A GOLGI-STUDY OF THE SHORT-AXON INTERNEURONS OF THE CELL LAYER AND INNER PLEXIFORM LAYER OF THE MEDIAL CORTEX OF THE LIZARD PODARCIS-HISPANICA

The medial cortex of lizards is a three-layered brain region displayin g cyto-and chemoarchitectonical, connectional, and ontogenetic charact eristics that relate it to the hippocampal fascia dentata of mammals. Three interneuron types located in the cell layer and ten others in th e inner plexiform layer (six in the juxtasomatic zone and four in the deep zone) are described in this study. The granuloid neurons, web-axo n neurons, and deep-fusiform neurons lay within the cell layer. These neurons were scarce; they were probably gamma-aminobutyric acid (GABA) -, and parvalbumin-immunoreactive and presumably participated in feed forward as well as in feed back inhibition of the principal projection cells of the lizard medial cortex. In the juxtasomatic inner plexifor m layer, the smooth vertical neurons, smooth horizontal neurons, small radial neurons, large radial neurons, pyramidal-like radial neurons, and spheroidal neurons were found. They were all probably GABA-, and p arvalbumin-immunoreactive and were involved in feed forward inhibition of principal medial cortex cells. In the deep inner plexiform layer l ay the giant-multipolar neurons, long-spined polymorphic neurons, peri ventricular neurons, and alveus-horizontal neurons. These neurons were probably GABA-immunoreactive and either neuropeptide- (somatostatin-n europeptide Y) or parvalbumin-immunoreactive. They seemed to be involv ed in feed back or even occasionally in feed forward inhibition phenom ena. (C) 1997 Wiley-Liss, Inc.