigating circadian rhythms use hamsters, but the majority of the anatomical data on the presence and distribution of selected glutamate receptor subunits in the suprachiasmatic nucleus has been collected from rat. In the present study, we examined the distribution of ionotropic glutamate receptor subunits in the hamster suprachiasmatic nucleus using mono- and polyclonal antibodies directed against these subunits. In addition, we examined the distribution of immunostaining for these subunits in a second structure of the mammalian circadian system, the intergeniculate leaflet of the thalamus since it also is thought to receive glutamatergic input from the retina and is important in the entrainment of circadian rhythms. The results indicated that all of the subunits investigated (GluR1, GluR2/3, GluR4, GluR5/6/7, and NMDAR1) were present in the suprachiasmatic nucleus and that all but GluR4 were present in the intergeniculate leaflet. Each of the subunits investigated had a unique pattern of distribution and intensity of staining. The distribution of immunoreactivity for these subunits in the hamster suprachiasmatic nucleus and intergeniculate leaflet differed from that reported in the rat. The presence of these subunits in the suprachiasmatic nucleus and intergeniculate leaflet implies the presence of functional NMDA and non-NMDA receptors in these structures that may have a role in photic entrainment of the circadian pacemaker.

Distribution of NADPH-diaphorase staining and light-induced Fos expression in the rat suprachiasmatic nucleus region supports a role for nitric oxide in the circadian system.

Nitric oxide serves as a messenger molecule in some neuronal systems that use glutamate as a transmitter and it has been shown that glutamate mediates the transmission of photic signals by retinal ganglion cell axons terminating in the hypothalamic suprachiasmatic nucleus, site of the circadian pacemaker in rodents. Recent experiments have demonstrated that pharmacological treatments which block nitric oxide synthesis by nitric oxide synthase prevent glutamate-induced phase shifts of the cell firing rhythm in suprachiasmatic nucleus slice preparation in vitro; similar treatments were found to inhibit light transmission to the suprachiasmatic nucleus as well as light-induced phase shifts in activity rhythms in vivo, implicating nitric oxide in circadian light signalling in vivo. There is limited information, however, about the presence and function of nitric oxide synthase-containing neurons within retinorecipient regions of the rodent suprachiasmatic nucleus. In the present study we used NADPH-diaphorase histochemistry and immunostaining for the nuclear phosphoprotein Fos to assess the co-distribution of nitric oxide synthase-containing neurons and light-responsive cells in the rat suprachiasmatic nucleus region. A strong convergence between NADPH-diaphorase-stained cell bodies and fibres and cells that expressed Fos in response to photic stimulation was noted in the anterior periventricular nucleus, suprachiasmatic preoptic nucleus, retrochiasmatic area, the inter-suprachiasmatic nucleus region, and the dorsal aspect of the optic chiasm, below the suprachiasmatic nucleus. A similar convergence between NADPH-diaphorase-stained fibres and Fos-immunoreactive cells was noted inside the suprachiasmatic nucleus, but the number of NADPH-diaphorase-stained elements found in this region was substantially low compared with that found in retinorecipient regions bordering the nucleus. In many cases both inside and outside the suprachiasmatic nucleus, the Fos-immunoreactive cells appeared to make direct contact with NADPH-diaphorase-stained cells or fibres, but no co-localization of Fos immunoreactivity and NADPH-diaphorase histochemical activity within individual cells was detected. Extensive co-distribution of NADPH-diaphorase-stained cells and fibres and cells that express Fos in response to photic stimulation in the suprachiasmatic nucleus region is in line with the hypothesis that nitric oxide participates in the mechanism mediating circadian light signalling in the suprachiasmatic nucleus. However, lack of co-localization of the two markers to individual cells rules out the possibility that retinorecipient cells in the suprachiasmatic region synthesize and release nitric oxide when photically-activated. Instead, the results support the possibility that photic stimulation triggers nitric oxide synthesis in nitric oxide synthase-containing neurons located near the photically-activated cells.

Central administration of muscimol phase-shifts the mammalian circadian clock.

The suprachiasmatic nucleus (SCN) of the hypothalamus contains a neural oscillatory system which regulates many circadian rhythms in mammals. Immunohistochemical evidence indicates that a relatively high density of GABAergic neurons exist in the suprachiasmatic region. Since intraperitoneal injections of the benzodiazepine, triazolam, have been shown to induce phase shifts in the free-running circadian rhythm of locomotor activity in the golden hamster, the extent to which microinjections of muscimol, a specific agonist for gamma-aminobutyric acid (GABA), may cause phase-shifts in hamster activity rhythms was investigated. Stereotaxically implanted guide cannulae aimed at the region of the SCN were used to deliver repeated microinjections in individual animals. A phase-response curve (PRC) generated from microinjections of muscimol revealed that the magnitude and direction of permanent phase-shifts in the activity rhythm were associated with the time of administration. The PRC generated for muscimol was characterized by maximal phase-advances induced 6 h before activity onset and by maximal phase-delays which occurred 6 h after activity onset. The PRC for muscimol had a shape similar to a PRC previously generated for the short-acting benzodiazepine, triazolam. Single microinjections of different doses of muscimol given 6 h before activity onset induced phase-advances in a dose-dependent fashion. Histological analysis revealed that phase shifts induced by the administration of muscimol were associated with the proximity of the injection site to the SCN area. These data indicate that a GABAergic system may exist within the suprachiasmatic region as part of a central biological clock responsible for the regulation of the circadian rhythm of locomotor activity in the golden hamster.