ACUTE AND CHRONIC EFFECTS OF INTRATHECAL MORPHINE IN MONKEYS

In a double-blind study, seven Macaca fascicularis monkeys receivingintrathecal (i.t.) morphine in saline, 0.07 mgkg^–1, werecompared with a control group of four monkeys receiving eitherlumbar puncture alone (n = 1) or i.t. saline (n = 3). Neithermorphine nor saline solutions contained preservatives. Arterialblood gas tensions, respiration, arterial pressure, e.c.g.,state of consciousness and motor function were recorded for24 h. The control group was sacrificed 42 days later and thestudy group was sacrificed at 6 (n = 2) or 42 days (n = 5) afterinjection. The central nervous system, meninges, nerve rootsand dorsal root ganglia were examined macroscopically and microscopically.Respiratory depression did not occur in either the control orthe study groups. There were moderate but statistically significantdecreases in systolic and diastolic arterial pressures followingi.t. morphine. In both groups, the pathological findings werelocalized to the cauda equina region and characterized by mononuclearcell infiltration. In neither group was there evidence of demyelination,arachnoiditis or necrosis. Focal endoneurial fibrosis was foundin only one animal in the control group following multiple lumbarpunctures associated with paraesthesia. The features appearedto correlate with the physical trauma associated with lumbarpuncture rather than with the injectate.