We provided evidence for the formation of a novel phospholipase C-mediated calcium signal arising from coactivation of D1 and D2 dopamine receptors. In the present study, robust fluorescence resonance energy transfer showed that these receptors exist in close proximity indicative of D1-D2 receptor heterooligomerization. The close proximity of these receptors within the heterooligomer allowed for cross-phosphorylation of the D2 receptor by selective activation of the D1 receptor. D1-D2 receptor heterooligomers were internalized when the receptors were coactivated by dopamine or either receptor was singly activated by the D1-selective agonist (Ϯ)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF 81297) or the D2-selective agonist quinpirole. The D2 receptor expressed alone did not internalize after activation by quinpirole except when coexpressed with the D1 receptor. D1-D2 receptor heterooligomerization resulted in an altered level of steady-state cell surface expression compared with D1 and D2 homooligomers, with increased D2 and decreased D1 receptor cell surface density. Together, these results demonstrated that D1 and D2 receptors formed heterooligomeric units with unique cell surface localization, internalization, and transactivation properties that are distinct from that of D1 and D2 receptor homooligomers.The dopamine receptor family is subdivided into two distinct subclasses, based on structural similarities, pharmacological profiles, and signal transduction mechanisms, into D1-and D2-like receptors. Although D1 and D2 receptor subclasses are biochemically distinct in that D1 receptors couple positively and the D2 receptors couple negatively to adenylyl cyclase, many physiological functions are known to be mediated by the coactivation of both receptors. For example, the augmentative effect of cocaine on locomotion and intracranial self-stimulation is mediated by the activation of both D1 and D2 receptors (Kita et al., 1999). Dopamine receptor synergism could occur either at the level of neuronal networks through D1-and D2-like receptors expressed in separate neuronal populations or, on the other hand, within the same neurons through convergent postreceptor mechanisms. The latter mechanism of D1-D2 receptor synergism is possible because dopamine receptor subclasses are colocalized in rat brain, with colocalization of D1-and D2-like receptors in virtually every neuron in the neonatal striatum (Aizman et al., 2000). Furthermore, our own studies have demonstrated robust colocalization of D1 and D2 receptors in a subset of neurons in human caudate nucleus, rat striatum, and cortex . These data suggest, therefore, that functional synergism could occur within individual neurons. In fact, the coactivation of both D1 and D2 receptors has been shown to result in a significant increase in action potential frequency in neurons of the substantia nigra pars reticulata (Waszczak et al., 2002) and a potentiation of arachidonic acid release in Chinese hamster ovary cells coexpre...

Pneumomediastinum can result from blunt chest trauma in sports. Diagnosis is made using chest radiography. The natural history of isolated pneumomediastinum is benign; however, it can be associated with more serious injuries, such as disruption of the tracheobronchial tree or a perforated digestive viscus. Patients with isolated pneumomediastinum should be monitored with serial chest radiographs. Patients may return to full activity once their chest radiographs have returned to normal, they exhibit no symptoms, and they have regained their stamina.

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Of 30 patients, one patient was found to have multifocal biliary strictures requiring two biliary stents on endoscopic retrograde cholangiopancreatography five months post procedure (n ¼ 1, 3.3%). Two patients demonstrated grade 3/4 bilirubin toxicity (n ¼ 2, 6.7%). The average treatment dosage was 135 Gray (range, 95-341 Gy). Compared to the biliary complication rate described in the literature for HCC with 2.1% for biliary findings on imaging and 6.8% for grade 3/4 bilirubin toxicity 2 , our study showed comparable rates of 3.3% and 6.7%, respectively. Conclusions: Yttrium-90 radioembolization of segment IV HCC demonstrated no significant difference in biliary complication rates compared to nonsegment specific biliary complication rates reported in the literature.

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