Ascending Projections from the Solitary Tract Nucleus to the Hypothalamus. A Phaseolus vulgaris Lectin Tracing Study in the Rat

The course of the ascending pathways originating from the anterior gustatory and posterior visceral sensory part of the solitary tract nucleus and the topographic organization of the projections to the hypothalamus in the rat were studied with anterogradely transported Phuseolus vulgaris lectin. In general, the posterior visceral sensory part of the solitary tract nucleus has ascending projections as far as the septum-diagonal band complex and gives rise to heavy input to the bed nucleus of the stria terminalis, and to the dorsomedial and paraventricular hypothalamic nuclei. A more moderate projection is aimed at a variety of other hypothalamic nuclei, to the medial and central amygdaloid nuclei and to the paraventricular nucleus of the thalamus. The ventromedial hypothalamic nucleus is strikingly missing an afferent input from the nucleus of the solitary tract. Furthermore, it was shown that whereas the caudal solitary tract nucleus has predominant long ascending connections, the projections from the anterior taste related region of the nucleus of the solitary tract have only limited forebrain projections which do not reach beyond the level of the anterior dorsal hypothalamic nucleus.