Voluntary running attenuates behavioural signs of low back pain: dimorphic regulation of intervertebral disc inflammation in male and female SPARC-null mice.

OBJECTIVE: To examine the effect of running exercise on behavioral measures of pain and intervertebral disc (IVD) inflammation in the SPARC-null mouse model. METHODS: Male and female 8-month old SPARC-null and age-matched control mice received a home cage running wheel or a control, fixed wheel for 6 months. Behavioral assays were performed to assess axial discomfort (grip test) and radiating leg pain (von Frey, acetone tests) and voluntary running was confirmed. Expression of inflammatory mediators (TNF-α, IL-1ß, IL-2, IL-10, CCL5, CXCL1, CXCL5, RANKL, M-CSF, and VEGF) in IVDs was determined. Additional inflammatory (IL-1ß, IL-1Ra, CXCR1, CXCR2) and macrophage phenotypic markers (ITGAM, CD80, CD86, CD206, Arg1) in IVDs were investigated by qPCR. RESULTS: Voluntary running attenuated behavioral measures of pain in male and female SPARC-null mice. Increases in mediators including IL-1ß, CXCL1 and CXCL5 were observed in SPARC-null compared to control IVDs. After 6 months of running, increases in M-CSF and VEGF were observed in male SPARC-null IVDs. In females, pro-inflammatory mediators, including CXCL1 and CXCL5 were downregulated by running in SPARC-null mice. qPCR analysis further confirmed the anti-inflammatory effect of running in female IVDs with increased IL-1Ra mRNA. Running induced upregulation of the macrophage marker ITGAM mRNA in males. CONCLUSIONS: Voluntary running reversed behavioral signs of pain in male and female mice and reduced inflammatory mediators in females, but not males. Thus, the therapeutic mechanism of action may be sex-specific.

ISSLS Prize in Basic science 2019: Physical activity attenuates fibrotic alterations to the multifidus muscle associated with intervertebral disc degeneration.

PURPOSE: Chronic low back pain causes structural remodelling and inflammation in the multifidus muscle. Collagen expression is increased in the multifidus of humans with lumbar disc degeneration. However, the extent and mechanisms underlying the increased fibrotic activity in the multifidus are unknown. Physical activity reduces local inflammation that precedes multifidus fibrosis during intervertebral disc degeneration (IDD), but its effect on amelioration of fibrosis is unknown. This study aimed to assess the development of fibrosis and its underlying genetic network during IDD and the impact of physical activity. METHODS: Wild-type and SPARC-null mice were either sedentary or housed with a running wheel, to allow voluntary physical activity. At 12 months of age, IDD was assessed with MRI, and multifidus muscle samples were harvested from L2 to L6. In SPARC-null mice, the L1/2 and L3/4 discs had low and high levels of IDD, respectively. Thus, multifidus samples from L2 and L4 were allocated to low- and high-IDD groups compared to assess the effects of IDD and physical activity on connective tissue and fibrotic genes. RESULTS: High IDD was associated with greater connective tissue thickness and dysregulation of collagen-III, fibronectin, CTGF, substance P, TIMP1 and TIMP2 in the multifidus muscle. Physical activity attenuated the IDD-dependent increased connective tissue thickness and reduced the expression of collagen-I, fibronectin, CTGF, substance P, MMP2 and TIMP2 in SPARC-null animals and wild-type mice. Collagen-III and TIMP1 were only reduced in wild-type animals. CONCLUSIONS: These data reveal the fibrotic networks that promote fibrosis in the multifidus muscle during chronic IDD. Furthermore, physical activity is shown to reduce fibrosis and regulate the fibrotic gene network. These slides can be retrieved under Electronic Supplementary Material.

Tracking with the mind's eye.

The two components of voluntary tracking eye-movements in primates, pursuit and saccades, are generally viewed as relatively independent oculomotor subsystems that move the eyes in different ways using independent visual information. Although saccades have long been known to be guided by visual processes related to perception and cognition, only recently have psychophysical and physiological studies provided compelling evidence that pursuit is also guided by such higher-order visual processes, rather than by the raw retinal stimulus. Pursuit and saccades also do not appear to be entirely independent anatomical systems, but involve overlapping neural mechanisms that might be important for coordinating these two types of eye movement during the tracking of a selected visual object. Given that the recovery of objects from real-world images is inherently ambiguous, guiding both pursuit and saccades with perception could represent an explicit strategy for ensuring that these two motor actions are driven by a single visual interpretation.

Analgesic synergy between opioid and α2 -adrenoceptors.

