title: Involvement of alpha 1-adrenoceptors in the depolarizing but not the hyperpolarizing responses of motorneurones in the neonate rat to noradrenaline.
abstract: Superfusion of the hemisected lumbar spinal cord in the neonate rat with solutions containing 10(-6) to 10(-3) M noradrenaline (NA), elicited graded depolarizations recorded from ventral roots, with a mean EC50 value of 15.1 +/- 1.5 microM (mean +/- SEM, n = 37). Repeated concentration-response curves to NA could be determined from the same preparation. Adrenaline had a similar depolarizing action (EC50 9.9 +/- 1.7 microM, n = 11). Blockade of neuronal uptake of NA by desipramine (2 x 10(-6) M) caused some potentiation of submaximal responses to NA and shifted the EC50 to 6.0 +/- 1.7 microM (mean +/- SEM, n = 14). The depolarizing response to NA was unaffected by DL-propranolol (10(-7) M) or yohimbine (10(-7) M). Prazosin (5 x 10(-9), 10(-8) and 10(-7) M) reduced the responses and caused a progressive rightward shift of the concentration-response curve. The onset of blockade by prazosin was slow, superfusion for at least 90-120 min being required before the blockade plateaued. Prazosin (5 x 10(-9) and 10(-8) M) caused a surmountable blockade, the apparent pA2 being 8.3 +/- 0.2 (mean +/- SEM, N = 9). Depolarizations induced by NA were also antagonised by phentolamine (10(-6) M). An initial hyperpolarizing response to NA was unmasked after exposure to prazosin in 90% of preparations and was associated with a reduction in the spontaneous activity of the motorneurones. Both the hyperpolarization and reduction in spontaneous activity were attenuated by yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, University of Wales College of Cardiff, U.K.
authors.forename: L A
authors.initials: LA
authors.lastname: Connell
authors.forename: A
authors.initials: A
authors.lastname: Majid
authors.forename: D I
authors.initials: DI
authors.lastname: Wallis
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects*; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
chemical_list: D002395:Catecholamines; D014179:Neurotransmitter Uptake Inhibitors; D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine; D011224:Prazosin