minocycline and Peripheral-Nerve-Injuries

Some types of peripheral nerve injury lead to limb deafferentation, which leads to remodeling of body representation areas in different parts of the brain, such as in the primary motor cortex and primary sensory cortex. This plasticity is a consequence of several cellular events, such as the emergence and elimination of synapses in these areas. Beside neurons, microglial cells are intimately involved in synapse plasticity, especially in synaptic pruning. In this study, we investigated the transient changes in synaptic density in the primary motor and sensory cortex after different types of peripheral nerve injury, as well as the behavior of microglial cells in each scenario. Male C57/B6 mice were divided into a control group (no injury), sciatic-crush group, and sciatic-transection group, and treated with PBS or minocycline daily for different time points. Both types of sciatic lesion led to a significant decrease of synaptophysin and PSD-95 positive puncta counts compared to control animals 4 days after lesion (DAL), which recovered at 7 DAL and was sustained until 14 DAL. The changes in synaptic puncta density were concomitant with changes in the density and morphology of microglial cells, which were significantly more ramified in the primary motor cortex of injured animals at 1 and 4 DAL. Although the decreased synaptic puncta density overlapped with an increased number of microglial cells, the number of lysosomes per microglial cell did not increase on day 4 after lesion. Surprisingly, daily administration of minocycline increased microglial cell number and PSD-95 positive puncta density by 14 DAL. Taken together, we found evidence for transient changes in synaptic density in the primary motor, related to peripheral injury with possible participation of microglia in this plasticity process.

Topics: Animals; Brain; Male; Mice; Microglia; Minocycline; Motor Cortex; Peripheral Nerve Injuries

Injury that severs peripheral nerves often results in long-lasting motor behavioral deficits and in reorganization of related spinal motor circuitry, neither of which reverse even after nerve regeneration. Stretch areflexia and gait ataxia, for example, emerge from a combination of factors including degeneration of Ia-motoneuron synapses between peripherally damaged Ia muscle spindle afferents and motoneurons. Based on evidence that nerve injury acts via immune responses to induce synapse degeneration, we hypothesized that suppressing inflammatory responses would preserve Ia-motoneuron connectivity and aid in restoring normal function. We tested our hypothesis by administering the anti-inflammatory agent minocycline in male and female rats following axotomy of a peripheral nerve. The connectivity of Ia-motoneuron synapses was then assessed both structurally and functionally at different time points. We found that minocycline treatment overcame the physical loss of Ia contacts on motoneurons which are otherwise lost after axotomy. While necessary for functional recovery, synaptic preservation was not sufficient to overcome functional decline expressed as smaller than normal stretch-evoked synaptic potentials evoked monosynaptically at Ia-motoneuron connections and an absence of the stretch reflex. These findings demonstrate a limited capacity of minocycline to rescue normal sensorimotor behavior, illustrating that structural preservation of synaptic connectivity does not ensure normal synaptic function.

Topics: Animals; Female; Male; Minocycline; Motor Neurons; Peripheral Nerve Injuries; Rats; Sensory Receptor Cells; Spinal Cord; Synapses

Decrease of glutamate transporter-1 (GLT-1) in the spinal dorsal horn after nerve injury induces enhanced excitatory transmission and causes persistent pain. Histone deacetylases (HDACs)-catalyzed deacetylation might contribute to the decrease of GLT-1, while the detailed mechanisms have yet to be fully elaborated. Spinal nerve ligation (SNL) induced significant increases of HDAC2 and decreases of GLT-1 in spinal astrocytes. Intrathecal infusion of the HDAC2 inhibitors attenuated the decrease of GLT-1 and enhanced phosphorylation of glutamate receptors. GLT-1 and phosphorylated c-Jun N-terminal kinase (JNK) were highly colocalized in the spinal cord, and a large number of pJNK positive cells were HDAC2 positive. Intrathecally infusion of the JNK inhibitor SP600125 significantly inhibited SNL-induced upregulation of HDAC2. SNL-induced HDAC2 up-regulation could be inhibited by the neutralizing anti-tumor necrosis factor-α (TNF-α) binding protein etanercept or the microglial inhibitor minocycline. In cultured astrocytes, TNF-α induced enhanced phosphorylation of JNK and a significant increase of HDAC2, as well as a remarkable decrease of GLT-1, which could be prevented by SP600125 or the HDAC2 specific inhibitor CAY10683. Our data suggest that astrocytic JNK-HDAC2 cascade contributes to GLT-1 decrease and mechanical allodynia following peripheral nerve injury. Neuroimmune activation after peripheral nerve injury could induce epigenetic modification changes in astrocytes and contribute to chronic pain maintenance.

Topics: Animals; Anthracenes; Astrocytes; Carbamates; Cells, Cultured; Etanercept; Excitatory Amino Acid Transporter 2; Histone Deacetylase 2; Hyperalgesia; JNK Mitogen-Activated Protein Kinases; Male; Microglia; Minocycline; Neuralgia; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Signal Transduction; Spinal Nerves; Tumor Necrosis Factor-alpha

The central amygdaloid nucleus (CeA) is involved in processing and descending regulation of pain. Amygdaloid mechanisms underlying pain processing and control are poorly known. Here we tested the hypothesis that perioperative CeA administration of tetrapentylammonium (TPA), a non-selective THIK-1 channel blocker and thereby inhibitor of microglia, attenuates development of chronic neuropathic pain and comorbid anxiety-like behavior.. Rats with a spared nerve injury (SNI) model of neuropathy or sham operation had a chronic cannula for drug microinjections into the CeA or a control injection site. Monofilament test was used to evaluate pain, and light-dark box (LDB) to assess anxiety.. Perioperative CeA treatment with TPA (30 μg/day up to the third postoperative day, D3) significantly attenuated the development of pain and anxiety-like behavior. In the late phase (> D14), CeA administration of TPA (3-30 μg) failed to influence pain. Perioperative minocycline (microglia inhibitor; 25 μg), MK-801 (an N-Methyl-D-aspartate receptor antagonist; 0.1 μg), vehicle or TPA in a control injection site failed to attenuate pain development.. Perioperative treatment of the CeA with TPA delayed development of neuropathic pain and comorbid anxiety-like behavior, while TPA treatment failed to influence maintenance of established neuropathic pain. The failures to attenuate pain development with CeA administrations of minocycline or MK-801 do not support the hypothesis that the TPA-induced prophylactic effect was due to inhibition of amygdaloid microglia or N-methyl-D-aspartate receptors. While TPA in the CeA proved to have a prophylactic effect on SNI-induced pain behavior, the underlying mechanism still remains to be studied.

Topics: Amygdala; Analgesics; Animals; Anti-Anxiety Agents; Anxiety; Behavior, Animal; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Locomotion; Male; Microglia; Microinjections; Minocycline; Neuralgia; Pain Perception; Pain Threshold; Peripheral Nerve Injuries; Potassium Channels, Tandem Pore Domain; Quaternary Ammonium Compounds; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Minocycline has been reported to be both beneficial and detrimental for nerve regeneration after peripheral nerve injury. By reducing the inflammatory response, minocycline administration reduces pain and has neuroprotective effects, but it also inhibits Wallerian degeneration in the distal stump, and reduces microglia and macrophages activity on motor and sensory neurons, which could reduce their intrinsic regenerative capacity. The aim of this study was to determine if the administration of minocycline after nerve injury inhibits the regenerative capacity of motoneurons and sensory neurons after a conditioning lesion. We used two groups of mice: a control group and a group treated with minocycline (30 mg kg

Topics: Animals; Drug Evaluation, Preclinical; Female; Mice; Microglia; Minocycline; Motor Neurons; Nerve Regeneration; Peripheral Nerve Injuries; Sciatic Neuropathy; Sensory Receptor Cells

Microglia exhibit various activation phenotypes in the spinal cord after peripheral nerve injury, and promote neuropathic pain. Ibudilast is a phosphodiesterase inhibitor with anti-inflammatory activity, but its effect on activated microglia in chronic neuropathic pain is poorly understood. We investigated whether ibudilast was effective on established allodynia associated with activated microglial phenotypes in two rat models of peripheral and central neuropathic pain. A single intrathecal injection of ibudilast (25 μg) inhibited established allodynia on days 7-21 after sciatic nerve injury in rats. Repeated injections of ibudilast (25 μg/day) reduced the numbers of phosphorylated p38-positive cells without changing hypertrophic microglia, whereas minocycline (100 μg/day) decreased the numbers of hypertrophic microglia associated with phosphorylated p38 levels in the spinal cord. Gene analysis revealed that minocycline, but not ibudilast, increased the expression of anti-inflammatory cytokine genes Il10 and Tgfβ1 in the spinal cord. Propentofylline (100 μg/day) was less effective on microglial phenotypes and established allodynia. Ibudilast inhibited persistent allodynia after the recovery of motor deficits in experimental autoimmune encephalomyelitis rats. Therefore, ibudilast might be effective for chronic neuropathic pain after peripheral and central nerve damage. Ibudilast mediated these effects on activated microglia using a different mechanism compared with minocycline and propentofylline.

Topics: Animals; Encephalomyelitis, Autoimmune, Experimental; Female; Humans; Hyperalgesia; Injections, Spinal; Male; Microglia; Minocycline; Neuralgia; Neuroprotective Agents; p38 Mitogen-Activated Protein Kinases; Pain Measurement; Peripheral Nerve Injuries; Phosphodiesterase Inhibitors; Phosphorylation; Pyridines; Rats; Rats, Inbred Lew; Rats, Sprague-Dawley; Sciatic Nerve; Spinal Cord; Xanthines

Infant nerve injury causes delayed adolescent neuropathic pain, but whether it also leads to psychiatric illness is unknown. Environmental enrichment (EE) increases social communication and activity. Thus, our goal was to test anxiety- and depression-like behaviors after infant peripheral nerve injury and evaluate the effect of environmental enrichment on these models of affective disorders.. Open field, elevated plus maze, sucrose preference, and pain behaviors (paw withdrawal threshold, spontaneous guarding score, and cold response to acetone) were measured in rats that received infant spared nerve injury (SNI). Enzyme-linked immune absorbent assay of cytokines was performed to evaluate the inflammatory response in the brain. Then, the ability of intracerebroventricular (ICV) injection of a microglia inhibitor, minocycline (MIN), and EE (a free-running wheel, a staircase, a plastic tunnel, a raised platform, and various colored balls) to reverse the infant SNI effects on behaviors and cytokines was examined.. Infant nerve injury resulted in adolescent anxiety- and depression-like behaviors. The medial prefrontal cortex, basolateral amygdala, and ventral hippocampus were skewed to a pro-inflammatory profile. ICV injection of MIN reduced anxiety- and depression-like behaviors without affecting pain behaviors. In addition, ICV MIN skewed the brain towards an anti-inflammatory profile. Finally, environmental enrichment improved anxiety- and depression-like behaviors, as well as pain behaviors. EE increased brain IL-10 and decreased IL-1β and TNF-α.. Infant nerve injury induces adolescent anxiety- and depression-like behaviors and central nervous inflammation. Environmental enrichment reduces these behaviors by normalizing the inflammation balance in the brain.

