Tetrodotoxin does not affect circadian rhythms in neuronal activity and metabolism in rodent suprachiasmatic nucleus in vitro

Single unit activity of suprachiasmatic nucleus (SCN) neurons recorded from hamster and rat hypothalamic slices in vitro exhibits a circadian rhythm in firing rate. Tetrodotoxin (TTX) produces electrical silence during the period of administration but has no effect on the oscillatory activity of the circadian pacemaker in both hamster and rat SCN. TTX does not affect either the phase of the rhythm in firing rate at any time of the circadian day, or that of the rhythm in glucose metabolism as demonstrated by the 2-deoxyglucose method. These data are in accord with the view that SCN neuron firing rate and glucose utilization is an expression of pacemaker activity but that pacemaker function is maintained in the SCN independent of neuronal function manifested by sodium dependent action potentials.