Biomedical subjects

A I Basbaum

Publications and source records attributed to A I Basbaum.

At least 19 recordsLinked to original sources

PubMed2006

Differential contribution of TRPV1 to thermal responses and tissue injury-induced sensitization of dorsal horn neurons in laminae I and V in the mouse.

Our previous recordings from dorsal root ganglion and spinal lamina V neurons from TRPV1-mutant mice showed dramatic decreases in responses to temperatures near the activation threshold of this channel (43-49 degrees C). Somewhat unexpectedly, we only observed behavioral deficits in these mice at higher temperatures (50-58 degrees C). In the present study, we tested the hypothesis that the noxious heat-evoked pain behavior that persists in TRPV1-mutant mice reflects residual responsiveness of neurons in the superficial, but not deep, dorsal horn. To this end, we performed in vivo extracellular recordings of spinal nociresponsive neurons in laminae I and V in wild type (WT) and TRPV1 mutant mice. Neurons in WT and mutant mice from both laminae did not differ in their spontaneous activity or evoked responses to mechanical or cold stimuli. By contrast, most lamina I neurons from mutant mice responded to noxious heat with significantly higher thresholds than in WT mice. In contrast, lamina V neurons from mutant mice were virtually unresponsive to noxious heat before and after topical mustard oil-induced tissue injury. Interestingly, lamina I neurons in mutant mice displayed thermal sensitization following tissue injury, comparable in magnitude, but of shorter duration, than in WT mice. We conclude that TRPV1 is necessary for noxious heat-evoked responses of lamina V neurons, both before and after tissue injury. It is also an essential contributor to the normal activation threshold of lamina I neurons to noxious heat and for the full duration of thermal sensitization of lamina I neurons following injury. Finally, our results suggest that the processing of noxious thermal messages by neurons in lamina I involves convergent inputs from a heterogeneous population of primary afferent thermal nociceptors.

Analgesics, Non-Narcotic↗

PubMed2006

Absence of Reelin results in altered nociception and aberrant neuronal positioning in the dorsal spinal cord.

Mutations in reeler, the gene coding for the Reelin protein, result in pronounced motor deficits associated with positioning errors (i.e. ectopic locations) in the cerebral and cerebellar cortices. In this study we provide the first evidence that the reeler mutant also has profound sensory defects. We focused on the dorsal horn of the spinal cord, which receives inputs from small diameter primary afferents and processes information about noxious, painful stimulation. We used immunocytochemistry to map the distribution of Reelin and Disabled-1 (the protein product of the reeler gene, and the intracellular adaptor protein, Dab1, involved in its signaling pathway) in adjacent regions of the developing dorsal horn, from early to late embryonic development. As high levels of Dab1 accumulate in cells that sustain positioning errors in reeler mutants, our findings of increased Dab1 immunoreactivity in reeler laminae I-III, lamina V and the lateral spinal nucleus suggest that there are incorrectly located neurons in the reeler dorsal horn. Subsequently, we identified an aberrant neuronal compaction in reeler lamina I and a reduction of neurons in the lateral spinal nucleus throughout the spinal cord. Additionally, we detected neurokinin-1 receptors expressed by Dab1-labeled neurons in reeler laminae I-III and the lateral spinal nucleus. Consistent with these anatomical abnormalities having functional consequences, we found a significant reduction in mechanical sensitivity and a pronounced thermal hyperalgesia (increased pain sensitivity) in reeler compared with control mice. As the nociceptors in control and reeler dorsal root ganglia are similar, our results indicate that Reelin signaling is an essential contributor to the normal development of central circuits that underlie nociceptive processing and pain.

Adaptor Proteins, Signal Transducing↗

PubMed2004

[d-Ala2,N-MePhe4,Gly-ol5]enkephalin-induced internalization of the micro opioid receptor in the spinal cord of morphine tolerant rats.

Several theories of opioid tolerance predict that the magnitude of micro opioid receptor (MOR) internalization in response to ligand changes in the setting of morphine tolerance. Here we show that in rats rendered tolerant to the analgesic action of morphine, cross-tolerance to the analgesic action of intrathecally administered [d-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAMGO) can be produced without changes in the magnitude of DAMGO-induced internalization of the MOR in lamina II neurons of the rat spinal cord. These results suggest that opioid tolerance-related changes in signaling are located downstream from or in parallel with receptor activation and internalization and support the idea that key features of opioid signaling are maintained, rather than reduced, in the setting of morphine tolerance.

