Ketamine modulates hippocampal neurochemistry and functional connectivity: a combined magnetic resonance spectroscopy and resting-state fMRI study in healthy volunteers.

A growing body of evidence suggests glutamate excess in schizophrenia and that N-methyl-d-aspartate receptor (NMDAR) hypofunction on γ-aminobutyric acid (GABA) interneurons disinhibiting pyramidal cells may be relevant to this hyperglutamatergic state. To better understand how NMDAR hypofunction affects the brain, we used magnetic resonance spectroscopy and resting-state functional magnetic resonance imaging (MRI) to study the effects of ketamine on hippocampal neurometabolite levels and functional connectivity in 15 healthy human subjects. We observed a ketamine-induced increase in hippocampal Glx (glutamate+glutamine; F=3.76; P=0.04), a decrease in fronto-temporal (t=4.92, PFDR<0.05, kE=2198, x=-30, y=52, z=14) and temporo-parietal functional connectivity (t=5.07, PFDR<0.05, kE=6094, x=-28, y=-36, z=-2), and a possible link between connectivity changes and elevated Glx. Our data empirically support that hippocampal glutamatergic elevation and resting-state network alterations may arise from NMDAR hypofunction and establish a proof of principle whereby experimental modelling of a disorder can help mechanistically integrate distinct neuroimaging abnormalities in schizophrenia.

Effect of heating on lethality due to hyperthermia and selected chemotherapeutic drugs.

Because the rate of heating alters various cellular events associated with exposure to hyperthermia (including the rate of cell death), effect of this parameter on the cytotoxic interaction between selected anticancer drugs and hyperthermia was studied. The drugs cisplatin, 1,3-bis(2-chloroethyl)-1-nitrosourea, and adriamycin at 42.4 degrees C and bleomycin and methotrexate at 43 degrees C were tested in Chinese hamster ovary (CHO) cells in vitro. Heating times ranged from less than 3 minutes (immediate exposure) to 3 hours. For all drugs tested, synergistic cytotoxicity was not significantly altered by heating to peak temperature over 30 minutes as compared with immediate exposure. When heating to peak temperatures was prolonged to 3 hours, however, cell killing was markedly reduced, although significant sensitization to the drug remained. This was true despite the fact that, in CHO cells, heating to 42.4 degrees C over 3 hours produced no cell killing for up to 6 hours at that temperature. These results suggested that the mechanism(s) responsible for induced thermotolerance are probably different from those that cause cellular resistance to the cytotoxic effects of the drugs tested. These results may also partially explain the relative lack of clinical success with whole-body hyperthermia and chemotherapeutic drugs an anticancer treatment, because heating to therapeutic temperatures often requires 2-3 hours.

Rate of heating as a determinant of hyperthermic cytotoxicity.

In Chinese hamster ovary cells and in normal and transformed rat embryonic fibroblasts, survival as a function of time at 42.4 degrees was dependent upon the rate of heating from 37 degrees to 42.4 degrees. Unexpectedly, the untransformed rat fibroblasts were more heat sensitive than were the transformed cells, and the protective effect of slow rates of heating upon survival at 42.4 degrees was also more pronounced in the normal cells than in the transformed cells. In Chinese hamster ovary cells, total cellular cholesterol content and cell volume were found to change significantly with time at 42.4 degrees when cells were heated immediately (37 to 42.4 degrees within 3 min) but did not vary significantly during 6 hr at 42.4 degrees in cells heated from 37 to 42.4 degrees over 3 hr. Chinese hamster ovary cells heated immediately to 42.4 degrees also showed a significant drop in the protein content of the particulate fraction with time at 42.4 degrees. In contrast, cells heated over 3 hr showed a significant increase in the protein content of the particulate fraction with time at 42.4 degrees. These data suggest that, if cells are heated to hyperthermic temperatures over sufficiently long intervals, mechanisms have time to develop which protect the cell membrane against changes associated with cell death in rapidly heated cells. The protective effect of slow rates of heating may partially explain the relative lack of success thus far observed with the use of whole-body hyperthermia in which heating from 37 degrees to 42 degrees often requires 2 to 3 hr.

