Pain
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In response to concerns over the clinical relevance of analgesic testing paradigms which involve acute nociceptive stimuli, the present research examined the utility of the conditioned place preference (CPP) paradigm as a novel approach for determination of analgesic drug efficacy against chronic nociception. Rats display preferences for environments that have been previously paired with positively reinforcing drugs; whether place preference to the negatively reinforcing effects of analgesic drugs in an animal model of chronic pain occurs is yet unknown. The present research sought to determine whether animals experiencing chronic pain would display a place preference for an environment paired with analgesic drug treatment. ⋯ Indomethacin failed to produced place preference in either inflamed or non-inflamed groups. These data demonstrate that the negatively reinforcing properties of analgesic drugs can be assessed via the CPP paradigm. In addition, this paradigm offers greater clinical relevance as animals determine drug efficacy without the involvement of high-intensity, phasic nociceptive stimulation.
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In this study we examined the effect of partial sciatic nerve ligation (PSNL) on the receptive field size, the baseline firing rate (BFR) and the response of spinal dorsal horn (DH) neurons to mechanical stimulation. In addition, we tested the effect of adenosine agonist, 5'-N-ethylcarboxamide-adenosine (NECA), and the adenosine antagonist caffeine on these parameters. Adult male Sprague-Dawley animals were used. ⋯ The mean receptive field size (RFS) of neurons (both ipsilateral and contralateral to the ligation) in the operated animals was significantly larger than the RFS of unoperated animals (right side: 180 +/- 2.8 mm2 compared to 66 +/- 2.3 mm2; left side: 93 +/- 31 compared to 65 +/- 21). Twenty-four percent of all neurons in the operated group had bilateral receptive fields; in contrast, only 3% of the neurons in the control animals showed bilateral receptive fields. To examine the effects of adenosine agonist and antagonist, NECA and caffeine were applied next to the recording electrode.(ABSTRACT TRUNCATED AT 250 WORDS)
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Medullary on-cell activity during tail-flick inhibition produced by heterotopic noxious stimulation.
Reflex responses and neuronal excitation elicited by noxious stimuli applied to a given body site can be inhibited by application of noxious stimulation to another, even distant body region. Such heterotopic noxious stimulation (HNS) has been proposed to act via 'diffuse noxious inhibitory controls' (DNIC) which involve supraspinal components. The so-called on-cells of the rostral ventromedial medulla (RVM) in rats are thought to facilitate nociceptive transmission. ⋯ Such HNS elicited strong activation of on-cells, followed by depression even when HNS continued. When this depression was intense, tail-heating failed to elicit vigorous on-cell firing, and TF was retarded or abolished. These results are compatible with the hypothesis that antinociception elicited by HNS involves depression of on-cell firing and hence lack of facilitation of nociceptive transmission.
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Randomized Controlled Trial Clinical Trial
Long-term results of cervical epidural steroid injection with and without morphine in chronic cervical radicular pain.
To evaluate the long-term effectiveness of a single cervical epidural steroid injection (CESI) performed with or without morphine, 24 patients, without need of surgery, but suffering for more than 12 months from cervical radicular pain, were included in a prospective and randomised study. The cervical epidural space was injected (C7-D1; 18-ga needle) with an increasing volume (10 ml maximum) of isotonic saline solution to exacerbate the patient's radicular pain. The patients were then randomly allocated to 2 groups: the steroid group (group S, n = 14) received an equivalent volume of 0.5% lidocaine plus triamcinolone acetonide (10 mg/ml) and the steroid plus morphine group (group S + M, n = 10) received the same combination plus 2.5 mg of morphine sulphate. ⋯ Despite observing a better transient improvement the day after CESI in the S + M group, long-term results did not differ. The success rate was 78.5% in group S and 80% in group S + M providing pain relief of 86.8 +/- 14.7% and 86.9 +/- 17.9%, respectively. Pain relief remained stable with time (mean follow-up: 43 +/- 18.1 months).(ABSTRACT TRUNCATED AT 250 WORDS)
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Nerve lesions producing extensive axonal loss can induce painful hyperalgesic states in man. The affect of axonal regeneration and end-organ reinnervation on hyperalgesia and pain is controversial. This study used two axonotmetic models, the sciatic crush injury (CI) and the sciatic chronic constrictive injury (CCI), to investigate the affects of nerve regeneration and reinnervation on hyperalgesia and presumed painful behavior in rats. ⋯ Motor function recovery occurred primarily over days 23-59 post-ligature. During this prolonged period of motor function recovery there was a resolution of the sciatic-mediated plantar surface heat hyperalgesia and the saphenous-mediated heat ANH. The above data support the hypothesis that the successful regeneration of distal axons after axonotmetic lesions can initiate the resolution of neuropathic hyperalgesia.