American journal of physiology. Regulatory, integrative and comparative physiology
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2005
D1-dopamine receptor agonists prevent and reverse opiate depression of breathing but not antinociception in the cat.
Opioids depress respiration and decrease chest wall compliance. A previous study in this laboratory showed that dopamine-D(1) receptor (D(1)R) agonists restored phrenic nerve activity after arrest by fentanyl in immobilized, mechanically ventilated cats. The reinstated phrenic nerve rhythm was slower than control, so it was not known whether D(1)R agonists can restore spontaneous breathing to levels that provide favorable alveolar gas exchange and blood oxygenation. ⋯ Pretreatment with DHD prevented significant depression of spontaneous breathing by fentanyl (17.5 +/- 4.3 microg/kg). Tonic firing evoked by fentanyl in expiratory neurons was converted to rhythmic respiratory discharges by DHD (1 mg/kg). The results suggest that D(1)R agonists might be therapeutically useful for the treatment of opioid disturbances of breathing without impeding analgesia.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2005
Comparative StudyCardiovascular response to a group III mGluR agonist in NTS requires NMDA receptors.
Previous studies have demonstrated that microinjection of the putative group III metabotropic glutamate receptor (mGluR) agonist, l(+)-2-amino-4-phosphonobutyric acid (L-AP4), into the nucleus tractus solitarius (NTS) produces depressor and sympathoinhibitory responses. These responses are significantly attenuated by a group III mGluR antagonist and may involve ionotropic glutamatergic transmission. Alternatively, a previous report in vitro suggests that preparations of L-AP4 may nonspecifically activate NMDA channels due to glycine contamination (Contractor A, Gereau RW, Green T, and Heinemann SF. ⋯ Furthermore, although it is possible that glycine contamination or other nonspecific actions are responsible for the sympathoinhibitory actions of L-AP4, our data and data in the literature argue against this possibility. Thus we conclude that responses to L-AP4 in the NTS are mediated by an interaction between group III mGluRs and NMDA receptors. Finally, we also caution that nonselective actions of L-AP4 should be considered in future studies.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2005
Corticosterone suppresses mesenteric lymph node T cells by inhibiting p38/ERK pathway and promotes bacterial translocation after alcohol and burn injury.
Previous studies showed that alcohol (EtOH) intoxication before burn injury suppresses mesenteric lymph node (MLN) T cell functions and increases gut bacterial translocation. In this study, we examined whether corticosterone (Cort) plays any role in suppressing MLN T cell function and bacterial accumulation after EtOH intoxication and burn injury. Rats were gavaged with EtOH to achieve a blood EtOH level of approximately 100 mg/dl before receiving 25% total body surface area burn or sham injury. ⋯ Treatment of rats with metyrapone prevented the suppression of MLN T cell proliferation, IL-2 production, and p38 and ERK1/2 phosphorylation. Restoration of T cell function in metyrapone-treated animals was also associated with the decrease in bacterial accumulation in MLN. These findings suggest that EtOH intoxication before burn injury augments Cort release, which suppresses MLN T cell function by inhibiting p38 and ERK1/2 activation and promotes bacterial accumulation in MLN after EtOH and burn injury.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2005
Effects of high-fat diets with different carbohydrate-to-protein ratios on energy homeostasis in rats with impaired brain melanocortin receptor activity.
Changes in dietary macronutrient composition and/or central nervous system neuronal activity can underlie obesity and disturbed fuel homeostasis. We examined whether switching rats from a diet with high carbohydrate content (HC; i.e., regular chow) to diets with either high fat (HF) or high fat/high protein content at the expense of carbohydrates (LC-HF-HP) causes differential effects on body weight and glucose homeostasis that depend on the integrity of brain melanocortin (MC) signaling. In vehicle-treated rats, switching from HC to either HF or LC-HF-HP feeding caused similar reductions in food intake without alterations in body weight. ⋯ Relatively low plasma adiponectin levels likely contributed to this effect. Thus HF feeding amplifies obesity induced by impaired MC signaling, provided that the carbohydrate-to-protein (C/P) ratio is high enough. Reduction of the C/P ratio within a HF diet ameliorates hyperphagia and obesity in rats with impaired MC signaling but aggravates associated disturbances in fuel homeostasis.