Morning vs evening light treatment for winter depression. Evidence that the therapeutic effects of light are mediated by circadian phase shifts.

Bright light exposure has been found to alleviate the symptoms of recurrent winter depression in many patients. The mechanism of light therapy may involve shifts in the timing (phase) of circadian rhythms. In this study, morning light exposure (which shifts rhythms earlier) was compared with evening light exposure (which shifts rhythms later) in a double-blind, crossover design. The onset of melatonin secretion in the evening was measured under dim light conditions as a marker for circadian timing (phase) before and after each treatment. Eight patients with winter depression and five control subjects were studied. Morning light was found to be significantly better than evening light in reducing depressive symptoms. At baseline, there was a trend for the onset of melatonin production to be later in the patients than in the controls. Morning light shifted the melatonin onset significantly earlier in the patients but not the controls. Our findings suggest that patients with winter depression have circadian rhythms that are abnormally delayed and that bright light therapy benefits winter depression by providing a corrective advance.

Neurologic syndrome in 25 workers from an aluminum smelting plant.

BACKGROUND: This article expands on an earlier series of three patients with a neurologic syndrome, who had all worked in an aluminum smelting plant. METHODS: Twenty-five symptomatic workers from the same plant were referred for a standardized evaluation, including completion of a health questionnaire, neurologic examination, and neuropsychologic evaluation. An exposure index was calculated for each worker based on level and duration of exposure in the potroom, where exposures were the greatest. This index was correlated with symptoms, signs, and neuropsychologic test scores. RESULTS: Twenty-two (88%) of the patients reported frequent loss of balance, and 21 (84%) reported memory loss. Neurologic examination revealed signs of incoordination in 21 (84%) of the patients. Neuropsychologic test results showed preservation in certain spheres of functioning, such as verbal IQ, with substantial impairment in others, particularly memory functioning. On memory tests, 70% to 75% showed mild or greater impairment. The majority (17 of 19 tested, or 89%) showed depression on the Minnesota Multiphasic Personality Inventory. The exposure index was significantly correlated with signs and symptoms of incoordination. CONCLUSIONS: This study and others in humans and animals support the existence of a syndrome characterized by incoordination, poor memory, impairment in abstract reasoning, and depression. Aluminum exposure in the potroom seems the most likely cause.

Crystallization and preliminary crystallographic analysis of recombinant human P38 MAP kinase.

The recombinant human p38 MAP kinase has been expressed and purified from both Escherichia coli and SF9 cells, and has been crystallized in two forms by the hanging drop vapor diffusion method using PEG as precipitant. Both crystal forms belong to space group P2(1)2(1)2(1). The cell parameters for crystal form 1 are a = 65.2 A, b = 74.6 A and c = 78.1 A. Those for crystal form 2 are a = 58.3 A, b = 68.3 A and c = 87.9 A. Diffraction data to 2.0 A resolution have been collected on both forms.

An alternate splicing variant of the human telomerase catalytic subunit inhibits telomerase activity.

