Immunohistochemical investigation of γ‐aminobutyric acid ontogeny and transient expression in the central nervous system of Xenopus laevis tadpoles

Abstract

The ontogeny of the gamma-aminobutyric acid (GABA)-positive neurons in the brain of Xenopus laevis tadpoles was investigated by means of immunohistochemistry, using specific antibodies both against GABA and its biosynthetic enzyme, glutamate decarboxylase (GAD). The results obtained with the two antisera were comparable. The GABA system differentiates very early during development. At stages 35/36, numerous GABA-positive neurons were seen throughout the prosencephalon and formed two main bilateral clusters within the lateral walls of the forebrain that ran caudally toward the hindbrain. Other GABA-immunolabeled cell bodies, together with a conspicuous network of GABAergic fibers, were seen in the posterior hypothalamus. In the spinal cord, the lateral marginal zone was GABA-positive, as were Rohon-Beard neurons, interneurons, and Kolmer-Agdhur cells. A very rich GABA innervation was observed in the pars intermedia of the pituitary. At stage 50, plentiful immunopositive neurons and fibers were found in the telencephalic hemispheres, the diencephalon, and the mesencephalon (optic tectum and tegmentum). By stage 54, the number of GABA-immunoreactive neurons in the posterior hypothalamus had decreased, so that, at stage 58, there were very few GABA-labeled cell bodies in the dorsolateral walls of the infundibulum, despite a strong GABAergic innervation within the median eminence and the pars intermedia. From stage 58 to stage 66, the distribution pattern was very similar to that described in the adult X. laevis and in other amphibian species. These results point to transient GABA expression within the hypothalamus, possibly related to either 1) a naturally occurring cell death or 2) a phenotypic switch.

The distribution of GAD67‐mRNA in the adult zebrafish (teleost) forebrain reveals a prosomeric pattern and suggests previously unidentified homologies to tetrapods

“…This is not merely due to compact clustering of neuronal cell bodies in the subpallium versus more dispersed cell bodies in the pallium, but rather because a much smaller percentage of GAD67 -expressing cells is present in the pallium than in the subpallium. This finding is similar to reports on diverse tetrapod model organisms such as rodents (Swanson and Petrovich, 1998; Katarova et al, 2000), chick (Sun et al, 2005), and frog ( Xenopus : (Barale et al, 1996). All pallial subdivisions including the medial (Dm), dorsal (Dd), central (Dc), lateral (Dl) and posterior (Dp) zone of the dorsal telencephalic area exhibit scattered GAD67 -expressing neurons, but Dl is defined by even less numerous GAD67 -expressing cells compared to all other pallial areas.…”

Cannabinoid receptor CB1-like and glutamic acid decarboxylase-like immunoreactivities in the brain of Xenopus laevis

“…Specificity of the antibody GAD antibody had been demonstrated previously in rat (Oertel et al 1981) and in Xenopus (Barale et al 1996).…”

Distribution of pro-opiomelanocortin and its peptide end products in the brain and hypophysis of the aquatic toad, Xenopus laevis

“…According to the common POMC-function hypothesis, the ventral hypothalamic nucleus would be involved in some way in the control of melanotrope cell activity, in the regulation of the process of background adaptation, or in the control of the corticotropes or its related physiological functions. In Xenopus, data to support this assumption are lacking, but in Rana ridibunda the ventral hypothalamic nucleus contains a-MSH and is involved in the inhibitory control of the melanotrope cells (Andersen et al 1987(Andersen et al , 1993Tonon et al 1992;Artero et al 1994;Battaglia et al 1995;Lamacz et al 1995;Barale et al 1996). Moreover, several reports indicate the presence of POMC and POMC-derived products (ACTH, a-MSH and endorphins) in the mammalian homologue of the ventral hypothalamic nucleus, the arcuate nucleus, e.g.…”