UP-REGULATION OF BETA(1)-ADRENERGIC RECEPTORS IN RAT-BRAIN AFTER CHRONIC CITALOPRAM AND FLUOXETINE TREATMENTS

Quantitative receptor autoradiography was used to study the effects of the selective serotonin reuptake inhibitors citalopram and fluoxetine and the tricyclic antidepressant imipramine on the regulation of beta (1)-adrenergic receptors in the rat brain. Rats were treated with sali ne, citalopram (10 mg kg(-1)), fluoxetine (10 mg kg(-1)), or imipramin e (15 mg kg(-1)) SC once daily for 14 days. [I-125]Iodocyanopindolol b inding to beta(1)-adrenergic receptors was found to increase significa ntly in the caudate-putamen and the somatosensory areas of the frontal cortex after both citalopram and fluoxetine treatments. Imipramine tr eatment elicited a marked decrease in beta(1) binding in the outer lam inae of the cingulate cortex, as well as in the motor and somatosensor y areas of the frontal cortex. In a separate experiment, rats were tre ated with saline, citalopram (2.5, 10 and 20 mg kg(-1)) or fluoxetine (2.5, 10 and 20 mg kg(-1)) SC once daily for 14 days. The effects of c italopram and fluoxetine on beta(1) receptors in the somatosensory cor tex and caudate-putamen were replicated. These results demonstrate tha t chronic administration of selective serotonin reuptake inhibitors, i n contrast to imipramine, can cause a regional up-regulation of beta(1 )-adrenergic receptors in the rat brain.