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S P Hunt

Publications and source records attributed to S P Hunt.

At least 19 recordsLinked to original sources
PubMed2003

LTP but not seizure is associated with up-regulation of AKAP-150.

We have used differential display to profile and compare the mRNAs expressed in the hippocampus of freely moving animals after the induction of long-term potentiation (LTP) at the perforant path-dentate gyrus synapse with control rats receiving low-frequency stimulation. We have combined this with in situ hybridization and have identified A-kinase anchoring protein of 150 kDa (AKAP-150) as a gene selectively up-regulated during the maintenance phase of LTP. AKAP-150 mRNA has a biphasic modulation in the dentate gyrus following the induction of LTP. The expression of AKAP-150 was 29% lower than stimulated controls 1 h after the induction of LTP. Its expression was enhanced 3 (50%), 6 (239%) and 12 h (210%) after induction, returning to control levels by 24 h postinduction. The NMDA receptor antagonist CPP blocked the tetanus-induced modulation of AKAP-150 expression. Interestingly, strong generalized stimulation produced by electroconvulsive shock did not increase the expression of AKAP-150. This implies that the AKAP-150 harbours a novel property of selective responsiveness to the stimulation patterns that trigger NMDA-dependent LTP in vivo. Its selective up-regulation during LTP and its identified functions as a scaffold for protein kinase A, protein kinase C, calmodulin, calcineurin and ionotropic glutamate receptors suggest that AKAP-150 encodes is an important effector protein in the expression of late LTP.

A Kinase Anchor Proteins↗
PubMed2002

Primary sciatic nerve repair using titanium staples.

The primary epineural repair of human peripheral nerves is most often achieved using non-absorbable microsutures, which can elicit a foreign-body reaction. We describe a new system for neural-tissue approximation, consisting of non-penetrating vascular closure staples (VCS) applied to the epineurium. These clips were initially developed for use in microvascular anastomosis, with no knowledge of their effectiveness in neural-tissue approximation. We compare the efficacies of VCS clips and monofilament nylon microsutures in the repair of transected sciatic nerves in 36 adult Sprague Dawley rats (18 treated with 9/0 sutures and 18 treated with VCS clips). In the rat, regeneration starts by day 5, and is well advanced by 4 weeks. To assess the overall repair success, the site of injury, after perfusion fixation, was harvested at 5, 7 and 30 days. The two methods were compared in terms of operative time, the degree of self-mutilation (autotomy), the macroscopic specimens in vivo and the microanatomical continuity through the repair site. Continuity was studied by using PGP-9.5-labelled cryosections and fluorescent secondary antibodies to visualise axonal regeneration. Clip repair was significantly faster in the VCS group (mean +/- s.e.m. = 7.09 +/- 0.36 min versus mean +/- s.e.m. 11.56 +/- 0.51 min in the sutured group) and an equal and minimal degree of autotomy was observed. Macroscopically, all 36 nerves were in continuity and free from neuroma. The use of VCS clips resulted in equivalent visualised regeneration across the repair site at each time point. We believe the use of VCS clips to be a faster and comparable alternative to non-absorbable sutures in primary nerve repair in this experimental model.

Animals↗
PubMed2001

5-hydroxytryptamine (5-HT)1A autoreceptor adaptive changes in substance P (neurokinin 1) receptor knock-out mice mimic antidepressant-induced desensitization.

Antagonists at substance P receptors of the neurokinin 1 (NK1) type have been shown to represent a novel class of antidepressant drugs, with comparable clinical efficacy to the selective serotonin (5-HT) reuptake inhibitors (SSRIs). Because 5-HT(1A) receptors may be critically involved in the mechanisms of action of SSRIs, we examined whether these receptors could also be affected in a model of whole-life blockade of NK1 receptors, i.e. knock-out mice lacking the latter receptors (NK1-/-). 5-HT(1A) receptor labeling by the selective antagonist radioligand [(3)H]N-[2-[4-(2-methoxyphenyl)1-piperazinyl]-ethyl]-N-(2-pyridinyl)-cyclohexanecarboxamide (WAY 100635) and 5-HT(1A)-dependent [(35)S]GTP-gamma-S binding at the level of the dorsal raphe nucleus (DRN) in brain sections, as well as the concentration of 5-HT(1A) mRNA in the anterior raphe area were significantly reduced (-19 to -46%) in NK1-/- compared with NK1+/+ mice. Furthermore, a approximately 10-fold decrease in the potency of the 5-HT(1A) receptor agonist ipsapirone to inhibit the discharge of serotoninergic neurons in the dorsal raphe nucleus within brainstem slices, and reduced hypothermic response to 8-OH-DPAT, were noted in NK1-/- versus NK1+/+ mice. On the other hand, cortical 5-HT overflow caused by systemic injection of the SSRI paroxetine was four- to sixfold higher in freely moving NK1-/- mutants than in wild-type NK1+/+ mice. Accordingly, the constitutive lack of NK1 receptors appears to be associated with a downregulation/functional desensitization of 5-HT(1A) autoreceptors resembling that induced by chronic treatment with SSRI antidepressants. Double immunocytochemical labeling experiments suggest that such a heteroregulation of 5-HT(1A) autoreceptors in NK1-/- mutants does not reflect the existence of direct NK1-5-HT(1A) receptor interactions in normal mice.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2001

