The Potential Neural Mechanisms of Acute Indirect Vibration

There is strong evidence to suggest that acute indirect vibration acts on muscle to enhance force, power, flexibility, balance and proprioception suggesting neural enhancement. Nevertheless, the neural mechanism(s) of vibration and its potentiating effect have received little attention. One proposal suggests that spinal reflexes enhance muscle contraction through a reflex activity known as tonic vibration stretch reflex (TVR), which increases muscle activation. However, TVR is based on direct, brief, and high frequency vibration (>100 Hz) which differs to indirect vibration, which is applied to the whole body or body parts at lower vibration frequency (5-45 Hz). Likewise, muscle tuning and neuromuscular aspects are other candidate mechanisms used to explain the vibration phenomenon. But there is much debate in terms of identifying which neural mechanism(s) are responsible for acute vibration; due to a number of studies using various vibration testing protocols. These protocols include: different methods of application, vibration variables, training duration, exercise types and a range of population groups. Therefore, the neural mechanism of acute vibration remain equivocal, but spinal reflexes, muscle tuning and neuromuscular aspects are all viable factors that may contribute in different ways to increasing muscular performance. Additional research is encouraged to determine which neural mechanism(s) and their contributions are responsible for acute vibration. Testing variables and vibration applications need to be standardised before reaching a consensus on which neural mechanism(s) occur during and post-vibration.

Key points

• There is strong evidence to suggest that acute indirect vibration acts on muscle to enhance force, power, flexibility, balance and proprioception, but little attention has been given to the neural mechanism(s) of acute indirect vibration.
• Current findings suggest that acute vibration exposure may cause a neural response, but there is little consensus on identifying which neural mechanism(s) are specifically responsible. This is due to a number of studies using various vibration testing protocols (i.e.varying frequencies, amplitudes, durations, and methods of application).
• Spinal reflexes, muscle tuning and neuromuscular aspects and central motor command are all viable neuromechanical factors that may contribute at different stages to transiently increasing muscular performance.
• Additional research is encouraged to determine when (pre, during and post) the different neural mechanism(s) respond to direct and indirect vibration stimuli.

Key words: Spinal reflexes, muscle tuning, motor unit firing frequency, motor unit synchronisation, inter-muscular co-ordination     

Characterization of the Antinociceptive and Pronociceptive Effects of Methadone in Rats

Background: Recently, it has been appreciated that in addition to their antinociceptive properties, opioid analgesics also can enhance pain sensitivity (opioid-induced hyperalgesia [OIH]). OIH may enhance preexisting pain and contribute to dose escalation, tolerance, and misuse/abuse of opioids. Better information is needed to determine which opioid or opioid combinations may be least likely to produce OIH and therefore possibly represent better choices for pain management. Herein the authors have examined the hyperalgesic and antinociceptive properties of racemic methadone and its enantiomers alone and in combination with morphine in rats. Methadone is of particular interest because it possesses both [mu]-receptor agonist and N-methyl-d-aspartate receptor antagonist activities.

Methods: The antinociceptive and hyperalgesic properties of d,l-methadone, l-methadone, and d-methadone were characterized by dose and sex using the thermal tail-flick test (high and low intensity). The responses to l- and d-methadone combinations with morphine were also determined with this model.

Results: Antinociceptive and hyperalgesic effects of d,l-methadone were demonstrated. These effects were related to dose but not to sex. The degree of hyperalgesia was greater with l-methadone compared with d,l-methadone. In contrast, d-methadone (N-methyl-d-aspartate antagonist) did not produce hyperalgesia. Furthermore, d-methadone blocked morphine hyperalgesia, enhanced antinociception, and abolished sex-related differences. This seems to be the result of antagonistic activity of d-methadone at the N-methyl-d-aspartate receptor.     

Hypnosis and sex

Hypnosis is not a discipline to be thought of in isolation but is one of the techniques of psychotherapy, like abreaction, analysis, behaviour therapy, support and others, with which it may be combined. Hypnosis can often enhance the effect of other methods of treatment, and has no dangers apart from those inherent to psychotherapy. In the treatment of sexual dysfunction it is often, perhaps usually, necessary to interview and treat both partners, but this article is concerned with the role of hypnosis in this field; it will usually be employed with only one of the partners, and in some cases may be the only technique used. Hypnosis is useful in primary and secondary sexual dysfunction, and deserves wider recognition.     

Hypnosis and daycase anaesthesia

Fifty-two female patients who underwent gynaecological operations as day cases received either a short pre-operative hypnotic induction or a brief discussion of equal duration. Hypnotized patients who underwent vaginal termination of pregnancy required significantly less methohexitone for induction of anaesthesia. They were also significantly more relaxed as judged by their visual analogue scores for anxiety. Less than half of the patients were satisfied with their knowledge about the operative procedure even after discussions with the surgeon and anaesthetist. A significant correlation was found between anxiety and perceived knowledge of procedures. The results suggest that pre-operative hypnosis can provide a quick and effective way to reduce pre-operative patient anxiety and anaesthetic requirements for gynaecological daycase surgery.     

Physiologic and Antinociceptive Effects of Intrathecal Resiniferatoxin in a Canine Bone Cancer Model

Background: Resiniferatoxin is a potent capsaicin analog. Intrathecal administration leads to selective, prolonged opening of the transient receptor potential V1 ion channel, which is localized mainly to C-fiber primary afferent nociceptive sensory neurons. Following work in laboratory animals, the authors explored the use of intrathecal resiniferatoxin to control spontaneous bone cancer pain in companion (pet) dogs.

Methods: Normal canine population: Behavioral testing was performed to establish baseline paw withdrawal latency; subsequently, general anesthesia was induced and resiniferatoxin was administered intrathecally while hemodynamic parameters were recorded. Behavior testing was repeated for 12 days after administration of resiniferatoxin. Clinical canine population: Twenty companion dogs with bone cancer pain were recruited. The animal's baseline level of discomfort and analgesic use were recorded. Resiniferatoxin was administered intrathecally and hemodynamic parameters were monitored while the dogs were under general anesthesia. Dogs were reevaluated up to 14 weeks after resiniferatoxin administration.

Results: Normal canine population: In the first minutes after resiniferatoxin injection, there were significant (P < 0.05) increases in mean arterial blood pressure and heart rate from baseline. Two days after injection, limb withdrawal latencies increased to the point of cutoff in the dogs that received at least 1.2 [mu]g/kg resiniferatoxin. Clinical canine population: From baseline, there were significant (P < 0.05) increases in mean arterial blood pressure and heart rate after resiniferatoxin injection. Comfort scores were significantly improved at 2, 6, 10, and 14 weeks after resiniferatoxin administration (P < 0.0001). There was decreased or discontinued use of supplemental analgesics in 67% of the dogs 2 weeks after resiniferatoxin administration.