Neuroscience
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Reaction time (RT), a widely used measure of human performance in experimental psychology, has recently been included as a regressor of interest in functional magnetic resonance imaging (fMRI) data analysis. Few studies reported RT-related brain regions, but the nature of this activity is not fully understood. We aimed at exploring this topic by implementing a simple saccadic task which evokes fast and homogeneous reactions that require only the basic neural processes. ⋯ The results provide evidence that even a small difference in RTs can be linked with significant increase of HDR in task-related areas. Moreover, this increase is not linear, but rather quadratic. Our findings highlight the importance of controlling for RT in fMRI data analysis when contrasting conditions that vary in RT to avoid the misinterpretation of results.
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Auditory brainstem networks facilitate sound source localization through binaural integration. A key component of this circuitry is the projection from the ventral cochlear nucleus (VCN) to the medial nucleus of the trapezoid body (MNTB), a relay nucleus that provides inhibition to the superior olivary complex. This strictly contralateral projection terminates in the large calyx of Held synapse. ⋯ We then determined the distribution of glial cells following early (P2) unilateral cochlear removal, which results in formation of ectopic projections from the intact VCN to ipsilateral MNTB. We found that following perturbation, astrocytic markers showed expression near the ectopic ipsilateral calyx. Taken together, the developmental expression patterns are consistent with a role for glial cells in the maturation of the calyx of Held and suggest that these cells may have a similar role in maturation of lesion-induced connections.
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Heat shock protein 27 (HSP27) exerts cytoprotection against many cellular insults including cerebral ischemia. We previously indicated that intravenous injection of HSP27 purified from human lymphocytes (hHSP27) significantly reduced infarct volume following cerebral ischemia-reperfusion injury, while recombinant HSP27 (rHSP27) was less effective. Phosphorylation is important for HSP27 function, and hHSP27 was more highly phosphorylated than rHSP27. ⋯ Compared with BSA controls (30.7±3.1mm(3), n=5), infarct volume was reduced by 67% in the hHSP27 positive-control group (10.1±4.6mm(3), P<0.001, n=5), 17% following rHSP27 (25.4±3.6mm(3), P<0.05, n=5), and 46% following prHSP27 (16.5±4.0mm(3), P<0.001, n=9). Compared to the rHSP27 and BSA-treated groups, prHSP27 also reduced functional deficits, and significantly suppressed apoptosis, oxidative stress, and inflammatory responses. Here, we showed the superior neuroprotective effects of phosphorylated HSP27 by administering prHSP27. prHSP27 may be a useful therapeutic agent to protect against acute cerebral ischemic stroke.
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Single-cell injection with lipophilic dyes following immunocytochemistry is extremely valuable for revealing the morphology of a cell expressing a protein of interest, and is a more reliable technique for cell type classification than standard morphological techniques. This study focuses on calretinin (CR), which is used as a selective marker for distinct subpopulations of neurons in the rabbit retina. The present study used single-cell injection after immunocytochemistry to describe the density and types of CR-containing retinal ganglion cells (RGCs) in rabbit. ⋯ Our results show that 10 morphologically different types of rabbit RGCs expressed CR. CR-containing RGCs were heterogeneous in their morphology. This approach to integrate the selective expression of a particular protein with spatial patterns of dendritic arborization will lead to a better understanding of RGCs.
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Alterations in hippocampal neurogenesis affect spatial learning, though, the relative contributions of cell proliferation and cell survival on this process are poorly understood. The current study utilized mu opioid receptor (MOR-1) knockout (KO) mice on two background strains, C57BL/6 and 129S6, to assess cell survival as well as determine the impact on spatial learning using the Morris water maze. These experiments were designed to extend prior work showing that both C57BL/6 and 129S6 MOR-1 KO mice have an increased number of proliferating cells in the dentate gyrus (DG) when compared to wild-type (WT) mice. ⋯ These alterations collectively contribute to an increase in the granule cell number in the DG of C57BL/6 MOR-1 KO mice, while the total number of granule cells in 129S6 MOR-1 KO mice is unchanged. Thus, although C57BL/6 and 129S6 MOR-1 KO mice both exhibit increased cell proliferation in the DG, the impact of the MOR-1 mutation on cell survival differs between strains. Furthermore, the decrease in DG cell survival displayed by 129S6 MOR-1 KO mice is correlated with functional deficits in spatial learning, suggesting that MOR-1-dependent alterations in the survival of new neurons in the DG, and not MOR-1-dependent changes in proliferation of progenitor cells in the DG, is important for spatial learning.