Modulation of the mediodorsal thalamic nitric oxide system ameliorated amnesia and medial prefrontal abnormal network activity in a streptozotocin-induced rat model of Alzheimer's disease.

Abstract

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by amnesia and neuronal network dysfunction. Given that the mediodorsal thalamus (MD) is connected to the medial prefrontal cortex (mPFC), and nitric oxide (NO) signaling is crucial for synaptic plasticity in memory formation, the present study aimed to investigate the role of the MD nitric oxide system in a streptozotocin (STZ)-induced Alzheimer's rat model. Also, the mPFC electrophysiological activity with the local field potential (LFP) was assessed following memory formation under STZ and/or NO agents to evaluate the mPFC interictal epileptiform discharges (IEDs) rate. The results showed that the microinjection of STZ (3 mg/kg/10 μl, 2 times) into the lateral ventricle (LV-STZ) impaired memory formation. Acute intra-MD microinjection of a precursor of nitric oxide, L-Arginine (1.5-6 μg/rat), improved the LV-STZ-induced amnesia. Sub-chronic intra-MD microinjection of an NO system inhibitor, L-NAME (0.5 and 1 μg/rat, 5 times) from the 5th to 13th days after the LV-STZ microinjection, a critical period for producing the neurotoxic effects of STZ on the brain, improved STZ-induced amnesia. Interestingly, the LV-STZ microinjection increased the IEDs in the mPFC, reflecting heightened neuronal hyperexcitability. The manipulation of the MD-NO system was associated with a decrease in the mPFC-IEDs rate, suggesting a negative correlation between the IEDs rate and memory formation. Taken together, these findings highlight the critical role of the MD-NO system in STZ-induced amnesia. Moreover, the dual effects of the MD-NO system manipulation, depending on the context and timing, may counteract STZ-induced amnesia by modulating the mPFC neural activity.