Brain Research Bulletin, Vol. 20, pp. 857-861. 0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Pergamon Press plc, 1988. Printed in the U.S.A. 0361-9230/88 $3.00 + .OO Transmitter and Peptide Actions On Hypothalamic Neurons In Vitro: Implications for Lordosis zyxwvutsrqponmlkjihgfedcbaZY LEE-MING KOW AND DONALD W. PFAFF zyxwvutsrqponmlkjihgfedcbaZYXWV The Rockefeller University, 1230 York Avenue, New York, NY 10021 KOW, L.-M. AND D. W. PFAFF. Transmitter and peptide actions on hypothalamic neurons in vitro: Implications for lordosis. BRAIN RES BULL 20(6) 857-861, 1988.-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 (SHT), 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. Brain tissue slice Hypothalamic ventromedial nucleus In vitro Lordosis Neuropeptides Preoptic area Single-unit activity LORDOSIS is a feminine mating behavior of many quad- ruped mammals that requires both permissive estrogen ptim- ing and appropriate sensory stimulation for the response to be triggered. Therefore, it has been used extensively as a model for studying hormone-nervous systqm interactions. A crucial neural site for this interaction appears to be the ven- tromedial nucleus of the hypothalamus (VMN), because im- plantation of minute amounts of estrogen into the VMN alone is sufficient to induce lordosis [8]. The VMN is also important for the regulation of lordosis by other means, such as infusion of agonists or antagonists of acetylcholine [9,20], norepinephrine [ 13,481, and serotonin [ 14,321. Moreover, in- fusion of neuropeptides, such as luteinizing hormone- releasing hormone [ 121, arginine-vasopressin [3] and oxyto- tin [3,15] into the VMN and/or its vicinity has been shown to alter lordosis. Neurons in the VMN can transduce the chem- ical effects of these agents and estrogen into altered electri- cal activity. To learn about this transduction, a crucial step in behav- ior regulation, we have conducted a series of in vitro studies on the electrophysiological actions of the above mentioned neurotransmitters and neuropeptides on VMN neurons. In these studies, single-unit activity in VMN was recorded from hypothalamic slices. This preparation is better suited than in vivo preparations for studying transmitter and peptide ac- tions, because it is mechanically stable, and easier to control the chemical stability, concentration and time of application of transmitters and peptides. Our goals were to see: (1) what are the electrophysiological actions of lordosis-relevant agents, including estrogen, on VMN neurons; (2) if an agent has more than one type of action, which one is likely to be responsible for its effect on lordosis; and (3) whether lordosis-relevant actions are influenced by an in vivo lordosis-inducing estrogen treatment. METHOD The methods for tissue slice preparation, application of transmitters and peptides, and single unit recording have been described in detail elsewhere [23,24]. Briefly, 400 p hypothalamic slices containing the VMN were prepared from ovariectomized rats with or without an estrogen treat- ment sufficient to induce lordosis. Single-unit activity was recorded extracellularly by the conventional technique from visually discernible VMN neurons (or the medial preoptic area, POA, in one study) in a selected slice kept in a chamber, which was continuously perfused with artificial cerebrospinal fluid. To study neuronal responses to a chemi- cal agent, it was dissolved at a determined concentration and microinjected into the perfusion chamber. The average peak concentration of an agent reaching the slice was calculated from the volume of the solution injected and the volume of the perfusion chamber. The calculated concentrations were contirmed in pilot experiments. Effects of the estrogen treatment were determined by statistical comparison of re- sults from treated and untreated preparations. 857