Telomerase, a cellular reverse transcriptase, adds telomeric repeats to chromosome ends. In normal human somatic cells, telomerase is repressed and telomeres progressively shorten, leading to proliferative senescence. Introduction of the telomerase (hTERT) cDNA is sufficient to produce telomerase activity and immortalize normal human cells, suggesting that the repression of telomerase activity is transcriptional. The telomerase transcript has been shown to have at least six alternate splicing sites (four insertion sites and two deletion sites), and variants containing both or either of the deletion sites are present during development and in a panel of cancer cell lines we surveyed. One deletion (beta site) and all four insertions cause premature translation terminations, whereas the other deletion (alpha site) is 36 bp and lies within reverse transcriptase (RT) motif A, suggesting that this deletion variant may be a candidate as a dominant-negative inhibitor of telomerase. We have cloned three alternately spliced hTERT variants that contain the alpha, beta or both alpha and beta deletion sites. These alternate splicing variants along with empty vector and wild-type hTERT were introduced into normal human fibroblasts and several telomerase-positive immortal and tumor cell lines. Expression of the alpha site deletion variant (hTERT alpha-) construct was confirmed by Western blotting. We found that none of the three alternate splicing variants reconstitutes telomerase activity in fibroblasts. However, hTERT alpha- inhibits telomerase activities in telomerase-positive cells, causes telomere shortening and eventually cell death. This alternately spliced dominant-negative variant may be important in understanding telomerase regulation during development, differentiation and in cancer progression.

Immunohistochemical localization of substance P in postmortem rat and human spinal cord.

The stability of substance P-like immunoreactivity was examined in postmortem rat and human spinal cord using radioimmunoassay and indirect fluorescence immunohistochemistry. The distribution of fluorescence in rat and human spinal cord was unchanged at intervals up to 48 hours (h) and 87 h, respectively. Fine linear fluorescent fibers were seen only in rat spinal cord processed at time intervals up to two h postmortem; they were never observed in human spinal cord, which was routinely obtained more than 6 h postmortem. The content of substance P-like material in human spinal cord nd its immunohistochemical appearance was not affected by age, the nature of the terminal illness, or autopsy delay. However, no correlation was found between intensity of fluorescent staining and content as measured by radioimmunoassay. It may be possible to use postmortem analysis of substance P in diseases of the central nervous system, but radioimmunoassay and immunohistochemistry should be used concurrently.

Intrinsic connections in the caudal subdivision of the dorsolateral visual area (DL(C)) in squirrel monkeys.

Patterns of intrinsic connections and features of individual intrinsic axons in the caudal subdivision of the dorsolateral visual area (DL(C)) were investigated in four squirrel monkeys (Saimiri) following extracellular injections of the tracers biocytin, biotinylated dextran amine, and wheat germ agglutinin conjugated to horseradish peroxidase. Injections were defined in DL(C) by reference to architectonic borders and patterns of connections with other cortical areas. Intrinsic connections extended up to 6 mm from an injection and were usually anisotropic, extending farther dorsoventrally than anteroposteriorly. Injections that involved the supragranular layers produced up to 20 mainly supragranular patches of projections that had a width of 285 +/- 8 microm (mean +/- standard error) and area of 0.125 +/- 0.016 mm(2). Seventy-four intrinsic axon segments with a total of 3,290 boutons were drawn and their bouton spacing measured. The sample included axons in layers 1, 2-3, 5, and multiple (>2) layers; horizontally and vertically oriented axons; and axons in an injection halo, patch, or nonpatch region of projections. There were no differences in bouton spacing for axons in halo, patch, or nonpatch regions. Layer 1 axons (n = 7) had a significantly sparser distribution of boutons (median interbouton interval of 45.2 +/- 17.8 microm) than the layers 2-3 (n = 35) and layer 5 axons (n = 26), which did not differ in bouton spacing (median interbouton intervals of 8.1 +/- 0.4 microm and 8.4 +/- 0.8 microm, respectively). Patterns of intrinsic connections in DL(C) are related to neural organization and properties reported for DL or visual area V4, and are compared to intrinsic connections of other areas.

Mechanism of prostaglandin E2-induced substance P release from cultured sensory neurons.

Hyperalgesia (tenderness) is a prominent feature of the inflammatory response. It is thought to be mediated, in part, by humoral factors such as prostaglandin E2, which act directly to sensitize primary afferent nociceptors. Prostaglandin E2 also interacts with nociceptors to induce a release of substance P, which can feed back to enhance the inflammatory response and also induce a long-lasting hyperalgesia. This study examined the mechanism of prostaglandin E2-induced substance P release from cultured adult rat dorsal root ganglion cells. Release studies were performed by bathing cultures with Tyrode solution +/- test agents and substance P was measured by radioimmunoassay. Substance P release induced by 100 nM prostaglandin E2 was inhibited by the prostaglandin antagonist, SC19220, and modulated by the guanine nucleotide analogs, guanosine-5'-[gamma-thio]triphosphate and guanosine-5'-[beta-thio]diphosphate, which stimulate and inhibit, respectively, stimulatory G-proteins. Substance P release was found to be Ca(2+)-dependent, requiring an influx of Ca2+ via N-type voltage-sensitive Ca2+ channels, since it was blocked by omega-conotoxin, but not nifedipine. The results suggest that prostaglandin E2 acts via a G-protein-coupled binding site on dissociated dorsal root ganglion cells to induce a Ca(2+)-dependent release of substance P, and provide further insight into the possible mechanisms underlying hyperalgesia associated with inflammation.

Contribution of neurotrophin-3 to the neuropeptide Y-induced increase in neurite outgrowth of rat dorsal root ganglion cells.

Recent studies show that neuropeptide Y acts indirectly, via release of a neurotrophic factor(s) from the spinal cord, to increase the neurite outgrowth of dissociated adult rat dorsal root ganglion cells. This study examines further the neuropeptide Y-induced increase in neurite outgrowth. To characterize the factor(s) mediating the neuropeptide Y-induced increase in neurite outgrowth, we have examined whether antisera to either nerve growth factor or neurotrophin-3 influence the neuropeptide Y-induced increase in neurite outgrowth. Spinal cord slices were incubated with media alone or in combination with 10 nM neuropeptide Y for 2 h at 37 degrees C. The supernatant of spinal cord incubated with neuropeptide Y significantly enhanced the neurite outgrowth of normal dorsal root ganglion cells. Antiserum against nerve growth factor had no effect on the trophic actions of the supernatant. Antiserum against neurotrophin-3, however, significantly attenuated the increase in neurite outgrowth. Consistent with this finding, neurotrophin-3 also increased the percentage of cells with neurites. Transganglionic labelling of A-fibres with choleragenoid-horseradish peroxidase in animals treated intrathecally with neurotrophin-3 for 14 days via an osmotic pump showed that the area of choleragenoid-horseradish peroxidase label expanded into lamina II. In comparison, saline-treated animals had no label in lamina II. In addition, neurotrophin-3-treated animals also had a significant decrease in mechanical nociceptive threshold. The results suggest that neuropeptide Y acts via neurotrophin-3 to mediate an increase in neurite outgrowth of dorsal root ganglion cells. These results have important implications for the mechanisms underlying neuropathic pain.

Vasoactive intestinal polypeptide and neuropeptide Y act indirectly to increase neurite outgrowth of dissociated dorsal root ganglion cells.

Recent studies suggest that rearrangement of synaptic circuitry of primary afferent neurons in the spinal cord may contribute, in part, to hyperalgesia that is often associated with peripheral nerve injury. This study of cultured adult rat dorsal root ganglion cells examined whether vasoactive intestinal polypeptide and neuropeptide Y, which are up-regulated in sensory neurons following nerve transection, possibly contribute to the morphological alterations induced by nerve injury. Neurite outgrowth of dissociated dorsal root ganglion cells was examined two weeks following either sciatic nerve transection or intrathecal administration of test agents via osmotic pumps. Dissociated cells taken from rats with transected sciatic nerve or following intrathecal administration of either vasoactive intestinal polypeptide or neuropeptide Y had a significant increase in the percentage of cells with neurites as compared to dorsal root ganglion cells taken from normal animals. Intrathecal administration, into rats with nerve lesion, of the vasoactive intestinal polypeptide and neuropeptide Y antagonists, vasoactive intestinal polypeptide(10-28) and alpha-trinositol, respectively, significantly attenuated the nerve injury-induced increase in neurite outgrowth. Vasoactive intestinal polypeptide and neuropeptide Y had no influence on neurite outgrowth when applied to normal dissociated dorsal root ganglion cells, however, when added to cells co-cultured with spinal cord explants, both peptides significantly increased the percentage of cells with neurites. K252a, a protein kinase inhibitor, attenuated the trophic action of neuropeptide Y, but not that of vasoactive intestinal polypeptide. The action of vasoactive intestinal polypeptide on neurite outgrowth was attenuated by the protein kinase A inhibitor, the Rp-isomer of adenosine-3',5'-cyclic monophosphorothioate. The results suggest that the peptides may contribute, indirectly, to the nerve injury-induced increase in neurite outgrowth of sensory neurons via separate spinally-derived neurotrophic factors and the study provides further insight into the possible mechanisms underlying hyperalgesia associated with nerve injury.