Role of central and peripheral tachykinin NK1 receptors in capsaicin-induced pain and hyperalgesia in mice.

Substance P and its receptor (NK1) are thought to play an important role in pain and hyperalgesia. Here we have further examined this role by comparing the behavioural responses to intradermal capsaicin of mutant mice with a disruption of the NK1 receptor (NK1 KO) and wild-type (WT) mice. We have also evaluated the contribution of peripheral NK1 receptors to capsaicin-evoked behaviour by selective blockade of peripheral NK1 receptors in WT mice using a non-brain penetrant NK1 receptor antagonist. Injection of 6 microg capsaicin into the heel evoked paw licking with the same latency in WT and KO mice, but a significantly longer duration in WT mice. A higher dose (30 microg) evoked a similar duration of licking in both groups. There were no differences in mechanical sensitivity tested with von Frey hairs between WT and KO mice before capsaicin. Both capsaicin doses resulted in pronounced increases in responses to von Frey hairs (hyperalgesia) and novel responses to cotton wisps (allodynia) applied to the digits of the injected paw in WT mice, but no significant changes from baseline in KO mice. Selective blockade of peripheral NK1 receptors in WT mice resulted in a complete inhibition of capsaicin-evoked plasma extravasation, but the mechanical hyperalgesia induced by 30 microg capsaicin intraplantar was still significantly greater than that seen in KO mice. We conclude that the response to intradermal capsaicin is still present but abbreviated in mice lacking NK1 receptors, such that secondary hyperalgesia is not observed even after a high dose. Further, the lack of secondary hyperalgesia in NK1 KO mice is largely due to the loss of central rather than peripheral NK1 receptors. The phenotype of the NK1 KO mice is consistent with a loss of function of mechanically-insensitive nociceptors, and thus we propose that substance P may be expressed by this group of primary sensory neurones and required for their function.

Animals↗
PubMed2001

The NK1 receptor is essential for the full expression of noxious inhibitory controls in the mouse.

Behavioral analysis of the NK1 receptor gene knock-out (NK1-/-) mouse indicated that substance P was closely involved in orchestrating the physiological and behavioral response of the animal to major environmental stressors. In particular, endogenous pain control mechanisms, such as stress-induced analgesia were substantially impaired in mutant mice, suggesting a reduction in descending inhibitory controls to the spinal cord from the brainstem. To directly test the integrity of descending controls in NK1-/- mice, we have analyzed c-Fos expression in laminae I-II of the lumbar and cervical cord and in the rostral ventromedial medulla in an experimental paradigm known to require recruitment of descending inhibitory controls. Anesthetized mice were stimulated with water at 50 degrees C either on their forepaw, hindpaw, or on both the hindpaw plus forepaw concurrently. Wild-type mice, naive or treated with an NK1 antagonist (RP67580) or its inactive isomer (RP68651), were compared with NK1-/- mice. C-Fos expression at the lumbar laminae I-II level was significantly reduced, whereas it was significantly greater in the raphe magnus and pallidus nuclei in the double stimulation situation in wild-type compared with NK1-/- mice. Blocking the NK1 receptor pharmacologically reproduced, in an enantiomere-selective manner, the data from NK1-/- mice, with no evidence for recruitment of descending inhibition at the lumbar cord level after forepaw stimulation. The present study demonstrates that the NK1 receptor is essential for the full development of noxiously evoked descending inhibition.

Animals↗
PubMed2001

The molecular dynamics of pain control.

