A preclinical model of hyperalgesia following spinal stenosis/compression.

BACKGROUND: Identification of mechanisms for pain/hyperalgesia following spinal cord injury requires long-term evaluation of individual subjects because of the variability in effect over time for humans. METHODS: Rats were trained on an operant escape task that determined their preference for occupancy of a brightly lit compartment versus a dark compartment with a floor preheated to 10, 32 or 44.5 °C. Following determination of baseline preferences, the animals received extradural implantation of a small piece of polymer in the thoracic spinal canal. The polymer narrowed the spinal canal and compressed the spinal cord. Post-operative tests of escape preference were conducted over 23 weeks (experiments 1 and 2) and 62 weeks (experiment 3), permitting statistical evaluation of individual effects. RESULTS: Spinal stenosis/compression produced hyperalgesia for cold and/or heat stimulation (17 animals; 77%), no post-operative change in sensitivity (4 animals) or hypoalgesia for cold or heat (2 animals). When hyperalgesia occurred, it developed gradually over 4 months. Following removal of the polymer in experiment 3, heat sensitivity returned to baseline levels for four of four animals that had been hyperalgesic when the polymer was in place, but cold hyperalgesia was retained for four of five animals. Overall, post-operative changes in cold and heat sensitivity were not strongly related, indicating that different mechanisms were responsible for enhanced sensitivity to 10 and 44.5 °C. CONCLUSIONS: Histology revealed that hyperalgesia occurred when there was: (1) damage to spinal white matter; or (2) cystic cavitation; or (3) compression and distortion of the spinal cord without an obvious loss of grey or white matter.

Abnormal sensitization and temporal summation of second pain (wind-up) in patients with fibromyalgia syndrome.

Although individuals with fibromyalgia syndrome (FMS) consistently report wide-spread pain, clear evidence of structural abnormalities or other sources of chronic stimulation of pain afferents in the involved body areas is lacking. Without convincing evidence for peripheral tissue abnormalities in FMS patients, it seems likely that a central pathophysiological process is at least partly responsible for FMS, as is the case for many chronic pain conditions. Therefore, the present study sought to obtain psychophysical evidence for the possibility that input to central nociceptive pathways is abnormally processed in individuals with long standing FMS. In particular, temporal summation of pain (wind-up) was assessed, using series of repetitive thermal stimulation of the glabrous skin of the hands. Although wind-up was evoked both in control and FMS subjects, clear differences were observed. The perceived magnitude of the sensory response to the first stimulus within a series was greater for FMS subjects compared to controls, as was the amount of temporal summation within a series. Within series of stimuli, FMS subjects reported increases in sensory magnitude to painful levels for interstimulus intervals of 2-5 s, but pain was evoked infrequently at intervals greater than 2 s for control subjects. Following the last stimulus in a series, after-sensations were greater in magnitude, lasted longer and were more frequently painful in FMS subjects. These results have multiple implications for the general characterization of pain in FMS and for an understanding of the underlying pathophysiological basis.

The effect of maximal exercise on temporal summation of second pain (windup) in patients with fibromyalgia syndrome.

Exercise activates endogenous opioid and adrenergic systems, but attenuation of experimental pain by exercise has not been shown consistently. In this study, effects of exercise on temporal summation of late pain responses to stimulation of unmyelinated (C) nociceptors were assessed. When a preheated thermode was applied repetitively to glabrous skin of the hand in a series of brief contacts at rates of 0.2 to 0.5 Hz, the perceived intensity of late thermal sensations increased after successive contacts. This summation of pain sensations provides information regarding the status of central opioid and N-methyl-D-aspartate receptor systems. For normal subjects, temporal summation of late pain sensations was substantially attenuated when testing began 1.5 or 10 minutes after exercise. Individuals diagnosed with fibromyalgia syndrome (FMS) report generalized chronic pain that is increased after exercise. Therefore, we hypothesized that strenuous exercise would increase summation of late pain sensations in this cohort. Patients with FMS and control subjects exerted to similarly high metabolic rates, as shown by physiologic monitoring. Ratings of late pain sensations increased for patients with FMS after exercise, an effect opposite to a decrease in ratings for age/sex-matched control subjects. In contrast to this result for experimentally induced pain, clinical pain ratings were not substantially altered after strenuous exercise by patients with FMS.

