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

Abstract

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 2.0mA). Some rats from each group were sacrificed 45min after training for immunohistochemical Arc protein detection in dorsal and ventral striatum; other rats were tested for extinction during six consecutive days, starting 48h after training. The results showed that training with 1.0 and 2.0mA produced optimal retention scores, which were significantly higher than those of the 0.5 and 0.0mA groups. Also, a higher resistance to extinction was obtained with 2.0mA 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 2.0mA 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.

Keywords: Corticosterone; Immediate-early genes; Learning and memory; Over-training; Striatum.