GABAergic synaptic innervation of catecholaminergic neurons in the area postrema of the rat

Immunoelectron microscopy using the preembedding double immunostaining technique was applied to examine synaptic relationships between gamma-aminobutyric acid (GABA)-ergic neurons and catecholaminergic neurons in the area postrema of the rat. The catecholaminergic neuronal somata received only a few synapses from GABAergic axon terminals, whereas the catecholaminergic dendrites received many synapses from GABAergic axon terminals. Most of the synapses were symmetrical. GABAergic axon terminals could be found presynaptically to two catecholaminergic dendrites or both catecholaminergic and nonimmunoreactive dendrites. Conversely, a few catecholaminergic axon terminals were found presynaptically to GABAergic dendrites although such synapses were few. These findings suggest that in the area postrema, GABAergic neurons may modulate the functions of catecholaminergic neurons and may also be influenced by them.