Pressure ejection of acetylcholinesterase within the guinea-pig substantia nigra has non-classical actions on the pars compacta cells independent of selective receptor and ion channel blockade.

In the substantia nigra, acetylcholinesterase may have a non-classical function unrelated to cholinergic transmission. Acetylcholinesterase is released from the dendrites of dopamine-containing nigrostriatal neurons and has a subsequent action on these cells, independent of hydrolysis of acetylcholine. The aim of this study was to explore further the precise nature of this "non-cholinergic" action of acetylcholinesterase. Acetylcholinesterase was pressure-ejected in the vicinity of the dendrites of putative nigrostriatal neurons in vitro, in near-physiological amounts, and the effects of this treatment on neuronal membrane properties were investigated. It was found that acetylcholinesterase reversibly hyperpolarized the nigrostriatal cell membrane independent of sodium and calcium channel blockade. Acetylcholinesterase pretreated with an irreversible inhibitor (Soman) of its classical catalytic site produced the same hyperpolarizing effect: however, butyrylcholinesterase, which hydrolyses acetylcholine, was inefficacious. These effects persisted in the presence of the dopamine receptor antagonist sulpiride. It is suggested the acetylcholinesterase can facilitate the generation of a long-duration conductance, which enhances the firing of nigrostriatal cells if the neuron is first hyperpolarized. Hence the action of acetylcholinesterase would be to modulate inputs. These actions are independent of direct interaction with acetylcholine and dopamine systems. Hence, in the substantia nigra, acetylcholinesterase might serve as a "neuromodulatory" secretory protein.