In any case, it has been elucidated that acute blockade of NMDA receptors in the brain results in an activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPA receptors), which in turn modulate a variety of downstream signaling pathways to influence neurotransmission in the limbic system and mediate antidepressant effects of NMDA receptor antagonists like ketamine. Such downstream actions of this activation of AMPA receptors include upregulation of brain-derived neurotrophic factor (BDNF) and activation of its signaling receptor tropomyosin receptor kinase B (TrkB), activation of the mammalian target of rapamycin (mTOR) pathway, deactivation of glycogen synthase kinase 3 (GSK-3), and inhibition of the phosphorylation of the eukaryotic elongation factor 2 (eEF2) kinase. In addition to blockade of the NMDA receptor, the active metabolite of ketamine hydroxynorketamine, which does not interact importantly with the NMDA receptor, but nonetheless indirectly activates AMPA receptors similarly, may also or alternatively be involved in the rapid-onset antidepressant effects of ketamine. Recent research has elucidated that an acute inhibition of the lateral habenula, a part of the brain in the limbic system that has been referred to as the "anti-reward center" (projecting to and inhibiting the mesolimbic reward pathway and modulating other limbic areas), may be involved in the antidepressant effects of ketamine.Ketamine is a mixture of equal amounts of two enantiomers: esketamine and arketamine. Esketamine is a more potent NMDA receptor antagonist and dissociative hallucinogen than arketamine. Because of the hypothesis that NMDA receptor antagonism underlies the antidepressant effects of ketamine, esketamine was developed as an antidepressant.
When air and fluid mix together in the pericardial sac, a tinkling sound superimposed over a succussion splash is heard. This is known as a “Bruit de Moulin”, which is French for “Mill–wheel” murmur. Air between the anterior parietal pericardium and the thoracic cage may also give rise to the “Hamman’s Sign” – which is a crunching sound typically heard on auscultation of the chest, but may sometimes be heard even with the unaided ear. Treatment
See also
Hammans sign

References
Further reading
Karoui, Mehdi; Bucur, Petru Octav (2 October 2008). "Pneumopericardium". New England Journal of Medicine. 359 (14): e16. doi:10.1056/NEJMicm074422. Franklin, WJ; Arora, G; Ayres, NA (2003). "Pneumopericardium and pneumomediastinum in an adolescent after blunt chest trauma". Texas Heart Institute Journal. 30 (4): 338–9. PMC 307727. PMID 14677752. == External links ==