Professor Philip Bolton

We previously showed that dynamic, but not static, neck displacement modulates muscle sympathetic nerve activity (MSNA) to lower limbs of humans. However, it is not known whether dynamic neck displacement modulates skin sympathetic nerve activity (SSNA). Tungsten microelectrodes inserted into the common peroneal nerve were used to record SSNA in 5 female and 4 male subjects lying supine on a table that fixed their head in space but allowed trapezoidal ramp (8.1 ± 1.2°/s) and hold (17.5° for 53 s) or sinusoidal (35° peak to peak at 0.33¿0.46 Hz) horizontal displacement of the body about the head. SSNA recordings were made before, during, and after trapezoidal and sinusoidal displacements of the body. Spike frequency analysis of trapezoidal displacements and cross-correlation analysis during sinusoidal displacements revealed that SSNA was not changed by trapezoid body-only displacement but was cyclically modulated during sinusoidal angular displacements (median, 95% CI: 27.9%, 19.6¿ 48.0%). The magnitude of this modulation was not statistically (P > 0.05) different from that of cardiac and respiratory modulation at rest (47.1%, 18.7¿56.3% and 48.6%, 28.4¿59.3%, respectively) or during sinusoidal displacement (10.3%, 6.2¿32.1% and 26.9%, 13.6¿43.3%, respectively). Respiratory frequency was entrained above its resting rate (0.26 Hz, 0.2¿0.29 Hz) during sinusoidal neck displacement; there was no significant difference (P > 0.05) between respiratory frequency (0.38 Hz, 0.25¿0.49 Hz) and sinusoidal displacement frequency (0.39 Hz, 0.35¿0.42 Hz). This study provides evidence that SSNA is modulated during neck movement, raising the possibility that neck mechanoreceptors may contribute to the cutaneous vasoconstric-tion and sweat release associated with motion sickness. NEW & NOTEWORTHY This study demonstrates that dynamic, but not static, stretching of the neck modulates skin sympathetic nerve activity in the lower limbs.

There is a rapidly accumulating body of evidence regarding the influential role of early life stress (ELS) upon medical and psychiatric conditions. While self-report instruments, with their intrinsic limitations of recall, remain the primary means of detecting ELS in humans, biological measures are generally limited to a single biological system. This paper describes the design, rationale and feasibility of a study to simultaneously measure neuroendocrine, immune and autonomic nervous system (ANS) responses to psychological and physiological stressors in relation to ELS. Five healthy university students were recruited by advertisement. Exclusion criteria included chronic medical conditions, psychotic disorders, needle phobia, inability to tolerate pain, and those using anti-inflammatory medications. They were clinically interviewed and physiological recordings made over a two-hour period pre, during and post two acute stressors: the cold pressor test and recalling a distressing memory. The Childhood Trauma Questionnaire and the Parental Bonding Index were utilised to measure ELS. Other psychological measures of mood and personality were also administered. Measurements of heart rate, blood pressure, respiratory rate, skin conductance, skin blood flow and temporal plasma samples were successfully obtained before, during and after acute stress. Participants reported the extensive psychological and multisystem physiological data collection and stress provocations were tolerable. Most (4/5) participants indicated a willingness to return to repeat the protocol, indicating acceptability. Our protocol is viable and safe in young physically healthy adults and allows us to assess simultaneously neuroendocrine, immune and autonomic nervous system responses to stressors in persons assessed for ELS.

Low-frequency sinusoidal linear acceleration (0.08 Hz, ±4 mG) modulates skin sympathetic nerve activity (SSNA) in seated subjects (head vertical), suggesting that activation of the utricle in the peripheral vestibular labyrinth modulates SSNA. The aim of the current study was to determine whether SSNA is also modulated by input from the saccule. Tungsten microelectrodes were inserted into the common peroneal nerve to record oligounitary SSNA in 8 subjects laying supine on a motorized platform with the head aligned with the longitudinal axis of the body. Slow sinusoidal (0.08 Hz, 100 cycles) linear acceleration-decelerations (peak ±4 mG) were applied rostrocaudally to predominately activate the saccules, or mediolaterally to predominately activate the utricles. Cross-correlation histograms were constructed between the negative-going sympathetic spikes and the positive peaks of the sinusoidal stimuli. Sinusoidal linear acceleration along the rostrocaudal axis or mediolateral axis both resulted in sinusoidal modulation of SSNA (Median, IQR 27.0, 22-33% and 24.8, 17-39%, respectively). This suggests that both otolith organs act on sympathetic outflow to skin and muscle in a similar manner during supine displacements.

The aim of this study was to define the temporal and spatial (postural) characteristics of the head and cervical vertebral column (spine) of behaving rats in order to better understand their suitability as a model to study human conditions involving the head and neck. Time spent in each of four behavioral postures was determined from video tape recordings of rats (n=10) in the absence and presence of an intruder rat. Plain film radiographic examination of a subset of these rats (n=5) in each of these postures allowed measurement of head and cervical vertebral column positions adopted by the rats. When single they were quadruped or crouched most (~80%) of the time and bipedal either supported or free standing for only ~10% of the time. The introduction of an intruder significantly (P<0.0001) reduced the proportion of time rats spent quadruped (median, from 71% to 47%) and bipedal free standing (median, from 2.9% to 0.4%). The cervical spine was orientated (median, 25-75 percentile) near vertical (18.8°, 4.2°-30.9°) when quadruped, crouched (15.4°, 7.6°-69.3°) and bipedal supported (10.5°, 4.8°-22.6°) but tended to be less vertical oriented when bipedal free standing (25.9°, 7.7°-39.3°). The range of head positions relative to the cervical spine was largest when crouched (73.4°) and smallest when erect free standing (17.7°). This study indicates that, like humans, rats have near vertical orientated cervical vertebral columns but, in contrast to humans, they displace their head in space by movements at both the cervico-thoracic junction and the cranio-cervical regions. Anat Rec, 298:455-462, 2015.

Background context One theory within chiropractic proposes that vertebral subluxation in the upper cervical region induces spinal cord compression sufficient to alter spinal cord efferent output. We report on the feasibility of three different experimental approaches to test this theory. Methods A high threshold electrical-evoked somatosympathetic reflex was recorded in adrenal or renal nerves of 10 anaesthetized adult male rats before and after (1) graded pressure was applied directly to the C1/C2 spinal cord segment in eight rats by the use of either direct compression or inflation of an extradural balloon and (2) displacement, less than a dislocation applied posterior to anterior, to the C2 vertebra in two rats. The latency and amplitude of the pre- and postintervention reflex responses were compared. Results The reflex amplitude was not significantly changed by pressure (26 mmHg) from an extra-dural balloon or direct compression of the dura mater onto the dorsal spinal cord. Additional pressure, at least sufficient to occlude the dorsal vessels, induced a significant reduction in the amplitude of the reflex, and this reduction persisted for 20 minutes after removal of the pressure (Dunn's method for all pairwise multiple comparison Q stat=3.437; critical value for k=6 with a=0.05 is 2.936). Maximal vertebral (C2) displacement (4 mm), without dislocation did not induce significant changes compared with the control period. Conclusions Although this feasibility study suggests it is unlikely that upper cervical vertebral subluxation, displacement less than a dislocation, compromises the sympathetic outflow in the adrenal or renal nerves, further vertebral displacement studies are necessary to formally test this.