Responses of Viscerosomatic VPL Neurons to Intracardiac Bradykinin

Responses of VPL neurons to intracardiac injection of bradykinin (2μg/kg) were examined in urethane-chloralose-anesthetized cats. A total of 39 VPL neurons were subjected to the study. Nociceptive specific (NS) and wide dynamic range (WDR) neurons receiving both cutaneous nociceptive and cardiac sympathetic afferent inputs regularly exhibited an increased discharge in response to intracardiac bradykinin. NS neurons responsive to intracardiac bradykinin had a circumscribed cutaneous receptive field in the area corresponding to tactile dermatomes C_5 -T_13 . WDR neurons responsive to intracardiac bradykinin had at least a part of their receptive fields in the same area. In contrast, NS and WDR neurons unresponsive to cardiac sympathetic afferents, and low threshold mechanoreceptive (LTM) neurons having a circumscribed receptive field in C_5 -T_13 dermatomes did not respond to intracardiac bradykinin. Both NS and WDR neurons responsive to intracardiac bradykinin were located in the shell region of the medial part of caudal VPL. These cutaneous nociceptive neurons may be involved in transmitting cardiac nociceptive information to the cerebral cortex in the cat.