Streptococcus equi Detection Polymerase Chain Reaction Assay for Equine Nasopharyngeal and Guttural Pouch Wash Samples.

BACKGROUND: Bacterial culture and polymerase chain reaction (PCR) assays for the detection of Streptococcus equi in nasopharyngeal washes (NPW) and guttural pouch lavage (GPL) samples have low sensitivity. In human diagnostics, processing of samples with flocked swabs has improved recovery rates of bacterial agents because of improved surface area and elution factors. HYPOTHESIS: For S. equi subsp. equi (S. equi) detection in NPW and GPL samples we hypothesized that: direct-PCR would be more reliable than flocked swab culture (FS culture); flocked swab PCR (FS-PCR) would be equivalent to direct-PCR; and FS culture would be more reliable than traditional culture. SAMPLES: A total of 193 samples (134 NPW and 59 GPL) from 113 horses with either suspected S. equi infection, convalescing from a known S. equi infection, or asymptomatic horses screened for S. equi. METHODS: Prospective study. Samples were submitted for S. equi direct-PCR. Using logistic regression, direct-PCR (gold standard) was compared to FS culture, traditional culture, and FS-PCR also performed. RESULTS: Direct-PCR was statistically more sensitive than FS-PCR, FS culture, and traditional culture (P < .001). All methods had sensitivities <70% relative to the direct-PCR. FS culture had a similar sensitivity relative to traditional culture. The odds of GPL samples being positive on direct-PCR (P = .030) and FS-PCR were greater than those for NPW samples (P = .021). CONCLUSIONS AND CLINICAL IMPORTANCE: Use of flocked swabs during laboratory preprocessing did not improve detection of S. equi via either PCR or bacterial culture from samples. Direct-PCR is the preferred method of detection of S. equi.

Opioid antagonists and antisera to endogenous opioids increase the nociceptive response to formalin: demonstration of an opioid kappa and delta inhibitory tone.

The present experiments explored the role of endogenous opioids in the behavioral response to a formalin-induced nociceptive stimulus in the rat. Flinching was taken as a measure of the intensity of the nociceptive stimulus after the administration of formalin into the dorsal surface of the paw of control animals, or in animals receiving i.p. administration of receptor-selective doses of opioid antagonists including naloxone, naltrindole (delta opioid antagonist), nor-binaltorphimine (kappa opioid antagonist) or beta-funaltrexamine (mu opioid antagonist). Additionally, antisera to [Leu5]enkephalin, [Met5]enkephalin and dynorphin A (1-13) (dynorphin) were administered intrathecally before formalin to explore the contribution of endogenous opioids in modulation of the flinching response. Formalin-induced flinching was increased significantly by naloxone, and receptor selective doses of naltrindole and nor-binaltorphimine, but not beta-funaltrexamine. Additionally, antisera to [Leu5]enkephalin and dynorphin also resulted in a significant increase in formalin-induced flinching, whereas antisera to [Met5]enkephalin had no effect. On the basis of significant increases in formalin-induced flinching produced by 1) receptor-selective doses of delta and kappa, but not mu, opioid antagonists and 2) antisera to [Leu5]enkephalin and dynorphin A, but not [Met5]enkephalin, these data suggest the presence of an opioid inhibitory tone which acts to limit the intensity of the pain signal. This tone appears to be mediated via activation of delta and kappa receptors, possibly by a [Leu5]enkephalin- and dynorphin-like substance, respectively.

Naloxone causes apparent antinociception and pronociception simultaneously in the rat paw formalin test.

Naloxone is known to decrease, increase or have no effect on nociceptive thresholds. Here, using two commonly accepted pain-related behaviors (licking and flinching) associated with injection of noxious formalin into a hind paw in rats, naloxone (0.1-1 mg/kg s.c.) simultaneously decreases and increases nociceptive responding in the same animal. Licking, which is reduced by naloxone, is enhanced by low doses but attenuated by high doses of morphine. However, although licking initially increases with a rise in formalin concentration, at higher concentrations the time spent licking the injected paw actually declines. By contrast, flinching, which is enhanced by naloxone, is only antagonized by morphine and increases linearly with formalin concentration. Both actions of naloxone can be interpreted in terms of a leftward shift in the formalin concentration-response curves. This study demonstrates that naloxone can increase formalin-induced flinching while simultaneously decreasing licking behavior. These findings suggest that, on its own, an unexpected decrease in a single nociceptive index may be an inadequate criterion for demonstrating antinociception.

