Electric fish of the genus Sternopygus produce a sinusoidal electric organ discharge (EOD) of low frequencies in males, high frequencies in females, and overlapping and intermediate frequencies in juveniles. Correspondingly, the cells of the electric organ, the electrocytes, generate action potentials which are of long duration in mature males, short duration in females, and intermediate duration in immatures. The androgen dihydrotestosterone (DHT) lowers EOD frequency and increases electrocyte action potential duration. We examined the electrocytes under voltage clamp to determine whether variations in the kinetic properties of the Na+ current might underlie these phenomena. We found that the fast inactivation time constants of the peak Na+ current (0 mV) ranged from 0.5 to 4.7 msec and varied systematically with EOD frequency and action potential duration. Voltage dependence of steady- state inactivation also varied with EOD frequency with the midpoint of inactivation being more positive in fish with low EOD frequencies. There was no correlation between the voltage at which the Na+ current activates, voltage at peak current, reversal potential, rate of recovery from inactivation, or TTX sensitivity and EOD frequency. We tested whether DHT influenced Na+ current inactivation by recording from electrocytes before and after juvenile fish of both sexes were implanted with a DHT-containing or empty capsule. We found that inactivation time constants were significantly slower in DHT implanted, but not control, fish. This is the first observation of functionally relevant individual variation in the kinetics of a Na+ current and the first demonstration that the kinetics of a Na+ current may be modulated by an androgen.

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The electric organ cells of Sternopygus generate action potentials whose durations vary over a fourfold range. This variation in action potential duration is the basis for individual variation in a communication signal. Thus, action potential duration must be precisely regulated in these cells. We had observed previously that the inactivation kinetics of the electrocyte Na(+) current show systematic individual variation. In this study, using a two-electrode voltage clamp, we found that the voltage-dependent activation and deactivation kinetics of the delayed rectifying K(+) current in these cells covary in a graded and predictable manner across fish. Furthermore, when Na(+) and K(+) currents were recorded in the same cell, their voltage-dependent kinetics were highly correlated. This finding illustrates an unprecedented degree of coregulation of voltage-dependent properties in two molecularly distinct ionic channels. Such a coregulation of ionic channels is uniquely observable in a cell specialized to generate individual differences in electrical activity and in which the results of biophysical control mechanisms are evident in behaving animals. We propose that the precise coregulation of the voltage-dependent kinetics of multiple ionic currents may be a general mechanism for regulation of membrane excitability.

Electric fish strengthen their communication signals nightly and during social encounters by rapidly trafficking ion channels into cell membranes, demonstrating a direct relationship between environmental stimuli, channel trafficking, and behavior.

Prolonged flight behavior in females of the grasshopper, Melanoplus sanguinipes (Fab.), decreases as ovarian tract weight increases relative to body weight. However, reproductive maturation does not always permanently terminate the migratory phase of the grasshopper's life cycle; long flights are also made after ovipositions. We examine the hypothesis that migration (measured as long-duration tethered flight behavior) decreases reproductive potential, either by delaying first oviposition or by decreasing production of egg pods. No negative effects of flight on oviposition were observed. Instead, age at first oviposition tended to decrease in females flown repeatedly compared to those flown only twice. Further, oviposition was greatly enhanced in females flown for several hours relative to unflown controls. We suggest that selection pressure for rapid and successful colonization has resulted in the evolution of a suite of characters including enhanced migratory behavior and accelerated reproduction in highly migratory populations.