Animals↗

PubMed2004

The contribution of autophosphorylated alpha-calcium-calmodulin kinase II to injury-induced persistent pain.

Increases in neuronal activity in response to tissue or nerve injury can lead to prolonged functional changes in the spinal cord resulting in an enhancement/sensitization of nociceptive processing. To assess the contribution of alpha-calcium-calmodulin kinase II (alpha-CaMKII) to injury-induced inflammation and pain, we evaluated nociceptive responses in mice that carry a point mutation in the alpha-CaMKII gene at position 286 (threonine to alanine). The mutated protein is unable to autophosphorylate and thus cannot function independently of calcium and calmodulin. Responses to acute noxious stimuli did not differ between alpha-CaMKII T286A mutant and wild type mice. However, the ongoing pain produced by formalin injury was significantly reduced in the mutant mice, as was formalin-evoked spinal Fos-immunoreactivity. In contrast, the decreased mechanical and thermal thresholds associated with nerve injury, Complete Freund's Adjuvant-induced inflammation or formalin-evoked tissue injury were manifest equally in wild-type and mutant mice. Double-labeling immunofluorescence studies revealed that in the mouse alpha-CaMKII is expressed in the superficial dorsal horn as well as in a population of small diameter primary afferent neurons. In summary, our results suggest that alpha-CaMKII, perhaps secondary to an N-methyl-D-aspartate-mediated calcium increase in postsynaptic dorsal horn nociresponsive neurons, is a critical contributor to the spontaneous/ongoing component of tissue-injury evoked persistent pain.

Animals↗

PubMed2001

Impaired response to chemical irritation of the urinary tract in mice with disruption of the preprotachykinin gene.

Previous studies demonstrated that acute irritation of the lower urinary tract (LUT) induces the expression of the immediate early gene, c-fos, in lumbo-sacral spinal cord neurons "J. Neurosci. 12 (1992) 4878" "Am. J. Physiol. 265 (1993) 326" "Somatosens. Mot. Res. 15 (1998) 5". This effect was mediated in part by activation of capsaicin-sensitive bladder afferents "Am. J. Physiol. 265 (1993) 326". Here we investigate the role of preprotachykinin gene products (neurokinin A and substance P) in the response to bladder irritation in urethane-anesthetized mice. Acute irritation of the LUT (intravesical acetic acid) induced smaller numbers of Fos-positive neurons in the spinal cord of mice with a mutated preprotachykinin gene than in wild type mice. Increased Fos expression following LUT irritation or a sham operation in wild type mice was also significantly reduced by pretreatment with the NK2 antagonist, MEN 11420, but Fos expression in mutant mice was not altered by the antagonist. During cystometrograms, a significantly higher percentage (83%) of mutant mice exhibited urinary retention and overflow incontinence as compared to wild type controls. These findings suggest an involvement of tachykinins and NK2 receptors in the response to chemical irritation of the LUT in mice and also suggest that tachykinins contribute to the regulation of normal reflex bladder activity.

Acetic Acid↗

PubMed2001

Molecular mechanisms of nociception.

The sensation of pain alerts us to real or impending injury and triggers appropriate protective responses. Unfortunately, pain often outlives its usefulness as a warning system and instead becomes chronic and debilitating. This transition to a chronic phase involves changes within the spinal cord and brain, but there is also remarkable modulation where pain messages are initiated - at the level of the primary sensory neuron. Efforts to determine how these neurons detect pain-producing stimuli of a thermal, mechanical or chemical nature have revealed new signalling mechanisms and brought us closer to understanding the molecular events that facilitate transitions from acute to persistent pain.

Animals↗

PubMed2001

The paired homeodomain protein DRG11 is required for the projection of cutaneous sensory afferent fibers to the dorsal spinal cord.

