Search

Interleukin (IL)-1[beta] is a pluripotent proinflammatory cytokine that signals through the type-I IL-1 receptor (IL-1RI), a member of the Toll-like receptor family. In hypothalamic neurons, binding of IL-1[beta] to IL-1RI mediates transcription-dependent changes that depend on the recruitment of the cytosolic adaptor protein myeloid differentiation primary-response protein 88 (MyD88) to the IL-1RI/IL-1 receptor accessory protein (IL-1RAcP) complex through homomeric Toll/IL-1 receptor (TIR)--TIR interactions. Through design and synthesis of bifunctional TIR mimetics that disrupt the interaction of MyD88 with the IL-1RI/IL-1RAcP complex, we analyzed the involvement of MyD88 in the signaling of IL-1[beta] in anterior hypothalamic neurons. We show here that IL-1[beta]-mediated activation of the protein tyrosine kinase Src depended on a MyD88 interaction with the IL-1RI/IL-1RAcP complex. The activation of the protein kinase Akt/PKB depended on the recruitment of the p85 subunit of PI3K to IL-1RI and independent of MyD88 association with the IL-1RI/ IL-1RAcP complex. These bifunctional TIR-TIR mimetics represent a class of low-molecular-weight compounds with both an anti-inflammatory and neuroprotective potential. These compounds have the potential to inhibit the MyD88-dependent proinflammatory actions of IL-1[beta], while permitting the potential neuronal survival supporting actions mediated by the MyD88-independent activation of the protein kinase Akt. cytokine | interleukin | protein-protein interaction | inflammation

IL-1[beta] was identified after a long search for the endogenous pyrogen. It acts by inducing synthesis of prostaglandin [E.sub.2], which mediates the late phase of IL-1[beta]-induced fever. Here we show by radiotelemetry that the early phase of the fever response to IL-1[beta] is mediated by ceramide. Hypothalamic application of the cell-penetrating C2-ceramide mimics the rapid phase of the IL-1[beta]-induced fever. Inhibition of ceramide synthesis blocks the rapid phase of fever but does not affect the slower prostaglandin [E.sub.2]-dependent phase, which is blocked by indomethacin or by null mutation of the EP3 prostanoid receptor. Electrophysiological experiments on preoptic area/anterior hypothalamic neurons show that C2-ceramide, but not dihydroceramide, mimics the rapid hyperpolarizing effects of IL-1[beta] on the activity of warm-sensitive hypothalamic neurons. IL-1[beta]-mediated hyperpolarization is blocked by PP2, the selective inhibitor of the protein tyrosine kinase Src, which is known to be activated by ceramide. These in vivo and in vitro data suggest that ceramide fulfills the criteria for an endogenous pyrogen. fever | neutral sphingomyelinase | preoptic area

Selective serotonin reuptake inhibitors, such as fluoxetine (FLX), are the most commonly used drugs in the treatment of major depression. However, there is a limited understanding of their molecular mechanism of action. Although the acute effect of selective serotonin reuptake inhibitors in elevating synaptic serotonin concentrations is well known, the clinical amelioration of depressive symptoms requires 14-21 days of treatment, suggesting that numerous other rearrangements of function in the CNS must take place. In the present study, we demonstrated that 14 days of FLX treatment up-regulated galanin mRNA levels by 100% and GalR2-binding sites by 50%, in the rat dorsal raphe nucleus, where galanin coexists with serotonin. Furthermore, a galanin receptor antagonist, M40, attenuated the antidepressant-like effect of FLX in the forced swim test, a rodent preclinical screen commonly used to evaluate antidepressant-like efficacy. Direct activation of galanin receptors by a galanin receptor agonist, galnon, was found to produce an antidepressant-like effect in the same task. Two other antidepressant treatments also affected the galaninergic system in the monoaminergic nuclei: Electroconvulsive shock elevated galanin mRNA levels in dorsal raphe nucleus, whereas sleep deprivation increased galanin mRNA levels in the locus coeruleus, further underlining the connection between activation of the galaninergic system and antidepressant action of various clinically proven treatments.

Temperature responses of anterior hypothalamic neurons are considered key elements in the regulation of the temperature setpoint of homeotherms. We have investigated the sensitivity to warming of cultured neurons of the AH from mice with electrophysiological and immunocytochemical techniques. in control experiments, only [approximately] 9% of the 3- to 5-week-old cells exhibited changes of their basic firing rate when the temperature was raised from 37[degrees]C to 40[degrees]C. This ratio was increased to 27% after the cultures were 'primed' by adding prostaglandin [E.sub.2] (PG[E.sub.2]), an endogenous pyrogen, in the extracellular medium. in these neurons the firing rate was significantly increased, and the frequency of the gamma [gamma],-aminobutyric acid (GABA) inhibitory postsynaptic potentials was markedly decreased. in contrast, the resting potential and membrane resistance of the recorded cells remained unchanged. PG[E.sub.2] was found to decrease the level of phosphorylation of the extracellular signal-regulated kinases 1 and 2 in a subset of GABAergic neurons that express the E-prostanoid receptor type 3. inhibition of ERK1/2 by U0126 mimicked the effects of PG[E.sub.2]. These data indicate that PG[E.sub.2] acts primarily on the excitability of GABAergic presynaptic cells, most likely via alterations of voltage-gated [K.sup.+] channels. Our results also suggest that far from being an inherent property of a specialized class of neurons, the degree of thermosensitivity can be strongly modulated by synaptic activity and is a more adaptive property of hypothalamic neurons than previously thought.

Toll-like receptors (TLRs) and the type I IL-1 receptor (IL-1RI) are key components of the innate immune system activated by microbial infections and inflammation. The signaling cascade from agonist-occupied TLRs and IL-1Rs involves recruitment of the small cytosolic adapter protein MyD88 that binds to IL-1RI via homotypic interactions mediated by Toll/IL-1R/resistance (TLR) domains. Dominant negative forms and null mutations of MyD88 have recently been shown to preclude bacterial product or IL-1-mediated activation of NF-[kappa]B pathways, demonstrating that MyD88 is an essential component of the Toll receptor signaling. Here, we report the synthesis and pharmacological effects of a low molecular weight MyD88 mimic, hydrocinnamoyl-L-valyl pyrrolidine (compound 4a), modeled on a tripeptide sequence of the BB-loop [(F/Y)-(V/L/I)-(P/G)] of the TIR domain. Results are presented showing that compound 4a interferes with the interactions between mouse MyD88 and IL-1RI at the TIR domains. Compound 4a inhibited IL-1[beta]-induced phosphorylation of the mitogen-activated protein kinase p38 in EL4 thymoma cells and in freshly isolated murine lymphocytes in a concentration-dependent manner. In vivo, compound 4a produced a significant attenuation of the IL-1[beta]-induced fever response (200 mg/kg, i.p.). Inhibition of the TIR domain-mediated MyD88/IL1-RI interaction by a low molecular weight, cell-penetrating TR domain mimic suggests an intracellular site for antiinflammatory drug action.

Zinc is coreleased with glutamate from excitatory nerve terminals throughout the central nervous system and acutely inhibits N-methyl-D-aspartate (NMDA) receptor activation. Here we report that cultured murine cortical neurons briefly exposed to sublethal concentrations of zinc developed increased intracellular free [Na.sup.+], phosphorylation of Src kinase at tyrosine 220, and tyrosine phosphorylation of NMDA receptor 2A/2B subunits, in a fashion sensitive to the Src family kinase inhibitor 4-amino-5-(4-chlorophenyl)7-(t-butyl)pyrazolo[3,4-d]pyrimidine, PP2. Functionally, this zinc exposure produced a delayed increase in NMDA receptor current in perforated patch but not conventional whole-cell recordings, as well as an increase in NMDA receptor-mediated cell death. These observations suggest that the effect of synaptically released zinc on neuronal NMDA receptors may be biphasic: acute block, followed by Src family kinase-mediated up-regulation of NMDA receptor activity and cytotoxicity.

Selective serotonin reuptake inhibitors, such as fluoxetine (FIX), are the most commonly used drugs in the treatment of major depression. However, there is a limited understanding of their molecular mechanism of action. Although the acute effect of selective serotonin reuptake inhibitors in elevating synaptic serotonin concentrations is well known, the clinical amelioration of depressive symptoms requires 14-21 days of treatment suggesting that numerous other rearrangements of function in the CNS must take place. In the present study, we demonstrated that 14 days of FIX treatment up-regulated galanin mRNA levels by 100% and GaIR2-binding sites by 50%, in the rat dorsal raphe nucleus, where galanin coexists with serotonin. Furthermore, a galanin receptor antagonist, M40, attenuated the antidepressant-like effect of FIX in the forced swim test a rodent preclinical screen commonly used to evaluate antidepressant-like efficacy. Direct activation of galanin receptors by a galanin receptor agonist galnon, was found to produce an antidepressant-like effect in the same task. Two other antidepressant treatments also affected the galaninergic system in the monoaminergic nuclei: Electroconvulsive shock elevated galanin mRNA levels in dorsal raphe nucleus, whereas sleep deprivation increased galanin mRNA levels in the locus coeruleus, further underlining the connection between activation of the galaninergic system and antidepressant action of various clinically proven treatments. [ABSTRACT FROM AUTHOR]

Temperature responses of anterior hypothalamic neurons are considered key elements in the regulation of the temperature setpoint of homeotherms. We have investigated the sensitivity to warming of cultured neurons of the AH from mice with electrophysiological and immunocytochemical techniques. In control experiments, only ≈9% of the 3- to 5-week-old cells exhibited changes of their basic firing rate when the temperature was raised from 37°C to 40°C. This ratio was increased to 27% after the cultures were "primed" by adding prostaglandin E2 (PGE2), an endogenous pyrogen, in the extracellular medium. In these neurons the firing rate was significantly increased, and the frequency of the gamma γ-aminobutyric acid (GABA) inhibitory postsynaptic potentials was markedly decreased. In contrast, the resting potential and membrane resistance of the recorded cells remained unchanged. PGE2 was found to decrease the level of phosphorylation of the extracellular signal-regulated kinases 1 and 2 in a subset of GABAergic neurons that express the E-prostanoid receptor type 3. Inhibition of ERK1/2 by U0126 mimicked the effects of PGE2. These data indicate that PGE2 acts primarily on the excitability of GABAergic presynaptic cells, most likely via alterations of voltage-gated K+ channels. Our results also suggest that far from being an inherent property of a specialized class of neurons, the degree of thermosensitivity can be strongly modulated by synaptic activity and is a more adaptive property of hypothalamic neurons than previously thought. [ABSTRACT FROM AUTHOR]