THE SYNAPTIC INTERRELATIONSHIPS BETWEEN PRIMARY AFFERENT TERMINALS, CUNEOTHALAMIC RELAY NEURONS AND GABA-IMMUNOREACTIVE BOUTONS IN THE RAT CUNEATE NUCLEUS

The present study described an ultrastructural synaptic configurations between primary afferent terminals (PATs), cuneothalamic relay neuron s (CTNs) and GABA-immunoreactive (GABA-IR) boutons in the cuneate nucl eus of rats using cervicothoracic dorsal rhizotomies, retrograde trans port of wheat germ agglutinin conjugated with horseradish peroxidase c omplex (WGA-HRP) and anti-GABA immunogold labelling methods. With this procedure, direct synaptic relationships between the PATs, CTNs and G ABA-IR boutons have been demonstrated. The most remarkable feature was the observation whereby an immunogold-labelled GABA-IR bouton was pre synaptic to a WGA-HRP labelled dendrite of CTN and a degenerating PAT; the same PAT was in turn presynaptic to the HRP-labelled dendrite. Th is was evident in ten out of a total of 133 synaptic configurations th at were closely scrutinized. Results of this study support the concept that GABA-IR boutons are not only involved in presynaptic inhibition on the primary afferent input to the cuneothalamic relay neurons, but also exert a simultaneous postsynaptic inhibition on these cells.