Effects of melatonin on behavioral dopaminergic supersensitivity

Exploring the potential use of melatonin as a modulator of tramadol-induced rewarding effects in rats

Background

Melatonin is responsible for regulating the sleep-wake cycle and circadian rhythms in mammals. Tramadol, a synthetic opioid analgesic, is used to manage moderate to severe pain but has a high potential for abuse and dependence. Studies have shown that melatonin could be a potential modulator to reduce tramadol addiction.

Methods

Male Wistar rats were used to investigate the effect of melatonin on tramadol-induced place preference. The rats were divided into four groups: control, tramadol, tramadol + melatonin (single dose), and tramadol + melatonin (repeated doses). Tramadol was administered intraperitoneally at 40 mg/kg, while melatonin was administered at 50 mg/kg for both the single dose and repeated-dose groups. The study consisted of two phases: habituation and acquisition.

Results

Tramadol administration produced conditioned place preference (CPP) in rats, indicating rewarding effects. However, melatonin administration blocked tramadol-induced CPP. Surprisingly, repeated doses of melatonin were ineffective and did not reduce the expression of CPP compared to that of the single dose administration.

Conclusion

The study suggests that melatonin may be a potential therapeutic option for treating tramadol addiction. The results indicate that melatonin attenuates the expression of tramadol-induced CPP, supporting its uses as an adjunct therapy for managing tramadol addiction. However, further studies are needed to investigate its effectiveness in humans.

Beneficial effects of voluntary wheel running on activity rhythms, metabolic state, and affect in a diurnal model of circadian disruption

Emerging evidence suggests that disruption of circadian rhythmicity contributes to development of comorbid depression, cardiovascular diseases (CVD), and type 2 diabetes mellitus (T2DM). Physical exercise synchronizes the circadian system and has ameliorating effects on the depression- and anxiety-like phenotype induced by circadian disruption in mice and sand rats. We explored the beneficial effects of voluntary wheel running on daily rhythms, and the development of depression, T2DM, and CVD in a diurnal animal model, the fat sand rat (Psammomys obesus). Voluntary exercise strengthened general activity rhythms, improved memory and lowered anxiety- and depressive-like behaviors, enhanced oral glucose tolerance, and decreased plasma insulin levels and liver weight. Animals with access to a running wheel had larger heart weight and heart/body weight ratio, and thicker left ventricular wall. Our results demonstrate that exercising ameliorates pathological-like daily rhythms in activity and blood glucose levels, glucose tolerance and depressive- and anxiety-like behaviors in the sand rat model, supporting the important role of physical activity in modulating the “circadian syndrome” and circadian rhythm-related diseases. We suggest that the utilization of a diurnal rodent animal model may offer an effective way to further explore metabolic, cardiovascular, and affective-like behavioral changes related to chronodisruption and their underlying mechanisms.

Cannabidiol Prevents Motor and Cognitive Impairments Induced by Reserpine in Rats

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa that presents antipsychotic, anxiolytic, anti-inflammatory, and neuroprotective effects. In Parkinson's disease patients, CBD is able to attenuate the psychotic symptoms induced by L-DOPA and to improve quality of life. Repeated administration of reserpine in rodents induces motor impairments that are accompanied by cognitive deficits, and has been applied to model both tardive dyskinesia and Parkinson's disease. The present study investigated whether CBD administration would attenuate reserpine-induced motor and cognitive impairments in rats. Male Wistar rats received four injections of CBD (0.5 or 5 mg/kg) or vehicle (days 2-5). On days 3 and 5, animals received also one injection of 1 mg/kg reserpine or vehicle. Locomotor activity, vacuous chewing movements, and catalepsy were assessed from day 1 to day 7. On days 8 and 9, we evaluated animals' performance on the plus-maze discriminative avoidance task, for learning/memory assessment. CBD (0.5 and 5 mg/kg) attenuated the increase in catalepsy behavior and in oral movements - but not the decrease in locomotion - induced by reserpine. CBD (0.5 mg/kg) also ameliorated the reserpine-induced memory deficit in the discriminative avoidance task. Our data show that CBD is able to attenuate motor and cognitive impairments induced by reserpine, suggesting the use of this compound in the pharmacotherapy of Parkinson's disease and tardive dyskinesia.