Characteristics of temporal summation of second pain sensations elicited by brief contact of glabrous skin by a preheated thermode.

Temporal summation of sensory intensity was investigated in normal subjects using novel methods of thermal stimulation. A Peltier thermode was heated and then applied in a series of brief (700 ms) contacts to different sites on the glabrous skin of either hand. Repetitive contacts on the thenar or hypothenar eminence, at interstimulus intervals (ISIs) of 3 s, progressively increased the perceived intensity of a thermal sensation that followed each contact at an onset latency > 2 s. Temporal summation of these delayed (late) sensations was proportional to thermode temperature over a range of 45-53 degrees C, progressing from a nonpainful level (warmth) to painful sensations that could be rated as very strong after 10 contacts. Short-latency pain sensations rarely were evoked by such stimuli and never attained levels substantially above pain threshold for the sequences and temperatures presented. Temporal summation produced by brief contacts was greater in rate and amount than increases in sensory intensity resulting from repetitive ramping to the same temperature by a thermode in constant contact with the skin. Variation of the interval between contacts revealed a dependence of sensory intensity on interstimulus interval that is similar to physiological demonstrations of windup, where increasing frequencies of spike train activity are evoked from spinal neurons by repetitive activation of unmyelinated nociceptors. However, substantial summation at repetition rates of > or = 0.33 Hz was observed for temperatures that produced only late sensations of warmth when presented at frequencies < 0.16 Hz. Measurements of subepidermal skin temperature from anesthetized monkeys revealed different time courses for storage and dissipation of heat by the skin than for temporal summation and decay of sensory intensity for the human subjects. For example, negligible heat loss occurred during a 6-s interval between two trials of 10 contacts at 0.33 Hz, but ratings of sensory magnitude decreased from very strong levels of pain to sensations of warmth during the same interval. Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches. In the first, a moderate degree of temporal summation was observed during alternating stimulation of adjacent but nonoverlapping skin sites at 0.33 Hz. Second, temporal summation was significantly attenuated by prior administration of dextromethorphan, a N-methyl-D-aspartate receptor antagonist.

Effects of trimethyltin (TMT) on choline acetyltransferase activity in the rat hippocampus. Influence of dose and time following exposure.

Trimethyltin (TMT) destroys specific subfields of the hippocampus in the rat. TMT also increases choline acetyltransferase (ChAT) activity in CA1 of Ammon's horn and the outer molecular layer of the dentate gyrus. This observation suggests that axonal sprouting occurs in the cholinergic septohippocampal system in response to TMT. However, neither does-response nor time course data are available for the effects of TMT on this enzyme. The effects of three dose levels of TMT on ChAT activity in CA1 and the dentate gyrus were determined in Experiment 1 and ChAT activity in these two areas was measured at six time points following exposure to TMT in Experiment 2. Only the highest dose of TMT (6 mg/kg) significantly increased ChAT activity. ChAT activity in the dentate gyrus increased significantly by 3 d after administration and continued to increase until 21 d after exposure. A significant increase was not observed in CA1 until 7 d after exposure to TMT. Asymptotic levels were still reached at d 21. These results indicate a steep dose-response curve for TMT-induced changes in ChAT activity in the hippocampal formation and that this marker of cholinergic activity is more sensitive to perturbation by TMT in the dentate gyrus than Ammon's horn.

The effect of time following exposure to trimethyltin (TMT) on cholinergic muscarinic receptor binding in rat hippocampus.

