Adam L. Halberstadt, Ph.D. - US grants

DESCRIPTION (provided by applicant): The goal of this research project is to characterize the organization of projections from the raphe nuclei to the vestibular system. Although fibers originating from raphe nuclei are known to innervate the vestibular nuclei, little is known about the specific organization of the raphe-vestibular pathway. The first part of this project will use anterograde tracing to examine the topography of raphe projections to the vestibular nuclei. However, because raphe projections arise from both serotonergic and non-serotonergic neurons, we have devised a novel combination of experimental techniques that will allow the termination patterns of the serotonergic and non-serotonergic components to be analyzed independently. The present research is also concerned with the organization of raphe projections to an ascending network that contributes to vestibular interactions with autonomic pathways. We will test the hypothesis that serotonergic and non-serotonergic raphe neurons are sources of collateralized axon projections to components of this ascending network - specifically the vestibular, lateral parabrachial, central amygdaloid, and hypothalamic paraventricular nuclei. We will use multiple retrograde tracer methods to identify these collateralized projections.

DESCRIPTION (provided by applicant): The goal of this project is to use rodent models to elucidate the mechanisms underlying the behavioral effects of hallucinogenic drugs of abuse, including LSD and DOI,as well as natural products used in recreational, ritual, or religious contexts, including SMeODMT and Ayahuasca tea. Based on the profound effects of hallucinogens on responses to sensory and emotional stimuli, behavioral effects will be measured using a multivariate profile of exploratory and investigatory behavior provided by rat and mouse Behavioral Pattern Monitor systems. These computerized systems assess activity, exploration, and behavioral organization - three major aspects of rodent behavior in an open field. The project has two specific aims. The first aim is to characterize and identify the specific mechanisms by which LSD and synthetic equivalents of Ayahuasca ("Pharmahuasca") alter exploratory behavior in rats. These studies will extend initial investigations into the nature of the biphasic, LSD-like profile of Pharmahuasca, in which exploratory behavior is initially suppressed and then increases as time progresses. We will test whether metabolic interactions between Pharmahuasca components contribute to the LSD-like behavioral profile, or whether specific neurochemical or receptor interactions are involved. The second aim is to assess the respective contributions of 5HT1A and 5HT2A serotonin receptors to the effects of hallucinogens on exploratory and investigatory behavior in mice. Both selective antagonists and knockouts of 5HTIA and 5HT2A receptors will be studied in order to develop converging evidence to test the hypothesis that both receptors contribute to the behavioral effects. This research is designed to elucidate the neurobiological mechanisms responsible for the acute effects of hallucinogens, which are presumably responsible for the recreational use of these drugs of abuse. These studies should also further our basic understanding of the behavioral functions of serotonergic systems. Collectively, this work is consistent with the stated mission of NIDA to bring "thepower of science to bear on drug abuse and addiction." Additionally, the study of psychoactive properties of natural products has been identified by NIDA as a priority area for research. Relevance: The recreational use of hallucinogens is a concern from a public health standpoint. This work will further our understanding of the basic neural mechanisms mediating the behavioral effects of these drugs of abuse.

