Distribution of GABA, glycine, and glutamate immunoreactivities in the vestibular nuclear complex of the frog

Abstract

This study describes the localization of gamma-aminobutyric acid (GABA), glycine, and glutamate immunoreactive neurons, fibers, and terminal-like structures in the vestibular nuclear complex (VNC) of the frog by using a postembedding procedure with consecutive semithin sections at the light microscopic level. For purposes of this study, the VNC was divided into a medial and lateral region. Immunoreactive cells were observed in all parts of the VNC. GABA-positive neurons, generally small in size, were predominantly located in the medial part of the VNC. Glycine-positive cells, more heterogeneous in size than GABA-positive cells, were scattered throughout the VNC. A quantitative analysis of the spatial distribution of GABA glycine immunoreactive cells revealed a complementary relation between the density of GABA and glycine immunoreactive neurons along the rostrocaudal extent of the VNC. In about 10% of the immunolabeled neurons, GABA and glycine were colocalized. Almost all vestibular neurons were, to a variable degree, glutamate immunoreactive, and colocalization of glutamate with GABA and/or glycine was typical. GABA, glycine, or glutamate immunoreactive puncta were found in close contact to somata and main dendrites of vestibular neurons. A quantitative analysis revealed a predominance of glutamate-positive terminal-like structures compared to glycine or GABA containing profiles. A small proportion of terminal-like structures expressed colocalization of GABA and glycine or glycine and glutamate. The results are compared with data from mammals and discussed in relation to vestibuloocular and vestibulo-spinal projection neurons, and vestibular interneurons. GABA and glycine are the major inhibitory transmitters of these neurons in frogs as well as in mammals. The differential distribution of GABA and glycine might reflect a compartmentalization of neurons that is preserved to some extent from the early embryogenetic segmentation of the hindbrain.

Transgenic Mouse Lines Subdivide Medial Vestibular Nucleus Neurons into Discrete, Neurochemically Distinct Populations

“…2). GABA and glycine share the vesicular GABA transporter VGAT (Wojcik et al, 2006), and a subset of MVN neurons colocalizes GABAergic and glycinergic markers (Reichenberger et al, 1997;Takazawa et al, 2004;Tanaka and Ezure, 2004). Our data indicate that there are two types of glycinergic commissural neurons with distinct processing properties (Fig.…”

An indirect basal ganglia pathway in anuran amphibians?

“…Reactivity with frog glutamate has not been confirmed yet for this antibody, although glutamate immunoreactivity has been demonstrated in anuran brains before (e.g. Reichenberger et al, 1997).…”

“…No cross-reaction was observed with aspartate and taurine. Reactivity with frog GABA has been demonstrated (Reichenberger et al, 1997).…”

Morphometric analysis of the AMPA-type neurons in the Deiters vestibular complex of the chick brain

“…Concerning the position of output descending neurons, no indication of lateral or medial differences were at this point described for those above mentioned spinal target areas except for the thoracic medulla that is innervated by dND neurons positioned at the lateral portion of both rostral and caudal poles (Wold, 1978a). As the dND lack primary projections from cells of the peripheral vestibular apparatus, there is high probability that the origin of glutamate input at dND comes from an additional territory as for instance, the spinal cord (Pompeiano and Brodal, 1957;Wold, 1978aWold, , 1979aReichenberger et al, 1997;Xiong and Matsushita, 2001). Ascendant medullar projections may provide feedback information to adjust the discharge rate of DC neurons as a lower motor looping and the differentiated distribution of AMPA subunits in DC subdivisions is suggestive that the glutamate release is supplied by additional brain areas than medulla; all capable to modulate the reflexes under vestibular influence.…”

“…Both commissural connections and primary afferents from vestibular receptors use glutamate as their major neurotransmitter suggesting that this neurotransmitter has a key role in excitatory processes within vestibular nuclei (Li et al, 1996;Straka et al, 1996;Vidal et al, 1996;Popper et al, 1997;Reichenberger et al, 1997;Bü ttner-Ennever, 2000;Vibert et al, 2000). Glutamatergic influence is exerted through ionotropic and metabotropic receptor classes, but those that usually guarantee fast responses (Watkins et al, 1990;Gerber et al, 1991) controlling neural reflexes, are typically performed by ion channel receptor-type (Currie and Stein, 1992;Smith and Darlington, 1996;Priesol et al, 2000).…”