Activity-dependent conduction latency changes in A beta fibers of neuropathic rats

Immune variations in bipolar disorder: phasic differences

OBJECTIVES

To characterize the immunological variations of patients with a bipolar disorder (BD) diagnosis in manic (BDm) and depressive (BDd) phases, by the quantification of the serum levels of interleukin (IL)-1beta, -2, -4, -6 and tumor necrosis factor alpha (TNF-alpha).

METHODS

Twenty physically healthy patients with a BD type I diagnosis and 33 matched controls were studied, after giving informed consent. The inclusion criteria included at least three weeks without any kind of psychopharmacological treatment, Young Mania Rating Scale score > or =20 for BDm (n = 10) and Hamilton Depression Rating Scale score > or =21 for BDd patients (n = 10). Exclusion criteria included any infectious diseases, allergies or any other kind of medical illness that required treatment with immunosuppressors, as well as any other diagnosis in Axis I. Physical and laboratory examinations were performed to rule out any clinical illness. Enzyme-linked immunosorbent assay (ELISA) was used to analyze the serum cytokines concentration.

RESULTS

BD patients, when compared to controls, showed significant differences (p < or = 0.05) in the serum levels of the measured cytokines. The sub-group of BDd patients showed an increase in IL-6 and TNF-alpha, as well as a decrease in IL-2 concentration. The BDm sub-group, on the other hand, showed an increase in TNF-alpha and IL-4 values, with a low concentration of IL-1 and IL-2. The comparison between both sub-groups suggests that there is a distinctive cytokine pattern for the specific phases of the disorder: for mania, we found a high IL-4 and low IL-1beta and IL-6 concentration, while in the depressive phase, the inverse pattern was found.

CONCLUSIONS

Our results show the existence of phasic differences in the serum levels of cytokines in BD.

Sensory afferents regenerated into dorsal columns after spinal cord injury remain in a chronic pathophysiological state

Axon regeneration after experimental spinal cord injury (SCI) can be promoted by combinatorial treatments that increase the intrinsic growth capacity of the damaged neurons and reduce environmental factors that inhibit axon growth. A prior peripheral nerve conditioning lesion is a well-established means of increasing the intrinsic growth state of sensory neurons whose axons project within the dorsal columns of the spinal cord. Combining such a prior peripheral nerve conditioning lesion with the infusion of antibodies that neutralize the growth inhibitory effects of the NG2 chondroitin sulfate proteoglycan promotes sensory axon growth through the glial scar and into the white matter of the dorsal columns. The physiological properties of these regenerated axons, particularly in the chronic SCI phase, have not been established. Here we examined the functional status of regenerated sensory afferents in the dorsal columns after SCI. Six months post-injury, we located and electrically mapped functional sensory axons that had regenerated beyond the injury site. The regenerated axons had reduced conduction velocity, decreased frequency-following ability, and increasing latency to repetitive stimuli. Many of the axons that had regenerated into the dorsal columns rostral to the injury site were chronically demyelinated. These results demonstrate that regenerated sensory axons remain in a chronic pathophysiological state and emphasize the need to restore normal conduction properties to regenerated axons after spinal cord injury.

Activity-dependent slowing of conduction velocity in uninjured L4 C fibers increases after an L5 spinal nerve injury in the rat

Growing evidence suggests that uninjured afferents may play an important role in neuropathic pain following nerve injury. The excitability of nociceptive neurons in the L4 spinal nerve appears to be enhanced following an injury to the adjacent L5 spinal nerve. In this study, we investigated whether the action-potential conduction properties of unlesioned, unmyelinated fibers are also altered. A teased-fiber technique was used to record from single C fibers from the L4 spinal nerve of the rat in vitro. Repeated electrical stimulation of the tibial nerve was used to investigate activity-dependent slowing of conduction velocity. Twin pulse stimulation at a 50 ms interpulse interval allowed investigation of supranormal conduction velocity. Blinded experiments were performed 8-10 days after sham surgery and after an L5 spinal nerve ligation (L5 SNL). Activity-dependent slowing revealed two populations of C fibers, a "nociceptor" population with a large degree of activity-dependent slowing and a "non-nociceptor" population with a smaller degree of activity-dependent slowing. Both populations showed enhanced activity-dependent slowing of conduction velocity and enhanced supranormal conduction velocities in lesioned animals compared to sham animals. Activity-dependent slowing was also enhanced after an L5 SNL in the mouse. These alterations in conduction velocity may reflect changes in expression of ion channels responsible for the membrane excitability. These data provide additional evidence that a nerve injury leads to persistent alterations in the properties of adjacent uninjured, unmyelinated fibers.

Chronic pain/dysfunction in whiplash-associated disorders

OBJECTIVE

The purposes of this article are (1) to review current knowledge of and recent concepts pertaining to the causes of chronic pain and/or dysfunction following whiplash-type injuries and (2) to acquaint those who treat these types of injuries with possible mechanisms of continued pain and or dysfunction following whiplash.

DATA COLLECTION

A review of the literature on mechanisms of injury and neurologic considerations was undertaken. A hand search of relevant medical, neuroscience, chiropractic, and online Index Medicus sources and other sources involving mechanisms of nociception, neurotransmitters, and receptors that might evolve from whiplash-type soft tissue injuries was conducted.

RESULTS

Pain is a complex phenomenon that has great variability. Chronic pain appears to involve a deficient descending inhibitory process and/or ongoing excitatory input.

CONCLUSIONS

There is a wide variety of reactions by individuals to any given type of stimulus. Injury may lead to increases in neuronal activity and prolonged changes in the nervous system. Chronic pain may be seen as part of a central disturbance accompanied by disinhibition or sensitization of central pain modulation, mirrored in the immune and endocrine systems. Patients with chronic whiplash syndrome may have a generalized central hyperexcitability from a loss of tonic inhibitory input (disinhibition) and/or ongoing excitatory input contributing to dorsal horn hyperexcitability. Dysfunction of the motor system may also occur, with or without pain. The purpose of treatment should be not only to relieve pain but also to allow for proper proprioception.

Description of a short-term Taxol-induced nociceptive neuropathy in rats

This work describes a new animal model of neuropathic pain produced by the single intraperitoneal administration of Taxol (32 mg/kg) to male Sprague-Dawley rats. During the course of the experiment, the clinical status of the rats remained satisfactory and motor function was not altered. A number of classical behavioural tests of nociception as well as histological and electrophysiological investigations were performed. Taxol administration produced an important and rapidly developing mechanical hyperalgesia, a thermal hypoalgesia but no mechanical or thermal allodynia. Degenerative changes were observed in the sciatic nerve, the nerve fibres in the paw subcutaneous tissue and in the lumbar spinal cord. When Taxol or vehicle (a mix of Cremophor and ethanol) were repeatedly injected once a week for 5 weeks, similar nociceptive disorders were observed in addition to a decrease in peripheral nerve conduction velocity. The selective dysfunction of high-diameter myelinated fibres observed after one single administration of Taxol (32 mg/kg) may be attributable to paclitaxel-induced neuropathy, however other mechanisms causing neurochemical dysfunction must also be involved.