Neuroscience
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Comparative Study
Distinct types of non-cholinergic pedunculopontine neurons are differentially modulated during global brain states.
The pedunculopontine nucleus (PPN) is critically involved in brain-state transitions that promote neocortical activation. In addition, the PPN is involved in the control of several behavioral processes including locomotion, motivation and reward, but the neuronal substrates that underlie such an array of functions remain elusive. Here we analyzed the physiological properties of non-cholinergic PPN neurons in vivo across distinct brain states, and correlated these with their morphological properties after juxtacellular labeling. ⋯ The majority of non-cholinergic neurons have an ascending axonal trajectory, with the exception of some irregular firing neurons that have descending axons. Furthermore, we observed asymmetric synaptic contacts within the PPN arising from the axon collaterals of labeled neurons, suggesting that excitatory, non-cholinergic neurons can shape the activity of neighboring cells. Our results provide the first evidence of distinct firing properties associated with non-cholinergic neuronal subtypes in the PPN, suggesting a functional heterogeneity, and support the notion of a local network assembled by projection neurons, the properties of which are likely to determine the output of the PPN in diverse behavioral contexts.
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Previous studies have demonstrated that merlin acts as a tumor suppressor by blocking Ras-mediated signaling. However, the mechanism by which merlin controls cell proliferation has remained obscure. Here we show that merlin deficient tumors exhibited loss of p21, concomitant with elevated CDKs/cyclin D1 levels in sporadic vestibular schwannomas (VS) from clinic patients. ⋯ Furthermore, we find that merlin-enhanced p21 protein stability, rather than increased RNA accumulation, was responsible for the elevated p21 levels. Interestingly, p21 was required to maintain merlin levels and the inhibitory effect of merlin on Ras signaling was partially overridden by knockdown of p21. Consistent with the observation that over-expression of merlin arrested cell growth at G1-phase, the current study indicates that merlin exerts its antiproliferative effect, at least in part, by maintaining p21 expression, and loss of p21 is a prominent feature of merlin deficient schwannomas.
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Studies show a change in sodium channel (NaCh) expression after inflammatory lesions, and this change is implicated in the generation of pain states. We are using the extracted human tooth to study NaCh expression and here examine the expression of the major NaCh isoform located at nodes of Ranvier, Na(v)1.6, in normal and painful samples. Pulpal sections were double-labeled with human-specific Na(v)1.6 antibody and caspr antibody (paranodal protein to identify nodes). ⋯ The unchanged expression of Na(v)1.6 contrasts to our previous finding that showed an increased expression of Na(v)1.7 at both typical and atypical nodal sites within painful samples. Together, these findings suggest there is not a simple replacement of one isoform with another, but rather an increased co-expression of multiple isoforms at both intact and remodeling/demyelinating (atypical) nodal sites within the painful dental pulp. The resultant heterogeneous population of isoforms may produce unique axonal excitability properties that could contribute to spontaneous pain sensations that are common in toothache.
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About 50% of subarachnoid hemorrhage (SAH) survivors have cognitive or neurobehavioral dysfunction. The mechanisms are not known. This study characterized behavioral deficits in a rat SAH model, and correlated these changes with histological alterations. ⋯ There was a significant increase in apoptotic neurons in all regions of brain examined. However, cell death in the hippocampus was not sufficient to cause the neurobehavioral deficits observed in the Morris water maze. This suggests that other factors such as dysfunction of neurotransmission or plasticity in hippocampal pathways might contribute to the impairments.
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Glutamate neurotransmission is highly regulated, largely by glutamate transporters. In the spinal cord, the glutamate transporter GLT-1 is primarily responsible for glutamate clearance. Downregulation of GLT-1 can occur in activated astrocytes, and is associated with increased extracellular glutamate and neuroexcitation. ⋯ Lastly, ceftriaxone normalized CCI- and EAE-induced astrocyte activation in lumbar spinal cord. Together, these data indicate that increasing spinal GLT-1 expression attenuates opioid-induced paradoxical pain, alleviates neuropathic pain, and suppresses associated glial activation. GLT-1 therefore may be a therapeutic target that could improve available treatment options for patients with chronic pain.