Interstitial deletions of the short arm of chromosome 4 in patients with a similar combination of multiple minor anomalies and mental retardation.

Interstitial deletions of chromosome 4 have been described rarely and have had variable presentations. We describe the phenotypic characteristics associated with interstitial deletion of the p14-16 region of chromosome 4 in 7 patients with multiple minor anomalies in common, and with mental retardation. A review of published cases of interstitial deletions of the short arm of chromosome 4 is provided. These deletions present a distinct phenotype which is different from that of Wolf-Hirschhorn syndrome.

Cognition and metacognition at extreme altitudes on Mount Everest.

The FACTRETRIEVAL2 test battery, which assesses both retrieval of general information from memory and metacognition about that retrieval, was administered to people before and after a recent expedition to Mount Everest and at extreme altitudes above 6,400 m (higher than any mountain in North America or Europe). The major findings were as follows: First, the same extreme altitudes already known to impair learning did not affect either accuracy or latency of retrieval, and this robustness of retrieval occurred for both recall and forced-choice recognition. Second, extreme altitude did affect metacognition: The climbers showed a decline in their feeling of knowing both while at extreme altitude and after returning to Kathmandu (i.e., both an effect and an aftereffect of extreme altitude). Third, extreme altitude had different effects than alcohol intoxication (previously assessed by Nelson. McSpadden, Fromme, & Marlatt, 1986). Alcohol intoxication affected retrieval without affecting metacognition, whereas extreme altitude affected metacognition without affecting retrieval; this different pattern for extreme altitude versus alcohol intoxication implies that (a) hypoxia does not always yield the same outcome as alcohol intoxication and (b) neither retrieval nor metacognition is strictly more sensitive than the other for detecting changes in independent variables.

Assessment of proliferative activity in leukaemic bone marrow using the monoclonal antibody Ki-67.

AIMS: To investigate proliferative activity in leukaemic and lymphomatous bone marrow infiltrates and to assess the feasibility of transport of specimens among institutions. METHODS: Proliferative activity in bone marrow trephine cryosections from 99 patients with non-Hodgkin's lymphoma (NHL), 23 patients with acute myeloid leukaemia (AML), 11 with acute lymphoblastic leukaemia (ALL), and two with acute undifferentiated leukaemia (AUL) was investigated. Infiltration was seen in 52 out of 99 cases of NHL on bone marrow cryosections. A score was devised to assess pathological infiltrates in bone marrow trephine cryosections using the monoclonal antibody Ki-67. This method of scoring gave a measure of non-erythroid proliferative activity. RESULTS: Mean Ki-67 positivity in bone marrow infiltrates in 31 low grade B cell lymphomas (Kiel classification) was 0.3% before and 4.7% after treatment, 16.4% in seven high grade B cell lymphomas, and 17.8% in 12 peripheral T cell lymphomas. In 48 cases of NHL, bone marrow cryosections had not been infiltrated, and in all but one case the percentage of Ki-67 positive cells in normal marrow was less than 3%; the remaining case showed coexistent myelodysplasia and 8% bone marrow Ki-67 positivity. In eight cases of common ALL at diagnosis, the mean Ki-67 positivity in marrow cryosections was 24.9%, significantly higher than the 2.4% Ki-67 positivity seen in AML (p < 0.05). One of the two cases of common ALL with less than 1% Ki-67 positivity was refractory to treatment. CONCLUSIONS: Proliferative activity of erythroid elements in the bone marrow varies greatly. Immunostaining of bone marrow cryosections using Ki-67 permits accurate assessment of non-erythroid proliferative activity in lymphomas and leukaemia. High grade B cell lymphomas and peripheral T cell lymphomas invading the marrow have very similar mean proliferative activities. Such levels of proliferation are of the same order as those seen in common ALL, but much higher than those seen in AML.

