Spontaneous synaptic transmission in dissociated Meynert neurons with the attached synaptic boutons

1. Neurons acutely dissociated from the nucleus basalis of Meynert of adult rats showed spontaneous currents with rapid onset and slow decay under the whole-cell patch-clamp recording. 2. The current had the reversal potential close to the theoretical Cl- equilibrium potential (ECl) and was suppressed by 2 x 10(-6) M bicuculline and 3 x 10(-6) M strychnine. 3. The spontaneous current was suppressed reversibly in the Ca(2+)-free solution containing either EGTA or BAPTA (5 mM). The enhancement of the frequency and amplitude of the current was observed with elevated extracellular K+ concentration, which was also suppressed in the presence of the Ca(2+)-free solution. 4. Nicardipine, a blocker of voltage-dependent Ca2+ channels, had an inhibitory effect as well. 5. A selective GABAB agonist, baclofen, blocked the spontaneous current, whereas a selective antagonist, phaclofen, potently enhanced the current. 6. It is concluded that the observed spontaneous current was a spontaneous inhibitory postsynaptic current (IPSC) due to the release of GABA from the attached synaptic boutons. The release was suppressed by a GABAB receptor activation, indicating that the GABAB receptor regulates the release of GABA from nerve terminals and acts as a negative autoreceptor.