Sensory innervation of the guinea pig extraocular muscles: A 1,1?-dioctadecyl-3,3,3?3?-tetramethylindocarbocyanine perchlorate tracing and calcitonin gene-related peptide immunohistochemical study

Abstract

The sensory apparatus of the extraocular muscles attains special interest because of the great variation among different species with respect to the proprioceptors. The sensory innervation of the guinea pig extraocular muscles, lacking both muscle spindles and tendon organs, was investigated with a fluorescence double-labelling method. Primary sensory perikarya were assessed by postmortem application of 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (Di-I) to the extraocular muscle nerves. Traced neurons were found in the ipsilateral ophthalmic part of the trigeminal ganglion. This is in line with findings in other species. Calcitonin gene-related peptide (CGRP) was detected immunohistochemically within the trigeminal ganglion. No somatotopic organization was observed for CGRP-like immunoreactive perikarya. Small (maximal diameter below 30 microm), medium (maximal diameter between 30 and 50 microm), and large (maximal diameter larger than 50 microm) trigeminal ganglion cells were found among the primary afferent perikarya from extraocular muscles. Among CGRP-like immunoreactive cells, only small and medium cells were observed. Double-labelling experiments indicated the CGRP content of primary afferents of the guinea pig extraocular muscles. The relationship to former morphological categories of ganglion cells is discussed. Primary afferent neurons with CGRP-like immunoreactivity might have efferent functions and might also be involved in inflammatory processes of extraocular muscles.

Trigeminal ganglion innervates the auditory brainstem

“…The present investigation demonstrates that secondorder auditory neurons in the cochlear nucleus are innervated by both the ophthalmic and mandibular divisions of the trigeminal ganglion, which also project to the cochlea and middle ear, respectively (Vass et al, 1997(Vass et al, , 1998b. The ophthalmic division of the trigeminal ganglion also innervates the extraocular muscles (Aigner et al, 1997), raising the interesting possibility of interactions among these three systems. A second major finding indicates that a reciprocal connection exists between neurons in the shell regions of the lateral superior olivary complex and the trigeminal ganglion.…”

“…Furthermore, the ophthalmic portion of the trigeminal ganglion also innervates extraocular muscles (Aigner et al, 1997). This raises another interesting possibility that these connections might be involved in vestibulo-ocular reflexes.…”

Axons Giving Rise to the Palisade Endings of Feline Extraocular Muscles Display Motor Features

“…Here, we confirmed that palisade endings are cholinergic and have demonstrated for the first time that palisade endings are also CGRP immunoreactive like motor terminals on singly and multiply innervated muscle fibers in cat EOMs. CGRP has been detected in spinal/cranial motoneurons (Forsgren et al, 1993; Moreno-López et al, 1998; González-Forero et al, 2002) as well as in guinea pig sensory trigeminal ganglion cells (Aigner et al, 1997). We also observed some cells containing CGRP in the trigeminal ganglion of cats, but these elements were noncholinergic and thus cannot contribute to the formation of palisade endings.…”

Somatosensory influence on the cochlear nucleus and beyond

“…Sensory information from the head and face is conveyed to the central trigeminal sensory nuclear complex via the ophthalmic, maxillar, and mandibular branches of the trigeminal nerve. The ophthalmic nerve innervates the forehead, upper eyelid, or extraocular muscles; the maxillary nerve supplies the upper lip, the lower eyelid and the upper jaw and roof of the mouth; and the mandibular nerve innervates the lower lip, the mucous membranes of the lower jaw, the floor of the mouth, and anterior two thirds of the tongue (Aigner et al, 1997).…”