UNLABELLED: Opioid and α2 -adrenoceptor agonists are potent analgesic drugs and their analgesic effects can synergize when co-administered. These supra-additive interactions are potentially beneficial clinically; by increasing efficacy and/or reducing the total drug required to produce sufficient pain relief, undesired side effects can be minimized. However, combination therapies of opioids and α2 -adrenoceptor agonists remain underutilized clinically, in spite of a large body of preclinical evidence describing their synergistic interaction. One possible obstacle to the translation of preclinical findings to clinical applications is a lack of understanding of the mechanisms underlying the synergistic interactions between these two drug classes. In this review, we provide a detailed overview of the interactions between different opioid and α2 -adrenoceptor agonist combinations in preclinical studies. These studies have identified the spinal cord as an important site of action of synergistic interactions, provided insights into which receptors mediate these interactions and explored downstream signalling events enabling synergy. It is now well documented that the activation of both µ and δ opioid receptors can produce synergy with α2 -adrenoceptor agonists and that α2 -adrenoceptor agonists can mediate synergy through either the α2A or the α2C adrenoceptor subtypes. Current hypotheses surrounding the cellular mechanisms mediating opioid-adrenoceptor synergy, including PKC signalling and receptor oligomerization, and the evidence supporting them are presented. Finally, the implications of these findings for clinical applications and drug discovery are discussed. LINKED ARTICLES: This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Cytotoxic targeting of isolectin IB4-binding sensory neurons.

The isolectin I-B4 (IB4) binds specifically to a subset of small sensory neurons. We used a conjugate of IB4 and the toxin saporin to examine in vivo the contribution of IB4-binding sensory neurons to nociception. A single dose of the conjugate was injected unilaterally into the sciatic nerve of rats. The treatment resulted in a permanent selective loss of IB4-binding neurons as indicated by histological analysis of dorsal root ganglia, spinal cord, and skin from treated animals. Behavioral measurements showed that 7-10 days after the injection, conjugate-treated rats had elevated thermal and mechanical nociceptive thresholds. However, 21 days post-treatment the nociceptive thresholds returned to baseline levels. These results demonstrate the utility of the IB4-saporin conjugate as a tool for selective cytotoxic targeting and provide behavioral evidence for the role of IB4-binding neurons in nociception. The decreased sensitivity to noxious stimuli associated with the loss of IB4-binding neurons indicates that these sensory neurons are essential for the signaling of acute pain. Furthermore, the unexpected recovery of nociceptive thresholds suggests that the loss of IB4-binding neurons triggers changes in the processing of nociceptive information, which may represent a compensatory mechanism for the decreased sensitivity to acute pain.

Effects of peripheral nerve injury on alpha-2A and alpha-2C adrenergic receptor immunoreactivity in the rat spinal cord.

Neuropathic pain resulting from peripheral nerve injury can often be relieved by administration of alpha-adrenergic receptor antagonists. Tonic activation of alpha-adrenergic receptors may therefore facilitate the hyperalgesia and allodynia associated with neuropathic pain. It is currently unclear whether alpha2A- or alpha2c-adrenergic receptor subtypes are involved in the pro-nociceptive actions of alpha-adrenergic receptors under neuropathic conditions. We therefore investigated the effects of peripheral nerve injury on the expression of these subtypes in rat spinal cord using immunohistochemical techniques. In addition, neuropeptide Y immunoreactivity was examined as an internal control because it has previously been shown to be up-regulated following nerve injury. We observed a decrease in alpha2A-adrenergic receptor immunoreactivity in the spinal cord ipsilateral to three models of neuropathic pain: complete sciatic nerve transection, chronic constriction injury of the sciatic nerve and L5/L6 spinal nerve ligation. The extent of this down-regulation was significantly correlated with the magnitude of injury-induced changes in mechanical sensitivity. In contrast, alpha2c-adrenergic receptor immunoreactivity was only increased in the spinal nerve ligation model; these increases did not correlate with changes in mechanical sensitivity. Neuropeptide Y immunoreactivity was up-regulated in all models examined. Increased expression of neuropeptide Y correlated with changes in mechanical sensitivity. The decrease in alpha2A-adrenergic receptor immunoreactivity and the lack of consistent changes in alpha2C-adrenergic receptor immunoreactivity suggest that neither of these receptor subtypes is likely to be responsible for the abnormal adrenergic sensitivity observed following nerve injury. On the contrary, the decrease in alpha2A-adrenergic receptor immunoreactivity following nerve injury may result in an attenuation of the influence of descending inhibitory noradrenergic input into the spinal cord resulting in increased excitatory transmitter release following peripheral stimuli.

