Investigation of molecular changes in small selectively activated neural groups (neuronal ensembles) of the nucleus acumbens, which mediate the incubation of the fissure to cocaine induced by the environment

Abstract

Drug addiction is a public health problem with heavy social impacts in Brazil and around the word. In South America and the Caribbean, about 40% of individuals treating drug addiction are cocaine addicted. Drug addiction is a long-lasting condition, in which individuals present intense craving and high risk of relapse even after long periods of abstinence. Thus, a large part of the studies are concentrated on understanding craving and consequent relapse mechanisms. Craving and relapse can be initiated by the exposition of the individual to contexts previously associated with drug use. In this sense, one of the theories of drug addiction proposes that this psychopathology involves associative learning behaviors. Associative learning is codified by small neural groups sparsely distributed through the brain, connected by strong synapses, now called, neuronal ensembles. Studies demonstrate that molecular alterations located in these neural groups are associated with drug addiction related behaviors. It is demonstrated that drug environmental cues-induced craving, progressively increases over the first few weeks of abstinence and remains high for long periods. This phenomenon is called incubation of craving. The incubation of craving is associated with the development of plasticity in the mesocorticolimbic system. The present study aims to investigate the role of the molecular alterations in the nucleus accumbens neuronal ensembles, induced by associations between cocaine self-administration and environment on the incubation of craving. With this propose, rats will be trained to self-administrate cocaine in a specific context for twelve days. Then, they will be subjected to a period of abstinence in their home cages. Then, the incubation of craving will be assessed by exposing distinct animals groups to the cocaine self-administration context 1 and 30 days after the end of the training. The present study is designed to: i) identify, quantify and to characterize the cell phenotypes of the nucleus accumbens neuronal ensembles that will be activated during the incubation of craving tests (1st or 30th days of abstinence); ii) verify if the neural plasticity which mediate the incubation of craving are incubated in the same neuronal ensembles along the abstinence period; iii) evaluate the role of the neuronal ensembles activated in the first day of abstinence on the incubation of craving observed 30 days later (using optogenetic inhibition technic); iv) investigate the molecular alterations presents in the nucleus accumbens neuronal ensembles, activated by the reexposure to the self-administration environment after 1 or 30 days of abstinence (we will use the technique of cell sorting of flow cytometry (FACS), followed by proteomic analysis by mass spectrometry); v) from the data obtained by proteomic analysis we will define one or two relevant molecular targets and then we will realize the manipulation of the expression of these targets (we will increase and suppress these genes expression using viral vectors). To guarantee the specific manipulation of the neuronal ensembles we will use c-Fos_TETOp::iCRe transgenic rats which will allow the manipulation of the activated neurons related to our behavioral tests. (AU)