Inhibition of synaptic transmission and epileptiform activity in central neurones by fluspirilene

1. Recent studies have shown that fluspirilene, a dopamine D₂ receptor antagonist which is a long-acting neuroleptic useful in the maintenance therapy of schizophrenic patients, also displays Ca²⁺ channel blocking activity. In the present study, we have investigated the effect of fluspirilene on synaptic transmission and epileptiform activity induced in slices of hippocampus and amygdala.
2. Fluspirilene reversibly suppressed the field excitatory postsynaptic potential (f-e.p.s.p) in a concentration-dependent manner in the area CAl of the hippocampus without affecting the size and shape of fibre volley. Fluspirilene also inhibited the intracellularly recorded e.p.s.p. in amygdala neurones without affecting the resting membrane potential or neuronal input resistance.
3. Fluspirilene increased the ratio of paired-pulse facilitation suggesting a presynaptic mode of action.
4. Epileptiform activity induced in the disinhibited slices was suppessed by fluspirilene in a concentration-dependent manner. This antiepileptic effect was occluded in slices pretreated with the adenosine A₁ receptor agonist, N⁶-cyclopentyladenosine (CPA).
5. It is concluded that fluspirilene-induced synaptic inhibition is probably due to a reduction in presynaptic Ca²⁺ currents. In clinical trials, the low incidence of seizures provoked by fluspirilene might be related to its intrinsic ability to inhibit synaptic transmission and epileptiform activity.