Cutaneous sensory neurons that detect noxious stimuli project to the dorsal horn of the spinal cord, while those innervating muscle stretch receptors project to the ventral horn. DRG11, a paired homeodomain transcription factor, is expressed in both the developing dorsal horn and in sensory neurons, but not in the ventral spinal cord. Mouse embryos deficient in DRG11 display abnormalities in the spatio-temporal patterning of cutaneous sensory afferent fiber projections to the dorsal, but not the ventral spinal cord, as well as defects in dorsal horn morphogenesis. These early developmental abnormalities lead, in adults, to significantly attenuated sensitivity to noxious stimuli. In contrast, locomotion and sensori-motor functions appear normal. Drg11 is thus required for the formation of spatio-temporally appropriate projections from nociceptive sensory neurons to their central targets in the dorsal horn of the spinal cord.

Afferent Pathways↗

PubMed2001

PKCgamma contributes to a subset of the NMDA-dependent spinal circuits that underlie injury-induced persistent pain.

In previous studies we provided evidence that the gamma isoform of protein kinase C (PKCgamma) is an important contributor to the increased pain sensitivity that occurs after injury. Here we combined electrophysiological and behavioral approaches in wild-type and PKCgamma-null mice to compare the hyperexcitability of wide dynamic range neurons in lamina V of the spinal cord dorsal horn with the behavioral hyperexcitability produced by the same injury [application of a C-fiber irritant, mustard oil (MO), to the hindpaw]. Wild-type and null mice did not differ in their response to mechanical or thermal stimuli before tissue injury, and the magnitude of the response to the MO stimuli was comparable. In wild-type mice, MO produced a dramatic and progressive enhancement of the response of lamina V neurons to innocuous mechanical and thermal stimuli. The time course of the neuronal hyperexcitability paralleled the time course of the MO-induced behavioral allodynia (nocifensive behavior in response to a previously innocuous mechanical stimulus). Neuronal hyperexcitability was also manifest in the PKCgamma-null mice, but it lasted <30 min. By contrast, the behavioral allodynia produced by MO in the PKCgamma-null mice, although reduced to approximately half that of the wild-type mice, persisted long after the lamina V hyperexcitability had subsided. Because the MO-induced behavioral allodynia was completely blocked by an NMDA receptor antagonist, we conclude that PKCgamma mediates the transition from short- to long-term hyperexcitability of lamina V nociresponsive neurons but that the persistence of injury-induced pain must involve activity within multiple NMDA-dependent spinal cord circuits.

Action Potentials↗

PubMed2001

Bradykinin and nerve growth factor release the capsaicin receptor from PtdIns(4,5)P2-mediated inhibition.

Tissue injury generates endogenous factors that heighten our sense of pain by increasing the response of sensory nerve endings to noxious stimuli. Bradykinin and nerve growth factor (NGF) are two such pro-algesic agents that activate G-protein-coupled (BK2) and tyrosine kinase (TrkA) receptors, respectively, to stimulate phospholipase C (PLC) signalling pathways in primary afferent neurons. How these actions produce sensitization to physical or chemical stimuli has not been elucidated at the molecular level. Here, we show that bradykinin- or NGF-mediated potentiation of thermal sensitivity in vivo requires expression of VR1, a heat-activated ion channel on sensory neurons. Diminution of plasma membrane phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) levels through antibody sequestration or PLC-mediated hydrolysis mimics the potentiating effects of bradykinin or NGF at the cellular level. Moreover, recruitment of PLC-gamma to TrkA is essential for NGF-mediated potentiation of channel activity, and biochemical studies suggest that VR1 associates with this complex. These studies delineate a biochemical mechanism through which bradykinin and NGF produce hypersensitivity and might explain how the activation of PLC signalling systems regulates other members of the TRP channel family.

Animals↗

PubMed2001

Differential contribution of substance P and neurokinin A to spinal cord neurokinin-1 receptor signaling in the rat.

