James T. Porter - US grants

The overall goal of my research is to understand the mechanisms by which the activation of cortical inhibitory and excitatory circuits by incoming sensory information is modulated. The central hypothesis of this proposal is that presynaptic GABAB, adenosinc, and metabotropic glutamate receptors modulate thalamocortical stimulation of cortical inhibition. It is becoming increasingly clear that cortical inhibitory circuits play very important roles in sensory processing and cortical reorganization. Therefore, understanding how the activation of these inhibitory cortical circuits is regulated will provide important insights into how sensory processing can be altered pharmacologically. Perhaps in the future one would have the ability to alter sensory processing via receptor agonists or antagonists in order to assist in new skill learning, relearning after an accident or stroke, or treatment of conditions like phantom limb pain which have aberrant cortical reorganization. However, before any such interventions can be done we need more detailed information on the types and subtypes of receptors that regulate the activation of inhibitory cortical circuits via incoming sensory information. To begin to address; this deficit in our knowledge and extend the initial observations found during the first three years of this grant, the following aims are proposed. Specific Aim 1: To test the hypothesis that metabotropic glutamate receptors modulate thalamocortical excitation of inhibitory neurons. Specific Aim 2: To test the hypothesis that endogenously released GABA, adenosine. and glutamate can modulate thalamocortical excitation of inhibitory neurons. Specific Aim 3: To test the hypothesis that presynaptic GABAn, adenosine A1 and metabotropic glutamate receptors modulate thalamocortical stimulation in adult animals. Specific Aim 4: To test the hypothesis that intracortical and thalamocortical synapses are differentially reg,ulated by GABAB, adenosine and metabotropic glutamate receptors. Detailed knowledge of the pharmacology and physiology of the mechanisms which regulate the thalamic activation of cortical inhibitory circuits could improve treatments for people recovering from strokes or accidents.

The ability to adapt behavioral response to environmental cues is critical for survival and requires learning to associate a given cue with a given consequence so that an appropriate response can be made. The extinction of Pavlovian fear conditioning is a commonly used model of associative learning in which an animal must learn that a neutral stimulus (tone) that was previously paired with an aversive stimulus (footshock) no longer predicts the aversive stimulus. Rather than erase fear memory, extinction is thought to form a new memory that signals safety. Activity in the medial prefrontal cortex (mPFC) is critical for the recall of fear extinction memory. In this project investigators from two Puerto Rican institutions will combine their expertise in slice recording and neural systems of fear learning to examine the intrinsic cellular mechanisms that mediate the extinction-induced enhancement of mPFC activity. The investigators will use a multidisciplinary approach combining in vitro patch-clamp electrophysiology, histology, in vivo single neuron recordings, behavioral training, and in vitro and in vivo neuropharmacology.

The investigators expect to demonstrate that extinction training enhances the intrinsic excitability of mPFC neurons, that metabotropic glutamate receptor subtype 5 (mGluR5) controls the intrinsic excitability in mPFC neurons, and that the stimulation of mGluR5 receptors in vivo augments the recall of extinction memory. The results of this study will provide important groundwork for understanding how extinction memory is encoded at the level of single neurons.

This project creates a unique opportunity for Puerto Rican graduate and undergraduate students to learn a multidisciplinary and collaborative approach to science. Students in both laboratories will be involved in the project and will present their results at the Society for Neuroscience Annual Meetings.

DESCRIPTION (provided by applicant): Functional imaging studies in PTSD patients suggest that reduced activation of the medial prefrontal cortex (mPFC) contributes to the excessive fear response seen in these patients. To understand why the mPFC is less activated in PTSD patients, we need to understand the mechanisms by which fear conditioning and extinction alter mPFC excitability. Patch-clamp recordings of infralimbic (IL) neurons in the mPFC revealed that the intrinsic excitability of IL neurons was depressed by fear conditioning in rats. The depressed IL excitability could reduce IL activation and enhance conditioned fear responses. Consistent with this, reducing IL intrinsic excitability enhances conditioned fear response. These findings imply that intrinsic plasticity in IL contributes to the consolidation of the conditioned fear memory. The goal of this proposal is to extend these results by examining the mechanisms and circuits involved in this fear conditioning-induced depression of IL intrinsic excitability. In Aim1, the role of NMDA receptors, D2-like dopamine receptors, and glucocorticoid receptors in the fear conditioning-induced depression of IL intrinsic excitability will be examined. In Aim 2, the role of hippocampal inputs in the fear conditioning-induced depression of IL excitability will be evaluated. In Aim 3, we will evaluate whether sustained voltage-gated K+ channels contribute to the fear conditioning-induced depression of IL excitability. A better understanding of the mechanisms leading to intrinsic plasticity in this brain structure may provide direction for the development of novel treatments for PTSD.

In this proposal, we are requesting funds to further develop the RCMI Behavioral Research and Integrated Neuroscience (BRAIN) Core that was initiated during the previous cycle to provide enhanced infrastructure support for the further development of neuroscience research projects. Currently there are five Ponce School of Medicine (PSM) investigators with funded neuroscience-related projects. As the number of neuroscience investigators at PSM has grown over the years, the need for neuroscience-related core facilities to support and encourage the further development of neuroscience research at PSM has increased. During the initial phase, we focused on strengthening the translational preclinical behavioral research present at PSM while developing the beginnings of clinical behavioral investigations. The goal of this phase in the development of the BRAIN Core is to further enhance translational preclinical and clinical research at PSM and to build bridges for the development of collaborative projects involving preclinical and clinical faculty. Several collaborative projects involving clinical psychologists and basic scientists, developed during the first phase, would benefit from the enhanced BRAIN Core. In addition, the enhanced BRAIN Core will interact closely with the RCMI Molecular And Genomics (MAGIC) and AIDS Research Infrastructure Cores in the development of investigations into the role of genetics and inflammation in various mental health disparities and will continue to provide an attractive strength to our institution in terms of recruitment.

Project Summary/Abstract: The widely accepted model proposes that the infralimbic cortex (IL) is a key structure for fear extinction that plays no role in fear conditioning. Surprisingly, we found that selectively decreasing expression of FK506 binding protein 5 (FKBP5) in IL reduced acquisition and recall of conditioned fear. Although clinical data suggest that FKBP5 plays a role in PTSD, it is unclear whether differences in FKBP5 expression alone could predispose or protect individuals from the development of PTSD. Our data suggests that higher expression of FKBP5 in the ventral medial prefrontal cortex (equivalent of IL in humans) could predispose people to the development of PTSD following trauma. Since direct stimulation of IL inputs in the amygdala do not reduce fear acquisition, the reduced fear acquisition after knocking down IL FKBP5 is likely to be mediated by IL projections to other subcortical structures. The acquisition of conditioned fear requires glucocorticoid and beta adrenergic receptor stimulation in the basolateral amygdala. Therefore, IL could modulate fear learning by modulating glucocorticoid or catecholamine release via inputs to the lateral hypothalamus (LHA), bed nucleus of the stria terminalis (BNST), or nucleus tractus solitarius (NTS). In this project, we will test the novel hypothesis that signaling via Fkpb5 modulates fear learning and memory by modulating the excitability of IL projections to the BNST, LHA, or NTS. To test this hypothesis, we will first evaluate whether reducing or overexpressing FKBP5 selectively in IL projection neurons modulates acquisition or recall of conditioned fear. Next, we will evaluate whether FKBP5 modulates the intrinsic or synaptic excitability of IL neurons projecting to the BNST, LHA, or NTS using patch-clamp recordings of retrogradely labeled IL projections in brain slices. Finally we will use optogenetics to evaluate whether IL inputs to the BNST, LHA, or NTS modulate fear learning and memory.

PROJECT SUMMARY The high degree of comorbidity between substance use disorder (SUD) and post-traumatic stress disorder (PTSD) in the US population suggests that similar underlying mechanisms contribute to both disorders such that having one disorder may predispose one to develop the other. A study of a mostly African-American urban civilian population found that their levels of cocaine use highly correlated with levels of childhood abuse and PTSD symptoms. This suggests that childhood abuse, cocaine addiction, and PTSD interact in minority populations and likely contribute to worse outcomes and health disparities. The vast majority of animal models examine cocaine use and PTSD separately. However, to be able to design better treatment plans for real-life clinical scenarios, we need to understand how these two disorders interact. In this project, we propose to combine animal models of child abuse and neglect with models of cocaine abuse and PTSD to examine to what degree one condition affects the other and to examine whether exposure to cocaine at different developmental stages increases the severity of PTSD-like phenotypes. Our central hypothesis is that developmental stress and cocaine abuse interact to increase the susceptibility to and worsen the severity of PTSD-like symptoms after trauma exposure in adulthood by altering overlapping neuronal circuits. Substance abuse often begins during adolescence, during which time the prefrontal circuits and hippocampal modulation of behavior is still being refined. Therefore, early life stress and adolescent cocaine exposure could alter hippocampal modulation of conditioned fear, potentially leading to increased susceptibility to more severe PTSD-like behaviors in adulthood. To begin to address these issues, in Aim 1, we will first evaluate whether early life neglect and adolescent cocaine use interact to increase susceptibility to and generalization of conditioned fear or impair fear extinction in a rat model. In Aim 2, we will evaluate whether fibroblast growth factor-2 mediates the effects of early life neglect and adolescent cocaine use on fear generalization and extinction. In Aim 3, we will evaluate how early life neglect and adolescent cocaine use interact to alter the excitability of the ventral hippocampus-to-infralimbic cortex portion of the fear circuit. Thus, we will examine the effects of developmental stress and cocaine use on PTSD- related behaviors from a behavioral, circuit, cellular, and molecular level. The Research Resources Core will provide essential support for this project, since the completion of this project's aims will require behavioral and molecular analysis.

Capacity building is necessary for supporting research on issues affecting human health in under-resourced communities such as Puerto Rico. The Technologies and Resources for Research Laboratories Core (TRRCL) is a component of the Hispanic Alliance for Clinical and Translational Research (the Alliance) composed of the University of Puerto Rico Medical Sciences Campus (UPR-MSC), the Ponce Medical School Foundation (PMSF), and the Universidad Central del Caribe (UCC). TRRCL services to clinical and translational investigators in Puerto Rico has increased steadily from 2014 until 2019. Under the newly conceived Alliance, the TRRCL team proposes to continue developing the capacity of TRRCL to fulfill the needs of clinical and translational investigators who require specialized laboratory equipment and services to conduct their research. It is expected that continuous access to cutting-edge technologies and laboratory resources facilitated by the TRRCL will motivate more investigators to conduct clinical and translational research successfully and increase the institutional capacity to address health issues impacting underserved Hispanic populations in Puerto Rico and the rest of the US. The TRRCL´s main goal for this project is to improve shared research facilities for investigators, and to improve access for investigators to these facilities. The objective of TRRCL is to ensure that investigators that require laboratory space and technical support receive access to core laboratory services thereby allowing for the timely completion and publication of their research projects. The central hypothesis is that the TRRCL will catalyze an increase in active clinical and translational research projects in the Alliance institutions. The TRRCL will achieve this by: 1) supporting the training of researchers in the Alliance institutions and increasing researchers´ access to TRRCL cores and highly trained staff; 2) providing investigators the technical expertise and infrastructure they need to produce reliable data that is of publication quality, and; 3) enhancing the impact and outreach of the TRRCLby establishing collaborative agreements with other institutions and by participation in community engagement activities. As the TRRCL usage increases, the team expects to satisfy the increased demand by collaborating INBRE and COBRE research cores in Puerto Rico and in other IDeA states. TRRCLwill complement this support and accelerate progress on research projects that will translate to health benefits for the Puerto Rico population and underserved Hispanic/Latino populations across the nation, and will result in a more competitive biomedical workforce in Puerto Rico supported by state-of-the-art research f ac ilities.