On the interaction of 5-hydroxytryptophan and 5-hydroxytryptamine with dopamine metabolism in the rat striatum

Parkinson's disease: carbidopa, nausea, and dyskinesia

When l-dopa use began in the early 1960s for the treatment of Parkinson's disease, nausea and reversible dyskinesias were experienced as continuing side effects. Carbidopa or benserazide was added to l-dopa in 1975 solely to control nausea. Subsequent to the increasing use of carbidopa has been the recognition of irreversible dyskinesias, which have automatically been attributed to l-dopa. The research into the etiology of these phenomena has identified the causative agent of the irreversible dyskinesias as carbidopa, not l-dopa. The mechanism of action of the carbidopa and benserazide causes irreversible binding and inactivation of vitamin B6 throughout the body. The consequences of this action are enormous, interfering with over 300 enzyme and protein functions. This has the ability to induce previously undocumented profound antihistamine dyskinesias, which have been wrongly attributed to l-dopa and may be perceived as irreversible if proper corrective action is not taken.

The Parkinson's disease death rate: carbidopa and vitamin B6

The only indication for carbidopa and benserazide is the management of L-3,4-dihydroxyphenylalanine (L-dopa)-induced nausea. Both drugs irreversibly bind to and permanently deactivate pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, and PLP-dependent enzymes. PLP is required for the function of over 300 enzymes and proteins. Virtually every major system in the body is impacted directly or indirectly by PLP. The administration of carbidopa and benserazide potentially induces a nutritional catastrophe. During the first 15 years of prescribing L-dopa, a decreasing Parkinson's disease death rate was observed. Then, in 1976, 1 year after US Food and Drug Administration approved the original L-dopa/carbidopa combination drug, the Parkinson's disease death rate started increasing. This trend has continued to the present, for 38 years and counting. The previous literature documents this increasing death rate, but no hypothesis has been offered concerning this trend. Carbidopa is postulated to contribute to the increasing Parkinson's disease death rate and to the classification of Parkinson's as a progressive neurodegenerative disease. It may contribute to L-dopa tachyphylaxis.

5-HTP efficacy and contraindications

L-5-hydroxytryptophan (5-HTP) is the immediate precursor of serotonin. It is readily synthesized into serotonin without biochemical feedback. This nutrient has a large and strong following who advocate exaggerated and inaccurate claims relating to its effectiveness in the treatment of depression and a number of other serotonin-related diseases. These assertions are not supported by the science. Under close examination, 5-HTP may be contraindicated for depression in some of the very patients for whom promoters of 5-HTP advocate its use.

Amino acid management of Parkinson's disease: a case study

An extensive list of side effects and problems are associated with the administration of l-dopa (l-3, 4-dihydroxyphenylalanine) during treatment of Parkinson's disease. These problems can preclude achieving an optimal response with l-dopa treatment.

PURPOSE

To present a case study outlining a novel approach for the treatment of Parkinson's disease that allows for management of problems associated with l-dopa administration and discusses the scientific basis for this treatment.

PATIENTS AND METHODS

The case study was selected from a database containing 254 Parkinson's patients treated in developing and refining this novel approach to its current state. The spectrum of patients comprising this database range from newly diagnosed, with no previous treatment, to those who were diagnosed more than 20 years before and had virtually exhausted all medical treatment options. Parkinson's disease is associated with depletion of tyrosine hydroxylase, dopamine, serotonin, and norepinephrine. Exacerbating this is the fact that administration of l-dopa may deplete l-tyrosine, l-tryptophan, 5-hydroxytryptophan (5-HTP), serotonin, and sulfur amino acids. The properly balanced administration of l-dopa in conjunction with 5-HTP, l-tyrosine, l-cysteine, and cofactors under the guidance of organic cation transporter functional status determination (herein referred to as "OCT assay interpretation") of urinary serotonin and dopamine, is at the heart of this novel treatment protocol.