Topics: Age Factors; Animals; Animals, Newborn; Anti-Bacterial Agents; Anxiety; Brain; Cytokines; Depression; Disease Models, Animal; Environment; Exploratory Behavior; Injections, Intraventricular; Male; Maze Learning; Minocycline; Pain; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Sucrose

Neuropathic pain is a refractory clinical problem. Certain drugs, such as tramadol, proved useful for the treatment of neuropathic pain by inhibiting the activity of nociceptive neurons. Moreover, studies indicated that suppression or modulation of glial activation could prevent or reverse neuropathic pain, for example with the microglia inhibitor minocycline. However, few present clinical therapeutics focused on both neuronal and glial participation when treating neuropathic pain. Therefore, the present study hypothesized that combination of tramadol with minocycline as neuronal and glial activation inhibitor may exert some synergistic effects on spinal nerve ligation (SNL)-induced neuropathic pain. Intrathecal tramadol or minocycline relieved SNL-induced mechanical allodynia in a dose-dependent manner. SNL-induced spinal dorsal horn Fos or OX42 expression was downregulated by intrathecal tramadol or minocycline. Combination of tramadol with minocycline exerted powerful and synergistic effects on SNL-induced neuropathic pain also in a dose-dependent manner. Moreover, the drug combination enhanced the suppression effects on SNL-induced spinal dorsal horn Fos and OX42 expression, compared to either drug administered alone. These results indicated that combination of tramadol with minocycline could exert synergistic effects on peripheral nerve injury-induced neuropathic pain; thus, a new strategy for treating neuropathic pain by breaking the interaction between neurons and glia bilaterally was also proposed.

Topics: Analgesics, Opioid; Animals; Anti-Bacterial Agents; Astrocytes; Dose-Response Relationship, Drug; Drug Synergism; Drug Therapy, Combination; Hyperalgesia; Male; Microglia; Minocycline; Neuralgia; Pain Measurement; Peripheral Nerve Injuries; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Rotarod Performance Test; Spinal Cord; Tramadol

Minocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds.. Animal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague-Dawley rats. Animals with SNI and uninjured animals were then injected with/without USPIOs (300 μmol/kg i.v.) and with/without minocycline (50 mg/kg i.p.). Bilateral sciatic nerves were scanned with a volume coil in a 7 T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/-0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/-4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/-2.3%) (p < 0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment.. Animals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline to retards the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.

Topics: Animals; Cell Movement; Dextrans; Hyperalgesia; Iron; Macrophages; Magnetic Resonance Imaging; Magnetite Nanoparticles; Minocycline; Peripheral Nerve Injuries; Rats; Rats, Sprague-Dawley; Sciatic Nerve

Neuropathic pain is an intractable clinical problem, affecting millions of people worldwide. Preemptive administration of minocycline has been confirmed useful for treating neuropathic pain by inhibiting spinal microglia activation and consequently lowering proinflammatory cytokine expression. However, most patients with neuropathic pain have no chance to receive preemptive treatment and it remains unclear whether there is a therapeutic time window for post treatment with minocycline. The present study is to confirm the effect and the therapeutic time window of intrathecal minocycline on spinal nerve ligation (SNL)-induced neuropathic pain after lesion. Behavioral test and immunohistochemistry are utilized to determine the variation of mechanical allodynia and microglia phosphorylated-p38 (p-p38) expression respectively after intrathecal minocycline. Results showed that post-injury intrathecal minocycline attenuated mechanical allodynia effectively together with inhibiting spinal microglia p-p38 expression on post operative day (POD) 1, POD 3 and POD 7. Additionally, results from POD 10 and POD 21 showed that intrathecal minocycline suppressed spinal microglia p-p38 expression but without any effects on reversing mechanical allodynia. It is concluded that post-injury intrathecal minocycline is an effective therapeutic intervention for treating SNL-induced neuropathic pain by inhibiting spinal microglia activation. Accordingly, there is indeed a therapeutic time window for post-injury intrathecal minocycline, which is the initiation stage of neuropathic pain development.

Topics: Animals; Male; Minocycline; Neuralgia; Peripheral Nerve Injuries; Peripheral Nerves; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley