SUPRACHIASMATIC NUCLEUS PROJECTION TO MESENCEPHALIC CENTRAL GREY IN THE WOODMOUSE (APODEMUS-SYLVATICUS L)

The efferent connections of the suprachiasmatic nucleus of the hypothalamus have been studied in the woodmouse using several techniques: the Nauta degeneration method, anterograde axoplasmic transport of tritiated proline, and retrograde transport of horseradish peroxidase or Evans blue. Many degenerating nerve fibres resulting from the destruction of the suprachiasmatic nucleus converge on the ipsilateral ventrolateral segment of the mesencephalic central grey matter. Detailed analysis of autoradiographs after injection of [3H]proline in the suprachiasmatic nucleus agrees with these results. This projection is confirmed by injections of horseradish peroxidase or Evans blue into the mesencephalic central grey matter which result in a retrograde labelling of the suprachiasmatic nucleus. Formed by very thin and diffusely distributed axons, this projection belongs, at least caudally, to the descending periventricular system and is partially mixed with fibres from the medial anterior hypothalamic area. It is suggested that the suprachiasmaticomesencephalic pathway may be the first link in the neuron chain that connects the suprachiasmatic nucleus with the peripheral nervous system. © 1979.