Related Neural Mechanism in Reward Learning and Memory

Learning and memory are two corresponding neural processes. Learning is a neural actitivity depending on experience and changing organ’s behaviour to adapt the enviorement.Memory is a neural processing which storages and retrieves learned information. Reward and punishment learning and memory protect animals to approach the benefits and avoid risks for better life. Although researches are exploring the mechanism of the brain work, a large amount of studies are required to reveal the truth in the future. In the first chapter of this thesis, I will explain the research on neural circuits underlying appetitive olfacotory associated learning and memory in Drosophila melanogaster. I will introduce the methods and technics to study the olfactory learning and memory in flies such as classical olfactory conditioning and gene manipulation (i.e., GAL4/UAS system), introduce the current status of studies on neural circuits in olfactory associative learning and memory, and my project: a subset of dopamine neurons signal reward for odour memory. Previous studies revealed that dopamine signals aversive reinforcement in insects, and identified that PPL1 cluster and MB-M3 neurons in PAM convey aversive reinforcement to vertical lobes and tip of horizontal lobes of the mushroom body, respectively. Octopamine was thought to be involved in appetitive learning and memory, but no cellular identification and circuit description. In our study, by transient activation and inactivation of target neurons in intact behaving flies, we show that a group of dopamine neurons in the protocerebral anterior medial (PAM) cluster signals the sugar reward. In vivo calcium imaging revealed that these dopamine neurons are activated by sugar stimulus and the activation is increased in starved flies. Our results highlight the cellular specificity underlying the various roles of dopamine and the importance of spatially segregated local circuits within the mushroom bodies.We identified the specific dopamine cluster neurons tht signal reward to the horizontal lobes of the mushroom body for the first time, and suggested a prelimary relationship between octopamine and dopamine signaling. Drug addiction is a particular and extreme rewarded memory, and a concerned social issue. In the second chapter, I will introduce conditioned place preference model of drug related memory and local leision in the rats’brain as the tools to investigate the characters of drug related memory and the role of corresponding brain area in reward conditioning.We revealed that somatosensory cortices are required for the acquisition of morphine related memory whereas the urge to seek drugs requires the insular cortex. Although our studies have demonstrated neural circuits of reward learning and memory in flies, and one of important brain cortices in morphine related memory formation in rats. However, we can not completely understand the mechanism of reward learning and memory, and solve the drug abuse problems. Thus, lots of works need to be done in future