Brain amines have become increasingly implicated in several types of mental illness, either the amine-containing cells themselves or discrete populations of target cells which bear receptors for amines. The proposed studies take advantage of two properties of these amine-containing cells to investigate the cellular consequences of activation of the various amine receptors in mammalian brain. First, the cell bodies of the neurones are densely clustered. Second, the cells themselves bear receptors for the amines which they release (autoreceptors). This enables a study to be made of the actions of the amine transmitters on the membrane of the same cells that produce them. Intracellular recordings will be made from single neurones in slices of rat midbrain superfused at 37 degrees C. Three series of experiments will be conducted - involving the 5-hydroxytryptamine (5-HT) cells of the dorsal raphe, the noradrenaline (NA) containing cells of the locus coeruleus and the dopamine (DA) cells of the substantia nigra. First, the ion channels affected by the natural agonists 5-HT, NA and DA will be determined by single-electrode voltage clamp experiments. In these experiments, stable analogues of the natural amines which are selective for particular receptor sub-types will be used. Second, receptors on the neurones will be characterized by pharmacological null methods at equilibrium (antagonist affinities by the Schild method and agonist affinities by the Furchgott technique). Third, the intracellular second messengers (linkage) which couple receptor activation to ion channel will be investigated. Fourth, transmitter release will be measured from the single tissue slice in vitro using tritium labeling techniques. The action of various agonists on transmitter release will be correlated with their actions on membrane conductances measured simultaneously. The proposed studies will significantly increase our understanding of mental illness because the receptors for a variety of psychomimetic and psychotherapeutic agents will be characterized on intact, single brain neurones and because the consequences of receptor activation or blockade will be determined at the level of membrane ion channel and neurotransmitter release.
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