| Research Abstract |
The weakly electric fish, Mormyrid, generates a biphasic electric field from it's own pulse-type electric organ discharges (EOD. In the electrosensory systems, variations in the discharge rate and amplitude of own EOD enable the fish to detect local distortions of the electric field as electrolocation, and broad distortions evoked by other fish as electrocommunication. To avoid jamming, fish evokes the EOD with a delay after the other's EOD called as echo response. In the present work, we examined how sensory stimuli changed the frequency of EOD as follows; 1. in the behavioral experiments, how each fish extracted the characteristics of sensory stimuli and responds. 2. The neural network to induce the EODs with short latency were studied (1) in the pathway of electrosensory processing, (2) in the sensory-motor integration at higher level, and (3) in the feedback system to motor commandneurons. 3. Does pace making neurons for EOD exist in the brainstem as likely as respiratory neural network. We find that, <1> when a metal rod was placed near the side of the fish, the frequency of EOD transiently increased from 5-10 Hz to c.20 Hz, while with the broad stimuli applied between the head and tail, the fish responded with a interval of EOD tuned to the stimulus frequency, with a minimum latency of c.11 ms. In the presence of activator for GABA-A receptor, EOD frequency decreased, but with a sharp tuning. The minimum latency of EOD for stimulus did not change. <2-(1)>In the ELL, K channel contributed to the shape of the large broad spike, which is important for the plastic modification of senseory input shown by dye imaging and slice patch recording. These evidence suggests that sensory inputs are necessary for frequency tuning of EOD, and that the inhibitory GABAeargic neurons modulate the EOD frequency.
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