30 - The Entorhinal Cortex, a Hub for Hippocampal-Neocortical Circuits Mediating Learning and Memory, Has Cholinergic Interneuron Pathology in Adult Mice with Neonatal HI

Poster Number: 30
Publication Number: 30.434

Leslie Doucette, Johns Hopkins Children's Center, Laurel, MD, United States; Lee J. Martin, Johns Hopkins University School of Medicine Department of Pathology, Baltimore, MD, United States; Nazli Kuter, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Katherine M. Carlin, United States Air Force, FPO, Armed Forces - AP, United States; Victoria Turnbill, Johns Hopkins University, Baltimore, MD, United States; Debbie Flock, Johns Hopkins University School of Medicine, Fallston, MD, United States; Shenandoah Robinson, Johns Hopkins Children's Center, Baltimore, MD, United States; Lauren Jantzie, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Raul Chavez-Valdez, Johns Hopkins University School of Medicine, CATONSVILLE, MD, United States; Frances J.. Northington, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Background: Genetic makeup contributes to worse outcome after experimental neonatal traumatic brain injury. Mutations of the APP and PS genes may lead to familiar early onset AD.  Mice transgenic (Tg) for human mutant amyloid precursor protein (APP-Swedish variant) and mutant presenilin (PS1-deltaE9) manifest Aβ proteinopathy, cholinergic denervation, and cognitive impairment as adults.

Objective: To test if neonatal hypoxia-ischemia (HI) would accelerate learning and memory impairment in APP/PS1 mice related with cholinergic degeneration in the entorhinal cortex (EC). 

Design/Methods: Mice mutant or not for APP/PS1 genes had neonatal HI at postnatal day (P) 10 (Vannucci model). Anesthesia exposed littermate were sham controls. Visual discrimination (VD) was used to rigorously test learning and memory. Fifty test days were allowed to achieve 85% correct of 30 trials/day on 2 consecutive days; a score of 51 was assigned otherwise.  Brains were studied at P180. Choline acetyltransferase (ChAT) was used to visualize cholinergic interneurons. ChAT+ interneurons in the EC ipsilateral to ligation were assessed as normal, abnormal, or dystrophic based on somatodendritic morphology. (n=6-7 Tg HI, Tg shams, WT HI, WT sham x 4-5 sections/mouse).

Results: There was a greater % of abnormal interneurons in the EC (mean with SD, ANOVA p=0.001) of APP/PS1 HI vs APP/PS1  sSham mice (p=0.03) and nTgHI vs nTg Sham mice (p=0.03). In VD, APP/PS1 HI mice (n=24) required median of 34.5 test days (IQR 15.25-50.5) to pass VD vs 15 days (IQR 19.5-18.75) for APP-PS1shams (n=22) (p=0.007), nTg HI mice (n=28) required 28.5 test days (IQR 16.5-50.75) to pass VD vs 11 days (IQR 9-16) for nTg shams (n=19) (p<0.001).  There was no effect of genotype in either HI or shams and no correlation between sessions to pass VD and % abnormal interneurons in mice analyzed for both VD and EC interneurons.

Conclusion(s): Neonatal HI has significant effects on adult learning and memory and EC cholinergic interneurons in mice, but these anomalies are unaffected by a mutant APP/PS1 genotype . EC is key to memory and learning and is an important hub linking hippocampus and neocortex, both areas known to be damaged after neonatal HI.  The cholinergic interneuronopathy in EC discovered here adds a cell-level detail to how circuits important to learning and memory are damaged by early life brain injury but without an effect by a mutant APP/PS1 genotype. The apparent genotype insensitivity of  VD and interneuron pathology suggests that early life brain injury has a permanent potent effect unalterable by mechanisms involving Aβ proteinopathy.