Properties of neurons of the central nervous system of the freshwater gastropod mollusc

Abstract

The following observations must be specially emphasized: 1. The high nucleo-cytoplasmic ratio of neurons ofPlanorbis, variation in the size and shape of the nucleus, the high chromatin content, cyclic changes in the localization of RNA, and the accumulation and disappearance of Nissl substance and glycogen and, in some neurons, of neurosecretion—all these taken together are evidence of the extremely high activity of trophic processes in mollusc neurons, and also that these neurons fall into the class with a predominantly nuclear type of protein synthesis. 2. Ganglia of the central nervous system ofPlanorbis corneus contain the following components: a) efferent unipolar, pseudo-unipolar and multipolar neurons, forming intraganglionic and peripheral connections; b) afferent bipolar neurons forming interganglionic connections; c) afferent neurons with multiple processes providing for intraganglionic reception; d) intermediate multipolar neurons forming connections within the neuropil; e) neurosecretory cells. 3. Interneuronal connections are maintained by axo-somatic and axo-axonal contacts at the ganglionic level, and by axo-dendritic and dendro-dendritic contacts at the neuropil level.