Daily changes in the mouse cingulate cortex responsivity to neurotransmitters and depolarizing medium: an extracellular in vitro study

1. The reaction of the mouse cingulate cortex neurons to the applied substances, measured as changes in the spontaneous activity, was investigated for daily variations in the in vitro slice preparation. 2. Glutamate- and GABA-evoked excitation and inhibition, respectively, were followed by long-lasting after-effects which showed greater potency in slices prepared in the evening. 3. Acetylcholine evoked excitation, inhibition and multiphasic effects. The incidence of an excitatory reaction prevailed in slices prepared in the evening. 4. The majority of cells studied in the evening were inhibited after application of a depolarizing medium, while in the morning the reaction was equally divided between excitation and inhibition. 5. The obtained results suggest that a day-night modulation is imposed upon the reactivity of the cingulate cortex neurons, and that daily changes in the reactivity are observed in vitro.