ONTOGENY OF SOMATOSTATIN-IMMUNOREACTIVE NEURONS IN THE MEDIAL CEREBRAL-CORTEX AND OTHER CORTICAL AREAS OF THE LIZARD PODARCIS-HISPANICA

The ontogeny of somatostatin immunoreactive interneurons in the cerebr al cortex of the lizard Podarcis hispanica has been studied in histolo gical series of embryos, perinatal specimens, and adults. Somatostatin immunoreactive interneurons appear in the early stages of lizard cere bral cortex ontogeny, their number increases during embryonary develop ment, reaches a peak in early postnatal life, and decreases in adult l izards. The first somatostatin immunoreactive somata in the Lizard for ebrain appeared an E36, and they were located in non cortical areas. T hen, on E39 and later, somatostatin immunoreactive neurons were seen i n the lizard cortex in a rostral-to-caudal spatial gradient, which par allels that of the normal histogenesis of the Lizard cerebral cortex. On E39, labelled somata were seen in the medial and dorsal cortex inne r 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 lat eral cortex; labelled processes were found in the inner plexiform laye rs (dorsomedial, dorsal, and lateral cortices) and the outer plexiform layers (medial and dorsomedial cortices). At hatching: (P0), some som atostatin immunoreactive neurons populated the external plexiform laye r of the dorsomedial cortex. On P28, groups of labelled neurons appear ed in the cell layer of dorsal and lateral cortices, reaching the adul t-mature pattern of somatostatin immunoreactivity in the lizard cerebr al cortex, i.e., labelled somata and dendritic processes populating th e inner plexiform layers in addition to an axenic labelled plexus in t he outermost part of the outer plexiform layers. Immunoreactive somata and processes occupied all the cortical areas, but they were especial ly abundant in the dorsomedial cortex. Proliferating Cell Nuclear Anti gen (PCNA) immunostaining in the same histological series revealed tha t the number of PCNA immunoreactive nuclei in the subjacent proliferat ive neuroepithelium followed an inverse-complementary evolution to som atostastin. suggesting some temporal relationship between somatostatin immunoreactive cells and neurogenesis in the lizard cerebral cortex. (C) 1996 Wiley-Liss, Inc.