MULTIPLE INPUTS OF GABA-IMMUNOREACTIVE NEURONS IN THE CUNEATE NUCLEUSOF THE RAT

Using anterograde transport of WGA-HRP and the experimental degenerati on method for identification of corticocuneate (CCT) and primary affer ent (PAT) terminals in conjunction with gamma-amino butyric acid (GABA ) and glutamate immunocytochemistry, this study has demonstrated that the GABA-immunoreactive (GABA-IR) neurons in the rat cuneate nucleus w ere post-synaptic to PATs (some of them being glutamate-IR), GABA-IR a nd GABA-negative terminals. The HRP-labelled CCTs did not make any syn aptic contacts with GABA-IR neurons but with some GABA-negative dendri tes. PATs labelled by HRP or showing degenerating features made direct synaptic contacts with the dendrites of GABA-IR neurons. Beside the a bove GABA-IR boutons also showed axosomatic and axodendritic synapses with the GABA-IR neurons. In 'triple labeling' method for GABA, PAT an d glutamate, it was found that the PATs which were usually glutamate-p ositive were presynaptic to the dendrites of GABA-IR neurons. Furtherm ore, some glutamate-IR terminals which were of non-PAT's origin also s ynapsed with the dendrites and somata of GABA-IR neurons. It is conclu ded from this study that the major inputs of GABA-IR neurons were from glutamate immunopositive PATs and glutamate terminals of non-PATs ori gin; other GABA-IR terminals either intrinsic or extrinsic also contri buted to the afferent sources of GABA-IR neurons. The CCTs contributed very little, if any, to this input. It is suggested that the PATs and glutamate-IR terminals on GABA-IR neurons may be involved in lateral inhibition for increase of spatial precision. The synaptic contacts be tween GABA-IR boutons and dendrites or somata of GABA-IR neurons may p rovide a possible means for disinhibition. (C) 1997 Elsevier Science I reland Ltd.