The distribution of zebrin-II, acetylcholinesterase, and NADPH -diaphorase in the cerebellar cortex of the turtle Chrysemys picta

The distribution of neurons containing zebrin-II, acetylcholinesterase, and NADPH-diaphorase in the cerebellar cortex of turtles was investigated with immunohistochemical and histochemical techniques. Hypotheses regarding the pattern of distribution of each substance were generated according to previous research. Specifically, it was predicted that parasagittal bands of labeled and unlabeled compartments of cells would be observed for each substance. A camera lucida was used to generate maps of labelling patterns for consecutive cerebellar sections. None of the three substances investigated produced labelling patterns indicative of compartmentation of the Purkinje layer. In the case of zebrin-II, no previous research had been reported regarding its distribution in turtles. The results using immunohistochemistry supported the hypothesis that zebrin-II labelling is limited to the Purkinje cells. The hypothesis that parasagittal bands of zebrin-II-positive and zebrin-II-negative cells would be observed was not supported, however. Comparisons with brain sections stained with cresyl violet, which is known to stain all cell bodies, supported the conclusion that all Purkinje cells were zebrin-II-positive. In the case of acetylcholinesterase, histochemistry was performed with and without the cholinesterase inhibitor ethopropazine, which inhibits non-specific “pseudocholinesterases.” Histochemistry without ethopropazine produced large amounts of non-specific staining throughout the cerebellar cortex. Histochemistry with ethopropazine revealed positively-labelled cells in the granular layer, which was consistent with predictions. Once again, the hypothesis that compartments of labelled and non-labelled cells would be observed was not supported. NADPH-diaphorase histochemistry was used to identify neurons containing nitric oxide (NO). As found in previous research, NADPH-diaphorase activity in the cerebellar cortex was limited to cells in the granular layer and the parallel fibers of the molecular layer. The hypothesis that discernible patches of cells and fibers would be observed was not supported, however. In the case of zebrin-II, the lack of compartmentation was consistent with studies of cartilaginous fishes and some teleosts, but inconsistent with findings in mammals. Results with acetylcholinesterase and NADPH-diaphorase histochemistry were not consistent with published reports in mammals regarding the presence of parasagittal compartments. The lack of compartmentation of cerebellar cortex in the turtle Chrysemys picta suggests that compartmentation may be a derived condition found only in mammals.