Reward center

Dackis C.A., O Brien C.P. Cocaine dependence a disease of the brain s reward centers. J. Subst. 

Typical Antipsychotics. Since their introduction in the 1950s, antipsychotics have played a prominent role in the treatment of bipolar mania. When we recognized that dopamine activity is critical in the brain s reward centers, the notion arose that dopamine hyperactivity may contribute to the euphoria of bipolar mania. Therefore, it was natural to assume that the dopamine-blocking antipsychotics would be effective antimanic medications. 

Reward Therapy. A similar (yet nonspecific) approach is to use a medication that stimulates the brain s reward centers. Reward medications usually do not work in quite the same way as the substance of abuse however, the net effect in the final common pathway (i.e., the reward centers) may be the same. For the most part, these reward centers are activated by either dopamine or endogenous opioid agonists. One common feature of most abused drugs is that they stimulate these reward centers. This lies at the heart of their addictive potential. Some attempts have been made to use medications that activate these reward centers in place of the abused substance. The hypothesis is that the addict will have less intense craving for his/her preferred substance of abuse in the presence of these other agents. This is, of course, a relatively nonspecific approach that could theoretically be used to treat the abuse of many different substances. It has not yet, however, demonstrated any utility in the treatment of substance abuse. 

Figure 2.3 Many drugs of abuse act on the brain s reward center, which is illustrated above. The drugs cause neurons in the ventral tegmental area to release dopamine. The dopamine, in turn, initiates a chain of events that results in feelings of enjoyment and pleasure.

Dopamine plays a significant role in activating the brains reward center, which is located in the hypothalamus, an area at the lower middle of the brain, as illustrated in Figure 14.22. The hypothalamus is the main control center for emotional response and behavior. Stimulation of the reward center by dopamine... 

Amphetamines and cocaine work the same way in the body, but cocaine is much more vigorous at blocking the reuptake of dopamine. How cocaine works is illustrated in Figure 14.26. The great buildup of dopamine in synaptic clefts in the brains reward center is the source of cocaines euphoric effect. As cocaine keeps dopamine from being reabsorbed by the presynaptic neuron, the dopamine remains active in the synaptic cleft, and as a result the reward center stays stimulated. This euphoric state is only temporary, however, because enzymes in the deft metabolize, and hence deactivate, the dopamine. Once the cocaine is metabolized by enzymes, dopamine reuptake is again permitted. By this time, however, there is very little dopamine in the deft to be reabsorbed. Nor is there an adequate supply of dopamine in the presynaptic neuron, which is unable to make sufficient quantities of dopamine without the recycling process. The net result is a depletion of dopamine that causes severe depression. 

Cocaine affects dopamine levels in the synaptic clefts of the brains reward center. 

Which neurotransmitter functions most in the brains reward center ... 

The first stage, libido, is linked to desire for sex, or sex drive, and is hypothetically a dopaminergic phenomenon mediated by the mesolimbic dopaminergic reward center (Fig. 14—1). This pathway has already been discussed in Chapter 13 and is well known for being the site of action of drugs of abuse as well as the site of... 

The compelling and overwhelming nature of cocaine addiction is impressive and tells us something profound about how the brain is built. It is apparently comprised of critically important internal neural systems that can produce a powerful rewarding experience usually connected to activities that are the basis for the survival of our species eating and reproduction. Drugs such as cocaine can hijack these neural processes and stimulate the brain s reward centers so excessively and unnaturally that users will crave more stimulation, as they would normally crave food and sex. From the brain s perspective, there is no real... 

And as we ve seen before, what happens after a drug exits the brain tells us something about what parts of the brain were affected under the influence of that drug. With regard to cocaine, these include the arousal systems within the brainstem, the feeding centers within the hypothalamus, and the reward centers within the frontal lobes and limbic system. Thus, cocaine reduces the need for sleep, and its absence produces extreme... 

A useful model of the action of these two drugs in the reward centers of the CNS is shown in Figure 32-1. Cocaine reduces reuptake of dopamine into the neuron by inhibiting the dopamine reuptake transporter. Amphetamine causes the intracellular release of dopamine within the terminal and reverses the transporter direction so that dopamine is released into the synapse by reverse transport rather than ordinary exocytosis. In addition, amphetamine inhibits intracellular MAO metabolism of dopamine. Note that both drugs result in an increase in the concentration of dopamine in the synapse. 

Natural reward centers have developed over the course of evolution to reinforce useful behaviors (e.g., pleasure, sexual satisfaction, eating, and drinking). These reward... 

These natural reward centers have developed over the course of evolution to reinforce useful behaviors (e.g., pleasure, sexual satisfaction, eating, and drinking). It is believed that drugs such as cocaine and amphetamine directly stimulate these centers, while opiates free the pathways from inhibitory control. Nicotine, on the other hand, reaches the brain in as little as 10-20 seconds, where it stimulates nicotine receptors to cause dopaminergic neurons to release large quantities of dopamine. After a few hours, dopamine levels decline, causing withdrawal symptoms to readily appear (e.g., anxiety, irritability, and inattentiveness). When cigarette smokers say they need a smoke to steady their nerves, what they really mean is that they have to contend with nicotine withdrawal. 

With respect to these reward centers, it has been suggested that aU roads lead to the neurotransmitter dopamine. Stimulation of two specific reward centers in the brain, both featuring dopamine as the... 

Interestingly, the natural hallucinogens, such as peyote and mescaline (and nearly all other hallucinogens) do not engender compulsive drug seeking or addiction, nor do they lead to chemical dependence. Part of the reason is that these compounds do not stimulate the dopaminergic reward center in the brain, as they lack affinity for the dopamine receptor and the dopamine uptake transporter. 

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