Comparison of Threshold and Tolerance Nociceptive Withdrawal Reflexes in Horses

The nociceptive withdrawal reflex (NWR) is used to investigate nociception in horses. The NWR threshold is a classical model endpoint. The aims of this study were to determine NWR tolerance and to compare threshold and tolerance reflexes in horses. In 12 horses, the NWR was evoked through electrical stimulation of the digital nerve and recorded via electromyography from the deltoid. Behavioral reactions were scored from 0 to 5 (tolerance). First, the individual NWR threshold was defined, then stimulation intensity was increased to tolerance. The median NWR threshold was 7.0 mA, whereas NWR tolerance was 10.7 mA. Upon visual inspection of the records, two main reflex components R1 (median latency 44 ms) and R2 (median latency 81 ms) were identified at threshold. Increasing stimulation intensity to tolerance led to a significant increase in the amplitude and duration of R1 and R2, whereas their latency decreased. At tolerance, a single burst of early, high-amplitude reflex activity, with a median latency of 39 ms, was detected in 15 out of 23 stimulations (65%). The results of this study suggest that (1) it is feasible to determine NWR tolerance in horses and (2) high-intensity stimuli initiate ultrafast bursts of reflex activity, which is well known in practice and has now been quantified using the NWR model.

Preserved Thermal Pain in 3xTg-AD Mice With Increased Sensory-Discriminative Pain Sensitivity in Females but Affective-Emotional Dimension in Males as Early Sex-Specific AD-Phenotype Biomarkers

The increase of the aging population, where quite chronic comorbid conditions are associated with pain, draws growing interest across its investigation and the underlying nociceptive mechanisms. Burn injuries associated problems might be of relevance in the older adult’s daily life, but in people with dementia, exposure to high temperatures and heat sources poses a significantly increased risk of burns. In this brief report, the hind paws and tail pain withdrawal reflexes and the emotional responses to thermal nociception in 3xTg-AD mice were characterized for the first time in the plantar test and compared to their non-transgenic (NTg) counterparts. We studied a cohort of male and female 3xTg-AD mice at asymptomatic (2 months), early (6 months), middle (9 months), and advanced (12 and 15 months) stages of the disease and as compared to sex- and age-matched NTg control mice with normal aging. At 20 and 40W intensities, the sensorial-discriminative thresholds eliciting the withdrawal responses were preserved from asymptomatic to advanced stages of the disease compared to NTg counterparts. Moreover, 3xTg-AD females consistently showed a greater sensory-discriminative sensitivity already at premorbid ages, whereas increased emotionality was shown in males. False-negative results were found in “blind to sex and age” analysis, warning about the need to study sexes independently. The current results and previous report in cold thermal stimulation provide two paradigms unveiling sex-specific early AD-phenotype nociceptive biomarkers to study the mechanistic underpinnings of sex-, age- and AD-disease-dependent thermal pain sensitivity.

Effect of Sedation on the Neurological Examination of the Patellar and Withdrawal Reflexes in Healthy Dogs

Introduction: Pain, temperament, fear, and anxiety can prevent safe and accurate evaluation of common neurologic reflexes in dogs. When sedation is used it is unknown how the neurological examination, and specifically patellar and withdrawal reflexes are affected, and, if present, how long any effect might last. The purpose of this study is to investigate the effect of sedation on the evaluation of select common limb spinal reflexes in healthy dogs.Material and Methods: Fourteen healthy dogs with normal neurologic exams were included. After placing joint landmarks, patellar reflex and pelvic and thoracic limb withdrawal reflexes were tested. Joint angles were measured, obtaining reflex angle endpoints, change in angle, and change in time to reflex completion. These measurements were recorded at different time points: prior to sedation (awake timepoint), 15 and 30 min following administration of standardized sedation protocol of dexmedetomidine and butorphanol, and 15 and 30 min following administration of a standardized reversal agent, atipamazole.Results: For patellar reflex, the stifle end angle increased from 91.5 to 108.55 degrees (p < 0.0001) 15 min following sedation, and remained increased at 104.5 degrees (p < 0.0001) 30 min following sedation. Stifle change in angle increased from 9.6 to 24.4 degrees (p < 0.0001) 15 min following sedation, and remained increased at 20.85 degrees (p < 0.0001) and 11 degrees (p = 0.012) at 30 min sedation and 15 min reversal. Tarsal joint in pelvic withdrawal and elbow in thoracic withdrawal reflexes did not differ in at any timepoint of sedation or reversal when compared with the awake timepoint, for end angle or change in angle. The increases in end angle and change in angle for patellar reflex generated a change in time for patellar reflex from 0.12 s (awake) to 0.129 s (15 min sedation) which was statistically significant (p = 0.041). Change in time did not differ for pelvic withdrawal or thoracic withdrawal.Discussion/Conclusions: Reflexes were elicited in all dogs under sedation. Sedation does not affect the evaluation of the withdrawal reflex on any limb but improves the visualization of the patellar reflex in this group of neurologically normal dogs.

