Behavioural brain research
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Vigilance levels of 12 morning types (M-types) and 12 evening types (E-types) were investigated after a baseline night, 2 nights of sleep fragmentation (5 min of forced awakening every half-hour) and a recovery night. Sleep timing was adjusted to the preferred sleep schedule of each subject. Daytime vigilance levels were assessed with test series including a scale of subjective alertness, a psychomotor vigilance task (PVT), a waking EEG recording, and a sleep latency test. ⋯ Diurnal variations of subjective alertness and sleep latencies differed between "Extreme" chronotypes but were identical between "Intermediate" chronotypes. There were no major differences in the response to sleep fragmentation in any subgroup. Since phase angles differed by the same amount between chronotypes within each subgroup, the results suggest that a difference in phase angle cannot be the only source of the differences observed in diurnal variations between "Extreme" chronotypes.
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The APP23 model is a transgenic mouse model for Alzheimer's disease. Cognitive performance in the APP23-model was assessed by Morris Water Maze (MWM) and passive avoidance learning, but the latter failed to show any difference between the genotypes. In search of a non-spatial alternative for assessment of hippocampus-dependent memory, we evaluated an odour paired-associate test, which is based on learning an association between two sets of odours. ⋯ Subsequently, mice are tested for transitive inference and subjected to a symmetry test. Impairment was seen in the APP23 mice, in comparison with wild type mice, in training; however, both groups failed the transitivity and symmetry test. Possible explanations for this discrepancy with earlier published results are the advanced age of the mice or the C57Bl/6J background, in which the model was established.
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Comparative Study
Hypobaric hypoxia induces dendritic plasticity in cortical and hippocampal pyramidal neurons in rat brain.
Hypobaric hypoxia (HH), a predisposing environmental condition at high altitude (HA) encountered by many mountaineers jeopardizes their normal physiology like motor coordination and cognitive functions. Our previous studies revealed that the HH induces oxidative stress and neurodegeneration, which is associated with spatial memory impairment in rats. However, the dendritic changes after exposure to different duration of HH remain largely unknown. ⋯ There was a significant decrease in dendritic arborization and spine number along with increased number of damaged neurons, after 3, 7 and 14 days of HH but after 21 days of HH exposure the structural recovery was noted in all the regions. There was impairment of spatial memory after 3 and 7 days of exposure, but slight improvement of spatial memory was noted after 14 and 21 days of exposure. Our studies suggested that HH induces dendritic plasticity of PFC and hippocampal pyramidal neurons of rat brain, which might be associated with improvement of spatial memory function after 21 days of HH exposure.