Abstract
Background:
Diabetes mellitus (DM) is a common metabolic disorder with well-known serious secondary complications. It is also associated with central nervous system damage. This damage is characterized by impairments in brain functions, with neurochemical and structural abnormalities.

Aim:
The study was conducted to clarify the neuroprotective effects of olive leaves supplement on brain and brain histological structure of diabetic adult rats.

Methods:
Thirty adult male rats were allocated into three groups, The first group (CC), received an oral supplement containing olive leaves (OLS) and served as a control; another group (DM), diabetes mellitus was induced in these animals and left for 40 days; and the third group was DM+OL, which induced diabetes mellitus, then treated with oral (OLS) for 40 days. The investigation included serum glycemic index measurements, in addition, the level of malondialdehyde (MDA), glutathione (GSH), dopamine (DOP), acetylcholinesterase (AchE) in brain tissue, and histopathology of brain and pancreas.

Results:
We demonstrated a significant increase in glycemic index measurements in diabetic groups (DM, DM+OL) at the beginning of a trial, however, the same parameters were significantly decreased after treatment with OLS in only DM+OL group after 40 days. Study also showed differences in the levels of malondialdehyde (MDA), and glutathione (GSH), in the diabetic groups, which returned to normal levels after being treated with OLS. Moreover, acetylcholinesterase (AchE), and dopamine (DOP) exhibited a significant decline in diabetic rats. However, OLS induced a considerable rise in these neurotransmitters after treatment with it in DM+OL group. The histopathological section of the pancreas and brain showed histopathological changes in (DM) groups, whereas, the tissue was shielded from chemical damage from DM by the (OLS) treatment in DM+OL animals.

Conclusion:
Overall, diabetes impairs glucose hemostasis by affecting glucose concentration, insulin level, and insulin resistance, However, olive leaves supplement restored the glucose hemostasis close to the normal in diabetic rats. Furthermore, diabetes affected neurotransmitters by increasing the level of oxidative stress in brain tissue, and brain cell damage. Nevertheless,
olive leave supplements can ameliorate diabetes mellitus harmful effects by retrieving normal oxidative environment in brain.

Key words: Diabetes, Olive leaves, Brain, Dopamine, Alloxan