Systemic treatment of mice with the herbicide paraquat causes the selective loss of nigrostriatal dopaminergic neurons, reproducing the primary neurodegenerative feature of Parkinson's disease. To elucidate the role of oxidative damage in paraquat neurotoxicity, the time-course of neurodegeneration was correlated to changes in 4-hydroxy-2-nonenal (4-HNE), a lipid peroxidation marker. When mice were exposed to three weekly injections of paraquat, no nigral dopaminergic cell loss was observed after the first administration, whereas a significant reduction of neurons followed the second exposure. Changes in the number of nigral 4-HNE-positive neurons suggest a relationship between lipid peroxidation and neuronal death, since a dramatic increase in this number coincided with the onset and development of neurodegeneration after the second toxicant injection. Interestingly, the third paraquat administration did not cause any increase in 4-HNE-immunoreactive cells, nor did it produce any additional dopaminergic cell loss. Further evidence of paraquat-induced oxidative injury derives from the observation of nitrotyrosine immunoreactivity in the substantia nigra of paraquat-treated animals and from experiments with ferritin transgenic mice. These mice, which are characterized by a decreased susceptibility to oxidative stress, were completely resistant to the increase in 4-HNE-positive neurons and the cell death caused by paraquat. Thus, paraquat exposure yields a model that emphasizes the susceptibility of dopaminergic neurons to oxidative damage.

Certain modified gravity theories predict the existence of an additional, non-conformally coupled scalar field. A disformal coupling of the field to the Cosmic Microwave Background (CMB) is shown to affect the evolution of the energy density in the radiation fluid and produces a modification of the distribution function of the CMB, which vanishes if photons and baryons couple in the same way to the scalar. We find the constraints on the couplings to matter and photons coming from the measurement of the CMB temperature evolution and from current upper limits on the µ-distortion of the CMB spectrum. We also point out that the measured equation of state of photons differs from wγ = 1/3 in the presence of disformal couplings. PACS numbers:Among the extensions of General Relativity (GR) which have attracted a lot of attention in the literature are scalar-tensor theories, which are also well motivated by some extensions of the standard model such as theories with extra spatial dimensions. In cosmology, those theories have been studied in the context of inflation and models for dark energy as they provide a natural mechanism to drive a period of accelerated expansion in the very early or late universe, see e.g. [1][2][3]. There are some open questions regarding scalar-tensor theories, such as whether the Einstein frame (EF) or Jordan frame (JF) formulation of a given theory is the most "physical", see e.g. [4] and references therein for a discussion.The EF is the frame in which the gravity and scalar sector look like GR plus a scalar field, but matter fields feel a metric which is usually conformally related to the EF metric g µν . In the JF formulation of the theory, matter fields are uncoupled to the scalar, but the spin-2 and spin-0 fields are coupled in a non-trivial way. One could also consider more general transformations of the metric, in which the EF and the JF metrics are not related by a conformal transformation, but a so-called disformal transformation, which includes derivatives of the scalar field (see the definition in Eq. (2) In this paper, we consider scalar-tensor theories with disformally coupled scalar fields and study in particular the consequences on the properties of the CMB. We express observables in terms of the metric a (baryonic) observer feels, to side-step the question about a frameindependent formulation for disformally coupled fields. * Email address: C.vandeBruck@sheffield.ac.uk † Email address: app12jam@sheffield.ac.uk ‡ Email address: Susan.Vu@sheffield.ac.ukFrame-independence in conformally coupled theories has been discussed in [14,15]. The theory we consider is given in the EF aswhere the different matter fields χ i propagate on geodesics for metrics given bỹFrom now on, reduced Planck units are assumed: c = = k B = M Pl = 1. We consider a cosmological setting for eq. (1), where g µν is the standard flat FRW metric, with dsVariation of the action with respect to the fields yields the Klein-Gordon equation for the scalar field φ and the energy conservation equations:where the couplin...

We study the effect of sudden transitions in the effective Planck mass during inflation on primordial power spectra. Specifically, we consider models in which this variation results from the non-minimal coupling of a Brans-Dicke type scalar field. We find that the scalar power spectra develop features at the scales corresponding to those leaving the horizon during the transition. In addition, we observe that the tensor perturbations are largely unaffected, so long as the variation of the Planck mass is below the percent level. Otherwise, the tensor power spectra exhibit damped oscillations over the same scales. Due to significant features in the scalar power spectra, the tensor-to-scalar ratio r shows variation over the corresponding scales. Thus, by studying the spectra of both scalar and tensor perturbations, one can constrain sudden but small variations of the Planck mass during inflation. We illustrate these effects with a number of benchmark singleand two-field models. In addition, we comment on their implications and the possibility to alleviate the tension between the observations of the tensor-to-scalar ratio performed by the Planck and BICEP2 experiments.

The evolution of the nonadiabatic pressure perturbation during inflation driven by two scalar fields is studied numerically for three different types of models. In the first model, the fields have standard kinetic terms. The other two models considered feature noncanonical kinetic terms, the first containing two fields which are coupled via their kinetic terms and the second where one field has the standard kinetic term with the other field being a Dirac-Born-Infeld field. We find that the evolution and the final amplitude of the nonadiabatic pressure perturbation depends strongly on the kinetic terms.

No abstract