Ethanol is a vasoactive agent as well as psychoactive drug. The neurovascular response, coupled with neuronal activity, can be disturbed by alcohol intake. Hence, blood oxygenation level-dependent (BOLD) fMRI, which relies on neurovascular coupling, might not be reliable to reflect alcohol-induced neuronal responses. Recently, diffusion fMRI has been shown to be more sensitive to neural activity than BOLD fMRI even when neurovascular coupling is disrupted. Especially, the apparent diffusion coefficient (ADC) is sensitive to changes occurring in the cellular tissue structure upon activation. In the present study, we compared BOLD fMRI signals, ADC, and local field potentials (LFPs) in the nucleus accumbens (NAc) following injection of an ethanol solution (0.4 g/kg body weight) in rats under medetomidine anesthesia. An increase in the gamma oscillation power of LFP and an ADC decrease were observed 5 min after the injection of EtOH. The BOLD signals showed a negative slow drift, similar to mean arterial pressure with a peak approximately 10 min after the injection. These results confirm that DfMRI can be a better marker of the neuronal activity than BOLD fMRI, especially when the brain hemodynamic status is changed by vasoactive drugs such as ethanol.
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