Presynaptic alpha 2- and postsynaptic beta-adrenoceptor sensitivity in slices of rat neocortex after chronic treatment with various antidepressant drugs

The effect of chronic (4 weeks) treatment of rats with the antidepressant drugs desipramine, maprotiline, chlorimipramine, zimelidine or iprindol on the sensitivity of presynaptic alpha 2- and postsynaptic beta-adrenoceptors in neocortical slices was investigated. Acute (1 day) treatment with the antidepressants did not affect the efflux of cyclic-AMP induced by isoprenaline (1 microM) from neocortical slices, while after chronic treatment the efflux of cyclic AMP was consistently reduced. Following acute administration the electrically-evoked release of [3H]noradrenaline (NA) from radiolabelled cortical slices remained unchanged. Upon chronic treatment with desipramine the release of [3H]NA was enhanced by about 45%. In contrast, after chronic treatment with maprotiline or chlorimipramine the electrically-evoked release of [3H]NA was not affected, whereas release was even slightly reduced after chronic administration of zimelidine or iprindol. In all cases, however, a similar inhibitory effect of exogenous NA (0.1 microM) on the release of [3H]NA was found. These data indicate that the desensitization of postsynaptic beta-adrenoceptors in rat brain after chronic treatment with antidepressant drugs is not paralleled by a reduction of presynaptic alpha 2-adrenoceptor sensitivity.