Alpha 2- and beta-adrenoceptors differentially modulate GABAA- and GABAB-mediated inhibition of red nucleus neuronal firing.
In mesencephalic red nucleus (RN), GABA-induced inhibition of neuronal firing is modulated by noradrenaline acting on alpha2- and beta-adrenoceptors. Since both GABAA and GABAB receptors are present in the rat RN, we have recorded the firing activity of RN neurons in vivo from anaesthetized rats to study how GABAA- and GABAB-mediated effects are modulated by either alpha2- or beta-adrenoceptor activation. Both the GABAA agonist isoguvacine and the GABAB agonist baclofen depressed the firing of RN neurons. During simultaneous application of clonidine, an alpha2-adrenoceptor agonist, half of the isoguvacine- and baclofen-mediated responses were modified: isoguvacine-mediated inhibition was enhanced by 97% without any change in effect duration, whereas baclofen responses were either increased or slightly reduced in the same number of cases. Application of isoprenaline, a beta-adrenoceptor agonist, increased isoguvacine effect in 66% of neurons without modifying effect duration; the amount of increase (43%) was significantly lower than that induced by clonidine. On the other hand, in the presence of isoprenaline, baclofen response was reduced in 72% of neurons with respect to both the amount (52%) and the duration (34%) of effect. Taken together, these results indicate that alpha2-adrenoceptors mainly enhance GABAA-induced inhibition and induce mixed effects on GABAB response; on the other side, beta-adrenoceptors exert an opposite modulation on GABA effects, respectively, enhancing and depressing GABAA- and GABAB-mediated responses.
Ciranna
L
L
Dipartimento di Scienze Fisiologiche, Università di Catania, I-95125, Catania, Italy. ciranna@unict.it
Licata
F
F
Li Volsi
G
G
Santangelo
F
F
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D058647:Adrenergic alpha-2 Receptor Agonists; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D011963:Receptors, GABA-A / Q000502:physiology*; D018080:Receptors, GABA-B / Q000502:physiology*; D012012:Red Nucleus / Q000187:drug effects / Q000502:physiology*
D058647:Adrenergic alpha-2 Receptor Agonists; D018341:Receptors, Adrenergic, alpha-2; D011943:Receptors, Adrenergic, beta; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D007545:Isoproterenol; D003000:Clonidine