Uniformity and specificity of function of monoaminergic receptors in the caudate nucleus and nucleus accumbens

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1. Electrophysiological study was performed to examine the actions of haloperidol and sulpiride on the nucleus accumbens neurons of rats receiving input form the parafascicular nucleus of thalamus, and to investigate whether or not the drugs antagonize the effects of exogenously applied dopamine and methamphetamine. The results indicated that exogenously applied dopamine as well as endogenously released dopamine produced an inhibition of the neuronal activities in the nucleus accumbens.2. Methamphetamine also inhibited the nucleus accumbens neurons receiving input from the parafascicular nucleus of thalamus, probably by releasing dopamine form dopaminergic nerve terminals from the ventral tegmental area.3. Microiontophoretic studies using anesthetized cats were performed to determine whether or not depamine D-1 and D-2 receptors co-exist in the same caudate nucleus neurons that receive inputs from the substantia nigra, and in which spikes elicited by nigral stimulation were blocked by domperidone, a selective D-2 antagonist. The results strongly suggested that the inhibitory D-1 and excitatory D-2 receptors co-exist on the same caudate neurons.4. Effects of dopamine at low (1<mu>M) and high (100<mu>M) concentration on the rat caudate nucleus neurons were examined in a slice preparation using an intracellular recording technique. The results indicated that the postynaptic sites of caudate nucleus neurons have at least two subtype of dopamine receptors, D-1 and D-2 receptors, that mediate inhibitory and excitatory responses of the neuron to dopamine, respectively.5. Effects of bromocriptine, a selective agonist for dopamine D-2 receptor, on the rat caudate nucleus neurons were examined in a slice preparation. The results implied that dopamine D-2 receptors activated by bromocriptine and a low concentration of dopamine mediated an excitation of the caudate nucleus neurons.