Pain is necessary for survival, but persistent pain can result in anxiety, depression and a reduction in the quality of life. The discriminative and affective qualities of pain are both thought to be regulated in an activity-dependent fashion. Recent studies have identified cells and molecules that regulate pain sensitivity and the parallel pathways that distribute nociceptive information to limbic or sensory areas of the forebrain. Here, we emphasize the cellular and neurobiological consequences of pain, especially those that are involved in the generation and maintenance of chronic pain. These new insights into pain processing will significantly alter our approach to pain control and the development of new analgesics.

Animals↗
PubMed2001

Seizure-induced gene expression in area CA1 of the mouse hippocampus.

Synaptic plasticity in the hippocampus requires activity-dependent gene expression. We have therefore profiled gene expression in area CA1 following the induction of an electroshock-evoked maximal seizure. Using cDNA microarrays, the differential expression of approximately 9000 cDNAs was examined. In situ hybridization on 14 transcripts that showed strongest modulation in the microarray screen (1.8-2-fold) confirmed the differential expression of a single gene that encodes for the nuclear hormone receptor NGFI-B (Nur77, N10). Although this gene is only modestly up-regulated (approximately 2-fold) in area CA1, in situ hybridization revealed that maximal seizures induce a marked (approximately 12-fold) up-regulation of NGFI-B in the dentate gyrus. These data support the notion [French et al. (2001) Eur. J. Neurosci., 13, 968-976] that CA1 pyramidal neurons are more refractory than granule cells of the dentate gyrus with respect to activity-dependent gene transcription. Furthermore, our results argue against a large cohort of activity-dependent genes in area CA1.

Animals↗
PubMed2001

Comparison of the phenotype of NK1R-/- mice with pharmacological blockade of the substance P (NK1 ) receptor in assays for antidepressant and anxiolytic drugs.

The phenotype of NK1R-/- mice was compared with that of acute pharmacological blockade of the tachykinin NK1 receptor on sensorimotor function and in assays relevant to depressive illness and anxiety. The dose range for L-760735 and GR205171 that was associated with functional blockade of central NK1 receptors in the target species was established by antagonism of the behavioural effects of intracerebroventricular NK1 agonist challenge in gerbils, mice and rats. The caudal grooming and scratching response to GR73632 was absent in NK1R-/- mice, confirming that the receptor had been genetically ablated. There was no evidence of sedation or motor impairment in NK1R-/- mice or following administration of L-760735 to gerbils, even at doses in excess of those required for central NK1 receptor occupancy. In the resident-intruder and forced swim test, the behaviour of NK1R-/- mice, or animals treated acutely with L-760735 or GR205171, resembled that seen with the clinically used antidepressant drug fluoxetine. However, the effects of GR205171 were not clearly enantioselective in mice. In contrast, although NK1R-/- mice also exhibited an increase in the duration of struggle behaviour in the tail suspension test, this was not observed following pharmacological blockade with L-760735 in gerbils or GR205171 in mice, suggesting that this may reflect a developmental alteration in the knockout mouse. There was no effect of NK1 receptor blockade with L-760735 in guinea-pigs or GR205171 in rats, or deletion of the NK1 receptor in mice, on behaviour in the elevated plus-maze test for anxiolytic activity. These findings extend previous observations on the phenotype of the NK1R-/- mouse and establish a broadly similar profile following acute pharmacological blockade of the receptor. These studies also serve to underscore the limitations of currently available antagonists that are suitable for use in rat and mouse behavioural assays.

Animals↗
PubMed2000

Rewarding effects of opiates are absent in mice lacking the receptor for substance P.

Modulation of substance P activity offers a radical new approach to the management of depression, anxiety and stress. The substance P receptor is highly expressed in areas of the brain that are implicated in these behaviours, but also in other areas such as the nucleus accumbens which mediate the motivational properties of both natural rewards such as food and of drugs of abuse such as opiates. Here we show a loss of the rewarding properties of morphine in mice with a genetic disruption of the substance P receptor. The loss was specific to morphine, as both groups of mice responded when cocaine or food were used as rewards. The physical response to opiate withdrawal was also reduced in substance P receptor knockout mice. We conclude that substance P has an important and specific role in mediating the motivational aspects of opiates and may represent a new pharmacological route for the control of drug abuse.

Animals↗
PubMed2000

Substance P and central respiratory activity: a comparative in vitro study in NK1 receptor knockout and wild-type mice.

