Midbrain, diencephalic and cortical relationships of the basal nucleus of meynert and associated structures in primates

TLDR

The peripeduncular nucleus, part of the central auditory pathway, projects via a large fiber bundle to the lateral hypothalamic area and, together with other brainstem inputs, forms a complex that projects diffusely to all telencephalic cortical structures. The study used retrograde and anterograde axonal transport techniques in New and Old World monkeys to map the connectivity of the basal nucleus of Meynert and the substantia innominata. Retrograde labeling confirmed that the basal nucleus and substantia innominata project heavily and topographically to the neocortex, while anterograde tracing revealed a complex pathway linking them with the lateral hypothalamus, amygdala, and peripeduncular nucleus, including dense projections to the posterior lateral amygdala and medial/intercalated nuclei, a less dense projection to the bed nucleus of the stria terminalis, and complementary descending fibers that cross in the ventral supraoptic commissure, leading to the conclusion that the basal nucleus comprises most large cells in the substantia innominata and adjacent regions.

Abstract

Abstract The structure and connectivity of the basal nucleus of Meynert, the substantia innominata in which it lies, and certain related areas have been examined in New World and Old World Monkeys, using retrograde and anterograde axonal transport methods. Experiments using the retrograde, horseradish peroxidase method confirm the observations of Kievet and Kuypers ('75) that the basal nucleus and substantia innominata project directly, heavily and with a somewhat crude topography upon the neocortex. Experiments involving the anterograde, autoradiographic method show that the basal nucleus and substantia innominata form part of a complex pathway that links them together with the lateral hypothalamus, certain parts of the amygdala and the peripeduncular nucleus of the midbrain. The peripeduncular nucleus is often regarded as a part of the central auditory pathway; it gives rise to a fiber bundle of considerable size that ascends on the dorsal surface of the ipsilateral optic tract and terminates ultimately in the lateral hypothalamic area of both sides. As well as distributing fibers to the basal nucleus, substantia innominata and lateral hypothalamus, this pathway provides a heavy projection to a cytoarchitectonically distinct posterior part of the lateral nucleus of the amygdala, the medial and intercalated nuclei of the amygdala and a less dense projection to the bed nucleus of the stria terminalis. Certain parts of the hypothalamus and possibly the preoptic areas give rise to a complementary descending pathway that distributes fibers to the ipsilateral basal nucleus, substantia innominata and amygdala, and ends in the peripeduncular nuclei of both sides. Decussating fibers in both the ascending and descending pathways cross in the ventral supraoptic commissure. It is concluded that the basal nucleus should include most of the aggregated and unaggregated large cells that lie in the substantia innominata and which in places intrude upon the preoptic regions and the nucleus of the diagonal band of Broca. Together, these may form a complex that receives inputs from a variety of brainstem sources, and projects widely and diffusely upon all cortical structures of the telencephalon.