Should I stay or should I go? On the importance of aversive memories and the endogenous cannabinoid

September 25, 2015
Should I stay or should I go? On the importance of aversive memories and the endogenous cannabinoid
© Charlie Padgett

Memory is not a simple box of souvenirs; it is also, and most importantly, a safety system for organisms. With the help of negative memories, known as "aversive" memories, we can avoid a threat that we have already confronted. Researchers from Inserm and University of Bordeaux have just discovered that the cannabinoid receptors of the brain control these memories that are crucial for survival. This study is published in Neuron.

When confronted by danger, every individual has to make a crucial choice. This type of "simple" decision may determine his/her destiny: if the fire alarm goes off, we have learned to heed it and flee, and not to ignore it. In the same way, we avoid food and drinks that might have made us sick in the past.

The body is thus equipped with neurological mechanisms that help it to adjust its behaviour in response to a stimulus. Such is the case with aversive memories, a key survival process, which prepares the body to avoid these potential dangers effectively. These memories are accompanied by physiological responses (fright and flight) that enable one to get away from a dangerous situation.

Although the role of the habenula, a central region of the brain, in this phenomenon has received a great deal of attention in recent years, the same is not true of the endogenous cannabinoid system of the habenular neurons, on which Giovanni Marsicano and his team (particularly Edgar Soria-Gomez) have focused. This system involves the type 1 . These receptors, the activity of which is normally regulated by endocannabinoids - the body's own molecules - are the target of the main psychoactive components of cannabis.

The researchers conditioned mice so that they reacted to certain danger signals (sounds or smells). When they exposed them to these signals, mice that were deficient in cannabinoid receptors in the habenula expressed neither the fear nor the repulsion observed in normal mice. Interestingly, this impaired reaction did not apply to neutral or , which remained unchanged in these mice.

At molecular level, the scientists observed that, although the functioning of the habenula normally involves two molecules (acetylcholine and glutamate), the defect observed in these mice is caused by an imbalance in neurotransmission involving only acetylcholine.

"These results demonstrate that the endogenous cannabinoid system in the habenula exclusively controls the expression of aversive memories, without influencing neutral or positive memories, and does so by selectively modulating acetylcholine in the neural circuits involved," explains Giovanni Marsicano, Inserm Research Director.

The control of these particular memories is an integral part of diseases associated with the emotional process, such as depression, anxiety or drug addiction. As a consequence, the endogenous cannabinoid system of the habenula might represent a new therapeutic target in the management of these conditions.

Explore further: How traumatic memories hide in the brain, and how to retrieve them

More information: dx.doi.org/10.1016/j.neuron.2015.08.035

Related Stories

Natural 'high' could avoid chronic marijuana use

December 1, 2014

Replenishing the supply of a molecule that normally activates cannabinoid receptors in the brain could relieve mood and anxiety disorders and enable some people to quit using marijuana, a Vanderbilt University study suggests.

How marijuana impairs memory

March 1, 2012

A major downside of the medical use of marijuana is the drug's ill effects on working memory, the ability to transiently hold and process information for reasoning, comprehension and learning. Researchers reporting in the ...

Recommended for you

Chatter in the deep brain spurs empathy in rats

June 23, 2017

It's a classic conundrum: while rushing to get to an important meeting or appointment on time, you spot a stranger in distress. How do you decide whether to stop and help, or continue on your way?

The neural relationship between light and sleep

June 23, 2017

Humans are diurnal animals, meaning that we usually sleep at night and are awake during the day, due at least in part to light or the lack thereof. Light is known to affect sleep indirectly by entraining—modifying the length ...

How brains surrender to sleep

June 23, 2017

Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna study fundamental aspects of sleep in roundworms. Using advanced technologies, they monitor the activity of all nerve cells in the brain while they ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.