3H-atipamezole binding sites in mouse cerebral cortex: possible involvement of alpha 2-adrenoceptors in sexual behavior
Rägo, L.; Saano, V.; Tupala, E.; Nieminen, S.A.; Airaksinen, M.M.
Methods and Findings in Experimental and Clinical Pharmacology 14(1): 23-27
1992
ISSN/ISBN: 0379-0355 PMID: 1352369 Document Number: 391082
Atipamezole is a new specific alpha 2-adrenoceptor antagonist. In this study, first, the presence of specific 3H-atipamezole binding sites in the sagittal and coronal sections of mouse brain was established using autoradiography. In vitro experiments with mouse cerebral cortex membranes indicated that d-medetomidine, a new alpha 2-adrenoceptor agonist structurally related to atipamezole, displaces labelled atipamezole more potently than noradrenaline. The saturation isotherm with d-medetomidine demonstrated high affinity binding with the apparent number of binding sites KD 1.36 nM and 760 fmol/mg, respectively. In the next series of experiments male mice were sacrificed immediately after copulation and cerebral cortex 3H-atipamezole and 3H-flumazenil binding was studied. Oxymetazoline and prazosin are known to label preferably alpha 2A and alpha 2B subtypes of alpha 2-adrenoceptors. Therefore, parallelly with noradrenaline both these compounds were used to determine non-specific binding of 3H-atipamezole. When noradrenaline or oxymetazoline were used as displacing agents copulation caused a significant increase of 3H-atipamezole binding sites. No significant changes were observed when prazosin was used. 3H-Flumazenil binding remained unchanged by copulation. The up-regulation of 3H-atipamezole binding sites indicates that not only alpha 2-adrenoceptors in the periphery but also in the CNS may participate in the regulation of sexual behavior. Moreover, in regulation of sexual behavior central alpha 2-adrenoceptors may be more important than benzodiazepine receptors.