Reciprocal synaptic relations between enkephalinergic and GABAergic neurons in the area postrema of the rat

A preembedding, double immunostaining technique was used to study synaptic relations between enkephalinergic and GABAergic neurons in the area postrema of the rat. As a main result, the enkephalinergic dendrites received many synapses from GABAergic axon terminals, and most of the synapses were symmetrical. Enkephalinergic neuronal perikarya received a few synapses from GABAergic axon terminals, and a few enkephalinergic axon terminals were found presynaptic to GABAergic neurons. Synapses between enkephalinergic profiles were frequent, but no axo-axonic synapses were seen. These findings suggest that GABAergic innervation of enkephalinergic neurons is the main relation between the two kinds of neurons in the area postrema. The synapses between the enkephalinergic axon terminals and GABAergic neurons might be explained as being part of the local servo system of the area postrema.