Effect of Interleukin-10 on Localization of AMPA Receptors in Synapses during Long-Term Posttetanic Potentiation in Cultured Hippocampal Slices.

The effect of the anti-inflammatory cytokine IL-10 on the ultrastructural distribution of AMPA receptor GluR1 subunit in CA1 field of cultured hippocampal slices was studied by using immunohistochemical technique. It was found that long-term posttetanic potentiation increased the content of GluR1 in the postsynaptic density of the axo-spinous synapse. Addition of IL-10 in concentrations of 1 and 10 ng/ml to the medium facilitated long-term posttetanic potentiation thereby changing the distribution of GluR1 in the spine: the number of receptors increased in the cytoplasm and decreased in the postsynaptic density. It is assumed that activation of neuronal IL-10 receptors affects the distribution of AMPA receptors in axo-spinous synapses of hippocampal field CA1 through interplay of intracellular signaling pathways, thereby participating in the mechanisms of synaptic plasticity under normal conditions.

Effect of TGF-beta1 on long-term synaptic plasticity and distribution of AMPA receptors in the CA1 field of the hippocampus.

Using the methods of electrophysiology and immunohistochemistry, the effect of the transforming factor beta-1(TGF-ß1), an anti-inflammatory cytokine, on the long-term post-tetanic potentiation (LTP) in CA1 field hippocampal slices and the distribution of the GluR1 subunit of the AMPA receptor has been studied. It was shown that TGF-ß1 at a concentration of 10 ng/ml did not significantly affect the initial stage of LTP and substantially changed the distribution of synaptic AMPA receptors in response to tetanic stimulation. Twenty five minutes after the tetanization, the main pool of AMPA receptors (90%) was due to the postsynaptic density (PSD). By contrast, LTP in the presence of TGF-ß1 was accompanied by less pronounced changes in the distribution of AMPA receptors. Their localization in both pre- and postsynaptic regions remained nearly the same as that in the control. It may be suggested that the normal distribution of AMPA receptors in spinous synapses promotes the stabilization of potentiated synapses, thereby retaining LTP for longer terms.

Modulating Effect of Cytokines on Mechanisms of Synaptic Plasticity in the Brain.

After accumulation of data showing that resident brain cells (neurons, astrocytes, and microglia) produce mediators of the immune system, such as cytokines and their receptors under normal physiological conditions, a critical need emerged for investigating the role of these mediators in cognitive processes. The major problem for understanding the functional role of cytokines in the mechanisms of synaptic plasticity, de novo neurogenesis, and learning and memory is the small number of investigated cytokines. Existing concepts are based on data from just three proinflammatory cytokines: interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha. The amount of information in the literature on the functional role of antiinflammatory cytokines in the mechanisms of synaptic plasticity and cognitive functions of mature mammalian brain is dismally low. However, they are of principle importance for understanding the mechanisms of local information processing in the brain, since they modulate the activity of individual cells and local neural networks, being able to reconstruct the processes of synaptic plasticity and intercellular communication, in general, depending on the local ratio of the levels of different cytokines in certain areas of the brain. Understanding the functional role of cytokines in cellular mechanisms of information processing and storage in the brain would allow developing preventive and therapeutic means for the treatment of neuropathologies related to impairment of these mechanisms.

Role of BK(Ca) Potassium Channels in the Mechanisms of Modulatory Effects of IL-10 on Hypoxia-Induced Changes in Activity of Hippocampal Neurons.

We studied the contribution of large conductance Ca(2+)-activated potassium channels (BKCa) in the mechanisms of neuromodulatory effects of anti-inflammatory cytokine IL-10 on hypoxiainduced changes in activity of CA1 pyramidal neurons in rat hippocampus. We used the method of registration of population spikes from CA1 pyramidal neurons in hippocampal slices before, during, and after exposure to short-term episodes of hypoxia. Selective blocker (iberiotoxin) and selective activator of BKCa (BMS-191011) were used to evaluate the contribution of these channels in the mechanisms of suppressive effects of IL-10 on changes in neuronal activity during hypoxia and development of post-hypoxic hyperexcitability. It was shown that BKCa are involved in the modulatory effects of IL-10 on hypoxia-induced suppression of activity of CA1 pyramidal neurons in the hippocampus and development of post-hypoxic hyperexcitability in these neurons.

Comparison of effects of ATP-gated potassium channel blockers on activity variations of rat CA1 pyramidal neurons in hippocampal slices triggered by short-term hypoxia.

The study compared the effects of KATP channels blockers 5-hydroxydecanoat and glibenclamide on rapid hypoxic preconditioning and posthypoxic hyperexcitability of CA1 pyramidal neurons in rat hippocampal slices induced by short-term hypoxia. The population spikes of CA1 neurons were recorded before, during, and after exposure to a short-term hypoxia. The blockers of KATP channels significantly degraded the potency of hypoxia episodes to inhibit the evoked neuronal population activity. In contrast to glibenclamide, 5-hydroxydecanoat eliminated the preconditioning action of hypoxia. Despite mitochondrial KATP channels play an important role in the mechanisms of rapid hypoxic preconditioning in hippocampal CA1 pyramidal neurons, the tested KATP channels blockers produced no significant effect on the development of posthypoxic hyperexcitability in these neurons.

[Role of Ca(2+)-activated potassium channels with high-conductivity in hypoxic preconditioning and posthypoxic hyperexcitability in CA1 hippocampal neurons in vitro].

