Alcohol's effects on gene expression in the central nervous system

Alcohol's primary target is the central nervous system (CNS), where it influences neurotransmission to produce intoxication. Scientists can now use microarray technology to study brain function gene by gene. Symposium proceedings published in the February issue of Alcoholism: Clinical & Experimental Research address the effects of alcohol on what is called "gene expression" in the CNS regions of animal models.
"All of our cells have exactly the same deoxyribonucleic acid (DNA), which means they all have the same genes," explained William J. McBride, symposium organizer and professor of neurobiology at the Indiana University School of Medicine. "The reason that different cells can appear and work so differently with the same genes – giving us, for example, unique eyes, skin, or hair – is that only some genes are used or 'turned on' in each cell. This is called gene expression."
McBride said that researchers now know that alcohol can change gene expression in the brain, and that these changes are likely responsible for many of the 'symptoms' of addiction, such as tolerance, physical dependence, and craving, as well as the 'consequences' of alcoholism, such as brain damage.
"The challenge has been to find out which genes – out of more than 50,000 – are turned on or off in the brains of alcoholics," he said. "Microarray studies – the examination of a small glass microscope slide that has thousands of different DNA samples attached to it – that are applied to brain function are just beginning in the field of alcoholism. Several years ago, it was impossible to analyze more than a handful of these genes, however, microarray technology has changed that."
Symposium speakers at the June 2004 Research Society on Alcoholism meeting in Vancouver, B.C. presented the following findings from recent studies that used genetic animal models:


# Gene expression profiling in the nucleus accumbens, prefrontal cortex, and ventral tegmental areas show that distinct biological pathways are associated with alcohol's action in specific brain regions and certain mouse strains.


"We were able to use gene expression profiling to determine that alcohol produces multiple effects on different biological processes," said McBride, "and that these changes are different in several brain regions which may be involved in alcohol addiction."


# Researchers have identified individual genes and gene networks that may play an important role in determining the behavioral responses to alcohol as well as possibly influencing drinking behavior.


"Thus far, genes that appear to be responsive to alcohol include genes involved in the intracellular signaling process (which can alter how the neuron functions), neuropeptide signaling (which modulates nerve cell activity), and myelin structure (which is needed for communication between nerve cells)," said McBride. "Gene expression profiling has also been used to identify chromosomes and chromosomal regions that influence alcohol drinking and response to alcohol."


# Intracranial self-administration of ethanol into the posterior ventral tegmental area (VTA) of alcohol-preferring rats produced results suggesting that the reinforcing effects of alcohol are activating VTA dopamine neurons and producing changes in synaptic connections that resemble those that occur in memory and learning.


"Learning and memory require enhanced synaptic function between neurons," explained McBride. "Enhanced synaptic function is characterized by increased formation of synaptic proteins. The stimulation of VTA dopamine neurons by alcohol increases the expression of genes involved in the synthesis of synaptic proteins in target regions of the VTA. In short, these results suggest that alcohol can produce changes in the brain reward system that can further increase the rewarding effects of alcohol."


# Microarray techniques confirmed earlier reports indicating that chronic alcohol exposure/withdrawal differentially alters gene expression in the prefrontal cortex of mice. More than 300 genes were found to be altered by acute alcohol treatment.


"The prefrontal cortex is involved in motivated behaviors," noted McBride. "Studies with humans indicate that this brain region is sensitive to the effects of heavy alcohol drinking and repeated withdrawals. The microarray technique provides insight into cellular changes that occur over time with chronic alcohol drinking and repeated withdrawals."


Collectively speaking, added McBride, findings presented at the symposium demonstrate the quantitative and qualitative applications of microarrays to studying the genetic and biological bases of alcoholism and alcohol abuse within discrete brain regions.
"For researchers, microarray technology has the potential of studying the genetic and biological bases of alcohol's rewarding effects, sensitivity to the effects of alcohol, development of tolerance to the effects of alcohol, development of alcohol dependence, and alcohol withdrawal severity," he said. "For the average reader, knowing which genetic profiles might contribute to excessive alcohol drinking could be used to identify risk factors that contribute to alcoholism and alcohol abuse, and could aid in the development of selective treatment strategies for different subgroups of alcoholics."
McBride added that, despite recent advances, researchers need further developments in microarray technologies and bioinformatic approaches to better understand the complex neurobiological mechanisms underlying alcohol addiction. "Future research will need to determine changes in gene expression in very discrete neuronal pathways that may be involved in mediating the effects of alcohol that lead to addiction," he said. "Future studies will also require the integrative efforts of many investigators working with different animal models in order to identify the multiple genetic factors that contribute to the risk for alcoholism and alcohol abuse."

Source : Indiana University School of Medicine

Memories may skew visual perception

Taking a trip down memory lane while you are driving could land you in a roadside ditch, new research indicates. Vanderbilt University psychologists have found that our visual perception can be contaminated by memories of what we have recently seen, impairing our ability to properly understand and act on what we are currently seeing.


