Pain
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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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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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The communication of pain requires a sufferer to encode and transmit the experience and an observer to decode and interpret it. Rosenthal's (1982) model of communication was applied to an analysis of the role of facial expression in the transmission of pain information. Videotapes of patients with shoulder pain undergoing a series of movements of the shoulder were shown to a group of 5 judges. ⋯ The results indicated that although observers can make coarse distinctions among patients' pain states, they (1) are not especially sensitive, and (2) are likely to systematically downgrade the intensity of patients' suffering. Moreover, observers appear to make insufficient use of information that is available in patients' facial expression. Implications of the findings for pain patients and for training of health-care workers are discussed as are directions for future research.
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Comparative Study
Spinal nociceptive transmission in the spontaneously hypertensive and Wistar-Kyoto normotensive rat.
Background and noxious heat-evoked responses of wide-dynamic-range (WDR) and high-threshold (HT) lumbosacral spinal dorsal horn neurons were recorded in spontaneously hypertensive rats (SHRs), Wistar-Kyoto normotensive rats (WKYs), lifetime captopril-treated SHRs, SHRs with bilateral cervical vagotomy, SHRs with bilateral sino-aortic deafferentation (SAD), and SHRs with either a single or repeated administration of naloxone methobromide (NMB). Stimulus-response functions (SRFs) were generated for neurons using 15 sec of heating of the foot at temperatures ranging from 38 to 52 degrees C. Comparisons were made of neuronal response thresholds, slopes of the SRFs, mean discharge frequency during heat stimulation, arterial blood pressure (ABP), and heart rate (HR). ⋯ However, repeated administration of NMB in SHRs resulted in a parallel, leftward shift in SRFs of both WDR and HT neurons. In all strains and treatments studied, there were no significant differences in background activities of these neurons that might contribute to the observed outcomes. In conclusion, the hypoalgesia reported in human essential hypertensives and animals with chronic hypertension may be due to a significant attenuation in spinal nociceptive transmission.(ABSTRACT TRUNCATED AT 400 WORDS)