An in vitro circadian rhythm of melatonin sensitivity in the suprachiasmatic nucleus of the djungarian hamster, Phodopus sungorus.
Past studies in the rat and Syrian hamster show that metabolic and electrical activity of the suprachiasmatic nuclei (SCN) is inhibited by melatonin (MEL) at about circadian time (ct) 8-11 h. The present experiment examined the effect of MEL on the firing frequency of SCN cells in brain slices prepared from long day (LD 16:8) Djungarian hamsters to determine the timing of MEL sensitivity and if sensitivity persists in vitro. Pressure ejection of MEL (2 mM in 165 mM NaCl) suppressed the firing rate of 26% of SCN neurons recorded, excited 13%, and had no effect on 61% of the 161 cells tested. MEL elicited the highest percent response (64%) during the 4-h time bin immediately preceding the dark phase of the projected light:dark cycle on day 1 (ct 8-12 h). A similar temporal pattern of MEL sensitivity was found during the second day of recording. In contrast, application of vehicle to 52 SCN cells had little effect on firing rate. These results demonstrate that a sensitivity rhythm to MEL is present in the SCN of the Djungarian hamster and persists with a period of about 24 h in vitro.
Department of Biology, Wesleyan University, Middletown, CT 06459.
R R
RR
Margraf
G R
GR
Lynch
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008550:Melatonin / Q000494:pharmacology*; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D017111:Phodopus; D017440:Photoperiod; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
D008550:Melatonin