Human Brain & Mind
  • Neurotransmitters Catecholamines

    Norepinephrine and dopamine are utilized in brain circuits which regulate all body functions, mood, emotions, and cognitive abilities. These transmitters are made from amino acids, supplied as proteins in foods or as free amino acids in formulas such as Alpha ENF. Phenylalanine and tyrosine are first converted to l-dopa, then dopamine, which can be converted to norepinephrine and epinephrine.

    The oldest, most automatic and the most reliable systems in the brain control all body functions and keep us alive. The term autonomic refers to the autonomous function of these old systems that do not require consciousness or learning and do not permit the intervention of the personal self. The dialectic of approach avoidance is expressed in the two divisions of the autonomic nervous system (ANS); the parasympathetic (PNS) network corresponds to eating, rest and pleasure; the sympathetic system (SNS) corresponds to action, fight and flight. Both systems are continuously active, but one system tends to dominate depending on what is going on outside. THE ANS is an expression of norepinephrine acting within the nervous system and as a hormone distributed in the blood to all tissues, The ANS creates feelings in consciousness as a way of controlling our activities. Emotions are strong programs that integrate the ANS with information arising from cognitive processors. You may be quietly enjoying dinner with friends until someone insults you. Within milliseconds, your SNS activates flight and fight responses and you become angry. Your upset may last for hours or days and you may never forgive the person who insulted you.

    Some of the effects of SNS activation are: your pupils dilate, you sweat, blood flow to muscles increases, your breathing and heart rate increases, your blood pressure increases, digestive activity slows or stops. You become angry or fearful, sometimes both. Drugs that stimulate the SNS are referred to as sympathomimetic agents.

    The parasympathetic system uses acetylcholine (not a catecholamine) as the neurotransmitter and is found everywhere in the body. For example, acetylcholine sends signals to muscle cells to contract. In the brain, acetylcholine has arousal functions in the right amounts but tends to cause depression in overdose. Alzheimer's disease is associated with declining levels of acetylcholine and degeneration of neurons which use this neurotransmitter. PNS activity causes pupil constriction, increased salivary gland secretions and digestive activity; heart and breathing rate decreases as does blood pressure. You tend to feel relaxed. Drugs that stimulate the PNS are referred to as parasympathomimetic agents. The two systems collaborate on sexual activity, for example. Male erections are a SNS responsibility and ejaculation is a PNS responsibility.


    Norepinephrine is widely distributed in the brain and is the neurotransmitter in neurons that determines consciousness, sleep rhythms, attention, and vigilance. NE cell clusters within the brain's arousal complex (locus coeruleus) organize sleep patterns. In rats, painful, uncontrollable electrical shocks induce “depression” and are associated with early depletion of NE in the locus coeruleus. Underproduction of NE may lead to depression. Some antidepressants, especially imipramine, selectively alter the synthesis of NE, but paradoxical experimental results tell us that therapeutic changes are not achieved by just increasing one transmitter but rather influencing the net arousal balance in the mesh of arousal circuits.

    Imipramine, the grandmother of the family of tricyclic antidepressants, has at least a triple action on NE, acetylcholine, and histamine circuits. Imipramine's cousin, amitriptyline, works more on the serotonin neurons and also has marked anti-acetylcholine activity. Both drugs are also good antihistamines.

    The substrates of NE, phenylalanine, tyrosine, and l-dopa are not powerful antidepressants, but they may have a contributing role in a well thought-out neurochemical recipe. Stimulants, including caffeine, cocaine and amphetamines act in a NE-increasing mode with temporary increase in psychic energy and a sense of well-being. They also influence the dopamine system. Repeated use of these drugs leaves the over stimulated brain circuits in a state of confusion, with disturbances of psychic energy, thinking, feeling, and behaving. Withdrawal from these drugs is associated with other marked disturbances.

    Amphetamines act on NE receptors and will induce agitated, paranoid, and violent states in susceptible people. As street drugs, amphetamines have major antisocial consequences. Antidepressants of the MAO-inhibitor group (parnate, nardil) increase norepinephrine levels but not serotonin. Withdrawal from these drugs is associated with other marked disturbances. Bromocritptine, a drug imitating the action of dopamine, is helpful in reducing cocaine withdrawal symptoms. Antidepressants of the MAO-inhibitor group (parnate, nardil) increase norepinephrine levels but not serotonin.

  • You are viewing the Brain Mind Center at Alpha Online. Understanding the human brain is essential to become a well-informed, modern citizen.
    Stephen Gislason MD is the author of the Human Brain. 2018 edition. 238 Pages.

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