Heritability of symptoms in an experimental model of neuropathic pain.

Male and female rats underwent transection and ligation of the sciatic and saphenous nerves, and the development of autonomy was monitored. The deafferented animals were then interbred, always selecting males and females that expressed relatively high and, alternatively, relatively low levels of autotomy. Offspring were similarly operated and interbred. By the sixth generation of selective breeding, lines were achieved in which autotomy was consistently high (HA) or consistently low (LA). There was no indication of sex linkage. Thermal and mechanical nocifensive responsiveness co-selected with propensity to express autotomy following nerve injury: response thresholds were lower in HA than in LA rats. F1 hybrids formed by crossing homozygous HA and LA animals showed low levels of autotomy, similar to LA stock. This indicates recessive inheritance of the autotomy trait. Backcrossing F1 hybrids onto the LA line yielded a low autotomy phenotype in almost all cases; backcrossing F1 hybrids onto HA stock yielded about 50% high autotomy and 50% low autotomy. These ratios are consistent with simple mendelian inheritance of a single gene. Taken together, the data suggest that autotomy is inherited as a single-gene autosomal recessive trait.

Correlation of intact sensibility and neuropathic pain-related behaviors in eight inbred and outbred rat strains and selection lines.

In some rat strains, total hindpaw denervation triggers autotomy, a behavior of self mutilation presumably related to neuropathic pain. Partial sciatic ligation (PSL) in rats produces tactile allodynia and heat hyperalgesia but not autotomy. Our aims in this study were to examine: (1) whether sensibility of intact rats to noxious and non-noxious stimuli is strain-dependent; (2) whether sensibility of intact rats could predict levels of autotomy, or of allodynia and hyperalgesia in the PSL model; and (3) whether autotomy levels are correlated with levels of allodynia or hyperalgesia. Here we report that in two inbred rat strains (Lewis and Fisher 344), two outbred rat strains (Sabra and Sprague-Dawley) and four selection lines of rats (Genetically Epilepsy-Prone Rats, High Autotomy, Low Autotomy and Flinders Sensitive Line), tactile sensitivity and response duration to noxious heat of intact animals were strain-dependent. Levels of autotomy following hindpaw denervation and of allodynia and hyperalgesia in the PSL model were also strain-dependent. Thus, these traits are determined in part by genetic factors. Sensory sensibility of intact rats was not correlated with levels of autotomy following total denervation, or allodynia and hyperalgesia following partial denervation. We suggest that preoperative sensibility of intact rats is not a predictor of levels of neuropathic disorders following nerve injury. Likewise, no correlation was found between autotomy, allodynia and hyperalgesia, suggesting that neuropathic pain behaviors triggered by nerve injury of different etiologies are mediated by differing mechanisms.

Heritability of nociception I: responses of 11 inbred mouse strains on 12 measures of nociception.

It is generally acknowledged that humans display highly variable sensitivity to pain, including variable responses to identical injuries or pathologies. The possible contribution of genetic factors has, however, been largely overlooked. An emerging rodent literature documents the importance of genotype in mediating basal nociceptive sensitivity, in establishing a predisposition to neuropathic pain following neural injury, and in determining sensitivity to pharmacological agents and endogenous antinociception. One clear finding from these studies is that the effect of genotype is at least partially specific to the nociceptive assay being considered. In this report we begin to systematically describe and characterize genetic variability of nociception in a mammalian species, Mus musculus. We tested 11 readily-available inbred mouse strains (129/J, A/J, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, C58/J, CBA/J, DBA/2J, RIIIS/J and SM/J) using 12 common measures of nociception. These included assays for thermal nociception (hot plate, Hargreaves' test, tail withdrawal), mechanical nociception (von Frey filaments), chemical nociception (abdominal constriction, carrageenan, formalin), and neuropathic pain (autotomy, Chung model peripheral nerve injury). We demonstrate the existence of clear strain differences in each assay, with 1.2 to 54-fold ranges of sensitivity. All nociceptive assays display moderate-to-high heritability (h2 = 0.30-0.76) and mediation by a limited number of apparent genetic loci. Data comparing inbred strains have considerable utility as a tool for understanding the genetics of nociception, and a particular relevance to transgenic studies.

Heritability of nociception II. 'Types' of nociception revealed by genetic correlation analysis.

Clinical pain syndromes, and experimental assays of nociception, are differentially affected by manipulations such as drug administration and exposure to environmental stress. This suggests that there are different 'types' of pain. We exploited genetic differences among inbred strains of mice in an attempt to define these primary 'types'; that is, to identify the fundamental parameters of pain processing. Eleven randomly-chosen inbred mouse strains were tested for their basal sensitivity on 12 common measures of nociception. These measures provided for a range of different nociceptive dimensions including noxious stimulus modality, location, duration and etiology, among others. Since individual members of inbred strains are identical at all genetic loci, the observation of correlated strain means in any given pair of nociceptive assays is an index of genetic correlation between these assays, and hence an indication of common physiological mediation. Obtained correlation matrices were subjected to multivariate analyses to identify constellations of nociceptive assays with common genetic mediation. This analysis revealed three major clusters of nociception: (1) baseline thermal nociception, (2) spontaneously-emitted responses to chemical stimuli, and (3) baseline mechanical sensitivity and cutaneous hypersensitivity. Many other nociceptive parameters that might a priori have been considered closely related proved to be genetically divergent.

