Supraspinally mediated analgesic effect of antidepressant drugs

Imipramine and amitriptyline, nonselective monoamine reuptake inhibitors, citalopram, selective serotonin reuptake inhibitor, and maprotiline, selective noradrenaline reuptake inhibitor, were tested after intracerebroventricular (icv) and intrathecal (it) administration in the rat writhing test to establish the role of the spinal and/or supraspinal structures in their effects. All drugs evoked dose-dependent analgesia after icv but not after it microinjections. The changes in the nociceptive behavior of rats pre-treated with antidepressants were not due to the non-specific influences of the drugs on the animals' gross behavior, as revealed by the open field test. The obtained results suggest that an antidepressant-induced analgesia mainly depends on the supraspinal effect with minor, if any, contribution from the spinal mechanisms.