Differential effects of amfonelic acid on the haloperidol- and clozapine-induced increase in extracellular dopac in the nucleus accumbens and the striatum

Oleanolic acid alleviates the extrapyramidal symptoms and cognitive impairment induced by haloperidol through the striatal PKA signaling pathway in mice

Haloperidol, one of the representative typical antipsychotics, is on the market for schizophrenia but shows severe adverse effects such as extrapyramidal symptoms (EPS) or cognitive impairments. Oleanolic acid (OA) is known to be effective for tardive dyskinesia which is induced by long-term treatment with L-DOPA. This study aimed to investigate whether OA could ameliorate EPS or cognitive impairment induced by haloperidol. The balance beam, catalepsy response, rotarod and vacuous chewing movement (VCM) tests were performed to measure EPS and the novel object recognition test was used to estimate haloperidol-induced cognitive impairment. Levels of dopamine and acetylcholine, the phosphorylation levels of c-AMP-dependent protein kinase A (PKA) and its downstream signaling molecules were measured in the striatum. OA significantly attenuated EPS and cognitive impairment induced by haloperidol without affecting its antipsychotic properties. Valbenazine only ameliorated VCM. Also, OA normalised the levels of dopamine and acetylcholine in the striatum which were increased by haloperidol. Furthermore, the increased phosphorylated PKA, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB) levels and c-FOS expression level induced by haloperidol were significantly decreased by OA in the striatum. In addition, cataleptic behaviour of haloperidol was reversed by sub-effective dose of H-89 with OA. These results suggest that OA can alleviate EPS and cognitive impairment induced by antipsychotics without interfering with antipsychotic properties via regulating neurotransmitter levels and the PKA signaling pathway in the striatum. Therefore, OA is a potential candidate for treating EPS and cognitive impairment induced by antipsychotics.

Dopac distribution and regulation in striatal dopaminergic varicosities and extracellular space

DOPAC, the major intermediate metabolite of dopamine, is found in the cytosolic compartment of dopaminergic terminals/varicosities and in the extracellular space. It has been proposed that extracellular DOPAC is derived from newly synthesized dopamine rather than from dopamine in the signaling pool. On the basis of literature data supporting such a concept, we hypothesize a DOPAC synthesis/secretory complex producing extracellular DOPAC and use a computational simulation model of dopaminergic varicosities to estimate the distribution of DOPAC between cytosolic and extracellular compartments, amount of newly synthesized dopamine entering the DOPAC synthesis/secretory complex, and potential regulatory processes in the complex. Results suggest that about two-thirds of DOPAC is in the extracellular space. Approximately one-third of newly synthesized dopamine is immediately processed to DOPAC, which is then secreted into extracellular space. Extracellular DOPAC concentration is approximately 300 times higher than extracellular dopamine, and cytosolic DOPAC is ∼18-fold higher than cytosolic dopamine. We suggest that the high levels of extracellular DOPAC coupled with evidence for its production from newly synthesized dopamine imply the existence of an as yet undiscovered regulatory/signaling role for DOPAC.

Complicated interaction between psychostimulants and morphine in expression of phenotype of behavior in the dopaminergic system of BALB/c mice

It is believed that BALB/c mice appear to be less sensitive to the locomotor effects of abused drugs compared to other strains, and several behaviors induced by abused drugs depend on genetic factors. The present study was designed to investigate the effects of the interaction between psychostimulants and morphine on behavior in BALB/c mice. Morphine and cocaine induced hyperlocomotion and hypolocomotion, respectively, while methamphetamine did not affect locomotor activity and high doses of methamphetamine significantly increased self-injurious behavior. Cocaine or methamphetamine increased the effects of morphine on locomotor behavior. Haloperidol (a dopamine-receptor antagonist) attenuated the hyperlocomotion induced by the combination of cocaine or methamphetamine plus morphine. These results indicate that the synergistic effects of methamphetamine or cocaine and morphine on locomotor activity are mediated through enhancement of the dopaminergic system and that combinations of psychostimulants and morphine enhance the locomotor activity in BALB/c mice. On the other hand, morphine completely attenuated methamphetamine-induced self-injurious behavior. Furthermore, a low dose (0.01 mg/kg) of haloperidol significantly increased the effects of methamphetamine and morphine on the locomotor activity. Hyperlocomotion induced by psychostimulants is mediated by the mesolimbic dopaminergic system, whereas stereotyped behaviors is mediated by the nigrostriatal dopaminergic system. Our findings suggest that balances of the activation of dopaminergic neurons (between mesolimbic and nigrostriatal systems) may play an important role to engender corresponding behavioral outcomes in BALB/c mice.

