title: Median preoptic nucleus neurons: an in vitro patch-clamp analysis of their intrinsic properties and noradrenergic receptors in the rat.
abstract: The median preoptic nucleus is recognized as an important forebrain site involved in hydromineral and cardiovascular homeostasis. In the present 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 small ovoid somata with two to three aspiny main dendrites and axons that branched sparingly. Median preoptic neurons displayed varying degrees of hyperpolarization-activated time-dependent and/or time-independent inward rectification, and 86% of cells demonstrated low threshold spikes. Median preoptic nucleus is known to receive a prominent noradrenergic innervation from the medulla, and 59% of 156 tested neurons were found to respond to bath applied noradrenaline (1-100 microM). In the majority (n = 62) of cells, the response was an alpha 2 adrenoreceptor-mediated, tetrodotoxin-resistant, membrane hyperpolarization that was associated with a 43 +/- 6% increase in membrane conductance. The net noradrenaline-induced current (5-45 pA) was inwardly rectifying, cesium-resistant 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 noradrenaline with an alpha 1-mediated, tetrodotoxin-resistant membrane depolarization. These observations imply a functional diversity among median preoptic neurons, and the prevalence of hyperpolarizing alpha 2 and, to a lesser extent, depolarizing alpha 1 adrenoreceptors on median preoptic neurons suggests that noradrenergic inputs can exert a prominent influence on their cellular excitability.
authors.affiliation: Loeb Research Institute, Ottawa Civic Hospital, Ontario, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Bai
authors.forename: L P
authors.initials: LP
authors.lastname: Renaud
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002552:Cerebral Ventricles; D004594:Electrophysiology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D016548:Prosencephalon / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*
chemical_list: D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine