Size-related properties of vestibular afferent fibers in the frog: uptake of and immunoreactivity for glycine and aspartate/glutamate.
Vestibular afferent fibers and their somata in the ganglion of Scarpa colocalize glutamate and glycine in a size-related manner. In this study tritiated aspartate, glycine or GABA was injected in the vestibular nuclear complex of frogs to investigate the uptake by afferent fibers and the retrograde transport of these amino acids to the cell bodies in the ganglion by autoradiographical methods. Ganglion cells were labeled by [3H]aspartate or [3H]glycine but not by [3H]GABA. The intensity of labeling with [3H]glycine increased and the intensity of labeling with [3H]aspartate decreased with cell size. On consecutive semithin sections the immunoreactivity of the same neurons was investigated with antibodies against glutamate or glycine. The results of this combined study showed that smaller, strongly glutamate immunopositive ganglion cells exhibited only weak or no labeling with [3H]glycine whereas larger, less strongly glutamate immunopositive ganglion cells were more intensely labeled with [3H]glycine. A similar size-related labeling pattern was observed in ganglion cells for [3H]aspartate and glycine-immunoreactivity. Both glycine uptake and glutamate immunoreactivity, as well as aspartate uptake and glycine-immunoreactivity, tended 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 afferents. In an accompanying paper [Straka H. et al. (1995) Neuroscience 70, 697-707], we provide evidence for a size-related, monosynaptic activation of different glutamate receptors by vestibular afferent fibers.
Straka
H
H
Physiologisches Institut, München, Germany.
Reichengerger
I
I
Dieringer
N
N
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001224:Aspartic Acid / Q000493:pharmacokinetics*; D001345:Autoradiography; D001933:Brain Stem; D005724:Ganglia / Q000166:cytology / Q000378:metabolism; D018698:Glutamic Acid / Q000493:pharmacokinetics*; D005998:Glycine / Q000493:pharmacokinetics*; D007150:Immunohistochemistry; D007267:Injections; D009412:Nerve Fibers / Q000502:physiology; D011896:Rana temporaria; D014726:Vestibular Nuclei / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics
D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005998:Glycine