Kathryn G. Commons - US grants

This application proposes using combined anatomical and electrophysiological means to understand how opioids function to modulate neuronal activity in the ventrolateral periaqueductal gray (PAG) and furthermore to understand mechanisms of plasticity within the PAG-opioid system. The applicant is an experienced ultrastructural neuroanatomist and will be trained under this support mechanism in electrophysiological techniques, as well as in stress neurobiology. The PAG subserves several behavioral functions but has been most well characterized as a site of morphine-produced and stress-induced analgesia. Mu opioids are thought to act in the PAG by inhibiting local GABAergic interneurons and subsequently disinhibiting PAG output, however, several anatomical observations suggest the mu opioids may act through additional mechanisms. Most strikingly, mu opioid receptor (MOR) is present on a large subpopulation (approx. 40%) of medullary projecting neurons in the ventrolateral PAG. Here we hypothesize the MOR may function distinctly on GABAergic vs. nonGABAergic PAG neurons. This hypothesis will be tested by determining the effects of MOR agonists on PAG cells using intracellular recording techniques. Studied cells will be filled with neurobiotin and immunohistochemically labeled for GABA. Certain stress paradigms, for example a prolonged exposure to intermittent and inescapable shock (IS) have long lasting effects on the opioid system. Specifically, exposure to IS potentates the analgesic effects of low doses of morphine 24 hours later. The PAG is involved in both the acute response to stressors, and morphine and stress induced analgesia. This suggests the hypothesis that changes in MOR and/or delta opioid receptor (DOR) functioning in the PAG may participate in IS produced changes in morphine's analgesic potency. In Specific Aims 2 and 3, anatomical and electrophysiological methods will be used in concert to determine the changes in MOR and DOR function relating to this phenomenon. These studies will shed insight into the cellular mechanisms that underlie morphine's analgesic effects. Furthermore, understanding stress effects on the opioid system are particularly important since stress has been implicated as a major factor contributing to addiction and relapse to drug seeking behavior.

DESCRIPTION (provided by applicant): The periaqueductal gray (FAG) and the adjoining dorsal raphe nucleus (DRN) are mesencephalic cell groups that can act to control pain perception. A consensus has arisen that the PAG functions in initiating and implementing behavioral coping strategies to situations involving stress, fear or pain. The DRN is a major source of forebrain serotonin, which modulates many behaviors and has been implicated in the pathophysiology of depression. Control of pain by these two nuclei is likely a single element of a multimodal response pattern to stressful situations. Substance P (SP) is a neuropeptide well known for playing a role in pain transmission. When released, SP binds the neurokinin 1 (NK1) receptor and precipitates receptor activation and internalization. The NK1 receptor is enriched within the dorsal and ventrolateral FAG as well as the DRN. In this region, focal application of SF is antinociceptive, eliciting the local release of endogenous opioids. In addition, SP neurotransmission is associated with anxiety, cardiovascular adjustments and grooming behavior. Therefore the PAG and DRN represent potential sites where SP may influence several individual components of behavioral coping strategies. The proposed experiments will examine internalization of the NK1 receptor produced by exogenous and endogenous SP using immunohistochemical methods to gain insight into the role of SP neurotransmission in the FAG and DRN. The topography of NK1 internalization by these stimuli will reveal the potential overlap of neural circuits used in coping with these stimuli. In addition, the proposed AIMS will broadly establish the neural circuitry that SP engages to modulate these areas. That is, the hypothesis that enkephalin- or serotonin-containing neurons have the NK1 receptor will be tested using light and electron microscopic analysis. The results of these studies will-yield insight into how distinct modes of stressful stimuli impact SP neurotransmission within neural circuits that coordinate defensive coping strategies.

DESCRIPTION (provided by applicant): Project Summary Addiction to nicotine through tobacco use is the leading preventable cause of death in the US, contributing to almost half a million deaths per year. There are over 20 diseases associated with smoking include lung cancer, chronic obstructive pulmonary disease, cardiovascular disease, and stroke. Many smokers have the desire to reduce or stop using tobacco;however less then 7% are successful for a year or more. Accumulating evidence suggests that serotonin neurotransmission plays a role in the establishment and maintenance of nicotine addiction. Modified serotonergic neurotransmission is thought to contribute to the rewarding and anxiolytic properties of acute nicotine administration, as well as to symptoms of nicotine withdrawal. Therefore understanding how nicotine acts on serotonergic neurons may give insight into the mechanisms participating in addictive behavior that underlie the negative health impact of tobacco use. The Aims of this proposal are designed to systematically determine how acute and chronic nicotine treatment or nicotine withdrawal influences ascending serotonergic pathways. Neuroanatomical and pharmacological methods in a rat model are used. The hypothesis tested in Aim 1 is that nicotine administration and withdrawal have topographically organized and distinct effects on the ascending raphe. Subsequent Aims investigate the mechanisms underlying these topographic effects. In Aim 2, the role of 5-HT-1A receptors have in contributing to the topographic control of activation of the ascending raphe will be determined. In Aim 3 is test the hypotheses that the differential subcellular distribution of the alpha4 nicotinic receptor subunit could contribute t to the topographically selective effects, and that alpha4 containing receptors shift in subcellular distribution as a consequence of nicotine exposure by using immunolabeling techniques coupled with ultrastructural analysis. A further understanding of how nicotine acts on the ascending serotonergic pathways will give insight into the basic neurochemical changes nicotine produces in the brain that are implicated in addictive behavior. This information will likely have relevance for understanding how serotonin contributes to drug addiction in general.Project Narrative The proposed studies are designed to help understand the neurobiological basis of how nicotine addiction develops and why it often co-occurs with mood disorders. The results may suggest treatment strategies for both of these important health issues.

Objective: The Neuroanatomy Core will provide a resource of state-of-the-art neuroanatomic and neuroimaging techniques to the program project. The overall goal of the Neuroanatomy Core is to link neurochemical architecture of rodent model systems with the neuropathologic findings in human SIDS cases to yield a greater understanding of the biological basis of SIDS. Anatomical labeling techniques supported by the Neuroanatomy Core include multiple immunolabeling, anterograde and retrograde tract tracing, combined tract-tracing and immunolabeling, identification and immunolabeling of intra-cellularly labeled cells, and tissue receptor autoradiography. Visualization techniques include conventional brightfield or fluorescence microscopy, as well as confocal imaging. Qualitative and quantitative analyses include 2- and 3-dimensional computer based mapping, quantitative densitometry, and unbiased 2- and 3- dimensional stereology methods.

Project Summary It remains poorly understood how serotonin circuits in the brain dysfunction in depression, drug addiction and other disorders. Understanding the role of serotonin neurotransmission in psychopathology is complicated by one of the most salient features of the serotonin system: it?s neuroanatomy. In this project we examine how serotonin neuron function changes in animal models of depression and nicotine abstinence, and after antidepressant treatment. Our work seeks to reconcile behavioral pharmacology with neuroanatomy to resolve some of the contradictory findings in the field. The over- riding hypothesis is that there are topographically organized changes in the activation of serotonin neurons in depression and these are resolved by antidepressant treatment. In addition, we examine how feedback inhibition mediated by 5-HT1A receptors changes in coordination with altered patterns of serotonin-neuron activity. Finally we examine the functional impact of topographically selective changes in activation state on behavior. The specific aims integrate cellular, systems and behavioral approaches to understand function and dysfunction of serotonin neurotransmission. The broad long-term goal of this research program is to provide a better understanding of the role of serotonin in affective and addictive disorders.