Differential Arc protein expression in dorsal and ventral striatum after moderate and intense inhibitory avoidance training

- Intense avoidance training induces Arc expression in ventral striatum.
- Intense avoidance training does not change Arc expression in dorsal striatum.
- Arc expression is related to strength of memory but not to foot-shock intensity.

Intense training refers to training mediated by emotionally arousing experiences, such as aversive conditioning motivated by relatively high intensities of foot-shock, which produces a strong memory that is highly resistant to extinction. Intense training protects memory consolidation against the amnestic effects of a wide variety of treatments, administered systemically or directly into brain structures. The mechanisms of this protective effect are unknown. To determine a potential neurobiological correlate of the protective effect of intense training, rats were trained in a one-trial step-through inhibitory avoidance task using different intensities of foot-shock (0.0, 0.5, 1.0, and 2.0 mA). Some rats from each group were sacrificed 45 min after training for immunohistochemical Arc protein detection in dorsal and ventral striatum; other rats were tested for extinction during six consecutive days, starting 48 h after training. The results showed that training with 1.0 and 2.0 mA produced optimal retention scores, which were significantly higher than those of the 0.5 and 0.0 mA groups. Also, a higher resistance to extinction was obtained with 2.0 mA than with the other intensities. A high number of neurons expressed Arc in ventral, but not in dorsal striatum in both the 1.0 and 2.0 mA groups, with a larger area of Arc signal in the latter group. We conclude that an increased Arc expression may be related to enhanced synaptic plasticity in the ventral striatum, suggesting that it may be one of the physiological substrates of enhanced learning.