Joel Felipe Horn

Quinolinic acid promotes seizures and decreases glutamate uptake in young rats: reversal by orally administered guanosine

Quinolinic acid (QA) has been used as a model for experimental overstimulation of the glutamatergic system. Glutamate uptake is the main mechanism involved in the maintenance of extracellular glutamate below toxic levels. Guanosine systemically administered prevents quinolinic acid-induced seizures in adult mice and increases basal glutamate uptake by cortical astrocyte culture and slices from young rats. The immature brain differs from the adult brain in its susceptibility to seizures, seizure characteristics, and responses to antiepileptic drugs (AED). Here we investigated the effect of guanosine p.o. on QA-induced seizures in young rats (P12-14) and upon ex vivo glutamate uptake by cortical slices from these animals. I.c.v. infusion of 250 nmol QA induced seizures in all animals and decreased glutamate uptake. I.p. injection of MK-801 and phenobarbital 30 min before QA administration prevented seizures in all animals. Guanosine (7.5 mg/kg) 75 min before QA prevented seizures in 50% of animals as well as prevented the decrease of glutamate uptake in the protected animals. To investigate if the anticonvulsive effect of guanosine was specific for QA-induced seizures, the picrotoxin-induced seizures model was also performed. Pretreatment with phenobarbital i.p. (60 mg/kg-30 min) prevented picrotoxin-induced seizures in all animals, whereas guanosine p.o. (7.5 mg/kg-75 min) and MK-801 i.p. (0.5 mg/kg-30 min) had no effect. Thus, guanosine protection on the QA-induced seizures in young rats and on the decrease of glutamate uptake showed some specificity degree towards the QA-induced toxicity. This points that guanosine could be considered for treatments of epilepsy, and possibly other neurological disorders in children.

Phosphorylation of glial fibrillary acidic protein is stimulated by glutamate via NMDA receptors in cortical microslices and in mixed neuronal/glial cell cultures prepared from the cerebellum

In previous work we showed that phosphorylation of glial fibrillary acidic protein (GFAP), an astrocyte marker, is increased by glutamate in hippocampal slices from immature rats via a type II metabotropic receptor. In the present work we show that glutamate also stimulates GFAP phosphorylation in microslices prepared from immature cerebellar cortex, but by a different receptor mechanism from that observed in the hippocampus. Thus, in cerebellar microslices, NMDA consistently stimulated GFAP phosphorylation, whereas no effect of metabotropic or non-NMDA ionotropic agonists was observed. Glutamate and NMDA also stimulated GFAP phosphorylation in mixed neuronal/glial cell cultures from the cerebellum, although no effect of these agonists was observed in primary cultures of cerebellar astrocytes. In both models, the effects of glutamate and NMDA were dependent on external Ca(2+), were reversed by the NMDA receptor antagonist AP5 and were not blocked by tetrodotoxin. In the slice study the effect of NMDA was confined to a period starting with the first detectable expression of GFAP at 10 days and finishing at 16 days postnatal, as previously observed with metabotropic agonists in hippocampal slices. This period in the rat corresponds to the start of synaptogenesis when astrocyte hypertrophy is occurring. The results are discussed in the light of information in the literature on the occurrence of functional NMDA receptor subunits in glia.

Descarte de bolsas de sangue devido à reatividade para doença de Chagas em um laboratório de triagem sorológica de doadores em Porto Alegre-RS

A transmissao transfusional (DCT) da doenca de Chagas foi aventada nos anos 30 e comprovada nos anos 50. Inicialmente a sorologia pre-transfusional nao era obrigatoria e nas decadas seguintes os testes foram aperfeicoados com tecnicas mais adaptadas e fidedignas, chegando ao Elisa, mais utilizada atualmente. O presente trabalho se propoe a analisar o perfil sorologico para doenca de Chagas dos doadores de sangue oriundos dos bancos de sangue atendidos pelo Laboratorio de Sorologia da Universidade Luterana do Brasil - Hospital Independencia (Ulbra-HI) em Porto Alegre, RS, Brasil com o objetivo de relacionar os indices encontrados com os disponiveis em nosso pais. A populacao deste estudo foi composta por 36.720 doadores de sangue usuarios dos servicos do Laboratorio de Sorologia da Ulbra-HI durante o periodo de marco de 2006 a maio de 2008. Foram consideradas sorologicamente inaptas para doenca de Chagas 150 doacoes (0,41% do total). Esta taxa e similar a encontrada na regiao Sul, indicando que a triagem realizada em nosso laboratorio esta de acordo com o observado em nosso pais.

Role of intracellular calcium stores on the effect of metabotropic glutamate receptors on phosphorylation of glial fibrillary acidic protein in hippocampal slices from immature rats.

Phosphorylation of glial fibrillary acidic protein (GFAP) in slices from immature rats is stimulated by glutamate via a group II metabotropic glutamate receptor (mGluR II) and by absence of external Ca2+ in reactions that are not additive (Wofchuk and Rodnight, Neurochem. Int. 24:517–523, 1994). These observations suggested that glutamate, via an mGluR, inhibits Ca2+-entry through L-type Ca2+ channels and down-regulates a Ca2+-dependent dephosphorylation event coupled to GFAP. Because ryanodine receptors are present on internal Ca2+ stores and are associated with L-type Ca2+-channels, we investigated the possibility that the glutamatergic modulation of GFAP phosphorylation involves internal Ca2+ stores regulated by ryanodine receptors and whether the Ca2+ originating from these stores acts in a similar manner to external Ca2+. The results showed that the ryanodine receptor–agonists, caffeine and ryanodine and thapsigargin, all of which in appropriate doses increase cytoplasmic Ca2+, reversed the stimulation of GFAP phosphorylation given by 1S,3R-ACPD, an mGluR II agonist.