Role of CB2 Cannabinoid Receptors in the Rewarding,Reinforcing, and Physical Effects of Nicotine

This study was aimed to evaluate the involvement of CB2 cannabinoid receptors (CB2r) in the rewarding, reinforcing and motivational effects of nicotine. Conditioned place preference (CPP) and intravenous self-administration experiments were carried out in knockout mice lacking CB2r (CB2KO) and wild-type (WT) littermates treated with the CB2r antagonist AM630 (1 and 3 mg/kg). Gene expression analyses of tyrosine hydroxylase (TH) and α3- and α4-nicotinic acetylcholine receptor subunits (nAChRs) in the ventral tegmental area (VTA) and immunohistochemical studies to elucidate whether CB2r colocalized with α3- and α4-nAChRs in the nucleus accumbens and VTA were performed. Mecamylamine-precipitated withdrawal syndrome after chronic nicotine exposure was evaluated in CB2KO mice and WT mice treated with AM630 (1 and 3 mg/kg). CB2KO mice did not show nicotine-induced place conditioning and self-administered significantly less nicotine. In addition, AM630 was able to block (3 mg/kg) nicotine-induced CPP and reduce (1 and 3 mg/kg) nicotine self-administration. Under baseline conditions, TH, α3-nAChR, and α4-nAChR mRNA levels in the VTA of CB2KO mice were significantly lower compared with WT mice. Confocal microscopy images revealed that CB2r colocalized with α3- and α4-nAChRs. Somatic signs of nicotine withdrawal (rearings, groomings, scratches, teeth chattering, and body tremors) increased significantly in WT but were absent in CB2KO mice. Interestingly, the administration of AM630 blocked the nicotine withdrawal syndrome and failed to alter basal behavior in saline-treated WT mice. These results suggest that CB2r play a relevant role in the rewarding, reinforcing, and motivational effects of nicotine. Pharmacological manipulation of this receptor deserves further consideration as a potential new valuable target for the treatment of nicotine dependence.     

Slowed atrial and atrioventricular conduction and depressed HRV in a murine model of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common heritable cardiac disorder with diverse clinical outcomes including sudden death, heart failure, and stroke. Depressed heart rate variability (HRV), a measure of cardiac autonomic regulation, has been shown to predict mortality in patients with cardiovascular disease. Cardiac autonomic remodelling in animal models of HCM are not well characterised. This study analysed Gly203Ser cardiac troponin‐I transgenic (TG) male mice previously demonstrated to develop hallmarks of HCM by age 21 weeks. 33 mice aged 30 and 50 weeks underwent continuous electrocardiogram (ECG) recording for 30 min under anaesthesia. TG mice demonstrated prolonged P‐wave duration (P < 0.001) and PR intervals (P < 0.001) compared to controls. Additionally, TG mice demonstrated depressed standard deviation of RR intervals (SDRR; P < 0.01), coefficient of variation of RR intervals (CVRR; P < 0.001) and standard deviation of heart rate (SDHR; P < 0.001) compared to controls. Additionally, total power was significantly reduced in TG mice (P < 0.05). No significant age‐related difference in either strain was observed in ECG or HRV parameters. Mice with HCM developed slowed atrial and atrioventricular conduction and depressed HRV. These changes were conserved with increasing age. This finding may be indicative of atrial and ventricular hypertrophy or dysfunction, and perhaps an indication of worse clinical outcome in heart failure progression in HCM patients.     

Selective re-expression of β2 nicotinic acetylcholine receptor subunits in the ventral tegmental area of the mouse restores intravenous nicotine self-administration

Beta-2 (β2) nicotinic acetylcholine receptor subunits have been particularly related with nicotine reinforcement. However, the importance of these subunits in the chronic aspects of nicotine addiction has not been established. In this study we evaluated the role of ventral tegmental area (VTA) β2 receptor subunits in the acquisition and maintenance of nicotine self-administration. We used an operant mouse model of intravenous self-administration of different doses of nicotine (15, 30, and 60 μg/kg/infusion) during 10 days in constitutive knockout mice lacking β2 receptor subunits (β2KO), wild-type (WT) controls, mice with β2 receptor subunits re-expressed in the VTA using a lentiviral vector (β2-VEC), and control knockout mice with a sham injection (KO-GFP). The results showed that β2KO mice did not reliably acquire nicotine self-administration at any of the doses tested, while WT controls showed dose-dependent acquisition of this behaviour. β2-VEC mice readily acquired and maintained nicotine self-administration at the effective dose of 15 μg/kg/infusion, while sham KO-GFP mice did not. The recovery of the WT phenotype by the re-expression of β2 receptor subunits within the VTA supports the role of this specific population in nicotine reinforcement, and reveals that they are sufficient for the acquisition and maintenance of systemic nicotine self-administration.     

Effect of the α4β2∗ nicotinic acetylcholine receptor partial agonist varenicline on dopamine release in β2 knock-out mice with selective re-expression of the β2 subunit in the ventral tegmental area

We studied the effects of 1 mg/kg doses of nicotine and the α4β2* nicotinic acetylcholine receptor (nAChR) partial agonist, varenicline, on extracellular dopamine (DA) levels in the nucleus accumbens (NuAcc) of lentivirally vectorized male mice. Three separate experimental groups were injected with a lentiviral vector transducing the ventral tegmental area (VTA): wild-type C57BL/6J mice with a vector expressing eGFP only, β2 knock-out mice (β2KO) with the eGFP-only vector, and β2KO mice with a bicistronic vector reintroducing β2 and eGFP into the VTA as recently described (Maskos et al., 2005). Our results suggest that the neurochemical effects of varenicline as measured by using microdialysis in awake, freely moving mice are mainly mediated via β2* nAChR subunits localized in the VTA.     

Implitapide, a microsomal triglyceride transfer protein inhibitor, reduces progression of atherosclerosis in apolipoprotein E knockout mice fed a Western-type diet: involvement of the inhibition of postprandial triglyceride elevation

Microsomal triglyceride transfer protein (MTP) is essential for the synthesis of both chylomicron in the intestine and very low-density lipoprotein in the liver. An MTP inhibitor, (2S)-2-cyclopentyl-2-[4-[(2,4-dimethyl-9H-pyrido[2,3-b]indol-9-yl)methyl]phenyl]-N-[(1S)-2-hydroxy-1-phenylethyl]ethanamide (implitapide), has been shown to suppress atherosclerosis in apolipoprotein E knockout (apoE KO) mice. To elucidate the antiatherosclerotic mechanisms of implitapide in the mice, we examined the effects on plasma lipid levels, triglyceride (TG) elevation after oral fat loading, and development of atherosclerosis in apoE KO mice fed a Western-type diet. Implitapide at a dosage of approximately 3.2 mg/kg/day significantly reduced both total cholesterol and TG levels during the 8-week treatment period. In addition, implitapide significantly inhibited the increase in plasma TG levels after oral olive oil loading tests conducted after 4 weeks of treatment. After the treatment, implitapide significantly suppressed the atherosclerotic lesion area by 83% compared with a control group. These results provide direct evidence that the antiatherosclerotic effects of implitapide in apoE KO mice are associated with the inhibition of postprandial TG elevation, in addition to the reduction of both plasma total cholesterol and TG levels.     

Particle effects on heart-rate regulation in senescent mice

Because epidemiology studies consistently identify the elderly at risk for air pollution-related morbidity and mortality, we developed a model of senescent-dependent susceptibility based on indices of physiological aging. In the current study, we hypothesized that heart-rate regulation during particulate matter (PM) exposure differs with senescence-dependent susceptibility owing to variation in autonomic nervous control. Heart rate (HR) and heart-rate variability (HRV) parameters were measured from 162 samples of 2-min electrocardiograph (ECG) recordings in age-matched healthy (n = 5) and terminally senescent (n = 3) AKR mice during 3-h exposures to filtered-air (FA, day 1) and carbon black (CB, day 4; <200 microg/m(3)). On day 1, HR was significantly (p <.01) depressed during FA in terminally senescent mice. By day 4, HR was further slowed significantly (p <.01) due to the effects of CB exposure for 3 days. The combined effects of terminal senescence and CB exposure acted to depress HR to an average (+/-SEM) 445 +/- 40 bpm, or approximately 80 bpm lower compared to healthy HR responses. The change in rMSSD, an HRV parameter corresponding to relative influences of parasympathetic tone on HR, was significantly (p <.01) greater on day 1 and day 4 in terminally senescent mice compared to healthy mice. In contrast, the LF/HF ratio, an HRV parameter derived from spectral analysis indicating relative changes in cardiac sympathetic tone, was significantly (p <.01) depressed in terminally senescent mice on day 1. By day 4, significant increases in LF/HF were evident in healthy mice during CB exposure, suggesting that HR regulation was associated with an increase in sympathetic tone. Alternatively, terminally senescent mice appeared to modulate a lower HR without change in LF/HF ratio during CB exposure, suggesting an absence of sympathetic tone. In conclusion, older healthy mice increase cardiac sympathetic tone during PM exposure while terminally senescent mice show a greater PM-induced parasympathetic tone in regulating HR. The significance of the current results suggest that PM-induced HR regulatory changes may ultimately depend on the degree of physiological aging.     

Effects of morphine on pain-elicited and pain-suppressed behavior in CB1 knockout and wildtype mice

Rationale  

Pharmacological manipulations of the type 1 cannabinoid receptor (CB1) suggest a role for CB1 in morphine-induced antinociception, but studies utilizing CB1 knockout (KO) mice do not support this conclusion. Since studies using CB1 KO mice to study morphine’s antinociceptive effects have only examined thermal nociception, this study examines these interactions in models that employ a chemical stimulus.     

AQP4 knockout mice manifest abnormal expressions of calcium handling proteins possibly due to exacerbating pro-inflammatory factors in the heart

We tested the hypothesis that aquaporin-4 (AQP4) knockout (KO) mice might exhibit abnormal Ca²⁺ modulating proteins resulting from the exacerbation of pro-inflammatory factors in the heart. Downregulation of FKBP12.6, SERCA2a, and CASQ2 and calcium leak in diastole have been recognized as endpoints for assessing cardiac failure and arrhythmias. The AQP4 KO mice and wild-type (WT) mice were randomly divided into 3 groups, such as control, isoproterenol (ISO, β-receptor agonist) injected (1 mg/kg, sc, 5 d), and treated with aminoguanidine (AMG, 100 mg/kg, po, a selective inhibitor of the iNOS) during the last 3 d. RT-PCR, western blot and calcium transient measurements were conducted. The results demonstrated that the cardiac weight index was increased in AQP4 KO mice and further increased following treatment with ISO. The expression levels of FKBP12.6, SERCA2a, and CASQ2 were downregulated and diastolic calcium concentrations were elevated in the AQP4 KO mice, indicative of a calcium leak. In the myocardium, expressions of pro-inflammatory biomarkers, including ET_A, pPKC?, NADPH oxidase p67^phox were upregulated and associated with downregulation of Cx43. The aforementioned changes were exacerbated in response to ISO medication and were attenuated by AMG; however, its treatment effectiveness was less in the AQP4 KO mice. We concluded AQP4 KO caused abnormalities of calcium modulating proteins leading to an exacerbation of risk for cardiac arrhythmias and failure. These changes are likely due to an increase in pro-inflammatory factors which are exacerbated by stress. Therefore, AQP4 KO mice are prone to cardiac failure and arrhythmias through exacerbating pro-inflammatory factors in the myocardium.     

Blockage of histamine H1 receptor attenuates social isolation-induced disruption of prepulse inhibition: a study in H1 receptor gene knockout mice

Rationale Histaminergic neurotransmission has been implicated in the pathophysiology of stress-related psychiatric diseases. Although several atypical antipsychotics are potent H1 anagonists, the clinical significance of interaction between atypical antipsychotics and H1 receptors is still unknown.Objective In this study, we investigated the effects of H1 receptors blockage on social isolation-induced behavioral changes in H1 receptor gene knockout (H1KO) mice and their wild-type (WT) mice.Methods Both H1KO and their WT mice were subjected to 4-week social isolation rearing after weaning (21 postnatal days). After the 4-week isolation period, mice behavioral changes were evaluated using behavioral tests.Results Locomotor activity in home cages was significantly lower in isolation-reared WT mice than in socially reared WT mice. However, no change in locomotor activity was observed between socially and isolation-reared H1KO mice. Social isolation significantly impaired prepulse inhibition (PPI) of startle response in WT mice but not in H1KO mice. In addition, social isolation significantly impaired spatial learning and memory in WT mice but not in H1KO mice. Furthermore, H1KO mice treated with methamphetamine (METH) showed no enhancement in isolation-induced disruption of PPI. A neurochemical study revealed that isolation-reared WT mice had significantly lower dopamine (DA) levels and slightly increased DA turnover in the cortex than socially reared WT mice. Conversely, isolation-reared H1KO mice showed significantly higher DA contents as compared with socially reared H1KO mice. Conclusion: The results of our study indicate that blockage of H1 receptor-mediated neurotransmission attenuates social isolation-induced behavioral changes and that the therapeutic effects of atypical antipsychotics are mediated, at least in part, by interaction with H1 receptors in the brain.     

Effects of activation of central nervous histamine receptors in cardiovascular regulation; studies in H<Subscript>1</Subscript> and H<Subscript>2</Subscript> receptor gene knockout mice

To elucidate the central roles of histamine receptors in cardiovascular regulatory system, systolic, mean, and diastolic blood pressures (BPs) and heart rate (HR) were examined in conscious H₁ receptor gene knockout (H₁KO) mice, H₂ receptor gene knockout (H₂KO) mice, H₁ and H₂ receptor gene double knockout (DKO) mice, and their respective control mice by the tail-cuff system. Histamine, histamine-trifluoromethyl-toluidine derivative (HTMT, an H₁ agonist), dimaprit (an H₂ agonist), and immepip (an H₃ agonist) were intrathecally administered to these KO mice and control mice. Basal BPs and HR were not different among these three KO mice and their control or wild-type mice. Intrathecal administration of histamine significantly increased BPs and decreased HR in control mice. The increases in BPs were produced by histamine in H₁KO and H₂KO mice and by HTMT and dimaprit in C57BL mice. The pressor responses by HTMT and dimaprit in C57BL mice were greater than those by histamine in H₁KO and H₂KO mice, although the same decreases in HR were induced by histamine in C57BL and H₁KO mice and by dimaprit in C57BL mice. The selective stimulation of H₃ receptors by immepip produced a consistent decrease in BPs in control mice. These results obtained with the exogenous selective agonists of three histamine receptors suggest that the pressor responses to histamine are mediated through the stimulation of both H₁ and H₂ receptors, whereas the atropine-sensitive decrease in heart rate is mainly due to H₂ receptors which activate the vagal output to the heart.     

Fumonisin B1-Induced Toxicity Was Not Exacerbated in Glutathione Peroxidase-1/Catalase Double Knock Out Mice

Fumonisin B1 (FB1) structurally resembles sphingolipids and interferes with their metabolism leading to sphingolipid dysregulation. We questioned if FB1 could exacerbate liver or kidney toxicities in glutathione peroxidase 1 (Gpx1) and catalase (Cat) knockout mice. While higher serum levels of thiobarbituric acid reactive substances (TBARS) and sphinganine (Sa) were measured in Gpx1/Cat knockout mice (Gpx1/Cat KO) than wild type mice after 5 days of FB1 treatment, serum levels of alanine aminotransferase (ALT), sphingosine-1 phosphate (So-1-P), and sphinganine-1 phosphate (Sa-1-P) were found to be relatively low. Although Sa was highly elevated in Gpx1/Cat KO mice and wild mice, lower levels of So and Sa were found in both the kidney and liver tissues of Gpx/Cat KO mice than wild type mice after FB1 treatment. Paradoxically, FB1-induced cellular apoptosis and necrosis were hastened under oxidative stress in Gpx1/Cat KO mice.     

Particle Effects on Heart-Rate Regulation in Senescent Mice

Because epidemiology studies consistently identify the elderly at risk for air pollution-related morbidity and mortality, we developed a model of senescent-dependent susceptibility based on indices of physiological aging. In the current study, we hypothesized that heart-rate regulation during particulate matter (PM) exposure differs with senescence-dependent susceptibility owing to variation in autonomic nervous control. Heart rate (HR) and heart-rate variability (HRV) parameters were measured from 162 samples of 2-min electrocardiograph (ECG) recordings in age-matched healthy (n = 5) and terminally senescent (n = 3) AKR mice during 3-h exposures to filtered-air (FA, day 1) and carbon black (CB, day 4; < 200 μ g/m³). On day 1, HR was significantly (p <. 01) depressed during FA in terminally senescent mice. By day 4, HR was further slowed significantly (p <. 01) due to the effects of CB exposure for 3 days. The combined effects of terminal senescence and CB exposure acted to depress HR to an average (±SEM) 445 ± 40 bpm, or ～ 80 bpm lower compared to healthy HR responses. The change in rMSSD, an HRV parameter corresponding to relative influences of parasympathetic tone on HR, was significantly (p <. 01) greater on day 1 and day 4 in terminally senescent mice compared to healthy mice. In contrast, the LF/HF ratio, an HRV parameter derived from spectral analysis indicating relative changes in cardiac sympathetic tone, was significantly (p <. 01) depressed in terminally senescent mice on day 1. By day 4, significant increases in LF/HF were evident in healthy mice during CB exposure, suggesting that HR regulation was associated with an increase in sympathetic tone. Alternatively, terminally senescent mice appeared to modulate a lower HR without change in LF/HF ratio during CB exposure, suggesting an absence of sympathetic tone. In conclusion, older healthy mice increase cardiac sympathetic tone during PM exposure while terminally senescent mice show a greater PM-induced parasympathetic tone in regulating HR. The significance of the current results suggest that PM-induced HR regulatory changes may ultimately depend on the degree of physiological aging.     

Quantitative analysis of the loss of muscarinic receptors in various peripheral tissues in M1�CM5 receptor single knockout mice

Background and purpose:

To compare loss in binding to muscarinic receptor (mAChR) subtypes with their known functions, the total density of muscarinic receptors was measured in peripheral tissues from wild type (WT) and mAChR knockout (KO) mice.

Experimental approach:

Binding parameters of [N-methyl-³H]scopolamine methyl chloride ([³H]NMS) were determined in 10 peripheral tissues of WT and M₁–M₅ receptor KO mice. Competition between [³H]NMS and darifenacin (selective M₃ receptor antagonist) was also measured

Key results:

There was an extensive loss of [³H]NMS-binding sites (maximal number of binding sites, B_max) in heart and smooth muscle from M₂KO mice, compared with WT mice. Smooth muscle from M₃KO mice also showed a moderate loss of B_max. B_max fell in pancreas and bladder of M₄KO mice and in prostate in M₁KO and M₃KO mice. There was a large loss of B_max in exocrine and endocrine glands of M₃KO mice with a moderate decrease in M₂KO mice. Darifenacin inhibited specific [³H]NMS binding in submandibular gland and bladder of WT, M₂KO and M₃KO mice. K_i (inhibition constant) values for darifenacin in the submandibular gland were the same in WT and M₂KO mice but increased in M₃KO mice. However, K_i values in bladder were decreased in M₂KO mice and increased in M₃KO mice.

Conclusions and implications:

Single mAChR KO mice exhibit a loss of mAChR in peripheral tissues that generally paralleled the reported loss of function. Quantitative analysis of data, however, also suggested that, in some instances, normal expression of a receptor subtype depended on expression of other subtypes.     

FKBP5 Moderates Alcohol Withdrawal Severity: Human Genetic Association and Functional Validation in Knockout Mice

Alcohol withdrawal is associated with hypothalamic–pituitary–adrenal (HPA) axis dysfunction. The FKBP5 gene codes for a co-chaperone, FK506-binding protein 5, that exerts negative feedback on HPA axis function. This study aimed to examine the effects of single-nucleotide polymorphisms (SNPs) of the FKBP5 gene in humans and the effect of Fkbp5 gene deletion in mice on alcohol withdrawal severity. We genotyped six FKBP5 SNPs (rs3800373, rs9296158, rs3777747, rs9380524, rs1360780, and rs9470080) in 399 alcohol-dependent inpatients with alcohol consumption 48 h before admission and recorded scores from the Clinical Institute Withdrawal Assessment-Alcohol revised (CIWA-Ar). Fkbp5 gene knockout (KO) and wild-type (WT) mice were assessed for alcohol withdrawal using handling-induced convulsions (HICs) following both acute and chronic alcohol exposure. We found the minor alleles of rs3800373 (G), rs9296158 (A), rs1360780 (T), and rs9470080 (T) were significantly associated with lower CIWA-Ar scores whereas the minor alleles of rs3777747 (G) and rs9380524 (A) were associated with higher scores. The haplotype-based analyses also showed an association with alcohol withdrawal severity. Fkbp5 KO mice showed significantly greater HICs during withdrawal from chronic alcohol exposure compared with WT controls. This study is the first to show a genetic effect of FKBP5 on the severity of alcohol withdrawal syndrome. In mice, the absence of the Fkbp5 gene enhances sensitivity to alcohol withdrawal. We suggest that FKBP5 variants may trigger different adaptive changes in HPA axis regulation during alcohol withdrawal with concomitant effects on withdrawal severity.     

Kappa Opioid Receptors on Dopaminergic Neurons Are Necessary for Kappa-Mediated Place Aversion

Kappa-opioid receptor (KOR) agonists have dysphoric properties in humans and are aversive in rodents. This has been attributed to the activation of KORs within the mesolimbic dopamine (DA) system. However, the role of DA in KOR-mediated aversion and stress remains divisive as recent studies have suggested that activation of KORs on serotonergic neurons may be sufficient to mediate aversive behaviors. To address this question, we used conditional knock-out (KO) mice with KORs deleted on DA neurons (DAT^Cre/wt/KOR^loxp/loxp, or DATCre-KOR KO). In agreement with previous findings, control mice (DAT^Cre/wt/KOR^wt/wt or WT) showed conditioned place aversion (CPA) to the systemically administered KOR agonist U69,593. In contrast, DATCre-KOR KO mice did not exhibit CPA with this same agonist. In addition, in vivo microdialysis showed that systemic U69,593 decreased overflow of DA in the nucleus accumbens (NAc) in WT mice, but had no effect in DATCre-KOR KO mice. Intra- ventral tegmental area (VTA) delivery of KORs using an adeno-associated viral gene construct, resulted in phenotypic rescue of the KOR-mediated NAc DA response and aversive behavior in DATCre-KOR KO animals. These results provide evidence that KORs on VTA DA neurons are necessary to mediate KOR-mediated aversive behavior. Therefore, our data, along with recent findings, suggest that the neuronal mechanisms of KOR-mediated aversive behavior may include both dopaminergic and serotonergic components.     

Enhanced antinociception by intrathecally-administered morphine in histamine H1 receptor gene knockout mice

We previously reported that histamine H₁ receptor gene knockout mice (H1KO) showed lower spontaneous nociceptive threshold to pain stimuli when compared to wild-type mice. The objective of the present study was to examine the antinociceptive effect of intrathecally-administered morphine in H1KO mice. The antinociceptive effects of morphine were examined using assays for thermal (tail-flick, hot-plate, paw-withdrawal), mechanical (tail-pressure) and chemical nociception (formalin and capsaicin tests) using H1KO and wild-type mice. In these nociceptive assays, intrathecally-administered morphine produced significant antinociceptive effects in wild-type mice. The antinociceptive effect produced by intrathecally administered morphine was enhanced in the knockout mice. We also examined the effect of an histamine H₁ receptor antagonist, an active (d-) isomer of chlorpheniramine, on morphine-induced antinociception in ICR mice. The intrathecal co-administration of d-chlorpheniramine enhanced the effect of morphine in all nociceptive assays examined. The pharmacological experiments using d-chlorpheniramine further substantiate the evidence for the histamine H₁ receptor-mediated suppression of morphine-induced antinociception. These results suggest that existing H₁ receptors play an inhibitory role in morphine-induced antinociception at the spinal cord level.     

Group I metabotropic glutamate receptor antagonists alter select behaviors in a mouse model for fragile X syndrome

Rationale  

Studies in the Fmr1 knockout (KO) mouse, a model of fragile X syndrome (FXS), suggest that excessive signaling through group I metabotropic glutamate receptors (mGluRs), comprised of subtypes mGluR1 and mGluR5, may play a role in the pathogenesis of FXS. Currently, no studies have assessed the effect of mGluR1 modulation on Fmr1 KO behavior, and there has not been an extensive behavioral analysis of mGluR5 manipulation in Fmr1 KO mice.     

Glutathione peroxidase‐1 gene rescues cocaine‐induced conditioned place preference in mice by inhibiting σ‐1 receptor expression

The aim of this study was to investigate whether the glutathione peroxidase‐1 gene (GPx‐1) affects cocaine‐induced conditioned place preference (CPP) using a mouse model. Cocaine‐induced CPP was accompanied by an increase in the level of σ‐1 receptor in the nucleus accumbens (NAc). This phenomenon was more pronounced in the GPx‐1 gene knockout (GPx‐1 KO) than in wild type (WT) mice. In contrast, the CPP and expression of σ‐1 receptor were much less pronounced in GPx‐1‐overexpressing transgenic (GPx‐1 TG) mice than non‐transgenic (non‐TG) mice. Treatment of the mice with BD1047 , a σ‐1 receptor antagonist, significantly attenuated both cocaine‐induced CPP and c‐Fos‐immunoreactivity (c‐Fos‐IR) in WT and GPx‐1 KO mice, although the effects were more evident in the latter group. Despite the protective effects of BD1047 on cocaine‐induced CPP and c‐Fos in non‐TG mice, there were no additional protective effects in cocaine‐treated GPx‐1 TG mice, indicating that the σ‐1 receptor is a critical target for GPx‐1‐mediated psychoprotective activity. Overall, our results suggest that GPx‐1 attenuates cocaine‐induced CPP via inhibition of σ‐1 receptor expression.     

Genetic variation in 5-hydroxytryptamine transporter expression causes adaptive changes in 5-HT₄ receptor levels

Genetic variation in 5-HT transporter (5-HTT) expression is a key risk factor for psychiatric disorder and has been linked to changes in the expression of certain 5-HT receptor subtypes. This study investigated the effect of variation in 5-HTT expression on 5-HT? receptor levels in both 5-HTT knockout (KO) and overexpressing (OE) mice using autoradiography with the selective 5-HT? receptor radioligand, [3H]SB207145. Compared to wild-type (5-HTT?/?) controls, homozygous 5-HTT KO mice (5-HTT?/?) had reduced 5-HT? receptor binding site density in all brain regions examined (35-65% of 5-HTT?/?). In contrast, the density of 5-HT? receptor binding sites was not significantly different between heterozygous 5-HTT KO mice (5-HTT?/?) and 5-HTT?/? mice. The 5-HT synthesis inhibitor p-chlorophenylalanine (250 mg/kg twice daily for 3 d) abolished the difference in 5-HT? binding between 5-HTT?/? and 5-HTT?/? mice in all brain regions. Compared to wild-type (WT) littermate controls, 5-HTT OE mice had increased 5-HT? binding density across all brain regions, except amygdala (118-164% of WT) and this difference between genotypes was reduced by the 5-HTT inhibitor, fluoxetine (20 mg/kg twice daily, 3 d). Together, these findings suggest that variation in 5-HTT expression causes adaptive changes in 5-HT? receptor levels which are directly linked to alterations in 5-HT availability.