Decrease of synaptic plasticity associated with alteration of information flow in a rat model of vascular dementia

Abstract

This investigation examined whether the directional index of neural information flow (NIF) could be employed to characterize the synaptic plasticity in the CA3-CA1 pathway of the hippocampus and assessed which oscillatory rhythm was associated with cognitive impairments induced by vascular dementia (VD). Rats were randomly divided into control and VD groups. The animal model of VD used the two-vessel occlusion (2VO) method. Behavior was measured using the Morris water maze (MWM). Local field potentials (LFPs) from CA3 and CA1 were recorded after behavioral tests, followed by recording long-term potentiation (LTP) of the same CA3-CA1 pathway. General partial directed coherence (gPDC) approach was utilized to determine the directionality of NIF between CA3 and CA1 over five frequency bands, which were delta, theta, alpha, beta, and gamma. The results showed that the escape latencies were significantly prolonged in the VD group, whereas the swimming speeds of these two groups remained constant throughout testing. Moreover, the phase synchronization values between CA3 and CA1 regions were reduced in theta, alpha, beta, and gamma bands in the VD state compared to that in the normal state. The coupling directional index was considerably decreased in the previously given four frequency bands in VD rats, whereas the strength of CA3 driving CA1 was significantly reduced in the same frequency bands. Interestingly, LTP was significantly decreased in the VD group, which was consistent with the LFPs findings. The data suggest that the directionality index of NIF in these physiological oscillatory rhythms could be used as a measure of synaptic plasticity in the hippocampal CA3-CA1 pathway in VD states. The potential mechanism of the relationship between NIF direction and synaptic plasticity in VD state was discussed.