Oxidative stress in methamphetamine-induced self-injurious behavior in mice

Previous studies have shown that N-methyl-D-aspartate, the formation of free radicals and poly(ADP-ribose) polymerase are related to methamphetamine-induced neurotoxicity. This study was designed to investigate the involvement of oxidative stress in methamphetamine-induced self-injurious behavior in mice. In this study, methamphetamine (20 mg/kg) induced continuous self-injurious behavior in six of seven mice. N-methyl-D-aspartate-receptor antagonists (MK801 and 3-((R)-2-carboxypiperazin-4-yl) propyl-1-phosphonic acid) significantly attenuated this methamphetamine-induced self-injurious behavior. These results suggest that the activation of N-methyl-D-aspartate receptors is involved in methamphetamine-induced self-injurious behavior. Furthermore, we found that the nonselective nitric oxide synthase inhibitor l-N-nitro-L-arginine methyl ester hydrochloride and the neuronal nitric oxide synthase inhibitor 7-nitroindazole, but not the inducible nitric oxide synthase inhibitor aminoguanidine, the free-radical inhibitors fullerene and 3-methyl-1-phenyl-2-pyrazolin-5-one-186, or the poly(ADP-ribose) polymerase inhibitor benzamide, significantly attenuated methamphetamine-induced self-injurious behavior. The present results show that oxidative stress, which is mediated by the activation of neuronal nitric oxide synthase, is associated with methamphetamine-induced self-injurious behavior. These findings may help us to better understand the clinical phenomenon of self-injurious behavior.

Effects of mu-, delta- and kappa-opioid receptor agonists on methamphetamine-induced self-injurious behavior in mice

Opioid receptor agonists can differentially modify the behavioral effects of direct/indirect dopamine receptor agonists, such as methamphetamine, cocaine and apomorphine. However, the effects of opioid receptor agonists on high-dose methamphetamine-induced behavior have not yet been clarified. Therefore, the present study was undertaken to investigate the effects of mu (morphine)-, delta (SNC80)- and kappa (U50,488H)-opioid receptor agonists on methamphetamine-induced self-injurious behavior and locomotor activity in mice. Methamphetamine (20 mg/kg) induced severe self-injurious behavior. In a combination test, some opioid receptor agonists significantly attenuated methamphetamine-induced self-injurious behavior, with potencies in the order morphine>buprenorphine (mu-opioid and kappa-opioid receptor agonist/antagonist) >U50,488H, as maximum effects. These results suggest that the stimulation of mu- and kappa-opioid receptors plays an inhibitory role in high-dose methamphetamine-induced stereotypic self-injurious behavior in mice, without affecting locomotor activity.

Effects of dopamine- and serotonin-related compounds on methamphetamine-induced self-injurious behavior in mice

Methamphetamine induces hyperlocomotion, and high doses of methamphetamine induce self-injurious behavior (SIB) in rodents. It is well known that the monoaminergic system is involved in methamphetamine-induced behavior. However, the effects of dopamine- and serotonin (5-HT)-related compounds on high-dose methamphetamine-induced behavior have not been sufficiently clarified. Therefore, the present study was designed to investigate the effects of dopamine receptor antagonists and indirect 5-HT receptor agonists on high-dose methamphetamine-induced behavior in mice. Methamphetamine (20 mg/kg) initially increased locomotor activity. As the dosage increased, continuous SIB accompanied by a reduction in locomotor activity was observed. The hyperlocomotion and SIB induced by 20 mg/kg of methamphetamine was abolished by high doses of SCH23390 and haloperidol, indicating that the hyperlocomotion and SIB induced by high doses of methamphetamine are mediated by the activation of D1- and D2-receptors. Furthermore, haloperidol (0.1 mg/kg) potently increased locomotor activity in combination with 20 mg/kg methamphetamine. These results suggest that excess dopaminergic activation, especially activation of dopamine D2-receptors, may be involved in the decrease in locomotor activity induced by a high dose of methamphetamine. On the other hand, indirect 5-HT receptor agonists attenuated methamphetamine-induced SIB, suggesting that the stimulation of 5-HT receptors plays an important role in high-dose methamphetamine-induced SIB in mice.

Effects of dopamine agonists on appetitive and consummatory male sexual behavior in Japanese quail

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with exogenous testosterone. Appetitive male sexual behavior was assessed by measuring a learned social proximity response and consummatory behavior was assessed by measuring copulatory behavior per se. The nonselective dopamine receptor agonist, apomorphine, inhibited in a dose-dependent manner both components of male sexual behavior. Two indirect dopamine agonists were also tested. Nomifensine, a dopamine re-uptake inhibitor, decreased appetitive sexual behavior but increased the frequency of mount attempts, a measure of consummatory sexual behavior. Amfonelic acid, a compound that enhances dopaminergic tone by a complex mechanism, increased aspects of both appetitive and consummatory behaviors. These data suggest that, in quail, as in rodents, increases in dopaminergic tone facilitate both appetitive and consummatory aspects of male sexual behavior. Apomorphine may be inhibitory in quail because it acts primarily on D2-like receptors, unlike in rats, where it stimulates sexual behavior and acts primarily on D1-like receptors at low doses but interacts with D2-like receptors at higher doses. This is supported by the observation that stereotyped pecking, a behavior stimulated selectively in quail by D2 agonists, was increased by apomorphine but not by the two indirect agonists. The observed partial dissociation between the effects of these dopaminergic agonists on appetitive and consummatory sexual behaviors suggests that these two components of male sexual behavior may be controlled by the action of dopamine through different neuronal systems.

Effects of chronic neuroleptic treatment on dopamine release: insights from studies using 3-methoxytyramine

Antipsychotic medications appear to exert their therapeutic effects by blocking D2 receptors. While D2 blockade occurs rapidly, reduction in psychotic symptoms is often delayed. This time discrepancy has been attributed to the relatively slow development of depolarization inactivation (DI) of dopaminergic neurons. The reduced firing rates associated with DI has been hypothesized to reduce dopamine release and thus psychotic symptoms. Studies assessing changes in dopamine release during chronic neuroleptic treatment, using microdialysis and voltammetry, have been inconsistent. This may be due to methodological differences between studies, the invasive nature of these procedures, or other confounds. To investigate the effects of DI on dopamine release, 3-MT accumulation, an index of dopamine release that does not involve disruption of brain tissue, was measured during acute and chronic neuroleptic treatment. These results are compared with those using other techniques. 3-MT levels remained elevated after chronic treatment, suggesting that DI does not markedly reduce release. Regulation of dopamine release during DI was examined using two techniques known to block dopamine neuronal impulse flow. 3-MT levels were markedly reduced by both, implying that DI does not alter the portion of dopamine release mediated by neuronal impulse flow. Overall, studies to date suggest that the delayed therapeutic effects of neuroleptics are not due to reductions in impulse dependent dopamine release. Recent studies using a neurodevelopmental animal model of schizophrenia have pointed to altered pre- and post-synaptic indices of dopamine neurotransmission. The results suggest that neuroleptics may exert their therapeutic effects, in part, by limiting the fluctuations in dopamine release, and raise new issues for future research.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Effects of various dopamine uptake inhibitors on striatal extracellular dopamine levels and behaviours in rats

In vivo central effects of some dopamine uptake inhibitors were evaluated in both brain microdialysis and behavioural studies in rats, and compared with their in vitro affinities to dopamine uptake sites. IC50 values of GBR12909 (1-[2- bis(4-fluorophenyl)methoxy]ethyl]-4-(3- phenylpropyl)piperazine), diclofensine, mazindol, amfonelic acid and nomifensine for inhibiting 1 nM [3H]GBR12935 (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine) binding to rat striatal membrane were 7.0, 36, 81, 187 and 290 nM, respectively. In the brain microdialysis study, dopamine levels in the striatal dialysates were increased to 16.3- (GBR12909), 14.1- (nomifensine), 4.8- (diclofensine) and 1.9-fold (amfonelic acid) the respective basal levels 40-60 min after i.p. administration (0.1 mmol/kg) and thereafter decreased slowly but remained at the elevated levels for a further 3 h, while mazindol gradually increased dopamine levels though less pronouncedly than others (1.7-fold 200 min after administration). Remarkable and comparable stereotyped behaviours (licking and forepaw treading) were continuously observed at least for 3 h after administration of GBR12909, nomifensine and amfonelic acid, while stereotypies induced by diclofensine and mazindol were moderate and marginal, respectively. In vivo potencies of dopamine uptake inhibitors to increase the extracellular dopamine levels in the striatum tended to correlate with their in vitro affinities to dopamine uptake sites except in the case of nomifensine, and correlated significantly with their potencies to induce stereotyped behaviours except in the case of amfonelic acid. Based on these findings, pharmacological characteristics of these dopamine uptake inhibitors are discussed.