Spinal analgesic actions of the new endogenous opioid peptides endomorphin-1 and -2.

Two highly-selective mu-opioid receptor agonists, endomorphin-1 and -2, were recently purified from bovine brain and are postulated to be endogenous mu-opioid receptor ligands. We sought to determine the effects of these ligands at the spinal level in mice. Endomorphin-1 and -2 produced short acting, naloxone-sensitive antinociception in the tail flick test and inhibited the behavior elicited by intrathecally injected substance P. Both endomorphin-1 and -2 were anti-allodynic in the dynorphin-induced allodynia model. Although acute tolerance against both endomorphins developed rapidly, endomorphin-1 required a longer pretreatment time before tolerance was observed. We conclude that the endomorphins are potent spinal antinociceptive and anti-allodynic agents and that they or related compounds may prove therapeutically useful as spinal analgesics.

Screening for depression in pregnancy: characteristics of the Beck Depression Inventory.

OBJECTIVE: To determine the test characteristics of a self-report questionnaire, the Beck Depression Inventory, when used as a screening test for depression in a population of ambulatory pregnant women. METHODS: One hundred five pregnant women completed the Beck Depression Inventory and underwent a structured interview using the National Institute of Mental Health Diagnostic Interview Schedule-version III. Current depression was diagnosed according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders-III-R. A receiver operating characteristic curve was constructed for the Beck Depression Inventory score as a predictor of current depression. A table of sensitivities, specificities, predictive values, and likelihood ratios was created for various cutoff values. RESULTS: For the 105 women enrolled, the median Beck Depression Inventory score was 8.0. Twelve women (11%) were diagnosed with current depression and had a median Beck Depression Inventory score of 25.5, compared with those without current depression, who had a median score of 8.0 (P = .001). The area under the receiver operating characteristic curve was 0.9940. Using a cutoff range of greater than 16, the sensitivity of the Beck Depression Inventory to detect current depression was 0.83, the specificity was 0.89, the positive predictive value was 0.50, and the negative predictive value was 0.98. CONCLUSIONS: The Beck Depression Inventory can serve as a rapid screening test for depression during pregnancy. A higher cutoff value is required for pregnant women than is customarily used outside of pregnancy.

Detection of tracking errors by visual climbing fiber inputs to monkey cerebellar flocculus during pursuit eye movements.

The activity of cerebellar Purkinje cells was monitored in alert monkeys during visually guided smooth pursuit eye movements. The climbing fiber input evokes 'complex-spikes' which show increased firing during the contralateral phase of sinusoidal pursuit. 'Complex-spike triggered averaging' revealed that the increased firing is a visual response to the retina slip which results from inaccurate tracking. The complex-spikes in turn cause a transient reduction in the simple-spike pursuit command signal that emanates from the flocculus and this may contribute to the corrective eye movement. We postulate that the detection (and possibly the correction) of small errors in motor performance may be a general function of climbing fiber inputs to the cerebellum.

Immunofluorescence analysis of antisense oligodeoxynucleotide-mediated 'knock-down' of the mouse delta opioid receptor in vitro and in vivo.

We have previously used antisense oligodeoxynucleotides (ODN) to the cloned delta opioid receptor (DOR) to inhibit the antinociceptive response to spinally administered delta opioid receptor selective agonists in mice. Here we have examined the effect of DOR antisense ODN treatment on the level of DOR expressed in NG 108-15 cells and the spinal cord, through immuno-fluorescence microscopy, to determine the efficiency and selectivity of the antisense ODN-mediated "knock-down' of the DOR in these tissues. Antisense ODN, but not mismatch control, treatment resulted in a significant reduction in DOR immunoreactivity (-ir) in NG 108-15 cells and spinal cord. Thus, the inhibition of antinociceptive response to intrathecal delta selective agonists by DOR antisense ODN correlates with the loss of DOR-ir in the superficial layers of the dorsal horn of the spinal cord.

Bilateral nodular sarcoid choroiditis with vitreous haemorrhage.

A 21-year-old black man with presumed systemic sarcoidosis had bilateral choroidal nodules, unilateral retinal neovascularisation and vitreous haemorrhage, and non-caseating granulomas on percutaneous liver biopsy. The choroidal nodules were serially documented by fundus photography and fluorescein angiography over a 22-month period. Fluorescein angiography was more accurate than ophthalmoscopy in demonstrating choroidal inflammation. The choroidal nodules resolved after systemic corticosteroid therapy. A vitreous haemorrhage occurred probably secondary to neovascularisation related to occlusion of an inferotemporal branch vein. The non-resolving vitreous haemorrhage and associated traction retinal detachment were treated with vitrectomy and membrane sectioning.

