Cerebral interneurons controlling fictive feeding in Limax maximus - I. Anatomy and criteria for re-identification

We have used anatomical and electrophysiological techniques to locate and identify neurons in the CNS of Limax maximus which are important for the initiation and modulation of feeding behavior. We have identified a population of 14-18 neurons with somata in the cerebral ganglia (CG) which project to the buccal ganglia (BG) via the cerebral-buccal connectives (CBC). We describe electrophysiological criteria which permit reliable identification of 8 of these cerebral to buccal interneurons (CBs) in different preparations. All CBs are characterized anatomically by having extensive arborizations in the CG, a single axonal projection via the ipsilateral CBC to BG and extensive branching in one or both BG. Two major classes of CBs are distinguished, phasic and tonic, based on their activity patterns during fictive feeding. A small population of cerebral to cerebral interneurons with axonal projections to the contralateral CG via the subcerebral commissure (SCC) is described, together with the synaptic interactions between these subcerebral commissure cells (SCs) and the CBs. Axonal staining techniques were used to locate neurons with somata in the BG which project to CG. Anatomical and physiological evidence for direct connections between the lips and BG was obtained.