Radi Masri, DDS, MS, PhD - US grants

DESCRIPTION (provided by applicant): Following spinal cord injury, a majority of patients develop maladaptive plastic changes within the central nervous system (CNS). These changes result in abnormal regulation of peripheral inputs, and impaired perception of tactile and painful stimuli. The majority of these patients suffer because conventional treatments fail to reverse these maladaptive changes. An alternative and potentially effective modality of treatment-motor cortex stimulation (MCS)-offers hope for these patients. However, treatment outcomes with MCS are variable mainly because of the lack of understanding of how stimulation of the motor cortex reverses these maladaptive changes in the CNS. The goal of this application is to elucidate the neurobiological basis of regained sensory processing in the CNS following MCS. To this end, we use a rodent model of spinal cord injury. We demonstrated recently that activity in the GABAergic nucleus zona incerta (ZI) is suppressed in animals following spinal cord injury, resulting in enhanced activity in the posterior thalamus (PO) and enhanced flow of peripheral inputs to the neocortex. We also demonstrate that electrical stimulation of ZI mimics the effects of MCS and reverses maladaptive plastic changes observed following spinal cord injury. Based on these findings, and because the motor cortex projects densely upon ZI, we propose that MCS produces pain relief by enhancing inhibitory inputs to the posterior thalamus from zona incerta and that chronic MCS results in long term synaptic changes in the incerto-thalamic circuit. We will test the following aims: Aim 1: MCS suppresses hyperalgesia by enhancing inhibitory inputs from ZI to PO. Aim 2: Reduction of hyperalgesia is causally related to the activation of the incerto-thalamic pathway. Aim 3: MCS produces long lasting changes in the incerto-thalamic circuitry. PUBLIC HEALTH RELEVANCE: One of the most debilitating consequences of spinal cord injury is the development of chronic intractable neuropathic pain (central pain syndrome). The pain is severe and relentless and current treatment methods offer no hope. Motor cortex stimulation (MCS) was introduced-almost 20 years ago-as a modality for the treatment of central pain syndrome when all other treatments have failed. However, the outcome of the treatment is variable. A major impediment to implementing MCS in the clinical setting and improving the success rate is the fact that the mechanisms by which MCS affects pain processing are unknown. Here, we take advantage of an animal model of central pain produced by spinal cord injury to study the mechanisms by which MCS affects the activity of specific neuronal circuits.

DESCRIPTION (provided by applicant): Inflammation of the dental pulp, or pulpitis, is a common, painful, and costly global public health problem that affects quality of life of patients. n most cases, pulpitis is a consequence of moderate or advanced dental caries (tooth decay), the most common chronic disease in the world. Pulpitis can also result from repeated thermal insults to a sensitive tooth, tooth attrition, trauma, microleakage of dental restorations, and periodontitis (inflammation of tissues supporting the teeth). Pulpitis is characterized by sharp shooting pain evoked by thermal stimuli (reversible pulpitis) or debilitating, dull, throbbing pain that occurs spontaneously or can be evoked by mechanical or thermal stimuli and lingers after cessation of the stimulus, necessitating emergency care (irreversible pulpitis). The quality and severity of the pain correlates with the extent of irritation from bacteria and other etiologies. Diagnosis can be complicated because the pain can be referred to other orofacial structures, or to adjacent teeth. We recently invented a new technique to deliver therapeutic agents to the pulp without affecting the integrity of the pulp chamber. To do so, we take advantage of naturally occurring dentinal tubules (~0.3 - 2 ?m diameter channels in dentin), and use magnetic forces to direct therapeutic magnetic particles into the tooth pulp. Preliminary experiments demonstrated efficient delivery of 100-500 nm starch-coated particles to the pulp chamber of extracted human teeth in approximately 30 minutes, using magnet arrays of our design. In this application, we seek funds to allow us to develop this innovative technique and to test its effect on pulpal tissues and tissues surrounding the teeth. We aim: Aim 1. To test the magneto-dynamics and pharmacokinetics of biocompatible nanoparticles guided to the pulp through dentinal tubules. We will use an in vitro preparation of freshly extracted human teeth and investigate: (1) The optimum particle size for delivery into the pulp; (2) The effect of polysaccharide coating (starch vs. chitosan) on the delivery of particles to the pulp; and (3) The amount of therapeutic medication (prednisolone or ofloxacin) that can be delivered to the pulp and the rate of sustained release of these therapeutic agents after magnetic force application is stopped. Nanoparticle concentrations will be determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and drug levels will be quantified using high performance liquid chromatography coupled with mass spectrometry. Aim 2. To quantify delivery of drug-conjugated nanoparticles to the pulp in vivo, and to evaluate the effects of these nanoparticles on pulpal tissues under normal and pathologic conditions. We will prepare cavities of various depths in the molar teeth of rats. We will apply nanoparticles coated with polysaccharides or conjugated to prednisolone, or ofloxacin (particle size will be based on results from Aim 1) and: (1) Assess changes in pulpal biology and surrounding dental tissues after the application of polysaccharide-coated nanoparticles to experimentally prepared cavities in rat molars; and (2) Test the effect of drug-conjugated nanoparticles (prednisolone, and ofloxacin) on directly or indirectly injured pulp. We will use histological examination to test for changes in pulpal biology, inflammatory cell infiltration in the pulp and tissues surrounding the tooth, thickness of periodontal ligament (tissues surrounding the tooth). We will also use ICP-AES to determine nanoparticle concentration within the teeth.

