Mind switches

The laboratory of Eric J. Nestler is findings signs that epigenetic changes caused by drug use or chronic stress can change the way the brain responds to experience: priming an individual to react with resilience or to succumb to addiction, depression or a range of other psychiatric disorders.
Beyond genes
Like most common medical condition, these neurological addictions are highly heritable:roughly half the risk for addiction or depression is genetic-which is grater that the genetic risk for high blood pressure or most cancers. As we saw with Greg and Matt even having identical genes is no guarantee that two individuals will contact the same illness.
By what mechanisms can such inputs lead to metal illness? Nature and nurture come together in the nerve cell in the brain. Thesecells process everything with experience-and then share information with one another by releasing and recognizing chemical called neurotransmitters. Neurotransmitters can activate or inhibit individual nerve cells and switch a range of responsive genes on or off. Which genes a particular neurotransmitter affects will help to determine how a nerve cell will response to an experience and ultimatelyshapes the way an individual behaves.
Many off these effects last only briefly. For example, exposure to cocaine will activate the reward canter in the brain, leading to transient euphoria. That feeling soon fades, and the system resets itself. Still mysterious is how drugs, stress or other experiences can engender longer-term effects, causing an individual to succumb to depression or addition. Thatmany neuroscientists are to think, is where epigenetics comes in.
Making marks
A gene, in simplified terms, is a stretch of DNA that typically specifies the makeup of a protein; proteins carry out most processes in cells and thus control cell behavior. The combination of protein and DNA in chromosome is known as chromatin.
This packaging of DNA does more than keep the nucleus tidy. It alsohelps to regulate the behavior of the resident genes. Tighter packing tends to keep genes in an inactive state, preventing access by the machinery that turns genes on. In a nerve cell, for example, genes that encode liver enzymes are tucked away in densely packaged chromosomal regions. When a gene is needed, however, the section of DNA on which it resides unfurls somewhat, making the geneaccessible to cellular machinery that transcribes the DNA into a strand RNA.
Whether a segment of chromatin is relaxed (primed for activation) or condensed (shut down either permanently or temporarily) is influenced by epigenetic marks: chemical tags that are attached to the resident histones or to the DNA itself. An individual gene may be more-or less-active, depending on how its chromatin is marked.Epigenetic modification are made by a variety of enzymes, some of which add the chemical tags and some of which remove them. The environment can influence gene activity by regulating the behavior of epigenetic writers and eraser-and thus the tagging, and restructuring, of chromatin. The addition and removal of acetyl and methyl groups-and other marks-can thus help the brain to respond and adaptto an environmental challenge and experience. My lab and others are now finding in animal studies, however, that is beneficial epigenetic process can go awry in conditions such as addiction and depression, were alteration of the normal array of modification may serve to activate cravings, in thus feeling of defeat or otherwise predispose to an animal to a life time of maladaptive behavior.Examination of human brain tissue retrieved post-mortem, suggest that the same may be true in people.
Primed for addiction
The finding related to addiction build on past insights into how drugs of abuse usurp the brains natural reward center. Many studies, for instance have identified sweeping changes in the activation of genes in response to cocaine, opiates or other addictive substances. Some of...