Cholecystokinin-octapeptide enhances synaptic activity in neurons cultured from rat cerebral cortex

Cholecystokinin-octapeptide (CCK-8) was applied by local microperfusion techniques to neurons cultured from fetal rat cerebral cortex while membrane properties and synaptic activity were monitored with intracellular recording techniques. There were no consistent effects of CCK-8 on resting membrane potential, membrane input resistance, or excitability of the recorded neuron. Nevertheless, the application of CCK-8 was associated both with an increase in the frequency of ongoing synaptic activity and with an initiation of new synaptic activity not seen during control periods of recording prior to peptide application. CCK-8 was more potent evoking increased synaptic activity than its non-sulfated CCK-8 analogue. The existence of areas in proximity to the recorded neuron which were particularly sensitive to the effect of CCK-8 was noted. These results suggest that CCK-8 has a predominantly excitatory effect on cerebral cortical neurons. While a mechanism cannot be determined from the present data, a presynaptic site of action is suggested.