In a cultured network of rat embryonic hypothalamic cells, synaptic interaction is through GABAA-receptors, that mediate inhibition by an increase in Cl' conductance, and AMPA-receptors, that mediate excitation by an increase in monovalent cationic conductance. Changes in the balance of inhibition and excitation towards a predominance of excitation lead to phasic synchronous activity of the cells. Synaptic interaction through these receptors is thus capable of modulating neurosecretion rapidly.