Researchers at the Sahlgrenska Academy, University of Gothenburg,
Sweden, have pinned down a hormone that is produced when we are hungry that
interferes with rationality and decision-making.
Rats given the hormone ghrelin
were more likely to act on impulse.
Impulsivity affects everyone to differing degrees, and each
individual can be more or less impulsive depending on the situation.
Forgoing something pleasurable now, in favor of something better
later on, shows control. This so-called delayed gratification is regarded as
the opposite of impulsive behavior.
Impulsivity can be broken down into two types: Impulsive action,
in other words, the inability to stop one's self from making a physical action;
and impulsive choice, an inability to delay gratification.
Although most people can control their impulses sufficiently,
impulsivity is a major factor in a number of conditions, including attention
deficit hyperactivity disorder (ADHD),obsessive-compulsive disorder (OCD), eating
disorders, and substance abuse.
This connection to various psychiatric conditions makes
impulsivity an important area of study.
Earlier studies have uncovered a relationship between food
reward behavior and impulsivity. However, a mechanism has not yet been proven.
A new study, published recently in Neuropsychopharmacology, aimed to fill this gap. The
researchers investigated impulsivity in rats, specifically in relation to the
hormone ghrelin.
What
is ghrelin?
Ghrelin is a hormone, produced in the gastrointestinal tract,
that acts on the central nervous system. It is released when the
stomach is empty. Once the stomach has become filled, production of ghrelin
ceases. Ghrelin readies the body for food, and it also works on cells of the
hypothalamus to induce the feeling of hunger.
The role of ghrelin is not limited to the hunger response alone.
It has also been implicated in the reward behavior associated with drugs,
alcohol, and food intake.
Researchers at the Sahlgrenska Academy, led by Karolina
Skibicka, set out to investigate ghrelin's potential role in impulsive
behavior.
The team trained rats to perform a variety of tasks that allowed
them to measure impulsive behavior. The first, referred to as the
"go/no-go" test, measured the rats ability to restrain a response.
Rats were trained to either press a lever to get a reward -
referred to as a "go" signal - or they were rewarded for not pressing
a lever - a "no-go" signal. The rats were taught to either
"go," or "no-go," dependent on an auditory signal (a light
or buzzer).
A second trial, called the "differential reinforcement of
low rate," provided rats with a food pellet reward only if they were able
to withhold their response for a set period of time.
The third leg, called "delay discount," measured the
rats' ability to delay gratification. The rats were presented with two levers,
one of which would dispense one food pellet as soon as it was pressed, while
the other would dispense four food pellets, but only after a significant delay.
If the first lever was pressed, the second was blocked. In this
way, the rats were taught to reject their initial impulse in order to receive
the maximum reward later on.
Ghrelin
and impulsivity
During the experiment, ghrelin was injected directly into the
rats' brains, replicating how the hormone would normally behave when the
animals were hungry.
As expected, the injection made the rats unable to resist pressing
the lever in all three trials. In other words, impulsivity had increased.
In fact, in the "go/no-go" trial, the rats were almost
three times more likely to press the lever during a "no-go" period
when their brains were infused with ghrelin.
Further to this, the researchers found that just a short period
of fasting gave the same impulsive results in the rats.
Skibicka and her team managed to pinpoint the area of the brain
that appears to be involved in this impulsive behavior.
These findings are the first to demonstrate that ghrelin
increases impulsivity in rats. The researchers hope that the findings might
assist in the development of new psychoactive drugs.
Ghrelin antagonists (drugs that block ghrelin) are already being
studied for their potential use as anti-obesity medications, and to help manage drug intake in addicts.
As
researchers uncover more details about the actions of this fascinating hormone,
other therapeutic avenues look sure to open up. Skibicka hopes that,
eventually, the brain's ghrelin receptors could be a target for the
"treatment of psychiatric disorders that are characterized by problems
with impulsivity."
Source:
medicalnewstoday
No comments:
Post a Comment