IL-1β-mediated neuropeptide and immediate early gene mRNA induction is defective in Lewis hypothalamic cell cultures

L-arginine abolishes the hypothalamic serotonergic activation induced by central interleukin-1β administration to normal rats

IL-1β-induced anorexia may depend on interactions of the cytokine with neuropeptides and neurotransmitters of the central nervous system control of energy balance and serotonin is likely to be one catabolic mediator targeted by IL-1β. In the complex interplay involved in feeding modulation, nitric oxide has been ascribed a stimulatory action, which could be of significance in counteracting IL-1β effects.

The present study aims to explore the participation of the nitric oxide and the serotonin systems on the central mechanisms induced by IL-1β and the relevance of their putative interactions to IL-1β hypophagia in normal rats.

Serotonin levels were determined in microdialysates of the ventromedial hypothalamus after a single intracerebroventricular injection of 10 ng of IL-1β , with or without the pre-injection of 20 μg of the nitric oxide precursor L-arginine. IL-1β significantly stimulated hypothalamic serotonin extracellular levels, with a peak variation of 130 ±37% above baseline. IL- 1β also reduced the 4-h and the 24-h food intakes (by 23% and 58%, respectively). The IL-1β-induced serotonergic activation was abolished by the pre-injection of L-arginine while the hypophagic effect was unaffected.

The data showed that one central effect of IL-1β is serotonergic stimulation in the ventromedial hypothalamus, an action inhibited by nitric oxide activity. It is suggested that, although serotonin participates in IL-1β anorexia, other mechanisms recruited by IL-1β in normal rats are able to override the absence of the serotonergic hypophagic influence.

Strain-specific BDNF expression of rat primary astrocytes

By producing brain-derived neurotrophic factor (BDNF), astrocytes play a role in disease resistance. This study was undertaken to investigate whether primary astrocytes derived from LEW/N and F344/N rats differentially express BDNF. LEW/N astrocytes expressed more BDNF mRNA and protein than F344/N astrocytes in basal and valproic acid (VPA)-stimulated conditions. VPA suppresses HDAC enzyme activity without affecting HDAC gene and protein expression in astrocytes of both strains. Blockade of TrkB receptors resulted in similar fold decreases in basal BDNF mRNA levels between two strains. The results suggest that inhibition of HDAC activity and BDNF-TrkB autocrine loop are involved in regulation of astrocytic BDNF transcription, whereas the mechanisms for elevated constitutive gene BDNF expression of LEW/N astrocytes remain to be investigated.

Strain-dependent inflammatory responsiveness of rat microglial cells

The aim of this study is to test whether inflammatory responsiveness of rat microglial cells is strain-specific in primary microglia derived from neonatal LEW/N and F344/N rats. In contrast to F344/N microglia, LEW/N microglia constitutively and upon lipopolysaccharide challenge expressed higher levels of mRNA for the majority of inflammatory mediators studied. In addition, LEW/N microglia exhibited enhanced secretion of tumor necrosis factor-alpha and CCL2, as well as elevated nitric oxide production. On the contrary, activated LEW/N microglia transcribed and secreted less interleukin-10. Hence, compared to F344/N microglia, LEW/N microglia might be more reactive to lipopolysaccharide and incompetent to suppress inflammation.

Effects of carrageenan and morphine on acute inflammation and pain in Lewis and Fischer rats

The present study used inbred, histocompatible Fischer 344 (FIS) and Lewis (LEW) rats to begin to explore the role of the hypothalamic-pituitary-adrenal (HPA) axis in the immune processes and pain behavior associated with the carrageenan model of acute hindpaw inflammation. Because the HPA axis contributes in part to morphine's analgesic and immunomodulatory properties, the present study also assessed the effects of morphine in carrageenan-inflamed LEW and FIS rats. The results showed that carrageenan-induced hindpaw swelling and pain behavior were greater in FIS than in LEW rats. The enhanced hindpaw swelling in FIS rats correlated with an increase in myeloperoxidase (MPO; a measure of neutrophils) in the inflamed hindpaw. FIS rats showed lower circulating levels of TNFalpha, higher IL-6 levels, and similar IL-1beta and nitric oxide levels, when compared to LEW rats. Morphine produced a significant decrease in carrageenan-induced hindpaw swelling and MPO in both strains, but morphine did not significantly alter circulating cytokine/mediator levels. Morphine's analgesic effects were greater in the inflamed than the noninflamed hindpaw, and they did not correlate with morphine's anti-inflammatory effects. In fact, low doses of morphine produced a mechanical allodynia and hyperalgesia in the noninflamed hindpaw of FIS, but not LEW, rats. These results suggest a positive relationship between HPA axis activity and acute inflammation and inflammatory pain. In contrast, little evidence is provided for HPA axis involvement in morphine's anti-inflammatory or analgesic effects.

Acute inflammatory and neuropathic pain in Lewis and Fischer rats

Inbred, histocompatible Lewis and Fischer 344 rats (LEW and FIS) have been used to identify an inverse relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and susceptibility to autoimmune and chronic inflammatory disorders, with LEW showing blunted HPA axis activity and increased susceptibility toward the development of autoimmunity and chronic inflammation, and FIS showing the opposite relationship. In the present study, LEW and FIS were used to determine the relationship between HPA axis function and acute inflammatory pain (carrageenan-induced hindpaw inflammation) and neuropathic pain (partial sciatic nerve ligation; PSNL). The results showed that carrageenan-induced thermal and mechanical allodynia and hyperalgesia were greater in FIS than in LEW. Similarly, FIS showed more carrageenan-induced hindpaw swelling and higher levels of myeloperoxidase (a measure of neutrophils) in the carrageenan-inflamed hindpaw. After PSNL, LEW showed a profound mechanical allodynia and hyperalgesia, whereas mechanical sensitivity in FIS was unaltered. However, FIS, but not LEW, developed thermal allodynia and hyperalgesia after PSNL. These results provide strong evidence for a positive relationship between HPA axis activity and acute inflammatory pain. The results also support a relationship between HPA axis activity and neuropathic pain, but the relationship is complex and may depend on the pain assay.

Differences in the brain expression of c-fos mRNA after restraint stress in Lewis compared to Sprague–Dawley rats

In order to study the contribution of genetic factors to the pattern of stress-induced brain activation, we studied the expression of c-fos mRNA, a marker of neuronal activity, in male Sprague-Dawley and Lewis strains, the latter being known to have a deficient responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis. Immobilization (IMO) alone or combined with the immersion into water at 21 degrees C was applied for 15 or 60 min. The expression of c-fos mRNA was quantified by in situ hybridization in those brain areas that represent important parts of neuronal circuits activated by stress: medial prefrontal cortex, medial amygdala, lateral septum ventral part, paraventricular nucleus of the hypothalamus and locus coeruleus. While in controls, c-fos mRNA was not detectable in tested brain areas, both types of stressors induced a strong expression of this immediate early gene. There were only small differences in c-fos mRNA expression related to the type of stressor or the length of exposure to them. However, there were remarkable differences in the expression between the two rat strains. When compared to Sprague-Dawley rats, Lewis rats showed a reduced c-fos mRNA expression after both stressors in most brain areas, which may be related to the reduced responsiveness of HPA axis and also with other abnormal responses in this strain. However, this hyporesponsiveness was not observed in all brain areas studied, suggesting that there is not a generalized defective c-fos response to stress in Lewis rats and that some responses to stress may be normal in this strain.