The dorsal locus coeruleus is larger in male than in female Sprague-Dawley rats.

Previous studies indicate that the locus coeruleus (LC) can be divided into sub-areas depending upon dominant efferent projection zones. Ascending projections to the forebrain originate within the dorsal half and projections to the spinal cord and the cerebellum course from the ventral half of the LC. Using Sprague-Dawley rats, the present study analyzed sex differences in LC volume and in ascending and descending projection zones. Horizontal sections were stained with cresyl violet or by using antibodies to tyrosine hydroxylase. It was found that the dorsal ascending projection zone is larger in the male. One of the well-defined sub-areas within the dorsal half of the LC provides noradrenergic innervation of the hippocampus, a structure that exhibits various male-dominated sex differences in the rat, and post hoc analysis localized the sex difference to this region of the LC. No difference was found in total LC volume. As well, a sex difference in shape of the LC is indicated by a longer anterior-posterior extent in males, while females have a greater dorso-ventral extent.