Synaptic regulation of hypothalamic neurons containing ACTH by substance P

Synaptic connections between substance P (SP)- and ACTH-containing neurons in the rat arcuate nucleus were studied by a technique of combined pre- and postembedding immunohistochemical staining. The results showed that immunoreactive (ir) SP fiber terminals form synapses with ir ACTH cell bodies. This strongly suggests that the activity of ACTH neurons is under neuronal regulation by SP neurons.