Abstract
Response of membrane potential to substance P (SP) has well been examined in spinal dorsal horn neurons, but little is known about those to CGRP and somatostatin. Therefore, we addressed these issues by the blind patch clamp technique used freshly sliced spinal cord of the rat (3-4 weeks). Of the dorsal horn neurons (32/51 cells) in the deep lamina (III-VI), about 60% displayed the slow inward current by the bath application of SP (1 μM). This current has been considered to be evoked though G protein-coupled SP receptor on the patched cells. Many these neurons simultaneously increased excitatory post-synaptic currents (EPSCs). About 30% of deep dorsal horn neurons (9/27 cells) showed the slow inward current by the application of CGRP (1 μM), as well as SP. The responsive neurons to CGRP always displayed the inward current by SP. However, the amplitude of the inward current by CGRP was smaller than that by SP, and a little number of the neurons increased EPSPs. On the other hand, the application of somatostatin (1 μM) evoked the slow outward current in about 30% of the patched deep dorsal horn neurons (7/22 cells). Many these neurons also showed the inward current by SP. The outward current was not suppressed by the repetitive application of somatostatin, although the inward currents by SP and CGRP were desensitized. The present study suggests that CGRP and somatostatin, in addition to SP, play an important role in synaptic transmission to deep dorsal horn neurons. [J Physiol Sci. 2008;58 Suppl:S162]
