Dynamics of Dendritic Spines in Dorsal Striatum after Retrieval of Moderate and Strong Inhibitory Avoidance Learning

•Retrieval of moderate training induces mushroom spinogenesis in dorsal striatum.•Retrieval of strong training increases mushroom spinogenesis in dorsal striatum.•Retrieval reduces number of thin spines in dorsal striatum.•Spinogenesis in accumbens was due to the aversive stimulation, not to retrieval. In marked contrast to the ample literature showing that the dorsal striatum is engaged in memory consolidation, little is known about its involvement in memory retrieval. Recent findings demonstrated significant increments in dendritic spine density and mushroom spine counts in dorsal striatum after memory consolidation of moderate inhibitory avoidance (IA) training; further increments were found after strong training. Here, we provide evidence that in this region spine counts were also increased as a consequence of retrieval of moderate IA training, and even higher mushroom spine counts after retrieval of strong training; by contrast, there were fewer thin spines after retrieval. Similar changes in mushroom and thin spine populations were found in the ventral striatum (nucleus accumbens), but they were related to the aversive stimulation and not to memory retrieval. These results suggest that memory retrieval is a dynamic process which produces neuronal structural plasticity that might be necessary for maintaining or strengthening assemblies that encode stored information.