TENS augments blood flow in somatotopically linked spinal cord segments and mitigates compressive ischemia.

STUDY DESIGN: This was an acute basic physiological study in anesthetized adult male rats. OBJECTIVES: The purpose of this study was to determine, in an animal model, whether innocuous somatic stimulation, in the form of transcutaneous electrical nerve stimulation (TENS), could produce a sustained augmentation of spinal cord blood flow, and whether this effect was robust in the face of relatively mild, non-destructive compression of the spinal cord. SETTING: Neurophysiology laboratory, Canadian Memorial Chiropractic College, Toronto, Canada. METHODS: In anesthetized adult male Wistar rats, spinal cord blood flow was measured with laser Doppler flowmetry during 5- and 15-min epochs of TENS stimulation in uncompressed and compressed lumbar spinal cord. RESULTS: TENS applied to the L4/L5 dermatomes was associated with augmentation of blood flow in somatotopically linked spinal cord segments. This augmentation was robust in the face of non-destructive compression of the spinal cord, was sustained for periods of stimulation up to 15 min and occurred in the absence of any change in the mean arterial blood pressure. CONCLUSIONS: TENS augments spinal cord blood flow in the uncompressed spinal cord and during acute, non-destructive spinal cord compression. It remains to be seen whether similar results can be achieved in chronically compressed spinal cord and spinal nerve roots, and whether these results have clinical implications in human syndromes of spinal cord compression.

Influence of innocuous cervical vertebral movement on the efferent innervation of the adrenal gland in the rat.

In general, in central nervous system intact anesthetized animals, adrenal sympathetic efferent nerve activity and catecholamine secretion increase in response to noxious somatic stimulation, and decrease in response to innocuous somatic stimulation. In anesthetized rats, noxious chemical stimulation of the thoracic and lumbar interspinous tissues is associated with large increases in adrenal sympathetic efferent nerve activity and catecholamine secretion, with a clear segmental organization to the reflex apparent in spinalized animals. However, the adrenal sympathetic nerve responses to mechanical stimulation in the form of pressure applied laterally to the lower thoracic and lower lumbar vertebrae do not display segmental organization, and the depressor response is more characteristic of responses to innocuous somatic stimulation despite the use of large forces (up to 3.0 kg). Therefore, we sought to determine whether innocuous movements of the mechanoreceptor-rich deep tissues of the neck modulate the sympathetic outflow to the adrenal gland. We performed experiments in 14 anaesthetised (Urethane 1 g/kg and Chloralose 0.1 g/kg) adult rats. Rats were intubated and breathed spontaneously. A computer driven small animal manipulator was used to impose ramp and hold rotational displacements (12 degrees /s, hold duration 2 s) of the 2nd cervical vertebra (range 2-30 degrees ) while recording multi-unit activity from sympathetic nerves innervating the adrenal gland. While noxious forepaw pinch elicited an increase in sympathetic nerve activity to the adrenal gland, there was no significant change in sympathetic nerve activity with small (2 degrees or 6 degrees ) rotations. Significant changes (P<0.05) in sympathetic activity were observed in only 7% (n=21) of all trials at larger displacements (12 degrees , 20 degrees , 25 degrees , 30 degrees n=287 trials). Our data suggest that although noxious stimuli may modulate sympathetic outflow, it is rare for afferents signalling innocuous cervical vertebral movements to modulate sympathetic nerves innervating the adrenal gland.

Responses of adrenal function to stimulation of lumbar and thoracic interspinous tissues in the rat.

In urethane-anesthetized Wistar rats, the responses of adrenal sympathetic nerve activity and catecholamine secretion were measured following chemical stimulation of lumbar and thoracic interspinous tissues. Injection of normal saline into the lower lumbar or lower thoracic interspinous tissues produced no changes in adrenal sympathetic nerve activity or catecholamine secretion. On the other hand, the injection of capsaicin produced protracted increases in adrenal nerve activity and catecholamine secretion both in CNS-intact animals and in animals acutely spinalized at the Cl-2 level. Repetitive electrical stimulation of the medial branch of a lumbar primary dorsal ramus, the nerve which provides sensation to the lumbar interspinous tissues, produced A- and C-reflex discharges, mediated at the spinal and supraspinal levels, in the adrenal sympathetic nerve.

