TECTAL INPUT TO THE CENTRAL POSTERIOR PREPACEMAKER NUCLEUS OF WEAKLY ELECTRIC FISH, APTERONOTUS-LEPTORHYNCHUS - AN IN-VITRO TRACT-TRACING STUDY

The weakly electric fish Apteronotus leptorhynchus produces electric o rgan discharges which are highly stable in waveform and frequency. Sho rt-term modulations of these discharges, typically displayed during so cial interactions, are controlled by the prepacemaker nucleus (PPn). N eurons of this thalamic cell group intermingle with cells of the centr al posterior nucleus (CP) to form a complex called 'CP/PPn'. By employ ing in vitro tract-tracing techniques, we have, in the present investi gation, demonstrated that this complex receives input from the tectum opticum. The tectal input is mediated by varicose fibers forming an el ongated stripe at the ventral rim of the CP/PPn. As suggested by retro grade tracing from the CP/PPn, this projection is likely to arise from 'multipolar cells with an ascending axon' previously characterized in a Golgi study [14]. As this tectal cell type has been shown to be pre dominantly driven by electrosensory stimuli [6], information arising f rom these cells may be used in controlling modulations of the electric organ discharges.