Abstract
Changes of neural oscillations at a variety of physiological rhythms are effectively associated with cognitive performance. The present study investigated whether the directional indices of neural information flow (NIF) could be used to symbolize the synaptic plasticity impairment in hippocampal CA3-CA1 network in a rat model of melamine. Male Wistar rats were employed while melamine was administered at a dose of 300 mg/kg/day for 4 weeks. Behavior was measured by the Morris water maze(MWM)test. Local field potentials (LFPs) were recorded before long-term potentiation (LTP) induction. Generalized partial directed coherence (gPDC) and phase-amplitude coupling conditional mutual information (PAC_CMI) were used to measure the unidirectional indices in both theta and low gamma oscillations (LG, ∼30–50 Hz). Our results showed that melamine induced the cognition deficits consistent with the reduced LTP in CA1 area. Phase locking values (PLVs) showed that the synchronization between CA3 and CA1 in both theta and LG rhythms was reduced by melamine. In both theta and LG rhythms, unidirectional indices were significantly decreased in melamine treated rats while a similar variation trend was observed in LTP reduction, implying that the effects of melamine on cognitive impairment were possibly mediated via profound alterations of NIF on CA3-CA1 pathway in hippocampus. The results suggested that LFPs activities at these rhythms were most likely involved in determining the alterations of information flow in the hippocampal CA3-CA1 network, which might be associated with the alteration of synaptic transmission to some extent.
Highlights
Hippocampus is known to be an essential part for learning and memory [1] with synaptic plasticity as the accepted underling mechanism [2]
Morris Water Maze (MWM) Tests Table 1 displays the results of MWM test
It could be seen that the remarkable reduced platform crossings (Mel: 3.2561.58 vs. Con: 6.2561.55, p,0.01) and the quadrant dwell time (Mel: 18.1565.38% vs. Con: 33.8866.84%, p,0.01) in Mel group compared to that in Con group, suggesting that the memory abilities were impaired by melamine
Summary
Hippocampus is known to be an essential part for learning and memory [1] with synaptic plasticity as the accepted underling mechanism [2]. Synapses are crucial for neural cell communication through the release of neurotransmitter from presynaptic neurons to postsynaptic ones. A previous study showed that the synapses in hippocampus were most chemical ones with glutamate as the primary excitatory neurotransmitter [3]. Long-term potentiation (LTP) in hippocampal CA3-CA1 pathway, which is largely mediated by glutamate neurotransmitter, is one of the important indices of synaptic plasticity [4,5]. Neuronal oscillations are classified into delta 1–4 Hz, theta 4– 8 Hz, alpha 8–13 Hz, beta 13–30 Hz and gamma 30–100 Hz [7]. It was reported that theta oscillation could mediate the glutamate synaptic information flow in the hippocampus [10,11], which in reverse affected the activity of the hippocampal network [10,12]
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