ACETYLCHOLINE MEASUREMENT OF CEREBROSPINAL-FLUID BY IN-VIVO MICRODIALYSIS IN FREELY MOVING RATS

Acetylcholine (ACh) and choline (Ch) levels in rat cerebrospinal fluid (CSF) were determined by in vivo microdialysis (CSF microdialysis) in both halothane-anesthetized and freely-moving rats. The Ch/ACh ratio in CSF perfused with Ringer's solution (30 mu l/30 min) containing 10( -5) M physostigmine, a centrally active cholinesterase inhibitor, was significantly lower than that in unprocessed CSF due to significantly higher ACh levels in the former. The successive measurement on the 2nd and 7th day after the guide cannula implantation demonstrated the fea sibility of the CSF microdialysis method for repetitive monitoring of CSF ACh and Ch levels in freely moving rats without extensive tissue d amage. Intraperitoneal administration of physostigmine caused an incre ase in CSF ACh levels, whereas administration of neostigmine, which ca nnot penetrate into the blood brain barrier, did not. Furthermore, a c entrally active acetylcholinergic M(1)-receptor agonist, AF102B, produ ced an increase in CSF ACh and Ch levels. Thus, the present study demo nstrates that CSF microdialysis is a useful method for evaluating over all central cholinergic activity and investigating the pharmacological effects of various drugs that act via the central cholinergic system.