MEDIAN PREOPTIC NUCLEUS NEURONS - AN IN-VITRO PATCH-CLAMP ANALYSIS OFTHEIR INTRINSIC-PROPERTIES AND NORADRENERGIC RECEPTORS IN THE RAT

The median preoptic nucleus is recognized as an important forebrain si te involved in hydromineral and cardiovascular homeostasis. In the pre sent study whole cell patch-clamp recordings in parasagittal slices of adult rat brain were used to obtain information on the properties of median preoptic neurons. Lucifer Yellow-labelled cells demonstrated sm all ovoid somata with two to three aspiny main dendrites and axons tha t branched sparingly. Median preoptic neurons displayed varying degree s of hyperpolarization-activated time-dependent and/or time-independen t inward rectification, and 86% of cells demonstrated low threshold sp ikes. Median preoptic nucleus is known to receive a prominent noradren ergic innervation from the medulla, and 59% of 156 tested neurons were found to respond to bath applied noradrenaline (1-100 mu M). In the m ajority (n=62) of cells, the response was an alpha(2) adrenoreceptor-m ediated, tetrodotoxin-resistant, membrane hyperpolarization that was a ssociated with a 43+/-6% increase in membrane conductance. The net nor adrenaline-induced current (5-45 pA) was inwardly rectifying, cesium-r esistant but barium sensitive. Current reversal at -102+/-4 mV in 3.1 mM [K](o) and -62+/-3 mV in 10 mM [K](o) implied opening of potassium channels. By contrast, a minority (n=27) of cells responded to noradre naline with an alpha(1)-mediated, tetrodotoxin-resistant membrane depo larization. These observations imply a functional diversity among medi an preoptic neurons, and the prevalence of hyperpolarizing alpha(2) an d, to a lesser extent, depolarizing alpha(1) adrenoreceptors on median preoptic neurons suggests that noradrenergic inputs can exert a promi nent influence on their cellular excitability. (C) 1998 IBRO. Publishe d by Elsevier Science Ltd.