Neuroscience letters
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Neuroscience letters · Jul 2003
Periodic abstinence enhances nociception without significantly altering the antinociceptive efficacy of spinal morphine in the rat.
Naloxone administration in the opioid dependent rat is associated with spinal glutamate release and NMDA receptor activation which reportedly is also responsible for opioid tolerance. We hypothesized that episodic withdrawal during chronic infusion of spinal morphine might paradoxically enhance tolerance. Rats (24/group) infused with intrathecal morphine (M) for 4 days (20 nmol/microl per h) were given a daily subcutaneous (s.c.) injection of naloxone 0.6 mg/kg per 0.2 ml (MN) or saline 0.2 ml (MS). ⋯ The MN group showed a significantly greater decline in daily latencies compared with the MS group, but also had greater withdrawal hyperalgesia upon termination of the infusion. Dose response to spinal morphine was not significantly different in either MS or MN groups. Periodic abstinence thus enhanced nociception without significantly altering the antinociceptive effect of spinal morphine in this group.
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Neuroscience letters · Jun 2003
The dorsal portion of the lumbar intervertebral disc is innervated primarily by small peptide-containing dorsal root ganglion neurons in rats.
The intervertebral discs are innervated by the dorsal root ganglion (DRG) neurons. In the present study, we applied Fluoro-Gold (FG) to the dorsal portion of the L5-L6 intervertebral disc to label DRG neurons retrogradely, and then examined whether FG-labeled neurons were substance P (SP)-immunoreactive or isolectin B4 (IB4)-binding. Of the FG-labeled neurons, 44.0% were immunoreactive for SP, whereas only 0.6% were reactive for IB4. The rate of SP-immunoreactive neurons was significantly higher than that of IB4-binding neurons (P<0.001), suggesting that under physiological conditions the dorsal portion of the lumbar disc is mainly innervated by peptide-containing neurons.
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Neuroscience letters · Jun 2003
ATP-sensitive potassium channels in rat primary afferent neurons: the effect of neuropathic injury and gabapentin.
ATP-sensitive potassium (K(ATP)) currents were examined in dorsal root ganglion neurons from neuropathic and control rats using whole-cell voltage clamp recordings. K(ATP) channel openers (diazoxide and pinacidil) enhanced, and the blocker glibenclamide inhibited an outward current in control neurons in a manner dependent on the pipette ATP concentration. Analysis of reversal potentials showed that this current is carried by K(+) ions. ⋯ Gabapentin, a putative K(ATP) channel opener, had minimal effect on currents in either group of neurons. We conclude that normal primary afferent neurons express K(ATP) channels that conduct current which is eliminated by peripheral nerve injury. Gabapentin does not affect this current significantly.
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Neuroscience letters · Jun 2003
Comparative StudyNitrous oxide reverses the increase in striatal dopamine release produced by N-methyl-D-aspartate infusion in the substantia nigra pars compacta in rats.
Bilateral administration of NMDA (5 x 10(-10) mol) in the substantia nigra pars compacta increases the striatal dopamine (DA) release. However, this enhancing effect of NMDA was suppressed by nitrous oxide exposure at 0.1 MPa, which induced per se a decrease of the DA release. These results show that nitrous oxide exerts a reversal effect on the increase in striatal DA release produced by NMDA receptor activation in the substantia nigra pars compacta. This observation may be related to the fact that nitrous oxide is thought to produce its effects by acting as an NMDA receptor antagonist.
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Neuroscience letters · May 2003
Randomized Controlled Trial Clinical TrialHigh and low frequency transcutaneous electrical nerve stimulation inhibits nociceptive responses induced by CO2 laser stimulation in humans.
The aim of the study was to evaluate the effects of transcutaneous electric nerve stimulation (TENS) on CO(2) laser evoked potentials (LEPs) in 16 normal subjects. The volar side of the forearm was stimulated by 10 Hz TENS in eight subjects and by 100 Hz TENS in the remainder; the skin of the forearm was stimulated by CO(2) laser and the LEPs were recorded in basal conditions and soon after and 15 min after TENS. Both low and high frequency TENS significantly reduced the subjective rating of heat stimuli and the LEPs amplitude, although high frequency TENS appeared more efficacious. TENS seemed to exert a mild inhibition of the perception and processing of pain induced by laser Adelta fibres activation; the implications of these effects in the clinical employment of TENS remain to be clarified.