Acute and Chronic Effects of Intrathecal Morphine in Monkeys

In a double-blind study, seven Macaca fascicularis monkeys receiving intrathecal (i.t.) morphine in saline, 0.07 mg kg-1, were compared with a control group of four monkeys receiving either lumbar puncture alone (n = 1) or i.t. saline (n = 3). Neither morphine nor saline solutions contained preservatives. Arterial blood gas tensions, respiration, arterial pressure, e.c.g., state of consciousness and motor function were recorded for 24 h. The control group was sacrificed 42 days later and the study group was sacrificed at 6 (n = 2) or 42 days (n = 5) after injection. The central nervous system, meninges, nerve roots and dorsal root ganglia were examined macroscopically and microscopically. Respiratory depression did not occur in either the control or the study groups. There were moderate but statistically significant decreases in systolic and diastolic arterial pressures following i.t. morphine. In both groups, the pathological findings were localized to the cauda equina region and characterized by mononuclear cell infiltration. In neither group was there evidence of demyelination, arachnoiditis or necrosis. Focal endoneurial fibrosis was found in only one animal in the control group following multiple lumbar punctures associated with paraesthesia. The features appeared to correlate with the physical trauma associated with lumbar puncture rather than with the injectate.