Parabrachial internal lateral neurons convey nociceptive messages from thedeep laminas of the dorsal horn to the intralaminar thalamus

This study investigates the physiological properties of parabrachial intern al lateral (PBil) neurons that project to the paracentral thalamic (PC) nuc leus using antidromic activation and single-unit recording techniques in an esthetized rat. We reported here that most of these neurons responded exclu sively to the nociceptive stimulation of large receptive fields with a sust ained firing that often outlasted the stimulus up to several minutes. These responses were depressed by intravenous morphine. Our results demonstrated a novel spino-PBil-PC pathway, which transmits noc iceptive messages to the PC nucleus, which in turn projects to the prefront al cortex. Recent clinical imaging studies showed the important participati on of prefrontal cortex in emotional response to pain. This spino-PBil-PC p athway may explain how nociceptive messages reach the prefrontal cortex and thus trigger unbearable aversive aspects of pain.