Cocaine action

Transporters for dopamine (DAT), serotonin (SERT) and norepinephrine (NET) are the initial targets for psychomotor stimulants. By interacting with these transporters (Chs 12 and 13), psychomotor stimulants increase extracellular levels of monoamine neurotransmitters. Cocaine is a monoamine uptake inhibitor. The reinforcing effects of cocaine correlate best with its binding potency at the DAT. However, experiments with monoamine transporter-deficient mice suggest that cocaine actions at... 

Nitroindazole, an inhibitor of NOS-1, and L-NAME, a less selective inhibitor of neuronal NOS, have significant antinociceptive effects in humans and animals and 7-nitroindazol reduces the signs of opioid withdrawal and cocaine action in animal models. This inhibitor also reduces cerebral blood flow. Nevertheless, 7-nitroindazole can reduce the size of cerebral infarcts in animal models. In contrast, NOS-3-deficient mice are more susceptible to ischemic cerebral damage. NOS-1 inhibition by 7-nitroindazole also reduces the neurotoxicity of MPTP and MPP+ (see Chapter 28 Pharmacologic Management of Parkinsonism Other Movement Disorders) in several animal models. 

Electron Transfer Mechanism for Cocaine Action P. Kovacic, J.R. Ames, M. Jawdosiuk and M.D. Ryan... 

Z-Ecgonine, CgHigOgN. HjO. This substance was first obtained I Lossen as the final basic hydrolytic product of the action of acids c cocaine, and is obtainable in like manner from several of the alkaloii occurring with cocaine (see above). It crystallises from dry alcohol i monoclinic prisms, m.p. 198° (dec.), 205° (dry), [a]n — 45-4°, is soluble i water, sparingly so in alcohol, insoluble in most organic liquid Eegonine forms Salts with bases and acids the hydrochloride crystallis... 

Tropacocaine (Benzoyl-i/r-tropine). This resembles cocaine in action, but produces local anaesthesia more rapidly and for a shorter time and causes little or no mydriasis. 

Stereoisomerism in either the alkamine nucleus or the acyl residue has a considerable effect on the pharmacological action of the tropeines and cocaines. Differences in activity of tropine and i/i-tropine and their benzoyl derivatives have been mentioned already, and there seems to be a consensus of opinion that the i/i-cocaines (alkyl- or aryl- acyl esters of 0-ecgonine) are less toxic and more potent local anfesthetics than the corresponding cocaines, derived from 1-ecgonine. ... 

Several of these cocaine substitutes contain asymmetric carbon atoms, and King has sho-wn that in the case of benzamine (III) there is no difference in the anaesthetic action of the d- and Z- forms, but that the Z-fonn is twice as toxic as the [Pg.111]

The alkyl ethers of dihydrocupreine (II) are known to exhibit local anassthetic action, which appears to be at a maximum at woamyldihydro-cupreine, but local anassthetic action in this group does not depend on the intact quinuclidine nucleus, since woamyldihydrocupreicine (VII) is more potent than isoamyldihydrocupreine (II), producing local anassthesia in the cornea of the rabbit at 1 in 2,000 compared with cocaine at 1 in 50. ... 

Trachelantamine, according to Syrneva, has a weak atropine-like action and also produces local anaesthesia. Its hydrolytic product, trache-lantamidine, which is structurally identical with tsoretronecanol, yields a p-aminobenzoyl derivative of -which the crystalline hydrochloride, m.p. 230-2°, is said to be as potent a local anaesthetic as cocaine hydrochloride. The chloro- -heliotridane (p. 606) formed by the aetion of thionyl ehloride on trachelantamidine reacts with 6-methoxy-8-aminoquinoline to form 6-methoxy-8-(pseMdoheliotridylamino)-quinoline,... 

A series of papers on the pharmacological action of akuammine has been published by Raymond-Hamet in which it is established inter alia that the alkaloid has a local anaesthetic action almost equal to that of cocaine. 

The simplification of the local anesthetic phaimacophore of cocaine to an aryl substituted ester of ethanolamine has been described previously. Atropine (S2) is a structurally closely related natural product whose main biologic action depends on inhibition of the parasympathetic nervous system. Among its many other actions, the compound exerts useful spasmolytic effects. 

