ELECTRON-MICROSCOPIC ANALYSIS OF GAMMA-AMINOBUTYRIC-ACID AND GLYCINE COLOCALIZATION IN RAT TRIGEMINAL SUBNUCLEUS CAUDALIS

Postembedding immunogold methods were used to examine the distribution of gamma-aminobutyric acid (GABA) and glycine and especially their co localization in glomerular neuronal profiles adjacent to trigeminal pr imary afferent profiles in lamina II of rat subnucleus caudalis. We fo und that 60% of the profiles adjacent to the trigeminal primary affere nt terminals exhibited colocalization of GABA and glycine. GABA alone was found to localize in 17% of the adjacent profiles. Glycine alone w as found to localize in 18% of the adjacent profiles. Of interest, 10% of the trigeminal primary afferent fibers showed glycine localization . All the profiles with colocalization of GABA and glycine were identi fied as presynaptic axonal terminals, suggesting a possible cumulative effect by these two inhibitory neurotransmitters in presynaptic inhib ition. These findings show that GABA and glycine colocalize in a subpo pulation of presynaptic axonal terminals within lamina II of the subnu cleus caudalis. The possible origins of these axons are discussed, as well as their potential involvement in presynaptic inhibition of orofa cial nociception. (C) 1998 Elsevier Science B.V. All rights reserved.