Effects of exposure to the β-blocker propranolol on the reproductive behavior and gene expression of the fathead minnow, Pimephales promelas.

Human pharmaceutical drugs have been found in surface waters worldwide, and represent an increasing concern since little is known about their possible effects on wildlife. Propranolol is a common beta-adrenergic receptor antagonist (β-blocker) typically prescribed to people suffering from heart disease and hypertension. Propranolol has been detected in United States wastewater effluents at concentrations ranging from 0.026 to 1.90 μg/l. In mammals, there is evidence that β-blockers can cause sexual dysfunction, and alter serotonergic pathways which may impact reproductive behavior but little is known about the effects on fish behavior. The present study tested the effects of propranolol on fecundity, on brain gene expression and on reproductive behavior of the fathead minnow, Pimephales promelas, a fish that exhibits male parental care. Sexually mature fathead minnows were housed at a ratio of one male and two females per tank and exposed to nominal concentrations of 0, 0.1, 1, 10 μg/l for 21 days. Measured concentrations (±SD) of propranolol were 0.003±0.004, 0.05±0.02, 0.88±0.34 and 4.11±1.19 μg/l. There were no statistically significant differences in fecundity, fertilization rate, hatchability and time to hatch. Propranolol exposure was not associated with a change in nest rubbing behavior, time spent in the nest or approaching the females. There was a significant difference in the number of visits to the nest with males receiving low and medium propranolol treatments. The microarray analysis showed that there were 335 genes up-regulated and 400 genes down-regulated in the brain after exposure to the highest dose of propranolol. Among those genes, myoglobin and calsequestrin transcripts (fold change=10.84 and 5.49, respectively) were highly up-regulated. Ontological analyses indicated changes in genes involved in calcium ion transport, transcription, proteolysis and apoptosis/anti-apoptosis. Pathway analysis indicated that the reduced expression of caspases may lead to impaired neurite outgrowth, neurotransmitter secretion and brain function in developing organisms. The results showed that exposure to propranolol at concentrations as high as 4.11 μg/l did not significantly impact reproductive behavior or spawning abilities of fathead minnow but did alter the regulation of genes within the brain of fish.