Brain Regional Differences in the Developing Brain Using an Animal Model of Type C Hepatic Encephalopathy

Introduction: Type C hepatic encephalopathy (CHE) is a severe neuropsychiatric disorder associated with chronic liver disease (CLD) in both children and adults. For children with CLD the impairment of neurocognitive functions appears not to be reversible after liver transplant indicating that the developing CNS could be more vulnerable to disease. Our aim was to investigate longitudinally, using in vivo proton magnetic resonance spectroscopy (1H MRS), metabolic differences between hippocampus, cerebellum and striatum of a developing brain as key brain regions involved in a model of CHE. Methods: The bile duct ligation (BDL, model of CHE) surgery was performed on 5 male Wistar rats at postnatal day 21 (P21) (∼9 month- old human), and compared to sham operated animals at the same age (n=6). Hippocampus, cerebellum and striatum were scanned longitudinally using in vivo1H MRS at 9.4 T. First scan and blood tests, were performed at week2 after BDL and every 2 weeks up to week6. Results and Discussion: All BDL rats showed increase in blood bilirubin and ammonia validating CLD. Increase in brain Gln, as a response to NH4+ increase, was present in all 3 brain regions (week6: +173% cerebellum, +112% hippocampus, +68% striatum) (Figure 1). Cerebellum showed the most pronounced increase at week6 (Figure 1B). Increase in blood ammonia correlated significantly with brain Gln, being stronger in cerebellum. Main brain organic osmolytes decreased as a response to Gln increase (osmoregulation), stronger in cerebellum. Significant increase of lactate (Lac) concentration at week6 was observed in all brain regions, stronger in cerebellum (+150% cerebellum, +88% hippocampus, +114% striatum) indicating a possible energy metabolism perturbation. Neurotransmitter glutamate (Glu) and antioxidant ascorbate (Asc) also showed stronger decrease in cerebellum. Conclusion: This is the first study showing in vivo longitudinal overview of metabolic responses of the hippocampus, cerebellum and striatum to CLD in a developing brain. The changes in cerebellum seem to be the most pronounced suggesting increased vulnerability. Further delineation of regional changes in the brain in response to CLD may help elucidate the molecular and regional origins of neuromotor and neurocognitive changes associated with CLD.Figure 1.: A) Longitudinal evolution of Gln in hippocampus, cerebellum and striatum of BDL compared to a sham rats (Two-way ANOVA). B) Percentage change of Gln concentration in BDL rats compared to a shams at each time point. C) Representative spectra from a BDL and a sham operated rat at week6 in cerebellum, hippocampus and striatum with a visible increase of Gln and decrease of mIns in all brain regions studied; (all results are shown always in blue for cerebellum, green for hippocampus and red for striatum), *significance shown always compared to the sham rats.