Microglia are equipped with a strong proton (H ϩ ) extrusion pathway, a voltage-gated H ϩ channel, probably to compensate for the large amount of H ϩ generated during phagocytosis; however, little is known about how this channel is regulated in pathological states. Because neural damage is often associated with intracellular and extracellular acidosis, we examined the regulatory mechanisms of the H ϩ current of rat spinal microglia in acidic environments. More than 90% of round/amoeboid microglia expressed the H ϩ current, which was characterized by slow activation kinetics, dependencies on both intracellular and extracellular pH, and blockage by Zn 2ϩ . Extracellular lactoacidosis, pH 6.8, induced intracellular acidification and cell swelling. Cell swelling was also induced by intracellular dialysis with acidic pipette solutions, pH 5.5-6.8, at normal extracellular pH 7.3 in the presence of Na ϩ . The H ϩ currents were increased in association with cell swelling as shown by shifts of the half-activation voltage to more negative potentials and by acceleration of the activation kinetics. The acidosis-induced cell swelling and the accompanying potentiation of the H ϩ current required nonhydrolytic actions of intracellular ATP and were inhibited by agents affecting actin filaments (phalloidin and cytochalasin D). The H ϩ current was also potentiated by swelling caused by hypotonic stress. These findings suggest that the H ϩ channel of microglia can be potentiated via cell swelling induced by intracellular acidification. This potentiation might operate as a negative feedback mechanism to protect microglia from cytotoxic acidification and hence acidosis-induced swelling in pathological states of the CNS. Key words: H ϩ channel; lactoacidosis; cell swelling; microglia; pH regulation; ATP; cytochalasin D; cytoskeleton; spinal cordMicroglia are activated in response to various disorders of the CNS, including infection, ischemia, trauma, and neurodegenerative diseases, and they participate in both neuroprotective and neuropathological events (Streit, 1996). They are sensitive to the minor changes in their microenvironment present during very early stages of brain damage, such as subtle imbalances in ion homeostasis, and transform rapidly from the resting to the activated state (Gehrmann et al., 1993;Kreutzberg, 1996). Various ion channels in microglia are considered to contribute to the high responsiveness to pathological events and to be involved in maintenance of the neural microenvironment (Kettenmann et al., 1990;Nörenberg et al., 1994;Schlichter et al., 1996;Eder, 1998).A voltage-gated proton (H ϩ ) channel, first found in snail neurons (Thomas and Meech, 1982), has been suggested to be the mechanism for H ϩ extrusion responsible for compensation of intracellular acidification and for the dissipation of depolarization found in phagocytes that generate a massive amount of H ϩ during respiratory bursts (Lukacs et al., 1993;DeCoursey and Cherny, 1994). Similar H ϩ currents have been described in murine (Eder et al., 19...

To our knowledge, this is the first report of very early-onset Alzheimer disease with spastic paraparesis and with the visual variant form of the disease, which is associated with visuospatial cognitive disorder. The Leu85Pro mutation in PSEN1 was pathogenic.

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The demyelinated lesions observed in this case were similar to lesions found in multiple sclerosis. On the basis of our finding that the clinical progression of the disease and the associated symptoms paralleled changes in the CSF NMDAR antibody titer, we speculate that the lesions formed as a result of anti-NMDAR encephalitis.