Afferent connections of septal nuclei of the domestic chick (Gallus domesticus): a retrograde pathway tracing study.

The afferents to the septum of the domestic chicken were studied using retrograde tracers, rhodamine conjugated latex bead or Fast Blue, placed in different septal subregions. The results were verified by anterograde tracer injections deposited to selected areas. The main telencephalic afferents to the septum arise ipsilaterally from the hippocampal formation, dorsolateral corticoid area, piriform cortex, amygdaloid pallium, and the ventral pallidum. Contralateral afferents originate from the lateral septum and the amygdaloid pallium. A massive bilateral projection arises from the lateral hypothalamus. Other hypothalamic afferents arise from the periventricular, paraventricular and anterior medial nuclei, and the premammillary and mammillary areas. The dorsal thalamic nuclei (dorsal medial anterior and posterior) and the reticular dorsal nuclei also contribute septal afferents. Brainstem afferents arise bilaterally from the ventral tegmental area, substantia nigra, central gray, A8, locus coeruleus, ventral subcoeruleus nucleus, and raphe nuclei. The main terminal fields for septal afferents lie in the lateral septal nucleus and the belt of medial septal nucleus. The core of the latter is invaded mainly by fibers from the brainstem, presumably belonging to the ascending activating system. The septal afferents of the chicken are largely similar to those of other avian and nonavian species. The most prominent differences with previous pigeon data were found in the subregional selectivity of the hippocampal formation, dorsolateral corticoid area, mammillary nuclei, some dorsal thalamic nuclei, substantia nigra, and subcoeruleus nuclei in their projections to defined septal nuclei.