Immunohistochemical demonstration of cholinergic structures in central ganglia of the slug (Limax maximus, Limax valentianus)

Immunohistochemical techniques were used to study the distribution of cholinergic neurons containing choline acetyltransferase of the common type (cChAT), the synthetic enzyme of acetylcholine, in the central nervous system of the slug Limax maximus and Limax valentianus. Because the antiserum applied here was raised against a recombinant protein encoded by exons 7 and 8 of the rat gene for ChAT, three methods were used in order to validate antibody specificity for the Limax counterpart enzyme. Western blot combined with ChAT activity assay following native gel electrophoresis and immunoprecipitation analysis both indicated that immunoreactive Limax brain molecules were capable of synthesizing acetylcholine. Western blot after denatured gel electrophoresis of Limax brain extracts revealed a single band of about 67 kDa. All findings obtained with these three methods clearly indicated that the antiserum effectively recognized Limax cChAT. 1400 neuronal cell bodies positive for cChAT, mainly small to medium-sized, were found in various brain regions in the buccal, cerebral, pleural, parietal, visceral and pedal ganglia. cChAT immunoreactive nerve fibers were distributed extensively in the neuropil, connectives and commissures of these central ganglia. The map of cChAT-positive cells provided here are valuable for understanding the cholinergic mechanism in the slug brain, as well as giving an important hint to clarifying the mechanisms of learning and memory in higher vertebrates including humans.

Research highlights
► A cChAT antiserum recognizes specifically cholinergic neurons of Limax.
► Cholinergic neurons are distributed in all ganglia.
► 1400 neuronal cell bodies are positive for cChAT.