"This study shows that holding the memory of a visual event in our mind for a short period of time can 'contaminate' visual perception during the time that we're remembering," Randolph Blake, study co-author and Centennial Professor of Psychology, said.


"Our study represents the first conclusive evidence for such contamination, and the results strongly suggest that remembering and perceiving engage at least some of the same brain areas."


The study, led by research associate Min-Suk Kang, was recently published in the journal Psychonomic Bulletin & Review.


"There are numerous instances where we engage in visually guided activities, such as driving, while rehashing visual events in our mind's eye. Common sense tells us that this mental replay is harmless in that it does not interfere with our ability to register and react to objects within our visual field," Kang and his co-authors wrote. "Evidently, however, that is not always true when the contents of our working memories overlap with the contents of our perceptual world."


In this study, the researchers used a visual illusion called motion repulsion to learn whether information held in working memory affects perception. This illusion is produced when two sets of moving dots are superimposed, with dots in one set moving in a different direction from those in the other set. Under these conditions, people tend to misperceive the actual directions of motion, and perceive a larger difference between the two sets of motions than actually exists.


Ordinarily this illusion is produced by having people view both sets of motion at the same time. Kang and colleagues set out to determine if the illusion would occur when one set of motions, rather than being physically present, was held in working memory.


In the experiment, participants were shown a random pattern of dots and were asked to remember the direction in which the dots were moving. They were then were shown a second pattern of moving dots. They were asked to report on the direction of second dots' movement.


The research subjects' reports of the second dots' movement was exaggerated and influenced by what they had previously seen. If they were first shown dots moving in one direction and later shown dots moving in a slightly counterclockwise direction relative to the first presented dots, they reported the counterclockwise movement to be more dramatic than it had actually been.


"We find that observers misperceive the actual direction of motion of a single motion stimulus if, while viewing that stimulus, they are holding a different motion direction in visual working memory," the authors wrote.


The results provide further support for previous findings by Vanderbilt researchers Frank Tong and Stephanie Harrison that the contents of working memory may be represented in early visual areas in the brain, including the primary visual cortex, that were previously thought to play no role in higher cognitive functions such as memory.


"Our findings provide compelling evidence that visual working memory representations directly interact with the same neural mechanisms involved in processing basic sensory events," Kang and his colleagues wrote.

Source : Vanderbilt University

Bodyguard for the brain

Humans are getting older and older, and the number of people with dementia is increasing. The factors controlling degeneration of the brain are still mostly unknown. However, researchers assume that factors such as stress, accumulation of toxic waste products as well as inflammation accelerate aging. But, vice versa, there are also mechanisms that can - like a bodyguard - protect the brain from degenerating, or repair defective structures.


Researchers from the Universities of Bonn and Mainz have now discovered a hitherto unknown function of the cannabinoid-1 receptor (CB1). A receptor is a protein that can bind to other substances, triggering a chain of signals. Cannabinoids such as THC – the active agent in cannabis sativa – and endocannabinoids formed by the body bind to the CB1 receptors. The existence of this receptor is also the reason for the intoxicating effect of hashish and marijuana.


Not only does the CB1 receptor have an addictive potential, but it also plays a role in the degeneration of the brain. "If we switch off the receptor using gene technology, mouse brains age much faster," said Önder Albayram, principal author of the publication and a doctoral student on the team of Professor Dr. Andreas Zimmer from the Institut für Molekulare Psychiatrie at the University of Bonn. "This means that the CB1 signal system has a protective effect for nerve cells."


Mice prove their brain power in a pool


The researchers studied mice in different age categories – young six week old animals, middle-aged ones at five months, and those of an advanced age at 12 months. The animals had to master various tasks – first, they had to find a submerged platform in the pool. Once the mice knew its location, the platform was moved, and the animals had to find it again. This was how the researchers tested how well the rodents learned and remembered.


The animals in which the CB1 receptor had been switched off (the knock-out mice) clearly differed from their kind. "The knock-out mice showed clearly diminished learning and memory capacity," said Privatdozent Dr. Andras Bilkei-Gorzo from Professor Zimmer's team, who led the study. So, animals that did not have the receptor were less successful in their search for the platform. "In addition, they showed a clear loss of nerve cells in the hippocampus," he explained further. This part of the brain is the central area for forming and storing information. In addition, the researchers found inflammation processes in the brain. As the mice advanced in age, the degenerative processes became increasingly noticeable.


Amazing parallels with the human brain


The animals with the intact CB1 receptor, to the contrary, did clearly better with regard to their learning and memory capabilities, as well as the health of their nerve cells. "The root cause of aging is one of the secrets of life," commented Albayram. This study has begun to open the door to solving this enigma. The processes in the mouse brains have a surprising number of parallels with age-related changes in human brains. So, the endocannabinoid system may also present a protective mechanism in the aging of the human brain.


The principal author cautioned, "This will require additional research." The scientists would like to better understand the mechanism by which CB1 receptors protect the brain from inflammation processes. And based on these signal chains, it might then be possible to develop substances for new therapies.