RESULTS

When 5-HTP and l-dopa are administered in proper balance along with l-tyrosine, l-cysteine, and cofactors under the guidance of OCT assay interpretation, the long list of problems that can interfere with optimum administration of l-dopa becomes controllable and manageable or does not occur at all. Patient treatment then becomes more effective by allowing the implementation of the optimal dosing levels of l-dopa needed for the relief of symptoms without the dosing value barriers imposed by side effects and adverse reactions seen in the past.

Presynaptic control of serotonin on striatal dopamine function

RATIONALE

The influences of the serotonergic system on dopamine (DA) neuron activity have received considerable attention during the last three decades due to the real opportunity to improve disorders related to central DA neuron dysfunctions such as Parkinson's disease, schizophrenia, or drug abuse with serotonergic drugs. Numerous biochemical and behavioral data indicate that serotonin (5-HT) affects dopaminergic terminal function in the striatum.

OBJECTIVE

The authors propose a thorough examination of data showing controversial effects induced by striatal 5-HT on dopaminergic activity.

RESULTS

Inhibitory and excitatory effects of exogenous 5-HT have been reported on DA release and synthesis, involving various striatal 5-HT receptors. 5-HT also promotes an efflux of DA through reversal of the direction of DA transport. By analogy with the mechanism of action described for amphetamine, the consequences of 5-HT entering DA terminals might explain both the excitatory and inhibitory effects of 5-HT on presynaptic DA terminal activity, but the physiological relevance of this mechanism is far from clear. The recent data suggest that the endogenous 5-HT system affects striatal DA release in a state-dependent manner associated with the conditional involvement of various 5-HT receptors such as 5-HT(2A), 5-HT(2C), 5-HT(3), and 5-HT(4) receptors.

CONCLUSION

Methodological and pharmacological issues have prevented a comprehensive overview of the influence of 5-HT on striatal DA activity. The distribution of striatal 5-HT receptors and their restricted influence on DA neuron activity suggest that the endogenous 5-HT system exerts multiple and subtle influences on DA-mediated behaviors.

Serotonergic modulation of striatal D2 dopamine receptor binding in humans measured with positron emission tomography

The modulating effect of serotonergic drugs on the striatal dopamine neurotransmission has remained controversial, and there are no published data on serotonin-dopamine interaction obtained from living human brain. Citalopram is a selective serotonin reuptake inhibitor widely used in the treatment of depression (20-40 mg/day). We measured the effects of acute (20 mg, per os) and chronic (20 mg/day for 14 days) doses of citalopram and placebo intake on [11C]-raclopride binding to striatal D2-receptors in eight healthy volunteers by using positron emission tomography. Although the effect magnitude was not large, the results indicate that chronic citalopram intake slightly decreases the raclopride binding which may reflect increased dopamine release in the striatum. In addition, after 14 days there was a high correlation between the citalopam plasma levels and the decrease in the [11C]-raclopride binding in both the caudate and the putamen, although statistically significant effect in the raclopride binding potential was more pronounced in the putamen. This report suggests functional interaction of brain dopaminergic and serotonergic systems in vivo in man.

Serotonin may play a role in the anorexia induced by amphetamine injections into the lateral hypothalamus

Amphetamine (AMPH) injections into the lateral hypothalamus (LH) are known to inhibit feeding and this effect has been shown to be mediated by the release and the reuptake blockade of catecholamines. LH serotonin (5-HT) has been suggested to be involved in feeding inhibition and a recent study showed that LH amphetamine infusion increases extracellular dopamine (DA), norepinephrine (NE) and 5-HT, which suggests that 5-HT might also be involved in amphetamine anorexia. The present study investigated this possibility. A correlational study was performed between the anorectic effect of LH unilateral microinjections of each monoamine and the anorectic effect of AMPH. Six groups of male rats were used. The rats in each group were submitted to 2 series of 6 experimental sessions. Each session consisted of one microinjection in 24 h food-deprived rats, followed by the measurement of food intake 30 min later. The first series was similar for all groups and explored the AMPH effect (difference between the mean food intake after 3 AMPH injections (40 micrograms/0.5 microliter) and the mean food intake after 3 saline injections (0.5 microliter)). The second series explored the effects of DA (40 micrograms), NE (25 micrograms), EPI (25 micrograms), 5-HT (25 micrograms) or AMPH again, in a similar way as described for AMPH in the first series. Linear regression analysis on the first series AMPH effect and the amine effect of the 2nd series showed a positive correlation between both series of AMPH, AMPH and DA, and AMPH and 5-HT. This last correlation was replicated in a different group. No correlation was found between AMPH and NE or AMPH and epinephrine (EPI).(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic indications for serotonin-potentiating compounds: a hypothesis

The original antidepressants, tricyclics and MAO inhibitors, increase the availability in the brain of both 5-HT and NA. Prompted by clinical findings suggestive of 5-HT disturbances in depression, drugs were developed that increase 5-HT selectively. Data are presented that suggest that broad-spectrum compounds may provide better conditions for antidepressant effects than the 5-HT-selective ones. The hypothesis is proposed that 5-HT potentiators are partial antidepressants, in that they predominantly reduce the anxiety/aggressive component of the depressive syndrome, and deserve to be tested in conditions with heightened anxiety and/or aggression irrespective of the nosological diagnosis. Tentative evidence relates diminished 5-HT metabolism to disordered impulse control. Based on these data, trials of 5-HT potentiators in impulse control disorders unrelated to aggressive drives seem warranted.

Serotonin agonists reduce dopamine synthesis in the striatum only when the impulse flow of nigro-striatal neurons is intact

The effects of 5-methoxy-N, N-dimethyltryptamine (5-MeO-DMT) and m-chlorophenylpiperazine (CPP), two 5-hydroxytryptamine (5-HT, serotonin) agonists, on the accumulation of 3,4-dihydroxyphenylalanine (DOPA] were studied in the striatum of rats treated with gamma-butyrolactone (GBL). Unlike 2 mg/kg i.p. apomorphine, neither 5 mg/kg i.p. 5-MeO-DMT nor 2.5 mg/kg i.p. CPP significantly reduced the GBL-induced increase in DOPA accumulation in the striatum. 5-MeO-DMT and CPP significantly reduced DOPA accumulation in animals that had received the aromatic amino acid decarboxylase inhibitor Ro 4-4602 but not GBL. 5-HT (10 micrograms in 0.5 microliter) injected in the substantia nigra, pars compacta, like GBL, significantly increased Ro 4-4602-induced accumulation of DOPA in the striatum. The data indicate that 5-HT agonists can reduce 3,4-dihydroxyphenylethylamine (DA, dopamine) synthesis in the striatum of rats only when the impulse flow of DA neurons is intact. An indirect effect through mechanisms controlling DA synthesis in the striatum, for instance cholinergic and GABA-ergic neurons, is suggested.

Development of tolerance to the wet-dog shake behaviour but not the increase in seizure threshold induced by L-5-hydroxytryptophan during continued treatment in rats

The time course of different pharmacological effects of L-5-hydroxytryptophan (5-HTP) during continued treatment was studied in rats. 5-HTP was administered three times daily at 100 mg/kg IP in combination with the peripheral decarboxylase inhibitor carbidopa (10 mg/kg) for 14 days. 5-HTP induced a pronounced increase of the threshold for maximal electroconvulsions, decreased body temperature and body weight and induced characteristic "wet-dog" shake behaviour. Whereas the anticonvulsant effect increased during the 14 days of treatment, tolerance developed to the excitatory and, less rapidly, to the hypothermic and anorexigenic effects of 5-HTP. Biochemical determinations showed marked increases in 5-HTP and its metabolites, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid, in both plasma and brain throughout the period of treatment. The mechanisms underlying the different time-courses of the functional effects of 5-HTP during continued treatment are not clear, but effects on catecholaminergic systems as well as regional differences in 5-HT increases in the brain might be involved.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents: II

This survey begins a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1978, but data from many earlier papers are also tabulated.

