dynorphins and Nerve-Degeneration

Based upon evidence that opioid antagonists improve neurological outcome following either traumatic or ischemic spinal cord injury, endogenous opioids have been implicated in the pathophysiology of these disorders. Naloxone improved both spinal cord perfusion and neurological function following traumatic spinal cord injury in cats, and was subsequently observed to improve neurological outcome following ischemic spinal cord injury in rabbits. Using several opioid antagonists with varied selectivities for different types of opioid receptors, it was suggested that kappa opioid receptors are involved in both these models of spinal cord injury. In addition, spinal cord trauma in rats is associated with increased concentrations of the endogenous kappa agonist dynorphin A, and increased kappa opioid receptor binding capacity localized to the injury site. Furthermore, dynorphin A induces hindlimb and tail flaccidity following intrathecal injection in rats. Thus, the pathophysiological effects of endogenous opioids in spinal cord injury have been proposed to involve dynorphin A interactions with kappa opioid receptors. However, disparities between the actions of intrathecally injected dynorphin A in rats and the presumed actions of endogenous dynorphin A in cat and rabbit spinal cord injury have been revealed in recent experiments. Paralysis resulting from intrathecal dynorphin A is not altered by opioid receptor antagonists or TRH, produced by non-opioid dynorphin A fragments but not by other selective kappa opioid agonists, and associated with non-opioid mediated reductions in spinal cord blood flow. Furthermore, despite reports of endogenous opioid changes following rat spinal cord trauma, in contrast to cats and rabbits, naloxone failed to improve neurological outcome following traumatic rat spinal cord injury. Thus, the specific endogenous opioids and opioid receptor types involved in spinal cord injury remain to be resolved, and do not appear to be universal among different models of spinal cord injury in different species. Additionally, dynorphin A may participate in spinal cord injury mechanisms in the rat through non-opioid actions.

Topics: Animals; Blood Pressure; Dynorphins; Endorphins; Injections, Spinal; Naloxone; Nerve Degeneration; Receptors, Opioid; Spinal Cord; Spinal Cord Injuries

The opioid peptides dynorphins may be involved in pathogenesis of Alzheimer disease (AD) by inducing neurodegeneration or cognitive impairment. To test this hypothesis, the dynorphin system was analyzed in postmortem samples from AD and control subjects, and subjects with Parkinson or cerebro-vascular diseases for comparison. Dynorphin A, dynorphin B and related neuropeptide nociceptin were determined in the Brodmann area 7 by radioimmunoassay. The precursor protein prodynorphin, processing convertase PC2 and the neuroendocrine pro7B2 and 7B2 proteins required for PC2 maturation were analyzed by Western blot. AD subjects displayed robustly elevated levels of dynorphin A and no differences in dynorphin B and nociceptin compared to controls. Subjects with Parkinson or cerebro-vascular diseases did not differ from controls with respect to any of the three peptides. PC2 levels were also increased, whereas, those of prodynorphin and pro7B2/7B2 were not changed in AD. Dynorphin A levels correlated with the neuritic plaque density. These results along with the known non-opioid ability of dynorphin A to induce neurodegeneration suggest a role for this neuropeptide in AD neuropathology.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Brain; Dynorphins; Endorphins; Female; Humans; Male; Nerve Degeneration; Nociceptin; Opioid Peptides; Up-Regulation

Dynorphins are endogenous opioid peptide products of the prodynorphin gene. An extensive literature suggests that dynorphins have deleterious effects on CNS injury outcome. We thus examined whether a deficiency of dynorphin would protect against tissue damage after spinal cord injury (SCI), and if individual cell types would be specifically affected. Wild-type and prodynorphin(-/-) mice received a moderate contusion injury at 10th thoracic vertebrae (T10). Caspase-3 activity at the injury site was significantly decreased in tissue homogenates from prodynorphin(-/-) mice after 4 h. We examined frozen sections at 4 h post-injury by immunostaining for active caspase-3. At 3-4 mm rostral or caudal to the injury, >90% of all neurons, astrocytes and oligodendrocytes expressed active caspase-3 in both wild-type and knockout mice. At 6-7 mm, there were fewer caspase-3(+) oligodendrocytes and astrocytes than at 3-4 mm. Importantly, caspase-3 activation was significantly lower in prodynorphin(-/-) oligodendrocytes and astrocytes, as compared with wild-type mice. In contrast, while caspase-3 expression in neurons also declined with further distance from the injury, there was no effect of genotype. Radioimmunoassay showed that dynorphin A(1-17) was regionally increased in wild-type injured versus sham-injured tissues, although levels of the prodynorphin processing product Arg(6)-Leu-enkephalin were unchanged. Our results indicate that dynorphin peptides affect the extent of post-injury caspase-3 activation, and that glia are especially sensitive to these effects. By promoting caspase-3 activation, dynorphin peptides likely increase the probability of glial apoptosis after SCI. While normally beneficial, our findings suggest that prodynorphin or its peptide products become maladaptive following SCI and contribute to secondary injury.

Topics: Animals; Apoptosis; Caspase 3; Down-Regulation; Dynorphins; Enzyme Activation; Female; Gene Expression Regulation, Enzymologic; Gliosis; Mice; Mice, Inbred C57BL; Mice, Knockout; Nerve Degeneration; Nerve Regeneration; Neuroglia; Neurons; Recovery of Function; Spinal Cord Injuries

Dynorphin A is an endogenous opioid peptide that produces non-opioid receptor-mediated neural excitation. Here we demonstrate that dynorphin induces calcium influx via voltage-sensitive calcium channels in sensory neurons by activating bradykinin receptors. This action of dynorphin at bradykinin receptors is distinct from the primary signaling pathway activated by bradykinin and underlies the hyperalgesia produced by pharmacological administration of dynorphin by the spinal route in rats and mice. Blockade of spinal B1 or B2 receptor also reverses persistent neuropathic pain but only when there is sustained elevation of endogenous spinal dynorphin, which is required for maintenance of neuropathic pain. These data reveal a mechanism for endogenous dynorphin to promote pain through its agonist action at bradykinin receptors and suggest new avenues for therapeutic intervention.

Topics: Animals; Calcium; Calcium Channels; Dynorphins; Male; Mice; Mice, Knockout; Nerve Degeneration; Neuralgia; Neurons, Afferent; Rats; Rats, Sprague-Dawley; Receptors, Bradykinin; Signal Transduction; Single-Blind Method; Spinal Nerves

Narcolepsy with cataplexy is associated with a loss of orexin/hypocretin. It is speculated that an autoimmune process kills the orexin-producing neurons, but these cells may survive yet fail to produce orexin.. To examine whether other markers of the orexin neurons are lost in narcolepsy with cataplexy.. We used immunohistochemistry and in situ hybridization to examine the expression of orexin, neuronal activity-regulated pentraxin (NARP), and prodynorphin in hypothalami from five control and two narcoleptic individuals.. In the control hypothalami, at least 80% of the orexin-producing neurons also contained prodynorphin mRNA and NARP. In the patients with narcolepsy, the number of cells producing these markers was reduced to about 5 to 10% of normal.. Narcolepsy with cataplexy is likely caused by a loss of the orexin-producing neurons. In addition, loss of dynorphin and neuronal activity-regulated pentraxin may contribute to the symptoms of narcolepsy.

Topics: Aged; Autoantibodies; Autoimmune Diseases of the Nervous System; Brain Mapping; C-Reactive Protein; Dynorphins; Humans; Hypothalamus; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Male; Middle Aged; Narcolepsy; Nerve Degeneration; Nerve Tissue Proteins; Neural Pathways; Neurodegenerative Diseases; Neurons; Neuropeptides; Orexins; RNA, Messenger

Intraspinal injection of quisqualic acid, a mixed kainic acid/2-amino-3(3-hydroxy-5-methylisoxazol-4-yl)propionic acid and metabotropic glutamate receptor agonist, produces an excitotoxic injury that leads to the onset of both spontaneous and evoked pain behavior as well as changes in spinal and cortical expression of opioid peptide mRNA, preprodynorphin and preproenkephalin. What characteristics of the quisqualic acid-induced injury are attributable to activation of each receptor subtype is unknown. This study attempted to define the role of activation of the kainic acid/2-amino-3(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) and metabotropic glutamate receptor subtypes in the regulation of opioid peptide expression and the onset of spontaneous and evoked pain-related behavior following excitotoxic spinal cord injury by comparing quisqualic acid-induced changes with those created by co-injection of quisqualic acid and the kainic acid/AMPA antagonist, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline, (NBQX) or the metabotropic antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA). Therefore, 42 male Long-Evans adult rats were divided into seven treatment groups and received intraspinal microinjections of saline (sham), 0.5% dimethylsulphoxide (sham), quisqualic acid (1.2 microl, 125 mM), NBQX (1.2 microl, 60 microM), AIDA (1.2 microl, 250 microM), quisqualic acid/NBQX (1.2 microl, 125 mM/60 microM), or quisqualic acid/AIDA (1.2 microl, 125 mM/250 microM) directed at spinal levels thoracic 12-lumbar 2. Behavioral observations of spontaneous and evoked pain responses were completed following surgery. After a 10-day survival period, animals were killed and brain and spinal cord tissues were removed and processed for histologic analysis and in situ hybridization. Both AIDA and NBQX affected the quisqualic acid-induced total lesion volume but only AIDA caused a decrease in the percent tissue damage at the lesion epicenter. Preprodynorphin and preproenkephalin expression is increased in both spinal and cortical areas in quisqualic acid-injected animals versus sham-, NBQX or AIDA-injected animals. NBQX did not affect quisqualic acid-induced spinal or cortical expression of preprodynorphin or preproenkephalin except for a significant decrease in preproenkephalin expression in the spinal cord. In contrast, AIDA significantly decreases quisqualic acid-induced preprodynorphin and preproenkephalin expression within the spinal cord and cortex. AIDA, b

