H. Straka et al., SIZE-RELATED PROPERTIES OF VESTIBULAR AFFERENT-FIBERS IN THE FROG - UPTAKE OF AND IMMUNOREACTIVITY FOR GLYCINE AND ASPARTATE GLUTAMATE, Neuroscience, 70(3), 1996, pp. 685-696
Vestibular afferent fibers and their somata in the ganglion of Scarpa
colocalize glutamate and glycine in a size-related manner.(17) In this
study tritiated aspartate, glycine or GABA was injected in the vestib
ular nuclear complex of frogs to investigate the uptake by afferent fi
bers and the retrograde transport of these amino acids to the cell bod
ies in the ganglion by autoradiographical methods. Ganglion cells were
labeled by [H-3]aspartate or [H-3]glycine but not by [H-3]GABA. The i
ntensity of labeling with [H-3]glycine increased and the intensity of
labeling with [H-3]aspartate decreased with cell size. On consecutive
semithin sections the immunoreactivity of the same neurons was investi
gated with antibodies against glutamate or glycine. The results of thi
s combined study showed that smaller, strongly glutamate immunopositiv
e ganglion cells exhibited only weak or no labeling with [H-3]glycine
whereas larger, less strongly glutamate immunopositive ganglion cells
were more intensely labeled with [H-3]glycine. A similar size-related
labeling pattern was observed in ganglion cells for [H-3]aspartate and
glycine-immunoreactivity. Both glycine uptake and glutamate immunorea
ctivity, as well as aspartate uptake and glycine-immunoreactivity, ten
ded to be inversely correlated with the size of a given ganglion cell.
These results provide evidence for a specific, size-related uptake of
aspartate and glycine and are compatible with our hypothesis that the
two amino acids are coreleased by thick but not by thin vestibular af
ferents. In an accompanying paper [Straka H. et al. (1995) Neuroscienc
e 70, 697-707], we provide evidence for a size-related, monosynaptic a
ctivation of different glutamate receptors by vestibular afferent fibe
rs.