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John Yeomans, PhD |  |
John Yeomans is a behavioral neuroscientist who recently joined the Zoology Department neuroscientists working on the 3rd floor of Ramsay Wright. He obtained his PhD from the University of California, San Diego, and has done postdoctoral work at Penn, Yale and Harvard..
John has studied neural and chemical bases of emotions for 30 years. His work on brain-stimulation reward in rats (discovered at McGill by Olds and Milner in 1953) led to the discovery of the importance of an essential system of brain stem neurons that use the transmitter, acetylcholine. These cholinergic neurons directly activate the dopamine neurons that are known to mediate the rewarding effects of cocaine, amphetamine and nicotine. These cholinergic neurons are also important in triggering dream sleep, and cortical arousal by way of other pathways.
Recently, his group showed that a single gene, the M5 muscarinic receptor, mediates most of the activation of dopamine neurons from the brain stem in reward. They spent three years to make a knockout mouse that is missing the gene for the M5 muscarinic receptor to study the functions of that gene. They are testing whether alterations of the M5 gene are associated with schizophrenia and drug abuse, because both of these conditions depend on dopamine functions. He and his colleague Haoran Wang are often found checking the new databases for the human and mouse genome projects to learn more about the functions of this gene.
In other work, John and colleagues have used electrical stimulation of many pathways in the rat brain to study the circuits that mediate behaviour. For example, they showed that the startle reflex is mediated by pathways in the hindbrain that converge on a small number of giant neurons. These are all fast pathways that combine tactile, acoustic and vestibular inputs to estimate the strength of blows to the head and body. They showed that startle is facilitated by stimulating “fear” pathways from the amygdala, and inhibited by stimulating midbrain pathways, such as the superior colliculus and the brain stem cholinergic neurons. In each pathway they have studied the axons, synapses and transmitters mediating the effects on startle.
Although the brain is a very complicated organ, John believes that studying the simpler parts, such as the neurons, genes and transmitters, will help us understand how the brain is organized. In this way we can appreciate how human emotions can be organized, and be disorganized, in many different mental conditions.