Calcium-binding proteins in the dorsal ventricular ridge of the lizard Psammodromus algirus

The aim of the present work was to study further the intrinsic organization of the dorsal ventricular ridge of lizards. For that purpose, the morpholo gy and distribution of cells and fibers containing the calcium-binding prot eins calbindin-D28k, parvalbumin, and calretinin were investigated by using immunohistochemical methods. Colocalization of calcium-binding proteins wi th the neurotransmitter gamma-aminobutyric acid (GABA) was also studied bec ause they are shown to coexist in many areas of the telencephalon where the y define distinct subpopulations of GABAergic local circuit neurons. Neuron s containing calcium-binding proteins are limited to the anterior part of t he dorsal ventricular ridge (ADVR), whereas the posterior or caudal portion of the ridge is devoid of immunoreactive cells. This result gives further evidence for defining both regions of the dorsal ventricular ridge. Calcium -binding proteins mark three distinct populations of neurons within the ADV R. Two of them, parvalbumin- and calretinin-expressing cells, are GABAergic . On the other hand, calbindin-containing neurons do not express GABA, and the possibility is discussed that these cells are projection neurons. The d istribution and overall density of filers immunoreactive to calcium-binding proteins suggests that most fibers are of extrinsic origin, the thalamic n uclei projecting to the ADVR and the lateral amygdala being good candidates for their origin. The comparison of data on the populations of calcium-bin ding protein-containing neurons in the reptilian ADVR with those of mammals illustrate the difficulty in finding a mammalian homologue for this contro versial region of the reptilian telencephalon. (C) 1999 Wiley-Liss, Inc.