Bicuculline-induced complexity reduction of spike trains in rat suprachiasmatic nucleus neurons in vitro

Abstract

The suprachiasmatic nucleus (SCN) is the master biological clock in mammals. Despite the periodic mean firing rate, interspike interval (ISI) patterns of SCN neurons are quite complex and irregular. The aim of the present study was to investigate the role of neuronal interactions on the complex ISI patterns of SCN. neurons. ISI sequences were recorded from 56 neurons in rat hypothalamic slice preparations by using a cell-attached patch recording technique. Their correlation dimensions (D-2) were estimated and were then compared with those of randomly shuffled surrogate data. To see if the neuronal. coupling mediated by the gamma-aminobutyric acid (GABA), the major neurotransmitter in the SCN, contributed to the complex nature of the spikes, we examined the effect of the GABA(A) receptor antagonist bicuculline on the D-2 values of the neurons. Most SCN neurons exhibited decreased D-2 values after bicuculline application. This result suggests that the complex nature of the SCN neurons arises from GABA(A) receptor-mediated synaptic couplings.