Studies on the identity of the rat optic nerve transmitter.
The possible role of glutamate, aspartate, sulfur-containing excitatory amino acids and gamma-glutamyl peptides as major transmitters in the rat optic nerve was evaluated. Four days following optic nerve lesion the K(+)-evoked Ca(2+)-dependent glutamate release was reduced to 31 +/- 16% (+/- S.D., n = 9) comparing release from slices of the denervated (contralateral to the lesion) and non-denervated (ipsilateral) superior colliculus, indicative of a major transmitter function for glutamate. However, significant decreases in glutamate release could not be detected seven days following the lesion (n = 5). Other studies have shown that optic nerve denervation induce formation of synapses of non-retinal origin and cause other cellular changes which may reduce the effect of deafferentation on glutamate release after 7 days. No significant change was observed in aspartate release following the lesion. The concentrations of cysteine sulfinate, cysteate, homocysteine sulfinate, homocysteate and O-sulfo-serine in the optic layers of the superior colliculus were below 1 nmol/g tissue (n = 6). Theoretical considerations indicate that this level is too low for a function of any of these as a major optic nerve transmitter. All postsynaptic components in the rat superior colliculus response, evoked by electrical optic nerve stimulation, were reduced by kynurenate (1-10 mM), a broad spectrum glutamate-receptor antagonist. The study gives further support for the view that glutamate is a major transmitter in the rat optic nerve.
Li
X
X
Institute of Anatomy and Cell Biology, University of Göteborg, Sweden.
Hallqvist
A
A
Jacobson
I
I
Orwar
O
O
Sandberg
M
M
D000603:Amino Acids, Sulfur / Q000032:analysis; D000818:Animals; D001224:Aspartic Acid / Q000032:analysis; D003714:Denervation; D018846:Excitatory Amino Acids / Q000032:analysis; D018698:Glutamic Acid / Q000032:analysis; D066298:In Vitro Techniques; D009412:Nerve Fibers / Q000502:physiology; D009434:Neural Pathways / Q000737:chemistry* / Q000502:physiology; D009479:Neuropeptides / Q000032:analysis; D018377:Neurotransmitter Agents / Q000032:analysis*; D009900:Optic Nerve / Q000737:chemistry* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013477:Superior Colliculi / Q000737:chemistry* / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D000603:Amino Acids, Sulfur; D018846:Excitatory Amino Acids; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D001224:Aspartic Acid; D018698:Glutamic Acid