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: My sudden synaesthesia—how I went blind and started hearing colours

Related Stories

My sudden synaesthesia—how I went blind and started hearing colours

October 10, 2017
It took just 72 hours for me to lose my sight entirely, and for my hands and feet to feel like they were encased in ice. Just before my blindness hit, I had been laid up with an unknown virus that had left me suffering severe ...

Researchers report startling glaucoma protein discovery

October 20, 2017
A discovery in a protein associated with glaucoma was so unheard of that for over two years, researchers ran it through a gauntlet of lab tests and published a new research paper on it. The tests validated what they initially ...

After 15 years in a vegetative state, nerve stimulation restores consciousness

September 25, 2017
A 35-year-old man who had been in a vegetative state for 15 years after a car accident has shown signs of consciousness after neurosurgeons implanted a vagus nerve stimulator into his chest. The findings reported in Current ...

A new approach to improving hemispatial neglect after stroke

October 4, 2017
Jacinta O'Shea from the Nuffield Department of Clinical Neurosciences explains how stimulation of the brains of stroke patients can cause long-lasting improvements.

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 ...

Recommended for you

'Human chronobiome' study informs timing of drug delivery, precision medicine approaches

December 13, 2017
Symptoms and efficacy of medications—and indeed, many aspects of the human body itself—vary by time of day. Physicians tell patients to take their statins at bedtime because the related liver enzymes are more active during ...

Estrogen discovery could shed new light on fertility problems

December 12, 2017
Estrogen produced in the brain is necessary for ovulation in monkeys, according to researchers at the University of Wisconsin-Madison who have upended the traditional understanding of the hormonal cascade that leads to release ...

Time of day affects severity of autoimmune disease

December 12, 2017
Insights into how the body clock and time of day influence immune responses are revealed today in a study published in leading international journal Nature Communications. Understanding the effect of the interplay between ...

3-D printed microfibers could provide structure for artificially grown body parts

December 12, 2017
Much as a frame provides structural support for a house and the chassis provides strength and shape for a car, a team of Penn State engineers believe they have a way to create the structural framework for growing living tissue ...

Team identifies DNA element that may cause rare movement disorder

December 11, 2017
A team of Massachusetts General Hospital (MGH) researchers has identified a specific genetic change that may be the cause of a rare but severe neurological disorder called X-linked dystonia parkinsonism (XDP). Occurring only ...

Protein Daple coordinates single-cell and organ-wide directionality in the inner ear

December 11, 2017
Humans inherited the capacity to hear sounds thanks to structures that evolved millions of years ago. Sensory "hair cells" in the inner ear have the amazing ability to convert sound waves into electrical signals and transmit ...

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.