Meeting Abstract
Depending on the species, synodontid catfish produce swimbladder sounds, electric organ discharges (EODs), or both using the protractor muscle that is connected to the swimbladder via a bony plate. Neuronal modifications underlying the ability of this muscle to generate sonic and/or EOD signals are virtually unknown. Therefore, we performed a multidisciplinary comparison between a sound producer and an EOD producer. Notably, the tonal swimbladder sound of S. grandiops and the EOD burst of S. nigriventris had similar temporal and spectral features. The oscillation rate, for example, was very high (at least 100 Hz at 26±1°C). Tract tracing experiments following dextran biotin or neurobiotin labeling of the protractor nerve(s) revealed the same motoneuron and premotoneuron pools in both species. Transneuronal neurobiotin labeling of premotoneurons implied extensive gap junctional coupling throughout the premotor-motor network. Neurophysiology showed that motoneuron action potential firing depended on strong current injection in both S. grandiops and S. nigriventris (1163±461 pA and 431±322 pA, respectively). These neuronal features, among others, most likely promote highly synchronized motoneuronal activation which is required to produce high frequency tonal sounds and EODs. Our results suggest that, at least in synodontid catfish, the ability to be either sonic or electrogenic does not require extensive modifications at the level of the neural circuitry. Research support from F.R.S.-FNRS (LK) and NSF (AHB).
