A Golgi study of the principal projection neurons of the medial cortex of the lizardPodarcis hispanica

Abstract

The medial cortex of lizards is a simple three-layered brain region displaying many characteristics that parallel the hippocampal fascia dentata of mammals. Its principal neurons form a morphologically diverse population, partly as a result of the prominent continuous growth of this nervous center. By using the classic Golgi impregnation method, we describe here the morphology of the principal neurons populating the medial cortex of Podarcis hispanica. These were projection neurons giving off descending axons. These axons displayed deep collateral branches provided with prominent axonal boutons, while the main axonal branch reached adjacent cortical areas and the bilateral septum. According to three main classification criteria, dendritic tree pattern, dendritic spine covering, and soma size, we have distinguished eight different types of projection neurons. Five of them, "heavily spiny granular" (monotufted, medium-sized), "heavily spiny bitufted" (large), "spiny bitufted" (medium-sized), "sparsely spiny bitufted" (small), and "superficial multipolar" (small), were found in the cell layer, whereas the three others lay outside this layer and were regarded as ectopic types ("outer plexiform ectopic bitufted," "inner plexiform ectopic bitufted", and "inner plexiform monotufted"). Additional secondary criteria, soma position and shape, allowed us to further classify bitufted neurons into three distinct subtypes each: "superficial-round," "intermediate-fusiform," and "deep-pyramidal." Moreover, a variety of small impregnated cells were observed; they probably represented newly generated immature neurons that had not yet completed their development. These cell types were compared with those reported previously in Golgi, immunocytochemical, and electron-microscopy studies, both in the reptilian medial cortex and in the mammalian dentate area. Presumably age-related changes and synaptic relationships of these projection cells in the medial cortex circuitry were analyzed.

Neuronal classes in the corticoid complex of the telencephalon of the strawberry finch, Estrilda amandava

“…The classification criteria, such as the differential dendritic tree pattern, dendritic spine covering, axonal arborization and soma shape and size, suggest that three main types of neurons occur in the corticoid complex of E. amandava: projection neurons, local circuit neurons and stellate neurons. In the case of reptiles, the types of neurons seem to be variable (Wouterlood 1981;Berbel et al 1987;Guirado et al 1987;Luis de la Iglasia et al 1994;Luis de la Iglesia and Lopez-Garcia 1997;Maurya and Srivastava 2006), whereas in the present study on the strawberry finch and in previous reports of the types of neurons in the hippocampal region of birds (Montagnese et al 1996;Tömböl et al 2000aTömböl et al , 2000bSrivastava et al 2007a), neuronal types are consistent and independent of the number of individuals studied.…”

Heterogeneity of spine density in pyramidal neurons of isocortex of mongoose, Herpestes edwardsii (É. Geoffroy Saint‐Hilaire 1818)

“…The pyramidal neurons accounting for at least 70% of the total neocortical population in mammals form the principal element in neocortical circuit. The evolutionary trend of pyramidal neurons' development can be traced right from "extraverted" neurons observed in amphibian pallium; pyramid-like neurons in reptilian cortex (Luis de la Iglasia and Lopez Garcia, 1997;Srivastava et al, 2007Srivastava et al, , 2009b; in hippocampus of homing pigeon, chick (T€ omb€ ol et al, 2000); corticoid complex in strawberry finch (Srivastava et al, 2009a) to the well developed neocortical elements referred by Cajal as "psychic cells" (Nieuwenhuys, 1994). The different aspects of pyramidal cell microanatomy may influence different aspects of cellular, and systems function (Elston and DeFelipe, 2002;Ha€usser and Mel, 2003;Segev et al, 2001).…”

Adult Hippocampal Neurogenesis in Different Taxonomic Groups: Possible Functional Similarities and Striking Controversies

“…The medial cortex of the lizard is a trilaminar region that exhibits many characteristics similar to the mammalian dentate gyrus, as demonstrated by the Golgi impregnation method and immunocytochemistry studies [68,69]. The neuronal types of the dorsomedial cortex of reptiles, the parahippocampal area in birds, and the CA3 region in mammals may present with homology [70] (Figure 1).…”