THE COMBINATION OF SEVERAL ANTIDEPRESSANTS IS NOT SYNERGISTIC ON THE FIRING OF LATERAL SEPTAL NEURONS IN THE RAT CARLOS M. CONTRERAS, DOLORES BELTRAN, MARGARITA SAAVEDRA and MIGUEL MOLINA-HERN&iDEZ Laboratorio de Neurofarmacologla. Institute de Neuroetologla, Universidad Veracruzana. Departamento de Fisiologia, Institute de Investigaciones Biomedicas, Universidad National Autonoma de Mexico, Mexico. (Final form, May 1995) Abstract Contreras Carlos M., Dolores Beltrbn, Margarita Saavedra and Miguel Molina-Hernandez. The Combination of Several Antidepressants is not Synergistic on the Firing of Lateral Septal Neurons in the Rat, Prog. Neuro-Psychopharmacol & Biol Psychiat. 1995,19(7): 1157-1162. 1. Three kinds of antidepressants (clomipramine, sleep deprivation, and electroconvulsive shock) increase the firing rate in the lateral septal neurons of the rat. 2. The acute combination of these treatments, however, did not produce added effects on firing rate of lateral septal neurons in the rat. 3. 24 hours of sleep deprivation blocked the actions of a single electroconvulsive shock. 4. It is concluded that the firstly applied treatment modifies the receptors sensitivity from the very beginning, thus blocking the action of a second treatment. Kev words:antidepressants, clomipramine, electroconvulsive shock, lateral septal nucleus, sleep deprivation. Abbreviations: clomipramine (CMI), electroconvulsive shock (ECS), lateral septal nucleus (LSN), sleep deprivation (SD). Introduction From non-drug antidepressant treatments, sleep deprivation (SD) is used efficaciously in some depressed patients (Vogel et al. 1980), and electroconvulsive shock (ECS) is considered the most effective alternative for depression not responding to drug treatment (Fawcett and Scheftner, 1986); herein, clomipramine (CMI) is a tricyclic still used as an antidepressant in some countries, and currently in the treatment of phobic and obsessional states (Healy, 1991). Anhedonia is one the main ailments in depression, and the lateral septal nuclei (LSN) are limbic structures considered among the reward 1157