Stereological Evidence of Non-Selective Hippocampal Neurodegeneration, IGF-1 Depletion, and Behavioral Deficit following Short Term Bilateral Adrenalectomy in Wistar Rats

Abstract

The development of animal models to study cell death in the brain is a delicate task. One of the models, that was discovered in the late eighties, is the induction of neurodegeneration through glucocorticoid withdrawal by adrenalectomy in albino rats. Such a model is one of the few noninvasive models for studying neurodegeneration. In the present study, using stereological technique and ultrastructural examination, we aimed to investigate the impact of short-term adrenalectomy (2 weeks) on different hippocampal neuronal populations in Wistar rats. In addition, the underlying mechanism(s) of degeneration in these neurons were investigated by measuring the levels of insulin-like growth factor-1 (IGF-1) and β-nerve growth factor (β-NGF). Moreover, we examined whether the biochemical and histological changes in the hippocampus, after short-term adrenalectomy, have an impact on the cognitive behavior of Wistar rats. Stereological counting in the hippocampus revealed significant neuronal deaths in the dentate gyrus and CA4/CA3, but not in the CA2 and CA1 areas, 7 and 14 days post adrenalectomy. The ultrastructural examinations revealed degenerated and degenerating neurons in the dentate, as well as CA4, and CA3 areas, over the course of 3, 7 and 14 days. The levels of IGF-1 were significantly decreased in the hippocampus of ADX rats 24 h post adrenalectomy, and lasted over the course of two weeks. However, β-NGF was not affected in rats. Using a passive avoidance task, we found a cognitive deficit in the ADX compared to the SHAM operated rats over time (3, 7, and 14 days). In conclusion, both granule and pyramidal cells were degenerated in the hippocampus following short-term adrenalectomy. The early depletion of IGF-1 might play a role in hippocampal neuronal degeneration. Consequently, the loss of the hippocampal neurons after adrenalectomy leads to cognitive deficits.

Keywords

• hippocampus
• neurodegeneration
• adrenalectomy
• passive avoidance
• stereology