Resent epidemiological studies have associated type 2 diabetes mellitus with an increased risk of developing Alzheimer's disease (AD).
Previously, we examined the effects of intracerebral administration of streptozotocin (STZ) on cognitive performance in rats. This STZ-treated rats, one of the AD models showed significant declines in all the parameters of the MWM task compared to control rats. Immunohistochemical analysis using hippocampal formations revealed decreases in pCREB, Akt, somatostatin, insulin receptor, and insulin-degrading enzyme immunoreactivities and a meaningful increase in amyloid beta immunoreactivity that was especially marked in the crest of the dentate gyrus. An intraventricular injection of a long acting insulin analogue improved these STZ-induced behavioural and immunohistochemical changes
In this study, morphological analysis of the granule cell layer neurons of the dentate gyrus using Golgi-COX stain and spine density counting was done, since Alzheimer disease is a disease of synaptic failure in the hippocampus.
After the intracerebral STZ injection, there was the decrease of the ratio to which the granule cell layer fills the space that was recovered by intracerebral insulin administration. In addition, the STZ-3V-treated rats showed diminished spine densities in all the 3 types of spines.
It is concluded that in the STZ-rats, there are injuries in the primary recipients of excitatory input into the granule cell layer through the perforant pathway.