Antidepressants enhance neuronal plasticity in the visual system

April 17, 2008

In the April 18 issue of Science, scientists from the Scuola Normale Superiore in Pisa, Italy and the Neuroscience Centre at the University of Helsinki, Finland, provide new information about the mechanism of action of antidepressant drugs. In addition, the study suggests that antidepressants could also be used for the treatment of amblyopia. However, to produce a functional effect, antidepressant treatment also seems to require environmental stimuli, such as rehabilitation or therapy.

According to Professor Eero Castrén at the University of Helsinki, the original objective of the study was to learn more about why the antidepressant effect of fluoxetine (also known as Prozac) and other selective serotonin reuptake inhibitors develops so slowly, many weeks after starting treatment.

Castrén’s research group has approached this question by examining the growth factor, brain-derived neurotrophic factor (BDNF), which influences plasticity of the nervous system or in other words, the ability of brain cells to change their structure or function in response to stimuli. Antidepressants seem to act through BDNF, thus enhancing the plasticity of the nervous system, at least in certain brain areas. However, it has been unclear how antidepressant-induced increases in BDNF could relieve depression.

Neuronal plasticity of the developing visual cortex has been well characterised. Therefore, this classical model of the visual cortex was utilised to examine the effect of fluoxetine on neuronal plasticity, although there was previously no evidence that antidepressants would act on the visual system. During early childhood, if one eye remains weaker than the other eye, the neuronal connections of the stronger eye take over the visual cortex while the connections of the weaker eye retract. During a critical period of early childhood, neuronal connections are in a highly plastic state, and the vision of the weaker eye can be strengthened by covering the better eye, thus reinforcing the connections of the weaker eye to the visual cortex. In adolescence however, after the critical period has closed, plasticity is reduced and covering the better eye no longer strengthens the connections of the weaker eye which remains poor in vision throughout adulthood.

The experiments, mainly conducted by the research group of Professor Lamberto Maffei in Pisa, showed that treatment with the antidepressant, fluoxetine reopened the critical period of plasticity in the visual cortex of adult rats. In experiments where one eye of a young rat was covered during the critical period and reopened only in adulthood, vision improved in the weaker eye to finally equal that of the healthy eye when fluoxetine treatment was combined with covering the healthy eye. This fluoxetine-induced enhancement of plasticity was associated with increased BDNF and reduced cortical inhibition in the visual cortex, which advanced reorganisation of the neuronal connections.

Since fluoxetine, when combined with covering the better eye, improved vision in the weaker eye of adult rats, it is possible that antidepressants could be similarly used in amblyopic humans. The results suggest that the improved plasticity induced by antidepressants leads to a functional neuronal reorganisation in the cerebral cortex. The ability of an antidepressant to facilitate the reorganisation of neuronal connections in a brain area not associated with mood, suggests that similar treatment strategies might also be useful in the treatment of other brain disorders.

It is important to note that fluoxetine improved vision in the weaker eye only if the better eye was covered. This suggests that while antidepressants provide the possibility of rearranging cortical connections, environmental stimuli are required to guide the rearrangement to produce the desired effect.

It is possible that defective neuronal connections in cortical areas related to mood regulation might predispose people to depression. The enhanced plasticity provided by the antidepressant might allow reorganisation of cortical connections and function. However, Castrén emphasises that antidepressants do not repair the network on their own, but that functional recovery also requires environmental guidance, such as social interaction, rehabilitation or therapy.

Source: University of Helsinki

Explore further: Scientists restore youthful plasticity to the brains of adult mice

Related Stories

Scientists restore youthful plasticity to the brains of adult mice

August 8, 2017
Like much of the rest of the body, the brain loses flexibility with age, impacting the ability to learn, remember, and adapt. Now, scientists at University of Utah Health report they can rejuvenate the plasticity of the mouse ...

The sex workers who are stopping HIV

August 15, 2017
It's late when we reach Inhamízua on the outskirts of the city.

Fighting dehydration with wearables and big data

August 2, 2017
Dehydration is one of the most common causes of death among young children in the developing world – particularly during the hot summer months. ETH Professor Walter Karlen and his team of researchers have developed an inexpensive ...

Virtual reality headset gang gets yet another entrant: Huawei

April 18, 2016
(Tech Xplore)—A 360-degree sound field is one of the attributes of the newly announced Huawei VR headset. The Chinese manufacturer, said Forbes, " claims that its VR mobile headset is the first to support 3D sound." Engadget ...

Disinhibition plus instruction improve brain plasticity

April 12, 2011
(PhysOrg.com) -- The healthy brain has balance of excitatory and inhibitory signals that stimulate activity but also keep it under control. Some brain diseases, like autism and Down's syndrome, have too much inhibition, which ...

Surprisingly rapid regrowth of unused brain connections after decades of near blindness

July 15, 2015
Since 2007, clinical trials using gene therapy have resulted in often-dramatic sight restoration for dozens of children and adults who were otherwise doomed to blindness. Now, researchers from the Perelman School of Medicine ...

Recommended for you

Researchers describe mechanism that underlies age-associated bone loss

September 22, 2017
A major health problem in older people is age-associated osteoporosis—the thinning of bone and the loss of bone density that increases the risk of fractures. Often this is accompanied by an increase in fat cells in the ...

Researchers develop treatment to reduce rate of cleft palate relapse complication

September 22, 2017
Young people with cleft palate may one day face fewer painful surgeries and spend less time undergoing uncomfortable orthodontic treatments thanks to a new therapy developed by researchers from the UCLA School of Dentistry. ...

Exosomes are the missing link to insulin resistance in diabetes

September 21, 2017
Chronic tissue inflammation resulting from obesity is an underlying cause of insulin resistance and type 2 diabetes. But the mechanism by which this occurs has remained cloaked, until now.

Thousands of new microbial communities identified in human body

September 20, 2017
A new study of the human microbiome—the trillions of microbial organisms that live on and within our bodies—has analyzed thousands of new measurements of microbial communities from the gut, skin, mouth, and vaginal microbiome, ...

Study finds immune system is critical to regeneration

September 20, 2017
The answer to regenerative medicine's most compelling question—why some organisms can regenerate major body parts such as hearts and limbs while others, such as humans, cannot—may lie with the body's innate immune system, ...

Immune cells produce wound healing factor, could lead to new IBD treatment

September 20, 2017
Specific immune cells have the ability to produce a healing factor that can promote wound repair in the intestine, a finding that could lead to new, potential therapeutic treatments for inflammatory bowel disease (IBD), according ...

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.