Early socio-emotional experience induces expression of the immediate-early gene Arc/arg3.1 (activity-regulated cytoskeleton-associated protein/activity-regulated gene) in learning-relevant brain regions of the newborn chick

We have cloned a full-length complementary DNA from the chicken ( Gallus gallus domesticus), which encodes a polypeptide that exhibits ∼75% identity to the product of the mammalian gene Arc (activity-regulated cytoskeleton-associated protein), also known as arg3.1 (activity-regulated gene). Since this gene is an immediate-early gene that has been suggested to play a role in synaptic plasticity and learning and memory processes, its expression has been analyzed in a juvenile form of learning, namely, filial imprinting. Our results demonstrate that Arc/arg3.1 mRNA is detectable in the newborn chick brain, and that at this early age the level of this transcript can be altered by brief sensory/emotional experience. After postnatal exposure to a novel 30-min auditory imprinting stimulus, Arc/arg3.1 mRNA was found to be significantly increased in two higher associative areas, the mesopallium intermediomediale ( P=0.002) and the nidopallium dorso-caudale ( P=0.031), compared with naïve controls. The transcript level was also significantly elevated after imprinting in Area L pallii ( P=0.045), which is analogous to the mammalian auditory cortex. In addition, increases were seen in the medio-rostral nidopallium/mesopallium ( P=0.054), which is presumed to be the analog of the mammalian prefrontal cortex, and the hyperpallium intercalatum ( P=0.054), but these did not quite reach significance. We discuss these data in the light of those obtained in an earlier study, in the same paradigm, for the avian immediate-early gene, zenk (an acronym for zif-268, egr-1, ngfi-a and krox-24, which are different names for the orthologous mammalian gene). We conclude that, although both the Arc/ arg3.1 and zenk genes are induced by auditory imprinting, they are significantly up-regulated in different learning-relevant brain regions. It is, therefore, evident that they must be activated by different mechanisms.