IMR Press / JIN / Volume 23 / Issue 3 / DOI: 10.31083/j.jin2303060
Open Access Original Research
Optogenetic Inhibition of the Cortical Efferents to the Locus Ceruleus Region of Pontine Tegmentum Causes Cognitive Deficits
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1 Department of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA
*Correspondence: eugene.dimitrov@rosalindfranklin.edu (Eugene Dimitrov)
J. Integr. Neurosci. 2024, 23(3), 60; https://doi.org/10.31083/j.jin2303060
Submitted: 29 September 2023 | Revised: 15 November 2023 | Accepted: 27 November 2023 | Published: 19 March 2024
Copyright: © 2024 The Author(s). Published by IMR Press.
This is an open access article under the CC BY 4.0 license.
Abstract

Background: The medial prefrontal cortex (mPFC) is synaptically coupled to locus ceruleus (LC) located in the pontine tegmentum. The LC supplies norepinephrine (NE) to most of the central nervous system (CNS) via an elaborate efferent network. NE release in the cortex and various limbic structures regulates arousal, memory processes, adaptive behavior and cognitive control. Methods: The study investigated the role of the mPFC-LC circuit in the cognitive behavior of mice. The mPFC efferents were inhibited optogenetically at the level of dorso-rostral pons by virally delivered ArchT opsin. The mice were implanted bilaterally with optic fibers transmitting yellow light and tested for anxiety-like behavior on Elevated O-maze (EOM), for long-term memory with Novel Object Recognition test (NOR), for problem-solving ability with Puzzle test and for learning with Cued Fear Conditioning (FC). In addition, we used anterograde transsynaptic viral tracing to map a possible anatomical circuit allowing the mPFC to modulate the activity of LC neurons, which supply NE to the main limbic structures with a functional role in cognitive behavior. Results: The application of yellow light did not affect the anxiety-like behavior of the mice but impaired their ability to recognize a novel object and solve a problem. Optogenetic inhibition of mPFC to LC, in either acquisition or recall phase of FC similarly decreased freezing. The viral tracing identified the following tripartite circuits: mPFC-LC-dentate gyrus of the hippocampus (DG), mPFC-LC-amygdala (Amy), and mPFC-LC-mPFC. Conclusions: Our results reveal essential long-range regulatory circuits from the mPFC to LC and from LC to the limbic system that serves to optimize cognitive performance.

Keywords
medial prefrontal cortex
locus ceruleus
cognition
optogenetics
tripartite neuronal circuit
Figures
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