Electrical stimulation of the preoptic area in Eigenmannia: Evoked interruptions in the electric organ discharge

The functional role of the basal forebrain and preoptic regions in modulati ng the normally regular electric organ discharge was determined by focal br ain stimulation in the weakly electric fish, Eigenmannia. The rostral preop tic area: which is connected with the diencephalic prepacemaker nucleus, wa s examined physiologically by electrical stimulation in a curarized fish. E lectrical stimulation of the most rostral region of the preoptic area with trains of relatively low intensity current elicits discrete bursts of elect ric organ discharge interruptions in contrast to other forebrain loci. Thes e responses were observed primarily as after-responses following the termin ation of the stimulus train and were relatively immune to variations in the stimulus parameters. As the duration and rate of these preoptic-evoked bur sts of electric organ discharge interruptions (approximately 100 ms at 2 pe r s) are similar to duration and rate of natural interruptions, it is propo sed that these bursts might be precursors to natural interruptions. These d ata suggest that the preoptic area, consistent with its role in controlling reproductive behaviors in vertebrates, may be influencing the occurrence o f electric organ discharge courtship signals by either direct actions on th e prepacemaker nucleus or through other regions that are connected with the diencephalic prepacemaker nucleus.