Effects of acute and long-term typical or atypical neuroleptics on morphine-induced behavioural effects in mice

1. It has been suggested that the high prevalence of drug abuse in schizophrenics is related to chronic treatment with typical neuroleptics and dopaminergic supersensitivity that develops as a consequence. Within this context, atypical neuroleptics do not seem to induce this phenomenon. In the present study, we investigated the effects of acute administration or withdrawal from long-term administration of haloperidol and/or ziprasidone on morphine-induced open-field behaviour in mice. 2. In the first experiment, mice were given a single injection of haloperidol (1 mg/kg, i.p.) or several doses of ziprasidone (2, 4 or 6 mg/kg, i.p.) and motor activity was quantified by the open-field test. The aim of the second experiment was to verify the effects of an acute injection of haloperidol (1 mg/kg) or ziprasidone (6 mg/kg) on 20 mg/kg morphine-induced behaviours in the open-field test. In the third experiment, mice were treated with 1 mg/kg haloperidol and/or 2, 4 or 6 mg/kg ziprasidone for 20 days. Seventy-two hours after the last injection, mice were injected with 20 mg/kg, i.p., morphine and then subjected to the open-field test. Acute haloperidol or ziprasidone decreased spontaneous general activity and abolished morphine-induced locomotor stimulation. 3. Withdrawal from haloperidol or ziprasidone did not modify morphine-elicited behaviours in the open-field test. The results suggest that withdrawal from neuroleptic treatments does not contribute to the acute effect of morphine in schizophrenic patients.

Diurnal rodents as an advantageous model for affective disorders: novel data from diurnal degu (Octodon degus)

Circadian rhythms are strongly associated with affective disorders and recent studies have suggested utilization of diurnal rodents as model animal for circadian rhythms-related domains of these disorders. Previous work with the diurnal fat sand rat and Nile grass rat demonstrated that short photoperiod conditions result in behavioral changes including anxiety- and depression-like behavior. The present study examined the effect of manipulating day length on activity rhythms and behavior of the diurnal degu. Animals were housed for 3 weeks under either a short photoperiod (5-h:19-h LD) or a neutral photoperiod (12-h:12-h LD) and then evaluated by sweet solution test and the forced swim test for depression-like behavior, and in the light/dark box and open field for anxiety-like behavior. Results indicate that short photoperiod induced depression-like behavior in the forced swim test and the sweet solution preference test and anxiety-like behavior in the open field compared with animals maintained in a neutral photoperiod. No effects were shown in the light/dark box. Short photoperiod-acclimated degu showed reduced total activity duration and activity was not restricted to the light phase. The present study further supports the utilization of diurnal rodents to model circadian rhythms-related affective change. Beyond the possible diversity in the mechanisms underlying diurnality in different animals, there are now evidences that in three different diurnal species, the fat sand rat, the grass Nile rat and the degu, shortening of photoperiod results in the appearance of anxiety- and depression-like behaviors.

Association study of the vesicular monoamine transporter gene SLC18A2 with tardive dyskinesia

Tardive dyskinesia (TD) is an involuntary movement disorder that can occur in up to 25% of patients receiving long-term first-generation antipsychotic treatment. Its etiology is unclear, but family studies suggest that genetic factors play an important role in contributing to risk for TD. The vesicular monoamine transporter 2 (VMAT2) is an interesting candidate for genetic studies of TD because it regulates the release of neurotransmitters implicated in TD, including dopamine, serotonin, and GABA. VMAT2 is also a target of tetrabenazine, a drug used in the treatment of hyperkinetic movement disorders, including TD. We examined nine single-nucleotide polymorphisms (SNPs) in the SLC18A2 gene that encodes VMAT2 for association with TD in our sample of chronic schizophrenia patients (n = 217). We found a number of SNPs to be nominally associated with TD occurrence and the Abnormal Involuntary Movement Scale (AIMS), including the rs2015586 marker which was previously found associated with TD in the CATIE sample (Tsai et al., 2010), as well as the rs363224 marker, with the low-expression AA genotype appearing to be protective against TD (p = 0.005). We further found the rs363224 marker to interact with the putative functional D2 receptor rs6277 (C957T) polymorphism (p = 0.001), supporting the dopamine hypothesis of TD. Pending further replication, VMAT2 may be considered a therapeutic target for the treatment and/or prevention of TD.

Could dietary trans fatty acids induce movement disorders? Effects of exercise and its influence on Na⁺K⁺-ATPase and catalase activity in rat striatum

The influence of trans fatty acids (FA) on development of orofacial dyskinesia (OD) and locomotor activity was evaluated. Rats were fed with diets enriched with 20% soybean oil (SO; n-6 FA), lard (L; saturated FA) or hydrogenated vegetable fat (HVF; trans FA) for 60 weeks. In the last 12 weeks each group was subdivided into sedentary and exercised (swimming). Brains of HVF and L-fed rats incorporated 0.33% and 0.20% of trans FA, respectively, while SO-fed group showed no incorporation of trans FA. HVF increased OD, while exercise exacerbated this in L and HVF-fed rats. HVF and L reduced locomotor activity, and exercise did not modify. Striatal catalase activity was reduced by L and HVF, but exercise increased its activity in the HVF-fed group. Na(+)K(+)-ATPase activity was not modified by dietary FA, however it was increased by exercise in striatum of SO and L-fed rats. We hypothesized that movement disorders elicited by HVF and less by L could be related to increased dopamine levels in striatum, which have been related to chronic trans FA intake. Exercise increased OD possibly by increase of brain dopamine levels, which generates pro-oxidant metabolites. Thus, a long-term intake of trans FA caused a small but significant brain incorporation of trans FA, which favored development of movement disorders. Exercise worsened behavioral outcomes of HVF and L-fed rats and increased Na(+)K(+)-ATPase activity of L and SO-fed rats, indicating its benefits. HVF blunted beneficial effects of exercise, indicating a critical role of trans FA in brain neurochemistry.

The catechol-O-methyl-transferase gene in tardive dyskinesia

Tardive dyskinesia (TD) is a severe and potentially irreversible motor side effect linked to long-term antipsychotic exposure. Changes in dopamine neurotransmission have been implicated in the etiology of TD, and catechol-O-methyl-transferase (COMT) is an enzyme that metabolizes dopamine.

OBJECTIVES

We investigated five single-nucleotide polymorphisms in addition to the functional Val158Met variant spanning the COMT gene for association with TD.

METHODS

We analyzed the six COMT single-nucleotide polymorphisms in a sample of schizophrenia/schizoaffective disorder patients (n=226; 196 Caucasians and 30 African Americans).

RESULTS

We found a significant association between the marker rs165599 in the 3' untranslated region of COMT and TD (AA versus G-carrier: OR(AA)=2.22, 95% CI:1.23-4.03; P=0.007). The association appeared to be originating from males. We did not find a significant association of the other five tested polymorphisms with TD in our samples. We performed a sex-stratified meta-analysis across all of the published studies (n=6 plus our own data) of COMT and TD, and found an association between ValVal genotype and TD in females (OR(ValVal)=1.63, 95% CI: 1.09-2.45; P=0.019) but not in males.

CONCLUSIONS

Overall, our results suggest that the COMT gene may have a minor but consistent role in TD, although sex-stratified studies with additional markers in larger clinical samples should be performed.

Long-term haloperidol treatment (but not risperidone) enhances addiction-related behaviors in mice: role of dopamine D2 receptors

The high prevalence of psychostimulant abuse observed in schizophrenic patients may be related to the development of mesolimbic dopaminergic supersensitivity (MDS) or nigrostriatal dopaminergic supersensitivity (NDS) in response to the chronic blockade of dopamine receptors produced by typical neuroleptic treatment. We compared the effects of withdrawal from long-term administration of the typical neuroleptic haloperidol (Hal) and/or the atypical agent risperidone (Ris) on MDS and NDS, behaviorally evaluated by amphetamine-induced locomotor stimulation (AILS) and apomorphine-induced stereotypy (AIS) in mice, respectively. We further evaluated the duration of MDS and investigated the specific role of dopamine D2 receptors in this phenomenon by administering the D2 agonist quinpirole (Quin) to mice withdrawn from long-term treatment with these neuroleptics. Withdrawal (48 hours) from long-term (20 days) Hal (0.5 mg/kg i.p.) (but not 0.5 mg/kg Ris i.p.) treatment potentiated both AILS and AIS. Ris co-administration abolished the potentiation of AILS and AIS observed in Hal-withdrawn mice. Ten days after withdrawal from long-term treatment with Hal (but not with Ris or Ris + Hal), a potentiation in AILS was still observed. Only Hal-withdrawn mice presented an attenuation of locomotor inhibition produced by Quin. Our data suggest that the atypical neuroleptic Ris has a pharmacological property that counteracts the compensatory MDS and NDS developed in response to the chronic blockade of dopamine receptors imposed by Ris itself or by typical neuroleptics such as Hal. They also indicate that MDS may be long lasting and suggest that an upregulation of dopamine D2 receptors in response to long-term treatment with the typical neuroleptic is involved in this phenomenon.

Genetic study of BDNF, DRD3, and their interaction in tardive dyskinesia

Tardive dyskinesia (TD) is a neuroleptic-induced movement disorder. Its pathophysiology is unclear. The most consistent genetic findings have shown an association with the Ser9Gly polymorphism of the DRD3 gene. However, only few polymorphisms within DRD3 has been tested, and a comprehensive examination of DRD3 in TD is still lacking. Further, brain-derived neurotrophic factor (BDNF), a neuronal growth and survival peptide, regulates DRD3 expression and may be involved in the neuronal degeneration observed in TD. In the present study, we investigated 15 tag DRD3 polymorphisms and four tag BDNF polymorphisms for association with TD in our sample of Caucasian schizophrenia patients (N=171). While BDNF markers showed no association, a haplotype containing rs3732782, rs905568, and rs7620754 in the 5' region of DRD3 was associated with TD diagnosis (p[10,000 permutations]=0.007). We also found evidence of interaction between BDNF and DRD3 polymorphisms. Further studies are needed to confirm these findings.

We are in the dark here: induction of depression- and anxiety-like behaviours in the diurnal fat sand rat, by short daylight or melatonin injections

Circadian rhythms are considered an important factor in the aetiology, expression and treatment of major affective disorders, including seasonal affective disorder (SAD). However, data on the effects of daylight length manipulation or melatonin administration are complex. It has been suggested that since diurnal and nocturnal mammals differ significantly in their physiological and behavioural responses to daylight, diurnal rodents offer a preferable model of disorders related to circadian rhythms in the diurnal human. We previously found that diurnal fat sand rats maintained under short daylight (SD), show depression-like behaviour in the forced swim test (FST). The present study was designed to test additional behaviours related to affective disorders and study the involvement of melatonin in these behaviours. Sand rats were divided into short-daylight (SD, 5 h light:19 h dark) and long-daylight (LD, 12 h light:12 h dark) groups, and received 100 microg melatonin or vehicle administration for 3 wk (5 h and 8.5 h after light onset in the LD room). Animals were then tested for reward-seeking behaviour (saccharin consumption), anxiety (elevated plus-maze), aggression (resident-intruder test), and depression-like behaviour (FST). SD or melatonin administration resulted in a depressed/anxious-like behavioural phenotype including reduced reward seeking, increased anxiety, decreased aggression and decreased activity in the FST, supporting the notion that in a diurnal animal, reduced light results in a variety of behavioural changes that may model depression and anxiety; and that melatonin may be a significant factor in these changes. We suggest that the sand rat may offer an excellent model species to explore the interactions between daylight, affective behaviour and the related underlying mechanisms.

Association study of tardive dyskinesia and twelve DRD2 polymorphisms in schizophrenia patients

Tardive dyskinesia (TD) is a side-effect of chronic antipsychotic medication. Abnormalities in dopaminergic activity in the nigrostriatal system have been most often suggested to be involved because the agents which cause TD share in common potent antagonism of dopamine D2 receptors (DRD2), that notably is not balanced by effects such as more potent serotonin (5-HT)2A antagonism. Thus, a number of studies have focused on the association of dopamine system gene polymorphisms and TD. The most consistent findings have been found with the Ser9Gly polymorphism of the DRD3 gene. Although DRD2 has long been hypothesized to be the main target for antipsychotics, only a few polymorphisms in DRD2 have been investigated for their potential involvement in the aetiology of TD. In the present study, we investigated 12 polymorphisms spanning the DRD2 gene and their association with TD in our European Caucasian (n=202) and African-American (n=30) samples. Genotype frequencies for a functional polymorphism, C957T (Duan et al., 2003; Hirvonen et al., 2004), and the adjacent C939T polymorphism were found to be significantly associated with TD (p=0.013 and p=0.022 respectively). DRD2 genotypes were not significantly associated with TD severity as measured by AIMS (Abnormal Involuntary Movement Scale) with the exception of a trend for C939T (p=0.071). Both TD and total AIMS scores were found to be significantly associated with two-marker haplotypes containing C939T and C957T (p=0.021 and p=0.0087 respectively). Preliminary results indicated that C957T was also associated with TD in our African-American sample (p=0.047). Taken together, the present study suggests that DRD2 may be involved in TD in the Caucasian population, although further studies are warranted.

Haloperidol (but not ziprasidone) withdrawal enhances cocaine-induced locomotor activation and conditioned place preference in mice

It has been empirically suggested that the high incidence of drug abuse in schizophrenic patients is related to chronic neuroleptic treatment. We investigated the effects of withdrawal from long-term administration of the typical neuroleptic haloperidol and/or the atypical agent ziprasidone on the acute locomotor stimulant effect of cocaine as well as on cocaine-induced conditioned place preference (CPP). In the first experiment, mice were i.p. treated with haloperidol (1.0 mg/kg) and/or ziprasidone (4.0 mg/kg) for 15 days. At 72 h after the last injection, animals received an i.p. injection of cocaine (10 mg/kg) and their locomotor activity was quantified. In the second experiment, mice were withdrawn from the same haloperidol or ziprasidone treatment schedule and submitted to CPP. Withdrawal from haloperidol (but not ziprasidone or ziprasidone plus haloperidol) increased both cocaine-induced hyperactivity and CPP. These findings indicate that withdrawal from long-term treatment with typical neuroleptic drugs such as haloperidol (but not the atypical compound ziprasidone) may enhance some behavioral effects of cocaine in mice which have been related to drug dependence in humans.

