Evidence for the involvement of corticotrophin-releasing hormone in the pathogenesis of traumatic brain injury.

The aim of this study was to investigate the role of the neuropeptide corticotrophin-releasing hormone (CRH) in neurodegeneration induced by traumatic brain injury, using a well characterized model of lateral fluid percussion injury in male, Sprague-Dawley rats. In the first series of experiments, CRH gene expression was assessed by in situ hybridization after traumatic brain injury. A bilateral increase in CRH mRNA in the paraventricular nucleus was observed in rats subjected to traumatic brain injury compared with sham-operated controls. A maximal (40%) increase in hybridization signal was detected 2 h after trauma compared with control rat brains. In addition, marked induction of CRH transcripts was found in the ipsilateral amygdala after trauma, but no increase was detected in the ipsilateral cortex around the area of damage. In a separate experiment, the effects of the CRH antagonist, D-Phe CRH(12-41) (25 microg total dose), or appropriate vehicle injected intracerebroventricularly, was tested on infarct volume caused by brain injury. Repeated intracerebroventricular injection of D-Phe CRH(12-41) significantly reduced, by 45%, the volume of cortical damage in injured rats compared with vehicle-treated, trauma animals. The rapid upregulation of CRH gene expression in the paraventricular nucleus and amygdala following lateral fluid percussion injury and the marked neuroprotection achieved by inhibiting CRH action suggest that CRH is involved directly in the pathogenesis of traumatic brain injury. This observation may have important implications for the development of novel therapeutic strategies for treating the neurological consequences of brain trauma and related conditions.

Whole body metabolic responses to brain trauma in the rat.

Increases in metabolic rate reported in head-injured patients can contribute to increases in respiratory demand, raised body temperature, and host body wasting (cachexia). The objective of the present study was to quantify the metabolic responses to brain trauma in the rat and investigate the underlying mechanisms. Lateral fluid-percussion (FP) injury (applied cortical pressure 1.6-1.8 atm) in the rat resulted in consistent and reproducible cortical brain lesions (44 +/- 6 mm3). Body weight and food intake were reduced significantly 24 h after brain trauma compared to sham-operated (7 and 49%,p < 0.01) and control animals (14 and 65%,p < 0.001), respectively. Resting oxygen consumption (V(O2), measured at 24 degrees C) was increased significantly, by 9-16% above sham-operated, and 14-26% above control animals for 2-7 h after brain trauma (p < 0.05), but V(O2) was not raised thereafter (24-72 h) and colonic temperature was not changed. Raising the ambient temperature from 24 degrees C to 28 degrees C significantly reduced the hypermetabolism of brain-injured rats compared to sham-operated controls. Injection of the beta-adrenoceptor antagonist propranolol (10 mg/kg, i.p.) completely abolished the rise in metabolic rate of brain-injured rats, and reduced significantly the rise in metabolic rate of the sham-operated animals (26%, p < 0.01 and 11%, p < 0.05; respectively). Systemic injection of the cyclo-oxygenase inhibitor indomethacin (1 mg/kg, i.p.) significantly attenuated (by 11%,p < 0.01), but did not completely abolish the hypermetabolism of brain-injured animals. Lateral FP injury in the rat causes a significant cachexia. Weight loss is due to hypophagia, and an increase in energy expenditure, which is mediated by sympathetic activation of thermogenesis and in part by prostaglandins.

Involvement of prostaglandins in cachexia induced by T-cell leukemia in the rat.

We have previously demonstrated that experimentally induced T-cell leukemia in the rat results in a rapid and severe cachexia. This weight loss is largely due to a reduction in food intake, but is also accompanied by inappropriately high rates of energy expenditure. Increases in resting oxygen consumption (VO2) of 25% to 35% above the levels of pair-fed animals were observed over the period of weight loss. The present study investigated the possible involvement of prostaglandins in the cachexia induced by T-cell leukemia in the rat. Acute systemic injection of the cyclo-oxygenase inhibitors (indomethacin 1 mg/kg or flurbiprofen 1 mg/kg intraperitoneally [IP]) significantly reduced (by 14% and 10%, respectively) the increase in metabolic rate and also reversed the elevated body temperature of leukemic animals. Intracerebroventricular (ICV) injection of indomethacin (0.2 mg/kg) had only modest effects on the increase in temperature or hypermetabolism of leukemic animals. Long-term daily injection of indomethacin or flurbiprofen (1 mg/kg/d IP) had no significant effect on food intake or body weight of leukemic animals, and neither treatment significantly affected disease status. Indomethacin significantly reduced the decline in epididymal fat pad weight of leukemic animals. These data indicate that prostaglandins, produced peripherally, are involved in the acute hypermetabolism associated with T-cell leukemia, but have little or no effect on the hypophagia or body weight loss of leukemic rats.

Involvement of cytokines in cachexia induced by T-cell leukaemia in the rat.

The objective of this study was to investigate the involvement of cytokines (IL-1, IL-6 and TNF-alpha) in cachexia induced by T-cell leukaemia in the rat. Leukaemic rats exhibited a marked and significant increase in circulating IL-6 concentration from days 12-17 corresponding to the period of weight loss after induction of leukaemia. IL-6 plasma bioactivity correlated significantly with spleen weight and weight loss, implicating IL-6 in the cachectic response. In contrast, IL-1 and TNF-alpha plasma bioactivities were not increased compared to control rats, indicating that these cytokines are not circulating mediators of cachexia induced by T-cell leukaemia in the rat. These data suggest that IL-6 produced by the host may contribute to cachexia induced by T-cell leukaemia.

Agonist interactions with 5-HT3 receptor recognition sites in the rat entorhinal cortex labelled by structurally diverse radioligands.

1. The pharmacological properties of 5-HT3 receptor recognition sites labelled with [3H]-(S)-zacopride, [3H]-LY278,584, [3H]-granisetron and [3H]-GR67330 in membranes prepared from the rat entorhinal cortex were investigated to assess the presence of cooperativity within the 5-HT3 receptor complex. 2. In rat entorhinal cortex homogenates, [3H]-(S)-zacopride, [3H]-LY278,584, [3H]-granisetron and [3H]-GR67330 labelled homogeneous densities of recognition sites (defined by granisetron, 10 microM) with high affinity (Bmax = 75 +/- 5, 53 +/- 5, 92 +/- 6 and 79 +/- 6 fmol mg-1 protein, respectively; pKd = 9.41 +/- 0.04, 8.69 +/- 0.14, 8.81 +/- 0.06 and 10.14 +/- 0.04 for [3H]-(S)-zacopride, [3H]-LY278,584, [3H]-granisetron and [3H]-GR67330, respectively, n = 3-8). 3. Quipazine and granisetron competed for the binding of each of the radioligands in the rat entorhinal cortex preparation at low nanomolar concentrations (pIC50; quipazine 9.38-8.51, granisetron 8.62-8.03), whilst the agonists, 5-hydroxytryptamine (5-HT), phenylbiguanide (PBG) and 2-methyl-5-HT competed at sub-micromolar concentrations (pIC50; 5-HT 7.16-6.42, PBG 7.52-6.40, 2-methyl-5-HT 7.38-6.09). 4. Competition curves generated with increasing concentrations of quipazine, PBG, 5-HT and 2-methyl-5-HT displayed Hill coefficients greater than unity when the 5-HT3 receptor recognition sites in the entorhinal cortex preparation were labelled with [3H]-LY278,584, [3H]-granisetron and [3H]-GR67330. These competing compounds displayed Hill coefficients of around unity when the sites were labelled with [3H]-(S)-zacopride. Competition for the binding of [3H]-(S)-zacopride, [3H]-LY278,584, [3H]-granisetron and [3H]-GR67330 by granisetron generated Hill coefficients around unity.5. The nature of the interaction of competing compounds (quipazine, granisetron, PBG, 5-HT, 2-methyl-5-HT) for the [3H]-(S)-zacopride binding site in the rat entorhinal cortex preparation was not altered by the removal of the Krebs ions or the addition of the monoamine oxidase inhibitor, pargyline, to the HEPES/Krebs buffer.6. In conclusion, the present studies provide further evidence towards the presence of cooperativity within the 5-HT3 receptor macromolecule and indicate that either [3H]-(S)-zacopride labels a different site on the receptor complex from [3H]-LY278,584, [3H]-granisetron or [3H]-GR67330, or it binds in such a manner as to prevent the conformatory change in the receptor protein responsible for the cooperative binding of agonists (and quipazine).