Source : University of Bonn

Peptidomimetics

There are many instances where the native information within a natural peptide ligand can be conferred/duplicated or mimetized into a non-peptide molecule, preferably of low molecular weight, hence the basis for the field of peptidomimetics(PM's). The desire to convey the three dimensional information present in a peptide into small nonpeptide molecules is what encompasses the field of peptidomimetics.
Many research groups, both in academia and in pharmaceutical companies search constantly for non-peptide compounds that have better bioavailability and stability, perhaps even with greater receptor selectivity. The known structure-activity interactions and conformational foldings of peptide structures aid a great deal in the design of novel peptidomimetics. There are a number of factors that help in the rational design of PM's such us: binding site optimal fit, conformational stabilization, (given by rigid elements and the positioning of specific functional groups), polar or hydrophobic regions (inside strategic reactive pockets) that favor the basic atomic interactions provided by hydrogen , electrostatic and hydrophobic bonding.
The goal in PM's is to obtain molecules that mimic the specific molecular interactions of natural proteins and their ligands. The protein to protein interaction of biologivally active peptides at the receptor level can be obtained by small molecules, in an agonistic fashion or can be blocked, in an antagonistic fashion.
To obtain PM's generally the biological researcher will have to screen compound libraries(either natural products or synthetic products). Combinatorial chemistry, amethod that was heavily used in the mid to late 90's can be a tool to generate vast numbers of peptidic and non-peptidic molecules As an example of a PM's , an inhibitor of angiotensin-converting enzyme (ACE), was developed, this PM's is called Captopril. Also, morphine , an opiod alkaloid, represents a classic example of a nonpeptidic compound found that mimics an endogenous peptide. Morphine replicates the biological effect of beta endorphin, on the respective receptor. A number of important aspects regarding conformational resctriction, peptide bond replacement, addition of turn mimetics and combinatorial library screening ,are investigated in order to search and find novel ligands, within the field of peptidomimetics.

Molecular modelling-computational approach of drug designing

The molecular modelling is the general term used to describe the use of computer to construct the molecule and perform a variety of calculation on there molecule in order to predict their chemical characteristics and behavior.rational drug design is also introduce with the help of artificial intelligence.the protein folding problem entails the mathematical prediction of tertiary,3-dimensional protein structure given that the primary linear structure is defined by the sequence of coine acids of the protein.it is one of the most challenging problems in current biochemistry,and is a very rich source of interesting problems in mathematical modeling and numerical analysis,requiring an interplay of techniques in digen value calculations,stiff differential equations,stochastic differential equations,local and global optimization,nonlinear least squares.even topologibal concepts like the morse index and invariants in knot theory have been used.an extensive recent report from the US national research council on the mathematical challenges from theoretical and computational chemistry shows the protein folding problem embedded into a large variety of other mathematical challenges in chemistry.imatinib-acquired resistance related to the presence of secondary point mutations has become a frequent event in gastrointestinal stromal tumors.here transient transfection experiments with plasmies carrying two different KIT-acquired point mutations were performed clog with immunoprecipitation of total protein extracts,derived from imatinib-treated and untreated cells.the molecular mechanics/poisson boltzmann surface area computational techniques were applied to study the interactions of the wild type and mutated receptors with imatinib at the molecular level.biochemical analyses showed KIT phosphorylation in bell transfected with vectors carrying the specific mutant genes.imatinib treatment demonstrated that T670I was insensitive to the drug at all the applied concentrations,whereas V654A was inhibited by 6micro meter of imatinib.the modeling of the mutated receptors revealed that both substitutins affect imatinib-binding sites,but u2 a different extent:T670I substantially modifies the binding pocket,whereas V654A induces only relatively confined structural changes.

Finding DRUG for swine flu.

Many infectious diseases have been eliminated over the past century,but microorganism still pose a significant and increasing threat.the recent emergence (april-2009) of the new pandemic strain H1N1-SWINE FLU virus poses a challenge to the existing medical capabilities.the aim of the researchers is to find out the most effective drug among the existing ones for influenza virus.the current drug targets neuraminidase and lon-channel proteins (M2-protein) of H1N1 VIRUS proteins plays a major role in the effective replication and release of virion in spreading the disease.zanåmivir and oseltamivir are the neuraminidase-inhibitors.amantadine and rimatidine acts towards lon-channel protein(M2-protein) .among the 11 proteins of swine virus only two has been targeted towards drug designing.the protein PB1 and NS1(non structural) plays significant roles in the virulence and suppression of interferon response in the virus infected cells.the structure of proteins PB1 and NS1 were modeled using SWISS MODEL.it has been structurally and functionally determined in protein databases.the lead molecules binding to these targets were identified using structure based drug designing.

Structure based drug design

Access to the complete human genome sequence as well as to the complete sequences of pathogenic organisms provides information that can result in an avalanche of therapeutic targets.structure-based design is one of the first techniques to be used in drug design.structure based design refers specifically to finding and complementing the 3D structure (binding and/or active sites) of a target molecule such as a receptor protein.