title: The effects of hyperammonemia in learning and brain metabolic activity.
abstract: Ammonia is thought to be central in the development of hepatic encephalopathy. However, the specific relation of ammonia with brain energy depletions and learning has not been studied. Our work attempts to reproduce an increase in rat cerebral ammonia level, study the hyperamonemic animals' performance of two learning tasks, an allocentric (ALLO) and a cue guided (CG) task, and elucidate the contribution of hyperammonemia to the differential energy requirements of the brain limbic system regions involved in these tasks. To assess these goals, four groups of animals were used: a control (CHA) CG group (n = 10), a CHA ALLO group (n = 9), a hyperammonemia (HA) CG group (n = 7), and HA ALLO group (n = 8). Oxidative metabolism of the target brain regions were assessed by histochemical labelling of cytochrome oxidase (C.O.). The behavioural results revealed that the hyperammonemic rats were not able to reach the behavioural criterion in either of the two tasks, in contrast to the CHA groups. The metabolic brain consumption revealed increased C.O. activity in the anterodorsal thalamus when comparing the HA ALLO group with the CHA ALLO group. Significant differences between animals trained in the CG task were observed in the prelimbic, infralimbic, parietal, entorhinal and perirhinal cortices, the anterolateral and anteromedial striatum, and the basolateral and central amygdala. Our findings may provide fresh insights to reveal how the differential damage to the brain limbic structures involved in these tasks differs according to the degree of task difficulty.
authors.affiliation: Laboratory of Neuroscience, Departamento de Psicología, Universidad de Oviedo, Plaza Feijoo s/n 33003, Oviedo, Spain, ariasnatalia@uniovi.es.
authors.forename: Natalia
authors.initials: N
authors.lastname: Arias
authors.forename: Camino
authors.initials: C
authors.lastname: Fidalgo
authors.forename: Vicente
authors.initials: V
authors.lastname: Felipo
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Arias
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D002908:Chronic Disease; D003463:Cues; D004195:Disease Models, Animal; D003576:Electron Transport Complex IV / Q000032:analysis; D004734:Energy Metabolism; D022124:Hyperammonemia / Q000378:metabolism / Q000523:psychology*; D007859:Learning Disabilities / Q000209:etiology* / Q000378:metabolism; D008032:Limbic System / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D018782:Maze Learning; D057567:Memory, Long-Term; D009419:Nerve Tissue Proteins / Q000032:analysis; D009460:Neurologic Examination; D009949:Orientation; D010364:Pattern Recognition, Visual; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D045442:Rotarod Performance Test
chemical_list: D009419:Nerve Tissue Proteins; D003576:Electron Transport Complex IV