Hyperexcitability in sensory neurons of rats selected for high versus low neuropathic pain phenotype.

Selection line rats congenitally high or low for autotomy in the neuroma model of neuropathic pain (HA and LA rats) were found to be correspondingly high and low in a second type of neuropathic pain, the Chung model, which employs an alternative phenotypic endpoint, tactile allodynia. It has been proposed that both phenotypes reflect ectopic hyperexcitability in axotomized primary sensory neurons. To test this hypothesis we made in vitro recordings from sensory neurons in the L4 and 5 dorsal root ganglia. Baseline excitability was similar in HA and LA rats, and axotomy caused an increase in both lines. However, in the one neuronal subclass previously linked to neuropathic pain in these models the increase was significantly greater in HA than LA rats, and only at the time when pain scores in the two lines were diverging. Heritable differences in electrical response to axotomy in a specific afferent cell type appear to be a fundamental determinant of neuropathic pain.

Mechano- and thermo-sensitivity in rats genetically prone to developing neuropathic pain.

By selective breeding, lines of rats were derived which consistently expressed high (HA) or low (LA) levels of autotomy following sciatic nerve injury, autotomy being a behavior pattern presumed to reflect the presence of neuropathic paraesthesias and pain. We report here that intact (unoperated) HA and LA rats differ in their responsiveness to cutaneous mechanical and thermal stimuli. Thus, the autotomy trait, which was identified by its expression under conditions of nerve injury, shares determinants with sensory processing channels in the intact animal.

Contrasting time course of catecholamine accumulation and of spontaneous discharge in experimental neuromas in the rat.

Catecholamine-containing sympathetic axons in rat sciatic nerve-end neuromas were visualized histochemically. Within a few hours of ligating and sectioning the nerve, axons began to accumulate catecholamine histofluorescence. Density of labelled fibers peaked 2-5 days postoperative, then declined rapidly so that little or no label was observed beyond 12 days. Sympathectomy eliminated staining; neonatal treatment with capsaicin had no effect. Accumulation and dissipation of histofluorescence preceded the rise and fall of electrical hyperexcitability in neuromas by several days respectively.

Preoperative open field behavior predicts levels of neuropathic pain-related behavior in mice.

Exploratory open field (OF) activity was assessed in seven different mouse strains and selection lines. We counted the number of beam interruptions made by three cagemate mice at a time. This assay tests reactivity to aversive stimuli, anxiety and emotionality. One hindlimb was then totally denervated by transecting the sciatic and saphenous nerves on one side, and autotomy, a behavior thought to be related to neuropathic pain, was quantified over 35 days. We report that OF activity and autotomy are highly variable across different strains/lines. These results reaffirm the genetic control of these behaviors. We also found that these behaviors are inversely and significantly correlated. We suggest that common genetically-determined neural mechanisms may underlie anxiety, emotionality and neuropathic pain in mice.

Cardiovascular responses to adrenergic agents in different acclimation states in the rock pigeon (Columba livia).

The effect of propranolol on heart rate (fH) was measured in season-acclimatized pigeons. Propranolol treatment decreased fH in winter-acclimatized pigeons, accelerated fH in summer-acclimatized pigeons, but had no effect on fH in spring-acclimatized pigeons. The effect of propranolol in summer-acclimatized pigeons is opposite to that observed in mammals. Interestingly, isoproterenol produced a propranolol-like cardioacceleration in heat-acclimated pigeons. We suggest that propranolol affects fH in summer-acclimatized pigeons via two opposing routes-a direct and a peripheral indirect route. We also suggest that the cardiovascular effects of propranolol are involved in the capacity of the pigeon to evaporate water from its skin.

Anti-leukemic mechanisms of pegylated arginase I in acute lymphoblastic T-cell leukemia.

New treatments for adults with acute lymphoblastic T-cell leukemia (T-ALL) are urgently needed, as the current rate of overall remission in these patients is only about 40 percent. We recently showed the potential therapeutic benefit of the pegylated-human-arginase I (peg-Arg I) in T-ALL. However, the mechanisms by which peg-Arg I induces an anti-T-ALL effect remained unknown. Our results show the induction of T-ALL cell apoptosis by peg-Arg I, which associated with a global arrest in protein synthesis and with the phosphorylation of the eukaryotic-translation-initiation factor 2 alpha (eIF2α). Inhibition of eIF2α phosphorylation in T-ALL cells prevented the apoptosis induced by peg-Arg I, whereas the expression of a phosphomimetic eIF2α form increased the sensibility of T-ALL cells to peg-Arg I. Phosphorylation of eIF2α by peg-Arg I was mediated through kinases PERK and GCN2 and down-regulation of phosphatase GADD34. GCN2 and decreased GADD34 promoted T-ALL cell apoptosis after treatment with peg-Arg I, whereas PERK had an unexpected anti-apoptotic role. Additional results showed that phospho-eIF2α signaling further increased the anti-leukemic effects induced by peg-Arg I in T-ALL-bearing mice. These results suggest the central role of phospho-eIF2α in the anti-T-ALL effects induced by peg-Arg I and support its study as a therapeutic target.