Enkephalin-like immunoreactivity within the telencephalon of the reptile Caiman crocodilus

Abstract

Immunohistochemical methods were used to characterize the distribution of staining for leucine enkephalin-like and methionine enkephalin-like immunoreactivities in the telencephalon of Caiman crocodilus. Very similar distributions of both leucine enkephalin-like and methionine enkephalin-like immunoreactivity were observed. The greatest accumulations of enkephalin-like immunoreactive material were observed within the ventrolateral area of the telencephalon, a region considered comparable to the mammalian corpus striatum and avian paleostriatal complex (i.e. basal ganglia) on the basis of embryological, anatomical and histochemical criteria. Within the ventrolateral area, many small immunoreactive neuron cell bodies were observed, particularly within the rostromedial small-celled component of the ventrolateral telencephalic area. A rich plexus of fibers displaying enkephalin-like immunoreactivity invests the entire ventrolateral area including the large-celled subdivision. A system of thick, coarse, radially-directed immunoreactive fibers running between medial and dorsal portions of the ventrolateral area and more ventral portions was observed in this study. Other structures in the caiman telencephalon, containing large numbers of neural elements displaying enkephalin-like immunoreactivity, were the ventral paleostriatum (a region considered comparable to the ventral pallidum of mammals), the lateral septal nucleus and the nucleus accumbens. The corticoid areas contained far fewer elements displaying enkephalin-like immunoreactivity, although immunoreactive fibers and cell bodies were observed within the medial, dorsal and lateral corticoid areas, particularly at caudal levels. The dorsal ventricular ridge contains the lowest number of immunoreactive cells and fibers of any structure within the caiman telencephalon although occasional neurons displaying enkephalin-like immunoreactivity were encountered in the dorsal ventricular ridge. The results are compared to the distribution of enkephalin within the cerebral hemispheres of mammals, birds and other reptiles.