Contrast affects flicker and speed perception differently.

We have previously shown that contrast affects speed perception, with lower-contrast, drifting gratings perceived as moving slower. In a recent study, we examined the implications of this result on models of speed perception that use the amplitude of the response of linear spatio-temporal filters to determine speed. In this study, we investigate whether the contrast dependence of speed can be understood within the context of models in which speed estimation is made using the temporal frequency of the response of linear spatio-temporal filters. We measured the effect of contrast on flicker perception and found that contrast manipulations produce opposite effects on perceived drift rate and perceived flicker rate, i.e., reducing contrast increases the apparent temporal frequency of counterphase modulated gratings. This finding argues that, if a temporal frequency-based algorithm underlies speed perception, either flicker and speed perception must not be based on the output of the same mechanism or contrast effects on perceived spatial frequency reconcile the disparate effects observed for perceived temporal frequency and speed.

Combining speed information across space.

We used speed discrimination tasks to measure the ability of observers to combine speed information from multiple stimuli distributed across space. We compared speed discrimination thresholds in a classical discrimination paradigm to those in an uncertainty/search paradigm. Thresholds were measured using a temporal two-interval forced-choice design. In the discrimination paradigm, the n gratings in each interval all moved at the same speed and observers were asked to choose the interval with the faster gratings. Discrimination thresholds for this paradigm decreased as the number of gratings increased. This decrease was not due to increasing the effective stimulus area as a control experiment that increased the area of a single grating did not show a similar improvement in thresholds. Adding independent speed noise to each of the n gratings caused thresholds to decrease at a rate similar to the original no-noise case, consistent with observers combining an independent sample of speed from each grating in both the added- and no-noise cases. In the search paradigm, observers were asked to choose the interval in which one of the n gratings moved faster. Thresholds in this case increased with the number of gratings, behavior traditionally attributed to an input bottleneck. However, results from the discrimination paradigm showed that the increase was not due to observers' inability to process these gratings. We have also shown that the opposite trends of the data in the two paradigms can be predicted by a decision theory model that combines independent samples of speed information across space. This demonstrates that models typically used in classical detection and discrimination paradigms are also applicable to search paradigms. As our model does not distinguish between samples in space and time, it predicts that discrimination performance should be the same regardless of whether the gratings are presented in two spatial intervals or two temporal intervals. Our last experiment largely confirmed this prediction.

Spatial layout affects speed discrimination.

We address a surprising result in a previous study of speed discrimination with multiple moving gratings: discrimination thresholds decreased when the number of stimuli was increased, but remained unchanged when the area of a single stimulus was increased [Verghese & Stone (1995). Vision Research, 35, 2811-2823]. In this study, we manipulated the spatial- and phase relationship between multiple grating patches to determine their effect on speed discrimination thresholds. In a fusion experiment, we merged multiple stimulus patches, in stages, into a single patch. Thresholds increased as the patches were brought closer and their phase relationship was adjusted to be consistent with a single patch. Thresholds increased further still as these patches were fused into a single patch. In a fission experiment, we divided a single large patch into multiple patches by superimposing a cross with luminance equal to that of the background. Thresholds decreased as the large patch was divided into quadrants and decreased further as the quadrants were maximally separated. However, when the cross luminance was darker than the background, it was perceived as an occluder and thresholds, on average, were unchanged from that for the single large patch. A control experiment shows that the observed trend in discrimination thresholds is not due to the differences in perceived speed of the stimuli. These results suggest that the parsing of the visual image into entities affects the combination of speed information across space, and that each discrete entity effectively provides a single independent estimate of speed.

Human heading estimation during visually simulated curvilinear motion.

Recent studies have suggested that humans cannot estimate their direction of forward translation (heading) from the resulting retinal motion (flow field) alone when rotation rates are higher than approximately 1 deg/sec. It has been argued that either oculomotor or static depth cues are necessary to disambiguate the rotational and translational components of the flow field and, thus, to support accurate heading estimation. We have re-examined this issue using visually simulated motion along a curved path towards a layout of random points as the stimulus. Our data show that, in this curvilinear motion paradigm, five of six observers could estimate their heading relatively accurately and precisely (error and uncertainty < approximately 4 deg), even for rotation rates as high as 16 deg/sec, without the benefit of either oculomotor or static depth cues signaling rotation rate. Such performance is inconsistent with models of human self-motion estimation that require rotation information from sources other than the flow field to cancel the rotational flow.

