The highly prevalent parasite Toxoplasma gondii manipulates its host's behavior. In infected rodents, the behavioral changes increase the likelihood that the parasite will be transmitted back to its definitive cat host, an essential step in completion of the parasite's life cycle. The mechanism(s) responsible for behavioral changes in the host is unknown but two lines of published evidence suggest that the parasite alters neurotransmitter signal transduction: the disruption of the parasite-induced behavioral changes with medications used to treat psychiatric disease (specifically dopamine antagonists) and identification of a tyrosine hydroxylase encoded in the parasite genome. In this study, infection of mammalian dopaminergic cells with T. gondii enhanced the levels of K+-induced release of dopamine several-fold, with a direct correlation between the number of infected cells and the quantity of dopamine released. Immunostaining brain sections of infected mice with dopamine antibody showed intense staining of encysted parasites. Based on these analyses, T. gondii orchestrates a significant increase in dopamine metabolism in neural cells. Tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, was also found in intracellular tissue cysts in brain tissue with antibodies specific for the parasite-encoded tyrosine hydroxylase. These observations provide a mechanism for parasite-induced behavioral changes. The observed effects on dopamine metabolism could also be relevant in interpreting reports of psychobehavioral changes in toxoplasmosis-infected humans.

Parkinson's disease (PD) is the second most common neurodegenerative disease, affecting over a million people in the United States alone, and is characterized by rigidity, bradykinesia, resting tremor, and postural instability. Its main neuropathological feature is the loss of dopaminergic neurons of the substantia nigra pars compacta. However, the pathogenesis of this loss is not understood fully. One of the earliest biochemical changes seen in PD is a reduction in the levels of total glutathione, a key cellular antioxidant. Traditionally, it has been thought that this decrease in GSH levels is the consequence of increased oxidative stress, a process heavily implicated in PD pathogenesis. However, emerging evidence suggests that GSH depletion may itself play an active role in PD pathogenesis. This review aims to explore the contribution of GSH depletion to PD pathogenesis.

Parkinson’s disease is a neurodegenerative disorder that can, at least partly, be mimicked by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. S100B is a calcium-binding protein expressed in, and secreted by, astrocytes. There is increasing evidence that S100B acts as a cytokine or damage-associated molecular pattern protein not only in inflammatory but also in neurodegenerative diseases. In this study, we show that S100B protein levels were higher in post-mortem substantia nigra of patients with Parkinson’s disease compared with control tissue, and cerebrospinal fluid S100B levels were higher in a large cohort of patients with Parkinson’s disease compared with controls. Correspondingly, mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine showed upregulated S100B messenger RNA and protein levels. In turn, ablation of S100B resulted in neuroprotection, reduced microgliosis and reduced expression of both the receptor for advanced glycation endproducts and tumour necrosis factor-α. Our results demonstrate a role of S100B in the pathophysiology of Parkinson’s disease. Targeting S100B may emerge as a potential treatment strategy in this disorder.

Molecular recognition reagents are key tools for understanding biological processes and are used universally by scientists to study protein expression, localisation and interactions. Antibodies remain the most widely used of such reagents and many show excellent performance, although some are poorly characterised or have stability or batch variability issues, supporting the use of alternative binding proteins as complementary reagents for many applications. Here we report on the use of Affimer proteins as research reagents. We selected 12 diverse molecular targets for Affimer selection to exemplify their use in common molecular and cellular applications including the (a) selection against various target molecules; (b) modulation of protein function in vitro and in vivo; (c) labelling of tumour antigens in mouse models; and (d) use in affinity fluorescence and super-resolution microscopy. This work shows that Affimer proteins, as is the case for other alternative binding scaffolds, represent complementary affinity reagents to antibodies for various molecular and cell biology applications.DOI: http://dx.doi.org/10.7554/eLife.24903.001

SummaryParasite location has been proposed as an important factor in the behavioural changes observed in rodents infected with the protozoan Toxoplasma gondii. During the chronic stages of infection, encysted parasites are found in the brain but it remains unclear whether the parasite has tropism for specific brain regions. Parasite tissue cysts are found in all brain areas with some, but not all, prior studies reporting higher numbers located in the amygdala and frontal cortex. A stochastic process of parasite location does not, however, seem to explain the distinct and often subtle changes observed in rodent behaviour. One factor that could contribute to the specific changes is increased dopamine production by T. gondii. Recently, it was found that cells encysted with parasites in the brains of experimentally infected rodents have high levels of dopamine and that the parasite encodes a tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of this neurotransmitter. A mechanism is proposed that could explain the behaviour changes due to parasite regulation of dopamine. This could have important implications for T. gondii infections in humans.