Effects of Single and Repeated Footshock on Dopamine Release and Metabolism in the Brains of Fischer Rats

Abstract: Changes in the tissue levels of 3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and dopamine in the frontal cortex, hypothalamus, nucleus accumbens, and striatum were evaluated after 0.5-4 h of footshock (2 mA, for 3 s every 30 ± 5 s) in Fischer rats. 3-MT, DOPAC, and HVA levels in the four brain areas peaked at 0.5 h and in most cases returned to baseline values within 4 h. No changes were found in dopamine levels. Repeated footshock stress was evaluated by administering 10 footshock sessions (0.5 h, two per day for 5 days). At the end of the 10th footshock session, 3-MT levels were higher than at the end of the first footshock session in three of the four brain regions, indicating sensitization of dopamine release. No differences were found between the first and 10th footshock sessions in DOPAC and HVA levels. Fourteen days after the 10th footshock session, the levels of 3-MT, DOPAC, and HVA were the same as in control rats in all four brain regions. A 0.5-h footshock challenge presented 14 days after the 10th footshock session attenuated DOPAC levels in the hypothalamus and nucleus accumbens. In contrast, DOPAC and HVA levels in the frontal cortex showed sensitization after footshock challenge, and a similar trend was apparent for 3-MT levels. These results indicate that repeated footshock stress induces generalized sensitization of dopamine release and turnover in some areas of the brain of Fischer rats. This sensitization may persist in the cortical but not subcortical dopamine neurons after discontinuation of the treatment.