Histochemical localization of monoamines and cholinesterases in Mytilus pedal ganglion.

The pedal ganglion is a peripheral ganglion which gives rise to the innervation for both the somatic and visceral organs of the Mytilus foot. In the present study, different histofluorescence methods for the demonstration of monamines (formaldehyde-glutaraldehyde followed by polyethylene glycol embedding; aluminium-formaldehyde; Falck) and acetylcholinesterase histochemistry were applied in order to characterize the neuronal population of the ganglion. The fluorescence methods employed showed that the cortical region of the pedal ganglion is composed of roundish cells; these mainly contained an orange autofluorescent pigment. Yellow-fluorescing cells were scattered in the anterior region of the cortex, but they were more numerous and arranged in clusters in the posterior region. Green-fluorescing cells were mainly located at the border between the cortex and neuropile and in the neuropile itself, where a rich plexus of beaded green-fluorescing fibres was also present. Of the three methods, that using formaldehyde-glutaraldehyde followed by embedding in polyethylene glycol gave the best preservation of morphological details. Acetylcholinesterase histochemistry showed the presence of positive cells and fibres mainly in the anterior region of the ganglion.