title: The effects of catecholamines on electrical activity of neurons in the guinea pig supraoptic nucleus in vitro.
abstract: The role of the central noradrenergic system in the supraoptic neuroendocrine regulation was investigated using slices of the guinea pig hypothalamus. Noradrenaline produced a complex membrane effect comprising two distinct depolarizations: one, associated with a moderate increase in input resistance and resulting in an augmentation of the spontaneous firing rate; the other, unaccompanied by a detectable change in input resistance and resulting in depression of the firing rate. The former depolarization was reproducible by applying specific alpha-agonist, phenylephrine, whereas the latter was induced by a beta-adrenergic agonist, isoproterenol. The actions of phenylephrine and isoproterenol were blocked by phentolamine and propranolol, respectively. Amplitude of the phenylephrine-induced depolarization was voltage-dependent with the estimated reversal potential of about - 115 mV and changed as a function of [K+]o. On the contrary, amplitude of the isoproterenol-induced depolarization was voltage-independent and was insensitive to changes in external concentrations of K+, Na+, Cl- and Ca2+. We conclude that catecholamines directly modulate the activity of supraoptic neurons through two functionally distinct adrenoceptive sites on neurosecretory cells. The activation of alpha-receptors may increase cellular excitability through suppression of membrane K+ conductance while the activation of beta-receptors would depress neuronal firings, possibly through some mechanism which is not directly linked to ionic channels.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009638:Norepinephrine / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000502:physiology*
chemical_list: D010656:Phenylephrine; D011433:Propranolol; D007545:Isoproterenol; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine