Neural Mechanisms Of The Inhibition Of Odor Avoidance Behaviour By Electric Shock In Drosophila Melanogaster

Animals show innate responses toward environmental stimuli. However, the ecologic niche that they are living in, the environmental stimuli they encountered are dynamic. Adjusting their innate behaviors according to the environmental contexts is essential for their survival. These kind of adaptive behaviors are also known as context dependent behaviors. Studying the neural and molecular mechanisms of the context dependent behaviors is one of the hot topics in modern neuroscience.This thesis used Drosophila melanogaster as a model organism to study odor avoidance behaviors in the context of electric shock(ES). Although ES is not a natural stimulus to fruit flies, it has been widely used in animals for practical reasons:easy to use and can be controlled precisely. As a result, ES is one of the most studied external stimuli to animals. Studies of classical aversive olfactory conditioning have accumulated a huge amount of knowledge regarding the neural circuits and molecular mechanisms of olfactory and electrical signals in the central brain of Drosophila.However, odor avoidance behaviors with ES as a context are still lack of studies. In this thesis, behavioral and molecular genetic techniques are used to explore the neural circuits and molecular mechanisms of how ES inhibits odor avoidance behaviors.Specifically, our studies include the following three aspects:1.A behavioral paradigm is established to study the inhibition of odor avoidance behavior by ES. This behavioral paradigm uses the same T-maze as in the Tully parad-igm to probe the avoidance response to 3-octanol with ES as contextual background.Our data showed that background signal suppresses the fruit flies' avoidance from 3-octanol, and the suppressive effect is enhanced with increased voltage.As the voltage and odor we use keep the same with standard learning and memory paradigm,fruit flies can still get strong olfactory memory through training,so it is impossible because of loss of attention to odor,but weakening the aversive value of3-octanol by ES.Our behavior analysis results consistent with the hypothesis.2.Analysis of the neural circuits.We expressed temperature sensitive shibire specifically in neurons of mushroom body(MB).Before behavioral tests,normal neurotransmitters release will be blocked by increasing temperature.The result is that ES signal can not suppresses the fruit flies' avoidance from 3-octanol.Obviously, MB mediates ES weakening the aversive value of 3-octanol.In aversive olfactory learningprocess,odor obtains aversive value when ES(unconditioned stimulus,US) and odor(conditioned stimuli,CS)present at the same time,and we get higher avoidance index from the conditioned odor than without learning.So the extraction of olfactory memory(avoidance index enhanced)also needs the MB.Interesting,ES can not suppresses avoidance from conditioned odor.This shows that neural circuit that the MB mediates ES suppressing avoidance from odor,and neural circuits of classic olfactory memory are independent, parallel to each other.An inhibitory circuits is to be found under the downstream of the MB,that suppresses specifically the innate behavior of avoidance from odor.We guess it realizes through suppressing the circuit in LH.3.Genetic analysis.Except ES inhibition behavior we studied,the MB plays important roles in learning and memory, and attention.But it is not clearly whether they share key regulatory genes at the molecular level.In this paper a series of important mutants related to learning and memory,and attention are chosen for behavior analysis.However,behavioral controls prove that these genes above don not work. Dunce and rutabaga are wildly considered important genes in regulating fruit flies class attention behavior,so the negative result Support our hypothesis in the first part: ES signal suppresses the fruit flies' avoidance from odor by weakening the aversive value of odor not the interference on fruit flies' attention.