Enrichment of glutamate immunoreactivity in lemniscal terminals in the ventropostero lateral thalamic nucleus of the rat: an immunogold and WGA-HRP study.
BACKGROUND
The ventropostero lateral nucleus (VPL) is a thalamic somatosensory center receiving inputs from limbs and trunk; some of this input is via terminals of the dorsal column medial lemniscal pathway. These fibers convey non-noxious somesthesic information.


METHODS
In this study the neurochemical content of lemniscal afferents in VPL of rats was investigated at the electron microscopic level by combining anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin, injected in the dorsal dorsal column nuclei, with postembedding immunogold labeling for glutamate (Glu).


RESULTS
Anterograde labeling in VPL was detected only in myelinated axons and in large terminals containing round synaptic vesicles, interpreted as lemniscal afferents. Quantitative evaluation of gold particle density showed enrichment of Glu immunolabeling in the identified lemniscal terminals with respect to other neuronal profiles. Observation of serial sections immunoreacted for Glu demonstrated consistency of labeling, whereas in alternate sections immunoreacted for Glu and for the inhibitory amino acid GABA these two antigens were always present in distinct types of terminals.


CONCLUSIONS
These findings are in agreement with several lines of evidence, obtained with different experimental approaches, supporting the hypothesis that Glu plays a major role in conveying sensory stimuli to the thalamus from second order neurons in the dorsal column nuclei.
De Biasi
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Dipartimento di Fisiologia e Biochimica generali, Sezione di Isotologia e Anatomia umana, Milano, Italy.
Amadeo
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Spreafico
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Rustioni
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D000818:Animals; D001692:Biological Transport; D018698:Glutamic Acid / Q000032:analysis* / Q000276:immunology; D006735:Horseradish Peroxidase; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D013787:Thalamic Nuclei / Q000378:metabolism* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000032:analysis
D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D006735:Horseradish Peroxidase