The reciprocal synaptic relations between enkephalinergic neurons and catecholaminergic neurons in the area postrema

A preembedding double immunostaining technique using antibodies against methionine-enkephalin and tyrosine hydroxylase was used to study synaptic relations between enkephalinergic and catecholaminergic neurons in the area postrema of the rat at the electron microscopic level. The large nuclei-containing cell bodies of the catecholaminergic neurons displayed well-developed Golgi apparatus. The catecholaminergic somata and dendrites received synapses from ankephalinergic axon terminals, and most of the synapses were symmetrical. Occasionally, the catecholaminergic axon terminals were also found to be presynaptic to the enkephalinergic dendrites. Because the enkephalinergic neurons have been reported to be involved in cardiovascular function and the catecholaminergic neurons involved in the vomiting behavior, the synapses observed in this study may provide morphological evidence of the relationship between the vomiting and cardiovascular functions that are triggered in the area postrema.