Involvement of alpha 1-adrenoceptors in the depolarizing but not the hyperpolarizing responses of motorneurones in the neonate rat to noradrenaline.
Neuropharmacology
; 28(12): 1399-404, 1989 Dec.
Article
em En
| MEDLINE
| ID: mdl-2559351
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)
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Bases de dados:
MEDLINE
Assunto principal:
Norepinefrina
/
Receptores Adrenérgicos alfa
/
Animais Recém-Nascidos
/
Neurônios Motores
Limite:
Animals
Idioma:
En
Revista:
Neuropharmacology
Ano de publicação:
1989
Tipo de documento:
Article
País de afiliação:
Reino Unido