Although the tachykinins substance P (SP) and neurokinin A (NKA) are coreleased from primary afferent nociceptors and act via neurokinin (NK) receptors, their differential effects in vivo are not known. Despite pharmacological evidence that NKA preferentially binds NK-2 receptors, this receptor is not found in spinal cord neurons. Thus, in the present studies, we compared the extent to which SP and NKA contribute to spinal nociceptive processing via the NK-1 receptor. We found that SP and NKA induce NK-1 receptor internalization with identical dose dependence and induce increases in intracellular calcium at the same concentrations, suggesting that SP and NKA equally activate the NK-1 receptor. We found, however, that the selective NK-1 receptor antagonist GR 205171 blocked NKA but not SP-induced NK-1 receptor internalization in the rat spinal cord in vivo and in embryonic day 19 rat spinal neurons in vitro. Using this selectivity of GR 205171 for NKA-induced NK-1 receptor activation, we examined the relative contribution of SP and NKA to noxious stimulus-induced activation of spinal NK-1 receptors. We estimate that NKA contributes to at least 50% of the NK-1 receptor activation in lamina I. Under inflammatory conditions, all noxious stimulus-induced NK-1 receptor internalization in deep dorsal horn neurons was blocked by GR 205171, suggesting that it is entirely NKA-mediated. Substance P-mediated NK-1 receptor internalization was focused at the site of termination of stimulated nociceptors but NKA also activated NK-1 receptors at more distant sites. We conclude that NKA not only targets the NK-1 receptor but may be a predominant pronociceptive primary afferent neurotransmitter.

Animals↗

PubMed2001

Presynaptic regulation of spinal cord tachykinin signaling via GABA(B) but not GABA(A) receptor activation.

Internalization of spinal cord neurokinin-1 receptors following noxious stimulation provides a reliable measure of tachykinin signaling. In the present study, we examined the contribution of GABAergic mechanisms to the control of nociceptor processing involving tachykinins. Spinal administration of the GABA(B) receptor agonist R(+)-baclofen in the rat, at antinociceptive doses, significantly reduced the magnitude of neurokinin-1 receptor internalization in neurons of lamina I in response to acute noxious mechanical or thermal stimulation. By contrast, administration of even high doses of the GABA(A) receptor agonists, muscimol or isoguvacine, were without effect. CGP55845, a selective GABA(B) receptor antagonist, completely blocked the effects of baclofen, but failed to increase the incidence of internalization when administered alone. These results provide evidence for a presynaptic control of nociceptive primary afferent neurons by GABA(B) but not GABA(A) receptors in the superficial laminae of the spinal cord, limiting tachykinin release. Because CGP5584 alone did not increase the magnitude of neurokinin-1 receptor internalization observed following noxious stimulation, there appears to be little endogenous activation of GABA(B) receptors on tachykinin-releasing nociceptors under acute stimulus conditions. The contribution of pre- and postsynaptic regulatory mechanisms to GABA(B) receptor-mediated antinociception was also investigated by comparing the effect of baclofen on Fos expression evoked by noxious stimulation to that induced by intrathecal injection of substance P. In both instances, baclofen reduced Fos expression not only in neurons that express the neurokinin-1 receptor, but also in neurons that do not. We conclude that baclofen acts at presynaptic sites to reduce transmitter release from small-diameter nociceptive afferents. Presynaptic actions on non-tachykinin-containing nociceptors could similarly account for the reduction by baclofen of noxious stimulus-induced Fos expression in neurokinin-1 receptor-negative neurons. However, the inhibition of Fos expression induced by exogenous substance P indicates that actions at sites postsynaptic to tachykinin- and/or non-tachykinin-containing primary afferent terminals must also contribute to the antinociceptive actions of GABA(B) receptor agonists.

Animals↗

PubMed2001

Proteinase-activated receptor-2 and hyperalgesia: A novel pain pathway.

Using a combined pharmacological and gene-deletion approach, we have delineated a novel mechanism of neurokinin-1 (NK-1) receptor-dependent hyperalgesia induced by proteinase-activated receptor-2 (PAR2), a G-protein-coupled receptor expressed on nociceptive primary afferent neurons. Injections into the paw of sub-inflammatory doses of PAR2 agonists in rats and mice induced a prolonged thermal and mechanical hyperalgesia and elevated spinal Fos protein expression. This hyperalgesia was markedly diminished or absent in mice lacking the NK-1 receptor, preprotachykinin-A or PAR2 genes, or in rats treated with a centrally acting cyclooxygenase inhibitor or treated by spinal cord injection of NK-1 antagonists. Here we identify a previously unrecognized nociceptive pathway with important therapeutic implications, and our results point to a direct role for proteinases and their receptors in pain transmission.

Animals↗

PubMed2001

Contribution of alpha(2) receptor subtypes to nerve injury-induced pain and its regulation by dexmedetomidine.

There is evidence that noradrenaline contributes to the development and maintenance of neuropathic pain produced by trauma to a peripheral nerve. It is, however, unclear which subtype(s) of alpha adrenergic receptors (AR) may be involved. In addition to pro-nociceptive actions of AR stimulation, alpha(2) AR agonists produce antinociceptive effects. Here we studied the contribution of the alpha(2) AR subtypes, alpha(2A), alpha(2B) and alpha(2C) to the development of neuropathic pain. We also examined the antinociceptive effect produced by the alpha(2) AR agonist dexmedetomidine in nerve-injured mice. The studies were performed in mice that carry either a point (alpha(2A)) or a null (alpha(2B) and alpha(2C)) mutation in the gene encoding the alpha(2) AR. To induce a neuropathic pain condition, we partially ligated the sciatic nerve and measured changes in thermal and mechanical sensitivity. Baseline mechanical and thermal withdrawal thresholds were similar in all mutant and wild-type mice; and, after peripheral nerve injury, all mice developed comparable hypersensitivity (allodynia) to thermal and mechanical stimulation. Dexmedetomidine reversed the allodynia at a low dose (3 microg kg(-1), s.c.) and produced antinociceptive effects at higher doses (10 - 30 microg kg(-1)) in all groups except in alpha(2A) AR mutant mice. The effect of dexmedetomidine was reversed by intrathecal, but not systemic, injection of the alpha(2) AR antagonist RS 42206. These results suggest that neither alpha(2A), alpha(2B) nor alpha(2C) AR is required for the development of neuropathic pain after peripheral nerve injury, however, the spinal alpha(2A) AR is essential for the antinociceptive effects of dexmedetomidine.

Adrenergic alpha-Agonists↗

PubMed2001

Hypoalgesia and hyperalgesia with inherited hypertension in the rat.

Many studies indicate that blood pressure control systems can attenuate pain (hypoalgesia) of short duration; however, we recently found exaggerated nociceptive responses (hyperalgesia) of persistent duration in the spontaneously hypertensive rat (SHR). Here, we used SHR, Dahl Salt-Sensitive (SS), and normotensive control rats to evaluate the contribution of sustained elevations in arterial pressure to nociceptive responses. Compared with Sprague-Dawley and/or Wistar-Kyoto controls, SHR were 1) hypoalgesic in the hot plate test and 2) hyperalgesic in longer latency tail and paw-withdrawal tests and in two models of inflammatory nociception. These differences were not observed between SS and salt-resistant controls fed a high-salt diet. Inflammatory hyperalgesia in SHR was correlated with neither paw edema nor the number of Fos-positive spinal cord neurons. Our results indicate that "pain" phenotype of the SHR is not restricted to hypoalgesia. This phenotype is related to genetic factors or to the autonomic systems that control blood pressure and not to sustained elevations in blood pressure, differences in spinal neuron activity, or inflammatory edema.

Animals↗

PubMed2000

Postsynaptic signaling via the [mu]-opioid receptor: responses of dorsal horn neurons to exogenous opioids and noxious stimulation.

Although both pre- and postsynaptic mechanisms have been implicated in the analgesia produced by mu-opioids at the spinal cord, it is not known under what conditions these different controls come into play. Because the mu-opioid receptor (MOR) can be visualized in individual lamina II excitatory interneurons and internalizes into endosomes on ligand binding, we tested whether MOR internalization could be monitored and used to measure postsynaptic MOR signaling. To test whether endogenous opioids modulate these lamina II interneurons during noxious stimulation, we next assessed the magnitude of postsynaptic MOR internalization under a variety of nociceptive conditions. As observed in other systems, we show that MOR internalization in dorsal horn interneurons is demonstrated readily in response to opioid ligands. The MOR internalization is dose-dependent, with a similar dose-response to that observed for opioid-induced increases in potassium conductance. We demonstrate that MOR internalization in lamina II neurons correlates precisely with the extent of analgesia produced by intrathecal DAMGO. These results suggest that MOR internalization provides a good marker of MOR signaling in the spinal cord and that postsynaptic MORs on lamina II interneurons likely participate in the analgesia that is produced by exogenous opioids. We found, however, that noxious stimuli, under normal or inflammatory conditions, did not induce MOR internalization. Thus, endogenous enkephalins and endomorphins, thought to be released during noxious peripheral stimuli, do not modulate nociceptive messages via postsynaptic MORs on lamina II interneurons. We suggest that any endogenous opioids that are released by noxious stimuli target presynaptic MORs or delta-opioid receptors.

