PHYSIOLOGY AND PLASTICITY OF MORPHOLOGICALLY IDENTIFIED CELLS IN THE MORMYRID ELECTROSENSORY LOBE

The electrosensory robe (ELL) of mormyrid electric fish is the first s tage in the central processing of sensory input from electroreceptors. The responses of cells in ELL to electrosensory input are strongly af fected by corollary discharge signals associated with the motor comman d that drives the electric organ discharge (EOD). This study used intr acellular recording and staining to describe the physiology of three m ajor cell types in the mormyrid ELL: the medium ganglion cell, the lar ge ganglion cell, and the large fusiform cell. The medium ganglion cel l is a Purkinje-like interneuron, whereas the large ganglion and large fusiform cells are efferent neurons that convey electrosensory inform ation to higher stages of the system. Clear differences were observed among the three cell types. Medium ganglion cells showed two types of spikes, a small narrow spike and a large broad spike that were probabl y of axonal and dendro-somatic origin, respectively, whereas the large ganglion and large fusiform cells showed only large narrow spikes. Mo st of the medium ganglion cells and all of the large ganglion cells we re inhibited by electrosensory stimuli in the center of their receptiv e fields, whereas the large fusiform cells were excited by such stimul i. Responses to the EOD corollary discharge were different in the thre e cell types, and these responses underwent plastic changes after a fe w minutes of pairing with an electrosensory stimulus, Plastic changes were also observed in medium and large ganglion cells after the coroll ary discharge was paired with depolarizing, intracellular current puls es.