Reward endogenous opioids

Endogenous opioid systems are an integral part of the reward circuitry 916 PSYCHOMOTOR STIMULANTS 916... 

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. 

The behavioral effects of nicotine have been defined as both stimulant and depressant, effects that are influenced by the present mental status and expectations of the smoker. Smokers may feel alert and relaxed. Nicotine produces myriad effects on the central nervous system (CNS), almost all of which appear to be mediated through nicotinic receptors. Additionally, nicotine influences multiple neuronal systems. One of its most prominent effects is stimulated release of dopamine, particularly in the nucleus accumbens, which is a major component of the reward system. Nicotine also stimulates the release of endogenous opioids and glucocorticoids. 

Additionally, an opioid antagonist, naltrexone, has been used to treat children with autism. The results from these studies have been mixed, with some studies showing a mild decrease in hyperactivity and self-injurious behavior, and improved attention (Gillberg, 1995). The children who respond best to this medication appear to have more severe abnormalities in their beta endorphin levels (Bouvard et al., 1995). Overall, the research suggests that the endogenous opioid system, which is important in the reward aspects of affiliation, may also play a role in the neurobiology of autism. 

Opioids are known to alter mood states. For example, opiates such as morphine produce euphoria and pain relief. Prolonged use of and withdrawal from opiates produce depressive-like symptoms as well. Based on the mood-altering effects of opiates, the role of endogenous opiates in psychiatric symptoms of various diseases has been studied. In addition, endogenous opioids are believed to play a role in neuronal circuitry responsible for reward and pleasure. Therefore, it is thought that perhaps the anhedonia observed in depressed patients is due to dysregulation of endogenous opioids in neuronal reward circuitry. 

Gardner EL, Paredes W, Smith D, Zukin RS (1989) Facilitation of brain stimulation reward by D9-tetrahydrocannabinol is mediated by an endogenous opioid mechanism. Adv Biosci 75 671-674... 

D Amato, F.R. Pavone, F. 1993. Endogenous opioids a proximate reward mechanism for kin selection Behav. Neur. Biol., 60, 79-83. 

OPRK1 encodes the K-opioid receptor (KOP-r) and is located on chromosome 8qll.2. KOP-r is a G-protein coupled receptor involved in mood, motivation, reward, and cognitive function, for which dynorphin is its primary ligand [148]. Binding of dyn-orphin A [1-17], the endogenous ligand of KOP-r, decreases... 

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