The effect of nicotine in combination with various dopaminergic drugs on nigrostriatal dopamine in rats

Nicotine Rather Than Non-Nicotine Substances in 3R4F WCSC Increases Behavioral Sensitization and Drug-Taking Behavior in Rats

INTRODUCTION

Nicotine increases reinforcing effects of cigarette smoking by upregulating glutamate and dopamine releases via stimulation of nicotinic acetylcholine receptors (nAChRs) in the dorsal striatum (CPu). The present study was conducted to evaluate whether non-nicotine substances in cigarette smoke potentiate nicotine-induced behaviors by increasing glutamate and dopamine concentrations in the CPu.

AIMS AND METHODS

Changes in the levels of glutamate and dopamine in the CPu were analyzed using a glutamate colorimetric assay and dopamine enzyme-linked immunosorbent assay, respectively, after repeated administration of nicotine or whole cigarette smoke condensate (WCSC) in male Sprague-Dawley rats. Changes in locomotion and drug-taking behavior were analyzed using the measurements of locomotor activity and self-administration under a fixed ratio 1 schedule in response to repeated administration of nicotine or WCSC.

RESULTS

Repeated subcutaneous (s.c.) injections of nicotine (0.25 mg/kg/day) for 7 consecutive days significantly increased the levels of glutamate and dopamine in the CPu. Similar results were obtained from repeated injections of WCSC (0.25 mg/kg nicotine/day, s.c.) extracted from 3R4F Kentucky reference cigarettes. Parallel with the increases in the neurotransmitter levels in the CPu, both nicotine and WCSC increased locomotor activity and self-administration (0.03 mg/kg nicotine/infusion). However, repeated injections of WCSC did not change the nicotine-induced increases in neurotransmitter levels, locomotor activity, and self-administration.

CONCLUSIONS

Nicotine rather than non-nicotine substances in WCSC play a major role in potentiating behavioral sensitization and drug-taking behavior via elevation of glutamate and dopamine concentrations in the CPu of rats.

IMPLICATIONS

WCSC does not augment the nicotine-induced increases in behavioral sensitization, drug-taking behavior, and glutamate and dopamine concentrations, suggesting that non-nicotine substances do not potentiate the nicotine-induced behaviors by increasing the concentrations of the neurotransmitters in the CPu. These findings imply that nicotine, but not non-nicotine substances in WCSC, may be a major contributor that induces tobacco dependence in rats.

Phosphorylation of GluA1-Ser831 by CaMKII Activation in the Caudate and Putamen Is Required for Behavioral Sensitization After Challenge Nicotine in Rats

BACKGROUND

Phosphorylation of the glutamate receptor (GluA1) subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor plays a crucial role in behavioral sensitization after exposure to psychostimulants. The present study determined the potential role of serine 831 (Ser831) phosphorylation in the GluA1 subunit of the caudate and putamen (CPu) in behavioral sensitization after challenge nicotine.

METHODS

Challenge nicotine (0.4 mg/kg) was administered subcutaneously (s.c.) after 7 days of repeated exposure to nicotine (0.4 mg/kg, s.c.) followed by 3 days of withdrawal in rats. Bilateral intra-CPu infusions of drugs were mainly performed to test this hypothesis.

RESULTS

Challenge nicotine increased both phosphorylated (p)Ser831 immunoreactivity (IR) and pCa2+/calmodulin-dependentprotein kinases II (pCaMKII)-IR in the medium spiny neurons (MSNs) of the CPu. These increases were prevented by bilateral intra-CPu infusion of the metabotropic glutamate receptor 5 (mGluR5) antagonist MPEP (0.5 nmol/side) and the N-methyl-D-aspartate (NMDA) receptor antagonist MK801 (2 nmol/side). However, the dopamine D1 receptor (D1R) antagonist SCH23390 (7.5 nmol/side) prevented only pSer831-IR alone. Bilateral intra-CPu infusion of the Tat-GluA1D peptide (25 pmol/side), which interferes with the binding of pCaMKII to GluA1-Ser831, decreased the challenge nicotine-induced increase in locomotor activity.

CONCLUSIONS

These findings suggest that the GluA1-Ser831 phosphorylation in the MSNs of the CPu is required for the challenge nicotine-induced behavioral sensitization in rats. CaMKII activation linked to mGluR5 and NMDA receptors, but not to D1R, is essential for inducing the CaMKII-Ser831 interaction.

Selective inhibition of monoamine oxidase A or B reduces striatal oxidative stress in rats with partial depletion of the nigro-striatal dopaminergic pathway

Partial lesion (50%) of the nigro-striatal dopaminergic pathway induces compensatory increase in dopamine release from the remaining neurons and increased extracellular oxidative stress (OS(-ec)) in the striatum. The present study was designed to explore the role of monoamine oxidase types A and B (MAO-A, MAO-B) in producing this increased oxidative stress. Lesion of the dopaminergic pathways in the CNS was produced in rats by intra-cerebroventricular injection of 6-hydroxydopamine (6-OHDA; 250 μg) and striatal microdialysis was carried out 5 weeks later. Striatal OS(ec) was determined by measurement of oxidized derivatives of the marker molecule N-linoleyl-tyrosine. Striatal tissue MAO-A activity was unchanged by 6-OHDA lesion but MAO-B activity was increased by 16%, together with a 45% increase in glial cell content. The selective MAO-B inhibitor rasagiline (0.05 mg/kg s.c. daily for 14 days) did not affect microdialysate dopamine concentration [DA(ec)] in sham-operated rats, but decreased OS(ec) by 30%. In lesioned rats, rasagiline decreased [DA(ec)] by 42% with a 49% reduction in OS(ec). The decrease in [DA(ec)] was reversed by the dopamine D2 receptor antagonist sulpiride (10 mg/kg s.c.). The selective MAO-A inhibitor clorgyline (0.2 mg/kg s.c. daily for 14 days) increased striatal [DA(ec)] by 72% in sham-operated rats with no change in OS(ec). In lesioned rats clorgyline increased [DA(ec)] by 66% and decreased OS(ec) by 44%. Rasagiline and clorgyline were effective to a similar extent in reduction of tissue levels of 7-ketocholesterol and the ratio GSSG/GSH, indicative of reduced intracellular oxidative stress level. This data implies that gliosis in our 6-OHDA animals together with inhibition of glial cell MAO-B by rasagiline causes an increase in local levels of dopamine at the presynaptic receptors, and a reduction in dopamine release (and in [DA(ec)]) by presynaptic inhibition. Moreover, inhibition of MAO-A or MAO-B reduces the enhanced level of oxidative stress in the lesioned striatum, and while both clorgyline and rasagiline reduced DA oxidative metabolism, rasagiline possesses an additional antioxidant property, not only that resulting from MAO inhibition.

Effects of ningdong granule on DA, DRD2, and HVA in a rat model of Tourette's syndrome

OBJECTIVE

Ningdong granule is a traditional Chinese medicine preparation for the treatment of Tourette's syndrome.

METHODS

Sixty-four rats were randomly assigned to a control group and three experimental groups, respectively. Rat models of Tourette's syndrome were established via intraperitoneal injection of apomorphine (Apo). The rats in the experimental groups were subsequently intragastrically injected with haloperidol at 10 mg/kg (haloperidol group), ningdong granule at 370 mg/kg (NDG group), and normal saline (0.9%) at 10 mL/kg (Apo group), respectively. Rat behaviors were observed and recorded on a daily basis. After 12 w, all rats were sacrificed, and sera and striatal tissues were harvested. Homovanillic acid levels in sera, as well as dopamine and dopamine D2 receptor mRNA expression in the striatum, were measured to determine possible mechanisms of Ningdong granule on the dopamine system in a rat model ofTourette's syndrome.

RESULTS

Following intervention, stereotype actions of the Tourette's syndrome rats were significantly inhibited in the haloperidol and NDG groups, respectively (P < 0.01). Homovanillic levels were significantly greater in the haloperidol and NDG groups, respectively (P < 0.05). In addition, dopamine levels were significantly less in the NDG group (P < 0.01), and DRD2 mRNA expression was significantly reduced in the haloperidol and NDG groups, respectively (P < 0.05).

CONCLUSION

Results demonstrated that Ning-dong granule effectively inhibited stereotype actions and Tourette's syndrome symptoms by promoting dopamine metabolism, reducing dopamine levels in the striatum, increasing homovanillic acid content in sera, and reducing mRNA expression of DRD2 in the striatum.

α3β4 nicotinic acetylcholine receptors in the medial habenula modulate the mesolimbic dopaminergic response to acute nicotine in vivo

Habenulo-interpeduncular nicotinic receptors, particularly those containing α3, β4 and α5 subunits, have recently been implicated in the reinforcing effects of nicotine. Our laboratory has shown that injection of α3β4 nicotinic receptor antagonists into the medial habenula (MHb) decreases self-administration of multiple abused drugs, including nicotine (Glick et al., 2006, 2008; 2011). However, it is unclear whether blockade of MHb nicotinic receptors has a direct effect on mesolimbic dopamine. Here, we performed in vivo microdialysis in female rats. Microdialysis probes were implanted into the nucleus accumbens (NAcc) and α3β4 nicotinic receptor antagonists (18-methoxycoronaridine; 18-MC or α-conotoxin AuIB; AuIB), were injected into the ipsilateral MHb, just prior to systemic nicotine (0.4 mg/kg, s.c.). Dialysate samples were collected before and after drug administration and levels of extracellular dopamine and its metabolites were measured using HPLC. Acute nicotine administration increased levels of extracellular dopamine and its metabolites in the NAcc. Pre-treatment with intra-habenular AuIB or 18-MC prevented nicotine-induced increases in accumbal dopamine. Neither drug had an effect on nicotine-induced increases in dopamine metabolites, suggesting that α3β4 receptors do not play a role in dopamine metabolism. The effect of intra-habenular blockade of α3β4 receptors on NAcc dopamine was selective for acute nicotine: neither AuIB nor 18-MC prevented increases in NAcc dopamine stimulated by acute d-amphetamine or morphine. These results suggest the mesolimbic response to acute nicotine, but not to acute administration of other drugs of abuse, is directly modulated by α3β4 nicotinic receptors in the MHb, and emphasize a critical role for habenular nicotinic receptors in nicotine's reinforcing effects.

Positive allosteric modulation of α4β2 nAChR agonist induced behaviour

Neuronal cholinergic transmission is a prerequisite for proper CNS function. Consequently, disturbance of this system is associated with a number of pathophysiological conditions such as Parkinson's disease, Alzheimer's disease, schizophrenia and ADHD. Consequently, drug discovery efforts have spurred considerable research endeavours into identifying specific compounds for this system. Nicotinic acetylcholine receptors (nAChR) are ligand gated ion channels involved in cholinergic transmission. nAChRs are homo- or heteromeric pentamers with α4β2 receptors being the most abundant heteromer. The stoichiometry of α4β2 receptors can be either (α4)(3)(β2)(2) or (α4)(2)(β2)(3) representing channels with low (LS) or high (HS) sensitivity, respectively, to endogenous ligands. In the present study we applied the partial nAChR α4β2 LS and HS agonist NS3956 and the LS selective positive allosteric modulator NS9283 to investigate the role of α4β2 in Parkinson and pain models. In 6-OHDA lesioned rats, NS3956 increased rotational behaviour when rats were co-treated with nomifensine. This effect was absent in the presence of mecamylamine. In contrast, co-treatment with NS3956 and NS9283 reduced rotational behaviour in the animals. In a rat formalin pain model NS3956 induced an analgesic response that was strongly potentiated by NS9283. Finally in vitro experiments were applied to determine dopamine release from striatal minces. NS3956 induced a concentration dependent release while NS9283 was unable to potentiate agonist induced release. Together these results emphasize involvement of α4β2 nAChR in rotational and analgesic responses and confirm striatal α4β2 receptors to be of the HS form.

Effects of Ningdong granule on the dopamine system of Tourette's syndrome rat models

ETHNOPHARMACOLOGICAL RELEVANCE

Ningdong granula (NDG) is a traditional Chinese medicine (TCM) preparation for the treatment of Tourette's syndrome (TS).

AIM OF THE STUDY

To explore the effects of NDG on stereotyped behavior, homovanillic acid (HVA) in sera, dopamine (DA) and dopamine D2 receptor (DRD2) in striatum in TS rats.

MATERIALS AND METHODS

Sixty-four rats were randomly divided into control group and three experimental groups. TS rat models were induced by intraperitoneal injection (i.p.) of Apomorphine (Apo, 2 mg/kg) in the experimental groups. After Apo i.p., rats were intragastrically injected (i.g.) with NDG at 370 mg/kg (NDG+Apo group), haloperidol (Hal) at 1.0 mg/kg (Hal+Apo group), and normal saline (0.9%) at 10 ml/kg (control group and Apo group), respectively, once a day for 12 weeks. The behaviors of the rats were observed and recorded each day. After 12 weeks, all rats were sacrificed and sera and striatum were collected. The levels of HVA in sera, DA in striatum were examined by ELISA, and the expression of DRD2 mRNA in striatum was measured by RT-PCR.

RESULTS

NDG could increase the HVA content in sera (P<0.05), meanwhile downregulate the expression of DRD2 mRNA in striatum (P<0.05), and inhibit the stereotyped behaviors induced by Apo (P<0.01) in TS rats, the same effects with Hal. NDG could also reduce the DA content in striatum (P<0.01), while Hal could not.

CONCLUSIONS

NDG could effectively inhibit the stereotyped behaviors in TS rats, and the mechanisms may be related to the suppression of DA system by increasing the content of HVA in sera, decrease the content of DA and repressing the expression of DRD2 mRNA in striatum.

Constitutional mechanisms of vulnerability and resilience to nicotine dependence

The core nature of nicotine dependence is evident in wide variations in how individuals become and remain smokers. Individuals with pre-existing behavioral traits are more likely to develop nicotine dependence and experience difficulty when attempting to quit. Many molecular factors likely contribute to individual variations in the development of nicotine dependence and behavioral traits in complex manners. However, the identification of such molecules has been hampered by the phenotypic complexity of nicotine dependence and the complex ways molecules affect elements of nicotine dependence. We hypothesize that nicotine dependence is, in part, a result of interactions between nicotine and pre-existing behavioral traits. This perspective suggests that the identification of the molecular bases of such pre-existing behavioral traits will contribute to the development of effective methods for reducing smoking dependence and for helping smokers to quit.

Nicotine and amphetamine acutely cross-potentiate their behavioral and neurochemical responses in female Holtzman rats

RATIONALE

Psychostimulants are often used in close temporal proximity to nicotine and have been reported to enhance acutely nicotine's desirability in humans.

OBJECTIVE

To investigate the acute associations between amphetamine and nicotine, we examined the potentiative interactions between clinically relevant, low doses of these drugs on locomotor activity, and dopamine overflow in the rat.

MATERIALS AND METHODS

Locomotor activity was measured by telemetry in the home cage environment, and dopamine overflow was evaluated in striatal slice preparations from female Holtzman rats.

RESULTS

When administered simultaneously, nicotine and amphetamine produced a predominantly additive effect on locomotor behavior. However amphetamine, when given 2-4 h before nicotine, strongly potentiated nicotine-induced locomotor activity. Correspondingly, nicotine given 1-4 h before amphetamine robustly enhanced amphetamine-stimulated locomotor activity even when the effects of the nicotine pretreatment dissipated. Acute nicotine pretreatment similarly potentiated the effects of dopamine transporter ligands, cocaine, nomifensine, and methamphetamine but not a direct dopamine receptor agonist. Consistent with the behavioral studies, in vivo nicotine pretreatment exaggerated amphetamine-induced dopamine efflux from rat striatal slices. Likewise, in vivo pretreatment of rats with amphetamine potentiated nicotine-induced dopamine efflux from striatal slices. Direct pretreatment of striatal tissue by nicotine also potentiated subsequent amphetamine-stimulated dopamine overflow, further suggesting that the nicotine-amphetamine interaction occurs at the level of the dopamine terminal.

CONCLUSION

Overall, the present data demonstrate that acute interactions of nicotine and other psychomotor stimulants produce potentiative effects and that these transient interactions may play a role in the frequent co-use and abuse of nicotine and other stimulants.

