κ-Opioidireseptoriantagonistien vaikutus rottien alkoholin juomisen retkahtamisalttiuteen

lcohol addiction is a significant public health problem worldwide, and its treatment is extremely challenging. One major problem in the treatment of alcohol addiction are the later relapses to uncontrollable drinking. Approximately 60-70 % of addicts relapse to drinking within a year from the beginning of the treatment. The current treatment of alcohol addiction is based on a combined psychotheraphy and pharmacological treatments, but even at the best the efficacy remains quite modest. This is why further studies on the underlying mechanisms behind alcohol addiction and development of more effective pharmaceuticals to treat it are an important field of research. Chronic exposure to the rewarding effects of alcohol causes neurochemical adaptations in the brain reward system. These adaptations strive to restrain the recurring rewarding signals caused by alcohol and lead eventually to increased reward thresholds in the reward system. As the reward thresholds increase, the individual develops tolerance to the rewarding effects of alcohol, but also craving for the substance and a dysphoric mental state which are highlighted especially during periods of abstinence. It is known that the increase in reward thresholds is an important factor leading to relapses, but the exact nature of the neurochemical adaptations behind it are not known. According to recent studies dynorphin -peptides (DYN) and κ-opioid receptors (KOR) of the endogenous opioid system seem to have an important role in these neurochemical adaptations. It has been shown that chronic alcohol exposure increases the activity of DYN/ KOR -system especially within the nucleus accumbens (NAc), which is an essential structure of the brain reward system. The increased activity of the DYN/ KOR -system in the NAc has been shown to inhibit the development of rewarding signals. Previous studies have shown that inhibiting the increased activity of the DYN/ KOR -system with a selective KOR-antagonist, reduces voluntary alcohol intake and relapse-like alcohol seeking behavior during periods of abstinence, especially in physically addicted animals. In this study we studied the relapse-like alcohol drinking of Long-Evans rats in the alcohol deprivation effect (ADE) model. The effects of selective and long-acting KOR-antagonists, JDTic and nor-BNI, were tested on the ADE-effect which occurs after a period of deprivation. The ADE is defined as a transient increase in alcohol intake after a forced period of abstinence and it has been shown both in rodents with a history of alcohol consumption, and human alcohol addicts. In this study the rats were allowed to consume alcohol (10% ethanol-water solution) voluntarily during 90 minutes for 10 consecutive days after which followed a six days long deprivation period. According to results, both intra-accumbally (15 µg/ 0,3 µl/min/ site) or subcutaneously (10 mg/kg) administered JDTic decreased the ADEeffect significantly compared to vehicle, when administered 24 hours prior the end of the deprivation period. Also intra-accumbally administered nor-BNI (3 µg/0,3 µl/min/site) decreased the ADE-effect significantly compared to vehicle when administered 24 hour prior the end of deprivation. The results are in line with the theory that alcohol induces sensitization of the DYN/ KOR -system within the brain structures involved in reward. In theory it can be speculated that by suppressing the activity of the DYN/ KOR -system, KOR-antagonists can relieve craving for alcohol. This can be seen as a decrease in relapse-like consumption of alcohol. In conclusion, it can be suggested that by suppressing the increased activity of the DYN/ KOR -system induced by chronic alcohol exposure with a selective KOR-antagonist, like JDTic or nor-BNI, it could be possible to reduce the risk of relapse during abstinence and thus improve the efficacy of treatments for alcohol addiction.