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 soma tosensory center receving inputs from limbs and trunk; some of this in put is via terminals of the dorsal column medial lemniscal pathway. Th ese fibers convey non-noxious somesthesic information. Methods: In thi s study the neurochemical content of lemniscal afferents in VPL of rat s was investigated at the electron microscopic level by combining ante rograde transport of horseradish peroxidase conjugated to wheat germ a gglutinin, injected in the dorsal dorsal column nuclei, with postembed ding immunogold labeling for glutamate (Glu). Results: Anterograde lab eling in VPL was detected only in myelinated axons and in large termin als containing round synaptic vesicles, interpreted as lemniscal affer ents. Quantitative evaluation of gold particle density showed enrichme nt of Glu immunolabeling in the identified lemniscal terminals with re spect to other neuronal profiles. Observation of serial sections immun oreacted for Glu demonstrated consistency of labeling, whereas in alte rnate sections immunoreacted for Glu and for the inhibitory amino acid GABA these two antigens were always present in distinct types of term inals. Conclusions: These findings are in agreement with several lines of evidence, obtained with different experimental approaches, support ing the hypothesis that Glu plays a major role in conveying sensory st imuli to the thalamus from second order neurons in the dorsal column n uclei. (C) 1994 Wiley-Liss, Inc.