α(2A) adrenoceptor-mediated presynaptic inhibition of GABAergic transmission in rat tuberomammillary nucleus neurons.

Histaminergic neurons within the tuberomammillary nucleus (TMN) play an important role in the regulation of sleep-wakefulness. Here, we report the adrenergic modulation of GABAergic transmission in rat TMN histaminergic neurons using a conventional whole-cell patch clamp technique. Norepinephrine (NE) reversibly decreased the amplitude of action potential-dependent GABAergic inhibitory post-synaptic currents (IPSCs) and increased the paired pulse ratio. The NE-induced inhibition of GABAergic IPSCs was mimicked by clonidine, a selective α2 adrenoceptor agonist. However, cirazoline and isoproterenol, nonselective α1 and ß adrenoceptor agonists, respectively, had no effect on GABAergic IPSCs. The NE-induced inhibition of GABAergic IPSCs was significantly blocked by BRL44408, a selective α2A adrenoceptor antagonist, but not imiloxan or JP1302, a selective α2B and α2C adrenoceptor antagonists. The extent of NE-induced inhibition of GABAergic IPSCs was inversely proportional to the extracellular Ca(2+) concentration. Pharmacological agents affecting the activities of adenylyl cyclase or G-protein-coupled inwardly rectifying K(+) channels did not affect the NE-induced inhibition of GABAergic IPSCs. However, NE had no effect on the frequency and amplitude of GABAergic miniature IPSCs. These results suggest that NE acts on presynaptic α2A adrenoceptor to inhibit action potential-dependent GABA release via the inhibition of Ca(2+) influx from the extracellular space to GABAergic nerve terminals, and that this α2A adrenoceptor-mediated modulation of GABAergic transmission may be involved in regulating the excitability of TMN histaminergic neurons.

Dual functionality of myeloperoxidase in rotenone-exposed brain-resident immune cells.

Rotenone exposure has emerged as an environmental risk factor for inflammation-associated neurodegenerative diseases. However, the underlying mechanisms responsible for the harmful effects of rotenone in the brain remain poorly understood. Herein, we report that myeloperoxidase (MPO) may have a potential regulatory role in rotenone-exposed brain-resident immune cells. We show that microglia, unlike neurons, do not undergo death; instead, they exhibit distinctive activated properties under rotenone-exposed conditions. Once activated by rotenone, microglia show increased production of reactive oxygen species, particularly HOCl. Notably, MPO, an HOCl-producing enzyme that is undetectable under normal conditions, is significantly increased after exposure to rotenone. MPO-exposed glial cells also display characteristics of activated cells, producing proinflammatory cytokines and increasing their phagocytic activity. Interestingly, our studies with MPO inhibitors and MPO-knockout mice reveal that MPO deficiency potentiates, rather than inhibits, the rotenone-induced activated state of glia and promotes glial cell death. Furthermore, rotenone-triggered neuronal injury was more apparent in co-cultures with glial cells from Mpo(-/-) mice than in those from wild-type mice. Collectively, our data provide evidence that MPO has dual functionality under rotenone-exposed conditions, playing a critical regulatory role in modulating pathological and protective events in the brain.

The differential effect of high and low molecular weight fucoidans on the severity of collagen-induced arthritis in mice.

Fucoidans have been extensively studied for their various biological activities but the exact role of fucoidans on the inflammatory processes associated with arthritic disease has not been studied. The effect of the treatment of high, medium and low molecular weight fucoidans (HMWF, MMWF and LMWF, respectively) on the progression of collagen-induced arthritis (CIA) was tested. A daily oral administration of HMWF enhanced the severity of arthritis, inflammatory responses in the joint cartilage and the levels of collagen-specific antibodies, while LMWF reduced the severity of arthritis and the levels of Th1-dependent collagen-specific IgG(2a). Further in vitro analyses, using macrophage cell lines, revealed that the HMWF induced the expression of various inflammatory mediators, and enhanced the cellular migration of macrophages. These stimulatory effects of fucoidan decreased in fucoidans with lower molecular weights and LMWF did not exhibit any pro-inflammatory effects. Interestingly, the oral administration of HMWF enhanced the production of IFN-gamma, one of the Th1 cytokines, in collagen-stimulated spleen cells that had been isolated from CIA mice, while LMWF had the opposite effect. These results indicate that HMWF enhances arthritis through enhancing the inflammatory activation of macrophages while LMWF reduces arthritis through the suppression of Th1-mediated Immune reactions.

Soluble Fas ligand-susceptible "memory" cells in mice but not in human: potential role of soluble Fas ligand in deletion of auto-reactive cells.

Human soluble Fas ligand (sFasL) has an apoptotic activity in contrast to murine sFasL. The physiological function of human sFasL is not known, while the pathological consequence of sFasL overproduction has been reported. To understand the physiological function of (human) sFasL, murine and human lymphocytes were treated with sFasL. sFasL treatment significantly decreased CD45RBlo "memory" CD4+ lymphocyte fraction and increased propidium iodide (PI)+ apoptotic CD45RBloCD4+ lymphocytes among murine peripheral lymphocytes. However, sFasL treatment neither decreased CD45RO+ "memory" CD4+ lymphocyte fraction nor increased PI+ CD45RO+CD4+ lymphocytes among human peripheral lymphocytes, suggesting that the deletion of memory cells by sFasL had already occurred in vivo. Patients with systemic lupus erythematosus had sFasL-susceptible "memory" cell fraction suggesting an incomplete deletion of such "memory" cells. These results suggest that the physiological function of human sFasL is to delete the potentially auto-reactive "memory" lymphocytes, which complements membrane FasL (mFasL)-mediated deletion of auto-reactive cells in human beings but not in mice.