Molecular changes in the intermediate medial mesopallium after a one trial avoidance learning in immature and mature chickens

Translational control of auditory imprinting and structural plasticity by eIF2α

The formation of imprinted memories during a critical period is crucial for vital behaviors, including filial attachment. Yet, little is known about the underlying molecular mechanisms. Using a combination of behavior, pharmacology, in vivo surface sensing of translation (SUnSET) and DiOlistic labeling we found that, translational control by the eukaryotic translation initiation factor 2 alpha (eIF2α) bidirectionally regulates auditory but not visual imprinting and related changes in structural plasticity in chickens. Increasing phosphorylation of eIF2α (p-eIF2α) reduces translation rates and spine plasticity, and selectively impairs auditory imprinting. By contrast, inhibition of an eIF2α kinase or blocking the translational program controlled by p-eIF2α enhances auditory imprinting. Importantly, these manipulations are able to reopen the critical period. Thus, we have identified a translational control mechanism that selectively underlies auditory imprinting. Restoring translational control of eIF2α holds the promise to rejuvenate adult brain plasticity and restore learning and memory in a variety of cognitive disorders.

DOI:http://dx.doi.org/10.7554/eLife.17197.001

Shortly after hatching, a chick recognizes the sight and sound of its mother and follows her around. This requires a type of learning called imprinting, which only occurs during a short period of time in young life known as the “critical period”. This process has been reported in a variety of birds and other animals where long-term memory formed during a critical period guides vital behaviors. In order to form imprinted memories, neurons must produce new proteins. However, it is not clear how new experiences trigger the production of these proteins during imprinting. Unraveling such mechanisms may help us to develop drugs that can recover plasticity in the adult brain, which could help individuals with brain injuries relearn skills after critical periods are closed.

It is possible to imprint newly hatched chicks to arbitrary sounds and visual stimuli by placing the chicks in running wheels and exposing them to repeated noises and videos. Later on, the chicks respond to these stimuli by running towards the screen, mimicking how they would naturally follow their mother. This system allows researchers to measure imprinting in a carefully controlled laboratory setting.

A protein called elF2α plays a major role in regulating the production of new proteins and has been shown to be required for the formation of long-term memories in adult rodents. Batista et al. found that elF2α is required to imprint newly hatched chicks to sound. During the critical period, this factor mediates an increase in “memory-spines”, which are small bumps on neurons that are thought to be involved in memory storage. On the other hand, elF2α was not required to imprint newly hatched chicks to visual stimuli, suggesting that there are different pathways involved in regulating imprinting to different senses. Batista et al. also demonstrate that using drugs to increase the activity of eIF2α in older chicks could allow these chicks to be imprinted to new sounds.

The next steps following on from this work are to identify proteins that eIF2α regulates to form memories, and to find out why eIF2α is only required to imprint sounds. Future research will investigate the mechanisms that control visual imprinting and how it differs from imprinting to sounds.

DOI:http://dx.doi.org/10.7554/eLife.17197.002

Ischemia and status epilepitcus result in enhanced phosphorylation of calcium and calmodulin-stimulated protein kinase II on threonine 253

Ca2+-stimulated protein kinase II (CaMKII) is critically involved in the regulation of synaptic function and is implicated in the neuropathology associated with ischemia and status epilepticus (SE). The activity and localization of CaMKII is regulated by multi-site phosphorylation. In the present study we investigated the effects of global ischemia followed by reperfusion and of SE on the phosphorylation of CaMKII on T253 in rat forebrains and compared this to the phosphorylation of T286. Both ischemia and SE resulted in marked increases in the phosphorylation of T253, and this was particularly marked in the postsynaptic density (PSD). Phosphorylation of T286 decreased rapidly towards basal levels following ischemia whereas phosphorylation of T253 remained elevated for between 1 and 6 h before decreasing to control values. Following SE, phosphorylation of T253 remained elevated for between 1 and 3 h before decreasing to control levels. In contrast, phosphorylation of T286 remained elevated for at least 24 h following the termination of SE. Total CaMKII associated with PSDs transiently increased 10 min following ischemia, but only several hours following SE. The results demonstrate that phoshorylation of CaMKII on T253 is enhanced following both ischemia/reperfusion and SE and indicate that the phosphorylation of T253 and T286 are differentially regulated.

Biochemical, behavioural and electrophysiological investigations of brain maturation in chickens

It is convenient to divide the development of synaptic networks into two phases: synapse formation during which synaptic contacts are established, and a subsequent maturation phase during which synaptic circuits are fine tuned and the properties of individual synapses are modified. Understanding the complex factors that control the protracted maturation process in humans is likely to be important for understanding a variety of neurological and psychiatric disorders. Chickens provide an ideal experimental model in which maturation specific changes can be identified and the mechanisms controlling them can be elucidated because the maturation phase is protracted and temporally separated from the formation phase. This paper reviews the knowledge about the biological mechanisms involved in the maturation phase of brain development in chickens and presents some new data. Studies of synaptic physiology suggest that maturation may alter the basal set point for stimulus induced synaptic plasticity. Biochemical and pharmacological studies of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and metabotropic glutamate receptors (mGluRs) revealed major changes in receptor regulation and the intracellular signalling pathways linked to receptor activation. Not surprisingly, therefore, when immature or mature chickens learn the same behavioural task the learning induced molecular events at the synapse are different. Changes in the features of auditory event related potentials and the basal EEG provide non-invasive techniques for monitoring maturation changes in chicken brain but prepulse inhibition (PPI) is too small and variable in chickens to be useful. Experimentally induced mild late-onset hypothyroidism retards some aspects of brain maturation and may help identify some of the mechanisms controlling maturation.