Mapping the encoding of innate versus learned aversive threat in the amygdala.

Sammanfattning: The amygdala is essential in the process of learned aversive signals. Its implication in processing an innately aversive threat remains to be decoded. This implies asking questions on how a learned and an innate aversive threat is processed. Learned aversive threat involves changes in synaptic plasticity while the responses to the innate aversive threat are hard-wired in the animal’s brain. A way to answer this question is to visualize the neurons activated by both behaviors in the same animal. To do so, a set of behavioral experiments were done with the help of a cross of Rosa td Tomato and TRAP2-Cre mice in combination with c-Fos staining. Following this, a combination of techniques including behavioral studies, immunohistochemistry and apotome microscopy for cell quantification were being used. This was intended to find the number of TRAP cells and c-Fos cells in the areas of LA, BA, CeL and CeM respectively. A heat map was further being plotted to measure the density of the cells in each area. The percentage of cells which got activated when a specific stimulus was being repeated twice were also being quantified using the Fiji software. The results section discusses the analysis of shock-shock and loom-loom experiments wherein the freezing percentages of the first set of mice (aversive threat measurement experiments) and the looming behavior of the second set of mice were being analyzed. It was observed that the freezing rate of all the mice used for the aversive threat measurement experiments increased steadily with time. The responses of the mice to the looming stimulus were also significant. The quantification of the number of cells which got activated when the mice were exposed to the shock stimulus twice indicated that Lateral amygdala (50%) exhibited the maximum percentage of cells in the case of shock-shock experiments and the central amygdala in the case of loom-loom experiments (30-50%). This helped us to identify some of the primary areas involved when the mice were being exposed to a shock or loom stimulus. It also helped us to infer the percentage of cells which got activated when the same stimulus was being repeated twice. These experiments serve as a foundation for the future experiments to learn about the specific cell types involved in each area and whether these cell populations get activated when the same stimulus is being repeated twice.