Norepinephrine neurotransmitter

Monoamine Oxidase Inhibitors. MAOIs inactivate the enzyme MAO, which is responsible for the oxidative deamination of a variety of endogenous and exogenous substances. Among the endogenous substances are the neurotransmitters, norepinephrine, dopamine, and serotonin. The prototype MAOI is iproniazid [54-92-2] (25), originally tested as an antitubercular dmg and a close chemical relative of the effective antitubercular, isoniazid [54-85-3] (26). Tubercular patients exhibited mood elevation, although no reHef of their tuberculosis, following chronic administration of iproniazid. In... 

Prazosin, a selective a -adrenoceptor antagonist, exerts its antihypertensive effect by blocking the vasoconstrictor action of adrenergic neurotransmitter, norepinephrine, at a -adrenoceptors in the vasculature (200,227,228). Prazosin lowers blood pressure without producing a marked reflex tachycardia. It causes arteriolar and venular vasodilation, but a significant side effect is fluid retention. Prazosin increases HDL cholesterol, decreases LDL cholesterol, and does not cause glucose intolerance. 

Analogous side-chain oxidations occur in various biosynthetic pathways. The neurotransmitter norepinephrine, for instance, is biosynthesized from dopamine by a benzylic hydroxylation reaction. The process is catalyzed by the copper-containing enzyme dopamine /3-monooxygenase and occurs by a radical mechanism. A copper-oxygen species in the enzyme first abstracts the pro-R benzylic hydrogen to give a radical, and a hydroxyl is then transferred from copper to carbon. 

O Classic views as to the cause of major depressive disorder focus on the monoamine neurotransmitters norepinephrine (NE), serotonin (5-HT), and to a lesser extent, dopamine (DA) in terms of both synaptic concentrations and receptor functioning. 

The exact cause of attention-deficit hyperactivity disorder is unknown, but dysfunction in neurotransmitters norepinephrine and dopamine has been implicated as a key component. 

In the vertebrate CNS monoamines have been associated with a number of physiological functions (reviewed in Kandel et al., 1991). Serotonin has functions associated with mood, pain, sleep, learning, and memory. Dopamine has functions associated with schizophrenia, Parkinson s disease, and cocaine addiction. In vertebrates, dopamine is further metabolized into two additional neurotransmitters, norepinephrine and epinephrine. Norepinephrine increases the excitability of cells in response to sudden sensory input such as fear. Epinephrine has been identified in specific neurons of the brain, but the function of these cells is unknown. In addition, AADC has also been found in a class of neurons that do not have any of the four neurotransmitters discussed above (Jaeger et al., 1983). These neurons may use one of the trace amines, tyramine, tryptamine, or phenylethylamine, as a neurotransmitter. 

Iproniazid and imipramine seemed to work as antidepressants, but how did they achieve their effects It would be another decade before the chemical-imbalance theory was launched. In 1965, Joseph Schildkraut at the National Institute of Mental Health in Washington, DC, published a groundbreaking paper in which he argued that depression was caused by a deficiency of the neurotransmitter norepinephrine in the gaps between neurons in the brain.8 Two years later Alec Coppen, a physician at West Park Hospital in Surrey, published another version of the chemical-imbalance theory. His version differed from Schildkraut s in that it put most of the blame on a different neurotransmitter, emphasizing serotonin rather than norepinephrine as the neurotransmitter that was lacking.9... 

Adrenal medulla. Derived from neural crest tissue, the adrenal medulla forms the inner portion of the adrenal gland. It is the site of production of the catecholamines, epinephrine and norepinephrine, which serve as a circulating counterpart to the sympathetic neurotransmitter, norepinephrine, released directly from sympathetic neurons to the tissues. As such, the adrenal medulla and its hormonal products play an important role in the activity of the sympathetic nervous system. This is fully discussed in Chapter 9, which deals with the autonomic nervous system. 

Angiotensin II causes vasoconstriction by direct stimulation of ATj receptors on the vascular smooth muscle. It also enhances release of the neurotransmitter norepinephrine from the sympathetic nerve fibers present in the blood vessels. The vasopressor effects of Ag II may be inhibited pharmacologically in order to decrease TPR and treat hypertension. An important class of orally active drugs is the ACE inhibitors, including captopril and enalopril, which prevent formation of Ag II. More recently, angiotensin receptor antagonists have been developed that act at the vascular smooth muscle. These drugs, which include losartin and valsartan, are also orally active. 

Beta Blockers. Beta blockers such as propranolol (Inderal) and atenolol (Tenormin) act by blocking the activity of the neurotransmitter norepinephrine. They have been nsed in the treatment of patients with panic disorder in an effort to alleviate the physical (antonomic) symptoms of the panic attack, bnt they proved no better than placebo and have no place in the treatment of panic disorder. 

Dopamine P-monooxvgenase This enzyme (DBM) catalyzes the hydroxylation of dopamine to the neurotransmitter norepinephrine and is found in a number of higher organisms (17). 

The mechanism of antidepressive action of this series of drugs is likely associated with their inhibition of the oxidizing deamination process of the neurotransmitters norepinephrine, epinephrine, dopamine, and serotonin, which participate in the transmission of nerve excitement in the CNS. A major drawback of these drugs is the high toxicity associated with their inhibition of not only MAO, but also a number of other nonspecific enzymes. 

There is a lot of evidence that the major neurotransmitter system affected by benzodiazepines is the one that controls the release of the neurotransmitter norepinephrine (also known as noradrenaline). Studies suggest that people with anxiety illnesses have increased release of norepinephrine and that this continued release causes a depletion of this neurotransmitter and a shutdown of the neurons that are releasing it. This is important because norepinephrine is involved in making an animal or person focused or attentive to what is going on in the environment. When this neurotransmitter is overreleased, it causes anxiety. When no more norepinephrine is available for release, it causes a feeling of exhaustion. 

