Fibromyalgia is a prevalent and burdensome disorder characterized by chronic widespread pain and complex comorbid symptoms. To develop better treatments for pain-centered fibromyalgia symptoms, there is still a need for animal models which mimic the features of fibromyalgia patients. In the present study, we have established a fibromyalgia animal model by utilizing a never-before-published pharmacological effect of reserpine. Repeated administration of reserpine (1mg/kg s.c., once daily, for three consecutive days) causes a significant decrease in the muscle pressure threshold and tactile allodynia, which are sustained for 1week or more in both male and female rats. This treatment regimen decreases the amount of biogenic amines (dopamine, norepinephrine, and 5-hydroxytryptamine) in the spinal cord, thalamus, and prefrontal cortex, which are deeply involved in pain signal processing. It also significantly increases immobility time in the forced swim test, which is indicative of depression, a common comorbid symptom of fibromyalgia. Pregabalin, duloxetine, and pramipexole significantly attenuated the reserpine-induced decrease in muscle pressure threshold, but diclofenac did not. The validity of the use of this reserpinized animal as a fibromyalgia model is demonstrated from three different aspects, i.e., face validity (manifestation of chronic pain and comorbid symptoms), construct validity (dysfunction of biogenic amine-mediated central nervous system pain control is involved), and predictive validity (similar responses to treatments used in fibromyalgia patients). This animal model is expected to contribute to the better understanding of fibromyalgia pathophysiology and the evaluation of drugs, especially those which would activate biogenic amine system.

Chk1, a nuclear DNA damage/replication G2 checkpoint kinase, phosphorylates Cdc25 and causes its nuclear exclusion in yeast and mammalian cells, thereby arresting the cell at the G2 phase until DNA repair/replication is completed. Chk1 is also involved, at least in part, in the natural G2 arrest of immature Xenopus oocytes, but it is unknown how Chk1 inhibits Cdc25 function and undergoes regulation during oocyte maturation. By using enucleated oocytes, we show here that Chk1 inhibits Cdc25 function in the cytoplasm of G2-arrested oocytes and that Cdc25 is activated exclusively in the cytoplasm of maturing oocytes. Moreover, we show that Chk1 activity is not appreciably altered during maturation, being maintained at basal levels, and that C-terminal truncation mutants of Chk1 have very high kinase activities, strong abilities to inhibit maturation, and altered subcellular localization in oocytes. These results, together with other results, suggest that the Chk1/Cdc25 pathway is involved cytoplasmically in G2 arrest of Xenopus oocytes, but moderately and independent of the G2 checkpoint, and that the C-terminal region of Chk1 negatively regulates its kinase activity and also determines its subcellular localization. Based on these results, we discuss the possibility that Chk1 (with the basal activity) may function as an ordinary regulator of Cdc25 in oocytes (and in other cell types) and that Chk1 might be hyperactivated in response to the G2 checkpoint via its dramatic conformational change.

Chk1 kinase, a DNA damage/replication G2 checkpoint kinase, has recently been shown to phosphorylate and inhibit Cdc25C, a Cdc2 Tyr-15 phosphatase, thereby directly linking the G2 checkpoint to negative regulation of Cdc2. Immature Xenopus oocytes are arrested naturally at the first meiotic prophase (prophase I) or the late G2 phase, with sustained Cdc2 Tyr-15 phosphorylation. Here we have cloned a Xenopus homolog of Chk1, determined its developmental expression, and examined its possible role in prophase I arrest of oocytes. Xenopus Chk1 protein is expressed at approximately constant levels throughout oocyte maturation and early embryogenesis. Overexpression of wild-type Chk1 in oocytes prevents the release from prophase I arrest by progesterone. Conversely, specific inhibition of endogenous Chk1 either by overexpression of a dominant-negative Chk1 mutant or by injection of a neutralizing anti-Chk1 antibody facilitates prophase I release by progesterone. Moreover, when ectopically expressed in oocytes, a Chk1-nonphosphorylatable Cdc25C mutant alone can induce prophase I release much more efficiently than wild-type Cdc25C; if endogenous Chk1 function is inhibited, however, even wild-type Cdc25C can induce the release very efficiently. These results suggest strongly that Chk1 is involved in physiological prophase I arrest of Xenopus oocytes via the direct phosphorylation and inhibition of Cdc25C. We discuss the possibility that Chk1 might function either as a G2 checkpoint kinase or as an ordinary cell cycle regulator in prophase-I-arrested oocytes.

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