Transmitter and peptide actions on hypothalamic neurons in vitro: implications for lordosis

This article summarizes a series of studies using brain tissue slices of rats to record single-unit activity from the hypothalamic ventromedial nucleus (VMN) and preoptic area (POA), both of which are crucial for the regulation of the estrogen-dependent feminine mating behavior, lordosis. In these studies the actions of acetylcholine (ACh), serotonin (5HT), norepinephrine (NE), luteinizing hormone-releasing hormone (LHRH), arginine-vasopressin (AVP), and oxytocin (OXY) on neuronal activity were investigated. The results show that these agents could evoke either direct responses or neuromodulatory changes from VMN or POA cells in vitro. Comparison of the net neuronal actions of each of these agents with their effects on lordosis behavior revealed interesting correlations. All the excitatory agents, i.e., ACh, AVP, OXY, and LHRH, have been indicated by intracerebral application studies to be facilitatory on lordosis. The inhibitory agent, 5HT, could inhibit lordosis, when applied to the VMN and its vicinity. Such correlations indicate that these transmitters and peptides can facilitate or inhibit lordosis by increasing or decreasing, respectively, the frequency of action potentials in the types of hypothalamic neurons recorded here.