Iproniazid and other MOAIs act by inhibiting the action of the enzyme monoamine oxidase. This enzyme is found inside and outside of cells and helps break down several molecules, including the monoamine neurotransmitters norepinephrine. 

Receptor plasticity could be invoked as the underlying common trait of multiple receptors. For example, although the multiple adrenergic isoreceptors are similar, they react to the common neurotransmitter norepinephrine (2.4) in a quantitatively different manner. They also show a drug specificity that varies from organ to organ and differs in various species of animals. In subsequent chapters of this book, receptor multiplicity as the rule rather than the exception will become amply evident. It is to be hoped that, in time, the comparison of isoreceptor molecular structures will provide precise criteria for their differentiation. 

All of the major psychedelic drugs have a close chemical resemblance to the neurotransmitters norepinephrine, serotonin, and dopamine. 

The chemical structures of the stress neurotransmitter norepinephrine and the maintenance neurotransmitter acetylcholine. 

Amphetamines are a family of compounds structurally related to the neurotransmitters norepinephrine and dopamine. 

Was this youT answer Caffeine stimulates the release of the stress neurotransmitter norepinephrine, and nicotine both depresses the action of the maintenance neurotransmitter acetylcholine and enhances the release of norepinephrine. 

An example of negative allosteric modulation is the case of the antidepressants, which act as neurotransmitter reuptake blockers for the neurotransmitters norepinephrine and serotonin. This has already been discussed in Chapter 2. When the neurotransmitters norepinephrine and serotonin bind to their own selective receptor sites, they are normally transported back into the presynaptic neuron, as shown in Figure 2-23- Thus the empty reuptake carrier (Fig. 2—20) binds to the neurotransmitter (Fig. 2—21) to begin the transport process (Fig. 2—23). However, when certain antidepressants bind to an allosteric site close to the neurotransmitter transporter (represented as an icon in Figs. 2—22 and 2—24), this causes the neurotransmitter to no longer be able to bind there, thereby blocking synaptic re-... 

FIGURE 5—13. This figure represents the normal state of a monoaminergic neuron. This particular neuron is releasing the neurotransmitter norepinephrine (NE) at the normal rate. All the regulatory elements of the neuron are also normal, including the functioning of the enzyme monoamine oxidase (MAO), which destroys NE, the NE reuptake pump which terminates the action of NE, and the NE receptors which react to the release of NE. 

Obsessive-compulsive disorder may be linked to abnormalities of the neurotransmitters serotonin and dopamine. The neuroanatomical basis of OCD may be related to dysfunction in the basal ganglia. The hallmark of treatment for OCD is use of SSRIs plus the tricyclic antidepressant clomipramine. Panic disorder is characterized by unexpected panic attacks, possibly linked to abnormalities in the neurotransmitters norepinephrine and GABA, in the sensitivity of benzodiazepine receptors, or even in the regulation of respiration. Drag treatments include SSRIs, several of the newer antidepressants, high-potency benzodiazepines, many tricyclic antidepressants, and MAO inhibitors. 

However, the exact problem in CNS amine neurotransmission remains a subject of much debate. One leading theory is that depression may be caused by an increased sensitivity of the presynaptic or postsynaptic receptors for these transmitters. That is, the neurochemistry of the brain has been changed in some way to make the amine receptors more sensitive to their respective amine neurotransmitters (norepinephrine, serotonin, and to a lesser extent, dopamine).21 This theory is based primarily on the finding that antidepressant drugs prolong the activity of amine neurotransmission in the brain, thereby causing a compensatory decrease in the sensitivity of the amine receptors.21,47... 

In addition to the cholinergic deficit, Alzheimer s disease has also been shown to be characterized by marked deficits in the monoamine neurotransmitters norepinephrine and serotonin, as well as in glutamate and some neuropeptide neurotransmitters (Figure 27.6). 

Levodopa (L-dopa) is a natural intermediate in the biosynthesis of catecholamines in the brain and peripheral adrenergic nerve terminals. In the biologic sequence of events it is converted to dopamine, which in turn serves as a substrate of the neurotransmitter norepinephrine. Levodopa is used successfully in the treatment of Parkinson s syndrome, a disease characterized by dopamine deficiency. When levodopa is administered to an individual with this syndrome, the symptoms of Parkinson s disease are ameliorated, presumably because the drug is converted to dopamine and thereby counteracts the deficiency. Individuals treated with levodopa, especially older men, have been observed to experience a sexual rejuvenation. This effect has led to the belief that levodopa stimulates sexual powers. Consequently, studies with younger men complaining of decreased erectile ability have shown that levodopa increases libido and the incidence of penile erections. Overall, however, these effects are short lived and do not reflect continued satisfactory sexual function and potency. Thus, levodopa is not a true aphrodisiac. The increased sexual activity experienced by parkinsonian patients treated with levodopa may reflect improved well-being and partial recovery of normal sexual functions that were impaired by Parkinson s disease. 

The physiological action of antidepressants is not fully understood. However, they are thought to influence the metabolism, reuptake, or selective receptor antagonism of the neurotransmitters serotonin and norepinephrine. The MAOIs cause an increase of the neurotransmitters norepinephrine, serotonin, and dopamine in the brain by inhibiting their breakdown. The SSRIs prevent the reabsorbtion of serotonin, one of the 50-odd neurotransmitters in the brain. 

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