IntroductionHeatstroke is defined as a form of excessive hyperthermia (>40 °C) associated with a systemic inflammatory response that leads to multi-organ dysfunction in which central nervous system (CNS) disorders such as delusion, convulsion and coma predominate [1] . Our recent results have demonstrated that heatstroke rodents display hypotension, systemic inflammatory responses, hypothalamic ischemia and neuronal damage, and multi-organ dysfunction [2][3][4] .Kynurenic acid (KYNA) or its metabolic precursor L-kynurenine may be of therapeutic value in neurodegenerative diseased models [5,6] . For example, systemically administered high doses of KYNA had a neuroprotective effect in the gerbil model of global ischemia [7] . Both the homocysteine-induced impairment of endothelial cells [8] and the motility and inflammatory activation in the early phase of acute experimental colitis in the rat [9] were significantly reduced by administration of KYNA. The aim of this study was to investigate whether the heatstroke induced hypotension, systemic inflammatory responses, hypothalamic ischemia and damage, and multiorgan dysfunction could be attenuated by KYNA preconditioning. Accordingly, the temporal profiles of the apoptotic cell numbers of spleen, kidney, liver, lung, and hypothalamus, Kynurenic acid attenuates multiorgan dysfunction in rats after heatstroke Aim: To assess whether systemic delivery of kynurenic acid improves the outcomes of heatstroke in rats. Methods: Anesthetized rats were divided into 2 major groups and given vehicle solution (isotonic saline 0.3 mL/kg rat weight) or kynurenic acid (30-100 mg in 0.3 mL saline/kg) 4 h before the start of thermal experiments. They were exposed to an ambient temperature of 43 ºC for 68 min to induce heatstroke. Another group of rats were exposed to room temperature (26 ºC) and used as normothermic controls. Their core temperatures, mean arterial pressures, serum levels of systemic inflammatory response molecules, hypothalamic values of apoptotic cells and neuronal damage scores, and spleen, liver, kidney and lung values of apoptotic cells were determined. Results: The survival time values during heatstroke for vehicle-treated rats were decreased from the control values of 475-485 min to new values of 83-95 min. Treatment with KYNA (30-100 mg/kg, iv) 4 h before the start of heat stress significantly and dose-dependently decreased the survival time to new values of 152-356 min (P<0.05). Vehicle-treated heatstroke rats displayed hypotension, hypothalamic neuronal degeneration and apoptosis, increased serum levels of tunor necrosis factor-α (TNF-α), intercellular adhesion molecule-1 (ICAM-1), and interleukin-10 (IL-10), and spleen, liver, kidney, and lung apoptosis. KYNA preconditioning protected against hypotension but not hyperthermia and attenuated hypothalamic neuronal degeneration and apoptosis during heatstroke. KYNA preconditioning attenuated spleen, kidney, liver, and lung apoptosis and up-regulated serum IL-10 levels but down-regulated serum TNF-α and ICAM-1 lev...
Our previous studies showed that electrical stimulation of the nuclei ambiguous (NA) or dorsomotor nuclei of the vagus (DMV) complex in the brain stem of spontaneously breathing pond turtles (Cyclemys fiavomarginata), anesthetized with chloralose (4 mg/100 g) and urethane (40 mg/100 g), produced a marked slowing or even cessation of the heart rate, and resulted in an immediate fall of blood pressure. Results of the present study further demonstrated that the cardioinhibitory responses could also be elicited by microinjection of monosodium glutamate (0.2-20 nl, 50 mM) into the NA/DMV complex in turtles. A two-barrel glass micropipette held in a manipulator was connected to a pneumatic pressure pump for microinjection. The glutamate-induced cardioinhibitory responses could be significantly reduced in a dose-dependent manner by pretreatment with AP-5 (a NMDA receptor antagonist, at 1-8 nmole) or CNQX (a non-NMDA receptor antagonist; at 0.1-0.8 nmole) 20 min before glutamate administration. Histochemical verification by injecting horseradish peroxidase into the cervical vagus nerves revealed that retrogradely labeled glutamatergic neurons in the NA/DMV complex were observed. These results suggest that glutamatergic receptors in the caudal medulla may mediate vagal cardioinhibitory responses in the turtle.
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