The effects of catecholamines on electrical activity of neurons in the guinea pig supraoptic nucleus in vitro.
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.
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*
D010656:Phenylephrine; D011433:Propranolol; D007545:Isoproterenol; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine