Development of opioid analgesic tolerance in rat to extended-release buprenorphine formulated for laboratory subjects.

Buprenorphine in an extended-release formulation intended for use in laboratory subjects is frequently administered to rats to provide extended analgesia without repeated handling. While levels of buprenorphine may persist in serum once extended-release buprenorphine has been introduced, exposure to opioids can cause opioid tolerance or opioid-induced hypersensitivity. This work examined the analgesic duration and efficacy of a single administration of extended-release buprenorphine intended for use in laboratory subjects in models of inflammatory pain and post-operative pain and the development of opioid tolerance in rat.

Adeno-associated virus-mediated gene transfer of arginine decarboxylase to the central nervous system prevents opioid analgesic tolerance.

Agmatine, a decarboxylated form of L-arginine, prevents opioid analgesic tolerance, dependence, and self-administration when given by both central and systemic routes of administration. Endogenous agmatine has been previously detected in the central nervous system. The presence of a biochemical pathway for agmatine synthesis offers the opportunity for site-specific overexpression of the presumptive synthetic enzyme for local therapeutic effects.

Comparative dose effectiveness of intravenous and intrathecal AAV9.CB7.hIDS, RGX-121, in mucopolysaccharidosis type II mice.

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal disease caused by iduronate-2-sulfatase (IDS) deficiency, leading to accumulation of glycosaminoglycans (GAGs) and the emergence of progressive disease. Enzyme replacement therapy is the only currently approved treatment, but it leaves neurological disease unaddressed. Cerebrospinal fluid (CSF)-directed administration of AAV9.

Biodistribution of Agmatine to Brain and Spinal Cord after Systemic Delivery.

Agmatine, an endogenous polyamine, has been shown to reduce chronic pain behaviors in animal models and in patients. This reduction is due to inhibition of the GluN2B subunit of the N-methyl-D-aspartate receptor (NMDAR) in the central nervous system (CNS). The mechanism of action requires central activity, but the extent to which agmatine crosses biologic barriers such as the blood-brain barrier (BBB) and intestinal epithelium is incompletely understood.

AAV-mediated gene transfer to colon-innervating primary afferent neurons.

Investigation of neural circuits underlying visceral pain is hampered by the difficulty in achieving selective manipulations of individual circuit components. In this study, we adapted a dual AAV approach, used for projection-specific transgene expression in the CNS, to explore the potential for targeted delivery of transgenes to primary afferent neurons innervating visceral organs. Focusing on the extrinsic sensory innervation of the mouse colon, we first characterized the extent of dual transduction following intrathecal delivery of one AAV9 vector and intracolonic delivery of a second AAV9 vector.

Long-term reversal of chronic pain behavior in rodents through elevation of spinal agmatine.

Chronic pain remains a significant burden worldwide, and treatments are often limited by safety or efficacy. The decarboxylated form of L-arginine, agmatine, antagonizes N-methyl-d-aspartate receptors, inhibits nitric oxide synthase, and reverses behavioral neuroplasticity. We hypothesized that expressing the proposed synthetic enzyme for agmatine in the sensory pathway could reduce chronic pain without motor deficits.

Targeting the somatosensory system with AAV9 and AAV2retro viral vectors.

Adeno-associated viral (AAV) vectors allow for site-specific and time-dependent genetic manipulation of neurons. However, for successful implementation of AAV vectors, major consideration must be given to the selection of viral serotype and route of delivery for efficient gene transfer into the cell type being investigated. Here we compare the transduction pattern of neurons in the somatosensory system following injection of AAV9 or AAV2retro in the parabrachial complex of the midbrain, the spinal cord dorsal horn, the intrathecal space, and the colon.

Central Nervous System Distribution of an Opioid Agonist Combination with Synergistic Activity.

Novel combinations of specific opioid agonists like loperamide and oxymorphindole targeting the - and -opioid receptors, respectively, have shown increased potency with minimized opioid-associated risks. However, whether their interaction is pharmacokinetic or pharmacodynamic in nature has not been determined. This study quantitatively determined whether these drugs have a pharmacokinetic interaction that alters systemic disposition or central nervous system (CNS) distribution.

Biodistribution of Adeno-Associated Virus Serotype 5 Viral Vectors Following Intrathecal Injection.

