Naloxone-induced morphine withdrawal increases the number and degranulation of mast cells in the thalamus of the mouse

Transcriptomic Characterization of the Human Habenula Highlights Drug Metabolism and the Neuroimmune System

Due to size and accessibility, most information about the habenula is derived from rodent studies. To better understand the molecular signature of the habenula we characterized the genes that have high expression in the habenula. We compared anatomical expression profiles of three normal adult human brains and four fetal brains. We used gene set enrichment analyses to determine if genes annotated to specific molecular functions, cellular components, and biological processes are enriched in the habenula. We also tested gene sets related to depression and addiction to determine if they uniquely involve the habenula. As expected, we observed high habenular expression of GPR151, nicotinic cholinergic receptors, and cilia-associated genes (medial division). Genes identified in genetic studies of smoking and associated with nicotine response were enriched in the habenula. Genes associated with major depressive disorder did not have enriched expression in the habenula but genes negatively correlated with hedonic well-being were, providing a link to anhedonia. We observed enrichment of genes associated with diseases that are comorbid with addictions (hematopoiesis, thrombosis, liver cirrhosis, pneumonia, and pulmonary fibrosis) and depression (rheumatoid arthritis, multiple sclerosis, and kidney disease). These inflammatory diseases mark a neuroimmune signature that is supported by genes associated with mast cells, acute inflammatory response, and leukocyte migration. We also found enrichment of cytochrome p450 genes suggesting the habenula is uniquely sensitive to endogenous and xenobiotic compounds. Our results suggest the habenula receives negative reward signals from immune and drug processing molecules. This is consistent with the habenular role in the "anti-reward" system and suggests it may be a key bridge between autoimmune disorders, drug use, and psychiatric diseases.

Clinical Toxicology and Its Relevance to Asthma and Atopy

Although both the prevalence of asthma and the prescription drug use, notably the opiate analgesic class, epidemics are increasing, there is a complex interplay between both disorders, with both protective and exacerbating factors involved in the effect of opiates on asthma pathogenesis and clinical severity. This review examines the airway effects, both immunologic and neurologic, of opiates, which may interact and result in protection or exacerbation of asthma.

Endoneurial pathology of the needlestick-nerve-injury model of Complex Regional Pain Syndrome, including rats with and without pain behaviors

Current rodent models of neuropathic pain produce pain hypersensitivity in almost all lesioned animals and not all identified experimental effects are pain specific. 18G needlestick-nerve-injury (NNI) to one tibial nerve of outbred Sprague-Dawley rats models the phenotype of Complex Regional Pain Syndrome (CRPS), a post-traumatic neuropathic pain syndrome, leaving roughly half of NNI rats with hyperalgesia. We compared endoneurial data from these divergent endophenotypes searching for pathological changes specifically associated with pain-behaviors. Tibial, sural, and common sciatic nerves from 12 NNI rats plus 10 nerves from sham-operated controls were removed 14 days post-surgery for morphometric analysis. PGP9.5(+) unmyelinated-fibers were quantitated in plantar hindpaw skin. Distal tibial nerves of NNI rats had endoneurial edema, 30% fewer axons, twice as many mast cells, and thicker blood-vessel walls than uninjured tibial nerves. However the only significant difference between nerves from hyperalgesic versus non-hyperalgesic NNI rats was greater endoneurial edema in hyperalgesic rats (p < 0.01). We also discovered significant axonal losses in uninjured ipsilateral sural nerves of NNI rats, demonstrating spread of neuropathy to nearby nerves formerly thought spared. Tibial and sural nerves contralateral to NNI had significant changes in endoneurial blood-vessels. Similar pathological changes have been identified in CRPS-I patients. The current findings suggest that severity of endoneurial vasculopathy and inflammation may correlate better with neuropathic pain behaviors than degree of axonal loss. Spread of pathological changes to nearby ipsilateral and contralateral nerves might potentially contribute to extraterritorial pain in CRPS.

Degranulated mast cells in the skin of adults with self-injurious behavior and neurodevelopmental disorders

The role of nociceptive processes in relation to chronic, tissue-damaging self-injury among individuals with neurodevelopmental disorders is poorly understood. Scientific investigation has been limited, in part, by the clinical reality that the majority of individuals with severe intellectual impairments have co-morbid communicative impairments making it difficult to ascertain information regarding pain. Recently, we found abnormal patterns of peripheral epidermal nerve fiber (ENF) innervation and increased neuropeptide (substance P; SP) content among a subset of individuals with chronic self-injury. Here, we provide initial evidence for peripheral neuro-immune activity specific to self-injury. Skin samples from non-injury body-matched sites were compared between non-verbal adults with and without self-injury matched on gender and disability level. Relative to disability-matched controls, individuals with chronic self-injury had significantly more degranulated mast cells and were more responsive to tactile stimulation during a sensory testing procedure. Thus, nociceptive mechanisms and peripheral afferent sensitization may play a part in mediating and maintaining chronic self-injury.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Differential effects of two analgesic drugs, morphine chlorhydrate and acetylsalicylic acid, on thalamic mast cell numbers in rat

Thalamic mast cells (TMCs), the only immunocytes known to infiltrate the brain in physiological conditions, respond to pharmacological agents including sumatriptan - a serotonergic anti-migraine agent - that increases their number. We analysed the effects of two other main analgesics: morphine chlorhydrate, a micro opioid agonist, and acetylsalicylic acid (ASA), a non-steroidal anti-inflammatory drug. All three drugs have specific modes of action, and morphine and ASA, unlike sumatriptan, are also known to interact with peripheral mast cells. Only ASA was effective in promoting TMC number decrease. TMCs, unlike other mast cells, do not express cyclooxygenase (COX) - the key enzyme in the production of prostanoids and the main site of action of ASA - thus dismissing a direct local cellular COX-mediated action. Direct TMC COX-independent mechanisms or effects mediated via distant populations of COX-positive cells such as platelets, leptomeningeal, endothelial and peripheral mast cells are thus probable. ASA, morphine and sumatriptan have distinct TMC effects, suggesting that the TMC number variations they induce are more likely to derive from systemic vasoactive actions than from pharmacological mechanisms devoted to pain relief.

Chronic daily intrathecal injections of a large volume of fluid increase mast cells in the thalamus of mice

Mast cells are found in the central nervous system (CNS) as well as in the periphery. In the brain of mice, they are localized primarily in the thalamus and meninges. Although their numbers increase in response to stress, the mediator of their recruitment is not known. During studies in which drugs were delivered intrathecally in a volume sufficiently large to distribute to the brain, we discovered that repeated daily injections of this large volume increased the number of mast cells in the thalamus. The increase was not due to changes in electrolyte composition of the cerebrospinal fluid (CSF) as chronically administered artificial CSF produced similar effects. Repeated injections of even small volumes (2 mul) increased mast cells in the medial intralaminar (Med), ventral posterior (VP) and posterior (Po) nuclei. Increasing the volume injected daily to 20 mul increased mast cells in the lateral intralaminar (Lat), laterodorsal (LD), ventrolateral (VL) and lateral geniculate (LG) nuclei and further increased those in the lateral extension of the Po nucleus. Thus, small and large volumes augment distinct populations of mast cells. While stem cell factor (SCF) is abundant in the CNS and is chemotactic to mast cells in the periphery, thalamic mast cells in the rodent do not express c-kit, the SCF receptor, suggesting that this factor may not be responsible for the effect. Consistent with this, centrally injected SCF was incapable of increasing thalamic mast cell populations after either single or chronic (21 days) daily injections compared to the effect of saline alone. Although the mechanism is not known, repeated injections of a large volume of fluid dramatically increase mast cells in the CNS, a phenomenon that may be relevant to clinical conditions of increased CSF pressure or volume.

The role of mast cells in migraine pathophysiology

Mast cells are critical players in allergic reactions, but they have also been shown to be important in immunity and recently also in inflammatory diseases, especially asthma. Migraines are episodic, typically unilateral, throbbing headaches that occur more frequently in patients with allergy and asthma implying involvement of meningeal and/or brain mast cells. These mast cells are located perivascularly, in close association with neurons especially in the dura, where they can be activated following trigeminal nerve, as well as cervical or sphenopalatine ganglion stimulation. Neuropeptides such as calcitonin gene-related peptide (CGRP), hemokinin A, neurotensin (NT), pituitary adenylate cyclase activating peptide (PACAP), and substance P (SP) activate mast cells leading to secretion of vasoactive, pro-inflammatory, and neurosensitizing mediators, thereby contributing to migraine pathogenesis. Brain mast cells can also secrete pro-inflammatory and vasodilatory molecules such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF), selectively in response to corticotropin-releasing hormone (CRH), a mediator of stress which is known to precipitate or exacerbate migraines. A better understanding of brain mast cell activation in migraines would be useful and could lead to several points of prophylactic intervention.

Unilateral spinal nerve ligation leads to an asymmetrical distribution of mast cells in the thalamus of female but not male mice

Mast cells are restricted to the leptomeninges and thalamus of healthy mice. These populations are increased by stress and highly sensitive to reproductive hormones. To examine the influence of nociception, a form of stress, on thalamic mast cells, we ligated the left fifth lumbar spinal nerve of male and female mice to induce hyperalgesia. Two, 7 and 14 days later, mice were killed and thalami examined histologically using toluidine blue stain. The total number of thalamic mast cells was not influenced by ligation of the spinal nerve compared to sham-operation in either female or male mice. However, in females, the percent of thalamic mast cells located on the side of the thalamus contralateral to the ligation was greater on days 2 and 7, coincident with mechanical hyperalgesia. At these times, areas in which mast cells were most dense contralateral to nerve-injury included the posterior (Po) and lateral geniculate (LG) nuclei compared to their symmetrical distribution in sham-operated mice. These data suggest that local nociceptive signals to each side of the thalamus rather than stress hormones influence the location of mast cells during the development of allodynia and hyperalgesia. In addition, both hyperalgesia and mast cell distribution induced by nerve-ligation differ in females compared to males, reflecting a novel neuroimmune response to pain within the CNS.