Analgesics, Opioid↗

PubMed2000

Brainstem noradrenergic control of nociception is abnormal in the spontaneously hypertensive rat.

Nociceptive processing is altered in individuals with inherited hypertension. Because brainstem noradrenergic (NA) neurons have been implicated in both nociceptive transmission and hypertension, we compared behavioral and cardiovascular indices of pain in spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto controls (WKY) after intracerebroventricular administration of an anti-DbetaH-saporin immunotoxin. In WKY rats, NA lesions decreased indices of persistent pain in the formalin test, but did not change nociceptive responses in multiple models of acute pain. In SHR rats, NA lesions did not alter persistent nociception, but decreased thresholds in the hotplate test. We conclude that coeruleospinal inhibitory pathways modulate hypoalgesia but not hyperalgesia in the SHR rat. Brainstem noradrenergic inhibition of acute nociception in the hotplate test is enhanced in the SHR rat, but brainstem noradrenergic contribution to persistent nociceptive processing in the formalin test is reduced in the SHR rat.

Analysis of Variance↗

PubMed2000

Impaired nociception and pain sensation in mice lacking the capsaicin receptor.

The capsaicin (vanilloid) receptor VR1 is a cation channel expressed by primary sensory neurons of the "pain" pathway. Heterologously expressed VR1 can be activated by vanilloid compounds, protons, or heat (>43 degrees C), but whether this channel contributes to chemical or thermal sensitivity in vivo is not known. Here, we demonstrate that sensory neurons from mice lacking VR1 are severely deficient in their responses to each of these noxious stimuli. VR1-/- mice showed normal responses to noxious mechanical stimuli but exhibited no vanilloid-evoked pain behavior, were impaired in the detection of painful heat, and showed little thermal hypersensitivity in the setting of inflammation. Thus, VR1 is essential for selective modalities of pain sensation and for tissue injury-induced thermal hyperalgesia.

Animals↗

PubMed2000

Opioid inhibition of formalin-induced changes in plasma extravasation and local blood flow in rats.

Hindpaw injection of dilute formalin produces brief (Phase 1) and persistent (Phase 2) nociceptive responses in the rat. We recently showed that systemically-administered remifentanil during Phase 1 interacted with peripheral opioid receptors to delay the onset and termination of Phase 2 (Taylor et al., 1997b). To test the hypothesis that opioid inhibition of proinflammatory events during Phase 1 contributed to this delay, we evaluated the effects of remifentanil on the time course of formalin-induced inflammation. We found that formalin increased paw thickness (edema), plasma extravasation and local blood flow within minutes of its injection, i.e. during Phase 1. Each of these responses was blocked during remifentanil administration (30 microg/kg i.v. bolus, followed 90 s later with a 15 microg/kg/min infusion for 13.5 min), indicating that opioids inhibit Phase 1 inflammation. Opioid blockade of the blood flow response could be reversed with a peripherally-acting opioid antagonist, naloxone methiodide, indicating that remifentanil acted upon peripheral opioid receptors. Although the administration of remifentanil during Phase 1 did not reduce the magnitude of inflammatory responses during Phase 2, it did delay the onset and termination of edema during Phase 2. As this corresponds to the effects of remifentanil on nociceptive responses during Phase 2, we suggest that opioid analgesics act upon peripheral sites to inhibit inflammation during Phase 1, leading to a delay in the temporal profile of inflammatory (and likely nociceptive) responses during Phase 2.

Analgesics, Opioid↗