Cocaine and desipramine inhibit the reuptake of monoamine neurotransmitters whereas amphetamine, which is a phenylalkylamine - similar in structure to the catecholamines, see Fig. 4 - competes for uptake and more importantly, evokes efflux of the monoamine neurotransmitters. All of them exert antidepressant effects. Cocaine and amphetamine are addictive whereas tricyclic antidepressants and their modern successors are not. The corollaty of the addictive properties is interference with DAT activity. Blockade of DAT by cocaine or efflux elicited by amphetamine produces a psychostimulant effect despite the different mechanisms even the experienced individual can hardly discern their actions. Because of the risk associated with inhibiting DAT mediated dopamine clearance the antidepressant effects of psychostimulants has not been exploited. 

The various stimulants have no obvious chemical relationships and do not share primary neurochemical effects, despite their similar behavioral effects. Cocaines chemical strucmre does not resemble that of caffeine, nicotine, or amphetamine. Cocaine binds to the dopamine reuptake transporter in the central nervous system, effectively inhibiting dopamine reuptake. It has similar effects on the transporters that mediate norepinephrine and serotonin reuptake. As discussed later in this chapter in the section on neurochemical actions mediating stimulant reward, dopamine is very important in the reward system of the brain the increase of dopamine associated with use of cocaine probably accounts for the high dependence potential of the drug. 

Gawin FH, Ellinwood EH Jr Cocaine and other stimulants actions, abuse, and treatment. N Engl J Med 318 1173-1182, 1988... 

Serious adverse effects of epinephrine potentially occur when it is given in an excessive dose, or too rapidly, for example, as an intravenous bolus or a rapid intravenous infusion. These include ventricular dysrhythmias, angina, myocardial infarction, pulmonary edema, sudden sharp increase in blood pressure, and cerebral hemorrhage. The risk of epinephrine adverse effects is also potentially increased in patients with hypertension or ischemic heart disease, and in those using (3-blockers (due to unopposed epinephrine action on vascular Ui-adrenergic receptors), monoamine oxidase inhibitors, tricyclic antidepressants, or cocaine. Even in these patients, there is no absolute contraindication for the use of epinephrine in the treatment of anaphylaxis [1,5,6]. 

The removal of released DA from the synaptic extracellular space to facilitate its intraneuronal metabolism is achieved by a membrane transporter that controls the synaptic concentration. This transporter has been shown to be a 619 amino-acid protein with 12 hydrophobic membrane spanning domains (see Giros and Caron 1993). Although it has similar amino-acid sequences to that of the NA (and GABA) transporter, there are sufficient differences for it to show some specificity. Thus DA terminals will not concentrate NA and the DA transporter is blocked by a drug such as nomifensine which has less effect on NA uptake. Despite this selectivity some compounds, e.g. amphetamine and 6-OHDA (but not MPTP), can be taken up by both neurons. The role of blocking DA uptake in the central actions of cocaine and amphetamine is considered later (Chapter 23). 

Cocaine, a stimulant, blocks the reuptake of NA (and DA) and so has similar actions to those of the amphetamines which have a number of actions that include the release of NA and DA, and a block of reuptake and metabolism. 

Similarly, self-administration of MDMA in monkeys trained to self-administer amphetamine (Kamien et al. 1986) or in monkeys or baboons trained to self-administer cocaine (Beardsley et al. 1986 Lamb and Griffiths 1987) probably reflects a dopaminergic component to the pharmacology of MDMA. This would be consistent with current theories of dopamine involvement in the mechanism of action of drugs with dependence liability (Wise and Bozarth 1987). 

In view of the apparent pleasurable effects of MDMA, it becomes of considerable interest to understand the mechanism of action of substances with a similar effect. Major efforts have been directed toward the study of agents that have an effect on serotonin pathways, since that is the neurotransmitter system that seems most implicated in the mechanism of action of MDMA. This hypothesis is further reinforced by the observation that MDMA substitutes for fenfluramine (Schechter 1986). and fenfluramine substitutes for MBDB (Oberlender and Nichols, unpublished). The substitution data for (+)-amphetamine and cocaine in (-t-)-MBDB-trained rats are also similar to the data for substitution of these agents in fenfluramine-trained rats (White and Appel 1981). 

Antagonism of several characteristic effects of amphetamine and cocaine by the alpha adrenergic receptor antagonist prazosin is a most recent example of noradrenergic mechanisms in the actions of psychomotor stimulants (Tessel and Barrett 1986). We investigated whether or not prazosin may attenuate the disruptive effects of amphetamine on social and aggressive behavior in mice and squirrel monkeys (Miczek, unpublished observations). Pretreatment with prazosin (0.4 mg/kg) attenuated the disruption of attack... 

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