Neurophysiological Analysis of Circadian Rhythm Entrainment
Annual technical rept. 1 Jun-31 Dec 93,
DALHOUSIE UNIV HALIFAX (NOVA SCOTIA) DEPT OF PSYCHOLOGY
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Loss of melatonin secretion in hamsters can alter the rhythm of melatonin sensitivity in the suprachiasmatic nuclei SCN as tested in an in- vitro slice preparation. The effect on melatonin sensitivity depended on whether pinealectomy or brief constant light exposure was used to reduce melatonin levels, with constant light increasing sensitivity and pinealectomy decreasing it. The same treatments also eliminated or reduced the amplitude of the firing- rate rhythms monitored in the SCN slice preparation. These results imply a role for pineal melatonin in the maintenance of the normal amplitude of the SCN pacemakers output rhythms. Serotonin and melatonin were determined to suppress photic responses of SCN cells and intergeniculate leaflet cells studied in vivo. Serotonin appears to act at both targets via a receptor that is similar to the serotonin-1A receptor type, while melatonin acts via a non-serotonergic receptor. Gastrin-releasing peptide GRP causes increased firing of about 50 of SCN cells tested in a slice preparation the proportion of responsive cells depends on the circadian phase tested. GRB injected into the SCN in vivo causes phase-dependent phase shifts that resemble those caused by light pulses.
- Anatomy and Physiology