Mammillary body alterations and spatial memory impairment in Wistar rats with thioacetamide-induced cirrhosis

Brain tissue of patients diagnosed with hepatic encephalopathy exhibits cellular morphological changes that could be associated with memory impairment. The mammillary nuclei, located in the posterior part of the hypothalamus, are important for spatial memory formation. This work aimed to assess spatial reference memory and cellular changes in the mammillary nuclei of cirrhotic rats. Spatial reference memory of Wistar rats with thioacetamide-induced cirrhosis was assessed in the Morris water maze. Total cell number of neurons and glial cells and volume of the mammillary nuclei were quantified by stereology. Neuronal and astrocytic nuclear volume in mammillary nuclei and CA1 dorsal hippocampal subfield were assessed by nucleator probe. Cirrhotic rats showed an impaired spatial reference memory in comparison with control animals. Total number of neurons and glial cells were unaltered. In the medial mammillary nucleus (MMn), glial fibrillary acidic protein-immunoreactive astrocytes decreased in the cirrhotic group while the lateral part was unaffected. The medial part of the MMn was larger in the cirrhotic group. The cirrhotic rats showed morphometric cellular changes characterised by an increased neuronal and astrocytic nuclear volume in all the mammillary nuclei and CA1 hippocampal region. These findings suggest that cirrhotic rats show spatial memory impairment that could be linked to astrocytes and neuronal impairment in mammillary nuclei and hippocampus.