Topics: Animals; Behavior, Animal; Dynorphins; Enkephalins; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Grooming; Indans; Male; Nerve Degeneration; Neurons; Neurotoxins; Opioid Peptides; Pain; Pain Measurement; Protein Precursors; Quinoxalines; Rats; Rats, Long-Evans; Receptors, AMPA; Receptors, Glutamate; Receptors, Kainic Acid; Receptors, Metabotropic Glutamate; RNA, Messenger; Spinal Cord; Spinal Cord Injuries

The hallmark of Parkinson's disease is the death of nigral dopaminergic neurons, and inflammation in the brain has been increasingly associated with the pathogenesis of this neurological disorder. Dynorphins are among the major opioid peptides in the striato-nigral pathway and are important in regulating dopaminergic neuronal activities. However, it is not clear whether dynorphins play a role in the survival of nigral dopaminergic neurons. We have recently demonstrated that lipopolysaccharide (LPS) activates the brain immune cells microglia, in vitro and in vivo, to release neurotoxic factors to degenerate dopaminergic neurons. The purpose of this study was to explore the neuroprotective effect of dynorphins in the inflammation-mediated degeneration of dopaminergic neurons in rat midbrain neuron-glia cultures. LPS-induced neurotoxicity was significantly reduced by treatment with ultra low concentrations (10(-13)--10(-15) M) of the kappa-opioid receptor agonist dynorphin A (1--17) or the receptor binding ineffective [des-Tyr(1)]dynorphin A (2--17), but not by U50488, a synthetic kappa-receptor agonist. The glia-mediated neuroprotective effect of dynorphins was further supported by the finding that femtomolar concentrations of dynorphins did not prevent the killing of dopaminergic neurons by 6-hydroxydopamine. However, ultra low concentrations of dynorphins inhibited LPS-induced production of superoxide. These results suggest a glia-mediated and conventional opioid receptor-unrelated mechanism of action for the neuroprotective effect of ultra low concentrations of dynorphins. Understanding the underlying mechanisms of action should further define the roles of dynorphins in the regulation of dopaminergic neurons and help devise novel strategies to combat neurodegenerative diseases.

Topics: Animals; Cells, Cultured; Dopamine; Dynorphins; Immunohistochemistry; Lipopolysaccharides; Mesencephalon; Nerve Degeneration; Neuroglia; Neurons; Neuroprotective Agents; Nitrites; Peptide Fragments; Rats; Rats, Inbred F344; Receptors, Opioid; Superoxides; Tumor Necrosis Factor-alpha

Dynorphin A, a prodynorphin-derived peptide, is able to induce neurological dysfunction and neuronal death. To study dynorphin cytotoxicity in vitro, prodynorphin-derived peptides were added into the culture medium of nonneuronal and neuronal cells or delivered into these cells by lipofection or electroporation. Cells were unaffected by extracellular exposure when peptides were added to the medium. In contrast, the number of viable cells was significantly reduced when dynorphin A or "big dynorphin," consisting of dynorphins A and B, was transfected into cells. Big dynorphin was more potent than dynorphin A, whereas dynorphin B; dynorphin B-29; [Arg(11,13)]-dynorphin A(-13)-Gly-NH-(CH(2))(5)-NH(2), a selective kappa-opioid receptor agonist; and poly-l-lysine, a basic peptide more positively charged than big dynorphin, failed to affect cell viability. The opioid antagonist naloxone did not prevent big dynorphin cytotoxicity. Thus, the toxic effects were structure selective but not mediated through opioid receptors. When big dynorphin was delivered into cells by lipofection, it became localized predominantly in the cytoplasm and not in the nuclei. Big dynorphin appeared to induce toxicity through an apoptotic mechanism that may involve synergistic interactions with the p53 tumor-suppressor protein. It is proposed that big dynorphin induces cell death by virtue of its net positive charge and clusters of basic amino acids that mimic (and thereby perhaps interfere with) basic domains involved in protein-protein interactions. These effects may be relevant for a pathophysiological role of dynorphins in the brain and spinal cord and for control of death of tumor cells, which express prodynorphin at high levels.

Topics: Apoptosis; Cation Exchange Resins; Cell Compartmentation; Cell Survival; Central Nervous System; Cytoplasm; Cytotoxins; Dynorphins; Enkephalins; Immunohistochemistry; Lipids; Naloxone; Narcotic Antagonists; Nerve Degeneration; Peptide Fragments; Protein Precursors; Protein Structure, Tertiary; Receptors, Opioid; Receptors, Opioid, kappa; Transcription, Genetic; Tumor Cells, Cultured; Tumor Suppressor Protein p53