Circadian variations in behavioral and biological sensitivity to ethanol

In rats, behavioral (startle response and motor activity) and physiological (plasma corticosterone, nonesterified fatty acids, blood ethanol levels, liver alcohol and aldehyde dehydrogenase activity, and body temperature) responses to ethanol were measured over the 24-hr cycle. The response to ethanol for many of these measures showed circadian variations. Both stimulatory and inhibitory effects of ethanol were observed for several dependent variables at the same time, relative to controls. These results suggest that many discrepancies in the ethanol literature may be due to a light cycle X dependent variable interaction.

Pharmacological evidence for the existence of multiple functional pools of brain serotonin: analysis of brain perfusate from conscious rats

The serotonin reuptake inhibitor fluoxetine significantly reduced levels of endogenous 5-hydroxyindoleacetic acid (5-HIAA) in brain perfusate of rats implanted with push-pull cannulas. This occurred in conjunction with its suppressant effect upon fixed-ratio operant behavior. Behavior suppressed with the serotonin agonist lysergic acid diethylamide (LSD) occurred in conjunction with a reduction of 5-HIAA only after 5-HIAA was elevated, shortly before, by 5 mg/kg of the serotonin precursor 5-hydroxytryptophan. Our data demonstrate the likely existence of multiple functional pools of serotonin in brain and support the notion that LSD preferentially affects a newly synthesized pool of this transmitter.

Reserpine-induced rigidity in rats: drug effects on muscle tone from corpus striatum and nucleus accumbens

A study of the pathophysiological mechanisms of reserpine rigidity with the aid of a mechanographic method for the quantification of muscle tone. Apomorphine was used as a test substance to reduce reserpine rigidity by stimulation of dopamine receptors. Some experiments were made with additional drug treatment in an attempt to ascertain the dopaminergic specificity of the test. Apomorphine injected bilaterally to the corpus striatum has been shown to counteract the rigidity [6]. Microinjections of reserpine to corpus striatum induced rigidity with dominance in the hindleg ipsilateral to the side of injection. This rigidity was reduced by subcutaneous apomorphine. The effect of subcutaneous apomorphine on the rigidity was blocked by prior microinjection of trifluoperazine to the corpus striatum. Injections to nucleus accumbens were ineffective in all these respects. It is concluded that reserpine induces rigidity mainly by interference with the dopamine transmission in the corpus striatum.

Possible resolution of a paradox concerning the use of p-chlorophenylalanine and 5-hydroxytryptophan: evidence for a mode of action involving adrenaline in manipulating the surge of luteinizing hormone in rats

Various functions involving the central nervous system can be manipulated by the sequential administration of p-chlorophenylalanine and 5-hydroxytryptophan, compounds which respectively inhibit and restore the synthesis of 5-hydroxytryptamine in the brain. An involvement of 5-hydroxytryptamine in the control of a particular function has been considered established when the effect of p-chlorophenylalanine on that function can be overcome by treatment with 5-hydroxytryptophan. This assumption is not, however, invariably substantiated when the functional consequences of other methods of depleting 5-hydroxytryptamine are considered; studies on the control of the daily surge of luteinizing hormone in oestrogen-treated ovariectomized rats present such a paradox. The surge can be prevented by p-chlorophenylalanine and restored by 5-hydroxytryptophan. Nevertheless, neurotoxin-induced lesions of the 5-hydroxytryptamine projections from the raphe nuclei are compatible with a normal occurrence of the surge. We have therefore examined the effects of p-chlorophenylalanine and 5-hydroxytryptophan on hypothalamic monoamines in oestrogen-treated ovariectomized rats and find that the drugs respectively suppress and elevate the concentration of adrenaline in addition to that of 5-hydroxytryptamine. Phenylethanolamine N-methyltransferase, the enzyme responsible for converting noradrenaline to adrenaline, is shown to be inhibited in vivo by p-chlorophenylalanine and in vitro by its metabolite, p-chlorophenylethylamine. The reciprocal effects of p-chlorophenylalanine and 5-hydroxytryptophan on the concentration of adrenaline are of particular interest since drugs which inhibit adrenaline synthesis can block the luteinizing hormone surge. It is proposed that when the 5-hydroxytryptophan-reversible effects of treatment with p-chlorophenylalanine are not reproduced by other procedures which deplete 5-hydroxytryptamine, the significant action of these compounds may involve adrenaline.