The pharmacokinetic profile of AAV particles following intrathecal delivery has not yet been clearly defined. The present study evaluated the distribution profile of adeno-associated virus serotype 5 (AAV5) viral vectors following lumbar intrathecal injection in mice. After a single bolus intrathecal injection, viral DNA concentrations in mouse whole blood, spinal cord, and peripheral tissues were determined using quantitative polymerase chain reaction (qPCR).

Agmatine requires GluN2B-containing NMDA receptors to inhibit the development of neuropathic pain.

A decarboxylated form of L-arginine, agmatine, preferentially antagonizes NMDArs containing Glun2B subunits within the spinal cord and lacks motor side effects commonly associated with non-subunit-selective NMDAr antagonism, namely sedation and motor impairment. Spinally delivered agmatine has been previously shown to reduce the development of tactile hypersensitivity arising from spinal nerve ligation. The present study interrogated the dependence of agmatine's alleviation of neuropathic pain (spared nerve injury (SNI) model) on GluN2B-containing NMDArs.

Comparative Effectiveness of Intracerebroventricular, Intrathecal, and Intranasal Routes of AAV9 Vector Administration for Genetic Therapy of Neurologic Disease in Murine Mucopolysaccharidosis Type I.

Mucopolysaccharidosis type I (MPS I) is an inherited metabolic disorder caused by deficiency of the lysosomal enzyme alpha-L-iduronidase (IDUA). The two current treatments [hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT)], are insufficiently effective in addressing neurologic disease, in part due to the inability of lysosomal enzyme to cross the blood brain barrier. With a goal to more effectively treat neurologic disease, we have investigated the effectiveness of AAV-mediated IDUA gene delivery to the brain using several different routes of administration.

Sustained-release buprenorphine induces acute opioid tolerance in the mouse.

Sustained-release buprenorphine is widely used in mice with the intention of providing long-lasting analgesia. Statements about duration of therapeutic efficacy are based on persistence of serum buprenorphine levels over a minimum threshold, but behavioral data demonstrating sustained efficacy is not established. Additionally, chronic opioid exposure can induce tolerance and/or hyperalgesia; mice receiving sustained-release buprenorphine have not been evaluated for these effects.

Inhibition of HINT1 Modulates Spinal Nociception and NMDA Evoked Behavior in Mice.

The interactions between the mu-opioid (MOR) and -methyl-d-aspartate receptor (NMDAR) constitute an area of intense investigation because of their contributions to maladaptive neuroplasticity. Recent evidence suggests that their association requires the involvement of histidine triad nucleotide-binding protein (HINT1) with the enzyme's active site being critical in its regulatory role. Since it is known that spinal blockade of NMDA receptors prevents the development of opioid analgesic tolerance, we hypothesized that spinal inhibition of the HINT1 enzyme may similarly inhibit opioid tolerance.

Combination of a δ-opioid Receptor Agonist and Loperamide Produces Peripherally-mediated Analgesic Synergy in Mice.

Background: The long-term use of opioids for analgesia carries significant risk for tolerance, addiction, and diversion. These adverse effects are largely mediated by μ-opioid receptors in the central nervous system. Based on the authors' previous observation that morphine and δ-opioid receptor agonists synergize in spinal cord in a protein kinase Cε-dependent manner, they predicted that this μ-opioid receptor-δ-opioid receptor synergy would take place in the central terminals of nociceptive afferent fibers and generalize to their peripheral terminals.

AAV-Mediated Gene Delivery to the Enteric Nervous System by Intracolonic Injection.

The enteric nervous system of the lower gastrointestinal tract comprises intrinsic neural circuits as well as extrinsic afferent and efferent innervation. The development of strategies for neuronal gene transfer has created new opportunities for functional analysis, circuit mapping, and neuromodulation in the enteric nervous system. Studies of AAV-mediated gene transfer to enteric neurons and dorsal root ganglion neurons (DRG) have provided proofs-of-concept for the utility of AAV vectors for genetic manipulations of the intrinsic and extrinsic components of the enteric nervous system.

AAV-Mediated Gene Delivery to the Spinal Cord by Intrathecal Injection.

Gene therapy targeting the spinal cord is an important tool for analyzing mechanisms of nervous system diseases and the development of gene therapies. Analogous to a lumbar puncture in humans, the rodent spinal cord can be accessed through an efficient, noninvasive injection. Here we describe a method for AAV-mediated gene transfer to cells of the spinal cord by intrathecal injection of small quantities of AAV vector.

Detailed Method for Intrathecal Delivery of Gene Therapeutics by Direct Lumbar Puncture in Mice.

Delivery of viral vectors directly into the central nervous system (CNS) has emerged as an important tool for the refinement of gene therapy. Intrathecal delivery by direct lumbar puncture in conscious rodents offers a minimally invasive approach that avoids tissue damage and/or destruction. Here we describe delivery of small quantities of viral vector product to the intrathecal space of rodents via direct lumbar puncture aided by a catheter.

Involvement of the VGF-derived peptide TLQP-62 in nerve injury-induced hypersensitivity and spinal neuroplasticity.

Neuroplasticity in the dorsal horn after peripheral nerve damage contributes critically to the establishment of chronic pain. The neurosecretory protein VGF (nonacronymic) is rapidly and robustly upregulated after nerve injury, and therefore, peptides generated from it are positioned to serve as signals for peripheral damage. The goal of this project was to understand the spinal modulatory effects of the C-terminal VGF-derived peptide TLQP-62 at the cellular level and gain insight into the function of the peptide in the development of neuropathic pain.

Bivalent ligand that activates mu opioid receptor and antagonizes mGluR5 receptor reduces neuropathic pain in mice.

The mu opioid receptor (MOR) and metabotropic glutamate receptor 5 (mGluR5) are well-established pharmacological targets in the management of chronic pain. Both receptors are expressed in the spinal cord. MMG22, a bivalent ligand containing 2 pharmacophores separated by 22 atoms, which simultaneously activates MOR and antagonizes mGluR5, has been shown to produce potent reversal of tactile hypersensitivity in rodent models of lipopolysaccharide (LPS)-and bone cancer-induced chronic pain.

Complement 3a receptor in dorsal horn microglia mediates pronociceptive neuropeptide signaling.

The complement 3a receptor (C3aR1) participates in microglial signaling under pathological conditions and was recently shown to be activated by the neuropeptide TLQP-21. We previously demonstrated that TLQP-21 elicits hyperalgesia and contributes to nerve injury-induced hypersensitivity through an unknown mechanism in the spinal cord. Here we determined that this mechanism requires C3aR1 and that microglia are the cellular target for TLQP-21.

Prevention of Neurocognitive Deficiency in Mucopolysaccharidosis Type II Mice by Central Nervous System-Directed, AAV9-Mediated Iduronate Sulfatase Gene Transfer.

Mucopolysaccharidosis type II (MPS II; Hunter syndrome) is a rare X-linked recessive lysosomal disorder caused by defective iduronate-2-sulfatase (IDS), resulting in accumulation of heparan sulfate and dermatan sulfate glycosaminoglycans (GAGs). Enzyme replacement is the only Food and Drug Administration-approved therapy available for MPS II, but it is expensive and does not improve neurologic outcomes in MPS II patients. This study evaluated the effectiveness of adeno-associated virus (AAV) vector encoding human IDS delivered intracerebroventricularly in a murine model of MPS II.

Supraspinal gene transfer by intrathecal adeno-associated virus serotype 5.

We report the pattern of transgene expression across brain regions after intrathecal delivery of adeno-associated virus serotype 5 (AAV5). Labeling in hindbrain appeared to be primarily neuronal, and was detected in sensory nuclei of medulla, pontine nuclei, and all layers of cerebellar cortex. Expression in midbrain was minimal, and generally limited to isolated neurons and astrocytes in the cerebral peduncles.

Biodistribution of adeno-associated virus serotype 9 (AAV9) vector after intrathecal and intravenous delivery in mouse.

Adeno-associated virus serotype 9 (AAV9)-mediated gene transfer has been reported in central nervous system (CNS) and peripheral tissues. The current study compared the pattern of expression of Green Fluorescent Protein (GFP) across the mouse CNS and selected peripheral tissues after intrathecal (i.t.

The VGF-derived peptide TLQP-21 contributes to inflammatory and nerve injury-induced hypersensitivity.

VGF (nonacronymic) is a granin-like protein that is packaged and proteolytically processed within the regulated secretory pathway. VGF and peptides derived from its processing have been implicated in neuroplasticity associated with learning, memory, depression, and chronic pain. In sensory neurons, VGF is rapidly increased following peripheral nerve injury and inflammation.