title: Glutamate-like immunoreactivity in retinal terminals of the mouse suprachiasmatic nucleus.
abstract: With a view to identifying the neurotransmitter content of retinal terminals within the mouse suprachiasmatic nucleus, a highly specific antiserum to glutaraldehyde-coupled glutamate was used in a postembedding immunogold procedure at the ultrastructural level. Retinal terminals were identified by cholera toxin--horseradish peroxidase transported anterogradely from the retina and reacted with tetramethyl benzidine/tungstate/H2O2, or by their characteristically pale and distended mitochondria with irregular cristae. Controls included model ultrathin sections containing high concentrations of various amino acids. Alternate serial sections were labelled with anti-glutamate and anti-gamma-aminobutyric acid (GABA). Data were analysed by computer-assisted image analysis. Density of glutamate labelling (gold particles per micron2) on whole retinal terminals was > 3 times higher than that on postsynaptic dendrites, and > 5 times higher than that on miscellaneous non-retinal non-glutamatergic terminals in the suprachiasmatic nucleus. The overall density of gold particles over retinal terminals was approximately 3 times higher than that over GABAergic terminals, in which glutamate-like immunoreactivity was mainly mitochondrial. Labelling of vesicles in retinal terminals was almost 5 times greater than the apparent labelling of vesicles in GABAergic terminals, underscoring the location of transmitter glutamate within synaptic vesicles in retinal terminals. In the retino-recipient region of the suprachiasmatic nucleus there was also a small population of non-retinal glutamatergic terminals. Their overall immunoreactivity was similar to or exceeded that of retinal terminals, but morphological features clearly distinguished between these two types of glutamate-containing terminals. The present results indicate that the vast majority of retinal terminals may use glutamate as a transmitter, in keeping with electrophysiological and neuropharmacological data from other sources. The possibility of cotransmitters within retinal terminals, suggested by the presence of dense-core vesicles among the glutamate-containing synaptic vesicles, has still to be addressed.
authors.affiliation: Department of Cell and Animal Biology, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
authors.forename: M
authors.initials: M
authors.lastname: Castel
authors.forename: M
authors.initials: M
authors.lastname: Belenky
authors.forename: S
authors.initials: S
authors.lastname: Cohen
authors.forename: O P
authors.initials: OP
authors.lastname: Ottersen
authors.forename: J
authors.initials: J
authors.lastname: Storm-Mathisen
mesh_terms: D000818:Animals; D001560:Benzidines; D002772:Cholera Toxin; D002863:Chromogenic Compounds; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006735:Horseradish Peroxidase; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D001560:Benzidines; D002863:Chromogenic Compounds; D005971:Glutamates; C021758:3,3',5,5'-tetramethylbenzidine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D002772:Cholera Toxin; D006735:Horseradish Peroxidase