Dopamine (DA) mediates a number of important behavioral and motor events in the central nervous system. These events are governed by one of several subtypes of DA receptors and are influenced by several other neurotransmitter and neuromodulator systems. Past efforts to understand the regulation and function of DA receptors have utilized pharmacological agents that act directly on these receptors. However, in many cases these actions are not specific, as these agents interact with more than one subtype of DA receptor or even interact with receptors for other neurotransmitters. The present study aims to provide a new approach toward the goal of understanding the regulation and function of the DA receptor subtypes, utilizing antisense oligodeoxynucleotides (ODNs) targeted towards the individual mRNAs encoding each of the subtypes of DA receptors. Specifically, it will examine the hypotheses that: a) There is a pool of newly-synthesized DA receptors which constitute the functional pool of these receptors; a hypothesis that may explain why relatively small changes in the total pool of receptors can cause large functional changes in DA responses. To test this hypothesis, we will inhibit the total pool of receptors and then determine the effects of DA antisense ODNs on the rate of recovery of the DA receptors and dopaminergic function; b) There is a feedback control mechanism whereby inhibition of the expression of a specific DA receptor transcript can increase the rate of synthesis of that transcript. This hypothesis will be tested by administering specific DA antisense ODNs for long periods of time and measuring the rate of synthesis of the individual DA receptor mRNAs; c) Certain DA agonists may produce diverse behavioral effects by interacting with different DA receptor subtypes. This hypothesis will be tested by determining the effects of antisense ODNs directed toward the different DA receptor subtypes on the different behaviors mediated by the DA agonist quinpirole. DA receptor mRNAs will be assessed by in situ hybridization histochemistry, and the density and location of DA receptors will be assessed by receptor autoradiography. Biochemical events associated with altered DA activity will also be measured and correlated with the behavioral changes observed. Finally, as the function for the D3, D4 or D5 DA receptors is presently unknown, the effects of ODNs directed toward the mRNAs encoding for these subtypes of DA receptors will be assessed by measuring a battery of behaviors, again correlating these changes with alterations in DA receptors and their mRNAs. In all these studies, great care will be taken to determine whether or not the biological actions observed are, in fact, selective and whether they are due to inhibition of the synthesis of the specific DA receptor subtypes. For example, positive and negative controls for the ODNs will be included in these studies, and the behavioral, biochemical and molecular effects of the antisense ODNs will be examined in great detail, including time- and dose-response studies on the levels of specific DA receptor mRNAs and on the density of DA receptor subtypes. We expect that these studies will not only provide new information on the functional role of the newly-synthesized pool of DA receptors, but will also provide a new strategy for modifying specific DA-mediated events in the central nervous system and may provide the framework for uncovering the function of the newly-discovered subtypes of DA receptors and perhaps for the function of receptors for other neurotransmitter systems. They may also help lay the groundwork for developing novel therapeutic agents for treating certain disorders such as schizophrenia and tardive dyskinesia that are associated with abnormal DA activity.
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