NADPH diaphorase‐positive neurons in the lizard hippocampus: A distinct subpopulation of GABAergic interneurons

Abstract

We analyzed the distribution and light-microscopic features of the NADPH diaphorase-containing structures in the lizard hippocampus, likely to correspond to nitric oxide synthase-containing cells and fibers, and thus likely to release nitric oxide. We also studied co-localization of NADPH diaphorase with the neurotransmitter GABA, the calcium-binding protein parvalbumin, and the neuropeptide somatostatin, in order to examine whether putative nitric oxide-synthesizing neurons represent a different subpopulation of GABA cells, on which the authors recently reported in lizards. We also studied co-localization of NADPH diaphorase with parvalbumin or somatostatin in mice to ascertain whether the characteristics of this population in reptiles parallel the situation in mammals. Most of the positive NADPH diaphorase neurons were stained in a Golgi-like manner and were in the plexiform layers of the lizard hippocampus with morphologies ranging from bipolar to multipolar. Co-localization with GABA was 100%, and NADPH diaphorase-positive neurons in the lizard hippocampus did not contain parvalbumin or somatostatin. The results indicate that putative nitric oxide-synthesizing neurons represent a distinct subpopulation of GABA interneurons in the lizard hippocampus. Two different types of fibers were described in the plexiform layers: one type bearing thick varicosities, and the other thinner ones. We discuss the possibility that at least part of the positive fibers arise from a hypothalamic aminergic nucleus contacting the third ventricle, the periventricular hypothalamic organ. Most radial glia were stained almost completely and formed typical end-feet both at the pia and around capillaries. The results of this study confirm that the capacity for synthesizing nitric oxide is linked to a determined set of neuronal markers depending on the specific brain region, and they provide new resemblances between hippocampal regions in different classes of vertebrates.

The lizard cerebral cortex as a model to study neuronal regeneration

“…Most local interneurons are GABA-immunoreactive (Lopez-Garcia et al 1988 a, Schwerdtfeger and and display either parvalbumin (Fig. 1E), calbindin, or calretinin immunoreactivities (Martinez-Guijarro et al 1991a, Martinez-Guijarro andFreund 1992) as well as a wide spectrum of neuropeptide immunoreactivities (Davila et al 1991) or even NADPH diaphorase/ NOS synthetase (Davila et al 1995).…”

Characterization of NADPH Diaphorase- and Doublecortin-Positive Neurons in the Lizard Hippocampal Formation

“…This might have stemmed from the fact that all these works used 4% paraformaldehyde (PFA) as fixative, which has been reported to be suboptimal for completely staining NADPHd+ neurons in lizards [own observations; Dávila et al, 1995] and rodents [Valtschanoff et al, 1993;Dinerman et al, 1994].…”

“…In lizards, NADPHd+ neurons were reported in Gekko gecko PFA/ picric acid-fixed hippocampal formation [Smeets et al, 1997]. These neurons were shown to be GABAergic in the PFA/glutaraldehyde-fixed hippocampal formation of Psammodromus algirus [Dávila et al, 1995]. The same authors also tested different fixatives (PFA, PFA/picric acid, and PFA/glutaraldehyde mixtures) and concluded PFA/ glutaraldehyde yielded the clearest results.…”

“…Nitric oxide (NO) has been studied in a variety of systems and in virtually all groups of animals [Sandell, 1986;Johansson and Carlberg, 1994;Dávila et al, 1995;Martínez, 1995;Wallhäusser-Franke et al, 1995;Muñoz et al, 1996;Franca et al, 2000;Ashwell and Phillips, 2006]. It modulates the activity of endotheliocytes, macrophages, muscle cells, and neurons, playing roles in blood pressure control [Palmer et al, 1988], inflammatory responses [Nathan and Hibbs, 1991], muscle relaxation [Bolotina et al, 1994], and neurotransmission [Arnold et al, 1977], respectively.…”

Cholecystokinin Innervation of the Cerebral Cortex in a Reptile, the Lizard <i>Psammodromus algirus</i>

“…For example, some chemically defined neuronal types in mammalian hippocampus are also found in reptilian cortex [Dávila et al, 1988[Dávila et al, , 1991Martínez-Guijarro et al, 1991]. In addition, colocalization of GABA with neuropeptides (somatostatin or NPY) or the calcium-binding protein parvalbumin or with NADPH diaphorase activity indicates that a subclass of the GABAergic hippocampal interneurons in reptiles is very similar to one in mammals [Dávila et al, 1991[Dávila et al, , 1993[Dávila et al, , 1995Martínez-Guijarro et al, 1993]. Some of these neuronal types are also involved in similar synaptic circuits within the hippocampus of reptiles and mammals [Dávila et al, 1993].…”