ABSTRACT
Coherent oscillatory activities in procerebral neurones have been described in Limax maximus; however, the electrical properties of the procerebrum of other terrestrial molluscs are less well understood. We have examined oscillatory activity in the procerebrum of Incilaria bilineata and Limax marginatus. The local field potential measured in the procerebrum of I. bilineata showed repetitive peaks which had the opposite polarity from those measured in L. marginatus. Optical measurement of membrane potential using a potential-sensitive dye, di-4-ANEPPS, showed that the oscillations in I. bilineata occurred mainly in the internal mass while those in L. marginatus were located in the cell mass. An analysis of the waveform revealed that the depolarizing phase of the oscillations consists of both a slow and a rapid component in both species. The rapid component was most pronounced in the internal mass of I. bilineata but was prominent in the cell mass of L. marginatus. The superior tentacle nerve, which projects to the terminal mass, also showed oscillations in synchrony with those of the procerebrum. These results suggest that oscillations in procerebral interneurones are commonly generated in a region adjacent to the terminal mass and that these oscillations may affect the membrane potential of the neurones constituting the superior tentacle nerve.
