In normal guinea pigs the adrenergic agonists clonidine and norepinephrine are known to inhibit directly the cortical outflow of acetylcholine (ACh) through alpha-2 receptors and to increase the cortical outflow of γ-aminobutyric acid (GABA) through alpha-1 receptors. GABA, in turn, contributes to inhibit ACh through GABA(A) receptors. This scheme is changed drastically by morphine tolerance. In morphine-tolerant guinea pigs, clonidine at 7.5, 18.7 and 112 nmol/kg i.p. stimulates the cortical release of ACh through alpha-1 receptors. This effect is prevented by prazosin, 35.8 nmol/kg i.p. Clonidine reduces ACh release at high doses only (374 and 1122 nmol/kg i.p.). Futhermore, electrical stimulation of locus ceruleus also gives rise to a prazosin-sensitive increase in ACh release. In addition, locus ceruleus stimulation often causes behavioral activation rather than sedation. In morphine-tolerant guinea pigs, clonidine at 7.5 and 18.7 nmol/kg i.p. reduces GABA efflux through alpha-2 re...
Inversion of the alpha-2 and alpha-1 noradrenergic control of the cortical release of acetylcholine and gamma-aminobutyric acid in morphine-tolerant guinea-pigs
BEANI, Lorenzo;BIANCHI, Clementina;TANGANELLI, Sergio;ANTONELLI, Tiziana;SIMONATO, Michele;
1988
Abstract
In normal guinea pigs the adrenergic agonists clonidine and norepinephrine are known to inhibit directly the cortical outflow of acetylcholine (ACh) through alpha-2 receptors and to increase the cortical outflow of γ-aminobutyric acid (GABA) through alpha-1 receptors. GABA, in turn, contributes to inhibit ACh through GABA(A) receptors. This scheme is changed drastically by morphine tolerance. In morphine-tolerant guinea pigs, clonidine at 7.5, 18.7 and 112 nmol/kg i.p. stimulates the cortical release of ACh through alpha-1 receptors. This effect is prevented by prazosin, 35.8 nmol/kg i.p. Clonidine reduces ACh release at high doses only (374 and 1122 nmol/kg i.p.). Futhermore, electrical stimulation of locus ceruleus also gives rise to a prazosin-sensitive increase in ACh release. In addition, locus ceruleus stimulation often causes behavioral activation rather than sedation. In morphine-tolerant guinea pigs, clonidine at 7.5 and 18.7 nmol/kg i.p. reduces GABA efflux through alpha-2 re...I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
