Cell Tissue Res (1995) 282:445-453 Cell &Tissue Research 9 Springer-Verlag 1995 In vitro capsaicin-induced cytological changes and alteration in calcium distribution in giant serotonergic neurons of the snail Helix pomatia: a light- and electron-microscopic study L. Hermidi 1, L. Erd~lyF, A. Pfirducz3, H. Szabadi 3, G. Such 4, G. Jancs6 4 1BalatonLimnological Research Instituteof the HungarianAcademyof Sciences, Tihany,8237 Hungary 2Department of ComparativePhysiology, Attila J6zsef University,Szeged, 6701 Hungary 3Instituteof Biophysics,BiologicalResearch Center of the HungarianAcademyof Sciences, Szeged, 6701 Hungary 4 Department of Physiology, SzentgyOrgyi Albert Medical University,Szeged, 6720 Hungary Received: 19 September 1994/Accepted: 23 June 1995 Abstract. Morphological changes induced by capsaicin were studied in the serotonergic metacerebral giant neu- rons of the cerebral ganglia of Helix pomatia under in vitro conditions. Capsaicin at a concentration of 10-4 M caused characteristic structural alterations in the giant serotonergic neurons but did not significantly influence serotonin immunoreactivity in the neurons. At the light- microscopic level, the most conspiciuous structural alter- ations were swelling of the cell bodies, which contained a swollen pale nucleus. Under the electron microscope, the nuclei, mitochondria and the cisternae of the endo- plasmic reticulum were swollen in the capsaicin-affected metacerebral giant neurons. Electron-microscopic cyto- chemical techniques for calcium demonstration revealed electron-dense deposits in the swollen mitochondria and in the cisternae of the endoplasmic reticulum, suggesting an increased Ca 2+ influx. The serotonergic metacerebral giant neurons could be labelled by cobalt (1 mM) in the presence of capsaicin (10 .4 M) suggesting that capsaicin opens the cation chanels of the capsaicin-sensitive neu- ronal membrane. The morphological and cytochemical alterations induced by capsaicin in the serotonergic me- tacerebral giant neurons of Helix pomatia closely resem- ble those induced in sensory neurons of mammalian dor- sal root ganglion. Key words: Capsaicin - Cerebral ganglia - Nervous system, central - Serotonin (5-HT) - Calcium ions - Co- balt labeling - Helix pomatia (Mollusca) Introduction Capsaicin is a highly selective neurotoxin that affects a particular population of mammalian small primary sen- sory neurons in the dorsal root ganglion (DRG). Most of these neurons give rise to unmyelinated C-fibres (N. Jan- This work was supported by OTKA grants No.: 2477, T016861, T017127 and ETT 587/93. Correspondence to: L. Hernfidi cs6 1966; Jancs6 et al. 1977, 1980b, 1985a, b; Scadding 1980; Nagy et al. 1980, 1983; Szolcsfinyi 1983; Maggi and Meli 1988; Holzer 1991). Administration of capsa- icin to newborn or adult animals results in an irreversible impairment of predominantly polymodal nociceptor af- ferents (for references, see Buck and Burks 1986). Ac- cording to histochemical, biochemical and electrophysi- ological studies, capsaicin evokes an influx of Na § and Ca 2+ into the neurons of the DRG and hence affects the mitochondrial system (Bevan and Szolcsfinyi 1990; Jan- cs6 et al. 1978, 1984; Marsh et al. 1987; Wood et al. 1988). Capsaicin administration leads to the depletion of neuropeptides from sensory neurons of the DRG (Diez Guerra et al. 1988; Fitzgerald 1983; Gamse et al. 1980, 1981a, b; Jancs6 et al. 1981, 1985a, b; Jessel et al. 1978; Lawson and Nickels 1980; Papka et al. 1984; Priestly et al. 1982). The impairment of sensory function and the depletion of neuropeptide can at least partly be attributed to the degeneration of the population of primary sensory neurons (Kirfily et al. 1991; Holzer 1991; Diez Guerra et al. 1988; Buck and Burks 1986; Bevan and Szolcsfinyi 1990). Invertebrate neurons, including the crayfish giant ax- ons (Yanaka etal. 1984) and various snail neurons (Erddlyi and Such 1984, 1985, 1988; Erdtlyi et al. 1987) have also been shown to be sensitive to capsaicin under in vitro conditions. Capsaicin effects can be observed on both the membrane ionic currents and the action poten- tials of snail neurons. These effects develop immediately after the application of capsaicin, but are negated when capsaicin is washed out (Erddlyi and Such 1985; Erd~lyi et al. 1987). In spite of the clear effects of capsaicin on different identified Helix neurons (Erddlyi and Such 1988; Erdtlyi et al. 1987), capsaicin-induced structural alterations have not yet been reported in gastropod neurons. Our prelimi- nary light-microscopic study has shown that some capsa- icin-sensitive neurons exhibit structural alterations throughout the CNS of Helix pomatia after in vitro cap- saicin-treatment. Among them, the metacerebral giant neuron (MGC) (Cottrell and Osborne 1970; Croll 1987)