A possible spino (trigemino)-ponto-amygdaloid pathway for pain.

Small iontophoretic applications of wheat germ agglutinin-conjugated to horseradish peroxidase have been used to simultaneously observe, in the rat, the afferent and efferent connections of small parabrachial subregions in the same animal. The results demonstrate that a restricted region centered on the external portion of the lateral parabrachial area receives numerous afferents from the superficial laminae of the dorsal horn of the spinal cord and of the trigeminal subnucleus caudalis and sends a major projection to the nucleus centralis of the amygdala. This study suggests that the external portion of the lateral parabrachial area is a relay for messages evoked by noxious stimuli in a spino (trigemino)-ponto-amygdaloid pathway.