A vitamin as neuromodulator: ascorbate release into the extracellular fluid of the brain regulates dopaminergic and glutamatergic transmission

Ascorbate is an antioxidant vitamin that the brain accumulates from the blood supply and maintains at a relatively high concentration under widely varying conditions. Although neurons are known to use this vitamin in many different chemical and enzymatic reactions, only recently has sufficient evidence emerged to suggest a role for ascorbate in interneuronal communication. Ascorbate is released from glutamatergic neurons as part of the glutamate reuptake process, in which the high-affinity glutamate transporter exchanges ascorbate for glutamate. This heteroexchange process, which also may occur in glial cells, ensures a relatively high level of extracellular ascorbate in many forebrain regions. Ascorbate release is regulated, at least in part, by dopaminergic mechanisms, which appear to involve both the D1 and D2 family of dopamine receptors. Thus, amphetamine, GBR-12909, apomorphine, and the combined administration of D1 and D2 agonists all facilitate ascorbate release from glutamatergic terminals in the neostriatum, and this effect is blocked by dopamine receptor antagonists. Even though the neostriatum itself contains a high concentration of dopamine receptors, the critical site for dopamine-mediated ascorbate release in the neostriatum is the substantia nigra. Intranigral dopamine regulates the activity of nigrothalamic efferents, which in turn regulate thalamocortical fibers and eventually the glutamatergic corticoneostriatal pathway. In addition, neostriatonigral fibers project to nigrothalamic efferents, completing a complex multisynaptic loop that plays a major role in neostriatal ascorbate release. Although extracellular ascorbate appears to modulate the synaptic action of dopamine, the mechanisms underlying this effect are unclear. Evidence from receptor binding studies suggests that ascorbate alters dopamine receptors either as an allosteric inhibitor or as an inducer of iron-dependent lipid peroxidation. The applicability of these studies to dopamine receptor function, however, remains to be established in view of reports that ascorbate can protect against lipid peroxidation in vivo. Nevertheless, ample behavioral evidence supports an antidopaminergic action of ascorbate. Systemic, intraventricular, or intraneostriatal ascorbate administration, for example, attenuates the behavioral effects of amphetamine and potentiates the behavioral response to haloperidol. Some of these behavioral effects, however, may be dose-dependent in that treatment with relatively low doses of ascorbate has been reported to enhance dopamine-mediated behaviors. Ascorbate also appears to modulate glutamatergic transmission in the neostriatum. In fact, by facilitating glutamate release, ascorbate may indirectly oppose the action of dopamine, though the nature of the neostriatal dopaminergic-glutamatergic interaction is far from settled. Ascorbate also may alter the redox state of the NMDA glutamate receptor thus block NMDA-gated channel function.(ABSTRACT TRUNCATED AT 400 WORDS)

Blockade of striatal 5-hydroxytryptamine2 receptors reduces the increase in extracellular concentrations of dopamine produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine

5-Hydroxytryptamine2 (5-HT2) receptor antagonists have been shown to interfere with the stimulation of striatal dopamine synthesis and release produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA). To localize the receptors responsible for the attenuation of MDMA-induced release, 5-HT2 receptor antagonists were infused via the microdialysis probe directly into the brains of awake, freely moving rats before the systemic administration of MDMA. Intrastriatal infusions of the selective 5-HT2 antagonist MDL 100,907 produced a concentration-dependent inhibition of MDMA-induced dopamine release. Similar results were observed with intrastriatal infusions of the 5-HT2 antagonist amperozide. In contrast, infusion of MDL 100,907 into the mid-brain region near the dopaminergic cell bodies was without effect on the MDMA-induced elevation of extracellular dopamine in the ipsilateral striatum. Neither antagonist attenuated basal transmitter efflux nor the MDMA-stimulated release of [3H]dopamine from striatal slices in vitro indicating that the in vivo effect of the antagonists was not due to inhibition of the dopamine uptake carrier. Intrastriatal infusion of tetrodotoxin reduced both basal and MDMA-stimulated dopamine efflux and eliminated the effect of intrastriatal MDL 100,907. The results indicate that 5-HT2 receptors located in the striatum augment the release of dopamine produced by high doses of MDMA. Furthermore, these 5-HT2 receptors appear to be located on nondopaminergic elements of the striatum.