Effect of morphine on circling behaviour in rats with 6-hydroxydopamine striatal lesions and electrolesions of the raphe nucleus

Morphine antagonized d-amphetamine circling in rats which had received unilateral 6-OHDA lesions of the striatum but failed to reduce the circling in rats with both a unilateral 6-OHDA striatal lesion and a raphe (5-HT) lesion. Naloxone precipitated withdrawal of morphine tolerant rats greatly enhanced d-amphetamine circling when the rats had a 6-OHDA lesion but not when both 6-OHDA and raphe lesions were present. It is concluded that 5-HT is necessary for the morphine-induced inhibition of the circling. The effect of morphine tolerance and naloxone precipitated withdrawal on brain 5-HT function was investigated using a putative 5-HT rotation model in which both a dopamine and a 5-HT agonist were administered to rats with an asymmetrical medial raphe lesion. The findings suggest that chronic treatment with morphine increases striatal 5-HT function.

The effect of long-term concurrent administration of chlorpromazine and lithium on the striatal and frontal cortical dopamine metabolism in rats

The effects of lithium and chlorpromazine chronically administered alone and together on the dopamine metabolism in the rat striatum and frontal cortex were investigated by measurement of the levels of dopamine (DA) and its main metabolite, homovanillic acid (HVA). Long-term chlorpromazine administration caused a significant increase in the striatal DA level and a decrease in that of HVA and HVA/DA ratio without any changes in those of the frontal cortex. The prolonged administration of lithium elevated the striatal levels of both HVA and DA, but no change in the frontal cortex was observed. The concurrent administration of chlorpromazine and lithium caused a significant increase in the frontal cortical DA level and a decrease in that of HVA and HVA/DA ratio. The striatal DA and HVA levels increased under the effect of the combined treatment, while the HVA/DA ratio remained unchanged.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents

Drugs may alter body temperature by acting on any component of the thermoregulatory system. These components include heat production, heat conservation and heat loss effectors and their efferent pathways, thermosensors and their afferent pathways and neurons within the central nervous system that coordinate thermoregulatory effector activities. A thermostat is often thought to be involved although thermoregulation can be explained by models that do not incorporate a thermostat. An action on a particular component can be assessed by determining the effect of a drug on body temperature over a range of environmental temperatures and by observation and measurement of associated changes in effector activities. A scheme for such assessment is presented along with examples of its use. The study of drug-induced changes in body temperature has expanded greatly within the past decade. The primary purpose of this review is to provide a readily available source of information on interactions between certain drugs and the thermoregulatory system. Extensive tables are presented of body temperature changes after administration of amino acids, peptides, dopamine and related agents, phenothiazine neuroleptics and also phenothiazines that lack neuroleptic activity, butyrophenones, diphenylbutylpiperidines such as pimozide and miscellaneous neuroleptics. The information tabulated includes the species used, route of administration and dose of drugs, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug. Most of the cited literature was published since 1965.

Evidence against serotonin involvement in the tonic component of electrically induced convulsions and in carbamazepine anticonvulsant activity

Intraventricular injection of 5,7-dihydroxytryptamine, selective destruction of descending serotoninergic neurons by 5,6-dihydroxytryptamine or electrolytic and chemical lesions of the nucleus raphe dorsalis did not affect the electroconvulsive threshold in rats. No effect was observed after the systemic administration of drugs known to increase central serotonin transmission, such as quipazine, m-chlorophenylpiperazine, and moderate doses of d-fenfluramine, whereas p-chlorophenylalanine, an inhibitor of serotonin synthesis, decreased seizure susceptibility. The anticonvulsant activity of carbamazepine was not modified in animals with the same experimental lesions. The results, in relation to the high selectivity of the experimental procedures employed to deplete brain and spinal cord serotonin, do not bear out any involvement of serotonin in the tonic component of electrically induced convulsions or in the action of carbamazepine.