title: Kappa-opioid receptor activation inhibits post-spike depolarizing after-potentials in rat supraoptic nucleus neurones in vitro.
abstract: Endogenous agonists acting at kappa-opioid receptors modulate the discharge activity of hypothalamic supraoptic nucleus vasopressin cells in vivo. Phasic activity in vasopressin cells is known to depend critically on intrinsic mechanisms involving post-spike depolarizing after-potentials and we hypothesized that inhibition of phasic bursting by an endogenous kappa-agonist may result from reducing the magnitude of depolarizing after-potentials. To investigate this possibility, intracellular sharp electrode recordings were obtained from supraoptic nucleus cells impaled in superfused explants of rat hypothalamus. Bath application of the selective kappa-agonist, U50,488H (0.1-1 microM), decreased the spontaneous firing rate of magnocellular neurosecretory cells (by 94. 0+/-4.5% at 1 microM, mean+/-SEM; P = 0.02, n = 4). U50,488H did not alter membrane potential (0.9+/-0.8 mV hyperpolarization at 1 microM, P = 0.17, n = 8) or input resistance (11.0+/-4.5% increase at 1 microM, P = 0.09, n = 5). U50,488H (0.1 and 1 microM, both n = 5) reduced depolarizing after-potential amplitude (by 29.9+/-9.3 and 78.0+/-10. 6%, respectively, P<0.001) in eight cells in which the baseline membrane potential was kept constant by dc-current injection and in which a depolarizing after-potential was evoked every 25-40 s by a brief (40-80 ms) train of 3-6 action potentials (the number of spikes in the trains was kept constant for each cell). Thus, kappa-opioid receptor activation reduces depolarizing after-potential amplitude in supraoptic nucleus cells and this may underlie the reduction in burst duration of vasopressin cells caused by an endogenous kappa-agonist in vivo.
authors.affiliation: Centre for Research in Neuroscience, Montréal General Hospital and McGill University, Montréal, Canada. Colin.Brown@ed.ac.uk
authors.forename: C H
authors.initials: CH
authors.lastname: Brown
authors.forename: M
authors.initials: M
authors.lastname: Ghamari-Langroudi
authors.forename: G
authors.initials: G
authors.lastname: Leng
authors.forename: C W
authors.initials: CW
authors.lastname: Bourque
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D013495:Supraoptic Nucleus / Q000502:physiology*
chemical_list: D017473:Receptors, Opioid, kappa; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer