Reduced cerebellum volume and ataxia-like motoric phenotype in transgenic mouse, carrier of human CYP2C19 gene

Introduction: CYP2C19 transgenic mouse (2C19TG) is generated by the insertion of 12 copies of the human CYP2C19 gene into mouse genome. This animal model is a tool to study the neurodevelopmental role of CYP2C19 in vivo, since this enzyme is expressed in the foetal brains of 2C19TG mice and humans. Previous studies [1,2] showed anxiety and depression-like behaviour in these mice, while the aim of this study was to characterize the motoric function of the 2C19TG mouse. Methods: Whole brain dopamine concentration was measured in the brain homogenate of 23 adult mice by the HPLC-MS method. Motoric function in 50 mutant and 43 control mice of both genders was tested by the rotarod and beam walking tests. Beam walking test was repeated after treatment with dopaminergic receptor antagonists, Ecopipam (0.1 mg/kg) and Raclopride (0.25 mg/kg) as a follow-up. The sections of 10 6-month old and 8 15-months old mice were stained with anti-tyrosine hydroxylase antibody and the number of dopaminergic neurons was counted on histological slides under microscope. Next, after transcardial perfusion of 30 2C19TG and 30 control mice of both genders with contrast agent (4% Paraformaldehyde, 0.05M Gadoteridole, 0.01M Phosphate buffered saline, pH=7.4), cranium containing the whole brain was scanned overnight by the 9.4T MRI scanner. The volumes of 39 brain regions were quantified according to the mouse brain atlas [3]. Student's t-test and two-way ANOVA were used to evaluate statistical significance of between-group differences. Results: Adult 2C19TG mice are hyperdopaminergic, as they exhibit 15% increased dopamine concentration (p<0.001). They also show hyperkinetic motoric phenotype with the ataxia-like walking pattern and pathological clasping reflex. In the beam walking test 2C19TG mice had 20% longer beam crossing time (p=0.007) and 60% more paw slips (p<0.001) then the controls, and this motoric impairment could not be improved with antidopaminergic drugs. Both younger and older 2C19TG mice exhibited only a marginal reduction in the number of dopaminergic neurons of both substantia nigra and ventral tegmental area in a subset of coronal sections. This was confirmed by the gadolinium-enhanced neuroimaging that showed no change in substantia nigra volume in 2C19TG mice. On the other hand, significant differences in volume were identified in 11 regions, including cerebellum (-8.3% p<0.001) and striatum (+3.0%, p<0.001), which are the regions connected with the motoric function. The volumetric changes were detected in the hippocampus (-1.3%, p=0.027), amygdala (+2.8%, p<0.001), septum (+3.3%, p=0.014) and nucleus accumbens (+3.5, p=0.004) of 2C19TG mice. These brain regions are involved in emotional and motivational functions. Conclusion: Ataxia-like motoric phenotype in 2C19TG transgenic mice is probably caused by changes in cerebellum, while hyperdopaminergism is most likely the compensatory adaptation, whereas the changes in the hippocampus, amygdala, septum, and nucleus accumbens may be connected with the mutants’ depression-like phenotype and susceptibility to stress. Therefore, CYP2C19 transgenic mouse in potentially useful model of hyperkinetic disorders, and our findings hint at the possible impact of CYP2C19 enzyme on the development of the several brain regions involved in motor and emotional functioning.33rd ECNP Congress – Vienna 202

Developmental Hippocampal Neuroplasticity in a Model of Nicotine Replacement Therapy during Pregnancy and Breastfeeding

The influence of developmental nicotine exposure on the brain represents an important health topic in light of the popularity of nicotine replacement therapy (NRT) as a smoking cessation method during pregnancy.In this study, we used a model of NRT during pregnancy and breastfeeding to explore the consequences of chronic developmental nicotine exposure on cerebral neuroplasticity in the offspring. We focused on two dynamic lifelong phenomena in the dentate gyrus (DG) of the hippocampus that are highly sensitive to the environment: granule cell neurogenesis and long-term potentiation (LTP).Pregnant rats were implanted with osmotic mini-pumps delivering either nicotine or saline solutions. Plasma nicotine and metabolite levels were measured in dams and offspring. Corticosterone levels, DG neurogenesis (cell proliferation, survival and differentiation) and glutamatergic electrophysiological activity were measured in pups.Juvenile (P15) and adolescent (P41) offspring exposed to nicotine throughout prenatal and postnatal development displayed no significant alteration in DG neurogenesis compared to control offspring. However, NRT-like nicotine exposure significantly increased LTP in the DG of juvenile offspring as measured in vitro from hippocampal slices, suggesting that the mechanisms underlying nicotine-induced LTP enhancement previously described in adult rats are already functional in pups.These results indicate that synaptic plasticity is disrupted in offspring breastfed by dams passively exposed to nicotine in an NRT-like fashion

Brain CYP2E1 is induced by nicotine and ethanol in rat and is higher in smokers and alcoholics

Ethanol and nicotine are commonly coabused drugs. Cytochrome P 450 2E1 (CYP2E1) metabolizes ethanol and bioactivates tobacco-derived procarcinogens. Ethanol and nicotine can induce hepatic CYP2E1 and we hypothesized that both centrally active drugs could also induce CYP2E1 within the brain. Male rats were treated with saline, ethanol (3.0 g kg −1 by gavage) or nicotine (1.0 mg kg −1 s.c.) for 7 days. Ethanol treatment significantly increased CYP2E1 in olfactory bulbs (1.7-fold), frontal cortex (2.0-fold), hippocampus (1.9-fold) and cerebellum (1.8-fold), while nicotine induced CYP2E1 in olfactory bulbs (2.3-fold), frontal cortex (3.0-fold), olfactory tubercle (3.1-fold), cerebellum (2.5-fold) and brainstem (2.0-fold). Immunocytochemical analysis revealed that the induction was cell-type specific. Consistent with the increased CYP2E1 found in rat brain following drug treatments, brains from alcoholics and alcoholic smokers showed greater staining of granular cells of the dentate gyrus and the pyramidal cells of CA2 and CA3 hippocampal regions as well as of cerebellar Purkinje cells compared to nonalcoholic nonsmokers. Moreover, greater CYP2E1 immunoreactivity was observed in the frontal cortices in the alcoholic smokers in comparison to nonalcoholic nonsmokers and alcoholic nonsmokers. To investigate if nicotine could contribute to the increased CYP2E1 observed in alcoholic smokers, we treated human neuroblastoma IMR-32 cells in culture and found significantly higher CYP2E1 immunostaining in nicotine-treated cells (0.1–10 n M ). CYP2E1 induction in the brain, by ethanol or nicotine, may influence the central effects of ethanol and the development of nervous tissue pathologies observed in alcoholics and smokers

Induction of the drug metabolizing enzyme CYP2D in monkey brain by chronic nicotine treatment

Cytochrome P450 (CYP) 2D6, an enzyme found in the liver and the brain, is involved in the metabolism of numerous centrally acting drugs (e.g. antidepressants, neuroleptics, opiates), endogenous neurochemicals (e.g. catecholamines) and in the inactivation of neurotoxins (e.g. pesticides, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)). Although CYP2D6 is essentially an uninducible enzyme in the liver, we show that smokers have higher CYP2D6 in the brain, especially in the basal ganglia. In order to determine whether nicotine, a component of cigarette smoke, could increase brain CYP2D, African Green monkeys were treated chronically with nicotine (0.05 mg/kg for 2 days, then 0.15 mg/kg for 2 days followed by 0.3 mg/kg for 18 days s.c., b.i.d.). Monkeys treated with nicotine showed significant induction of CYP2D in brain when compared to saline-treated animals as detected by western blotting and immunocytochemistry. No changes in liver CYP2D were observed in nicotine-treated monkeys. Induction was observed in various brain regions including those affected in Parkinson's disease (PD) such as substantia nigra (3-fold, p = 0.01), putamen (2.1-fold, p = 0.001) and brainstem (2.4-fold, p = 0.001), with the caudate nucleus approaching significance (1.6-fold, p = 0.07). Immunocytochemistry revealed that the expression of CYP2D in both saline- and nicotine-treated monkeys is cell-specific particularly in the cerebellum, frontal cortex and hippocampus. These results suggest that monkey brain expresses CYP2D, which is induced in specific cells and brain regions upon chronic nicotine treatment. Smokers, or those using nicotine treatment, may have higher levels of brain CYP2D6 that may result in altered localized CNS drug metabolism and inactivation of neurotoxins

Smoking, alcoholism and genetic polymorphisms alter CYP2B6 levels in human brain

CYP2B6 metabolizes drugs such as nicotine and bupropion, and many toxins and carcinogens. Nicotine induces CYP2B1 in rat brain and in humans polymorphic variation in CYP2B6 affects smoking cessation rates. The aim of this study was to compare CYP2B6 expression in brains of human smokers and non-smokers and alcoholics and non-alcoholics ( n=26). CYP2B6 expression was brain region-specific, and was observed in both neurons and astrocytes. CYP2B6 levels were higher in brains of smokers and alcoholics, particularly in cerebellar Purkinje cells and hippocampal pyramidal neurons, cells known to be damaged in alcoholics. Significantly more ( p<0.05) CYP2B6 protein was seen in four brain regions of smoking alcoholics compared to non-smoking non-alcoholics: hippocampus (5.8-fold), caudate nucleus (3.3-fold), putamen (3.0-fold) and cerebellar hemisphere (1.6-fold). The genetic variant C1459T (R487C) has been associated with reduced hepatic enzyme levels, stability and activity. Preliminary genotyping of this small sample ( n=24) suggested that individuals with the CC genotype had higher brain CYP2B6 than those with the CT or TT genotype. Higher brain CYP2B6 activity in smokers and alcoholics may cause altered sensitivity to centrally acting drugs, increased susceptibility to neurotoxins and carcinogenic xenobiotics and contribute to central tolerance to nicotine

The neuroprotective enzyme CYP2D6 increases in the brain with age and is lower in Parkinson's disease patients

Cytochrome P450 2D6 (CYP2D6) is a drug-metabolizing enzyme expressed in the brain that also metabolizes endogenous neural compounds (e.g., catecholamines) and inactivates neurotoxins (e.g., 1-methyl-4-thenyl-1,2,3,6-tetrahydropyridine; MPTP). Genetically poor CYP2D6 metabolizers are at higher risk for developing Parkinson's disease (PD), a risk that increases with exposure to pesticides. As age is a risk factor for PD we measured the ontogenic expression of CYP2D6 in human brain, and compared brain CYP2D6 levels in PD cases with age-matched controls. CYP2D6 increased from fetal to 80 years of age (n = 76), exhibiting 3 distinct phases of change. Compared with PD controls, PD cases had approximately 40% lower CYP2D6 levels in the frontal cortex, cerebellum, and the hippocampus, even when controlling for CYP2D6 genotype. In contrast, CYP2D6 levels in cases were similar to controls in PD-affected brain areas, the substantia nigra, and caudate, consistent with higher astrocytic and cellular CYP2D6 staining observed in PD cases. In summary, the lower CYP2D6 levels in PD cases may have reduced their ability to inactivate PD-causing neurotoxins contributing to their disease risk

Sex difference in dopamine D1-D2 receptor complex expression and signaling affects depression- and anxiety-like behaviors

Abstract Depression and anxiety are more common among females than males and represent a leading cause of disease-related disability in women. Since the dopamine D1-D2 heteromer is involved in depression- and anxiety-like behavior, the possibility that the receptor complex may have a role in mediating sex differences in such behaviors and related biochemical signaling was explored. In non-human primate caudate nucleus and in rat striatum, females expressed higher density of D1-D2 heteromer complexes and a greater number of D1-D2 expressing neurons compared to males. In rat, the sex difference in D1-D2 expression levels occurred even though D1 receptor expression was lower in female than in male with no difference in D2 receptor expression. In behavioral tests, female rats showed faster latency to depressive-like behavior and a greater susceptibility to the pro-depressive and anxiogenic-like effects of D1-D2 heteromer activation by low doses of SKF 83959, all of which were ameliorated by the selective heteromer disrupting peptide, TAT-D1. The sex difference observed in the anxiety test correlated with differences in low-frequency delta and theta oscillations in the nucleus accumbens. Analysis of signaling pathways revealed that the sex difference in D1-D2 heteromer expression led to differences in basal and heteromer-stimulated activities of two important signaling pathways, BDNF/TrkB and Akt/GSK3/β-catenin. These results suggest that the higher D1-D2 heteromer expression in female may significantly increase predisposition to depressive-like and anxiety-like behavior in female animals