Physiology & behavior
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Physiology & behavior · Jun 2006
Comparative StudyLimbic and HPA axis function in an animal model of chronic neuropathic pain.
Chronic pain can be considered a form of chronic stress, and chronic pain patients often have disturbances of the hypothalamic-pituitary-adrenal (HPA) axis, including abnormal cortisol levels. In addition, chronic pain patients have an increased incidence of depression and anxiety, stress-related disorders that are frequently accompanied by disturbances in the limbic system (e.g. hippocampus and amygdala) and the HPA axis. Despite the fact that the literature supports a strong link between chronic pain, stress disorders, and limbic dysfunction, the mechanisms underlying the effects of chronic pain on the HPA axis and limbic system are not understood. ⋯ CCI increased the expression of corticotrophin releasing hormone mRNA in the central amygdala, and not the paraventricular nucleus of the hypothalamus or the bed nucleus of the stria terminalis. Moreover, glucocorticoid receptor mRNA expression in CCI rats was increased in the medial and central amygdala, unaffected in the paraventricular nucleus, and decreased in the hippocampus. These results suggest that increased nociceptive sensitivity during chronic pain is associated with alterations in the limbic system, but is dissociated from HPA axis activation.
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Physiology & behavior · Jun 2006
Comparative StudyInfluence of nitric oxide on morphine-induced amnesia and interactions with dopaminergic receptor agents.
The interactions of dopaminergic receptors and nitric oxide (NO) with morphine-induced memory of passive avoidance have been investigated in mice. Pre-training administration of morphine (1, 3 and 5 mg/kg, s.c.) dose-dependently decreased the learning of a one-trial passive avoidance task. Pre-training administration of L-arginine, a nitric oxide precursor (50, 100 and 200 mg/kg, i.p.), alone did not affect memory formation. ⋯ On the other hand, the inhibition of morphine-induced amnesia by L-arginine (200 mg/kg, i.p.) was significantly decreased by pretreatment with different doses of dopamine D1 receptor antagonist, SCH 23390 (0.001, 0.01 and 0.1 mg/kg, i.p.) or D2 receptor antagonist, sulpiride (12.5, 25, 50 and 100 mg/kg, i.p.). However, the dopamine receptor antagonists could not affect memory formation by themselves. It may be concluded that the morphine-induced impairment of memory formation can be prevented by nitric oxide donor and, in this effect, dopaminergic mechanism is involved.
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Physiology & behavior · Jun 2006
Comparative StudyLasting anxiogenic effects of feline predator stress in mice: sex differences in vulnerability to stress and predicting severity of anxiogenic response from the stress experience.
Previous work in male Swiss Webster (CFW) mice demonstrated a long lasting effect of predator stress on risk assessment in the elevated plus maze (EPM). Most severe effects (increases in risk assessment) were seen following a brief unprotected exposure to a cat. Lesser effects were produced by a brief exposure of mice to the cat exposure room without a cat in the room (room stress). ⋯ Finally, factor analysis indicated that different tests of anxiety-like behavior may be measuring different and independent aspects of mouse affect. Moreover, stressors had no lasting effects on sugar solution consumption. Implications of these findings for modeling PTSD and using transgenic strains of mice to study lasting effects of stress on affect are discussed.