Innocuous mechanical stimulation of the neck and alterations in heart-rate variability in healthy young adults.

The present study examined the effects of cervical spinal manipulation, a widely applied form of physical therapy, which involves innocuous mechanical stimulation, on heart rate and heart-rate variability, in a cohort of healthy young adults. Using a cross-over treatment design, with a one-week washout period and, in contrast to a sham procedure, the authentic manipulation produced significant alterations in both heart rate and measures of heart-rate variability calculated from power spectrum analysis. In particular, there was an increase in the ratio of low-frequency (LF)-to-high-frequency (HF) components of the power spectrum of heart-rate variability, which may reflect a shift in balance between sympathetic and parasympathetic output to the heart.

Reflex effects of subluxation: the autonomic nervous system.

BACKGROUND: The collective experience of the chiropractic profession is that aberrant stimulation at a particular level of the spine may elicit a segmentally organized response, which may manifest itself in dysfunction within organs receiving autonomic innervation at that level. This experience is at odds with classic views of neuroscientists about the potential for somatic stimulation of spinal structures to affect visceral function. OBJECTIVE: To review recent findings from basic physiologic research about the effects of somatic stimulation of spinal structures on autonomic nervous system activity and the function of dependent organs. DATA SOURCE: Findings were drawn from a major recent review of the literature on the influences of somatic stimulation on autonomic function and from recent original physiologic studies concerning somatoautonomic and spinovisceral reflexes. CONCLUSIONS: Recent neuroscience research supports a neurophysiologic rationale for the concept that aberrant stimulation of spinal or paraspinal structures may lead to segmentally organized reflex responses of the autonomic nervous system, which in turn may alter visceral function.

Inhibition of gastric motility by noxious chemical stimulation of interspinous tissues in the rat.

In urethane anesthetized, adult male Wistar rats, noxious chemical stimulation of the mid to lower thoracic interspinous tissues, in the form of capsaicin injection, was accompanied by a pronounced increase in gastric sympathetic nerve activity and inhibition of gastric motility. Much weaker effects on gastric sympathetic nerve activity and gastric motility were observed with similar stimulation of the lower lumbar interspinous tissues. The inhibitory response of gastric motility to thoracic stimulation was preserved in spinalized animals, somewhat diminished in vagotomized animals and was abolished in most animals from which the coeliac ganglion had been extirpated. In vagotomized animals, treatment with 1 mg/kg propranolol i.v. did not cause any further attenuation of the inhibitory reflex. However, the inhibitory reflex was extinguished in vagotomized animals which received 1 mg/kg propranolol plus 10 mg/kg phentolamine i.v. These results suggest that noxious chemical stimulation of the interspinous tissues elicits a segmentally organized reflex which is mediated principally at the spinal level and which expresses itself principally, but not exclusively via sympathetic efferents traversing the coeliac ganglion. The expression of the reflex response appears to be largely dependent upon the integrity of alpha adrenergic receptors.

The cervical subluxation and regional cerebral blood flow.

OBJECTIVE: This article specifically addresses the question of whether the manipulable cervical lesion is likely to cause extrinsic compression of the vertebral arteries sufficient to cause such symptoms of reduced regional cerebral blood flow as might be relieved by spinal manipulation. DATA SOURCES: Literature on normal and abnormal cerebral circulation, including vertebrobasilar insufficiency. DATA SYNTHESIS: Signs and symptoms produced by extrinsic compression of the vertebrobasilar system have been compared with those attributed elsewhere to the manipulable cervical lesion (cervical subluxation). RESULTS: Extrinsic compression of the vertebrobasilar system generally does not produce signs and symptoms consistent with those attributed to the manipulable cervical lesion. CONCLUSION: It has been hypothesized elsewhere that the manipulable cervical lesion may induce localized decreases in regional cerebral blood flow, and so signs and symptoms attributable to "cerebral hibernation." If a causal relationship does exist between the cervical subluxation and reduced regional cerebral blood flow, it is not likely to be caused by mechanical compression of the vertebral arteries.

