This application is for a new R21 under the Cutting-Edge Basic Research Awards (CEBRA) mechanism from NIDA. The majority of studies that examine the consequences of drug abuse and withdrawal focus on the impact of long-term administration of drugs. However, at this stage of use the brain has undergone substantial physiological changes that are typically resistant to effective treatment. On the other hand, it is clear that naive subjects show substantial negative affective responses upon withdrawal from even single doses of a psychostimulant, sufficient to cause the individual to seek more drug to obviate these actions. However, the neuronal circuitry and the physiological changes that underlie such acute actions are unknown. A dominant theory in drug abuse relates to the opponent-process model, in which taking a drug that is associated with a brief positive emotional effect leads to a homeostatic alteration that opposes this action with a long-term negative affective state. Given the involvement of the dopamine system in reward and in anhedonia, we recorded the activity of dopamine neurons in the ventral tegmental area. Our results show that animal models of depression are associated with a decrease in the number of dopamine neurons firing, termed population activity. Moreover, we find a similar effect 18 hours following administration of amphetamine, consistent with this negative affective state. In both animal models of depression and 18 hours after amphetamine, this depression in dopamine neuron activity can be reversed by inactivating the amygdala or by administering the NMDA channel blocker ketamine;a drug that is known to be a rapidly acting antidepressant. Taken together, these data support our central hypothesis: The negative affective state following amphetamine withdrawal, which drives individuals to take additional doses of the drug, is mediated via an amygdala-driven decrease in ventral tegmental area DA neuron firing;moreover, this state is reversed by ketamine administration. We propose to test this model in a rat using acute amphetamine administration and withdrawal according to these Specific Aims: 1) Test the effects of acute amphetamine administration on dopamine neuron activity states measured at different time points after administration. 2) Test whether amygdala inactivation or administration of propranolol or ketamine after amphetamine will prevent the decrease in ventral tegmental area dopamine neuron population activity. 3) Test whether the decrease in dopamine neuron activity state measured at 18 hours post-amphetamine correlates with a change in a progressive ratio scale of amphetamine self-administration, and if this can be altered by propranolol or ketamine pre-treatment. This is a highly novel approach that can provide both insights into the neural circuits underlying the opponent process-driven negative consequences of acute amphetamine intake, as well as a novel treatment that can potentially break the cycle of drug use leading to abuse.
The transition from drug use to abuse can occur as a consequence of taking a single dose of a drug in a susceptible individual;the negative feelings that occur after the drug wears off can cause an individual to seek more of the drug. In this proposal we identify the neural systems that are involved in these negative consequences following drug taking, and propose novel treatment strategies that may help an individual break the cycle from drug use to abuse.
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