GABAERGIC BOUTONS ESTABLISH SYNAPTIC CONTACTS WITH THE SOMA AND DENDRITES OF CUNEOTHALAMIC RELAY NEURONS IN THE RAT CUNEATE NUCLEUS

This study investigates the synaptic relation between gamma-aminobutyr ic acid-immunoreactive (GABA-IR) and cuneothalamic relay neurons (CTNs ) in the rat cuneate nucleus. Retrograde transport of wheat germ agglu tinin conjugated with horseradish peroxidase complex (WGA-HRP) was use d to label CTNs while anti-GABA immunogold serum was used for the dete ction of GABA-IR boutons associated with CTNs. With these procedures, immunogold-labelled GABA-IR boutons were found to form axosomatic, axo dendritic and axospinous synapses with the WGA-HRP-labelled but immuno negative CTNs. Quantitative estimation showed that the mean ratios of GABA-IR to GABA-immunonegative boutons making synaptic contacts with s omata, proximal dendrites, and distal dendrites were 47.9%, 49.1% and 34.7%, respectively. Statistical analysis showed that the incidence of GABA-IR boutons on the somata and proximal dendrites of CTNs was sign ificantly higher than on the distal dendrites. Our results indicate th at GABA is the primary inhibitory neurotransmitter in the cuneate nucl eus, thereby emphasizing the importance of postsynaptic inhibition on cuneothalamic relay neurons.