DIFFERENT PUTATIVE NEUROMODULATORS ARE PRESENT IN THE NERVES WHICH DISTRIBUTE TO THE TELEOST SKELETAL-MUSCLE

The presence of putative neuromodulators in the nerve fibres was inves tigated in white skeletal muscle of two teleost fish not taxonomically correlated and showing different patterns of innervation (multiple ve rsus focal innervation). Cryostat sections of epaxial, hypaxial and ad ductor mandibulae (AM) muscles of Sparus aurata and Anguilla anguilla were stained histochemically for reduced nicotinamide adenine dinucleo tide phosphate (NADPH)-diaphorase. Other sections were used for indire ct immunohistochemistry (streptavidin-biotin and rhodamine immunofluor escence methods), employing antibodies specific for putative excitator y or inhibitory peptides, including CGRP, substance P, met-enkephalin, bombesin, and VIP. In addition, ultrastructural observations were per formed in order to describe the morphology of the motor endplates. A s trong immunoreactivity for CGRP and substance P was found in many nerv e terminals. Met-enkephalin, bombesin and VIP immunoreactivities were less frequently observed. No immunoreactivity was observed to CCK, NPY or 5-HT. NADPH-diaphorase was identified in nerve fibres of the AM co mplex only of A. anguilla. Electron microscopy observations evidenced more than one type of synaptic vesicle in motor endplates. Some differ ences in putative neuromodulator distributions were observed in the tw o species and muscle complexes, which may be related to the different taxonomical position as well as the different pattern of innervation o f white muscle fibres.