Introduction
Optimism is a mental attitude that interprets situations as being best .
Today researches consider different types of optimism according to the context:dispositional optimism is one of them.
Dispositional optimism is a factor favorable for phisical well-being and for the ability to resist stress-inducing life experiences . It's a global expectation that good things will happen in the future; in other words it means one expects the best possible outcome from any given situation.
An important aspect of this world view is that it may be linked to health.
Dispositional optimism and pain
In 2009 a study was undertaken to analyze a possible relation between this kind of life orientation and coping with
pain.
Dispositional optimism and coping with pain, 2009
It was conducted in 65 persons , and were used some questionnaires to evaluate individual life expectations toward the future, the efficacy of individuals believes related to pain control and strategies applied to face pain. K Bargiel-Matusiewicz and A Krzyszkowska found out that dispositional optimism has a significative role in forming the mechanisms of coping with pain, specially cronic pain. According to table 2 of the article there is a strong correlation between optimism and pain control : the higher is the first , the stronger the second (r = 0.60, P < 0.01).
The article that summarizes this study does not focus on the possible molecular pathway of this correlation.
Which could be the biological component/s associated to this finding?
Dopamine and feeling well
A key role in increasing positive expectations regarding the future is played by DOPAMINE.
Last year it was discovered that administration of L-DOPA, a drug that enhances dopaminergic function, increases dispositional optimism.
How Dopamine Enhances an Optimism Bias in Humans, 2012
Dopamine is known to modulate cognition , through its projections from midbrain, the basal ganglia and some cortical areas in the frontal lobe
Catecholamine innervation of the basal forebrain. IV. Topography of the dopamine projection to the basal forebrain and neostriatum , 1978
The authors conducted a double-blind placebo-controlled pharmacological intervention study:on one of the days, participants received placebo and on the other they received L-DOPA (150 mg).
The trial was divided into two sessions: during both of them, patients had to estimate their likelihood of experiencing unpleasant situations.
It was reported that increasing dopamine function while people imagined future, the level of plesure enhanced. They showed that this chemical reduced the impact of unexpected negative information, too.
Dopamine and pain
Dopamine was demonstrated to play a role in processing pain.
Some studies evaluated its action in multiple levels of central nervous system (SNC), including the spinal cord,periaqueductal gray, thalamus, basal ganglia, insular cortex and cingulate cortex.
This analgesic capacity of dopamine occurs as a result of D2 receptor and sometimes D1 receptors activation.For example it was reported that dopamine microinjections at different doses increased action of dopaminergic projections in the rat anterior cingulate cortex, reducing pain.
Dopamine and NMDA systems modulate long-term nociception in the rat anterior cingulate cortex , 2004
According to this findings, in some painful disorders was found an abnormal dopaminergic system.
One of them is restless legs syndrome (RLS).
It's a clinical condition characterized by painful legs, specially at rest and in the evening.
Although it is thought that
RLS is ereditary, no genes have been identified.
In 2006 a study highlighted the role of dopamine in this patology.
The aim of this
PET study was to examine dopamine D2-receptors in 16
RLS patients and 16 control subjects. [11C]Raclopride and [11C]FLB 457 were used to estimate D2-receptor availability in striatum and extrastriatal regions, respectively.
In the striatum, patients had significantly higher [11C]raclopride binding potential values than controls, as well as in extrastriatal regions.Increased D2-receptor availability in
RLS may correspond to higher receptor densities or lower levels of endogenous dopamine.
However, both possibilities are a consequence of an abnormal dopaminergic system.
PET study on D2-receptor binding, 2006
Dopamine
Dopamine is a catecholamine synthesized in the body by neurons, whose metabolic pathway is rapresented here:
In the first two reactions, L-Tyrosine is converted into L-DOPA by the enzyme tyrosine hydroxylase, using tetrahydrobiopterin (THB), O2, and ferrous iron (Fe2+) as cofactors.
L -DOPA is converted into dopamine by the enzyme aromatic L-amino acid decarboxylase, using pyridoxal phosphate (PLP).
The native dopamine is stored in vesicles and when an action potential occurs, it is secreted by presynaptic cell . Once in the synapse, dopamine binds to and activates postsynaptic dopamine receptors (D1 - D5) and after it has performed its synaptic duties , it is taken up via reuptake back into the presynaptic cell and re-stored into vesicles.
Below there is dopamine degradation:
The two important enzymes are monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT). Homovanillic acid (HVA) is the final product of the metabolic pathway excreted in the urine.
Dopamine is created from:
- L-Phenylalanine (PHE)
- L-Tyrosine (TYR)
- L-DOPA (DOPA)
These three aminoacids can be found in some types of food :
chicken, turkey,fish,milk,yogurt,bananas,soy products are rich of them, specially Tyrosine.
There are also some herbal extracts containing L-DOPA: the most common source is
Mucuna Pruriens a tropical legume found in Africa, India and Caribbean.Another one is
Vicia Faba a type of bean come from North Africa, Southwest and South Asia.
L-DOPA , the precursor of dopamine, can cross the blood -brain-barrier, whereas dopamine itself cannot.
Thus, eating these food products increases levels of L-DOPA , which enters the central nervous system and as mentioned before it is converted into dopamine by the enzyme decarboxylase.
Conclusion
Dopamine, according to the studies analysed before, is important for optimism and helps to process pain.
Specific diets could help people to improve physical and mental health , thanks to these two effects of dopamine and it may be a non-pharmacological way , a first step for a better life.
