SENSORY INNERVATION OF THE GUINEA-PIG EXTRAOCULAR-MUSCLES - A '-DIOCTADECYL-3,3,3'3'-TETRAMETHYLINDOCARBOCYANINE PERCHLORATE TRACING AND CALCITONIN-GENE-RELATED PEPTIDE IMMUNOHISTOCHEMICAL STUDY

The sensory apparatus of the extraocular muscles attains special inter est because of the great variation among different species with respec t to the proprioceptors, The sensory innervation of the guinea pig ext raocular muscles, lacking both muscle spindles and tendon organs, was investigated with a fluorescence double-labelling method. Primary sens ory perikarya were assessed by postmortem application of -dioctadecyl- 3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) to the extrao cular muscle nerves. Traced neurons were found in the ipsilateral opht halmic 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 o rganization was observed for CGRP-like immunoreactive perikarya. Small (maximal diameter below 30 mu m), medium (maximal diameter between 30 and 50 mu m), and large (maximal diameter larger than 50 mu m) trigem inal ganglion cells were found among the primary afferent perikarya fr om extraocular muscles. Among CGRP-like immunoreactive cells, only sma ll and medium cells were observed. Double-labelling experiments indica ted the CGRP content of primary afferents of the guinea pig extraocula r muscles. The relationship to former morphological categories of gang lion cells is discussed. Primary afferent neurons with CGRP-like immun oreactivity might have efferent functions and might also be involved i n inflammatory processes of extraocular muscles. (C) 1997 Wiley-Liss, Inc.