Modulation of nitrergic pathway by sesamol prevents cognitive deficits and associated biochemical alterations in intracerebroventricular streptozotocin administered rats

Alzheimer's disease is a neurodegenerative disorder characterized by progressive cognitive decline and widespread loss of neurons and their synapses in the cerebral cortex and hippocampus. Increasing evidence indicates that factors such as oxidative–nitrergic stress, glutathione depletion, impaired protein metabolism and cholinergic deficit can interact in a vicious cycle, which is central to Alzheimer's disease pathogenesis. Intracerebroventricular (i.c.v.) streptozotocin induced-cognitive impairment has been widely used as an experimental paradigm to study Alzheimer's disease. In the present study, i.c.v. streptozotocin produced significant cognitive deficits as measured in Morris water maze and elevated plus maze task coupled with increased serum TNF-α levels and marked rise in brain acetylcholinesterase and oxidative–nitrergic stress in female Wistar rats. Sesamol (5-hydroxy-1,3-benzodioxole or 3,4-methylenedioxyphenol), a potent anti-oxidant and anti-inflammatory molecule markedly improved cognitive impairment, reduced acetylcholinesterase activity, TNF-α levels and attenuated oxidative–nitrergic stress in brain of i.c.v.-streptozotocin treated rats. Administration of l-arginine (125 mg/kg i.p), a nitric oxide donor, alone to i.c.v.-streptozotocin treated rats accentuated behavioral and biochemical deficits and also abolished the protective effect of sesamol (8 mg/kg). l-NAME (10 mg/kg i.p.), a non-specific NOS inhibitor significantly restored all the behavioral and biochemical indices in i.c.v.-streptozotocin rats. Moreover, combination of l-NAME with sub-effective dose of sesamol (4 mg/kg) potentiated its protective effect. Our findings demonstrate the effectiveness of sesamol in preventing intracerebroventricular streptozotocin-induced cognitive deficits by modulating nitrergic signaling and oxido-inflammatory cascade.