[Behavioral and neuropathological analyses of rats with intrahippocampal lesions]

Rats with intrahippocampal lesions produced by infusion of colchicine showed an impairment of learning ability and a decrease in local choline acetyl-transferase activity. In addition, these rats showed bizarre excitable behavior from 3 days after infusion for about an average of 10 days. This included daytime arousal, and easy jumping and squeak reactions against external stimuli as compared to the sham-operated control rats. Moreover, three-dimensional behavioral analysis disclosed: (i) the lesioned rats showed an increase ambulation compared to the control rats, (ii) a more centrally oriented sequence of wandering, while the control rats tended to display peripheral movement around the wall of the test cage, and (iii) they showed a decrease movement associated with rearing compared to the control rats. Neuropathologically, pyramidal neurons and fascia dentata of the lesioned hippocampus showed degeneration from 3 days with a marked astrocytic reaction. In addition, transient over expression of synaptophysin-immunoreactive material was seen in early stage of degeneration and this corresponded ultrastructurally to the presence of swollen synaptic boutons containing numerous non-core synaptic vesicles. These findings appeared to represent in part an abnormal excitement seen in patients with organic brain lesions, in which the excitement has been considered to correspond with neuronal death. Thus, the hippocampus-lesioned rats may provide an animal model to analyse the abnormal behaviors associated with neuronal death.