Abstract
Alzheimer`s disease (AD) is a neurodegenerative disorder caused by deposition of the amyloid-beta peptide (Aβ) in senile plaques and cerebral vasculature. Its neurotoxic mechanisms are associated with generation of oxidative stress and reactive astrogliosis that cause neuronal death and memory impairment. The most vulnerable part of the brain is the hippocampus, a key structure with important role in the adult neurogenesis and formation of long term memory. The hippocampus receives connections originating in the areas of cortex also severely affected in AD. The reported sparing of NADPH-d neurons in AD and the potential involvement of NO in the pathology of this disease led us to investigate whether NADPH-diaphorase (NADPH-d), a histochemical marker for NO activity, expression is altered in the hippocampus. Experimental model of AD was induced by intracerebroventricular injection of streptozotocin (STZ 3 mg/kg body weight, twice with an interval of 48 h). The cannulae were implanted in the lateral brain ventricle (AP =-0.8 mm, L=1.6mm, DV=- 4.2 mm) under anesthesia (ketalar 80 mg/kg and xylasine 4 mg/kg) using a stereotaxic apparatus. Four months later the animals were anaesthetized and perfused through the heart with fixative (4% paraformaldehyde in 0.1M phosphate buffer). Brains were removed and sectioned by a freezing microtome. Then a histochemical procedure for NADPH-diaphorase NO activity was estimated. Ten sections were utilized for calculation of the neuronal packing density. Our results showed that NADPH-d positive neurons were significantly less in the hippocampal formation of rats with AD. In conclusion, these findings indicate that NADPH-d expressing neurons are highly susceptible to neurodegeneration and that NO might contribute to the pathogenesis of AD. Clarifying the profiles of nitric oxide in the brain tissues and its participation in pathophysiological processes opens a new avenue for development of new therapeutic strategies.The research was supported by Grant 18/2016 of the Medical University of Sofia, Bulgaria.
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