Adult male Long-Evans rats were given 6 mg/kg trimethyltin (TMT). Rats were killed 1, 3, 7, 14, 21, 35, or 60 d later. An untreated control group was included. Brain sections were processed using film autoradiography to visualize in the hippocampus either total muscarinic receptor binding ([3H]quinuclidinyl benzilate; [3H]QNB), or M1 receptors ([3H]pirenzepine; [3H]PZ), or M2 receptors ([3H]oxotremorine-M; [3H]OXO-M). A reduction in [3H]QNB binding was found in CA1 and CA3c 7 d after TMT, but not in CA3a, b, or the dentate gyrus. [3H]PZ binding was decreased throughout Ammon's horn by 14 d after treatment. [3H]OXO-M binding decreased 1 d after exposure in CA1 and in all subfields of Ammon's horn by d 3. Neither [3H]PZ or [3H]OXO-M binding decreased in the dentate gyrus of TMT-treated rat at any time point. The temporal patterns of receptor loss may be explicable by reference to timing of fiber and cell body degeneration reported in previous studies and the regional differences may account for discrepancies between reports of either substantial decreases or no loss in hippocampal muscarinic receptors after TMT exposure.

Effects of trimethyltin on acquisition and reversal of a light-dark discrimination by rats.

The behavioral deficits produced by trimethyltin (TMT) are usually attributed to the hippocampal damage caused by this toxicant. The purpose of this experiment was to determine the effects of TMT administration on acquisition and reversal of a discrete trial light-dark discrimination. Acquisition of this task is impaired by hippocampal lesions but the effects of TMT on it are not known. Forty-five days after some of the rats were given one of three doses of TMT, adult, male Long-Evans rats were given 100 trials per day for 20 days to acquire a discrete trial lever press discrimination with lit cue lights located above the correct lever. At the end of this time the contingencies were reversed and the rats were given 30 more days of training. No significant group differences occurred during the first 20 days. A significant group effect was found for the 30 days of reversal training. The rats given the highest dose of TMT (6 mg/kg) obtained significantly more reinforcements during reversal training than the other groups. Because surgical hippocampal lesions generally impair both acquisition and reversal of visual discriminations, these data were unexpected and suggest that other factors than hippocampal damage enter into the behavioral effects of TMT.

Transplant-induced working memory deficits in hippocampectomized rats.

This experiment determined the effects of transplantation of fetal hippocampus on the ability of male rats with hippocampal lesions to acquire versions of a radial arm maze that depended on either extramaze cues or intramaze cues for solution. Rats receiving transplants took significantly more trials than control rats to emit three consecutive errorless trials in the extramaze cue (spatial) variation of the maze. Rats with just hippocampal lesions never differed from any other group. No differences in this measure were found for the intramaze cue condition. Rats receiving transplants made more repeat entries into reinforced arms in both versions of the maze than control rats and more reentries into neverbaited arms in the spatial maze. Rats with hippocampal lesions failed to differ from any other group on this measure in the spatial maze, but were different from normal rats in the intramaze cue maze. These data suggest that in some tasks transplants of fetal tissue lead to greater behavioral impairment than lesions alone.

Clinical features and linkage analysis of a family with autosomal dominant juvenile glaucoma.

