Efferent connections of the rat suprachiasmatic nucleus

Abstract

Listen

Translate article

The efferent projections of the suprachiasmatic nucleus were studied in rats using three different light-microscopic tracing techniques. These techniques included, (1) degeneration subsequent to lesions of the nucleus, (2) autoradiography of axoplasmically-transported molecules following injections of [ 3H]leucine into the nucleus, and (3) autoradiography of molecules which had been transneuronally-transported following injections of [ 3H]fucose and [ 3H]proline into the eye. Analysis of this material demonstrated that the suprachiasmatic nucleus has sparse but widespread efferent projections that extend ipsilaterally and sometimes bilaterally throughout much of the length of the periventricular system. With some exceptions, these projections tend to be confined within 0.4 mm of the midline. Four major efferent pathways were identified. (1) A ventro-caudal projection to the retrochiasmatic area, arcuate nucleus, median eminence, the ventro-medial aspect of the dorsomedial and ventromedial hypothalamic nuclei, baso-lateral hypothalamus, prelateral mammillary nucleus and lateral interpeduncular zone. A dorsal branch of this pathway followed the periventricular system into the central grey. (2) A lateral pathway to the anterior hypothalamus, a region dorsal to the supraoptic nucleus and the supraoptic nucleus. Some lateral projections may reach the anterior amygdaloid area. (3) A dorsal pathway to the paraventricular nucleus, a rostral branch to the fimbrial and triangular septal nuclei and a caudal branch via the paraventricular thalamus to the habenula, and further caudally to the mesencephalic central grey. These dorsal projections were not labeled by transneuronal transport. (4) A sparse rostral pathway through the preoptic-suprachiasmatic region. These results agree with and extend the results of other investigators. In addition, the diffuse and extensive pattern of projections of the suprachiasmatic nucleus as demonstrated here is consistent with the suggestion that the nucleus is a major component of a system of circadian pacemakers whose destruction disrupts or abolishes the circadian rhythms of a wide range of different behaviors.