CALRETININ-LIKE IMMUNOREACTIVITY IN MORMYRID AND GYMNARCHID ELECTROSENSORY AND ELECTROMOTOR SYSTEMS

Calretinin-like immunoreactivity was examined in the electrosensory an d electromotor systems of the two families of mormyriform electric fis h. Mormyrid fish showed the strongest immunoreactivity in the knolleno rgan electroreceptor pathway; in the nucleus of the b electrosensory l ateral line lobe (ELL) and the big cells of the nucleus exterolaterali s pars anterior. Mormyromast and ampullary zones of the ELL showed cal retinin-like immunoreactivity in the ganglion, granule, and intermedia te cell and fiber layers. Mormyromast zones additionally showed labeli ng of apical dendrites and commissural cells, but the ampullary zone d id not. In the electromotor system, two nuclei in the corollary discha rge pathway b showed labeling: in the paratrigeminal command-associate d nucleus and the juxtalobar nucleus. Gymnarchus niloticus (Gymnarchid ae) showed strongest calretinin-like immunoreactivity in part of the p hase-coding pathway; in S-type electroreceptor afferents. Zones of the ELL not receiving phase-coder input had weak labeling. The electromot or system showed labeling in the lateral relay nucleus and less strong ly in the medullary relay nucleus, but none in the pacemaker. The conc entration of calcium-binding proteins in mormyrid and gymnarchid time- coding electrosensory pathways is consistent with the hypothesis that they play a role in preserving temporal information across synapses. C ell types that encode temporal characteristics of stimuli in precise s pike times have high levels of calcium-binding proteins, but cells tha t re-code temporal information into presence or magnitude of activity have low levels. Some cell types in the electromotor pathways and earl y in the time-coding electrosensory pathways do not follow this hypoth esis, and therefore prf-serve temporal information using a mechanism i ndependent of calcium-binding proteins. In particular, electromotor sy stems may use extensive electrotonic coupling within nuclei to ensure precise timing. (C) 1997 Wiley-Liss, Inc.