DISTRIBUTION OF MOTONEURONS SUPPLYING DORSAL AND VENTRAL SUBOCCIPITALMUSCLES IN THE FELINE NECK

A combination of retrograde tracers was used to compare the relative d istributions of motoneurons supplying the ventral and lateral suboccip ital muscles, rectus capitis anterior (RCA), and rectus capitis latera lis (RCL), with those supplying dorsal muscles, including rectus capit is posterior muscles (RCP), complexus (CM), and the medial head of obl iquus capitis superior (OCS). Three of the tracers, horseradish peroxi dase, fluororuby, and fluorescein-conjugated dextran, were applied to cut nerve ends. Fast blue was applied by intramuscular injection, and fluorogold was delivered both by injection and by cut nerve exposure. Motoneurons supplying RCA and RCL were clustered on the medial wall of the ventral horn in a restricted region defined previously as the com missural nucleus. Labelled cells supplying RCL were confined to the C1 segment, but those supplying RCA were distributed from C1 to rostral C4. Motoneurons supplying RCA tended to he more dorsomedially than tho se supplying RCL, but there was substantial overlap between the two po pulations. Motoneurons supplying dorsal muscles had a separate, more v entral distribution. RCP motoneurons were located primarily in the ven tromedial nucleus, but a small proportion of cells was found in the wh ite matter of the ventral funiculus or the gray matter surrounding the central canal. Motoneurons supplying CM and OCS were located dorsomed ially to the RCP cell population. These results suggest that neck moto neurons are arranged according to a ''musculotopic'' pattern in which dorsal muscles have the most ventral locations, and progressively more lateral and then ventral muscles are layered dorsomedially along the medial wall of the ventral horn. (C) 1994 Wiley-Liss, Inc.