Methamphetamine reward in mice as assessed by conditioned place preference test with Supermex sensors: effect of subchronic clorgyline pretreatment

Monoamine Oxidase Inhibition by Plant-Derived β-Carbolines; Implications for the Psychopharmacology of Tobacco and Ayahuasca

The monoamine oxidases (MAOs) are flavin-containing amine oxidoreductases responsible for metabolism of many biogenic amine molecules in the brain and peripheral tissues. Whereas serotonin is the preferred substrate of MAO-A, phenylethylamine is metabolized by MAO-B, and dopamine and tyramine are nearly ambivalent with respect to the two isozymes. β-Carboline alkaloids such as harmine, harman(e), and norharman(e) are MAO inhibitors present in many plant materials, including foodstuffs, medicinal plants, and intoxicants, notably in tobacco (Nicotiana spp.) and in Banisteriopsis caapi, a vine used in the Amazonian ayahuasca brew. The β-carbolines present in B. caapi may have effects on neurogenesis and intrinsic antidepressant properties, in addition to potentiating the bioavailability of the hallucinogen N,N-dimethyltryptamine (DMT), which is often present in admixture plants of ayahuasca such as Psychotria viridis. Tobacco also contains physiologically relevant concentrations of β-carbolines, which potentially contribute to its psychopharmacology. However, in both cases, the threshold of MAO inhibition sufficient to interact with biogenic amine neurotransmission remains to be established. An important class of antidepressant medications provoke a complete and irreversible inhibition of MAO-A/B, and such complete inhibition is almost unattainable with reversible and competitive inhibitors such as β-carbolines. However, the preclinical and clinical observations with synthetic MAO inhibitors present a background for obtaining a better understanding of the polypharmacologies of tobacco and ayahuasca. Furthermore, MAO inhibitors of diverse structures are present in a wide variety of medicinal plants, but their pharmacological relevance in many instances remains to be established.

Metoprine, a histamine N-methyltransferase inhibitor, attenuates methamphetamine-induced hyperlocomotion via activation of histaminergic neurotransmission in mice

Metoprine increases the content of histamine in brain by inhibiting histamine N-methyltransferase (HMT), a centrally acting histamine degrading enzyme. We present data demonstrating that pretreatment with metoprine attenuates the hyperlocomotive effects of METH in mice using a multi-configuration behavior apparatus designed to monitor four behavioral outcomes [horizontal locomotion, appetitive behavior (food access), and food and water intake]. Metoprine pretreatment itself induced hyperlocomotion in mice challenged with saline during the large part of light phase. The trend was also observed during the following dark phase. This is the first report that metoprine has a long-lasting locomotor stimulating property. Similarly, in a tail suspension test, a single injection of metoprine significantly reduced total time of immobility in mice, consistent with the idea that metoprine possesses motor stimulating properties. Metoprine pretreatment did not affect other aspects of behavior. Metoprine did not affect the appetitive and drinking behavior while exerted an effect on stereotypy. No stereotyped behavior was observed in mice pretreated with vehicle followed by METH, while stereotyped sniffing was observed in mice pretreated with metoprine followed by METH. The metoprine pretreatment attenuated METH-induced hyperlocomotion during the first 2 h of light phase, suggesting that metoprine-induced locomotor stimulating property might be different from that of METH. The hypothalamic content of histamine (but not its brain metabolite) was increased after metoprine or METH administration. Both METH and metoprine reduced dopamine and histamine turnover in the striatum and the nucleus accumbens and the hypothalamus, respectively, and there is a significant metoprine pretreatment x METH challenge interaction in the histamine turnover. It is likely that metoprine may attenuate METH-induced hyperlocomotion via activation of histaminergic neurotransmission. Metoprine also might induce a long-lasting locomotor stimulating effect via a putative mechanism different from that whereby METH induces the locomotor stimulating effect.

Inhibitory effects of Shati/Nat8l overexpression in the medial prefrontal cortex on methamphetamine-induced conditioned place preference in mice

Shati/Nat8l is a novel N-acetyltransferase identified in the brain of mice treated with methamphetamine (METH). Shati/Nat8l mRNA is expressed in various brain areas, including the prefrontal cortex (PFC), where the expression level is higher than that in other brain regions. Shati/Nat8l overexpression in the nucleus accumbens (NAc) attenuates the pharmacological response to METH via mGluR3. Meanwhile, dopamine (DA) and glutamate dysregulations have been reported in the medial prefrontal cortex (mPFC) and NAc after METH self-administration and during reinstatement. However, the mechanism, the reward system, and function of Shati/Nat8l in the mPFC is unclear. Here, we injected an adeno-associated virus (AAV) vector containing Shati/Nat8l into the mPFC of mice, to overexpress Shati/Nat8l in the mPFC (mPFC-Shati/Nat8l). Interestingly, the METH-induced conditioned place preference (CPP) was attenuated in the mPFC-Shati/Nat8l mice, but locomotor activity was not. Additionally, immunohistochemical results from mice that were injected with AAV-GFP showed fluorescence in the mPFC and other brain regions, mainly the NAc, indicating an mPFC-NAc top-down connection. Finally, in vivo microdialysis experiments revealed that Shati/Nat8l overexpression in the mPFC reduced extracellular DA levels and suppressed the METH-induced DA increase in the NAc. Moreover, decreased extracellular glutamate levels were observed in the NAc. These results indicate that Shati/Nat8l overexpression in the mPFC attenuates METH-induced CPP by decreasing extracellular DA in the NAc. In contrast, Shati/Nat8l-mPFC overexpression did not alter METH-induced hyperlocomotion. This study demonstrates that Shati/Nat8l in the mPFC attenuates METH reward-seeking behaviour but not the psychomotor activity of METH.

Brain Histamine N-Methyltransferase As a Possible Target of Treatment for Methamphetamine Overdose

Stereotypical behaviors induced by methamphetamine (METH) overdose are one of the overt symptoms of METH abuse, which can be easily assessed in animal models. Currently, there is no successful treatment for METH overdose. There is increasing evidence that elevated levels of brain histamine can attenuate METH-induced behavioral abnormalities, which might therefore constitute a novel therapeutic treatment for METH abuse and METH overdose. In mammals, histamine N-methyltransferase (HMT) is the sole enzyme responsible for degrading histamine in the brain. Metoprine, one of the most potent HMT inhibitors, can cross the blood-brain barrier and increase brain histamine levels by inhibiting HMT. Consequently, this compound can be a candidate for a prototype of drugs for the treatment of METH overdose.

Critical role of cholinergic transmission from the laterodorsal tegmental nucleus to the ventral tegmental area in cocaine-induced place preference

Conditioned place preference (CPP) is widely used to investigate the rewarding properties of cocaine. Various brain regions and neurotransmitters are involved in developing cocaine CPP. However, the contribution of cholinergic transmission in the ventral tegmental area (VTA) to cocaine CPP remains largely unexplored. Here, we examined the role of cholinergic input arising from the laterodorsal tegmental nucleus (LDT) to the VTA in the acquisition and expression of cocaine CPP in rats. Intra-LDT injection of carbachol, which hyperpolarizes LDT neurons, and of NMDA and AMPA receptor antagonists before cocaine conditioning blocked and attenuated cocaine CPP, respectively, indicating the necessity of LDT activity for acquiring the CPP. Additionally, intra-VTA injection of scopolamine or mecamylamine before cocaine conditioning also attenuated cocaine CPP, demonstrating the contribution of cholinergic transmission via muscarinic and nicotinic acetylcholine receptors in CPP acquisition. Furthermore, intra-VTA injection of scopolamine or mecamylamine immediately before the test attenuated cocaine CPP, indicating that cholinergic signaling is also associated with the expression of CPP. These results suggest that cholinergic transmission from the LDT to the VTA is critically involved in both acquiring and retrieving cocaine-associated memories in cocaine CPP.

Attenuation of Methamphetamine-Induced conditioned place preference in Mice after a Drug-Free period and Facilitation of this effect by exposure to a Running Wheel

The effect of exposure of male mice to a horizontal running wheel (Fast-Trac™) on conditioned place preference (CPP) and hyperlocomotion induced by methamphetamine (METH) was determined. In the first experiment eleven-week-old male ICR mice were divided into three groups and exposed to three different environments (housed individually with (group A) or without a running wheel (group B), or housed in a group of eight mice without a running wheel (group C)) for two weeks except during periods of CPP conditioning and testing procedures. Administration of METH (0.5 mg/kg, i.p.) every other day during three conditioning sessions, with saline conditioning sessions in the other compartment on alternate days (ie, saline/METH conditioning), induced a significant CPP, compared to saline/saline conditioning, in mice of groups A and C, but not B. The increased CPP for METH was significantly attenuated by additional 5-day (drug-free)-exposure to a running wheel in mice of group A (but not group C). In the second experiment, pre-exposure of another set of mice to a running wheel for three days did not affect a subsequent METH (1.0 mg/kg)- or saline-induced horizontal locomotion or rearing, compared with the locomotor activities observed in mice without an experience of a running wheel. These observations suggest that experience of a running wheel may selectively facilitate an attenuation of drug-seeking behavior.

A critical role of sympathetic nerve regulation for the treatment of impaired daily rhythm in hypertensive Dahl rats

There is a deep relationship between impaired circadian rhythm and hypertension. However, the detailed mechanisms between the daily sleep-wake rhythm and cardiovascular disorders have not yet been elucidated. To clarify the mechanism, we examined salt-sensitive Dahl rats that were fed normal chow (n=10), high-salt chow (n=10) and high-salt chow with bisoprolol (n=10). Simultaneous electroencephalogram, electromyogram and locomotor activity were examined to analyze the sleep-wake state. We also examined heart rate, blood pressure and echocardiographic findings to verify the presence of hypertension. Hypertension with impaired ventricular contraction was observed in the rats with high-salt-chow consumption whereas normal-chow rats did not show these disorders. Although rats with the normal diet showed a standard daily rhythm with normal rapid eye movement (REM) sleep duration and locomotor activity, the high-salt-diet group exhibited an impaired daily rhythm with suppressed REM sleep and significant abnormal locomotor activity. Bisoprolol significantly improved the daily sleep-wake rhythm and locomotor activity. We showed that an impaired daily rhythm was closely related to the development of hypertension. Regulation of sympathetic nerve alterations may have a key role in the treatment of hypertension and circadian rhythm disorder.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Lack of effect of anticonvulsant topiramate on methamphetamine-induced stereotypy and rewarding property in mice

The effects of topiramate, a structurally novel anticonvulsant, on the methamphetamine (METH)-induced expression of stereotypy and conditioned place preference (CPP) in male ICR mice were investigated. After a single administration of METH (10 mg/kg, i.p.), mice showed stereotyped behaviors with a plateau level 25 min after drug challenge. Pretreatment with topiramate (1, 10, and 100 mg/kg, i.p.) 30 min prior to METH challenge had no effect on the expression frequency of stereotypy, compared with saline challenge. No differential effects of topiramate on METH-induced stereotyped behavior (that is, head-bobbing, circling, continuous sniffing, nail and/or wood-chip biting, and vigorous and compulsive grooming) were observed. In saline-challenged groups, the doses of topiramate examined did not induce any stereotyped behaviors. Although mice showed a significant CPP for METH (0.5 mg/kg, i.p.), pretreatment with subchronic topiramate did not affect the magnitude of CPP. Locomotor activity was not affected by the doses of topiramate tested. Conditioned rewarding or aversive effects of topiramate were not observed as indexed by the place preference procedure. These results suggested the lack of effect of topiramate on METH-induced stereotypy and rewarding property in mice.