Effects of intracerebroventricular beta-funaltrexamine on mu and delta opioid receptors in the rat: dichotomy between binding and antinociception.

The effects of intracerebroventricular (i.c.v.) beta-funaltrexamine (beta-FNA) pretreatment at -24 or -6 h were studied on mu and delta opioid receptor binding and on antinociception produced by i.c.v. morphine in rats. Mu and delta opioid receptor binding in brain membrane preparations was performed with [3H][D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO) and [3H][D-Pen2,D-Pen5]enkephalin (DPDPE) as radiolabeled ligands, respectively. Effects of i.c.v. beta-FNA (24 h) on mu and delta binding depended on dosage. For [3H]DAGO binding, 3 micrograms beta-FNA did not affect either the Kd or Bmax, whereas 10 micrograms increased the Kd without changing the Bmax. beta-FNA pretreatment for 24 h did not alter [3H]DPDPE binding at 3 micrograms; at 10 micrograms, the Kd was increased with no change in the Bmax. Pretreatment with 10 micrograms beta-FNA for 6 h gave similar results to the 24-h treatment in mu binding, but did not change delta binding. When mu binding was performed on various brain regions, pretreatment with 10 micrograms beta-FNA for 24 h increased the Kd in all regions studied (the periaqueductal gray, thalamus, striatum and cortex). However, this pretreatment decreased the Bmax only in the periaqueductal gray (by 22%) and cortex (by 14%). Pretreatment of rats with beta-FNA (3 or 10 micrograms at -24 h), which by itself caused some hyperalgesia, greatly antagonized the antinociceptive effect of morphine (10 micrograms i.c.v.) in the hot-plate test. Our work with beta-FNA has revealed an apparent discrepancy between binding and behavioral results. This dichotomy may, in part, be the result of the limited distribution of beta-FNA to the periventricular area.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurogenic and tissue-mediated components of formalin-induced edema: evidence for supraspinal regulation.

Injection of formalin into a hind paw of rats produces localized inflammation and pain. The nociceptive effect of formalin, recorded as flinching/shaking of the injected paw, is biphasic. The present study shows that formalin-induced inflammation and edema (assessed by measurement of paw volume up to 24 h post-injection) is also biphasic, an early neurogenic component being followed by a later tissue-mediated response. Rapid initiation of edema is closely related to early phase nociception and is dependent on activity in primary afferent neurons and axon reflexes, but not on transmission of the noxious stimulus and the perception of pain itself. The major site responsible for down-regulating the inflammatory response, particularly in the later stages when tissue-mediated components are most heavily involved, appears to be located supraspinally. Down-regulation occurs principally by means of descending neuronal pathways but may also involve a secondary humoral component. The perhaps surprising dependence on neuronal mechanisms which this study demonstrates promotes spinal and peripheral sites as potential therapeutic targets in certain inflammatory conditions.

Standardization of the rat paw formalin test for the evaluation of analgesics.

Administration of 5% formalin into the rat or guinea pig hind paw evokes two spontaneous responses: flinching/shaking and licking/biting of the injected paw. The temporal and behavioral characteristics of these objective endpoints are described. Additionally, several practical suggestions aimed at standardizing this test for the evaluation of analgesics are presented. The early/acute and late/tonic (0-10 and 20-35 min post-formalin, respectively) phases of flinching were used to quantitate antinociception in the rat. PD 117302, the kappa selective agonist, was three times more potent than morphine against tonic flinching after SC administration. Formalin may therefore be a noxious stimulus of choice in the evaluation of kappa agonists. Morphine was only twice as potent against tonic flinching as against acute flinching or the tail-dip reflex to water (50 degrees C). In contrast, PD 117302 was 27 times less potent on early phase and was inactive in the tail-dip test. Thus, while morphine is essentially equipotent across tests, PD 117302 shows a spectrum of activity with impressive potency and efficacy being obtained against tonic pain. Kappa receptors may therefore be prominently involved in tonic pain states. Aspirin given orally was not consistently antinociceptive in either phase of the formalin test. Spinal transection completely abolished late phase responding but only partly attenuated flinching in the early phase. This suggests that the relative involvement of spinal (as opposed to supraspinal) processing of noxious inputs may, at least in part, be a function of stimulus intensity and underlie the differences in antinociceptive potency observed in this work.