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Quantitative analysis of immunogold labeling indicates low levels and non‐vesicular localization of L ‐aspartate in rat primary afferent terminals
Author(s) -
Larsson Max,
Persson Stefan,
Ottersen Ole Petter,
Broman Jonas
Publication year - 2000
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/1096-9861(20010205)430:2<147::aid-cne1021>3.0.co;2-5
Subject(s) - immunogold labelling , biology , synaptic vesicle , glutamate receptor , axon , neurotransmitter , neuroscience , microbiology and biotechnology , vesicle , anatomy , biochemistry , central nervous system , ultrastructure , receptor , membrane
The role of L ‐aspartate as an excitatory neurotransmitter in primary afferent synapses in the spinal cord dorsal horn is disputed. To further investigate this issue, we examined the presence of aspartate‐like immunoreactivity in primary afferent nerve terminals and other tissue components of the dorsal horn. We also examined the relationship between aspartate and glutamate immunogold labeling density and the density of synaptic vesicles in primary afferent terminals and presumed inhibitory terminals forming symmetric synapses. Weak aspartate immunosignals, similar to or lower than those displayed by presumed inhibitory terminals, were detected in both C‐fiber primary afferent terminals in lamina II (dense sinusoid axon terminals, identified by morphological criteria) and in A‐fiber primary afferent terminals in laminae III–IV (identified with anterograde transport of choleragenoid‐horseradish peroxidase conjugate). The aspartate immunogold signal in primary afferent terminals was only about one‐fourth of that in deep dorsal horn neuronal cell bodies. Further, whereas significant positive correlations were evident between synaptic vesicle density and glutamate immunogold labeling density in both A‐ and C‐fiber primary afferent terminals, none of the examined terminal populations displayed a significant correlation between synaptic vesicle density and aspartate immunogold labeling density. Thus, our results indicate relatively low levels and a non‐vesicular localization of aspartate in primary afferent terminals. It is therefore suggested that aspartate, rather than being a primary afferent neurotransmitter, serves a role in the intermediary metabolism in primary afferent terminals. J. Comp. Neurol. 430:147–159, 2001. © 2001 Wiley‐Liss, Inc.