Mechanisms of Stress-Enhanced Aversive Conditioning

ABSTRACT Cognitive dysfunction, including the inappropriate generalization (i.e., overgeneralization) of negative episodic memories, is a core diagnostic criterion of major depression, and is recognized as a key determinant of severe affective symptoms. For this reason, we believe that studying the neurobiology of memory generalization could have considerable translational impact for depression. We propose to identify the cellular and circuit mechanisms subserving generalization of negative context (episodic-like) memories using a newly developed paradigm of stress-induced generalization (SIG). Aim 1 will rely on most recent approaches that allow us to visualize and manipulate neuronal populations coding either specific and general features of context memories. Through these techniques, we expect to determine whether stress promotes or disrupts the reactivation of these neuronal populations during memory retrieval. Aim 2 will utilize chemogenetic and optogenetic approaches, alone or in combination with neuronal labeling, to determine whether excitatory ventral tegmental area (VTA) to dorsal hippocampus (DH) projections, which signal negative valence, contribute to SIG. Inhibition of these projections is expected to reduce generalization, especially in females. Aim 3 will focus on the role of MS to DH projections, which we suspect play a more prominent role in SIG in males than in females. In addition to the approaches used in Aim 2, we will determine the effects of stress and cholinergic neuromodulation on hippocampal oscillations and acetylcholine release, and we will explore the stress-mediated changes of global brain activity using manganese-enhanced magnetic resonance imaging. Upon competition of this project, we expect to have identified the main cellular and circuit (mal)adaptations induced by stress that result in lasting generalization of negative context memories. Approaches that prove effective in reversing SIG could be the foundation for novel treatments of cognitive deficits associated with depression and affective disorders.