No abstract

Pilocarpine-induced seizures are mediated by the M 1 subtype of muscarinic acetylcholine receptor (mAChR), but little is known about the signaling mechanisms linking the receptor to seizures. The extracellular signal-regulated kinase (ERK) signaling cascade is activated by M 1 mAChR and is elevated during status epilepticus. Yet, the role of ERK activation prior to seizure has not been evaluated. Here, we examine the role of pilocarpine-induced ERK activation in the induction of seizures in mice by pharmacological and behavioral approaches. We show that pilocarpine induces ERK activation prior to the induction of seizures by both western blot and immunocytochemistry with an antibody to phosphorylated ERK. In addition, we show that the ERK pathway inhibitor SL327 effectively blocks the pilocarpine-induced ERK activation. However, SL327 pretreatment has no effect on the initiation of seizures. In fact, animals treated with SL327 had higher seizure-related mortality than vehicle-treated animals, suggesting activated ERK may serve a protective role during seizures. In addition, ERK inhibition had no effect on the development of the long-term sequelae of status epilepticus (SE), including mossy fiber sprouting, neuronal death and spontaneous recurrent seizures.

Muscarinic acetylcholine receptors (mAChRs) activate many downstream signaling pathways, some of which can lead to mitogen-activated protein kinase (MAPK) phosphorylation and activation. MAPKs play roles in regulating cell growth, differentiation, and synaptic plasticity. Here, the activation of MAPK was examined in PC12 cells endogenously expressing mAChRs. Western blot analysis using a phosphospecific MAPK antibody revealed a dose-dependent and atropine-sensitive increase in MAPK phosphorylation in cells stimulated with carbachol (CCh). The maximal response occurred after 5 min and was rapidly reduced to baseline. To investigate the receptors responsible for CCh activation of MAPK in PC12 cells, the mAChR subtypes present were determined using RT-PCR and immunoprecipitation. RT-PCR was used to amplify fragments of the appropriate sizes for m1, m4, and m5, and the identities of the bands were confirmed with restriction digests. Immunoprecipitation using subtype-specific antibodies showed that ϳ95% of the expressed receptors were m4, whereas the remaining ϳ5% were m1 and m5. A highly specific m1 toxin completely blocked MAPK phosphorylation in response to CCh stimulation. The mAChR-induced MAPK activation was abolished by protein kinase C down-regulation and partially inhibited by pertussis toxin. Although m1 represents a small proportion of the total mAChR population, pharmacological evidence suggests that m1 is responsible for MAPK activation in PC12 cells. Key Words: Muscarinic activation-Mitogen-activated protein kinase -PC12 cells-Acetylcholine.

Several families of G protein-coupled receptors (GPCR) have been shown to activate extracellular signal-regulated kinase (ERK) in transfected cells and non-neuronal systems. However, little is known about GPCR activation of ERK in brain. Because ERK is an important component in the regulation of synaptic plasticity, in this study we examined ERK activation by three families of GPCR that respond to major neuromodulatory neurotransmitters in the hippocampus. We used an immunocytochemical approach to examine ERK activation by muscarinic acetylcholine (mAChR), metabotropic glutamate (mGluR), and ␤-adrenergic (␤-AR) receptors in CA1 neurons of mouse hippocampal slices. Because these GPCR families comprise receptors coupling to each of the major heterotrimeric G proteins, we examined whether ERK activation differs according to Gprotein coupling. By using immunocytochemistry, we were able to examine not only whether each family of receptors activates ERK, but also the cellular populations and subcellular distributions of activated ERK. We demonstrated that M 1 mAChRs and group I mGluRs, both of which are G q -coupled receptors, activate ERK in CA1 pyramidal neurons, although activation in response to mAChR is more robust.

Immune reconstitution inflammatory syndrome (IRIS) is an increasingly recognized phenomenon of paradoxical worsening of patients with acquired immunodeficiency syndrome (AIDS) upon initiation of highly active antiretroviral therapy (HAART). To date, there have been limited reports of IRIS in the central nervous system (CNS). Here, the authors describe a 43-year-old man with AIDS who presented with subacute meningitis. No pathogenic organism was identified by routine diagnostic tests, and he was treated empirically with an antituberculous regimen and initiated on HAART therapy. Soon after, he had a precipitous neurologic decline leading to his death. Postmortem evaluation showed a basilar Candida meningitis as well as vasculitis characterized by CD8+ T-cell infiltration, consistent with IRIS. The authors discuss the challenges in diagnosing fungal meningitides and the risks of initiating HAART therapy in those with possible undiagnosed underlying opportunistic infections. Additionally, the authors review the literature regarding CNS IRIS.