The release of catecholamines (including both norepinephrine and dopamine) in response to novelty/unexpected reward and during times of stress or strong emotion has long been known to enhance long-term memory. Excessive catecholamine release may lead to stress-related memories such as Post- Traumatic Stress Disorder or, in the case of stimulant use, to unusually strong explicit contextual memories that can hinder efforts to abstain by producing strong context-specific ?reminders? of drug use. Synaptic plasticity?activity-dependent changes in the strength of synaptic connections between neurons?underlies many forms of memory. In addition to activity-dependent synaptic plasticity, brain circuits undergo metaplasticity, a process that alters the ability of neural circuits to undergo subsequent forms of synaptic plasticity. Catecholamines are known to induce a form of hippocampal metaplasticity that enhances long-term potentiation (LTP) of synapses in the hippocampus, a brain structure essential for encoding long-lasting explicit memories. Recent studies have reported that optogenetic activation of catecholamine-producing neuronal terminals originating from the locus coeruleus (LC) enhances hippocampal LTP and memory. In our studies, optogenetic stimulation of LC afferents at a frequency that mimics LC firing during stress (5 Hz) is sufficient to enhance LTP of CA3 to CA1 synapses in acute hippocampal slices. Previous studies have shown that catecholamine-induced metaplasticity of hippocampal LTP is dependent on transcription, but the specific program of transcription that is induced by catecholamines has not been characterized. In this R21 exploratory grant, we propose to undertake an unbiased analysis of the transcriptional program that is induced by LC activation. Towards this end, we combine optogenetic activation of LC afferents to the hippocampus with next- generation RNA sequencing approaches to identify changes in transcription induced by release of endogenous catecholamines.
In Aim 1, we will conduct nascent RNA sequencing in excitatory CA1 neurons in hippocampal slices in which LC afferents have been photostimulated at frequencies that mimic stress amd that enhance LTP.
In Aim 2, we follow up on our findings that LC activation triggers nuclear accumulation of the CREB co- activator CRTC1, performing CRTC1 chromatin-immunoprecipitation sequencing (ChIP-seq) to determine whether and how release of endogenous catecholamines alters DNA binding by CRTC1. Together, the results of our experiments will provide insight into the molecular mechanisms underlying catecholamine-induced hippocampal metaplasticity, opening a path towards developing treatments for drug addiction, PTSD and other forms of maladaptive memories.
It is a common phenomenon to have vivid memories of events in which one experienced an unexpected reward, did something new, or was in an emotionally charged or stressful situation. This is a result of the release of molecules called neuromodulators, especially norepinephrine and dopamine, into memory centers in the brain. This proposal examines how release of norepinephrine and dopamine controls the expression of genes in neurons to regulate the formation of long-term memories.
