IMMUNOHISTOCHEMICAL EVIDENCE FOR GABA AND GLYCINE-CONTAINING TRIGEMINAL PREMOTONEURONS IN THE GUINEA-PIG

Electrophysiological studies have suggested that inhibition of trigemi nal motoneurons during mastication and the jaw-opening reflex are medi ated by last-order interneurons (premotoneurons) utilizing GABA and gl ycine [Chandler et al. (1985), Brain Res., 325:181-186; Enomoto et al. (1987), Neurosci. Res., 4:396-412; Goldberg and Nakamura (1968), Expe rientia, 24:371-373; Kidokoro et, al. (1968), J. Neurophysiol., 31:695 -708; Nakamura et al. (1978), Exp. Neurol., 61:1-14]. In the present s tudy we performed a series of double-labeling experiments in guinea pi gs to determine the location of neurons which contain GABA (gamma amin obutyric acid) or glycine that project to the trigeminal motor nucleus (Mo5). This was accomplished by performing immunohistochemical staini ng in combination with a retrograde tract tracing technique using coll oidal gold bound to inactivated WGA-HRP (wheat germ agglutin-horseradi sh peroxidase) (gWGA-HRP) as our retrograde tracer. Neurons which had a positive immunoreactivity to GABA or GAD (glutamic acid decarboxylas e) and contained the retrograde marker were located in regions adjacen t to the Mo5 such as the intertrigeminal, supratrigeminal, peritrigemi nal and rostral portions of the parvocellular reticular formation alph a. Neurons which had a positive immunoreactivity to glycine and contai ned the retrograde marker were identified in the parvocellular reticul ar formation, the spinal trigeminal nucleus oralis, supratrigeminal an d intertrigeminal regions. These data provide anatomical evidence for GABAergic and glycinergic projections to Mo5. (C) 1994 Wiley-Liss, Inc .