Neuroscience
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Plasticity in intact A delta- and C-fibers contributes to cold hypersensitivity in neuropathic rats.
Cold hypersensitivity is a common sensory abnormality accompanying peripheral neuropathies and is difficult to treat. Progress has been made in understanding peripheral mechanisms underlying neuropathic pain but little is known concerning peripheral mechanisms of cold hypersensitivity. The aim of this study was to analyze the contribution of uninjured primary afferents to the cold hypersensitivity that develops in neuropathic rats. ⋯ This was in contrast to the numerous changes in A delta-fibers: the percentage of L4 cold sensitive A delta-, but not C-fibers, was significantly increased, the percentage of L4 icilin-sensitive A delta-, but not C-fibers, was significantly increased, the icilin-induced activity of L4 A delta-, but not C-fibers, was significantly increased. Icilin-induced activity was blocked by the TRPA1 antagonist Ruthenium Red. The results indicate plasticity in both A delta- and C-uninjured fibers, but A delta fibers appear to provide a major contribution to cold hypersensitivity in neuropathic rats.
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Ischemic brain injury is one of the leading causes of epilepsy in the elderly, and there are currently no adult rodent models of global ischemia, unilateral hemispheric ischemia, or focal ischemia that report the occurrence of spontaneous motor seizures following ischemic brain injury. The rodent hypoxic-ischemic (H-I) model of brain injury in adult rats is a model of unilateral hemispheric ischemic injury. Recent studies have shown that an H-I injury in perinatal rats causes hippocampal mossy fiber sprouting and epilepsy. ⋯ Three of 20 lesioned animals (15%) were observed to have at least one spontaneous motor seizure 6-12 months after treatment. Approximately 50% of the ipsilateral and contralateral hippocampal slices displayed abnormal electrophysiological responses in the dentate gyrus, manifest as all-or-none bursts to hilar stimulation. This study suggests that H-I injury is associated with synaptic reorganization in the lesioned region of the hippocampus, and that new recurrent excitatory circuits can predispose the hippocampus to abnormal electrophysiological activity and spontaneous motor seizures.
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Repetition of visually common objects was examined in relation to prior intentional learning and memory status using a delayed match-to-sample task in humans. Both response time and two temporally separate event-related potential (ERP) components indexed repetition. ⋯ Our source localization results indicate that the late and posterior repetition effect in visual cortex is consistent with repetition suppression results reported in monkey physiology and human fMRI studies. Meanwhile, the early and anterior repetition effect, in temporal pole and frontal cortices, is modulated by explicit memory mechanisms.
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We previously suggested that orientation-tuned surround suppression of responses of cells in the primary visual cortex (V1) is primarily caused by a decrease in geniculocortical input for the cell [Ozeki H, Sadakane O, Akasaki T, Naito T, Shimegi S, Sato H (2004) Relationship between excitation and inhibition underlying size tuning and contextual response modulation in the cat primary visual cortex. J Neurosci 24:1428-1438]. To further test this hypothesis, we compared the strength of orientation and spatial phase selectivity of surround suppression, and the spatial extent of the extraclassical receptive field (ECRF) between the lateral geniculate nucleus (LGN) and V1 neurons of anesthetized cats. ⋯ In 70% of the LGN neurons that exhibited significant orientation-tuned extraclassical surround suppression, the effective orientation of the suppression varied according to a change in the orientation of CRF stimulus, while the remaining 30% exhibited a fixed preferred orientation of the suppression regardless of the orientation of the CRF grating. These results suggest that the basic properties of surround suppression, such as orientation and spatial phase tuning, already exist in cat LGN and that a decrease of surround suppression in excitatory inputs from LGN by surround suppression is the primary cause of surround suppression in V1. Corticogeniculate feedback may further elaborate the properties of surround suppression in LGN.
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The aim of the present study is to investigate the changes in hippocampal synapses and their relation with learning-memory abilities at different ages, and evaluate the effects of 2,3,5,4'-tetrahydroxystilbene-2-O-beta-d-glucoside (TSG), which is one of the major components of a traditional Chinese herb Polygonum multiflorum, on brain aging. Sprague-Dawley rats at the age of 1, 3, 6, 18 and 24 months were used. TSG at doses of 30 and 60 mg/kg/day was intragastrically administered to 21-month-old rats for 3 months, respectively. ⋯ Treatment with high-dose TSG in rats at 24 months of age had significant improvement in the learning-memory abilities in the water maze tests associated with an increase in the number of synapses and synaptic vesicles, and an elevation of expression of SYP in the hippocampus. In conclusion, hippocampal synapses count and synaptophysin expression decreased in aged rats, which may be one of the mechanisms involved in learning-memory deficit. TSG reversed the above changes in aged rats, suggesting that TSG may be beneficial for the treatment of Alzheimer disease or cognitive impairment in old people.