Hedgehog signaling promotes endoneurial fibroblast migration and Vegf-A expression following facial nerve injury.

BACKGROUND: Peripheral nerve injuries are a common clinical problem which may result in permanent loss of motor or sensory function. A better understanding of the signaling pathways that lead to successful nerve regeneration may help in discovering new therapeutic targets. The Hedgehog (Hh) signaling pathway plays significant roles in nerve development and regeneration. In a mouse model of facial nerve injury, Hedgehog-responsive fibroblasts increase in number both at the site of injury and within the distal nerve. However, the role of these cells in facial nerve regeneration is not fully understood. We hypothesize that the Hh pathway plays an angiogenic and pro-migratory role following facial nerve injury. METHODS: Hedgehog pathway modulators were applied to murine endoneurial fibroblasts isolated from the murine facial nerve. The impact of pathway modulation on endoneurial fibroblast migration and cell proliferation was assessed. Gene expression changes of known Hedgehog target genes and the key angiogenic factor Vegf-A were determined by qPCR. In vivo, mice were treated with pathway agonist (SAG21k) and injured facial nerve specimens were analyzed via immunofluorescence and in situ hybridization. RESULTS: Hedgehog pathway activation in facial nerve fibroblasts via SAG21k treatment increases Gli1 and Ptch1 expression, the rate of cellular migration, and Vegf-A expression in vitro. In vivo, expression of Gli1 and Vegf-A expression appears to increase after injury, particularly at the site of nerve injury and the distal nerve, as detected by immunofluorescence and in situ hybridization. Additionally, Gli1 transcripts co-localize with Vegf-A following transection injury to the facial nerve. DISCUSSION: These findings describe an angiogenic and pro-migratory role for the Hedgehog pathway mediated through effects on nerve fibroblasts. Given the critical role of Vegf-A in nerve regeneration, modulation of this pathway may represent a potential therapeutic target to improve facial nerve regeneration following injury.

Inhibition of MAO-A fails to alter cocaine-induced increases in extracellular dopamine and norepinephrine in rat nucleus accumbens.

Monoamine oxidase (MAO) inhibitors are being investigated as possible medications for cocaine dependence, but there are potential problems with this approach. In the present study, we tested the hypothesis that inhibition of catecholamine metabolism with the MAO-A inhibitor, clorgyline, might enhance cocaine-induced increases in extracellular dopamine and norepinephrine in rat nucleus accumbens. Male rats were pretreated with clorgyline (1 mg/kg, s.c.) or its saline vehicle (1 ml/kg, s.c.), and microdialysis probes were inserted into previously implanted guide cannulae. After overnight perfusion of the probes in situ, rats received an acute challenge injection of either cocaine (1 mg/kg, i.v.) or its saline vehicle (1 ml/kg, i.v.). Clorgyline pretreatment alone caused significant elevations in basal levels of dialysate norepinephrine but not dopamine. Cocaine administration elicited significant increases in extracellular dopamine and norepinephrine in all groups of rats, and this effect was not altered by clorgyline pretreatment. The 1 mg/kg dose of clorgyline decreased dopamine metabolites in postmortem brain tissue by more than 80%. Our data are consistent with clinical studies that demonstrate pretreatment with the MAO-B selective inhibitor, selegeline, fails to alter cocaine-induced subjective effects in human drug users. Moreover, these findings suggest that adverse consequences related to altered catecholamine transmission would not occur if patients taking phenelzine, a non-selective MAO inhibitor, relapsed and used cocaine.