BACKGROUND: Juvenile glaucoma is an uncommon form of open-angle glaucoma that is usually recognized during childhood or early adulthood and which often has a strong family history. METHODS: The authors clinically characterized a large multigeneration family with autosomal-dominant, juvenile-onset, open-angle glaucoma. Linkage analysis with short tandem repeat polymorphisms was used to evaluate the Rieger's syndrome locus as the site of the disease-causing mutation. RESULTS: Forty members of a family with a five-generation history of open-angle glaucoma were examined. Clinical data were available from an additional five individuals, three of whom were decreased. Older family members provided limited information about the visual history of five other deceased individuals in the first three generations. Fifty-nine people were at 50% risk of harboring the disease-causing mutation; and of these, 30 were affected with glaucoma by examination or by family history. All affected patients had an affected parent. The average age at diagnosis was 18 years (range, 8-30 years). Affected family members tended to be myopic but lacked other ocular or systemic abnormalities. The intraocular pressures (IOPs) of affected individuals were commonly more than 50 mmHg when they were first examined. Gonioscopy showed the angles to be open, with no abnormal pigmentation, iris processes, or embryonic tissue. Topical medications were initially effective in controlling IOP, but surgery was usually required for long-term pressure control. The Rieger's syndrome locus on chromosome 4q25 was excluded as the site of the disease-causing mutation. CONCLUSION: Juvenile open-angle glaucoma can occur as an autosomal dominant trait with high penetrance. Genetic linkage analysis of the family reported here has the potential to identify the chromosomal location of a glaucoma-causing gene. This gene is genetically distinct from the chromosome 4 locus that was recently associated with Rieger's syndrome.

Trimethyltin increases choline acetyltransferase in rat hippocampus.

The environmental neurotoxin trimethyltin (TMT) destroys parts of the hippocampal formation as well as the entorhinal cortex but leaves the septal cholinergic projection to the hippocampus and dentate gyrus intact. In this study we measured choline acetyltransferase (ChAT) activity in micropunch samples of the dentate gyrus, the CA1 region of Ammon's horn, and the caudate-putamen as a measure of density of cholinergic innervation in control rats and rats exposed to 7 mg/kg TMT by means of gastric intubation. Three months after the rats were exposed to a single dose of TMT both the dentate gyrus and CA1 demonstrated significantly higher ChAT activity in TMT-exposed rats than in control rats. No differences were found between groups for the caudate-putamen samples. These results support the hypothesis that exposure to TMT causes reactive synaptogenesis in the cholinergic septohippocampal system.

Effect of bombesin on behaviors associated with ethanol satiation and blood ethanol levels.

The behavioral specificity and physiological significance of bombesin-induced inhibition of ethanol intake were assessed in water-deprived rats. The behavioral display accompanying suppression of 5% ethanol intake by bombesin tetradecapeptide (BBS-14, 1-4 micrograms/kg) was measured with an instantaneous time-sampling technique. Blood ethanol levels were measured after peripheral BBS-14 and bombesin nonapeptide (BBS-9) administration, and after either oral self-administration or peripheral injection of ethanol. The display accompanying BBS-14-reduced ethanol consumption differed from control in that less drinking and feeding behaviors were observed and resting increased, dose-dependently. The typical behavioral sequence of ethanol satiation was observed in all conditions. Both BBS-14 and -9 reduced blood ethanol levels when oral intake was suppressed, and BBS-14 did not affect blood ethanol levels or elimination rate when ethanol was injected. The results are compatible with an hypothesis of a functional role for endogenous bombesin-like peptides and receptors in a neuropeptide control of ethanol intake and energy balance.

Efficient Implementation of the Fuzzy c-Means Clustering Algorithms.

This paper reports the results of a numerical comparison of two versions of the fuzzy c-means (FCM) clustering algorithms. In particular, we propose and exemplify an approximate fuzzy c-means (AFCM) implementation based upon replacing the necessary ``exact'' variates in the FCM equation with integer-valued or real-valued estimates. This approximation enables AFCM to exploit a lookup table approach for computing Euclidean distances and for exponentiation. The net effect of the proposed implementation is that CPU time during each iteration is reduced to approximately one sixth of the time required for a literal implementation of the algorithm, while apparently preserving the overall quality of terminal clusters produced. The two implementations are tested numerically on a nine-band digital image, and a pseudocode subroutine is given for the convenience of applications-oriented readers. Our results suggest that AFCM may be used to accelerate FCM processing whenever the feature space is comprised of tuples having a finite number of integer-valued coordinates.