Anatomical organization of the sexually dimorphic perineal neuromuscular system in the house mouse

Abstract

The anatomy of the sexually dimorphic motoneuron nuclei of the bulbocavernosus (BC) and ischiocavernosus (IC) muscles, as well as the non-sexually dimorphic external anal sphincter (EAS), was examined in hybrid B6D2F1 mice using the retrograde tracer, cholera toxin-bound horseradish peroxidase. Motoneurons innervating the BC were located in the dorsomedial nucleus (DM), as well as in the ventral nucleus (V) and in the mid-region of the ventral horn (MVH). Following injections restricted to the IC, labelled neurons were found in the dorsolateral nucleus (DL), as well as in V, DM and MVH. Cells innervating the EAS in both males and females were located in the DM, as well as in the V and MVH. An elaborate network of dendrites extended between all labelled nuclei. The present results demonstrate that the anatomical specificity of the sexually dimorphic neuromuscular system of the mouse differs from that observed in other species.