The Anterior Paraventricular Thalamus Modulates Light- Induced Phase Shifts in Circadian Rhythmicity in Rats

SUMMARY The reciprocal connections between the paraventricular thalamic nucleus (PVT) and the suprachiasmatic nuclei suggest that PVT may participate in the regulation of circadian rhythms. We studied in rats the effect of lesions of the anterior and mid-posterior regions of the PVT on phase shifts of drinking circadian rhythm induced by light pulses at circadian times 6, 12 and 23, as well as the phase shifts produced by electrical or glutamatergic stimulation of the anterior PVT at the same circadian times. Lesion of the anterior PVT abolishes the advances induced by light during late subjective night, while mid-posterior PVT lesions did not affect the phase shifts. Electrical stimulation or glutamate injections in the anterior PVT mimic the phase shifting effects of light pulses. These results indicate the participation of the anterior PVT as a modulator of entrainment of circadian rhythms to light.