Transgenerational transduction of MPTP-induced alterations in a Parkinson's disease mouse model.

Susceptibility to Parkinson's disease (PD) increases more than threefold in first-degree relatives of PD patients. Using a mouse model, we investigated in a proof-of-principle approach whether toxin exposure of F0 affects the F1 generation. We provide first evidence that disturbance of the nigrostriatal pathway can be transferred to the next generation.

Deficiency of Aph1B/C-gamma-secretase disturbs Nrg1 cleavage and sensorimotor gating that can be reversed with antipsychotic treatment.

Regulated intramembrane proteolysis by gamma-secretase cleaves proteins in their transmembrane domain and is involved in important signaling pathways. At least four different gamma-secretase complexes have been identified, but little is known about their biological role and specificity. Previous work has demonstrated the involvement of the Aph1A-gamma-secretase complex in Notch signaling, but no specific function could be assigned to Aph1B/C-gamma-secretase. We demonstrate here that the Aph1B/C-gamma-secretase complex is expressed in brain areas relevant to schizophrenia pathogenesis and that Aph1B/C deficiency causes pharmacological and behavioral abnormalities that can be reversed by antipsychotic drugs. At the molecular level we find accumulation of Nrg1 fragments in the brain of Aph1BC(-/-) mice. Our observations gain clinical relevance by the demonstration that a Val-to-Leu mutation in the Nrg1 transmembrane domain, associated with increased risk for schizophrenia, affects gamma-secretase cleavage of Nrg1. This finding suggests that dysregulation of intramembrane proteolysis of Nrg1 could increase risk for schizophrenia and related disorders.

Quantitative [(123)I]FP-CIT pinhole SPECT imaging predicts striatal dopamine levels, but not number of nigral neurons in different mouse models of Parkinson's disease.

Single photon emission computed tomography (SPECT) using [(123)I]FP-CIT as radioligand for the dopamine transporter has become a widely used tool to monitor the integrity of the nigrostriatal dopaminergic projection in Parkinson's disease (PD). Previous studies with pinhole SPECT in small animals have demonstrated that the striatal [(123)I]FP-CIT binding indeed correlates with the striatal dopamine transporter protein level. It is unclear, however, if there is a stable relationship between the striatal [(123)I]FP-CIT binding and other functionally important parameters of the nigrostriatal system, such as the striatal dopamine levels and the number of dopaminergic neurons in the substantia nigra. To assess this question experimentally, we studied two different mouse models of PD, namely a mild 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication paradigm, to model mild nigrostriatal damage and the intrastriatal 6-hydroxydopamine paradigm to model more advanced nigrostriatal damage. Our data demonstrate that the striatal [(123)I]FP-CIT binding measured by SPECT in vivo precisely predicts the striatal dopamine concentrations, but does not necessarily correlate with the nigral dopaminergic cell number. Thus, the present work underscores that FP-CIT SPECT does only allow judging the integrity of the striatal dopaminergic nerve terminals, but not the nigral dopaminergic cells in PD. This finding may have significant impact on the use of [(123)I]FP-CIT SPECT as a surrogate marker for clinical trials aimed at measuring neuroprotection.

Effect of repeated treatment with high doses of selegiline on behaviour, striatal dopaminergic transmission and tyrosine hydroxylase mRNA levels.

The anti-parkinsonian drug selegiline is a monoamine oxidase B (MAO-B) inhibitor and a potential neuroprotective agent which facilitates dopaminergic transmission. Its metabolites (-)-amphetamine and (-)-metamphetamine might contribute to the pharmacological effects as they are also able to increase dopaminergic transmission and in addition might lead to behavioural sensitization after repeated administration. We investigated the effects of acute and repeated treatment with a high dose of selegiline on dopamine overflow in the striatum as well as on behaviour and on tyrosine hydroxylase (TH) mRNA levels in midbrain. Two experiments were performed. In the first one, rats were implanted with microdialysis probes into the striatum and received daily injections of selegiline (10 mg/kg, i.p.) for 1 or 8 days or a single dose of saline. In vivo microdialysis was carried out on days 1, 8 or 17 (after withdrawal of 9 days) to measure dopamine overflow. Motility was measured at the same time. In the second experiment, rats were injected daily with selegiline (10 mg/kg, i.p.) or saline over a time period of 6 weeks or only once before the brains were processed for in situ hybridization with a (35)S-radiolabelled probe for TH. Repeated treatment led to higher levels in motility scores than acute administration after administration of the same dose, indicating behavioural sensitization, which was still manifest after an interruption of 9 days in the supply of selegiline. In contrast, acute administration of selegiline increased dopamine levels to a similar degree as the same dose after subchronic treatment, with or without interruption of 9 days. The dopamine metabolite DOPAC was reduced by more than 50% after acute administration of selegiline and even more so on day 8 by the same dose, after repeated administration. The basal concentrations of dopamine (before challenge with selegiline) were not altered by the repeated administration, whereas the basal concentrations of DOPAC were decreased by more than 80% by the repeated administration of selegiline, suggesting a decrease in dopamine turnover. Acute administration did not have any influence on TH mRNA levels, whereas chronic treatment significantly reduced TH mRNA levels in substantia nigra and ventral tegmental area. In conclusion, repeated administration of selegiline leads to behavioural sensitization independent of altered dopamine levels. In addition, it leads to a decrease, probably due to a down-regulation, of dopamine turnover and tyrosine hydroxylase.

Sensitization to the behavioural effects of cocaine: alterations in tyrosine hydroxylase or endogenous opioid mRNAs are not necessarily involved.

After repeated administration of cocaine at intervals, sensitization phenomena can be observed, so that its behavioural effects are enhanced. Since this phenomenon is long-lasting, it was of interest to study which persistent alterations in the activity of dopaminergic neurones or of endogenous opioid systems downstream of dopaminergic synapses in the basal ganglia are involved in the sensitization. Cocaine (10 mg/kg i.p.) was administered to rats on days 1, 3, 5 and 7 and saline on days 2, 4 and 6 ("repeated cocaine"), or saline was injected on days 1-6 and cocaine on day 7 ("acute cocaine"), or saline was injected on days 1-7 ("saline group"). The "repeated cocaine" schedule led to a significant sensitization to the locomotor activation produced by cocaine on day 7 or on day 17, 10 days after the end of sensitization protocol. Microdialysis in the nucleus accumbens which was performed after administration of cocaine (10 mg/kg i.p.) on day 7, or after an administration of the same dose 10 days after the last administration of cocaine, respectively, revealed significant acute increases of extracellular dopamine to about 200% of basal values. These increases were similar in "acute cocaine" and in "repeated cocaine" animals both after 7 days and after 17 days. For in situ hybridization studies, rats were sacrificed on day 7, 4.5 h after the last cocaine or saline administration. The mRNA for tyrosine hydroxylase (TH) in substantia nigra + ventral tegmental area was significantly elevated to about 140% of saline controls both in the "repeated cocaine" and the "acute cocaine" group as compared with the "saline group". In contrast, there were no differences between the three groups in the mRNAs of preprodynorphin or preproenkephalin levels measured in the nucleus accumbens (core and shell). These results suggest that sensitization phenomena to cocaine are not necessarily connected with alterations in the dopaminergic activity in the mesolimbic system or in the transcription of precursors of endogenous opioid peptides which are located downstream of the dopaminergic synapses.