Effects of pinealectomy on SCN electrical firing rhythm in Djungarian hamsters.

Djungarian hamsters (Phodopus sungorus) from a long day photoperiod (16:8 h light-dark cycle) were either pinealectomized (PINX; n = 7) or sham-pinealectomized (SHAM; n = 6). One week after surgery coronal brain slices (500 microm), containing the suprachiasmatic nucleus (SCN), were prepared. The firing-rate rhythm of SCN neurons was recorded over at least a 22 h period. The amplitude of the firing rhythm for SHAM slices (3.42 +/- 0.26 Hz) was not significantly different from PINX slices (3.45 +/- 0.29 Hz). Maxima and minima of the firing rhythms also could not be distinguished statistically between PINX and SHAM groups. However, two-way ANOVA of 2 h firing-rate averages indicated a statistically significant effect of pinealectomy on the firing rhythm (P < 0.01). The results show that pinealectomy one week prior to brain slice preparation only had a minor effect on the in vitro neuronal firing rhythm in the SCN. In this study, SCN firing-rate rhythm in the Djungarian hamster is largely independent of endogenous melatonin secretion.