Peripheral T cell lymphoma: value of bone marrow trephine immunophenotyping.

Bone marrow infiltrates taken from 11 patients with peripheral T cell lymphoma were immunophenotyped as T cell lymphoma using monoclonal antibodies on frozen bone marrow trephine biopsy specimens. In nine these were taken at diagnosis and in two after failure of treatment to eradicate lymphoma in the marrow. Patterns of infiltration were as follows: diffuse (n = 4), interstitial (n = 1), nodular (n = 1), focal (n = 5). All cases were CD3 positive and 10 were CD2 positive; five lacked expression of either CD5 or CD7, or both markers. In nine the determination of T cell phenotype depended on analysis of the frozen bone marrow trephine biopsy specimen as there was no other biopsy tissue available for study. In the other two cases there was agreement between the immunophenotypes seen in lymph node and bone marrow infiltrates.

Eicosanoids, but not tachykinins, excite C-fiber endings in rat sciatic nerve-end neuromas.

Normal nociceptors are sensitized by hyperalgesic mediators such as eicosanoids and tachykinins. The possibility that these mediators contribute to hyperalgesic pain associated with neural injury was investigated by examining their effects on the excitability of injured afferent nerve endings. In amounts that sensitize normal nociceptors and are hyperalgesic in normal skin, the eicosanoids prostaglandin I2 (PGI2), and 8(R),15(S)-dihydroxyicosatetraenoic acid (8(R),15(S)-diHETE) both excited some C-fibers in chronic neuromas of rat sciatic nerve. In contrast, the selective tachykinin-receptor agonists septide and senktide did not excite C-fibers. None of the mediators affected A-fibers. We conclude that PGI2 and 8(R),15(S)-diHETE may contribute to post-injury pain and hyperalgesia by an action on injured afferent endings.

Neurotrophin-3 antisense oligonucleotide attenuates nerve injury-induced Abeta-fibre sprouting.

It is proposed that following peripheral nerve injury abnormal sprouting of Abeta-fibre primary afferent neurons in the spinal cord contributes to the allodynia that often occurs with such injury. Allodynia is characterized as pain due to a stimulus which is normally non-noxious. Our recent in vivo experiments show that intrathecal administration of neurotrophin-3 (NT-3), in normal animals, induces allodynia and sprouting of Abeta-fibres. In this study, we examine whether intrathecal administration of NT-3 antisense oligonucleotides (50 microM), via an osmotic pump for 14 days, attenuates nerve injury-induced sprouting and allodynia. The oligonucleotides used in this study were phosphorothioate modified and control experiments, using an ELISA, confirm that intrathecal administration of the antisense induces a significant decrease in NT-3 levels in the spinal cord. All surgery was conducted on anaesthetized Wistar rats (sodium pentobarbitone, i.p. 50 mg/kg). Consistent with previous studies, transganglionic labelling of Abeta-fibres with choleragenoid-horseradish peroxidase (C-HRP) shows that complete transection of the sciatic nerve induces an expansion of C-HRP label into lamina II of the spinal dorsal horn. Using image analysis, we find that intrathecal administration of NT-3 antisense attenuates the density of C-HRP labelling in lamina II in nerve injured animals. A NT-3 sense oligonucleotide (50 microM) has no effect. To test the effect of NT-3 antisense on allodynia, the nociceptive flexion reflex is examined, using an Ugo Basile Analgesymeter, in animals with partial sciatic nerve ligation. Intrathecal administration of 50 microM NT-3 antisense significantly attenuates nerve injury-induced allodynia, whereas the sense oligonucleotide has no effect. These results provide further evidence that endogenous NT-3 contributes to both nerve injury-induced Abeta-fibre sprouting and allodynia and demonstrates the potential of neurotrophin-3 antisense oligonucleotides as therapeutic agents for neuropathic pain.

