PRESYNAPTIC ALPHA(2A D)-AUTORECEPTORS IN THE BRAIN CORTEX OF CERCOPITHECUS-AETHIOPS/

The existence of presynaptic alpha(2)-autoreceptors, and the subtype t o which the receptors belong, were studied in the brain cortex from tw o African green monkeys (Cercopithecus aethiops). Slices of the brain cortex were preincubated with H-3-noradrenaline. The slices were then superfused with medium containing desipramine (1 mu M) and stimulated electrically with trains of 72 pulses, 3 Hz. Concentration-response cu rves of nine a-adrenoceptor antagonists were determined. All antagonis ts enhanced the stimulation-evoked overflow of tritium, i.e. the relea se of noradrenaline, indicating the existence of presynaptic alpha(2)- autoreceptors. The EC(30%) values of the antagonists (concentrations t hat increased the evoked overflow of tritium by 30%) were taken as a m easure of affinity for the autoreceptors. The subclassification was ba sed on a comparison of these affinity estimates with affinities for al pha(2A), alpha(2B), alpha(2C) and alpha(2D) radioligand binding sites and for previously classified alpha(2A)0 and alpha(2D)-autoreceptors. The comparison indicates that the alpha(2)-autoreceptors in the brain cortex of Cercopithecus aethiops belong to the genetic alpha(2A/D) and not the alpha(2B) or alpha(2C) subtype. In their pharmacological prop erties, the autoreceptors are closest to the pharmacological alpha(2D) subtype. The results support the notion that alpha(2)-autoreceptors b elong at least predominantly to the alpha(2A/D) subtype of alpha(2)-ad renoceptors.