Herring Impaired

Changing ion channel densities allows fish to tune their hearing to male reproductive calls during breeding periods. 

By | December 1, 2013

CAN YOU HEAR ME NOW?: Fluctuations in the number of big potassium channels in the ears of female midshipman fish help the animals tune in to males’ calls during mating season.© BRANDON D. COLE/CORBIS

EDITOR'S CHOICE IN NEUROSCIENCE

The paper
K.N. Rohmann et al., “Plasticity in ion channel expression underlies variation in hearing during reproductive cycles,” Curr Biol, 23:678-83, 2013.

The finding
Female midshipman fish (Porichthys notatus) are more interested in males’ reproductive calls during the summer breeding season than in the winter. Andrew Bass, a professor of neurobiology and behavior at Cornell University, and colleagues now show that seasonal variation in hearing occurs due to the alteration of the total number of a type of ion channel, called big potassium (BK) channels, in the sensory cells of the fish’s ears.
 
The background
P. notatus spends its winters deep in the ocean and its summers in the intertidal zone, where the male fish make humming noises that draw the females near. The authors previously showed that the hair cells in the ears of both male and female fish were tuned to the frequencies of the male mating calls during the reproductive season but not year-round.

The experiments
When the researchers blocked BK channels in reproductively active fish by applying iberiotoxin, the fish’s frequency tuning became more like that of nonreproductive-phase fish. “Blocking the BK channels so thoroughly mimicked the actions of seasonal change of tuning it seems unlikely that anything else is required,” says Harold Zakon, a neurobiologist at the University of Texas at Austin who was not involved in the study. Additionally, mRNAs encoding important subunits of BK channels were more highly expressed in reproductive fish’s saccules—the auditory organs containing the hair cells—than in those of fish caught in the winter.

The implications
Bass suspects that the BK channels proliferate in response to estrogen, which binds to steroid receptors in the fish’s hair cells. He hypothesizes that mammals, which also express estrogen receptors and BK channels, may show hormone-mediated changes in hearing as they age.

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