GLUTAMATERGIC AND GABAERGIC INPUT TO RAT SPINOTHALAMIC TRACT CELLS INTHE SUPERFICIAL DORSAL HORN

The distribution of synaptic terminals onto spinothalamic tract cells (types I and II) of the superficial dorsal horn was determined with sp ecial reference to the amino acid transmitters glutamate and gamma-ami nobutyric acid. Fifteen spinothalamic cells retrogradely labeled from the thalamus with the neuroanatomical tracer wheatgerm agglutinin conj ugated to horseradish peroxidase were sectioned for electron microscop y. Serial sections from several levels through each cell were immunost ained for glutamate and gamma-aminobutyric acid using a postembedding immunogold technique. Perimeter measurements of spinothalamic cell som ata and dendrites and the lengths of apposition for all terminal profi les in contact with the spinothalamic cells were obtained from electro n micrographs using a digitizing tablet. These data were used to deter mine the density of terminals on the soma and dendrites. In addition, the terminal population on these cells was categorized by transmitter content (glutamate, gamma-aminobutyric acid, or unlabeled). The result s demonstrate that terminal density increased on dendrites relative to their distance from the soma. Glutamatergic and GABAergic input compo sed 37% and 20% of the terminal population, respectively, and these pe rcentages remained uniform for the soma and dendrites. There were no s ignificant differences among the 15 cells analyzed for this study. The results, therefore, suggest that both type I and type II STT cells of the superficial DH have similar synaptic organizations. (C) 1995 Wile y-Liss, Inc.