Extraocular muscle representation in the brainstem of the carp

The representation of the extraocular muscles in the oculomotor nuclei in the brainstem of the carp was studied with the horseradish peroxidase technique. Some normal anatomical features of the various oculomotor nuclei are described. Following intramuscular HRP injections in the eye muscles and applying survival times of up to 25 days labeled perikarya were found in the various nuclei of the oculomotor complex. Rectus inferior, rectus internus, and obliquus inferior are represented in the ipsilateral nucleus oculomotorius, while the rectus superior was found to be innervated from the contralateral n III. The efferent cells innervating the obliquus superior are located mainly in the contralateral nucleus trochlearis and for a low percentage in the ipsilateral counterpart of the n IV. The rectus externus is represented in the rostral and caudal subnuclei of the ipsilateral nucleus abducens. These results show a remarkable resemblance with data on mammalian extraocular muscle representation, although the overlap of the various cell populations is larger in fish.