Planar cell polarity genes Frizzled3a, Vangl2, and Scribble are required for spinal commissural axon guidance.

BACKGROUND: A fundamental feature of early nervous system development is the guidance of axonal projections to their targets in order to assemble neural circuits that control behavior. Spinal commissural neurons are an attractive model to investigate the multiple guidance cues that control growth cone navigation both pre- and post-midline crossing, as well as along both the dorsal-ventral (D-V) and anterior-posterior (A-P) axes. Accumulating evidence suggests that guidance of spinal commissural axons along the A-P axis is dependent on components of the planar cell polarity (PCP) signaling pathway. In the zebrafish, the earliest born spinal commissural neuron to navigate the midline and turn rostrally is termed commissural primary ascending (CoPA). Unlike mammalian systems, CoPA axons cross the midline as a single axon and allow an analysis of the role of PCP components in anterior pathfinding in single pioneering axons. RESULTS: Here, we establish CoPA cells in the zebrafish spinal cord as a model system for investigating the molecular function of planar cell polarity signaling in axon guidance. Using mutant analysis, we show that the functions of Fzd3a and Vangl2 in the anterior turning of commissural axons are evolutionarily conserved in teleosts. We extend our findings to reveal a role for the PCP gene scribble in the anterior guidance of CoPA axons. Analysis of single CoPA axons reveals that these commissural axons become responsive to PCP-dependent anterior guidance cues even prior to midline crossing. When midline crossing is prevented by dcc gene knockdown, ipsilateral CoPA axons still extend axons anteriorly in response to A-P guidance cues. We show that this ipsilateral anterior pathfinding that occurs in the absence of midline crossing is dependent on PCP signaling. CONCLUSION: Our results demonstrate that anterior guidance decisions by CoPA axons are dependent on the function of planar cell polarity genes both prior to and after midline crossing.

Persistent lactic acidosis after chronic topical application of silver sulfadiazine in a pediatric burn patient: a review of the literature.

A 3-year old male who sustained 2(nd) and 3(rd) degree burns that covered approximately 60% TBSA presented to a large adult and pediatric verified burn center. On hospital day (HD) 26 of his stay, Candida fungemia was identified by blood culture, delaying operative management until HD 47. On HD 47, after his first operative intervention, the patient developed a persistent metabolic and lactic acidosis. On HD 66, a search for a cause of his osmol gap of 56 mOsm/kg revealed a potential source-propylene glycol. Previous studies have implicated the propylene glycol emulsifier in the silver sulfadiazine that was being applied to his skin as a rare cause of lactic acidosis in severely burned patients. Within 24 hours of stopping the silver sulfadiazine therapy, his lactic acidosis and osmol gap resolved; within 72 hours his metabolic acidosis resolved. Silver sulfadiazine is commonly used adjunct therapy in the treatment of 2(nd) and 3(rd) degree burns and generally has few adverse reactions. The absorption of propylene glycol systemically can rarely occur when applied to extensive burns, presumably due to the disruption of the skin barrier; the half-life of PG is 10 hours and can be prolonged with renal disease because ~50% of the sulfadiazine is excreted in the urine unchanged. When propylene glycol is present systemically, it is metabolized to lactic acid in the liver, which can cause a lactic acidosis. Several commonly used drugs also use propylene glycol as an emulsifier, including IV preparations of lorazepam, pentobarbital, phenobarbital, and phenytoin. In all of these clinical scenarios, including severe burn patients that are being treated with silver sulfadiazine, both lactic acid and propylene glycol levels should be measured to monitor for this rare, potentially serious co-morbidity.