I. V. Dyuizen

Changes in the nitric oxide system in the shore crab Hemigrapsus sanguineus (Crustacea, decapoda) CNS induced by a nociceptive stimulus

SUMMARY Using NADPH-diaphorase (NADPH-d) histochemistry, inducible nitric oxide synthase (iNOS)-immunohistochemistry and immunoblotting, we characterized the nitric oxide (NO)-producing neurons in the brain and thoracic ganglion of a shore crab subjected to a nociceptive chemical stimulus. Formalin injection into the cheliped evoked specific nociceptive behavior and neurochemical responses in the brain and thoracic ganglion of experimental animals. Within 5–10 min of injury, the NADPH-d activity increased mainly in the neuropils of the olfactory lobes and the lateral antenna I neuropil on the side of injury. Later, the noxious-induced expression of NADPH-d and iNOS was detected in neurons of the brain, as well as in segmental motoneurons and interneurons of the thoracic ganglion. Western blotting analysis showed that an iNOS antiserum recognized a band at 120 kDa, in agreement with the expected molecular mass of the protein. The increase in nitrergic activity induced by nociceptive stimulation suggests that the NO signaling system may modulate nociceptive behavior in crabs.

Analgetic effect of docosahexaenoic acid is mediated by modulating the microglia activity in the dorsal root ganglia in a rat model of neuropathic pain

The analgetic activity of docosahexaenoic acid (DHA, 22:6 n-3) was studied using a chronic constriction injury (CCI) model in rats, and the dynamics of iba-1 (+) microglia/macrophages in the dorsal root ganglia (DRG) were characterized. DHA reduced the intensity and duration of neurogenic pain. The application of DHA led to an earlier stabilization of weight bearing in the incapacitance test and prevented the development of cold allodynia and degenerative changes in tissues of the denervated limb. DHA treatment significantly reduced satellite glia reaction and expression of the pro-apoptotic p53 protein in the DRG. Thus, DHAs anti-pain effect may be a result of the modulation of microglia/macrophages activity and the development of neuroprotective effects at the level of the dorsal root ganglia.

Neuron-astrocyte interactions in spinal cord dorsal horn in neuropathic pain development and docosahexaenoic acid therapy

The analgesic activity of docosahexaenoic acid (DHA, 22:6 n-3) was studied using a chronic constriction injury (CCI) rat model. Animals were subcutaneously injected with DHA emulsion at a dose of 4.5mg/kg (125mМ/kg) daily during 2weeks after surgery. We characterized the dynamics of GFAP-positive astrocyte, substance P (SP) and nNOS-positive neurons activity in the spinal cord dorsal horn (SCDH) superficial lamina. We found that DHA treatment decrease the intensity and duration of neurogenic pain syndrome, results in earlier stabilization of weight distribution, prevents the cold allodynia and dystrophic changings in denervated limb tissue. DHA treatment reduced the reactive astrocyte number, decrease SP-immunopositive fibers and nNOS-positive neurons number in the SCDH in neuropathic pain.

Stress-induced changes in the nitric oxide system of shore crabs living under different ecological conditions

The NO synthesis system in the brain and hemolymph of shore crabs Hemigrapsus sanguineus (Decapoda: Varunidae) living under different ecological conditions was examined under normal conditions and under acute stress. Intact crabs sampled from an area with a high anthropogenic load had a higher initial level of NO compared to crabs from a relatively clean location. After acute damaging exposure, the dynamics of the NO system activity in crabs from different stations differed markedly. The number of NO-positive elements in the brain and the level of NO metabolites in the hemolymph dramatically increased immediately after injuries in all groups of crabs. One hour after acute exposure, the expression of inducible NO-synthase in the protocerebral neurons was observed in crabs inhabiting the chronically polluted area. These results demonstrate for the first time the influence of pollution on the activity of NO-ergic processes and the involvement of nitric oxide in the formation of behavioral defense response in crustaceans under acute stress.

The specific response of neurons and glial cells of the ventromedial reticular formation in the rat brainstem to acute pain

We studied the time course of changes in neurochemical modifications in neurons and glial cells of the ventromedial reticular formation of the rat brainstem during the development of acute inflammatory pain. The development of the pain response was associated with a twofold increase in the number of neurons that expressed NADPH diaphorase in the ventromedial reticular formation as compared to the norm. At 2 hours after the development of the pain response, we observed an increase in the number of tyrosine hydroxylase-positive elements, which was 1.5 times higher as compared to the norm. The development of acute pain was also associated with a glial response in the nucleus: the activity of mature astrocytes increased by a factor of 1.9 whereas the area of immunohistochemically stained microglia decreased by a factor of 7.6 compared to the norm. The results of our study demonstrate that development of the acute-pain response is related to the activation of both neurons and glial cells of the ventromedial nucleus of the reticular formation.

Docosahexaenoic acid improves motor function in the model of spinal cord injury

The present study demonstrates that docosahexaenoic acid (DHA, 22:6n-3) injected subcutaneously leads to recovery of locomotor functions observed within 5 weeks after traumatic spinal cord injury. This activity is confirmed by improving of BBB locomotor rating scale indicators. We assume that this activity is related to (1) enhancement of remyelination process, (2) proliferative activity, (3) antioxidant activity, (4) increase in GFAP staining and (5) enhancement of vimentin expression. In general, the results of the study show that DHA has a complex effect on post-traumatic central nervous system recovery, indicating its high therapeutic potential.

Neurochemical changes in the rostral ventromedial nucleus of the medulla oblongata in rats with developing neuropathic pain

The dynamics of neurochemical rearrangements in neurons in the ventromedial reticular formation of the medulla oblongata in rats during the development of neuropathic pain were investigated. Distinct populations of monoaminergic and NOergic projecting neurons and cells that metabolize agmatine were found in the nucleus. The change in the activity of these neurons during the initiation (week 1) and formation (4 weeks) of neuropathic pain has several phases. Decreased synthesis of catecholamines, increased catabolism of agmatine, and activation of NO synthesis were found in neurons by the end of the first week. At 4 weeks after the surgery, the parameters of the catecholaminergic system returned to the control level, NOergic activity was significantly reduced and the catabolism of agmatine continued to increase. These findings suggest the involvement of bulbar NOergic, mono- and polyaminergic neurotransmitter mechanisms in the initiation and maintenance of neuropathic pain.

The Involvement of Agmatine in Individual Pain Sensitivity

Distribution of agmatinase (AGM), an enzyme of agmatine metabolism, was studied in the spinal cord and dorsal root ganglia of rats with different levels of initial thermal pain sensitivity under normal conditions and during the development of inflammatory pain using immunohistochemistry. The initial type of pain threshold affects the specific pain response of an animal to pain so that the rats with a higher threshold exhibit a less-expressed behavioral pain response. We found a specific distribution and time course of activity of AGM in the brain regions of animals with different nociceptive thresholds. The animals with a lower threshold had a higher number of AGM-immunoreactive neurons in the ganglia and a lower density of fibers and neurons in the dorsal roots of the spinal cord compared to the animals with a higher threshold. The development of tonic pain was associated with differently directed changes of AGM activity in the studied structures and depended on the threshold of nociception. Our data suggest that the endogenous system of agmatine metabolism may be involved in the initial threshold of nociception, as well as in organization of the behavioral response to pain.

Docosahexaenoic acid induces changes in microglia/macrophage polarization after spinal cord injury in rats

Docosahexaenoic acid (DHA, 22:6 (n-3)) leads to recovery of locomotor functions observed of spinal cord injury (SCI) in rats. In present study, we characterized the expression of iba-1, CD86, CD163 in microglia/macrophages, to assess activation state and M1 (pro-inflammatory)/M2 (anti-inflammatory) phenotypes respectively, in the rostral, central and caudal segment of the spinal cord on 7 and 35 days after SCI. We found that DHA treatment leads to: (1) an increased activation and proliferation of microglial cells; (2) an alteration in the dynamics between M1 and M2 microglia/macrophages phenotypes (3) and increased production of an antioxidant enzymes. Overall, our data demonstrates that DHA has a complex effect in post-traumatic process within the central nervous system, and supports the therapeutic potential of DHA-based drugs.

Neuro-microglial interactions in the spinal centers of pain modulation in the neuropathic pain syndrome

The dynamics of the expression of the neuronal NO-synthase and microglia activity in the spinal centers of pain modulation were studied on the ligated rat sciatic nerve. The development of neuropathic pain causes an increase in the activity of neuronal NO-synthase and the iba-1-positive microglia in the spinal ganglia and the surface laminae of the posterior horn of the spinal cord, which dynamically corresponds to the severity of pain. At the same time, the dynamics of NO-ergic activity are parallel with the activation of microglia in these brain structures. Thus, we cannot exclude the direct inter-modulating effects of spinal microglia and NO-ergic nociceptive neurons.