The hamster circadian rhythm system includes nuclei of the subcortical visual shell

Abstract

The clock regulating mammalian circadian rhythmicity resides in the suprachiasmatic nucleus. The intergeniculate leaflet, a major component of the subcortical visual system, has been shown to be essential for certain aspects of circadian rhythm regulation. We now report that midbrain visual nuclei afferent to the intergeniculate leaflet are also components of the hamster circadian rhythm system. Loss of connections between the intergeniculate leaflet and visual midbrain or neurotoxic lesions of pretectum or deep superior colliculus (but not of the superficial superior colliculus) blocked phase shifts of the circadian activity rhythm in response to a benzodiazepine injection during the subjective day. Such damage did not disturb phase response to a novel wheel stimulus. The amount of wheel running or open field locomotion were equivalent in lesioned and control groups after benzodiazepine treatment. Electrical stimulation of the deep superior colliculus, without its own effect on circadian rhythm phase, greatly attenuated light-induced phase shifts. Such stimulation was associated with increased FOS protein immunoreactivity in the suprachiasmatic nucleus. The results show that the circadian rhythm system includes the visual midbrain and distinguishes between mechanisms necessary for phase response to benzodiazepine and those for phase response to locomotion in a novel wheel. The results also refute the idea that benzodiazepine-induced phase shifts are the consequence of induced locomotion. Finally, the data provide the first indication that the visual midbrain can modulate circadian rhythm response to light. A variety of environmental stimuli may gain access to the circadian clock mechanism through subcortical nuclei projecting to the intergeniculate leaflet and, via the final common path of the geniculohypothalamic tract, from the leaflet to the suprachiasmatic nucleus.

Fig. 1.

A, GFAP-IR identifying the scar (arrows) of a representative knife-cut thalamus between the dorsomedial dorsal lateral geniculate nucleus and the lateral posterior nucleus. B, CT-β-IR identifying visual projections in the lateral geniculate region, pretectum, and tectum of a representative hamster that received a knife cut (arrows) medial to the dorsal lateral geniculate nucleus. C, GFAP-IR in a control brain. The IGL is indicated by fairly dense GFAP-IR, as are numerous blood vessels.D, Normal visual projections identified with CT-β-IR in a control animal. In both B and D, animals received bilateral intraocular injections of the tracer. Scale bar, 470 μm. APT, Anterior pretectal nucleus;CPT, commissural pretectal nucleus; DLG,dorsal lateral geniculate; IGL, intergeniculate leaflet;LP, lateral posterior nucleus; MPT,medial pretectal nucleus; NOT, nucleus of the optic tract; OPT, olivary pretectal nucleus;pc, posterior commissure; PLi, posterior limitans nucleus; Po, posterior thalamic nucleus;PPT, posterior pretectal nucleus; VLG,ventral lateral geniculate.

Fig. 2.

A, GFAP-IR in a representative brain of an animal sustaining bilateral NMDA-induced lesions of the deep superior colliculus. B, GFAP-IR in a control brain showing the dense immunoreactivity along the injection needle track (arrows). C, GFAP-IR in a representative brain of an animal sustaining bilateral NMDA-induced lesions of the superficial superior colliculus. Scale bar, 470 μm.

Fig. 3.

A, GFAP-IR in a representative brain of an animal sustaining bilateral NMDA-induced lesions of the pretectum. B, GFAP-IR in the brain of a control animal showing one of the bilateral needle tracks (arrows). Scale bar, 470 μm.

Fig. 4.

Running wheel records of typical constant dark-housed (DD) animals that sustained (A) a deep superior colliculus lesion or (B) a control surgical procedure. A phase shift to triazolam (TZ) was not shown by the lesioned animal, but was by the control animal. Neither shifted in response to either 3 hr novel wheel access (NW) or vehicle treatment (DMSO). See Results for further details.

Fig. 5.

Mean (± SEM) phase–shift responses to 5 mg triazolam at CT6 shown by of the groups sustaining knife cuts (KC), neurotoxic lesions of the deep superior colliculus (DSC), superficial superior colliculus (SSC), or pretectum (PRT) or receiving a control procedure (CON). *p < 0.01 versus controls; **p< 0.003 versus controls; ***p < 0.0001 versus controls.

Fig. 6.

Mean (± SEM) phase–shift responses to 5 hr compound stimulus (novel wheel access in a dark box; see Materials and Methods, Experiment 1, Part B, for more detail) beginning at CT6. Eachdiamond indicates the response of a single individual in the groups sustaining knife cuts (KC), neurotoxic lesions of the deep superior colliculus (DSC), superficial superior colliculus (SSC), or pretectum (PRT) or receiving a control procedure (CON). There were was a significant main effect of surgical condition, but no group differed from any other group.

Fig. 7.

Mean (± SEM) number of meters traveled by lesioned or control hamsters during a 3 hr open field test after injection with 5 mg triazolam or vehicle. There was a main effect of drug treatment and an interaction between drug and lesion type, but no between-group differences were significant (see Results). The surgical treatment groups sustained knife cuts (KC), neurotoxic lesions of the deep superior colliculus (DSC), superficial superior colliculus (SSC), or pretectum (PRT) or received a control procedure (CON).

Fig. 8.

Phase–response curves of animals with deep superior colliculus lesions (DSC) or control surgery (CON) given either triazolam or vehicle. The deep superior colliculus failed to exhibit circadian rhythm phase shifts in response to TZ or vehicle at any time tested. Control animals had a normal phase–response curve to TZ injections. See Results for the statistical analysis.

Fig. 9.

A, Mean (± SEM) phase shifts of deep superior colliculus (DSC) or control (CON)-lesioned animals administered a 5 hr compound stimulus in the dark or in the light. There was a main effect of lighting condition on phase response. B, Mean (± SEM) wheel revolutions during the 5 hr compound stimulus. There was an interaction between lesion condition and lighting.

Fig. 10.

Immunoreactive FOS protein expression in representative suprachiasmatic nuclei (SCN) of animals receiving simultaneous light exposure and electrical stimulation of the deep superior colliculus (A), light plus sham electrical stimulation (B), sham electrical stimulation and no light (C), and no light plus electrical stimulation (D). Electrical stimulation significantly augmented expression of FOS-IR.SOX, Supraoptic commissures; 3, third ventricle.