Whole body vibration induces forepaw and hind paw behavioral sensitivity in the rat

Abstract

Whole body vibration (WBV) has been linked to neck and back pain, but the biomechanical and physiological mechanisms responsible for its development and maintenance are unknown. A rodent model of WBV was developed in which rats were exposed to different WBV paradigms, either daily for 7 consecutive days (repeated WBV) or two single exposures at Day 0 and 7 (intermittent WBV). Each WBV session lasted for 30 min and was imposed at a frequency of 15 Hz and RMS platform acceleration of 0.56 AE 0.07 g. Changes in the withdrawal response of the forepaw and hind paw were measured, and were used to characterize the onset and maintenance of behavioral sensitivity. Accelerations and displacements of the rat and deformations in the cervical and lumbar spines were measured during WBV to provide mechanical context for the exposures. A decrease in withdrawal threshold was induced at 1 day after the first exposure in both the hind paw and forepaw. Repeated WBV exhibited a sustained reduction in withdrawal threshold in both paws and intermittent WBV induced a sustained response only in the forepaw. Cervical deformations were significantly elevated which may explain the more robust forepaw response. Findings suggest that a WBV exposure leads to behavioral sensitivity. Keywords: whole body vibration; spine; pain; injury Several epidemiological studies have linked exposure to whole body vibration (WBV) with neck and back pain, [1][2][3][4] suggesting that vibration can lead to the onset of both pain syndromes. American male workers operating vibrating vehicles, such as industrial trucks and tractors, have been reported to have a higher prevalence of low back pain and are three-times more susceptible to acute herniated lumbar discs than workers whose occupations do not involve such exposures.3,5 Also, military helicopter aviators report increased pain during deployment compared to their pre-deployment reports of pain, with between 22-37% reporting neck and 39-70% reporting low back pain. 4 Further, the frequency of pain was significantly higher for aviators who experienced substantially increased flight hours during deployment compared to those who did not, 4 suggesting that the amount of exposure to WBV may affect the pain. 4 Despite the strong suggestive evidence of these epidemiological studies that pain can develop from WBV and may be influenced by the nature and frequency of the exposure, there is still little known about how these factors relate to the onset, maintenance, and resolution of pain.A limited number of studies have defined the biomechanical response to vibration and related resonance and vibration frequency to physiological responses known to be involved in pain-related injuries. The resonant frequency of the seated human undergoing vertical vibration has been reported to be 4.5 Hz from a series of studies using accelerometers on the first and third lumbar vertebrae (L1, L3) and the sacrum of volunteers exposed to vertical vibrations, ranging in frequencies from 2 to 15 Hz. 6 A later study using similarl...

Whole-body Vibration at Thoracic Resonance Induces Sustained Pain and Widespread Cervical Neuroinflammation in the Rat

“…Rats were placed in the prone position on a rigid vibrating platform to enable WBV along the spine's long axis using straps positioned behind the shoulders and above the pelvis (Fig. 1A) [11]. A sinusoidal input (1.5-mm peak-to-peak amplitude) was applied using a shaker (K2007E01; Modal Shop, Cincinnati, OH) at 3 Hz and increased to 15 Hz in 1-Hz increments for 1 minute each.…”

“…Rats (317 ± 20 g) were vibrated at resonance (8 Hz, n = 10) and also at a frequency (15 Hz, n = 10) that has been previously characterized [11,40]. Vibration was imposed under inhalation anesthesia (4% induction, 2% maintenance) in the two separate groups.…”

“…We have previously shown that WBV at 15 Hz can induce pain in the rat that either resolves or is sustained, depending on how often the exposure is presented, occasionally or daily [11]. Upregulation of neurotrophins in the intervertebral discs is also evident for the case with sustained pain [40].…”

“…Over half (69%) of military helicopter pilots exposed to WBV report pain with the frequency of symptoms correlated with the length of exposure [24,59]. Because the greatest injury risk exists at resonance [36], studies have defined the resonant frequency of many species, including humans (approximately 4 Hz) [11,63], Rhesus monkey (5-14 Hz) [72], and rabbit (4.5 Hz) [80]. Although several rat models have examined pain induction and maintenance after either vibration of isolated limbs or WBV [3,4,11,19,26,43], the vibration response, and its relevance to injury, in the rat is unknown.…”

“…Isolated vibration of the limb or tail in the rat produces damage in myelinated fibers [49,53]. WBV of the rat induces deformation in the cervical spine, which if repeated daily produces long-lasting behavioral sensitivity [11]. Although vibration may induce neural tissue damage, which may be a mechanism of pain, this has not been investigated for WBV.…”