Efferent projections from the external parabrachial area to the forebrain: a Phaseolus vulgaris leucoagglutinin study in the rat

Abstract

Small iontophoretic applications of Phaseolus vulgaris leucoagglutinin (PHA-L) were used to study the ascending efferent projections in the rat from the external parabrachial (PBe) area (i.e. external lateral (PBel) and external medial (PBem) subnuclei). It was found that fibers of the caudal two third of PBe project mainly to nucleus centralis of the amygdala (Ce) with a precise pattern: the PBel subnuclei mainly project to the caudomedial subdivision of the Ce and the PBem subnuclei mainly project to the rostrolateral subdivision of the Ce. Another dense and common projection of both subnuclei was found in the ventral pallidal area adjacent to the Ce. This study delineates and extends the terminal area of the spino(trigemino)-ponto-amygdaloid nociceptive pathway demonstrated by our previous studies.