[Effect of chronic desipramine treatment on rat brain adrenergic alpha 2-receptor]

Clonidine has been reported to be effective as an alpha 2-adrenoceptor agonist. Locomotor activity was measured by Automex after clonidine (100 micrograms/kg ip) administration. A significant reduction of locomotor activity was found during the 30th-45th-min period of experiment. 3-Methoxy-4-hydroxyphenylethyleneglycol (MHPG)-total was decreased significantly at 60 min after clonidine administration in rat cerebral cortex, hippocampus and hypothalamus. This might suggest that MHPG content at 60 min after clonidine administration can be used as functional index of the presynaptic alpha 2-adrenergic receptor. Desipramine (DMI) (20 mg/kg) was injected ip once daily for 14 d and experiments undertaken 60 min after the clonidine administration. Chronic DMI treatment had an effect on rat brain steady state levels of serotonin (5-HT) system. Chronic DMI administration was shown to attenuate the effect of clonidine that reduced MHPG levels on rat brain. The results suggest that the chronic DMI treatment may diminish the clonidine-induced reduction of MHPG via the subsensitivity of presynaptic alpha 2-adrenergic receptor.