Intrathecal neuropeptide Y exacerbates nerve injury-induced mechanical hyperalgesia.

In normal animals, spinal administration of neuropeptide Y induces analgesia to thermal stimuli, but has no effect on mechanical thresholds. Recent anatomical studies, however, have shown that following nerve injury there is an altered expression of neuropeptide Y and its receptors. The aim of this behavioural study, therefore, is to examine the effect of intrathecal administration of neuropeptide Y, its agonists and an antagonist on mechanical nociceptive thresholds in rats with partial injury to the sciatic nerve. Test agents were administered for 14 days via osmotic pumps (0.5 microliter/day) attached to intrathecal catheters and the nociceptive flexion reflex was quantified using an Ugo Basile Analgesymeter. Partial injury to the sciatic nerve, in animals treated intrathecally with saline, induces a significant decrease in mechanical threshold as compared to the sham operated, contralateral paw. The nerve injury-induced hyperalgesia is exacerbated by 2 microM neuropeptide Y and by 2 microM [Leu31,Pro34]-neuropeptide Y, a Y1 receptor agonist. The Y2 receptor agonist, N-acetyl-[Leu28,Leu31]-neuropeptide Y24-36 (2 microM), had no effect on the nerve injury-induced hyperalgesia. The putative neuropeptide Y antagonist, alpha-trinositol (10 microM), significantly attenuated the nerve injury-induced hyperalgesia. This study suggests that neuropeptide Y may contribute to nerve injury-induced mechanical hyperalgesia via the Y1 receptor and provides further insight into the possible mechanisms underlying nerve injury-induced hyperalgesia to mechanical stimuli.

Effect of subcutaneous administration of calcium channel blockers on nerve injury-induced hyperalgesia.

Recent studies suggest that calcium contributes to peripheral neural mechanisms of hyperalgesia associated with nerve damage. In this animal behavioural study, we examined further the contribution of calcium in neuropathic pain by testing whether subcutaneous administration of either a calcium chelating agent or voltage-dependent calcium channel blockers attenuate nerve injury-induced hyperalgesia to mechanical stimulation. Studies were carried out in animals with partially ligated sciatic nerves, an established animal model of neuropathic pain. The nociceptive flexion reflex was quantified using an Ugo Basile Analgesymeter. Partial nerve injury induced a significant decrease in mechanical threshold compared to the sham operated controls. Daily subcutaneous injections of the calcium chelating agent, Quin 2 (20 microgram/2.5 microliter), significantly attenuated the nerve injury-induced hyperalgesia. Similarly, SNX-111, a N-type channel blocker, also significantly attenuated the nerve injury-induced hyperalgesia. SNX-230, a P and/or Q-type channel blocker, and nifedipine, a L-type channel blocker, had no effect on the hyperalgesia to mechanical stimulation. In control experiments, SNX-111 had no effect on mechanical thresholds when administered subcutaneously in either the hindpaw of normal animals or the back of the neck in nerve injury animals. This study shows that neuropathic pain involves a local calcium-dependent mechanism in the receptive field of intact neurons of an injured nerve, since it can be alleviated by subcutaneous injections of either a calcium chelating agent or SNX-111, a N-type calcium channel blocker. These agents may be effective, peripherally acting therapeutic agents for neuropathic pain.