Author ORCID Identifier
https://orcid.org/0000-0003-2546-5288
Date Available
2-10-2025
Year of Publication
2025
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Medicine
Department/School/Program
Neuroscience
Advisor
Dr. Pavel I Ortinski
Abstract
Psychedelics are rapidly garnering research attention for their ability to successfully treat a variety of psychiatric diseases after one or a handful of treatments in recent clinical research. Among the conditions treated is substance use disorder (SUD), which afflicted 48.5 million (16.7%) Americans aged 12 and older in 2023 (NSDUH). As clinical trial results continue to show lasting positive effects of psychedelic psychotherapy, there remains an enormous gap in knowledge regarding how these drugs cause lasting changes in the brain to achieve these therapeutic effects. It has been suggested that psychedelics must induce rapid and long-lasting neuronal plasticity in order to achieve their lasting effects on behavior, yet most evidence of plasticity exists in the form of imaging dendritic growth while no one has shown confirmation of psychedelic-induced potentiation of spike-timing synaptic plasticity (STDP), a functional measure of synaptic strength between neurons based on the precise timing of pre- and post-synaptic action potentials. Radioligand studies have shown that a brain area called the claustrum (CLA) has among the highest levels of psychedelic drug binding in the entire brain, implying a large population of serotonin 2 receptors (5-HT2Rs), which psychedelics are partial agonists of, yet there is little published research on how serotonin may regulate synaptic and neuronal excitability in the CLA. Furthermore, there is no published research observing any effects of psychedelics on claustrum neuronal physiology. The aims of this research were to characterize the serotonin (5-HT) receptors within the CLA and show which receptors were responsible for the effects of 5-HT and the psychedelic drug, 2,5-Dimethoxy-4-iodoamphetamine (DOI) on neuronal excitability. Furthermore, we sought to confirm the presence of psychedelic induced synaptic plasticity in claustrum neurons that project to the anterior cingulate cortex (ACC) (CLA-ACC), potentially highlighting the mechanism and circuit by which psychedelics achieve their therapeutic effects. Finally, in rodent models of cocaine use disorder (CUD), we aimed to show negative effects of cocaine use on cognitive flexibility, a mental ability that is vital for drug users to resist relapse and maintain abstinence. By utilizing in vivo imaging of neuronal excitability, in vivo injections (both systemic and intra-CLA) of the psychedelic, DOI, and slice electrophysiology and calcium imaging, we further ventured to elucidate the relationship between psychedelics administered in vivo and cocaine-induced cognitive deficits alongside CLA neurotransmission. RT-qPCR was performed on CLA, ACC, and insular cortex (INS) brain tissue samples collected from male and female Sprague-Dawley rats to uncover the presence and relative abundance of 13 different 5-HTR subtypes. We found robust expression of the 5-HT2A and 5-HT2CR subtypes, with moderate expression of 5-HT1A, 5-HT1B, and 5-HT5ARs, and low levels of expression of other 5-HTRs in the CLA. To determine if these most abundant receptors were expressed on excitatory or inhibitory neurons within the CLA, we used RNAscope on male and female rat brain slices, confirming 5-HT1ARs on glutamatergic neurons and 5-HT2Rs on both glutamatergic and GABAergic neurons. These results characterize heterogeneity of a dense 5-HTR population in the CLA with cell type specificity of expression. We next performed whole-cell patch clamp electrophysiology on CLA neurons that project to the anterior cingulate cortex, measuring glutamatergic AMPA receptor-mediated spontaneous excitatory post-synaptic currents (sEPSCs), intrinsic membrane excitability properties and action potential generation in response to 5-HT, 5-HT antagonists, and the psychedelic, DOI. We found that 5-HT inhibits CLA-ACC sEPSC frequency and amplitude while also hyperpolarizing resting membrane potential (RMP) and attenuating action potential firing. Using a series of 5-HTR antagonists, we found that these effects were due to the 5-HT1A and 5-HT2CRs. Conversely, DOI increased sEPSC frequency and amplitude, effects that were surprisingly induced by DOI binding of the 5-HT2CR and not the canonical 5-HT2AR. Finally, to observe the effects of psychedelics on spike-timing-dependent plasticity (STDP), we performed stimulation protocols known to induce spike-timing-dependent long-term potentiation (t-LTP) on CLA-ACC neurons with and without the presence of DOI. We found that CLA-ACC neurons actually reduced synaptic strength after the LTP-induction protocol in the absence of DOI, whereas DOI application combined with the same stimulation protocol unlocked a robust t-LTP. These results characterize CLA projection neuron physiology in response to 5-HT and psychedelics with receptor subtype specificity and provide the first evidence of psychedelic drug effect on long-term synaptic plasticity in the CLA. Next, several cohorts of male and female rats performed set-shifting operant behavior tasks to access the effects of cocaine contingent and non-contingent administration on cognitive flexibility, with an emphasis on the relationship between task performance and intra-CLA vs. intraperitoneal DOI administration. Other measures were assessed in these in vivo models, such as ACC neurotransmission in the form of calcium imaging fiber photometry recordings and head twitch response. Upon the completion of drug administration and behavior tasks, rat brains were sliced and recorded using electrophysiology or calcium imaging to observe any lasting effects of drugs or behavior. Overall, we found that non-contingent injections of cocaine had no effect on set-shift performance, while extended access to cocaine self-administration robustly attenuated set-shift performance. Additionally, disruption of serotonergic signaling globally with the serotonin releasing agent, 5-Methoxy-6-methyl-2-aminoindane (MMAI) or locally with intra-CLA microinjections of DOI both acutely disrupted set-shift task performance. DOI microinjections given within 24 hours of cocaine withdrawal did not significantly rescue cocaine-induced cognitive flexibility deficits compared to saline controls at several long-term cocaine withdrawal timepoints. Cocaine animals had significantly reduced sEPSC frequency compared to saline animals after 8 days of withdrawal, an effect not seen at 24-hour withdrawal. These results suggest that psychedelics alter CLA-ACC signaling to impact cognitive flexibility, and that cocaine self-administration degrades cognitive flexibility performance, with lasting neurophysiological changes in CLA neurons, while non-contingent cocaine administration has no deleterious effects on behavioral flexibility. The results from these studies highlight newly discovered targets for the action of psychedelic drugs at the level of brain region, receptor subtype, and synaptic plasticity. These insights will guide novel research into the therapeutic potential of psychedelics in treating psychiatric diseases such as substance use disorder.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2025.03
Funding Information
This work was supported by the National Institute of Health and National Institute on Drug Abuse R01DA041513 , R01DA053070, F31DA055445, T32DA035200.
Recommended Citation
Anderson, Tanner L., "CELLULAR AND BEHAVIORAL CONSEQUENCES OF PSYCHEDELIC DRUG ACTION IN THE CLAUSTRUM" (2025). Theses and Dissertations--Neuroscience. 39.
https://uknowledge.uky.edu/neurobio_etds/39