Nicotine increases dopamine transporter function in rat striatum through a trafficking-independent mechanism

In previous in vivo voltammetry studies, acute nicotine administration increased striatal dopamine clearance. The current study aimed to determine whether nicotine also increases [(3)H]dopamine uptake across the time course of the previous voltammetry studies and whether dopamine transporter trafficking to the cell surface mediates the nicotine-induced augmentation of dopamine clearance in striatum. Rats were administered nicotine (0.32 mg/kg, s.c.); striatal synaptosomes were obtained 5, 10, 40 or 60 min later. Nicotine increased (25%) the V(max) of [(3)H]dopamine uptake at 10 and 40 min. To determine whether the increase in V(max) was due to an increase in dopamine transporter density, [(3)H]GBR 12935 (1-(2-[bis(4-fluorophenyl)methoxy]ethyl)-4-(3-phenylpropyl)piperazine dihydrochloride) binding was performed using rat striatal membranes; no differences were found between nicotine and saline-control groups at 5, 10 or 40 min post-injection, indicating that nicotine did not increase striatal dopamine transporter density; however, [(3)H]GBR 12935 binding assays determine both cell surface and intracellular dopamine transporter. Changes in cellular dopamine transporter localization in striatum were determined using biotinylation and subfractionation approaches; no differences between nicotine and saline-control groups were observed at 10 and 40 min post-injection. These results suggest that the nicotine-induced increase in dopamine uptake and clearance in striatum may occur via a trafficking-independent mechanism.

Differential nicotinic regulation of the nigrostriatal and mesolimbic dopaminergic pathways: implications for drug development

Neuronal nicotinic acetylcholine receptors (nAChRs) modulate dopaminergic function. Discovery of their multiplicity has lead to the search for subtype-selective nAChR agonists that might be therapeutically beneficial in diseases linked to brain dopaminergic pathways. The regulation and responses of the nigrostriatal and mesolimbic dopaminergic pathways are often similar, but some differences do exist. The cerebral distribution and characteristics of various nAChR subtypes differ between nigrostriatal and mesolimbic dopaminergic pathways. Comparison of nicotine and epibatidine, two nAChR agonists whose relative affinities for various nAChR subtypes differ, revealed differences in the nAChR-mediated regulation of dopaminergic activation between these dopamine systems. Nicotine preferentially stimulates the mesolimbic pathway, whereas epibatidine's stimulatory effect falls on the nigrostriatal pathway. Thus, it may be possible to stimulate the nigrostriatal pathway with selective nAChR agonists that do not significantly affect the mesolimbic pathway, and thus lack addictive properties. Furthermore, dopamine uptake inhibition revealed a novel inhibitory effect of epibatidine on accumbal dopamine release, which could form a basis for novel antipsychotics that could alleviate the elevated accumbal dopaminergic tone found in schizophrenia during the active psychotic state. Different regulation of nigrostriatal and mesolimbic dopaminergic pathways by nAChRs could be an important basis for developing novel drugs for treatment of Parkinson's disease and schizophrenia.

Monoamine oxidase A knockout mice exhibit impaired nicotine preference but normal responses to novel stimuli

Nicotine is thought to act on brain monoamine systems that normally mediate diverse motivational behaviors. How monoamine-related genes contribute to behavioral traits (e.g. responses to novel stimuli) comorbid with the susceptibility to nicotine addiction is still poorly understood. We examined the impact of constitutive monoamine oxidase A (MAOA) deficiency in mice on nicotine reward and responses to novel stimuli. Age-matched, male Maoa-knockout (KO) mice and wild-type (WT) littermates were tested for nicotine-induced conditioned place preference (CPP); voluntary oral nicotine preference/intake; spontaneous locomotor activity in a novel, inescapable open field; and novelty place preference. Nicotine preference in WT mice was reduced in Maoa-KO mice in the CPP and oral preference/intake tests. Control experiments showed that these phenotypes were not due to abnormalities in nicotine metabolism, fluid intake or response to taste. In contrast, Maoa-KO mice were normal in their behavioral response to a novel, inescapable open field and in their preference for a novel place. The observed phenotypes suggest that a constitutive deficiency of MAOA reduces the rewarding effects of nicotine without altering behavioral responses to novel stimuli in mice. Constitutive MAOA activity levels are likely to contribute to the vulnerability or resiliency to nicotine addiction by altering the rewarding effects of nicotine.