Cells of origin of fibres to the retrochiasmatic area: a horseradish peroxidase study.

The afferent connections of the retrochiasmatic area were examined in the rat after microintophoretic application of horseradish peroxidase. Labelled cells were found in amygdaloid nuclei, in the magnocellular preoptic nucleus, in the zona incerta and in all hypothalamic nuclei. In the brainstem reactive neurones were seen in the caudal part of the nucleus of the solitary tract (A2-C2 catecholaminergic cell groups), in and adjacent to the lateral reticular nucleus (A1-C1 catecholaminergic cell groups), in the nuclei reticularis pontis caudalis, pontis oralis, reticularis medullae oblongatae pars dorsalis and nucleus reticularis tegmenti pontis. The parabigeminal nucleus also contained a few labelled cells. A large number of labelled cells were seen around the superior cerebellar peduncle, in the caudal part of the periaqueductal grey and in the peripeduncular nucleus. Scattered cells appeared in the brainstem raphe nuclei, in the locus coeruleus and in the lateral part of the substantia nigra. Although it is not certain that all of these neurones terminate on retrochiasmatic cells, the extensive labelling suggests that this brain area is a critical station of many ascending and descending pathways. These may potentially affect a variety of neuro-endocrine mechanisms via the efferent projections of the retrochiasmatic area.