Please cite this article in press as: Osredkar D, et al. Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic–ischemic brain injury. Resuscitation (2013), http://dx.doi.org/10.1016/j.resuscitation.2013.12.006 ARTICLE IN PRESS G Model RESUS 5815 1–6 Resuscitation xxx (2013) xxx–xxx Contents lists available at ScienceDirect Resuscitation jo ur nal homep age: www.elsevier.com/locate/resuscitation Experimental paper Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic–ischemic brain injury  Damjan Osredkar a , Marianne Thoresen a,b,∗ , Elke Maes a , Torun Flatebø a , Q1 Maja Elstad a , Hemmen Sabir a,c a Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway b School of Clinical Sciences, University of Bristol, St Michael’s Hospital, Bristol, United Kingdom c Department of General Pediatrics, Neonatology and Pediatric Cardiology, University Children’s Hospital, Düsseldorf, Germany a r t i c l e i n f o Article history: Received 16 October 2013 Received in revised form 10 December 2013 Accepted 13 December 2013 Available online xxx Keywords: Infection Hypoxia–ischemia Hypothermia Neuroprotection Animal models a b s t r a c t Background: Therapeutic hypothermia (HT) is the standard treatment after perinatal hypoxic–ischemic (HI) injury. Infection increases vulnerability to HI injury, but the effect of HT on lipopolysaccharide (LPS) sensitized HI brain injury is unknown. Design/methods: P7 rat pups were injected either with vehicle or LPS, and after a 4 h delay they were exposed to left carotid ligation followed by global hypoxia inducing a unilateral stroke-like HI injury. Pups were randomized to the following treatments: (1) vehicle treated HI-pups receiving normothermia treatment (NT) (Veh-NT; n = 30); (2) LPS treated HI-pups receiving NT treatment (LPS-NT; n = 35); (3) vehicle treated HI-pups receiving HT treatment (Veh-HT; n = 29); or (4) LPS treated HI-pups receiving HT treatment (LPS-HT; n = 46). Relative area loss of the left/right hemisphere and the areas of hippocampi were measured at P14. Results: Mean brain area loss in the Veh-NT group was 11.2 ± 14%. The brain area loss in LPS-NT pups was 29.8 ± 17%, which was significantly higher than in the Veh-NT group (p = 0.002). The Veh-HT group had a significantly smaller brain area loss (5.4 ± 6%), when compared to Veh-NT group (p = 0.043). The LPS-HT group showed a brain area loss of 32.5 ± 16%, which was significantly higher than in the Veh-HT group (p < 0.001). LPS-HT group also had significantly smaller size of the left hippocampus, which was not found in other groups. LPS-sensitization significantly decreased the sizes of the right, unligated-hemispheres, independent of post-HI treatment. Conclusions: Therapeutic hypothermia is not neuroprotective in this LPS-sensitized unilateral stroke-like HI brain injury model in newborn rats. Lack of neuroprotection was particularly seen in the hippocampus. Pre-insult exposure to LPS also induced brain area loss in the unligated hemisphere, which is normally not affected in this model. © 2013 Published by Elsevier Ireland Ltd. 1. Introduction Perinatal hypoxic–ischemic (HI) injury is one of the major causes of long-term neurological disability or death in term newborns. Infection is known to be a major confounding factor for neona- tal morbidity and mortality, especially in developing countries. 1 Abbreviations: CNS, central nervous system; HI, hypoxia–ischemia; HT, therapeutic hypothermia; i.p., intraperitoneal; LPS, lipopolysaccharide; NT, nor- mothermia; SD, standard deviation.  A Spanish translated version of the abstract of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2013.12.006. ∗ Corresponding author at: Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway. E-mail addresses: marianne.thoresen@medisin.uio.no, marianne.thoresen@bristol.ac.uk (M. Thoresen). Perinatal infection increases the vulnerability of the newborn brain to HI. 2–5 In an established neonatal rat model of unilateral HI brain injury, 6 a longer period of exposure to hypoxia results in increased brain injury. 7 In the same model, increased injury can also follow a shorter period of hypoxia, if animals have been subjected to a mild infectious stimulus such as pre-exposure to bacterial lipopolysac- charide (LPS) before HI. 3 Therapeutic hypothermia (HT) is the standard treatment for term infants after perinatal HI injury, 8 as it has been shown to sig- nificantly reduce mortality and neurodevelopmental disability in survivors. 9 However, around 50% of cooled asphyxiated newborns still suffer poor outcomes, 9 some of which may have been exposed to perinatal infection. 10 It has been shown that HT influences many cascades that follow a HI injury, including inflammatory and anti- inflammatory pathways, 11–13 but this influence might be different following pre-exposure to an infectious stimulus. 0300-9572/$ – see front matter © 2013 Published by Elsevier Ireland Ltd. http://dx.doi.org/10.1016/j.resuscitation.2013.12.006 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44