gamma-aminobutyric acid- and glycine-immunoreactive neurons postsynaptic to substance P-immunoreactive axon terminals in the superficial layers of the rat medullary dorsal horn

gamma-Aminobutyric acid (GABA)ergic and glycinergic neurons were examined l ight- and electron-microscopically in laminae I and II of the medullary dor sal horn (MDH, i.e. spinal trigeminal nucleus caudalis in the rat). The maj ority of GABA- and glycine (Gly)-immunoreactive (-ir) neurons showed both G ABA- and Gly-immunoreactivities (-IRs). Noxious stimulation (subcutaneous i njection of formalin into perioral regions) induced Fos-IR in some of GABA- and Gly-ir neurons. GABA- and Gly-ir neuronal profiles were postsynaptic t o substance P-ir axon terminals. These results suggest that nociceptive inf ormation being carried by primary afferent SP-fibers may be relayed directl y to GABAergic and glycinergic neurons in laminae I and II of the MDH. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.