ELECTRIC ORGAN COROLLARY DISCHARGE PATHWAYS IN MORMYRID FISH .2. THE MEDIAL JUXTALABAR NUCLEUS

The electrosensory lobe of mormyrid fish Gnathonemus petersii is strongly affected by corollary discharge signals associated with the electric organ discharge (EOD) motor command. This study is a physiological examination of one important source of corollary discharge signals to the lobe, the medial juxtalobar nucleus. Intracellular recordings from neurons of the medial juxtalobar nucleus show a single corollary discharge driven spike occurring at about 7.5 ms after the initiation of the EOD motor command with a temporal jitter in individual cells of less than 0.05 ms. Responses to intracellular current injection suggest the presence of a low threshold outward current that is similar to outward currents that have been identified in those neurons of the auditory system in which precise temporal information is preserved. Results from stimulation and lesion experiments indicate that the medial juxtalobar nucleus is responsible for major corollary discharge effects in the mormyromast regions of the electrosensory lobe, including: 1) the gate-like excitation of granule cells; and 2) various excitatory effects on other cells of the lobe. The medial juxtalobar nucleus transmits precise temporal information about the timing of the EOD motor command to the electrosensory lobe. This information is probably used in decoding electrosensory afferent latency as a measure of stimulus intensity.