Spinoparabrachial tract neurons showing substance P receptor-like immunoreactivity in the lumbar spinal cord of the rat

By using substance P receptor (SPR) immunofluorescence histochemistry combined with fluorescent retrograde labeling, SPR-like immunoreactive (SPR-LI) neurons sending their axons to the lateral parabrachial region were observed in the lumbar spinal cord of the rat. After injection of Fluoro-Gold into lateral parabrachial region, retrogradely labeled neurons with SPR-LI were seen frequently in lamina I and the lateral spinal nucleus, and occasionally in laminae IV and V, with a predominantly contralateral distribution. Some of these neurons, especially those in lamina I, may convey nociceptive information to the lateral parabrachial region.