The role of highly conductive Ca(2+)-activated potassium channels (BK(Ca)-channels) of rat hippocampal CA1 neurons in the processes induced by repeated episodes of brief hypoxia was investigated. A specific blocker of BK(Ca)-channels iberiotoxin (10-20 nM) tended to decrease the efficiency of hypoxia in depressing the amplitude of population spikes during hypoxic episode. Iberiotoxin significantly abolished both the preconditioning effect of hypoxic episodes and the posthypoxic hyperexcitability of pyramidal neurons. It is suggested that BK(Ca)-channels play an important role in the mechanisms of such forms of neuroplasticity as rapid hypoxic preconditioning and posthypoxic hyperexcitability in hippocampal CA1 neurons.

The effects of interleukin-10 on the development of epileptiform activity in the hippocampus induced by transient hypoxia, bicuculline, and electrical kindling.

The comparative effects of the anti-inflammatory cytokine interleukin-10 on the development of epileptiform activity were studied in hippocampal field CA1 neurons in different models of epileptogenesis not accompanied by visible morphological lesions in brain cells: 1) a model of hypoxic kindling in rat hippocampal slices; 2) a disinhibitory model of epileptogenesis in rat hippocampal slices using the GABAA receptor blocker bicuculline; and 3) a partial electrical kindling model in intact rats. Interleukin-10 (1 ng/ml) blocked the development of post-hypoxic hyperexcitability of field CA1 pyramidal neurons in hippocampal slices, decreasing the effectiveness of hypoxia in suppressing neuron activity during the hypoxic episode. Interleukin-10 had no effect on the initiation of epileptiform activity in pyramidal neurons induced by the proconvulsant bicuculline. Single intrahippocampal injections of interleukin-10 at a dose of 1 ng in 5 microl suppressed the development of focal convulsions ("ictal" discharges) at the stimulation site in partial kindling in freely moving animals for several hours after administration. However, this cytokine had no effect on the duration of the "interictal" component of focal afterdischarges or on the severity of behavioral seizures. These results show that the anti-inflammatory cytokine interleukin-10, at the concentrations used here, has not only antihypoxic activity, but also a protective effect in relation to the initiation of the "ictal," but not the "interictal" component of epileptiform activity in hippocampal neurons.

[Effects of interleukin-10 on the epileptiform activity development in the hippocampus induced by brief hypoxia, bicuculline and electrical kindling].

The comparative effects of antiinflammatory cytokine interleukin-10 on the epileptiform activity development in CA1 hippocampal neurons were studied in different functional models of epileptogenesis that are not accompanied the visible morphological disturbances in the brain cells: --in vitro hypoxic model in the rat hippocampal slices; 2--in vitro disinhibitory model with using GABAA antagonist, bicuculline, in the rat hippocampal slices; 3--partial hippocampal kindling model in freely moving rats. Interleukin-10 (1 ng/ml) depressed the posthypoxic hyperexcitability in CA1 pyramidal neurons of the rat hippocampal slices through a decrease of the effectiveness of hypoxia to depresses the functional neuronal activity in the rat hippocampal slices during hypoxic episode. On the other hand, interleukin-10 (1 ng/ml) did not affect an initiation of epileptiform activity in CA1 pyramidal neurons of the rat hippocampal slices induced by bicuculline. Interleukin-10 (1 ng/5 microl) applied to the dorsal hippocampus in awake rats depressed an initiation of focal seizures ("ictal"-like components of afterdischarges) induced by hippocampal kindling during the first six hours after an application. However, this cytokine did not affect neither the duration of "interictal"-like component of afterdischarges nor motor seizure development. Thus, our findings showed that antiinflammatory cytokine interleukin-10, in addition to its antihypoxic action, exert the neuroprotective effect on the initiation of "ictal"-like, but not "interictal"-like, epileptiform discharges.

Protective effects of interleukin-10 on the development of epileptiform activity evoked by transient episodes of hypoxia in rat hippocampal slices.

The aim of the present work was to study the effects of interleukin-10 at concentrations of 1 and 10 ng/ml on the development of epileptiform discharges evoked in pyramidal neurons in field CA3 in rat hippocampal slices by transient episodes of hypoxia. Three 3-min episodes of hypoxia led to decreases in the generation threshold for evoked trains of population spikes and an increase in the number of population spikes per train in pyramidal neurons of field CA1. Interleukin-10 at a concentration of 1 ng/ml completely eliminated the development of epileptiform activity, while its protective effect was less marked at a concentration of 10 ng/ml. These effects of interleukin-10 on living hippocampal slices in in vitro conditions show that they may be associated with the functions of this cytokine as an intercellular mediator of the central nervous system itself rather than being mediated by the peripheral immune system. The results of these studies provide the first experimental evidence of the action of the anti-inflammatory cytokine interleukin-10 on the development of hypoxia-evoked epileptiform events in the hippocampus.

[Protective effect of interleukin-10 on the development of epileptiform activity induced by brief hypoxic episodes in the rat hippocampal slices].

The aim of the study was to investigate the effect of interleukin-10 (IL-10) (1 and 10 ng/ml) on the development of epileptiform activity induced by brief hypoxic episodes in CA1 area of rat hippocampal slices. Three three-minute hypoxic episodes induced a sustained decrease in the threshold of evoked population spike (PS) burst and an increase in the number of PSs in the PS response. IL-10 (1 ng/ml) completely abolished the development of epileptiform activity whereas the effect of IL-10 (10 ng/ml) was weaker. The protective effect of IL-10 on the hyperexcitability of the local neuronal network in hippocampal slices indicate that this cytokine can function as an intercellular mediator in the brain. The present results are the first experimental evidence of a protective role of anti-inflammatory IL-10 in the development of epileptiform events induced by brief episodes of hypoxia in the hippocampus.