title: Experimental evaluation and computational modeling of tissue damage from low-flow push-pull perfusion sampling in vivo.
abstract: BACKGROUND
  Neurochemical monitoring via sampling probes is valuable for deciphering neurotransmission in vivo. Microdialysis is commonly used; however, the spatial resolution is poor.
  
  
  METHODS
  Recently push-pull perfusion at low flow rates (50nL/min) has been proposed as a method for in vivo sampling from the central nervous system. Tissue damage from such probes has not been investigated in detail. In this work, we evaluated acute tissue response to low-flow push-pull perfusion by infusing the nuclear stains Sytox Orange and Hoechst 33342 through probes implanted in the striatum for 200min, to label damaged and total cells, respectively, in situ.
  
  
  RESULTS
  Using the damaged/total labeled cell ratio as a measure of tissue damage, we found that 33±8% were damaged within the dye region around a microdialysis probe. We found that low-flow push-pull perfusion probes damaged 24±4% of cells in the sampling area. Flow had no effect on the number of damaged cells for low-flow push-pull perfusion. Modeling revealed that shear stress and pressure gradients generated by the flow were lower than thresholds expected to cause damage. Comparison with existing methods.Push-pull perfusion caused less tissue damage but yielded 1500-fold better spatial resolution.
  
  
  CONCLUSIONS
  Push-pull perfusion at low flow rates is a viable method for sampling from the brain with potential for high temporal and spatial resolution. Tissue damage is mostly caused by probe insertion. Smaller probes may yield even lower damage.
authors.affiliation: University of Michigan, Department of Biomedical Engineering, 1101 Beal Ave, Ann Arbor, MI, 49109, United States; University of Michigan, Department of Chemistry, 930N University Ave, Ann Arbor, MI, 48109, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Cepeda
authors.affiliation: Wadsworth Center, NYS Department of Health, New York State Bicycle Route 5, Albany, NY 12201, United States.
authors.forename: Leah
authors.initials: L
authors.lastname: Hains
authors.affiliation: University of Michigan, Department of Biomedical Engineering, 1101 Beal Ave, Ann Arbor, MI, 49109, United States.
authors.forename: David
authors.initials: D
authors.lastname: Li
authors.affiliation: University of Michigan, Department of Biomedical Engineering, 1101 Beal Ave, Ann Arbor, MI, 49109, United States.
authors.forename: Joseph
authors.initials: J
authors.lastname: Bull
authors.affiliation: University of Michigan, Department of Internal Medicine, Division of Metabolism, Endocrinology & Diabetes, 6245 Brehm Tower, 1000 Wall Street, Ann Arbor, MI, 48105, United States.
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Lentz
authors.affiliation: University of Michigan, Department of Chemistry, 930N University Ave, Ann Arbor, MI, 48109, United States. Electronic address: rtkenn@umich.edu.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Kennedy
mesh_terms: D000818:Animals; D001562:Benzimidazoles; D002452:Cell Count; D002470:Cell Survival; D003198:Computer Simulation; D003342:Corpus Striatum / Q000473:pathology; D004867:Equipment Design; D008297:Male; D017551:Microdialysis / Q000295:instrumentation; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009930:Organic Chemicals; D010477:Perfusion / Q000295:instrumentation / Q000379:methods*; D011312:Pressure; D017207:Rats, Sprague-Dawley
chemical_list: D001562:Benzimidazoles; D009930:Organic Chemicals; C416802:SYTOX Orange dye; C017807:bisbenzimide ethoxide trihydrochloride
keywords: Brain tissue damage; Cell viability; Computational modeling; In vivo sampling; Microdialysis; Push–pull perfusion