Mormyrid electrosensory lobe in vitro: Morphology of cells and circuits

The electrosensory lobe (ELL) of mormyrid electric fish is a cerebellum-lik e brainstem structure that receives the primary afferent fibers from electr oreceptors in the skin. The ELL and similar sensory structures in other fis h receive extensive input from other central sources in addition to the per ipheral input. The responses to some of these central inputs are adaptive a nd serve to minimize the effects of predictable sensory inputs. Understandi ng the interaction between peripheral and central inputs to the mormyrid EL L requires knowledge of its functional circuitry, and this paper examines t his circuitry in the in vitro slice preparation and describes the axonal an d dendritic morphology of major ELL cell types based on intracellular label ing with biocytin. The cells described include medium ganglion cells, large ganglion cells, large fusiform cells, thick-smooth dendrite cells, small f usiform cells, granule cells, and primary afferent fibers. The medium gangl ion cells are Purkinje-like interneurons that terminate on the two types of efferent cells, i.e., large ganglion and large fusiform cells, as well as on each other. These medium ganglion cells fall into two morphologically di stinct types based on the distributions of basal dendrites and axons. These distributions suggest hypotheses about the basic circuit of the ELL that h ave important functional consequences, such as enhancement of contrast betw een "on" elements that are excited by increased afferent activity and "off" elements that are inhibited. (C) 1999 Wiley-Liss, Inc.