Protracted alcohol abstinence induces analgesia in rats: Possible relationships with BDNF and interleukin-10

Exposure to ethanol alters the expression of brain-derived neurotrophic factor (BDNF) in central regions such as, the hippocampus, cortex and striatum. Moreover, chronic alcohol intake is known to induce selective neuronal damage associated with an increase in the inflammatory cascade, resulting in neuronal apoptosis and neurodegeneration. In the present study, we investigated the nociceptive response after 24 h of protracted alcohol abstinence. Rats were submitted to a model of alcohol withdrawal syndrome and the nociceptive response was assessed by the tail-flick and the hot plate tests. In addition, we evaluated BDNF and interleukin-10 (IL-10) in the cerebral prefrontal cortex, brainstem and hippocampus of rats after protracted alcohol abstinence. Male adult Wistar rats were divided into three groups: non-treated group (control group), treated with water (water group), and alcohol (alcohol group). The water and alcohol administrations were done by oral gavage and were performed over three periods of five days of treatment with two intervals of two days between them. Alcohol (20% w/v) was given at 4 g/kg of body weight. There was a significant effect of treatment in the tail-flick and hot plate latencies with greater latencies in alcohol-treated rats after 10 days of abstinence. There was a significant increase in the prefrontal cortex BDNF levels in the alcohol group in relation to the water group, after 11 days of alcohol abstinence. In addition, alcohol withdrawal induced a significant increase in the hippocampus, prefrontal cortex and brainstem IL-10 levels compared with control group. Thus, the present study demonstrates that protracted alcohol withdrawal produced an analgesic effect indexed via increased nociceptive threshold. We suggest that these effects could be related to the increased levels of BDNF and IL-10 observed in the central nervous system.