IN-VITRO CAPSAICIN-INDUCED CYTOLOGICAL CHANGES AND ALTERATION IN CALCIUM DISTRIBUTION IN GIANT SEROTONERGIC NEURONS OF THE SNAIL HELIX-POMATIA - A LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC STUDY

Morphological changes induced by capsaicin were studied in the seroton ergic metacerebral giant neurons of the cerebral ganglia of Helix poma tia under in vitro conditions. Capsaicin at a concentration of 10(-4) M caused characteristic structural alterations in the giant serotonerg ic neurons but did not significantly influence serotonin immunoreactiv ity in the neurons. At the light microscopic level, the most conspiciu ous structural alterations were swelling of the cell bodies, which con tained a swollen pale nucleus. Under the electron microscope, the nucl ei, mitochondria and the cisternae of the endoplasmic reticulum were s wollen in the capsaicin-affected metacerebral giant neurons. Electron- microscopic cytochemical techniques for calcium demonstration revealed electron-dense deposits in the swollen mitochondria and in the cister nae of the endoplasmic reticulum, suggesting an increased Ca2+ influx, The serotonergic metacerebral giant neurons could be labelled by coba lt (1 mM) in the presence of capsaicin (10(-4) M) suggesting that caps aicin opens the cation chanels of the capsaicin-sensitive neuronal mem brane. The morphological and cytochemical alterations induced by capsa icin in the serotonergic metacerebral giant neurons of Helix pomatia c losely resemble those induced in sensory neurons of mammalian dorsal r oot ganglion.