Management of Blunt Cerebrovascular Injury.

PURPOSE OF REVIEW: This review provides an updated summary of blunt cerebrovascular injury (BCVI) to guide clinicians in its early diagnosis and prevention and treatment of stroke associated with such injury. RECENT FINDINGS: Untreated BCVI causes stroke in 10-40% of patients, but more than half will not present with stroke symptoms initially. Risk of stroke is highest in the first 7 days, with a peak in the first 24 h. Computed tomography (CT) angiography is currently the screening modality of choice, although digital subtraction angiography may still be required in some cases. Antithrombotic therapy is the mainstay of treatment and has proven safety in trauma patients. In carefully selected patients, endovascular intervention may also be beneficial. BCVI is a potentially preventable cause of stroke. A high index of suspicion is needed as emergent screening during initial evaluation can provide a window for stroke prevention. Screening all patients with injuries that would otherwise prompt CT scans of the neck or chest is recommended. Treatment is guided by grade of injury. Early treatment with antithrombotics has been shown to be both effective and safe.

STN Versus GPi Deep Brain Stimulation for Action and Rest Tremor in Parkinson's Disease.

OBJECTIVE: To investigate the effects of subthalamic nucleus (STN) and globus pallidus internus (GPi), deep brain stimulation (DBS) on individual action tremor/postural tremor (AT) and rest tremor (RT) in Parkinson's disease (PD). Randomized DBS studies have reported marked benefit in tremor with both GPi and STN and DBS, however, there is a paucity of information available on AT vs RT when separated by the surgical target. METHODS: We retrospectively reviewed the 1-year clinical outcome of PD patients treated with STN and GPi DBS at the University of Florida. We specifically selected patients with moderate to severe AT. Eighty-eight patients (57 STN and 31 GPi) were evaluated at 6 and 12 months for changes in AT and RT in the OFF-medication/ON stimulation state. A comparison of "response" was performed and defined as greater than or equal to a 2-point decrease in tremor score. RESULTS: STN and GPi DBS both improved AT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). The STN DBS group experienced a greater improvement in AT at 6 months compared to the GPi group (p = 0.005) but not at the 12 months follow-up (p = 0.301). Both STN and GPi DBS also improved RT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). There was no difference in RT scores between the two groups at 6 months (p = 0.23) or 12 months (p = 0.74). The STN group had a larger proportion of patients who achieved a "response" in AT at 6 months (p < 0.01), however, this finding was not present at 12 months (p = 0.23). A sub-analysis revealed that in RT, the STN group had a larger percentage of "responders" when followed through 12 months (p < 0.01). CONCLUSION: Both STN and GPi DBS reduced PD associated AT and RT at 12 months follow-up. There was no advantage of either brain target in the management of RT or AT. One nuance of the study was that STN DBS was more effective in suppressing AT in the early postoperative period, however, this effect diminished over time. Clinicians should be aware that it may take longer to achieve a similar tremor outcome when utilizing the GPi target.

Elimination of rapid potassium channel inactivation by phosphorylation of the inactivation gate.

The effect of protein kinase C (PKC) on rapid N-type inactivation of K+ channels has not been reported previously. We found that PKC specifically eliminates rapid inactivation of a cloned human A-type K+ channel (hKv3.4), converting this channel from a rapidly inactivating A type to a noninactivating delayed rectifier type. Biochemical analysis showed that the N-terminal domain of hKv3.4 is phosphorylated in vitro by PKC, and mutagenesis experiments revealed that two serines within the inactivation gate at the N-terminus are sites of direct PKC action. Moreover, mutating one of these serines to aspartic acid mimics the action of PKC. Serine phosphorylation may thus prevent rapid inactivation by shielding basic residues known to be critical to the function of the inactivation gate. The regulatory mechanism reported here may have substantial effects on signal coding in the nervous system.

Alcohols inhibit a cloned potassium channel at a discrete saturable site. Insights into the molecular basis of general anesthesia.

The molecular basis of general anesthetic action on membrane proteins that control ion transport is not yet understood. In a previous report (Covarrubias, M., and Rubin, E. (1993) Proc. Natl. Acad. Sci. 90, 6957-6960), we found that low concentrations of ethanol (17-170mM) selectively inhibited a noninactivating cloned K+ channel encoded by Drosophila Shaw2. Here, we have conducted equilibrium dos-inhibition experiments, single channel recording, and mutagenesis in vitro to study the mechanism underlying the inhibition of Shaw2K+ channels by a homologous series of n-alkanols (ethanol to 1-hexanol). The results showed that: (i) these alcohols inhibited Shaw2 whole-cell currents, the equilibrium dose-inhibition relations were hyperbolic, and competition experiments revealed the presence of a discrete site of action, possibly a hydrophobic pocket; (ii) this pocket may be part of the protein because n-alkanol sensitivity can be transferred to novel hybrid K+ channels composed of Shaw2 subunits and homologous ethanol-insensitive subunits: (iii) moreover, a hydrophobic point mutation within a cytoplasmic loop of an ethanol-insensitive K+ channel (human Kv3.4) was sufficient to allow significant inhibition by n-alkanols, with a dose-inhibition relation that closely resembled that of wildtype Shaw2 channels; and (iv) 1-butanol selectively inhibited long duration single channel openings in a manner consistent with a direct effect on channel gating. These results strongly suggest that a discrete site within the ion channel protein is the primary locus of alcohol and general anesthetic action.

