Hildebrand, M. A. | bioRxiv Science

bioRxiv2023

Uncovering circadian rhythm disruptions of synaptic proteome signaling in prefrontal cortex and nucleus accumbens associated with opioid use disorder

Opioid craving and relapse vulnerability is associated with severe and persistent sleep and circadian rhythm disruptions. Understanding the neurobiological underpinnings of circadian rhythms and opioid use disorder (OUD) may prove valuable for developing new treatments for opioid addiction. Previous work indicated molecular rhythm disruptions in the human brain associated with OUD, highlighting synaptic alterations in the dorsolateral prefrontal cortex (DLPFC) and nucleus accumbens (NAc)--key brain regions involved in cognition and reward, and heavily implicated in the pathophysiology of OUD. To provide further insights into the synaptic alterations in OUD, we used mass-spectrometry based proteomics to deeply profile protein expression alterations in bulk tissue and synaptosome preparations from DLPFC and NAc of unaffected and OUD subjects. We identified 55 differentially expressed (DE) proteins in DLPFC homogenates, and 44 DE proteins in NAc homogenates, between unaffected and OUD subjects. In synaptosomes, we identified 161 and 56 DE proteins in DLPFC and NAc, respectively, of OUD subjects. By comparing homogenate and synaptosome protein expression, we identified proteins enriched specifically in synapses that were significantly altered in both DLPFC and NAc of OUD subjects. Across brain regions, synaptic protein alterations in OUD subjects were primarily identified in glutamate, GABA, and circadian rhythm signaling. Using time-of-death (TOD) analyses, where the TOD of each subject is used as a time-point across a 24- hour cycle, we were able to map circadian-related changes associated with OUD in synaptic proteomes related to vesicle-mediated transport and membrane trafficking in the NAc and platelet derived growth factor receptor beta signaling in DLPFC. Collectively, our findings lend further support for molecular rhythm disruptions in synaptic signaling in the human brain as a key factor in opioid addiction.

neuroscience↗

bioRxiv2020

The Suprachiasmatic Nucleus Regulates Anxiety-Like Behavior in Mice

Circadian rhythms are commonly disrupted in individuals with depression and/or anxiety disorders. Animal studies indicate that circadian rhythm disruption can cause increased depressive and anxiety-like behavior, but the underlying mechanisms are unclear. Currently, there is conflicting evidence as to whether the master pacemaker in the brain, the suprachiasmatic nucleus (SCN), plays a key role in regulating psychiatric-related behavior. To investigate the role of the SCN in regulating depressive and anxiety-like behavior in mice, we directly manipulated the neural activity of the SCN using two chronic optogenetic stimulation paradigms. Repeated stimulation of the SCN late in the active phase (circadian time 21, CT21) shortened the period and dampened the amplitude of homecage activity rhythms. Repeated stimulation of the SCN at unpredictable times during the dark phase dampened, fragmented and reduced the stability of homecage activity rhythms. In both SCN optogenetic stimulation paradigms, dampened homecage activity rhythms (decreased amplitude) was associated with increased measures of anxiety-like behavior, but not in control mice. Increased fragmentation and decreased day-to-day stability of homecage activity also correlated with increased anxiety-like behavior. Unexpectedly the change in period of homecage activity rhythms was not directly associated with any psychiatric-related behavior. Furthermore, we did not observe consistent correlations between homecage activity amplitude and depressive-like behavior in stimulated mice. Taken together, these results indicate that SCN-mediated dampening of rhythms is directly correlated with increased anxiety-like, but not depressive-like behavior in mice. This work is an important step in understanding how specific SCN neural activity disruptions affect mood and anxiety-related behavior.

neuroscience↗