The effects of different monoaminergic antidepressants on the analgesia induced by spinal cord adrenal medullary transplants in the formalin test in rats.

We studied the effects of chronic intraperitoneal administration of antidepressants on the antinociception induced by adrenal medullary transplants into the subarachnoid space in rats using the formalin test. Administration of drugs started 28 days after operation and the formalin test was performed on Day 56. When amitriptyline (AMT; 15 mg . kg -1 . day -1 ) was administered to sham-operated rats, it decreased the licking time and increased the transplant-induced analgesia in Phase 1 when administered to transplanted rats. Chronic treatment with fluvoxamine (FVX, 10 mg kg -1 . day -1 ) had no influence on the licking response in sham rats, nor did it modify the transplant-induced analgesia when administered to transplanted rats. When desipramine (DMI; 10 mg . kg -1 . day -1 ) was administered to sham rats, it significantly reduced the licking response in Phase 1, but when administered to transplanted rats it did not increase the transplant-induced analgesia. None of the drugs administered showed any effect on Phase 2 of the formalin test. These results suggest that adrenal medullary transplants into the spinal cord induce analgesia as determined by the formalin test. This effect is more pronounced when AMT (a nonselective noradrenaline-serotonin reuptake inhibitor) is chronically administered, but not when FVX or DMI are chronically administered.