Researchers at the Penn Sate have discovered that daily alcohol use can change male sexual behaviour, in terms of sexual arousal, sexual inhibition, and sexual preferences.
The study on fruit flies found that daily alcohol consumption could increase sexual arousal, decrease sexual inhibitions, and even lead to same sex courtships among men.
The study led by Kyung-An Han, associate professor of biology and a neuroscientist at Penn State was conducted on fruit flies, as they can serve as a baseline for similar studies in humans also.
Fruit flies were given a daily dose of ethanol to imitate the drinking habits of alcoholics and chronic alcohol abusers more closely.
The team further examined various factors influencing the physiological effects of ethanol, including genetic and cellular components, age, and prior experience.
The findings revealed that male fruit flies, which typically court females, also actively court males when they are given a daily dose of ethanol.
"We identified three molecules that are crucial for "ethanol-induced courtship disinhibition," Han said.
Han and her students created transgenic flies whose brain activities were regulated by the neurotransmitter dopamine that could be turned off temporarily by changing the temperature to 32-degrees C.
"Without a temperature change, the transgenic males showed conspicuous inter-male courtship under the influence of ethanol; however, they exhibited negligible inter-male courtship when we changed the temperature to block the transmission of dopamine neurons in the brain," she said.
"This result suggests that dopamine is a key mediator of ethanol-induced inter-male courtship," she added.
The study also showed that repeated exposure to ethanol caused male flies to further inter-male courtship, a phenomenon known as "behavioural sensitisation."
"If a behaviour like alcohol consumption becomes more pleasurable the more often you do it, you are more likely to keep doing it," Han explained.
Researchers believe that behavioural sensitisation is the consequence of adaptive changes induced by chronic alcohol consumption, in the brain cells and molecules.
"This part of our study demonstrates that sexual behaviour is not determined only during an organism's development, but it also can be influenced by a post-developmental environmental factor; in this case, recurring exposure to ethanol," Han said.
Researchers also found that daily ethanol exposure induces chronic tolerance to the sedative effect of ethanol in flies, as it does in other animals.
Han and her students revealed that ethanol-induced inter-male courtship is also affected by aging.
"As flies get older, their cognitive capacities decline, making them more susceptible to the negative effect of ethanol on cognition," said Han.
Middle-aged and old male flies (2- to 4-weeks old) showed higher tendency of inter-male courtship compared to fully mature male flies (4-days old).
"As a result of our research with the fruit fly, we are now just beginning to discover the molecular and cellular mechanisms underlying neural changes in the brain that result from the chronic use of alcohol and that result in alcohol addiction and other behaviour changes in our fly model," Han said.
The findings appear in the scientific journal PLoS One.