First Documented Cases of Canine Neuroangiostrongyliasis Due to Angiostrongylus cantonensis in Hawaii

ABSTRACT Two young dogs domiciled in Honolulu, Hawaii, were presented in November and December 2018 (respectively) for spinal hyperesthesia, hindlimb weakness, and proprioceptive ataxia. Both dogs had neurologic findings referable to spinal cord disease. Both dogs had a combination of lower motor neuron signs (reduced muscle mass, decreased withdrawal reflexes, low tail carriage) and long tract signs (conscious proprioceptive deficits, crossed extensor response, increased myotatic reflexes). Peripheral eosinophilia was present in the second case, but hematology and serum biochemistries were otherwise unremarkable. Plain radiographs and computed tomography scans ± contrast were unremarkable. Cerebrospinal fluid (CSF) from both patients demonstrated eosinophilic pleocytosis, and real-time polymerase chain reaction testing demonstrated Angiostrongylus cantonensis deoxyribonucleic acid in CSF, confirming a diagnosis of neuroangiostrongyliasis. Treatment included glucocorticoid therapy, ± anthelmintic (fenbendazole). Both dogs made a complete recovery. These are the first confirmed cases of autochthonous neuroangiostrongyliasis in canine patients in the United States and the first dogs anywhere to be diagnosed definitively with A cantonensis infection based on real-time polymerase chain reaction testing of CSF. A clinician examining a patient with severe spinal hyperesthesia and a combination of upper and lower motor signs should consider A cantonensis as a differential, especially in endemic areas.

Anesthetic Effects of Intramuscular Alfaxalone–Ketamine in Naked Mole Rats (Heterocephalus glaber)

In this study, adult intact male and female (n = 10) naked mole rats (Heterocephalus glaber) were anesthetized by using a combination of ketamine (20 mg/kg IM), and alfaxalone (4.0 mg/kg IM). Induction and recovery times were recorded. Vital parameters, including heart rate, respiratory rate, and reflexes, were monitored every 5 min during the anesthetic period. Anesthetic induction was smooth and rapid. Induction time was significantly longer in male rats (median, 325 s; range, 180 to 385 s) than in females (median, 145 s; range, 118 to 180 s). In addition, overall duration of loss of righting reflex was shorter in male mole rats (median, 50 min; range, 36 to 65 min) than females (median, 70 min; range, 60 to 85 min). Males largely had intact withdrawal reflexes, whereas females showed variable loss of both forelimb and hindlimb withdrawal reflexes. Neither recovery time (mean ± 1 SD, 16 ± 13 min) nor vital parameters differed between sexes. None of animals showed any anesthesia-related adverse responses. According to these findings, intramuscular AK is a safe and effective protocol that provides brief, light anesthesia in male naked mole rats and deeper anesthesia in females. We recommend adding analgesics when this AK protocol is used for pain-inducing or invasive procedures, and further studies evaluating higher doses and different combinations are indicated.

Hindlimb motor responses to unilateral brain injury: spinal cord encoding and left-right asymmetry

Mechanisms of motor deficits (e.g. hemiparesis and hemiplegia) secondary to stroke and traumatic brain injury remain poorly understood. In early animal studies, a unilateral lesion to the cerebellum produced postural asymmetry with ipsilateral hindlimb flexion that was retained after complete spinal cord transection. Here we demonstrate that hindlimb postural asymmetry in rats is induced by a unilateral injury of the hindlimb sensorimotor cortex, and characterize this phenomenon as a model of spinal neuroplasticity underlying asymmetric motor deficits. After cortical lesion, the asymmetry was developed due to the contralesional hindlimb flexion and persisted after decerebration and complete spinal cord transection. The asymmetry induced by the left-side brain injury was eliminated by bilateral lumbar dorsal rhizotomy, but surprisingly, the asymmetry after the right-side brain lesion was resistant to deafferentation. Pancuronium, a curare-mimetic muscle relaxant, abolished the asymmetry after the right-side lesion suggesting its dependence on the efferent drive. The contra- and ipsilesional hindlimbs displayed different musculo-articular resistance to stretch after the left but not right-side injury. The nociceptive withdrawal reflexes evoked by electrical stimulation and recorded with EMG technique were different between the left and right hindlimbs in the spinalized decerebrate rats. On this asymmetric background, a brain injury resulted in greater reflex activation on the contra- versus ipsilesional side; the difference between the limbs was higher after the right-side brain lesion. The unilateral brain injury modified expression of neuroplasticity genes analysed as readout of plastic changes, as well as robustly impaired coordination of their expression within and between the ipsi- and contralesional halves of lumbar spinal cord; the effects were more pronounced after the left side compared to the right-side injury. Our data suggest that changes in the hindlimb posture, resistance to stretch and nociceptive withdrawal reflexes are encoded by neuroplastic processes in lumbar spinal circuits induced by a unilateral brain injury. Two mechanisms, one dependent on and one independent of afferent input may mediate asymmetric hindlimb motor responses. The latter, deafferentation resistant mechanism may be based on sustained muscle contractions which often occur in patients with central lesions and which are not evoked by afferent stimulation. The unusual feature of these mechanisms is their lateralization in the spinal cord.

