Tag Archives: dopamine

Phenylalanine Hydroxylase and Memory Performance

Phenylalanine, an essential amino acid, is the precursor to amino acid tyrosine, which helps regulate dopamine, noradrenaline and adrenaline. Found naturally in breast milk, phenylalanine is said to have analgesic and antidepressant qualities. Phenylalanine hydroxylase (PAH) is the enzyme that catalyzes phenylalanine to tyrosine. Mutations in PAH can cause phenylketonuria (PKU), the inability to metabolize phenylalanine and a genetic disorder that can lead to intellectual disability, seizures, motor disorder and skin rashes when not monitored. Because of this association of genetic variations to cognitive ability, researchers at the National Center of Neurology and Psychiatry in Japan set out to test the effect of variations, or single nucleotide polymorphisms, of PAH on memory performance in humans.

For the experiment, researchers Toshiya Teraishi et al. used 599 healthy participants. All participants underwent interviews to make sure they had no history with psychological disorders. They were then given the Wechsler Memory Scale-Revised to evaluate memory performance in five parts: verbal memory, visual memory, general memory, attention and delayed recall. Blood samples were also taken to determine the genomic DNA of the participants and tag six different single nucleotide polymorphisms (SNP) of PAH.

The effect of variations of PAH on memory

After analyzing the test scores and associated SNPs of phenylalanine hydroxylase of the participants, researchers Teraishi et al. found a significant association of the verbal memory set of the score with five SNPs. This suggests that common variations in PAH, specifically variations with SNP marker rs2037639 and haplotype markers rs2037639 and rs10860936, can have an effect on verbal memory performance.

Because SNP rs2037639 was found in previous studies to be associated with schizophrenia in sample of Bulgarian men, the researchers believe that the particular SNP variation increases an individual’s susceptibility to the mental disorder by affecting memory performance.

They report that verbal memory is one of the most altered neurocognitive function for schizophrenics.



Amino Acid Phenylalanine Helps Us Make Good — And Bad — Decisions

Are you an optimist, or a pessimist? Do you ever make bad decisions? The level of dopamine—created from the amino acid phenylalaninein your brain could be influencing your ability to make good decisions. A recent interesting study from University College London investigated whether high levels of dopamine makes us unrealistically optimistic.

Have you ever purchased a lottery ticket? Humans are generally optimistically biased when making predictions about our future. We habitually underestimate the likelihood of negative events. But why? Is the amino acid phenylalanine to blame?

Researchers Tali Sharot, Marc Guitart-Masip, et al., from the Department of Cognitive, Perceptual and Brain Sciences at the University College London, developed a double-blind placebo-controlled pharmacological intervention study to investigate.

Dopamine is a brain chemical—a neurotransmitter–produced from the essential amino acid phenylalanine. Phenylalanine can elevate mood, decrease pain, and help memory and learning.  But can we have too much?

The researchers created a test to see if dopamine makes us unrealistically optimistic. Test subjects were given dihydroxy-L-phenylalanine—to pharmacologically produce dopamine—and asked to perform a belief update test. They were asked to estimate the likelihood of experiencing 40 different types of adverse life events, such as developing Alzheimer’s disease, and having their car stolen.

Dihydroxy-L-phenylalanine raises dopamine, affects decision-making

The dopamine created from the dihydroxy-L-phenylalanine made every answer highly optimistic. Negative events were significantly underestimated with high levels of dopamine. In addition, raised levels of dopamine makes us less likely to learn from unpleasant experiences.

The researchers concluded that pharmacological manipulation of the neurotransmitter dopamine—by taking dihydroxy-L-phenylalanine—makes us unrealistically optimistic. So controlling dopamine can help us make better decisions.

And even better, enhancing dopamine levels with dihydroxy-L-phenylalanine could help people suffering from major depression.

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