Reciprocal synaptic relationships between angiotensin II-containing neurons and enkephalinergic neurons in the rat area postrema

A preembedding double immunostaining technique was used to study synaptic r elationships between angiotensin-II-like immunoreactive and enkephalin-like immunoreactive neurons in the rat area postrema. The angiotensin-II-like i mmunoreactive neurons were detected by silver-gold intensification of the D AB reaction results while the enkephalin-like immunoreactive neurons were d etected by simple ABC-DAB reaction. The synaptic relationships were recipro cal between the two neurons, Most of the synapses found between these two n eurons were the presynaptic enkephalin-like immunoreactive axon terminals t hat made synapses on the angiotensin-II-like immunoreactive perikarya and d endrites. Both the axe-somatic and axo-dendritic synapses were symmetrical. However, although angiotensin-II-like immunoreactive axon terminals also m ade synapses on enkephalin-like perikarya and dendrites, the axe-somatic sy napses were symmetrical, while the axo-dendritic synapses were asymmetrical . The present results confirm the presence of angiotensin-II-like immunorea ctive neurons in the area postrema and suggest that these angiotensinergic neurons in the area postrema may play a role in the regulation of blood pre ssure via coordinated synaptic interactions with enkephalinergic neurons. ( C) 2001 Wiley-Liss, Inc.