Ontogeny of somatostatin immunoreactive neurons in the medial cerebral cortex and other cortical areas of the lizardPodarcis hispanica

Abstract

The ontogeny of somatostatin immunoreactive interneurons in the cerebral cortex of the lizard Podarcis hispanica has been studied in histological series of embryos, perinatal specimens, and adults. Somatostatin immunoreactive interneurons appear in the early stages of lizard cerebral cortex ontogeny, their number increases during embryonary development, reaches a peak in early postnatal life, and decreases in adult lizards. The first somatostatin immunoreactive somata in the lizard forebrain appeared on E36, and they were located in non cortical areas. Then, on E39 and later, somatostatin immunoreactive neurons were seen in the lizard cortex in a rostral-to-caudal spatial gradient, which parallels that of the normal histogenesis of the lizard cerebral cortex. On E39, labelled somata were seen in the medial and dorsal cortex inner plexiform layers; immunoreactive puncta and dendritic processes were detectable in the inner plexiform layer of the medial cortex. On E40, labelled neurons were observed in the inner plexiform layer of the lateral cortex; labelled processes were found in the inner plexiform layers (dorsomedial, dorsal, and lateral cortices) and the outer plexiform layers (medial and dorsomedial cortices). At hatching (P0), some somatostatin immunoreactive neurons populated the external plexiform layer of the dorsomedial cortex. On P28, groups of labelled neurons appeared in the cell layer of dorsal and lateral cortices, reaching the adult-mature pattern of somatostatin immunoreactivity in the lizard cerebral cortex, i.e., labelled somata and dendritic processes populating the inner plexiform layers in addition to an axonic labelled plexus in the outermost part of the outer plexiform layers. Immunoreactive somata and processes occupied all the cortical areas, but they were especially abundant in the dorsomedial cortex. Proliferating Cell Nuclear Antigen (PCNA) immunostaining in the same histological series revealed that the number of PCNA immunoreactive nuclei in the subjacent proliferative neuroepithelium followed an inverse-complementary evolution to somatostatin, suggesting some temporal relationship between somatostatin immunoreactive cells and neurogenesis in the lizard cerebral cortex.

Development, evolution and pathology of neocortical subplate neurons

“…According to this hypothesis, the primordial plexiform layer (preplate)-derived subplate and marginal zone are the 'reptilian framework' of the mammalian cerebral cortex 118 , and a preplate is present during development of the dorsal cortex in reptiles 119 . Thus, the subplate originated as an embryonic structure before the appearance of the neocortex and the inversion of the cortical neurogenetic gradient observed in mammals.…”

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

“…Their neuronal populations share many similarities, but also display minor differences (see Nacher et al, 1996). Table 3 summarizes the main resemblances between medial cortex projection neurons of Podarcis, and dentate granule cells of the hippocampal formation of different mammalian species.…”

Characterization of adult neurogenesis in lizardPhrynocephalus vlangalii(Agamidae: Reptilia)

“…However, in the Tarentola mauritanica, the majority of newborn cells seemed to be incorporated into MC (Perez-Canellas & Garcia-Verdugo 1996), which is considered as an area homologous to dentate gyrus of hippocampus in mammals on grounds of their anatomy, cyto-and chemoarchitecture and postnatal development (Lopez-Garcia et al 1992;Nacher et al 1996), and closely involved with learning and memory (Day et al 2001;Rodriguez et al 2002); DVR in Trachemys scrypta was found to show the most intensive labeling accumulation (Perez-Canellas et al 1997). It is possible that these interspecific differences may depend on behavioral patterns induced by distinct environmental stimuli.…”