Neuroscience letters
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Neuroscience letters · May 2004
ReviewLaser evoked potentials for assessing sensory neuropathy in human patients.
Sensory neuropathy usually impairs tactile sensations related to large myelinated afferents (Abeta) as well as thermal-pain sense related to small myelinated (Adelta) and unmyelinated (C) afferents. By selectively affecting large or small fibres, some sensory neuropathies may also provoke a dissociated sensory loss. ⋯ From earlier studies and new cases we collected data on 270 patients with sensory neuropathy. LEPs often disclosed subclinical dysfunction of Adelta fibres and proved a sensitive and reliable diagnostic tool for assessing small-fibre function in sensory neuropathy.
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Neuroscience letters · May 2004
ReviewOpioids and opioid receptors in the enteric nervous system: from a problem in opioid analgesia to a possible new prokinetic therapy in humans.
The gut is a neurological organ, which implies that many neuroactive drugs such as opioid analgesics can seriously disturb gastrointestinal function, because many of the transmitters and transmitter receptors present in the brain are also found in the enteric nervous system. One of the most common manifestations of opioid-induced bowel dysfunction is constipation which results from blockade of peristalsis and intestinal fluid secretion. The discovery of opioid receptor antagonists with a peripherally restricted site of action, such as N-methylnaltrexone and alvimopan, makes it possible to normalize bowel function in opiate-treated patients without compromising central opioid analgesia. There is emerging evidence that opioid receptor antagonists may also have prokinetic actions, reversing pathological states of gastrointestinal hypomotility that are due to overactivity of the enteric opioid system.
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Neuroscience letters · May 2004
Effects of peripheral nerve injury on delta opioid receptor (DOR) immunoreactivity in the rat spinal cord.
Morphine and other opioids have direct analgesic actions in the spinal cord and chronic spinal administration of opioid agonists is used clinically in patients suffering from severe, chronic pain. Neuropathic pain resulting from peripheral nerve injury is often less sensitive to opioid therapy than other forms of chronic pain in both humans and animal models. Changes in spinal mu-opioid receptor (MOR) expression have been demonstrated in animal models of neuropathic pain. ⋯ We therefore performed quantitative image analysis to evaluate the effect of peripheral nerve injury on DOR-immunoreactivity in spinal cord sections from rats previously characterized for sensory responsiveness. We observed statistically significant decreases ipsilateral to nerve injury in all three models tested: sciatic nerve transection, chronic constriction injury of the sciatic nerve and L5/L6 spinal nerve ligation. These results suggest that decreases in the expression of DOR are a common feature of peripheral nerve injury.
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Neuroscience letters · May 2004
Methodologic factors which contribute to variations in experimental pain threshold reported for older people.
Using the same study groups and psychophysical methods, we have tested the hypothesis that variations in pain threshold with advancing age are best explained by variations in stimulus duration. Fifteen young adults and 15 older people without clinical evidence of neurologic disease or psychologic dysfunction had pain thresholds determined with heat and electrical stimuli using the method of limits; for electrical stimulation a double random staircase design was used. ⋯ It was found that older people have an increased threshold for thermal and electrically induced pain if the stimulus duration is kept short. This result explains much of the variability in age associated pain threshold in the literature.
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Spatial integration of cold pressor pain (CPP) in the hand was studied in healthy human subjects by measuring the latency to the ice water-induced first pain sensation with and without conditioning CPP. CPP alone showed a marked spatial summation effect. ⋯ A decrease in the test stimulus area increased the suppressive effect by conditioning CPP. Thus, CPP shows spatial summation or inhibition depending on experimental parameters.