Radioimmunoassay for acetylcholine in the rat brain

Specific antiserum against acetylcholine (ACh) was produced in the rabbit immunized with a choline hemiglutarate-bovine serum albumin conjugate. The antiserum significantly cross-reacted with choline carboxylates, such as butyrylcholine, succinylcholine, and carbamylcholine. However, neither choline itself nor choline phosphates, such as phosphatidylcholine and phosphorylcholine, showed any significant cross-reaction. The antiserum was used to develop a radioimmunoassay for ACh. The assay can reliably determine as little as 170 pg of ACh. Acetylcholine concentrations in two regions of the rat brain were determined directly from an aqueous extract. After inhibition of acetylcholinesterase with physostigmine, ACh increased more in the forebrain than in the brainstem.