BIOACTIVE PEPTIDES AND SEROTONIN IMMUNOCYTOCHEMISTRY IN THE CEREBRAL GANGLIA OF HIBERNATING HELIX-ASPERSA

The role of some neuromodulators and neurotransmitters in the function ing of molluskan cerebral neurons and in their metabolic changes durin g hibernation has been considered. The cerebral ganglion of mollusks i s a center for the integration of different inputs from the sensory ar eas of the head and for the generation of motor command impulses. Duri ng hibernation, animals are deprived of many external sensory stimuli and do not have locomotion and feeding. Immunocytochemistry for bioact ive peptides (BAPs), such as SP (Substance P), CCK8 (Cholecystokinin 8 /Gastrin), CGRP (Calcitonin-Gene-Related Peptide) and ET (Endothelin), and serotonin was performed on cerebral ganglia of active and hiberna ting Helix aspersa. The distribution of the immunopositivity was analy zed in different cell-containing areas (procerebrum, mesocerebrum, met acerebrum) and in the neuropiles. With all the antibodies raised again st peptides, we observed that only a few neurons, mainly of small and medium size, had immunopositivity during the period of activity, the p atterns of distribution being quite similar to those previously descri bed in Helix or other gastropods. Fibers and varicosities with BAP imm unopositivity were found in the procerebral and central neuropiles and sometimes around neurons. Serotonin-immunopositive neurons, including the giant neuron, were observed in the metacerebrum; numerous fibers and varicosities immunopositive for serotonin were present in the neur opile areas. In hibernating snails, the number of fibers with BAP and serotonin immunopositivity decreased in several areas of the neuropile s. Moreover, an increased number of neurons of the metacerebrum (two-t o four-fold) and mesocerebrum (8- to 28-fold) had BAP-like immunoposit ivity, and the intensity of the immunoreaction for serotonin of the me tacerebral neurons was also higher than in the active snails. These re sults are discussed, taking into account two hypotheses. The first hyp othesis assumes that the increased immunocytochemical staining was rea lly linked to accumulation of BAPs and serotonin. The second hypothesi s considers that the antibodies for BAPs recognized a preprotein, the synthesis of BAPs being completed during the active period only. Both the hypotheses account for the co-occurrence and colocalization of two or ore peptides and serotonin and stress that the hibernation conditi on is of interest for studies on the actual function of single neurons in the cerebral ganglia. Finally, the data are consistent with the ch anges recently found in other markers of the morphological and functio nal activity of neurons, demonstrating that the neuromodulation and th e neurotransmission are slowed during hibernation. (C) 1998 Wiley-Liss , Inc.