Avoidance conditioning in different strains of rats: Neurochemical correlates

Two-way avoidance conditioning was compared in three strains of rats: Roman high avoiders (RHA), Roman low avoiders (RLA) and control Sprague-Dawleys (SD). RHAs performed more and RLAs fewer avoidance responses than SDs. RLAs injected with d-amphetamine improved their performance to levels comparable to SDs; however, d-amphetamine caused a time-dependent increase in intertrial crossings for the RLAs. Of the three strains, the RLAs had the lowest activities of tyrosine hydroxylase, dopamine--hydroxylase and phenylethanolamine-N-methyltransferase in their adrenal glands. Although there were no significant differences among the strains in respect to tyrosine hydroxylase activity in whole brain or regions, RLAs had higher dopamine--hydroxylase activity in the whole brain and cerebral cortex as compared to the SDs. RLAs and RHAs together had a significantly different turnover of intracisternally administered ³H-norepinephrine than SDs. After the intracisternal injection of ³H-L-tyrosine, twice as much ³H-dopamine accumulated in the brains of RLAs as compared to RHAs and SDs.