A model of self-motion estimation within primate extrastriate visual cortex.

Perrone [(1992) Journal of the Optical Society of America A, 9, 177-194] recently proposed a template-based model of self-motion estimation which uses direction- and speed-tuned input sensors similar to neurons in area MT of primate visual cortex. Such an approach would generally require an unrealistically large number of templates (five continuous dimensions). However, because primates, including humans, have a number of oculomotor mechanisms which stabilize gaze during locomotion, we can greatly reduce the number of templates required (two continuous dimensions and one compressed and bounded dimension). We therefore refined the model to deal with the gaze-stabilization case and extended it to extract heading and relative depth simultaneously. The new model is consistent with previous human psychophysics and has the emergent property that its output detectors have similar response properties to neurons in area MST.

Human speed perception is contrast dependent.

When two parallel gratings moving at the same speed are presented simultaneously, the lower-contrast grating appears slower. This misperception is evident across a wide range of contrasts (2.5-50%) and does not appear to saturate (e.g. a 50% contrast grating appears slower than a 70% contrast grating moving at the same speed). On average, a 70% contrast grating must be slowed by 35% to match a 10% contrast grating moving at 2 degrees/sec (N = 6). Furthermore, the effect is largely independent of the absolute contrast level and is a quasi-linear function of log contrast ratio. A preliminary parametric study shows that, although spatial frequency has little effect, relative orientation is important. Finally, the misperception of relative speed appears lessened when the stimuli to be matched are presented sequentially.

Human motion perception and smooth eye movements show similar directional biases for elongated apertures.

Although numerous studies have examined the relationship between smooth-pursuit eye movements and motion perception, it remains unresolved whether a common motion-processing system subserves both perception and pursuit. To address this question, we simultaneously recorded perceptual direction judgments and the concomitant smooth eye-movement response to a plaid stimulus that we have previously shown generates systematic perceptual errors. We measured the perceptual direction biases psychophysically and the smooth eye-movement direction biases using two methods (standard averaging and oculometric analysis). We found that the perceptual and oculomotor biases were nearly identical, suggesting that pursuit and perception share a critical motion processing stage, perhaps in area MT or MST of extrastriate visual cortex.

Speed estimates from grating patches are not contrast-normalized.

We have previously shown that the perceived speed of a moving grating depends upon its contrast, with lower-contrast patterns appearing to move more slowly than otherwise identical higher-contrast patterns. To explain this finding while remaining consistent with the findings of McKee, Silverman and Nakayama [(1986) Vision Research, 26, 609-619], we proposed that this misperception might arise from a modified version of the contrast-normalization procedure, envisaged by Adelson and Bergen [(1986) The extraction of spatio-temporal energy in human and machine vision (pp. 135-139). Charleston, S.C.: IEEE Computer Society] as a necessary second stage of motion-energy models of human motion processing. Specifically, our previous results might be explained if the two gratings to be compared interfered with each other's normalization. To test this hypothesis we performed two experiments. Experiment 1 demonstrates that the contrast effects persist even when two grating patches to be compared are presented up to 5 sec apart so that they would not be expected to bias each other's normalization. Experiment 2 shows that the contrast effects are unchanged when the two grating patches are surrounded by a range of patterns whose contrast would be expected to interfere with any normalization process. These two results allow the rejection of the contrast-normalized motion-energy hypothesis as an explanation of human speed perception. We discuss the consequences of these results on models of speed processing in the human visual system.

Effect of contrast on the perceived direction of a moving plaid.

We performed a series of experiments examining the effect of contrast on the perception of moving plaids. This was done to test the hypothesis put forth by Adelson and Movshon (1982) that the human visual system determines the direction of a moving plaid in a two-staged process: decomposition into component motion followed by application of the intersection of constraints rule. Although there is recent evidence that the first tenet of their hypothesis is correct, i.e. that plaid motion is initially decomposed into the motion of the individual grating components (Movshon, Adelson, Gizzi & Newsome, 1986; Welch, 1989), the nature of the second-stage combination rule has not as yet been established. We found that when the gratings within the plaid are of different contrast, the perceived direction is not predicted by the intersection of constraints rule. There is a strong (up to 20 deg) bias in the direction of the higher-contrast grating. A revised model, which incorporates a contrast-dependent weighting of perceived grating speed as observed for 1-D patterns (Thompson, 1982), can quantitatively predict most of our results. We discuss our results in the context of various models of human visual motion processing and of physiological responses of neurons in the primate visual system.