Neuroscience
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Vasopressin (VP), oxytocin (OXT) and vasoactive intestinal polypeptide (VIP) in the brain modulate physiological and behavioral processes in many vertebrates. Day-active tree shrews, the closest relatives of primates, live singly or in pairs in territories that they defend vigorously against intruding conspecifics. However, anatomy concerning peptidergic neuron distribution in the tree shrew brain is less clear. ⋯ Both VP-ir and VIP-ir neurons were found in different subdivisions of the suprachiasmatic nucleus (SCN) with partial overlap. VIP-ir cells and fibers were also scattered in the cerebral cortex, anterior olfactory nucleus, amygdala and dentate gyrus of the hippocampus. These findings provide a comprehensive description of VIP and a detailed mapping of VP and OXT in the hypothalamus and extrahypothalamic regions of tree shrews, which is an anatomical basis for the participation of these neuropeptides in the regulation of circadian behavior and social behavior.
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RanBP9 is a multi-domain scaffolding protein known to integrate extracellular signaling with intracellular targets. We previously demonstrated that RanBP9 enhances Aβ generation and amyloid plaque burden which results in loss of specific pre- and postsynaptic proteins in vivo in a transgenic mouse model. Additionally, we showed that the levels of spinophilin, a marker of dendritic spines were inversely proportional to the RanBP9 protein levels within the synaptosomes isolated from AD brains. ⋯ Thus dendritic arbor and spine density were directly correlated to the levels of phosphorylated form of cofilin in the RanBP9 transgenic mice. Similarly, cortical synaptosomes showed a 20% (p<0.01) reduction in the levels of spinophilin in the RanBP9 transgenic mice. These results provided the physical basis for the loss of synaptic proteins by RanBP9 and most importantly it also explains the impaired spatial learning and memory skills previously observed in the RanBP9 transgenic mice.
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Aversive social interactions, such as social defeat, can alter a variety of behavioral and cognitive functions. In the present study, we examined the effects of social defeat and the subsequent housing on behavior as well as cell proliferation and cell survival in the solitary, male greater long-tailed hamster (Tscheskia triton). ⋯ In addition, subordinate males housed in close proximity to the dominant male (separated by a wire screen) following social defeat did not display differences in agonistic behaviors, but had enhanced cell proliferation in the anterior hypothalamus, ventromedial hypothalamus (VMH), and amygdala as well as increased cell survival in the VMH, compared to subordinate males that were housed individually. Together, our data indicate distinct effects of agonistic interactions and the social housing condition on behavior as well as cell proliferation and survival in the brain of the greater long-tailed hamster.
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Hyperactivity (increased spontaneous firing rates) following cochlear trauma and hearing loss has been well documented in the inferior colliculus (IC). This hyperactivity is associated with frequency regions in the IC that are closely related to regions of peripheral hearing loss. In other auditory nuclei, notably cochlear nucleus, hyperactivity has been shown to be more prevalent in particular cell types but this has not been investigated in the IC. ⋯ Most response categories, with the exception of cells showing an onset response classification, showed a significantly increased average spontaneous firing rate. These data suggest that hyperactivity in the IC is not confined to a particular response type in contrast to findings in the cochlear nucleus. This may be the result of factors intrinsic to the IC, or because of convergent input to the IC from a range of other auditory structures.
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Associative learning is encoded under anesthesia and involves the medial prefrontal cortex (mPFC). Neuronal activity in mPFC increases in response to a conditioned stimulus (CS+) previously paired with an unconditioned stimulus (US) but not during presentation of an unpaired stimulus (CS-) in anesthetized animals. Studies in conscious animals have shown dissociable roles for different mPFC subregions in mediating various memory processes, with the prelimbic (PL) and infralimbic (IL) cortex involved in the retrieval and extinction of conditioned responding, respectively. ⋯ However, PL and IL activity increased during the last CS- presentation, such that activity during presentation of the last CS+ and CS- did not differ. These results confirm previous findings and extend them by showing that increased PL and IL activity result from encoding of the CS+/US association rather than US presentation. They also suggest that extinction may occur under anesthesia and might be represented at the neural level in PL and IL.