Presynaptic ionotropic glutamate receptors modulate transmission at primary afferent synapses in several glutamatergic systems. To test whether primary gustatory afferent fibers express Ca2+-permeable AMPA/kainate receptors, we utilized kainate-stimulated uptake of Co2+ along with immunocytochemistry for the Ca2+-binding proteins (CaBPs) calbindin and calretinin to investigate the primary gustatory afferents in goldfish (Carassius auratus). In goldfish, the primary gustatory nucleus (equivalent to the gustatory portion of the nucleus of the solitary tract) includes the vagal lobe, which is a large, laminated structure protruding dorsally from the medulla. Kainate-stimulated uptake of Co2+ (a measure of Ca 2+-fluxing glutamate receptors) shows punctate staining distributed in the distinct laminar pattern matching the layers of termination of the primary gustatory afferent fibers. In addition, CaBP immunocytochemistry, which correlates highly with expression of Ca2+-permeable AMPA/kainate receptors, shows a laminar pattern of distribution similar to that found with kainate-stimulated cobalt uptake. Nearly all neurons of the vagal gustatory ganglion show Co2+ uptake and are immunopositive for CaBPs. Transection of the vagus nerve proximal to the ganglion results in loss of such punctate Co3+ uptake and of punctate CaBP staining as soon as 4 days postlesion. These results are consonant with the presence of Ca 2+-fluxing glutamate receptors on the presynaptic terminals of primary gustatory terminals, providing an avenue for modulation of primary gustatory input. © 2007 Wiley-Liss, Inc.
|Journal||Journal of Comparative Neurology|
|Publication status||Published - 1 Feb 2008|
- Calcium binding protein
- Presynaptic receptor
- Solitary tract
- Vagal lobe