Transient changes in nucleus accumbens amino acid concentrations correlate with individual responsivity to the predator fox odor 2,5-dihydro-2,4,5-trimethylthiazoline.

Predator odors elicit fear and defensive behavioral responses in rats, but a wide range of individual responsivity exists. The aim of this study was to examine whether individual differences in behavioral responsivity correlate with differences in amino acid neurotransmission to a predator fox odor, 2,5-dihydro-2,4,5-trimethylthiazoline (TMT). We investigated the time course of behaviorally evoked amino acid neurotransmitter changes in the nucleus accumbens using on-line microdialysis coupled to capillary electrophoresis with 14-s temporal resolution. One subset of animals (high responders) showed a large, biphasic increase in amino acids, such as glutamate and GABA, which lasted about 3 min. These neurochemical changes were highly correlated with increases in locomotion and burrowing, but lagged behind the behavioral changes by 2 min. A second subset of rats (low responders) showed neither behavioral activation nor changes in amino acid neurotransmission. As a positive control, rats were subjected to tail pinch, which evoked transient changes in amino acids in all animals. Cocaine (2 mg/kg, i.v.) increased locomotion but not amino acid levels. This work demonstrates that rapid and transient increases in amino acid neurotransmitters correlate with behavioral reactivity to salient stimuli.