Blood flow within the brain is highly regulated, but the mechanism of blood flow control is poorly understood. Glutamate is known as the major transmitter regulating it. Better understanding of the neurochemical basis for blood flow resulting oxygen changes will clarify the analysis of human neuroimaging scans (PET and fMRI) and aid our understanding of its disruption which can lead to headaches, ischemia, and neuronal death. We believe that other neurotransmitters including histamine and serotonin control blood flow in the substantia nigra pars reticulata and nucleus accumbens of the rat brain. Increasing serotonin, but not dopamine, in the entire brain attenuates oxygen levels in both regions. Local application of high concentrations of serotonin in these regions decreases oxygen levels, while application of low concentrations increases oxygen locally. Injecting histamine locally amplifies oxygen while dopamine has no effect. The results indicate that histamine dilates cerebral blood vessels and serotonin exhibits a concentration dependent effect on blood flow.