DESCRIPTION (provided by applicant): There is evidence from both rodents and humans that the serotonergic system regulates interval timing, a behavior that has been shown to be abnormal in patients with schizophrenia. This K01 Career Development application seeks support for a project that uses a mouse model to elucidate the neural and receptor mechanisms underlying the modulation of interval timing by both endogenous serotonin (5-HT) and hallucinogenic drugs. In light of the recent resumption of human studies with hallucinogens, and reports indicating that hallucinogens may possess clinical efficacy, a more complete understanding of the action of these drugs is urgently needed. The specific paradigm used is a discrete-trials interval timing task where rodents are trained to distinguish between short and long stimulus durations. The main training goals are for the applicant to: (1) develop expertise in the use of operant procedures in mice; (2) develop a cross-species operant task to assess interval timing in mice; and (3) gain expertise in the use of optogenetic techniques to control site-specific 5-HT release. The project has three specific aims. Aim 1 is to characterize the effects of serotonin agonists and hallucinogens on interval timing in a discrete-trials task that te applicant has developed for use in mice. The task will be validated by testing whether 5-HT agonists (including the hallucinogens psilocin and 2,5-dimethoxy-4-iodoamphetamine, which act as 5-HT2A agonists) disrupt interval timing behavior in mice, as indicated by limited studies in rats. Aim 2 will test the hypothesis that 5-HT acts specifically in the prefrontal cortex (PFC) to modulate interval timing. The PFC is a critical neural substrate for interval timing, and 5-HT receptor activation has profound effects on the activity of PFC neurons. Using optogenetic techniques based on a viral expression strategy to selectively activate serotonergic projections from the dorsal raphe nucleus to the PFC, studies in this aim will test the hypotheses that selectively increasing 5-HT release in PFC will disrupt interval timing in mice, and that the abiliy of 5-HT release in the PFC to disrupt interval timing is dependent on the 5-HT2A receptor. Aim 3 will test the hypothesis that metabotropic glutamate receptors (mGluR2/3) modulate the effects of both exogenously administered 5-HT agonists and endogenously released 5-HT on interval timing. mGluR2/3 agonists functionally antagonize 5-HT2A receptor effects in the PFC, and may possess antipsychotic efficacy in schizophrenia. These studies address novel mechanisms of receptor interactions that have important implications for understanding the interplay between serotonergic and glutamatergic systems and may shed light on the pathophysiology of psychosis and thereby aid in identifying novel pharmacotherapeutic agents for the treatment of schizophrenia.

Project Summary Synthetic Psychoactive Drugs (SPDs) are substances designed to mimic the effects of controlled substances and other abused drugs. Although designer drugs are not a new phenomenon, the number and availability of SPDs is unprecedented and has increased dramatically over the last 5 years. Many hallucinogenic SPDs are structurally similar derivatives of known serotonergic hallucinogens, including drugs such as 25I-NBOMe (?25- I?, ?N-Bomb?), 1-propionyl-LSD, and 5-MeO-DALT. The popularity and proliferation of hallucinogenic SPDs is causing a significant public health problem because they are often highly potent and pose greater risks of toxicity compared with older hallucinogens. Because very little is known about the mechanisms of action and behavioral effects of hallucinogenic SPDs, a NIDA program announcement (PAR-14-106) is soliciting research into ?Synthetic Psychoactive Drugs and Strategic Approaches to Counteract Their Deleterious Effects.? This application seeks support for a project to investigate the specific pharmacological mechanisms, receptor targets, and signaling pathways that mediate the behavioral effects of hallucinogenic SPDs. The proposed research program is part of a larger collaborative effort to rapidly identify and characterize new SPDs, define their structure-activity relationships (SAR), and determine the mechanisms of their hallucinogenic and toxic actions. Hallucinogenic drug effects in rodents are assessed using two complementary behavioral paradigms: exploratory locomotor behavior, which has a direct counterpart in human studies; and the head twitch response (HTR), which is a hallucinogen-sensitive behavioral assay. Aim 1 will elucidate the mechanisms of action of SPD analogs of indoleamine hallucinogens, testing the hypothesis that these hallucinogenic SPDs (including tryptamines, benzofurans, and LSD analogs) act through 5-HT1A and 5-HT2A receptors. Studies will compare SPD effects with the known profiles of serotonergic hallucinogens and define the SAR of SPD analogs of indoleamine hallucinogens. Aim 2 will elucidate the structural features and second messenger systems mediating the behavioral effects of the highly potent N-benzylphenethylamine class of hallucinogenic SPDs, known as ?NBOMes,? that are related to hallucinogens such as mescaline. Aim 2 studies are designed to assess (1) the link between specific structural features in NBOMes and their 5-HT2A affinities, and (2) the contributions of specific signaling pathways and 5-HT2A functional selectivity to the behavioral effects of these hallucinogenic SPDs. Aim 3 will assess the contributions of metabolites to the behavioral and toxicological effects of hallucinogenic SPDs. The idea that 1P-LSD acts as a pro-drug for LSD and the hypothesis that some SPD toxicity is due to O-demethylated metabolites will be tested. These studies address receptor interactions that have important implications for understanding the psychotomimetic effects of hallucinogens in general. The results of these studies will aid in predicting the effects and potential toxicities of new SPDs and will help clinicians to develop strategies to mitigate the effects and consequences of hallucinogenic SPD use.