THE SEPTAL COMPLEX OF THE TELENCEPHALON OF THE LIZARD PODARCIS-HISPANICA .1. CHEMOARCHITECTONICAL ORGANIZATION

In this paper we study the septal complex architecture in the lizard P odarcis hispanica (Lacertidae). Histochemical and immunohistochemical techniques were used to define the distribution of zinc (Timm stain), acetyl cholinesterase (AChase), gamma-aminobutyric acid (GABA), tyrosi ne hydroxylase (TH), dopamine (DA), serotonin (5-HT), and two neuropep tides: leu-enkephalin (L-ENK) and substance P (SP). These reactions de lineate a coherent map of nine septal nuclei that are named with a top ographical nomenclature: anterior, lateral, ventromedial, medial, dors olateral, ventrolateral, and dorsal septal nuclei, nucleus septalis im par, and nucleus of the posterior pallial commissure. The anterior sep tal nucleus is characterized by intense reaction for zinc and the pres ence of fibers immunoreactive for GABA, 5-HT, and L-ENK, which form pe ricellular nests. The lateral septal nucleus shows intense reaction fo r zinc, a high density of GABA-immunoreactive cells, and L-ENK-immunor eactive fibers forming basketlike figures around unstained somata. The ventromedial septal nucleus shows intense AChase reactivity, a dense network of 5-HT-immunoreactive fibers, and virtually no labeling for t he other histochemical stains. The medial septal nucleus is defined by heavy reactivity for zinc, dense DA/TH and L-ENK innervations, and th e presence of L-ENK-immunoreactive cells. The dorsolateral septal nucl eus shows intense AChase staining in the neuropile and a dense network of fibers immunoreactive for 5-HT and DA/TH, but it shows low stainin g for zinc. The ventrolateral septal nucleus shows L-ENK-immunoreactiv e cells and a dense L-ENK innervation, but low reactivity for zinc. Th e dorsal septal nucleus, intermingled with the fimbrial fibers, shows a dense population of GABA-immunoreactive cells and terminals, but it is unreactive for zinc. Two subdivisions can be established in this do rsal septal nucleus: the dorsal part, intensely reactive for AChase an d innervated by 5-HT fibers, and the central part, which shows L-ENK-i mmunoreactive neurons and fibers without reactivity for either AChase or 5-HT. The nucleus septalis impar, traversed by the fibers of the an terior pallial commissure (mildly reactive for zinc), shows reaction f or AChase but low (if present) reactivity for the remaining markers. T he nucleus of the posterior pallial commissure shows a generally low r eactivity for the histochemical reactions employed. The distribution o f these markers is similar to that found in other squamate reptiles an d allows for a direct comparison with the septal formation of mammals. Such a comparison reinforces the view that the limbic system has unde rgone a conservative evolution within vertebrates. (C) 1995 Wiley-Liss , Inc.