Christopher M. Flores - US grants

DESCRIPTION: (Applicant's Abstract) The use of smokeless tobacco products has been associated with an increased incidence of oral inflammation. However, the mechanisms underlying the pro-inflammatory effects of nicotine are unknown. Our preliminary studies indicate that nicotinic receptors are present on sensory neurons and that nicotine potentiates the evoked release of immunoreactive calcitonin gene related peptide (i-CGRP), a neuropeptide known to possess pro-inflammatory properties. These data provide a molecular basis for the ability of nicotine to influence the development of neurogenic inflammation. The multidisciplinary studies proposed here, therefore, will attempt to elucidate the molecular and pharmacological mechanisms whereby nicotine modulates peripheral neuronal function. The proposed research will: 1. Characterize pharmacologically neuronal nicotinic receptors in the trigeminal ganglion. 2. Identify the subunit composition of nicotinic receptor subtypes that are present in the trigeminal ganglion. 3. Determine the mechanisms by which nicotine alters evoked release of iCGRP from sensory neurons. 4. Determine the effect of chronic nicotine treatment on neuronal nicotinic receptor subtype expression in the trigeminal ganglion. 5. Determine the effect of chronic nicotine treatment on the ability of nicotine to alter evoked release of iCGRP from peripheral sensory neurons. Collectively, these specific aims will test the hypothesis that nicotine, acting at the level of the primary sensory neuron, is capable of modulating the development of neurogenic inflammation. To this end, we have developed a model for studying the ability of nicotine to modulate neurogenic inflammation in oral mucosal tissue. As first point of exposure to nicotine with the use of smokeless tobacco as well as cigarettes, the buccal mucosa offer significant, biomedically relevant advantages as a model system for investigations aimed at elucidating the various effects of nicotine in humans. Additionally, with the use of specific pharmacological, immunological and molecular probes for nicotinic receptors, the results should be able to contribute to a basic understanding on a biochemical level for the effects of nicotine on sensory neurons.

DESCRIPTION: (Applicant's Abstract) The management of pain and inflammation are too often unpredictable, with many patients reporting little-to-no relief with most available drugs. Therefore, research into novel drug mechanisms may offer potentially new clinically useful therapeutic agents. We propose to evaluate the hypothesis that cannabinoids, known to have central antinociceptive actions, also act in the periphery to modulate the activity of terminals of certain nociceptors. Such peripheral actions of cannabinoids would be physiologically and clinically significant, since inhibition of nociceptive primary afferent neurons could alter both peripheral secretion of neuropeptides (reducing neurogenic inflammation), and, possibly, membrane depolarization (inhibiting hyperalgesia). Specifically, we will test the hypothesis that cannabinoids modulate the development of neurogenic inflammation by inhibiting activation of peripheral terminals of capsaicin-sensitive primary afferent fibers, as measured by peripheral release of the pro-inflammatory neuropeptide calcitonin gene-related peptide (CGRP). Our research strategy takes advantage of a uniquely innervated tissue: dental pulp. Application of any physiologic stimulus to human dental pulp, including thermal, osmotic, chemical or mechanical, produces only a pain sensation. Thus, virtually all sensory neurons which innervate pulp appear to be nociceptors. Accordingly, application of drugs to pulpal sensory neurons targets a population of sensory neurons consisting predominantly of nociceptors. Our specific aims will: 1. Characterize the pharmacological effects of cannabinoids to modulate the development of neurogenic inflammation, as measured by inhibition of iCGRP secretion from superfused dental pulp. 2. Evaluate the molecular basis for cannabinoids to directly modulate iCGRP release via interaction with receptors expressed on peptidergic trigeminal sensory neurons. 3. Determine whether cannabinoid inhibition of iCGRP release is mediated by a direct mechanism (i.e., activation of sensory neuronal cannabinoid receptors), by an indirect mechanism (i.e., activation of receptors expressed on autonomic fibers or non-neuronal cells in pulp), or by a combination of the two. Since dental pulp is innervated primarily by nociceptors and is frequently involved with inflammation and healing, this tissue is a relevant biomedical model system. Moreover, the use of specific pharmacological, immunological and molecular probes for cannabinoids should contribute to an understanding on a biochemical level for the effects of cannabinoids on sensory neurons and open new avenues of research on the peripheral actions of these compounds. This knowledge base may provide a rationale for developing peripherally-selective cannabinoid analgesics with minimal CNS-mediated side-effect liability.