Sleep deprivation abolishes the locomotor stimulant effect of ethanol in mice

The present study aimed to investigate the effects of sleep deprivation (SD) on the dose-dependent stimulant effect of ethanol (ETOH) on the open-field behavior of female and male mice. Sleep-deprived (48 h, multiple platforms method) or home-cage control female mice were treated with saline (SAL) or 1.4, 1.8 or 2.2g/kg ETOH 5 min before behavioral testing. ETOH produced a dose-dependent increase in open-field locomotor behavior. This locomotor stimulant effect did not reflect a general stimulation in motor activity, since it was accompanied by a simultaneous decrease in rearing frequency as well as by no modification in immobility duration. The effects of ETOH on these three behavioral parameters were specifically modified by SD: the locomotor stimulant effect was abolished, the rearing inhibitory effect was potentiated and the lack of effect on immobility was changed to increase in immobility. Similar results were obtained for male mice although the effects of SD had a lower magnitude. The present findings demonstrate that the acute effect of ETOH on mice's motor activity are behaviorally complex and can be specifically modulated by SD.

The importance of housing conditions on behavioral sensitization and tolerance to ethanol

The differential outcomes of social isolation and crowding environment on the effects of single or repeated administration of ethanol on open-field behavior were examined in female mice. Whereas housing conditions did not alter the increase in locomotor activity induced by ethanol single administration, behavioral sensitization (a progressive increase of a drug effect following repeated drug administration) to the locomotor activating effect of ethanol was significantly greater in crowded mice as compared to isolated and control groups. Single administration of ethanol significantly decreased rearing frequency and increased immobility duration, there being tolerance to these ethanol behavior effects after repeated treatment. Social isolation attenuated the increase in immobility behavior induced by single administration of ethanol and potentiated the tolerance of ethanol-induced rearing decrease, verified after repeated treatment. These results point out that both sensitization and tolerance to the behavioral effects of ethanol can be critically influenced by housing conditions.

Behavioral characterization of morphine effects on motor activity in mice

A biphasic effect of morphine on locomotion has been extensively described. Nevertheless, the effects of this opioid on other behavioral parameters have been overlooked. The aim of the present study was to verify the effects of different doses of morphine on motor behaviors observed in an open-field. Adult female mice were injected with saline or morphine (10, 15 and 20 mg/kg, i.p.) and observed in an open-field for quantification of locomotor and rearing frequencies as well as duration of immobility and grooming. The lowest dose of morphine decreased locomotion (and increased immobility duration) while the highest dose increased it. All doses tested decreased rearing and grooming. Thus, the effects of morphine on locomotion do not parallel to its effects on rearing and grooming. Our results indicate that locomotion not always reflects the effect of drugs on motor activity, which can be better investigated when other behavioral parameters are concomitantly taken into account.

Diurnal rhythms in quinpirole-induced locomotor behaviors and striatal D2/D3 receptor levels in mice

Dopaminergic drugs, including the D2/D3 agonist quinpirole, produce lasting changes in the brain that lead to altered behavioral responses. The action of these drugs is dosing time-dependent; in fruit flies, behavioral response to quinpirole shows a marked circadian variability. Here we demonstrate diurnal rhythm-dependent variations both in quinpirole-induced locomotor behaviors and in striatal D2 and D3 protein levels in mice. We found opposing diurnal rhythms in striatal D2 and D3 protein levels, resulting in a high D2/D3 ratio during the day and a low D2/D3 ratio at night. Protracted quinpirole treatment differentially altered striatal D2/D3 rhythms depending on the time of injection (i.e., day or night). When quinpirole-induced locomotor activity was analyzed for 90 min, we found hypomotility after the first day or nighttime drug injection. By the seventh injection, daytime quinpirole treatment produced clear hyperactivity while nighttime quinpirole treatment continued to induce a significant initial hypoactivity followed by a hyperactivity period. Our data indicate that quinpirole-induced long-term alterations in the brain include dosing time-dependent changes in dopamine receptor rhythms. Therefore, we propose that diurnal mechanisms, which participate in drug-induced long-term changes in the dopamine system, are important for the development of dopaminergic behaviors.