Classical tone-shock conditioning induces Zenk expression in the pigeon (Columba livia) hippocampus

The hippocampus is involved in fear conditioning, although the molecular events underlying this function are still under investigation. The authors analyzed the expression of the Zenk proto-oncogene product within the pigeon (Columba livia) hippocampus after training with a classical aversive conditioning protocol using tone-shock associations. Control groups were trained with shock or tone alone or were only exposed to the experimental chamber and manipulated. Experimental pigeons showed significant increases of Zenk expression in the ventromedial region of the hippocampus, whereas both the experimental and shock groups had increased Zenk expression in the dorsal region. The expression of Zenk in specific neuronal populations within the pigeon hippocampus may be indicative of plasticity-associated aversive classical conditioning.