Abstract
To study the functional patterns of spinal projections of primary afferent fibers, EPSCs and IPSCs evoked by the electrical stimulation of single dorsal root were examined in the substantia gelationosa (SG) neurons at the lumbar segmental level in horizontal slices of the adult rat spinal cords using a blind whole-cell patch-clamp technique. In voltage-clamp mode, most of the EPSCs elicited by L5 dorsal root stimulation (DRS) were recorded from L3 to L6. SG neurons in L4 and L5 received Aδor C fiber-mediated EPSCs, or both, whereas the majority of SG neurons in L3 and L6 received only C fiber-mediated EPSCs (11/14; 78% in L3 and 13/18; 72% in L6). Aδ- and C-fibre-mediated IPSCs were recorded from L2 to S1. In current-clamp mode, L5 DRS evoked EPSPs and IPSPs, some of which were accompanied by action potentials (APs). The Aδ-fiber-mediated APs were almost limited within L5 level (40% of SG neurones showed AP in L5, and 5% in L4), while the C-fiber-mediated APs were distributed over two spinal cord segments from L5 to L4 (40% in L5, and 35% in L4). Furthermore, the spreaded inhibitory inputs were considered to be functional because the L2-DRS-evoked APs were suppressed by L5-DRS-evoked IPSPs in 45% of the L2 SG neurons tested. These findings suggest that the excitatory projection field of C fibers spreads more rosrocaudally than that of Aδ fibers and the differences between excitatory and inhibitory projection field extent in the SG may be related to the inhibitory modulation of nociceptive transmission. [Jpn J Physiol 54 Suppl:S172 (2004)]
