Docosahexaenoic acid (DHA) improves the age-related impairment of the coupling mechanism between neuronal activation and functional cerebral blood flow response: a PET study in conscious monkeys

The regional cerebral blood flow (rCBF) response to vibrotactile stimulation was compared in conscious young (5.9+/-1.8 years old) and aged (18.0+/-3.3 years old) monkeys using [15O]H(2)O and high-resolution positron emission tomography (PET). In addition, the effects of docosahexaenoic acid (DAH), an n-3 polyunsaturated fatty acid (PUFA), on the rCBF response to stimulation were evaluated in aged monkeys. Soybean milk (SBM) or DHA-containing SBM (DHA/SBM) was supplied to aged monkeys for 1 and 4 weeks. Under control conditions, vibrotactile stimulation elicited an increase in the rCBF response in the contralateral somatosensory cortices of both young and aged monkeys, but the degree of increase in the rCBF response was significantly lower in aged monkeys (116% of corresponding 'rest' condition) than that in young animals (141%). The regional cerebral metabolic rate of glucose (rCMRglc) response to the stimulation, an index of neuronal activation, was not significantly different between young and aged monkeys as measured by [18F]-2-fluoro-2-deoxy-D-glucose (FDG). Supply of DHA/SBM at a dose of 150 mg/kg/day as DHA for 1 week resulted in a significant increase in rCBF response to stimulation (127%) in aged monkeys, and 4-week supply of DHA induced further facilitation of the rCBF response (133%). In contrast, the reduced rCBF response in the aged monkeys was not affected by SBM alone for either 1 or 4 weeks. The neuronal activation itself elicited by the stimulation, as measured by [18F]FDG, was not affected by SBM or DHA/SBM. These results suggested the involvement of DHA in the coupling mechanism between the neuronal activation and rCBF response, possibly by modulation of cholinergic neuronal transmission.