BACKGROUND: Acetylcholinesterase inhibition at the spinal level has been shown to produce a potent antinociceptive effect. However, the site of cholinesterase inhibition is unknown. To determine whether the spinal meninges participate in acetylcholine metabolism, the spinal meninges of monkeys and pigs were assayed for cholinesterase activity. METHODS: Spinal cord, dura mater, and arachnoid mater specimens from anesthetized pigs and monkeys were mechanically homogenized and cholinesterase activity was determined quantitatively using a commercially available colorimetric assay. The ability of neostigmine to inhibit cholinesterase activity in vitro was also measured. Finally, the reverse transcriptase polymerase chain reaction (RT-PCR) was used to identify the cholinesterase metabolizing enzymes expressed by the spinal meninges. RESULTS: All spinal cord and meningeal specimens showed cholinesterase activity. In pigs, the dura mater showed less enzyme activity (36 +/- 17.7 U/mg protein) than the arachnoid mater (73.4 +/- 30.3 U/mg protein; P < 0.05), and the arachnoid mater showed less activity than the spinal cord (131.3 +/- 55.2 U/mg protein; P < 0.05). In monkeys, the dura mater again showed less cholinesterase activity (45.8 +/- 20.1 U/mg protein; P < 0.05), whereas cholinesterase activity in the arachnoid mater (90.3 +/- 45.9 U/mg protein) and spinal cord specimens (101.9 +/- 37.5 U/mg protein) were not significantly different. There were no significant species-related differences in cholinesterase activity. Neostigmine inhibited cholinesterase activity in a log-dose-dependent manner. The RT-PCR identified mRNA for acetylcholinesterase and butyrylcholinesterase in monkey pia-arachnoid mater. CONCLUSIONS: These data show that the spinal meninges express acetylcholinesterase and butyrylcholinesterase; for monkeys, although not pigs, the level of cholinesterase activity is comparable with that found in the spinal cord. This finding suggests that the meninges may be an important site for acetylcholine metabolism and may play a role in the analgesic effect produced by intrathecally administered cholinesterase inhibitors.
BACKGROUND:Acetylcholinesterase inhibition at the spinal level has been shown to produce a potent antinociceptive effect. However, the site of cholinesterase inhibition is unknown. To determine whether the spinal meninges participate in acetylcholine metabolism, the spinal meninges of monkeys and pigs were assayed for cholinesterase activity. METHODS: Spinal cord, dura mater, and arachnoid mater specimens from anesthetized pigs and monkeys were mechanically homogenized and cholinesterase activity was determined quantitatively using a commercially available colorimetric assay. The ability of neostigmine to inhibit cholinesterase activity in vitro was also measured. Finally, the reverse transcriptase polymerase chain reaction (RT-PCR) was used to identify the cholinesterase metabolizing enzymes expressed by the spinal meninges. RESULTS: All spinal cord and meningeal specimens showed cholinesterase activity. In pigs, the dura mater showed less enzyme activity (36 +/- 17.7 U/mg protein) than the arachnoid mater (73.4 +/- 30.3 U/mg protein; P < 0.05), and the arachnoid mater showed less activity than the spinal cord (131.3 +/- 55.2 U/mg protein; P < 0.05). In monkeys, the dura mater again showed less cholinesterase activity (45.8 +/- 20.1 U/mg protein; P < 0.05), whereas cholinesterase activity in the arachnoid mater (90.3 +/- 45.9 U/mg protein) and spinal cord specimens (101.9 +/- 37.5 U/mg protein) were not significantly different. There were no significant species-related differences in cholinesterase activity. Neostigmine inhibited cholinesterase activity in a log-dose-dependent manner. The RT-PCR identified mRNA for acetylcholinesterase and butyrylcholinesterase in monkey pia-arachnoid mater. CONCLUSIONS: These data show that the spinal meninges express acetylcholinesterase and butyrylcholinesterase; for monkeys, although not pigs, the level of cholinesterase activity is comparable with that found in the spinal cord. This finding suggests that the meninges may be an important site for acetylcholine metabolism and may play a role in the analgesic effect produced by intrathecally administered cholinesterase inhibitors.