CALRETININ IMMUNOREACTIVITY IN THE CEREBRAL-CORTEX OF THE LIZARD PSAMMODROMUS-ALGIRUS - A LIGHT AND ELECTRON-MICROSCOPIC STUDY

The present study describes the distribution and structural features o f calretinin-immunoreactive neurons and fiber plexuses in the cerebral cortex of a lacertid lizard, at the light and electron microscopic le vels, and also examines the colocalization of calretinin with parvalbu min and gamma-aminobutyric acid (GABA) in certain cortical regions. Ca lretinin-immunoreactive neurons are present throughout the cerebral co rtex of Psammodromus and can be classified according to morphological and neurochemical criteria. Neurons in the medial cortex are small, sp ine-free and lack parvalbumin, whereas in the lateral cortex, calretin in-immunoreactive neurons display sparsely spiny dendrites and also la ck parvalbumin. The dorsomedial and dorsal cortices contain most of th e calretinin cortical neurons, which were located almost exclusively i n the deep plexiform layer. These neurons are large, with an extensive spine-free dendritic tree. Most of the calretinin-immunoreactive neur ons of dorsomedial and dorsal cortices are GABAergic and contain parva lbumin. Calretinin-immunoreactive fibers form two main afferent system s in the cortical areas. One probably intrinsic inhibitory system, ari sing from the calretinin and parvalbumin GABAergic neurons in the dors omedial and dorsal cortices, makes symmetrical synapses on the soma an d proximal dendrites of neurons located in the cell layers of the same cortical areas. The other system is formed by extremely thin axons ru nning within the superficial plexiform layers of the medial, dorsomedi al and dorsal cortices. These axons make asymmetrical synapses on dend rites or dendritic spines. We suggest that this system, probably extri nsic excitatory, arises from neurons located in the basal forebrain. J . Comp. Neurol. 382:382-393, 1997. (C) 1997 Wiley-Liss, Inc.