An amygdalar neural ensemble that encodes the unpleasantness of pain

Pain is an unpleasant experience. How the brain’s affective neural circuits attribute this aversive quality to nociceptive information remains unknown. By means of time-lapse in vivo calcium imaging and neural activity manipulation in freely behaving mice encountering noxious stimuli, we identified a distinct neural ensemble in the basolateral amygdala that encodes the negative affective valence of pain. Silencing this nociceptive ensemble alleviated pain affective-motivational behaviors without altering the detection of noxious stimuli, withdrawal reflexes, anxiety, or reward. Following peripheral nerve injury, innocuous stimuli activated this nociceptive ensemble to drive dysfunctional perceptual changes associated with neuropathic pain, including pain aversion to light touch (allodynia). These results identify the amygdalar representations of noxious stimuli that are functionally required for the negative affective qualities of acute and chronic pain perception.

Intense and sustained pain reduces cortical responses to auditory stimuli: implications for the interpretation of Heterotopic Noxious Conditioning Stimulation in humans

Phasic pain stimuli are inhibited when they are applied concomitantly with a conditioning tonic stimulus at another body location (Heterotopic Noxious Conditioning Stimulation, HNCS). While this effect is thought to rely on a spino-bulbo-spinal mechanism in animals (Diffuse Noxious Inhibitory Controls, DNIC), the underlying neurophysiology in humans may further involve other pathways. In this study, we investigated the role of supraspinal mechanisms in HNCS by presenting auditory stimuli during a conditioning tonic painful stimulus (the Cold Pressor Test, CPT). Considering that auditory stimuli are not conveyed through the spinal cord, any changes in brain responses to auditory stimuliduringHNCS can be ascribed entirely to supraspinal mechanisms. High-density electroencephalography (EEG) was recorded during HNCS and auditory stimuli were administered in three blocks,before,during, andafterHNCS. Nociceptive Withdrawal Reflexes (NWRs) were recorded at the same time points to investigate spinal processing. Our results showed that AEPs were significantly reducedduringHNCS. Moreover, the amplitude of the NWR was significantly diminishedduringHNCS in most participants. Given that spinal and supraspinal mechanisms operate concomitantly during HNCS, the possibility of isolating their individual contributions to DNIC-like effects in humans is questionable. We conclude that the net effects of HCNS cannot be measured independently from attentional/cognitive influences.

Screening of analgesic activity of Phoenix sylvestris leaves in rodents

Aim: The present study evaluated the central and peripheral analgesic activity of methanolic leaf extract of Phoenix sylvestris (PSLME) in swiss albino mice. Method: Peripheral and central analgesic activity was evaluated by tail immersion and acetic acid writhing in swiss albino mice. Dextropropoxyphene was used as a standard drug in the dose of 65mg/kg body weight in both models. PSLME was tested at 100 and 500mg/kg dose level. Results: The result revealed that methanolic extract exhibit 48% and 40.5% writhing inhibition at 500 and 100 mg/kg doses whereas ~30% tail withdrawal reflexes inhibition at 500mg/kg which was analogous to the standard drug dextropropoxyphene. Conclusion: Methanolic extract of leaves of P. sylvestris possesses both peripheral and central analgesic activity in experimental animal.

Neurological examination in healthy chinchillas (Chinchilla lanigera)

Chinchillas are popular as laboratory models and companion animals, and they can be affected by a variety of infectious and non-infectious neurological diseases. Little information is available on making a neurological diagnosis in this species, in part because the neurological examination has not been standardized in chinchillas and the expected physiological findings in healthy chinchillas have not been reported. In this study, a standardized neurological examination was performed on 30 clinically normal chinchillas. The perineal reflex and the menace response were absent in all chinchillas evaluated and so should not be used as functional tests. Several tests were consistently positive, such as the oculocephalic reflex, maxillary, mandibular and auricular sensations, withdrawal reflexes, thoracic limb paw replacement, and the wheelbarrow test. Other tests, such as the cutaneous trunci reflex and pelvic limb paw replacement, had variable responses. Based on these findings, it is advised that clinicians prioritize tests that can be easily performed without undue stress to the animal, and give consistent results in a healthy patient.