Cooperative activation of myosin by light chain phosphorylation in permeabilized smooth muscle.

The purpose of this study was to determine the quantitative relationship between the number of myosin molecules that increase their ATPase activity and the degree of myosin light chain phosphorylation in smooth muscle. Single turnover experiments on the nucleotide bound to myosin were performed in the permeabilized rabbit portal vein. In the resting muscle, the rate of exchange of bound nucleoside diphosphate was biphasic and complete in approximately 30 min. When approximately 80% of the myosin light chain was thiophosphorylated, the nucleoside diphosphate exchange occurred at a much faster rate and was almost complete in 2 min. Thiophosphorylation of 10% of the myosin light chains caused an increase in the rate of ADP exchange from much more than 10% of the myosin subfragment-1. Less than 20% thiophosphorylation of the total myosin light chains resulted in the maximum increase in ADP exchanged in 2 min. It appears that a small degree of myosin light chain phosphorylation cooperatively turns on the maximum number of myosin molecules. Interestingly, even though less than 20% thiophosphorylation of the myosin light chain caused the maximum exchange of ADP within 2 min, higher degrees of thiophosphorylation were associated with further increases in the ATPase rates. We conclude that a small degree of myosin light chain thiophosphorylation cooperatively activates the maximum number of myosin molecules, and a higher degree of thiophosphorylation makes the myosin cycle faster. A kinetic model is proposed in which the rate constant for attachment of unphosphorylated cross bridges varies as a function of myosin light chain phosphorylation.

Cross-bridge cycling at rest and during activation. Turnover of myosin-bound ADP in permeabilized smooth muscle.

Single turnover experiments were performed on myosin-bound ADP by measuring the time course of incorporation of [3H]ADP following rapid formation of [3H]ATP by photolysis of caged [3H]ATP. Permeabilized rabbit portal veins were incubated in a solution at 20 degrees C with 1 mM MgATP, 20 mM phosphocreatine, 1 mg/ml creatine phosphokinase, and containing [14C]ATP and high specific activity caged [3H]ATP. At variable times following a UV flash, the muscle was frozen, nucleotides were extracted, and the ratio 3H:14C in ADP was compared to that in ATP. At rest, the exchange of bound ADP occurred with a rate constant of 0.004 s-1. When the myosin light chain was about 80% thiophosphorylated, and the muscle was generating maximum isometric force, there appeared a fast phase of ADP exchange (44% of the total) which had a rate constant of 0.2 s-1. The change in rate of ADP exchange on myosin is sufficient to explain the measured increase in ATPase activity upon thiophosphorylation of the myosin light chain. A simple analysis of the data suggests that there is a 50-fold increase in the cycling rate of cross-bridges in the muscle upon phosphorylation under isometric conditions. The fraction of ADP exchanged at 10 s following photolytic release of [3H]ATP was found to be approximately linearly related to the degree of thiophosphorylation of the myosin light chain. This supports the idea that phosphorylation of the light chain causes the transition of myosin from the resting (slow ATPase) cycle into the activated (fast ATPase) cycle, and that the fraction of myosin in the fast cycle is directly determined by the degree of light chain phosphorylation. The data are also consistent with the cooperativity model described previously by Vyas et al.

Prototypic G protein-coupled receptor for the intestinotrophic factor glucagon-like peptide 2.

Glucagon-like peptide 2 (GLP-2) is a 33-aa proglucagon-derived peptide produced by intestinal enteroendocrine cells. GLP-2 stimulates intestinal growth and up-regulates villus height in the small intestine, concomitant with increased crypt cell proliferation and decreased enterocyte apoptosis. Moreover, GLP-2 prevents intestinal hypoplasia resulting from total parenteral nutrition. However, the mechanism underlying these actions has remained unclear. Here we report the cloning and characterization of cDNAs encoding rat and human GLP-2 receptors (GLP-2R), a G protein-coupled receptor superfamily member expressed in the gut and closely related to the glucagon and GLP-1 receptors. The human GLP-2R gene maps to chromosome 17p13.3. Cells expressing the GLP-2R responded to GLP-2, but not GLP-1 or related peptides, with increased cAMP production (EC50 = 0.58 nM) and displayed saturable high-affinity radioligand binding (Kd = 0.57 nM), which could be displaced by synthetic rat GLP-2 (Ki = 0.06 nM). GLP-2 analogs that activated GLP-2R signal transduction in vitro displayed intestinotrophic activity in vivo. These results strongly suggest that GLP-2, like glucagon and GLP-1, exerts its actions through a distinct and specific novel receptor expressed in its principal target tissue, the gastrointestinal tract.