Innervation of posterior structures in the lumbar spine of the rat.

OBJECTIVE: To determine the nature and distribution of afferent fibers to the interspinous tissues and facet joints of the lumbar spine in the rat. DESIGN: Dissection and photography of medial branch of the primary dorsal ramus; histological and electron microscopic examination of the medial branch; measurement of conduction velocities of fibers within the medial branch; recording of compound nerve activity in medial branch in response to mechanical and chemical stimulation of interspinous tissues and facet joints. RESULTS: In the rat, the medial branch of the primary dorsal ramus of lumbar spinal nerves is normally distributed to the facet joints and interspinous tissues one and two segmental levels caudad to its origin. This nerve contains unmyelinated and myelinated afferents with conduction velocities within the ranges of C fibers, and A-delta and A-beta fibers. The tissues served by this nerve are sensitive to mechanical and noxious chemical stimulation. CONCLUSIONS: There are many structural and functional similarities in the innervation of the lumbar spine in rats and humans. However, there are anatomical variants and, in rats, the medial branch of the primary dorsal ramus, which serves the interspinous tissues and facet joints, is distributed more caudally than in humans. This information should be taken into account in extrapolating experimental results from rats to the human situation.

Reflex responses of bladder motility after stimulation of interspinous tissues in the anesthetized rat.

OBJECTIVES: To determine the effects of somatic stimulation, including noxious chemical stimulation of interspinous tissues, on bladder motility in the anesthetized rat. METHODS: Changes in pressure in the previously quiescent bladder were measured in anesthetized adult female Wistar rats after various forms of noxious and innocuous somatic stimulation, including injection of the thoracic and lumbar interspinous tissues with capsaicin. Measurements were taken in both central nervous system-intact and spinalized animals, as well as in animals in whom the pelvic nerves had been transected bilaterally. Changes in bladder pressure were also measured in response to electrical stimulation of the primary dorsal ramus of lumbar spinal nerves. RESULTS: Noxious and innocuous stimulation of the fore- and hindpaws and the skin overlying the sacrum generally failed to elicit discernible changes in bladder pressure. However, capsaicin injection of thoracic and lumbar interspinous tissues produced profound and long-lasting increases in bladder pressure. There were no significant differences in the responses to thoracic, as opposed to lumbar, stimulation. Spinalization above the level of stimulation abolished the response to capsaicin injection, as did bilateral transection of the pelvic nerves. CONCLUSION: In general, pressure in the quiescent bladder was relatively insensitive to somatic stimulation. However, noxious chemical stimulation of the interspinous tissues produced a nonsegmentally organized, supraspinal, parasympathetically mediated reflex increase in bladder tone.

Arterial tonometry in the measurement of the effects of innocuous mechanical stimulation of the neck on heart rate and blood pressure.

Arterial tonometry was used to continuously monitor the effects on heart rate and blood pressure of a series of innocuous mechanical stimuli applied to the neck in conscious humans. The stimuli used were derived from procedures commonly employed in clinical examination and physical therapy of the neck. In alert subjects, the stimuli used generally caused small and sometimes statistically significant decreases in heart rate, systolic pressure and diastolic pressure. In alert subjects, statistically significant decreases in systolic and diastolic pressure were particularly associated with stimuli which involved full rotation of the neck. In the course of the prolonged series of stimuli, some subjects slept or reported being on the verge of sleep. In these subjects, the same stimuli produced mixed effects on heart rate and increases in systolic and diastolic pressure which were significantly different from the effects obtained in fully alert subjects.