SYNCHRONIZED RHYTHMIC CONTRACTIONS AMONG FIVE GONADAL LOBES IN THE SHEDDING SEA URCHINS: COORDINATIVE FUNCTION OF THE ABORAL NERVE RING

¹ Department of Biology, Faculty of Science, Okayama University, Okayama 700, Japan
² Department of General Education, Niimi Women's College, Nishikata, Niimi, Japan
³ Third Department of Anatomy, Okayama University Medical School, Okayama 700, Japan

The gonadal lobe of the spontaneously shedding sea urchin, Temnopleurus toreumaticus, contracts rhythmically. The gonadal movement following electrical or KCl stimulation is a summed response of the rhythmic and arrhythmic contractions. The lobes pretreated with MgCl₂ show only the latter type. Contraction induced by acetylcholine is the latter type. The aboral nerve ring (ANR) connects proximal ends of five gonoducts. In a preparation with intact ANR, the rhythmic contraction occurs synchronously in all five gonadal lobes. When the ANR is separated into two sectors, lobes belonging to the same sector contract synchronously, but those belonging to the different sectors do not.

These results demonstrate rhythm generators (pacemakers) in the ANR that are responsible for individual and synchronous contractions among the gonadal lobes.