Soluble factors released by Toxoplasma gondii-infected astrocytes down-modulate nitric oxide production by gamma interferon-activated microglia and prevent neuronal degeneration

The maintenance of a benign chronic Toxoplasma gondii infection is mainly dependent on the persistent presence of gamma interferon (IFN-gamma) in the central nervous system (CNS). However, IFN-gamma-activated microglia are paradoxically involved in parasitism control and in tissue damage during a broad range of CNS pathologies. In this way, nitric oxide (NO), the main toxic metabolite produced by IFN-gamma-activated microglia, may cause neuronal injury during T. gondii infection. Despite the potential NO toxicity, neurodegeneration is not a common finding during chronic T. gondii infection. In this work, we describe a significant down-modulation of NO production by IFN-gamma-activated microglia in the presence of conditioned medium of T. gondii-infected astrocytes (CMi). The inhibition of NO production was paralleled with recovery of neurite outgrowth when neurons were cocultured with IFN-gamma-activated microglia in the presence of CMi. Moreover, the modulation of NO secretion and the neuroprotective effect were shown to be dependent on prostaglandin E(2) (PGE(2)) production by T. gondii-infected astrocytes and autocrine secretion of interleukin-10 (IL-10) by microglia. These events were partially eliminated when infected astrocytes were treated with aspirin and cocultures were treated with anti-IL-10 neutralizing antibodies and RP-8-Br cyclic AMP (cAMP), a protein kinase A inhibitor. Further, the modulatory effects of CMi were mimicked by the presence of exogenous PGE(2) and by forskolin, an adenylate cyclase activator. Altogether, these data point to a T. gondii-triggered regulatory mechanism involving PGE(2) secretion by astrocytes and cAMP-dependent IL-10 secretion by microglia. This may reduce host tissue inflammation, thus avoiding neuron damage during an established Th1 protective immune response.     

Solubilization and immunological identification of presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in the rat hippocampus

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have been identified mostly as postsynaptic receptors mediating fast glutamatergic synaptic transmission. However, neurochemical studies based on the modulation of neurotransmitter release have suggested the existence of presynaptic AMPA receptors. We have used a recently described technique that allows a high-purity fractionation of the pre- and postsynaptic proteins of synaptic junctions to evaluate the distribution of the different AMPA receptor subunits in rat hippocampal synapses. Surprisingly, we found very high levels of GluR1- and GluR2/3-like immunoreactivity in the presynaptic fraction, but also in the postsynaptic and extrasynaptic fractions. GluR4-like immunoreactivity was much less abundant but was still detected, predominantly in the postsynaptic fraction. This methodology appears to be far more sensitive than the classical immunogold electron microscopy to determine the localization of synaptic receptors.     

Toxoplasma gondii prevents neuron degeneration by interferon-gamma-activated microglia in a mechanism involving inhibition of inducible nitric oxide synthase and transforming growth factor-beta1 production by infected microglia

Interferon (IFN)-gamma, the main cytokine responsible for immunological defense against Toxoplasma gondii, is essential in all infected tissues, including the central nervous system. However, IFN-gamma-activated microglia may cause tissue injury through production of toxic metabolites such as nitric oxide (NO), a potent inducer of central nervous system pathologies related to inflammatory neuronal disturbances. Despite potential NO toxicity, neurodegeneration is not commonly found during chronic T. gondii infection. In this study, we describe decreased NO production by IFN-gamma-activated microglial cells infected by T. gondii. This effect involved strong inhibition of iNOS expression in IFN-gamma-activated, infected microglia but not in uninfected neighboring cells. The inhibition of NO production and iNOS expression were parallel with recovery of neurite outgrowth when neurons were co-cultured with T. gondii-infected, IFN-gamma-activated microglia. In the presence of transforming growth factor (TGF)-beta1-neutralizing antibodies, the beneficial effect of the parasite on neurons was abrogated, and NO production reverted to levels similar to IFN-gamma-activated uninfected co-cultures. In addition, we observed Smad-2 nuclear translocation, a hallmark of TGF-beta1 downstream signaling, in infected microglial cultures, emphasizing an autocrine effect restricted to infected cells. Together, these data may explain a neuropreservation pattern observed during immunocompetent host infection that is dependent on T. gondii-triggered TGF-beta1 secretion by infected microglia.     

Linkage analysis in Usher syndrome type I (USH1) families from Spain.

Usher syndrome (USH) is an autosomal recessive hereditary disorder characterised by congenital sensorineural hearing loss and gradual visual impairment secondary to retinitis pigmentosa (RP). The disorder is clinically and genetically heterogeneous. With regard to Usher type I (USH1), several subtypes have been described, the most frequent being USH1B located on chromosome 11q13.5. Of 18 USH1 families studied by linkage analysis, 12 (67%) showed significant lod score values for locus D11S527 (Zmax=14.032, theta=0.000) situated on chromosome 11q. Our findings suggest considerable genetic heterogeneity in the Spanish USH1 population. It is important to note that one of our families linked to the USH1B locus shows interesting intrafamilial clinical variability. As regards the remaining six USH1 families, the linkage analysis did not provide conclusive data, although two of them show slight linkage to markers located on chromosome 3q (Zmax=1.880, theta=0.000 for D3S1279), the same location that had previously been assigned to some USH3 families.     

