DISTRIBUTION OF ACETYLCHOLINESTERASE IN THE TELENCEPHALON OF AN INDIAN AIR BREATHING TELEOST HETEROPNEUSTES FOSSILIS: A HISTOCHEMICAL ANALYSIS
Acetylcholinesterase (AChE) is an enzyme belonging to hydrolase group which splits the acetylcholine in to choline and acetate. It is supposed to be a marker of cholinergic and cholinoceptive neurons. Present study has been carried out to histoenzymologically map the pallial and subpallial telencephalic nuclei of H. fossilis and to compare the present investigation with that of other vertebrates studied earlier to set a homology amongst different nuclei in the light of recent cytoarchitectural & connectional studies. In addition, the functional significance of the variable pattern of distribution of enzyme has also been discussed. Method: In the present study a modified histochemical technique has been employed to visualize acetylcholinesterase containing neurons described by Hedreen JC et al. Results: AChE is differentially expressed in the various pallial and subpallial zones, thus demarcating these centres. Among the pallial nuclei, medial (Dm) and dorsal lateral (Dld) nuclei showed intense activity while ventral dorso lateral (dlv) nucleus showed moderate reaction. Central nucleus (Dc) showed mild to negative activity for AChE. In contrast most of the subpallial nuclei viz. dorsal (Vd), Ventral (Vv), supracommussural (Vs) and entopeduncular (E) nuclei demonstrated high intensity. Fibre tracts and commisssures however exhibited no activty. Conclusion: In the light of the earlier & present findings, the highly intense nuclei might be considered as cholinergic, moderate intense nuclei, the cholinoceptive and the mild or negatively stained nuclei are supposed to be non cholinergic. Finally due to cholinergic and non cholinergic roles of AChE, it is inadequate to conclude about the exact nature of neurons since AChE might be present in noncholinergic neurons also. Thus a colocalizatin of AChE and ChAT (choline acetyltransferase) is further needed.