Release of acetylcholinesterase within the guinea-pig substantia nigra: effects of 5-hydroxytryptamine and amphetamine.

A soluble form of acetylcholinesterase is released from the substantia nigra of the cat, rabbit and rat. The possibility of spontaneous and evoked release of acetylcholinesterase within the substantia nigra of a different species, the guinea-pig, was tested using push-pull cannulae perfusion in vivo. Microinfusion of either potassium or amphetamine into the substantia nigra caused an increase in the local release of acetylcholinesterase. Furthermore, similar application of the neurotransmitter 5-hydroxytryptamine also caused an increase in the local release of the enzyme. However, in the presence of the 5-hydroxytryptamine receptor antagonist, cinanserin, or calcium-free perfusing medium, 5-hydroxytryptamine no longer had any significant effects. These results demonstrate that release of acetylcholinesterase within the substantia nigra appears to be, qualitatively but not quantitatively, a consistent phenomenon in different species. Furthermore, within the substantia nigra, release of acetylcholinesterase may be a function of interactions between local transmitters. The possible neurochemical and ionic mechanisms underlying these interactions is discussed.