Amphetamine and related drugs of abuse elicit species-specific motor responses characterized by repetitive or stereotyped patterns. Research on animals, typically rodents, as models of the human response, has implicated the striatum and related basal ganglia circuitry in the motor-activating effects of these drugs. Critical elements of this circuitry include both dopamine- and glutamate-containing fibers that contact neurons in dorsal striatum. During amphetamine-induced motor activation, these neurons establish a pattern of discharge activity mediated, at least in part, by a complex interaction between dopamine and glutamate inputs. Research in this application extends this line of work on behaving animals in two directions. One involves characterization of the neuronal response pattern to amphetamine in substantia nigra pars reticulata, a major target of striatal neurons and an important output nucleus of the basal ganglia. After basic neurobehavioral correlations are established, further studies will examine the extent to which amphetamine-induced changes in reticulata neurons are mediated by the striatum via descending GABA-containing projections.
The aim i s to determine how amphetamine-induced neuronal response patterns established in striatum are represented in reticulata neurons. A second focus of the proposed research is to examine at the single-neuron level how the major transmitters altered by amphetamine-- dopamine and glutamate--interact with each other and with GABA to influence the activity of striatal neurons in an intact, normally functioning animal. Dopamine, glutamate, and GABA will be applied directly by iontophoresis to electrophysiologically isolated single units in awake, unrestrained rats. Attention will center on the mechanisms by which synaptic dopamine modulates glutamate- and GABA- mediated responses. A major component of this work also involved iontophoresis of amphetamine and other indirect dopamine agonists in striatum to determine how local changes in dopamine transmission modulate striatal activity and to reveal the synaptic action of these drugs unaccompanied by concomitant activation of other neuronal pathways. Collectively, these lines of research will provide important new information on the neurochemical systems and processes by which amphetamine alters neuronal function and motor behavior.
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