Saturday, 14 December 2013

The Effects of Hormone Serotonin (1)

Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter derived from tryptophan,  primarily found in the gastrointestinal (GI) tract, platelets, and in the central nervous system (CNS). In Gut, serotonin regulates intestinal movements, in CNS, it regulates mood, appetite, sleep, memory and learning, etc.
1. Brain serotonin, carbohydrate-craving, obesity and depression
Serotonin-releasing brain neurons are unique in that the amount of neurotransmitter they release is normally controlled by food intake, according to the study by Massachusetts Institute of Technology, Cambridge serotonin release is also involved in such functions as sleep onset, pain sensitivity, blood pressure regulation, and control of the mood. Hence many patients learn to overeat carbohydrates (particularly snack foods, like potato chips or pastries, which are rich in carbohydrates and fats) to make themselves feel better. This tendency to use certain foods as though they were drugs is a frequent cause of weight gain, and can also be seen in patients who become fat when exposed to stress, or in women with premenstrual syndrome, or in patients with "winter depression," or in people who are attempting to give up smoking. (Nicotine, like dietary carbohydrates, increases brain serotonin secretion; nicotine withdrawal has the opposite effect.) It also occurs in patients with normal-weight bulimia. Dexfenfluramine constitutes a highly effective treatment for such patients. In addition to producing its general satiety-promoting effect, it specifically reduces their overconsumption of carbohydrate-rich (or carbohydrate-and fat-rich) foods(1).

2. Brain serotonin in excessive carbohydrate snacking craving
Brain neurotransmitter serotonin plays an essential role in a specific hunger for carbohydrate-rich foods  in animals and human beings, researchers found that consumption of a carbohydrate-rich meal increases the synthesis and release of brain serotonin (by enhancing the brain uptake of its precursor, tryptophan). As a consequence of this increased release of serotonin, carbohydrate intake is decreased at the next meal. Consumption of protein does not increase brain serotonin levels or decrease carbohydrate intake. A subgroup of obese individuals who consume carbohydrate-rich snack foods at specific times of day or evening has been identified. Such individuals do not routinely snack on protein-rich foods, and their consumption of calories and nutrients at meals is not excessive. Evidence is presented that carbohydrate snacking seems to be related to a "need" to increase the level of brain serotonin; treatment with a drug, d-1 fenfluramine, that increases serotoninergic neurotransmission significantly decreases carbohydrate snack consumption. Weight loss among the population of carbohydrate cravers might be most successful if treatment includes either a diet or drugs that increase brain serotonin activity when the need to snack on carbohydrate is most likely to occur(2).

3. Changes in mood after carbohydrate consumption 
In the study to identify two groups of obese individuals who consume excessive calories primarily as snack foods, found that using standardized self-report questionnaires, we measured mood before and 2 h after consumption of a high-carbohydrate lunch (104 g CHO). Responses to the meal differed significantly: noncarbohydrate cravers reported feeling considerably less alert, more fatigued and sleepy, while carbohydrate cravers described little or no change in these aspects of mood.(3)

4. Mood and carbohydrate cravings
In the study to investigate a sample of 113 males and 138 female college students of the relationship between mood and carbohydrate cravings, and the possible role of gender in these associations, found that  individuals classifying themselves as "carbohydrate cravers" reported foods rich in carbohydrates, and "protein cravers" reported protein-rich foods as being the ones they most strongly craved. Carbohydrate cravers reported feeling distressed prior to their cravings and satisfied, happy/good and relaxed following carbohydrate consumption. Protein cravers reported feeling anxious or hungry prior to their cravings and happy, normal, bored, and energetic following protein-rich food consumption(4).

5. Effects of protein and carbohydrate meals on mood and performance: interactions with sex and age
In the study to investigate the normal adult subjects (n = 184) consumed a high-protein or high-carbohydrate meal and were tested two hours later their mood and performance, found that females, but not males, reported greater sleepiness after a carbohydrate as opposed to a protein meal. Male subjects, but not females, reported greater calmness after a carbohydrate as opposed to a protein meal. When meals were eaten for breakfast (but not for lunch) individuals 40 yr of age or older felt more tense and less calm after a protein than after a carbohydrate meal. Although older subjects reported subjective discomfort after a morning protein meal, they displayed objective performance impairments after a carbohydrate lunch. Subjects 40 yr of age or older were impaired on a test of sustained selective attention (dichotic shadowing) after consuming a high-carbohydrate lunch(5).

6. Mood, performance, and pain sensitivity: changes induced by food constituents
In the study to examine the behavioral effects of the dietary constituents tryptophan and tyrosine on human mood, sensorimotor performance and pain sensitivity, found that tryptophan and tyrosine are neurotransmitter precursors present in varying amount in protein-containing foods. Tryptophan (50 mg/kg) increased subjective drowsiness and fatigue but unlike many hypnotics did not impair sensorimotor performance. Tryptophan also decreased human pain sensitivity in a manner that was more specific than certain analgesic drugs(6).

7. Effects of dietary neurotransmitter precursors on human behavior
In a double-blind, crossover study the possible effects of tryptophan and tyrosine on human behavior, single oral doses of these substances and matched placebos were administered to 20 men, found that
tryptophan increased subjective fatigue and decreased self-ratings of vigor and alertness, but did not impair performance on any of the tests. Tyrosine produced no effects in our young population compared with placebo, but did decrease reaction time relative to tryptophan. It may be concluded that tryptophan has significant sedative-like properties, but unlike other sedatives may not impair performance(7).

8. Serotonin: influences on male sexual behavior
 Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT(2C) receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT(1A) receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins, according to the study by State University of New York(8).

9. Neuroactive steroid effects on cognitive functions with a focus on the serotonin and GABA systems
In the study to review the neuroactive steroid effects on serotonin and GABA systems, along with the subsequent effects on cognitive functions, showed that Estrogen alone, or in combination with progesterone, affects the brain serotonin system differently in different parts of the brain, which can at least partly explain the opposite effects on mood of those hormones. Many of the progesterone effects in the brain are mediated by its metabolite allopregnanolone. Allopregnanolone, by changing GABA(A) receptor expression or sensitivity, is involved in premenstrual mood changes; and it also induces cognitive deficits, such as spatial-learning impairment(9).

10. Serotonin, aging and cognitive functions
Serotonin and acetylcholine interact to allow normal cognitive functions in the brain. Thus, a partial reduction in both cholinergic and serotonergic functions will cause severe memory impairment in young as well as in aged rats, according to the dtudy by Department of Neurobiology, Weizmann Institute(10).

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