A sodium-activated potassium current in intact ventricular myocytes isolated from the guinea-pig heart

A current generated by the Na-activated K channel has been identified in whole cell currents recorded from isolated guinea-pig ventricular myocytes. A partial activation of this current can be achieved near to the physiological range of intracellular sodium concentration [( Na+]i) when it contributes significantly to the global outward current. The decline of the Na-activated K current, the lengthening of the action potential duration and the recovery of [Na+]i occur with a similar time course during recovery from Na loading.     

The Na+-activated K+ channel contributes to K+ efflux in Na+-loaded guinea-pig but not rat ventricular myocytes

Activation of the Na+-activated K+ channels (KNa channels) has been suggested to contribute to the ischaemia-induced accumulation of extracellular K+ (K+e) in the mammalian myocardium. Recent evidence shows that these channels are not present in rat ventricular myocytes [9]. We have therefore investigated the effect of raised intracellular Na+ activity (aiNa) on intracellular K+ activity (aiK) in guinea-pig myocytes, which possess the channels, and on rat ventricular myocytes which do not. The Na+-activated K+ current was activated by an increase in aiNa induced by removing extracellular Ca2+ and Mg2+ and inhibiting the Na-pump. The aiNa increased and the aiK decreased in both guinea-pig and rat myocytes superfused with Ca2+- and Mg2+-free Tyrode. The new steady-state increase in aiNa and decline in aiK were similar in both species. Inhibition of the Na-pump resulted in an additional increase in aiNa and decrease in aiK in both species. However, both the increase in aiNa and decrease in aiK were greater in guinea-pig myocytes and the decline in aiK in guinea-pig myocytes followed the development of a large Na+-activated K+ current. When Li+ replaced Na+ in the superfusate the Na+-activated K+ current did not develop and the fall in aiK was reduced. In Na+-loaded rat myocytes, which do not have a Na+-activated K+ current, the decline in aiK was reduced and blocked by 2 mM Mg2+ suggesting that a Mg2+-sensitive non-specific cation channel may be involved in the K+ efflux from rat myocytes [12]. These data suggest that KNa channels are a major route for K+ efflux from Na+-loaded guinea-pig myocytes.     

Melanocytes in the Testes of Eupemphix nattereri (Anura,Leiuperidae): Histological,Stereological, and Ultrastructural Aspects

Ectothermic vertebrates have a well‐developed system of melanin‐containing cells, which localize in several organs and tissues and compose an extracutaneous pigmentary system. This research aimed at characterizing histological and ultrastructural patterns of pigmented cells in the testes of the anura Eupemphix nattereri (Steindachner, 1963), including the stereological and quantitative evaluation of this cell type in the gonads. Ten adult males were collected in Nova Itapirema, São Paulo, Brazil, and submitted to morphological studies with light and transmission electron microscopy. The testis presents a great number of large cells with many brown granules and long cytoplasmic processes. The pigmented cells found in the testis are structurally similar to melanocytes, characterized by large amounts of melanosomes. The cells may be in intimate contact with the same cell type, with myoid cells surrounded by a large amount of collagen fibers, Leydig cells, and next to fibroblasts. The distribution and amount of extracutaneous melanocytes is variable when other organs and membranes are analyzed, allowing the establishment of species‐specific patterns for the extracutaneous pigmentary system. Anat Rec, 2007. © 2007 Wiley‐Liss, Inc.     

DNA damage in cytologically normal urothelial cells of patients with a history of urothelial cell carcinoma

In order to determine if patients with a history of previous urothelial cell carcinoma (UCC) but with current normal urinary cytology have DNA damage in urothelial cells, the single-cell gel electrophoresis (comet) assay was conducted with cells obtained by urinary bladder washings from 44 patients (28 with a history of previous UCC). Increased DNA damage was observed in cytologically "normal" urothelial cells of patients with a history of UCC when compared with referents with no similar history and after correcting the data for smoking status and age (P < 0.018). Increased DNA damage also correlated with the highest tumor grade, irrespective of time or course of the disease after clinical intervention (Kendall tau correlation, 0.37, P = 0.016). Moreover, aneuploidy, as assessed by DNA content ratio (DCR; 75th/25th percentile of total DNA fluorescence of 50 comets/patient) was unaltered by smoking status, but increased with UCC grade: 1.39 +/- 0.12 (median +/- 95% confidence interval; referents); 1.43 +/- 0.11 (Grade I UCC; P = 0.264, against referents); 1.49 +/- 0.16 (Grade II UCC; P = 0.057); 1.57 +/- 0.16 (Grade III UCC; P = 0.003). Micronucleated urothelial cells (MNC) were also scored on Giemsa-stained routine cytological smears and were found not to correlate with DNA damage or DCR. MNC frequencies were higher for patients with a history of UCC and/or smoking than referents with neither history, but there was no statistical difference between groups. Taken together, these results suggest that the normal-appearing urothelium of patients resected for UCC still harbor genetically unstable cells.