Inhibition of Histone Deacetylases in the Chick Brain Modulates Expression of c-Fos and ZENK Transcription Factors and Facilitates Establishment of Long-Term Memory

The aim of the work was to examine the role of histone acetylation in memory consolidation in newborn chicks. We studied the effects of histone deacetylase inhibitor trichostatin A (TSA) on a "weak" memory for passive avoidance and on expression of two transcription factors c-Fos and ZENK known to play a role in neuronal plasticity in the chick brain. Intraventricular administration of trichostatin A prior to training produced a dose-dependent enhancement of memory when tested 24 hours after the training. It also increased neuronal expression of c-Fos and ZENK proteins: the density of ZENK immunopositive cells increased in the hippocampus and intermediate medial mesopallium and the density of c-Fos immunopositive cells increased in intermediate arcopallium and dorsocaudal nidopallium. Weak passive avoidance training did not produce further enhancement of c-Fos and ZENK expression in any of these brain areas. These data demonstrate possibility of facilitating long-term memory in day-old chicks by a histone deacetylases inhibitor, thus supporting the hypothesis on the role of histone acetylation in long-term memory formation. They also suggest that these effects might be mediated through modulation of transcriptional response in brain areas involved in consolidation of this form of memory.