Neuroscience
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Previous studies have demonstrated that opioid receptors in the prefrontal ventrolateral orbital cortex (VLO) are involved in anti-nociception. The aim of this current study was to examine whether opioid receptors in the VLO have effects on the hypersensitivity induced by contralateral L5 and L6 spinal nerve ligation (SNL), termed as mirror neuropathic pain (MNP) in the male rat. Morphine (1.0, 2.5, 5.0 microg) microinjected into the VLO contralateral to the SNL depressed the mechanical paw withdrawal assessed by von Frey filaments and the cold plate (4 degrees C)-induced paw lifting in a dose-dependent manner on the side without SNL. ⋯ The effects of both drugs were blocked by selective mu-receptor antagonist beta-funaltrexamine (beta-FNA, 3.75 microg), but the effect of the DADLE was not influenced by the selective delta-receptor antagonist naltrindole (5.0 microg). Microinjection of the kappa-opioid receptor agonist spiradoline mesylate salt (U-62066) (100 microg) had no effect on the MNP. These results suggest that the VLO is involved in opioid-induced inhibition of the MNP and the effect is mediated by mu- (but not delta- and kappa-) opioid receptors.
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Neurotrophic factors, including basic fibroblast growth factor (FGF-2) and brain-derived neurotrophic factor (BDNF) are known to be affected by exposure to stressful experiences. Here, we examine the effects of behaviorally controllable (escapable tailshock, ES) or uncontrollable (inescapable tailshock, IS) stress on the expression of FGF-2 and BDNF mRNA in subregions of the medial prefrontal cortex (mPFC) and the hippocampal formation (HF) of male Sprague-Dawley rats. ES rats were placed in Plexiglas boxes equipped with a free spinning wheel and IS rats were placed in identical boxes with the wheels fixed. ⋯ ES also produced an increase in BDNF mRNA expression in the anterior cingulate at 0 h post-stress. No effects of stressor controllability on BDNF were observed in the HF, although both ES and IS decreased BDNF mRNA in the DG. FGF-2 in the mPFC may be involved in emotional regulation ("coping") during stressful experiences.
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ATP-sensitive potassium (K(ATP)) channels are weak inward rectifiers that appear to play an important role in protecting neurons against ischemic damage. Cerebral stroke is a major health issue, and vulnerability to stroke damage is regional within the brain. Thus, we set out to determine whether K(ATP) channels protect cortical neurons against ischemic insults. ⋯ Imaging analyses of cortical slices exposed briefly to oxygen and glucose deprivation (OGD) revealed a substantial number of damaged cells (propidium iodide-labeled) in the Kir6.2(-/-) OGD group, but few degenerating neurons in the wildtype OGD group, or in the wildtype and Kir6.2(-/-) control groups. Slices from the three control groups had far more surviving cells (anti-NeuN antibody-labeled) than slices from the Kir6.2(-/-) OGD group. These findings suggest that stimulation of endogenous cortical K(ATP) channels may provide a useful strategy for limiting the damage that results from cerebral ischemic stroke.
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Persistent herpes zoster-associated pain is a significant clinical problem and an area of largely unmet therapeutic need. Progress in elucidating the underlying pathophysiology of zoster-associated pain and related co-morbidity behavior, in addition to appropriately targeted drug development has been hindered by the lack of an appropriate animal model. This study further characterizes a recently developed rat model of zoster-associated hypersensitivity and investigates (a) response to different viral strains; (b) relationship between viral inoculum concentration ('dose') and mechanical hypersensitivity ('response'); (c) attenuation of virus-associated mechanical hypersensitivity by clinically useful analgesic drugs; and (d) measurement of pain co-morbidity (anxiety-like behavior) and pharmacological intervention in the open field paradigm (in parallel with models of traumatic peripheral nerve injury). ⋯ This may reflect pain-related co-morbidity. Further, anxiety-like behavior was attenuated by acute i.p. administration of gabapentin (30 mg/kg) in nerve-injured, but not virus-infected animals. This model will prove useful in elucidating the pathophysiology of zoster-associated pain and provide a tool for pre-clinical screening of analgesic drugs.
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The involvement of cholinergic transmission in heroin self-administration and the reinstatement of heroin-seeking was examined in rats trained to nose-poke for i.v. heroin. Systemic treatment with physostigmine, an inhibitor of acetylcholinesterase, modestly reduced the acquisition and rate of heroin self-administration, and this suppression of heroin intake was reversed by pretreatment with scopolamine but not by mecamylamine. Following 10-14 days of self-administration, rats were left in the home environment for 14 days. ⋯ Inactivation of either NAc or VTA by microinjecting tetrodotoxin blocked both extinction responding and cue-induced reinstatement. These data demonstrate that cholinergic transmission influences heroin self-administration and reinstatement. Moreover, cue-induced reinstatement was inhibited by physostigmine in the NAc and potentiated by cholinergic stimulation in the VTA.