Proceedings of the National Academy of Sciences of the United States of America
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Proc. Natl. Acad. Sci. U.S.A. · Oct 2008
Activation of P2X7 receptors in glial satellite cells reduces pain through downregulation of P2X3 receptors in nociceptive neurons.
Purinergic ionotropic P2X7 receptors (P2X7Rs) are closely associated with excitotoxicity and nociception. Inhibition of P2X7R activation has been considered as a potentially useful strategy to improve recovery from spinal cord injury and reduce inflammatory damage to trauma. The physiological functions of P2X7Rs, however, are poorly understood, even though such information is essential for making the P2X7R an effective therapeutic target. ⋯ We further determine the roles of the P2X7R-P2Y1-P2X3R inhibitory control under injurious conditions. Activation of the inhibitory control effectively prevents the development of allodynia and increases the potency of systemically administered P2X7R agonists in inflamed rats. Thus, direct blocking P2X7Rs, as proposed before, may not be the best strategy for reducing pain or lessening neuronal degeneration because it also disrupts the protective function of P2X7Rs.
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Proc. Natl. Acad. Sci. U.S.A. · Oct 2008
Parkinsonism and impaired axonal transport in a mouse model of frontotemporal dementia.
Frontotemporal dementia (FTD) is characterized by cognitive and behavioral changes and, in a significant subset of patients, Parkinsonism. Histopathologically, FTD frequently presents with tau-containing lesions, which in familial cases result from mutations in the MAPT gene encoding tau. Here we present a novel transgenic mouse strain (K3) that expresses human tau carrying the FTD mutation K369I. ⋯ The impaired axonal transport in SN neurons affects, among others, vesicles containing the dopamine-synthesizing enzyme tyrosine hydroxylase. Distinct modes of transport are also impaired in sciatic nerves, which may explain amyotrophy. Together, the K3 mice are a unique model of FTD-associated Parkinsonism, with pathomechanistic implications for the human pathologic process.
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Proc. Natl. Acad. Sci. U.S.A. · Oct 2008
Neuregulin-1 regulates LTP at CA1 hippocampal synapses through activation of dopamine D4 receptors.
Neuregulin-1 (NRG-1) is genetically linked with schizophrenia, a neurodevelopmental cognitive disorder characterized by imbalances in glutamatergic and dopaminergic function. NRG-1 regulates numerous neurodevelopmental processes and, in the adult, suppresses or reverses long-term potentiation (LTP) at hippocampal glutamatergic synapses. Here we show that NRG-1 stimulates dopamine release in the hippocampus and reverses early-phase LTP via activation of D4 dopamine receptors (D4R). ⋯ Conversely, direct D4R activation mimics NRG-1 and reduces AMPA receptor currents and surface expression. These findings demonstrate that NRG-1 mediates its unique role in counteracting LTP via dopamine signaling and opens future directions to study new aspects of NRG function. The novel functional link between NRG-1, dopamine, and glutamate has important implications for understanding how imbalances in Neuregulin-ErbB signaling can impinge on dopaminergic and glutamatergic function, neurotransmitter pathways associated with schizophrenia.