Histoenzymological Distribution of Acetylcholinesterase in the Rostral Mesencephalic Torus Semicircularis and Tegmental Nuclei of an Indian air Breathing Teleost Heteropneustes fossilis

Abstract

Mesencephalon or mid brain of the fishes consists of dorsal roof or optic tectum and ventral roof or tegmentum. Optic tectum (OT) in the presently studied specimen is a bilobed structure which is composed of six stratified zones of differently shaped and differently sized neurons. Tegmental area is the major component of the mid brain of fishes which is responsible for diverse functions and it comprises many cholinergic and cholinoceptive nuclear groups particularly the rostral tegmental area in which many caudal thalamic and hypothalamic nuclei diffuse. Enzyme acetylcholinesterase (AChE) which hydrolyses the neurotransmitter acetylcholine in to choline and acetate at the synaptic cleft is a prime marker of cholinergic-cholinoceptive neurons in the vertebrate central nervous system. In the present study a histochemical technique was carried out to locate AChE in the tegmental area described by Hedreen J.C. et.al (1985).
In the tegmentum of Heteropneustes the density of acetylcholinesterase stained cells was very high. In the dorsal and rostral tegmental nuclei some AChE positive cells were observed which were abundant in latter. The nucleus anterioris tuberis and nucleus lataralis tuberis which are the hypothalamic nuclei diffused in mesencephalic area displayed very intense AChE positive cells while central pretectal nuclei exhibited medium to weak stained cells. Dorsal posterior nucleus and central posterior nucleus of thalamus also showed intensely AChE stained cells. AChE positive cells were observed in the whole rostro-caudal extension of the tuberal area and lateral recess nuclei. The present results corroborate the previously reported connection between the rostral tegmental nucleus and the nucleus of thalamus and pretectal area and to the hypothalamus on the basis of degree of AChE intensity. Present findings have also been discussed in the light of previous findings on other vertebrate groups