Project Summary/Abstract Chronic pain is the most common complaint of patients, affecting over 100 million Americans, and costing the nation more than $650 billion/year in medical treatment and lost productivity. Most chronic pain patients are resistant to pharmaceutical or surgical therapies, in large part because the underlying pathophysiology of their chronic pain condition is unknown. The ultimate goal of this research program is to rectify this deficiency. Most spinal cord pain-related afferents target the parabrachial nuclear complex (PB), which then projects to multiple pain-related cortical and subcortical targets. New preliminary data indicate that inhibitory inputs from the central nucleus of the amygdala (CeA) to PB are reduced in a rodent neuropathic pain model: chronic constriction of the infraorbital nerve (CCI). This reduced inhibition dramatically `amplifies' both spontaneous and evoked PB neural activity. As a consequence, there is increased PB excitation of several pain-related nuclei, including the rostral ventral medulla (RVM), a key node of the descending pain modulation system. Based on this exciting new evidence we hypothesize that chronic pain results from the development of a pathologic positive feedback network: Reduced inhibition from CeA to PB ?> amplified PB activity ?> increased activation of RVM neurons ?> increased activation of nociceptive neurons in the spinal cord. With the use of electrophysiological recordings from intact rodents and from brain slices, and taking advantage of behavioral approaches, optogenetics and pharmacogenetics, we will directly test this overarching hypothesis. Specifically, we will (1) Test the hypothesis CCI causes a progressive and significant reduction of inhibitory inputs to nociceptive PB neurons that project to RVM, and dramatically increases their firing; (2) Test the hypothesis that amplified PB activity is due to reduced inhibition from CeA.; (3) Test the hypothesis that reduced CeAI inhibition to PB is causally related to the development of CCI-Pain. The anticipated findings are expected to reveal novel mechanisms for the development of chronic pain, and may lead to development of novel therapies to ameliorate, and perhaps even prevent, this devastating condition.

Project Summary/Abstract Chronic pain is the most common complaint of patients. Most chronic pain patients are resistant to therapy, in large part because the underlying pathophysiology of their chronic pain condition is unknown. The ultimate goal of this research program is to fill this critical gap. Pain is strongly modulated by the rostroventral medulla (RVM) that directly regulates the activity of nociceptive dorsal horn neurons. Prominent in RVM are serotonin- containing neurons. However, the role of these neurons in chronic pain remains controversial, with evidence for both pathological increases and decreases in 5HT output. Our exciting preliminary findings?using a model of chronic pain after chronic constriction injury of the infraorbital nerve (CCI-Pain)?may resolve this important controversy. We show that, in CCI-Pain, RVM-5HT neuronal activity is amplified, resulting in abnormally high release of 5HT in the caudal dorsal horn ? trigeminal nucleus (SpVc). This causes SpVc neurons to produce a barrage of after-discharges (ADs) that far outlast nociceptive stimuli, and that are considered a manifestation of chronic pain. The increased 5HT release also potentiates the strength of nociceptive inputs to SpVc neurons. Coupled with our previous demonstration that reducing 5HT levels in RVM suppresses ADs and blocks pain sensitization, we hypothesize that increased serotonergic drive from RVM causes hyperexcitability of dorsal horn neurons, which results in chronic pain. Aim I tests the hypothesis that amplified activity of 5HT-RVM neurons results in increased release of 5HT in SpVc and the development of chronic pain. We test the prediction that the electrophysiological activity of optogenetically- identified 5HT RVM ?> SpVc projection neurons is amplified in CCI-Pain. We will also use in vivo fast scanning voltammetry, and quantitative mass spectrometry, to test the prediction that CCI-Pain is associated with increased 5HT release in SpVc. Aim II tests the hypothesis that increased 5HT release is causally related to the development of chronic pain. We will test the prediction that in vivo optogenetic release of 5HT from RVM terminals in SpVc results in signs of sensory and affective pain, and that these signs are exacerbated by repeated 5HT release. We will also test the converse prediction, that optogenetic inhibition of these 5HT terminals results in relief from CCI-Pain. Aim III tests the hypothesis that amplified 5HT activity produces chronic pain by inducing abnormal ADs in dorsal horn neurons. We will test the prediction that in vivo optogenetic release of 5HT induces ADs in SpVc neurons of uninjured animals, and that optogenetic inhibition of 5HT release will suppress ADs in CCI-Pain animals. Aim IV tests the hypothesis that amplified 5HT activity produces chronic pain by potentiating primary afferent inputs to dorsal horn neurons. We will test the prediction that optogenetic release of 5HT in vitro evokes potentiation of trigeminal inputs to SpVc neurons. The predicted findings have novel translational relevance for the development of new pharmaceuticals to treat chronic pain.