Nucleus Accumbens Corticotropin-Releasing Hormone Neurons Project to Bed Nucleus of the Stria Terminalis to Regulate Wakefulness and Positive Emotional States

Background

The nucleus accumbens (NAc) plays a crucial role in regulating motivation, reward, and many behaviors that depend on high levels of arousal. However, research on the neural mechanisms between arousal and emotional regulation in the NAc is not fully clear. Corticotropin-releasing hormone (CRH) is an important stress-related neuroendocrine signal, but its function in the NAc is unclear. In this study, researchers aimed to explore how a specific subgroup of CRH neurons in the NAc (NAcCRH) regulates arousal and emotional behavior in mice.

Research Source

This paper was co-authored by eight researchers including Gaojie Pan and Bing Zhao, with main institutions including Fudan University, Nantong University, and Naval Medical University. The paper was received on March 9, 2024, accepted on May 2, 2024, and published in the journal “Neuroscience Bulletin”.

Research Details

Research Methods and Procedures

Animal Model

The study used Crh-Cre mouse models, which can express Cre-dependent fluorescent protein GCamp7f in their nucleoli. These mice lived in a sound-insulated room with a 12-hour day-night cycle.

Preparation of Adeno-Associated Virus (AAV)

AAV vectors were used to express specific genes in specific brain regions of mice, including AAV-hsyn-dio-hm3dq-mcherry and AAV-hsyn-dio-chr2-mcherry.

Surgery and Virus Injection

Under anesthesia, researchers bilaterally injected Cre-dependent AAV vectors into the nucleoli of mice and injected tracing dye into the bed nucleus of the stria terminalis (BNST) to mark projection pathways.

Optogenetic and Chemogenetic Experiments

To investigate the effects of NAcCRH neurons on arousal and emotion, researchers activated or inhibited these neurons through optogenetic methods. Additionally, a chemogenetic method was employed using DREADD receptors (Designer Receptors Exclusively Activated by Designer Drugs), activating or inhibiting NAcCRH neuronal activity through injection of CNO (a specific ligand).

Research Results

Enhanced Activity of NAcCRH Neurons in Awake State

Through fiber photometry recording, researchers found that calcium signals in NAcCRH neurons were significantly higher in the awake state compared to REM and NREM sleep states. Moreover, NAcCRH neuronal activity increased during transitions from NREM sleep to wakefulness, NREM sleep to REM sleep, and REM sleep to wakefulness.

Activation of NAcCRH Neurons Promotes Wakefulness and Inhibits NREM Sleep

Optogenetic activation of NAcCRH neurons during NREM sleep rapidly induced transition to wakefulness, with good time dependence. Similar results were observed using chemogenetic methods to activate NAcCRH neurons, showing significantly increased wake time and decreased NREM sleep time.

Inhibition of NAcCRH Neurons Reduces Wakefulness and Increases NREM Sleep

Chemogenetic inhibition experiments showed that CNO injection reduced NAcCRH neuronal activity, leading to decreased wake time and increased NREM sleep time during the active phase (night) in mice.

Natural Reward Stimuli Induce Activation of NAcCRH Neurons

The study further found that calcium signals in NAcCRH neurons significantly increased during natural reward-related stimuli such as social interaction with the opposite sex, chocolate consumption, and sugar water licking, indicating the sensitivity of these neurons to reward stimuli.

Activation of NAcCRH Neurons Regulates Emotional Behavior

In real-time place preference (RTPP) tests, mice with optogenetically activated NAcCRH neurons showed clear place preference behavior. Additionally, in open field test (OFT) and elevated plus maze (EPM) tests, mice with activated neurons showed increased activity and reduced anxiety levels.

NAcCRH Neurons Project to BNST to Regulate Wakefulness and Emotion

Through further retrograde labeling and optogenetic experiments, the study found that NAcCRH neurons mainly project directly to BNST via GABAergic synapses. Activation of this specific pathway could induce transitions from NREM sleep to wakefulness and significantly increase preference time in RTPP tests and central activity area time in OFT tests.

Conclusions and Significance

This study reveals the key role of specific CRH neuron subgroups in the NAc in driving wakefulness and regulating positive emotional states, and identifies BNST as their main downstream projection area. This finding not only provides new insights into understanding the neural mechanisms of arousal and emotional behavior but may also offer potential targets for treating related disorders.

Research Highlights

1. Arousal and Emotion Regulation Function of NAcCRH Neurons: First systematic revelation of the important role of CRH neurons in the NAc in regulating natural wakefulness and emotional behavior.
2. Clarity of Projection Pathway: Through optogenetic and retrograde labeling experiments, it was clearly shown that these CRH neurons directly project to BNST via GABAergic synapses and exert their effects.
3. Comprehensiveness of Behavioral Experiments: Multiple behavioral experiments (such as RTPP, OFT, and EPM) verified the regulatory role of NAcCRH neurons in emotional and arousal behaviors.

This study lays an important foundation for future exploration of the neural circuit mechanisms of arousal and emotion regulation.