Somatotopic organization of primary afferent perikarya of the guinea-pig extraocular muscles in the trigeminal ganglion: a post-mortem DiI-tracing study

Apart from the somatotopic organization of the trigeminal ganglion (TG) int o the ophthalmic, maxillary and mandibular divisions along the mediolateral axis, there exist further somatotopic organizations within these three div isions. According to literature, the cell organization in the TG and the so matotopy in the brainstem develop together, formed by naturally occurring c ell death in the TG. Thus, the somatotopy of the primary afferent trigemina l perikarya is of special interest. The aim of this study was to investigat e the location of the primary afferent perikarya of the extraocular muscles (EOMs) in the TG of guinea-pig. The primary afferent perikarya were labele d by post-mortem application of the carbocyanine DiI on the oculomotor nerv e branches near their entrance into the single EOMs. The DiI-positive perik arya were found musculo-somatically organized in the ipsilateral ophthalmic part of the TG at a wide range along the dorsoventral axis, expressing an overlap of the representation areas. The primary afferent perikarya of the superior rectus and the superior oblique muscles were mainly localized in t he dorsal part of the ganglion while those of the inferior rectus and the i nferior oblique muscle mainly in ventral part. The lateral and the medial r ectus were predominantly represented in between. An organization along the mediolateral axis of the TG was not observed. Although guinea-pigs lack classical EOM proprioceptors, the somatotopic rep resentation of the extraocular muscle primary afferent perikarya in the TG found in this study is in line with findings in species with well known enc apsulated proprioceptors within the EOMs. (C) 2000 Academic Press.