Neuroscience
-
Increasing age is associated with a poor prognosis following traumatic brain injury (TBI). CNS axons may recover poorly following TBI due to expression of myelin-derived inhibitors to axonal outgrowth such as Nogo-A. To study the role of Nogo-A/B in the pathophysiological response of the elderly to TBI, 1-year-old mice deficient in Nogo-A/B (Nogo-A/B homozygous(-/-) mice), Nogo-A/B heterozygous(-/+) mice, and age-matched wild-type (WT) littermate controls were subjected to a controlled cortical impact (CCI) TBI. ⋯ Neither TBI nor the absence of NogoA/B caused an increased A beta expression. Myelin staining showed a reduced area and density in the corpus callosum in brain-injured Nogo-A/B(-/-) animals compared to their littermate controls. These novel and unexpected behavioral results demonstrate that the absence of Nogo-A/B may negatively influence outcome, possibly related to hypomyelination, following TBI in mice and suggest a complex role for this myelin-associated axonal growth inhibitor following TBI.
-
Morphine sensitization is a model of latent, functionally inducible increase in dopamine D(1) receptor-mediated transmission, which may be unmasked by an external stimulus. Morphine-sensitized rats present dopamine D(1) receptor-dependent stereotypies upon morphine challenge and resilience to unavoidable stress-induced behavioral deficits. This tonic increase in dopamine D(1) dopaminergic transmission is counter-adaptive to an enhanced mu-opioid receptor-dependent signaling in striatal areas. ⋯ The stress-induced neurochemical modifications and their sensitivity to receptor antagonists were similar to those observed after acute morphine administration. In conclusion, these results suggest that in the experimental conditions used an increase in dopamine output in striatal areas is followed by a complex neurochemical pattern, in which the initial stimulation of dopamine D(1) receptors triggers a sequence of signaling events that lead to an mGluR(5)-mediated increase in phospho-Thr75 DARPP-32 levels. Since DARPP-32 phosphorylated in Thr75 inhibits cAMP-dependent protein kinase (PKA) activity, the final result is a decrease in the dopamine D(1) receptor-dependent phosphorylation events.
-
Symptomatic ischemia following aneurysmal subarachnoid hemorrhage (SAH) is common but poorly understood and inadequately treated. Severe constriction of the major arteries at the base of the brain, termed vasospasm, traditionally has been thought to be a proximal event underlying these ischemias, although microvascular changes also have been described. The vast majority of studies aimed at understanding the pathogenesis of ischemic deficits, and vasospasm have focused on the interaction of the "spasmogen" of the extravasated blood with the smooth muscle and endothelium of the arteries. ⋯ Focal application of a GABA(A) receptor agonist and antagonist was used to respectively inactivate and activate the RVM. We show here that the RVM modulates cerebral blood flow under resting conditions, and further, contributes to restoration of cerebral perfusion following a high-grade SAH. Failure of this brainstem compensatory mechanism could be significant for acute perfusion deficits seen in patients following subarachnoid hemorrhage.
-
Dysfunctions of the brain 5-HT system are often associated with affective disorders, such as depression. The raphe nuclei target the limbic system and most forebrain areas and constitute the main source of 5-HT in the brain. All 5-HT neurons express tryptophan hydroxylase-2 (TPH2), the brain specific, rate-limiting enzyme for 5-HT synthesis. ⋯ No behavioral differences were found in the OF or on the EPM. These data indicate that ER beta acts at the level of the rat DRN to modulate tph2 mRNA expression and thereby influence 5-HT synthesis in DRN subregions. Our results also suggest that local activation of ER beta neurons in the DRN may be sufficient to decrease despair-like behavior, but not anxiolytic behaviors.
-
Little is known about the G protein-coupled receptor desensitization process during pregnancy. Wistar pregnant rats were treated with (-)N(6)-phenylisopropyladenosine (R-PIA), an adenosine A(1) receptor (A(1)R) agonist, in their drinking water during pregnancy, and the effect on A(1)R/adenylyl cyclase system was studied in both maternal and fetal brain. In maternal brain, binding assays revealed a significant decrease in total receptor numbers in plasma membranes (27%, P<0.05), with no significant changes in receptor affinity. ⋯ On the other hand, forskolin- and forskolin-plus guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S)-stimulated adenylyl cyclase activity was decreased in maternal (P<.01) and fetal brain (P<.001). Furthermore, adenylyl cyclase inhibition elicited by N(6)-cyclohexyladenosine (CHA), a selective A(1)R agonist, was significantly decreased in both maternal (P<0.05) and fetal brain (P<.01), suggesting a desensitization of the A(1)R/adenylyl cyclase pathway. Therefore, these results suggest that R-PIA intake during pregnancy causes desensitization of the A(1)R-mediated inhibitory transduction pathway in both maternal and fetal brain, probably due to the decreased density of A(1)R at the cell surface.