THE SEROTONIN INHIBITION OF HIGH-VOLTAGE-ACTIVATED CALCIUM CURRENTS IS RELIEVED BY ACTION POTENTIAL-LIKE DEPOLARIZATIONS IN DISSOCIATED CHOLINERGIC NUCLEUS BASALIS NEURONS OF THE GUINEA-PIG

The aim of the present study was to investigate whether the voltage-de pendent inhibition of calcium currents by serotonin 5-HT1A agonists ca n be alleviated (facilitated) by action potential-like depolarizations . In dissociated cholinergic basal forebrain neurons using whole-cell recordings, it is shown that a selective serotonin 5-HT1A agonist (8-O H-DPAT) predominantly blocks N-type HVA calcium current, although a mi nor reduction of P-type current was also observed. The inhibition may principally occur through G(i)-G(o) subtypes of G-proteins because it was prevented by N-ethylmaleimide, a substance known to block specific ally pertussis-sensitive G-proteins. The inhibitory effect of 8-OH-DPA T on calcium currents is voltage-dependent because it was alleviated b y longlasting depolarizing prepulses. Interestingly, the inhibition co uld also be reversed by prepulses made-up of action potential-like dep olarizations that were given at a frequency of 200 Hz. This observatio n may have important implications during periods of high-frequency rhy thmic bursts, a firing pattern that is prevalent in cholinergic basal forebrain neurons.