Inflammation contributes to seizure-induced hippocampal injury in the neonatal rat brain Introduction There is increasing clinical evidence that seizures in the neonatal period can produce injury that is demonstrable (1) and can contribute substantially to increased morbidity (2). However, in experi- mental neonatal seizures, brain injury has not been demonstrated convincingly in models involving kainic acid (3), hypoxia (4), or hyperthermic seizures (5). In detailed developmental studies involving the lithium–pilocarpine (LiPC) model of status epilepticus (SE), we found no evidence of seizure- induced hippocampal injury in postnatal day 7 (P7) (6), but noted a distinctive pattern of injury in the P14 rat pup with a CA1 predominant lesion with sparing of the CA3 sector and the hilus (7). The bacterial endotoxin lipopolysaccharide (LPS), derived from the outer cell membrane of gram-negative bacteria, has been used to produce an inflammatory response under experimental conditions. Administration of LPS prior to hyp- oxia–ischemia enhanced brain injury in P7 rat pups in a dose-dependent manner (8). Doses of LPS that produced a modest increase in core temperature have been shown to contribute to neuronal injury in P17 rats treated with kainic acid (9). Hippocampal signal changes in the magnetic resonance imaging (MRI) of children after pro- longed febrile convulsions were first reported by VanLandingham et al. (10). More recently, high- resolution MRI studies have revealed that the signal abnormality corresponds to the area of maximal cell loss in mesial temporal sclerosis, namely, area CA1 (11). In this report, we present our findings from experiments involving modest doses of LPS to immature rat pups in a model of SE that we had described as CA1 selective in terms of hippocampal cellular injury (7). Materials and methods Animals, injection of inflammatory factor, and induction of seizures Wistar rat pups (Charles River Laboratories, Wilmington, MA) of either sex were housed in standard laboratory conditions with controlled temperature/humidity, a 12-h light/dark cycle, and Acta Neurol Scand 2007: 115: (Suppl. 186):16–20 Copyright Ó 2007 The Authors Journal compilation Ó 2007 Blackwell Munksgaard ACTA NEUROLOGICA SCANDINAVICA Sankar R, Auvin S, Mazarati A, Shin D. Inflammation contributes to seizure-induced hippocampal injury in the neonatal rat brain. Acta Neurol Scand 2007: 115 (Suppl. 186): 16–20 Ó Blackwell Munksgaard 2007. Objective – The extent of neuronal injury in the hippocampus produced by experimental status epilepticus (SE) is age dependent and is not readily demonstrable in many models of neonatal seizures. Neonatal seizures often occur in clinical settings that include an inflammatory component. We examined the potential contributory role of pre- existing inflammation as an important variable in mediating neuronal injury. Materials and methods – Postnatal day 7 (P7) and P14 rat pups were injected with lipopolysaccharide (LPS), 2 h prior to SE induced by lithium–pilocarpine (LiPC). Neuronal injury was assessed by well- described histologic methods. Results – While LPS by itself did not produce any discernible cell injury at either age, this treatment exacerbated hippocampal damage induced by LiPC–SE. The effect was highly selective for the CA1 subfield. Conclusions – Inflammation can contribute substantially to the vulnerability of immature hippocampus to seizure-induced neuronal injury. The combined effects of inflammation and prolonged seizures in early life may impact long- term outcomes of neonatal seizures. R. Sankar 1,2 , S. Auvin 3 , A. Mazarati 1 , D. Shin 1 1 Division of Neurology, Department of Pediatrics, David Geffen School of Medicine at UCLA and Mattel Children's Hospital at UCLA, Los Angeles, CA, USA; 2 Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA; 3 Pediatric Neurology Department, Lille University Hospital, Lille, France All authors declare no conflict of interests Key words: brain injury; development; hippocampus; inflammation; lipopolysaccharide; rats; seizures Raman Sankar, Department of Pediatrics, Division of Neurology, 22-474 MDCC in CHS, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA Tel.: 310 794 1014 Fax: 310 825 5834 e-mail: rsankar@ucla.edu Accepted for publication 11 December, 2006 16