The influence of sex pheromones on the electrical activity in the brain and the nerve cord was studied in mature and immature nereids. The pheromone of the opposite sex induces an intense electrical activity in the brain and the nerve cord only when the nereid is mature and possesses transformed parapodial cirri (swollen cirri in this work). The integrity of the connections between brain and nerve cord is also required for the stimulation of the electrical activity of the brain but not for the nerve cord. The electrical activity of the brain and the nerve cord is also stimulated by heterospecific pheromones of the opposite sex in the same way as with homospecific sex pheromones. Thus, homospecific and heterospecific sex pheromones are both perceived by mature (epitokous) nereids. The stimulation is received by the transformed parapodial cirri and is transmitted to the brain through the nerve cord.In nereids, sensory cells have been reported in the body wall, cephalic appendages, and parapodial and anal cirri (Retzius, 1892; Langdon, 1900; Smith, '57; Dorsett, '64; Dorsett and Hyde, '69; Boilly-Marer, '72 a and b, '73). The function of these cells has been especially investigated in the parapodial cirri, which become swollen (first 5-7 pairs of parapodia in both sexes) or crenellated (dorsal parapodial cirri of the posterior part in males) a t the time of epitoky.' The swelling and the crenellations of the parapodial cirri correspond to the differentiation of organs made up of sensory cells surrounded by epidermal cells secreting a special protein material (BoillyMarer, '72 b, '73).In a previous work (Boilly-Marer and Lassalle, '78) it was established that the sex pheromones contained in the coelomic fluid induce a prolonged electrical activity in the brain of an epitokous N . succinea L. of the opposite sex, provided that the transformed parapodial cirri (swollen cirri in particular) are present. In order to better understand the processes of sex pheromone chemoreception and nervous stimulation leading to the nuptial dance and release of genital products, the present study deals with the electrophysiological reactions of the brain and of the nerve cord in various species of nereids, which are mature (epitokous) or not (atokous), and which are put in the presence of coelomic fluid from either the same or different species.
MATERIALS AND METHODSExperiments were carried out on anterior stumps of epitokous and atokous nereids. The species used were Platynereis dumerilii Aud. and M. Edwards, Nereis irroratu Malmgren and Perinereis cultrifera Griibe, captured near Luc-sur-Mer (Calvados, France); Nereis (Eunereis) longissina Jonhston and Nereis pelagica Linne, which came from Wimereux (Pasde-Calais); and Nereis succineu Leuckart, from the Caen canal (Calvados).The electrical activity of the brain was recorded on anterior stumps composed of the head, the peristomium and 6 segments each prolonged laterally by a pair of parapods with swollen cirri (Fig. 1A) and on isolated heads (Fig. 1B). As in a previous work (Bo...