7,8-DHF enhances SHH in the hippocampus and striatum during early abstinence but has minor effects on alcohol intake in IA2BC paradigm and abstinence-related anxiety-like behavior in rats

Abstract

A mimetic of brain-derived neurotrophic factor (BDNF), 7,8-dihydroxyflavone (7,8-DHF), alleviates some aspects of alcohol abstinence after voluntary alcohol intake in rodents. The interaction between BDNF and sonic hedgehog (SHH) was demonstrated in adult brain in some situations, though relationship between BDNF and SHH during alcohol abstinence remains obscure. We aimed to study effect of 7,8-DHF on drinking pattern, anxiety-like behavior and expression of SHH and a downstream transcription factor, GLI, in the limbic brain structures during early abstinence after voluntary ethanol intake.Male Wistar rats were subjected to intermittent access to 20% ethanol in a two-bottle choice procedure (IA2BC). The animals experienced twenty 24-h sessions of free access to two-bottle choice (water or 20% ethanol) with 24-h withdrawal periods (water only); 7,8-DHF (5 mg/kg, i.p.) was administered one hour prior to each alcohol access session. Anxiety-like behavior was estimated in the open-field (OFT) and elevated plus-maze (EPM) tests on the first and second days of abstinence, respectively. The expression of SHH and GLI was analyzed on the third day after withdrawal in the frontal cortex, hippocampus and striatum.Repeated measures ANOVA did not show significant main effect of 7,8-DHF injections during IA2BC on ethanol intake and ethanol preference over water. As expected, pair-wise comparisons of OFT and EPM data by Mann-Whitney U test revealed elevated anxiety-like behavior during early abstinence in IA2BC paradigm as compared with control group. When all groups were included in the analysis, Kruskal-Wallis ANOVA did not show significant differences in time spent in the center zone of the OFT and number of entries. However, time spent in the open arms of the EPM but not number of entries differed significantly between the groups studied according to Kruskal-Wallis ANOVA. Factorial ANOVA followed by Tukey’s HSD post hoc test demonstrated significant elevation of SHH protein levels in the hippocampus and striatum but not in the frontal cortex of animals with access to ethanol and administered with 7,8-DHF as compared with respective animals without 7,8-DHF. GLI expression changed only in the hippocampus; its protein level increased in control animals administered 7,8-DHF.Thus, 7,8-DHF administration during IA2BC procedure induces region-specific levels elevation of SHH in the brain, but does not significantly change drinking pattern and anxiety-like behavior during early abstinence.