Neurokinin-1 receptors (NK1) are present within the respiratory medullary network and in the phrenic nucleus, which controls the diaphragm. We compared the efficacy of substance P (SP) at inducing changes in respiratory frequency or the amplitude of the respiratory motor output between NK1 knockout (NK1-/-) and wild-type mice, using the in vitro brainstem-spinal cord preparation. The in vitro respiratory frequency, as well as the variability of the rhythm and the amplitude of the motor output were similar in both lines. In wild-type mice, application of exogenous SP induced either an increase in respiratory frequency (superfusion of the medulla) or an increase of the inspiratory motor output, as defined by the integral of C4 cervical ventral root activity (superfusion of the spinal cord). These two effects were not apparent in NK1-/- mice. In conclusion, NK1 receptors mediate the respiratory responses to SP but the lack of NK1 receptors in newborn NK1-/- mice does not change the respiratory activity.

Action Potentials↗
PubMed2000

Deficits in visceral pain and hyperalgesia of mice with a disruption of the tachykinin NK1 receptor gene.

Studies in mice lacking genes encoding for substance P or its receptor (NK1), or with NK1 antagonists, have shown that this system contributes to nociception, but the data are complex. Here, we have further examined the role of NK1 receptors in pain and hyperalgesia by comparing nociceptive responses to mechanical and chemical stimulation of viscera and the resulting hyperalgesia and inflammation in NK1 knockout (-/-) and wild-type (+/+) mice. We concentrated on visceral nociception because substance P is expressed by a much greater proportion of visceral than cutaneous afferents. NK1 -/- mice showed normal responses to visceral mechanical stimuli, measured as behavioural responses to intraperitoneal acetylcholine or hypertonic saline or reflex responses to colon distension in anaesthetized mice, although -/- mice failed to encode the intensity of noxious colon distensions. In contrast, NK1 -/- mice showed profound deficits in spontaneous behavioural reactions to an acute visceral chemical stimulus (intracolonic capsaicin) and failed to develop referred hyperalgesia or tissue oedema. However, in an identical procedure, intracolonic mustard oil evoked normal spontaneous behaviour, referred hyperalgesia and oedema in -/- mice. The inflammatory effects of capsaicin were abolished by denervation of the extrinsic innervation of the colon in rats, whereas those of mustard oil were unchanged, showing that intracolonic capsaicin evokes neurogenic inflammation, but mustard oil does not. Tests of other neurogenic inflammatory stimuli in NK1 -/- mice revealed impaired behavioural responses to cyclophosphamide cystitis and no acute reflex responses or primary hyperalgesia to intracolonic acetic acid. We conclude that NK1 receptors have an essential role mediating central nociceptive and peripheral inflammatory responses to noxious stimuli that evoke neurogenic inflammation, and modulating responses to noxious mechanical stimuli. We propose that two separate hyperalgesia pathways exist, one of which is NK1 receptor dependent, whereas the other does not require intact substance P/NK1 signalling.

Acetic Acid↗
PubMed1999

Effect of pre-emptive NMDA antagonist treatment on long-term Fos expression and hyperalgesia in a model of chronic neuropathic pain.

The unilateral sciatic nerve chronic constriction injury (CCI) model of Bennett and Xie [G.J. Bennett, Y.-K. Xie, A peripheral neuropathy in rat that produces disorders of pain sensation like those seen in man, Pain, 33 (1988) 87-108] shows features of a neuropathic pain state. We examined mechanical hyperalgesia and Fos protein staining in the lumbar spinal cord 1, 7, 14 and 28 days after unilateral CCI to the sciatic nerve or sham operation. In addition, we examined the effect of the NMDA antagonist MK-801 (0.3 mg/kg s.c. administered 30 min prior to and 6 h following operation) on Fos expression and hyperalgesia at 28 days. CCI animals were hyperalgesic compared to the sham operated animals at 14 and 28 days post injury. MK-801 reduced hyperalgesia by 68% in CCI animals on day 28 (p=0.0001). In the spinal cord, Fos positive cells were present bilaterally in deeper laminae in both sham and CCI animals at all time points examined. Relatively few Fos positive cells were present in laminae 1-2 at any time point examined. At days 1 and 7, there were increased numbers of Fos positive cells ipsilaterally in the deeper laminae of the spinal cord in CCI animals compared to sham animals, but by 14 and 28 days Fos counts were similar in sham and CCI despite the obvious behavioural differences between the two groups. Fos counts ipsilateral to the injury in laminae 3-10 correlated with hyperalgesia scores in the CCI but not sham animals. Analysis at the 28-day time point showed that MK-801 differentially affected Fos expression: MK-801 significantly reduced the Fos count bilaterally in laminae 3-10 in the CCI but not in the sham group animals. These results indicate that Fos expression is initiated by different peripheral and central mechanisms following nerve injury or sham operation.

Animals↗
PubMed1999

Effect of post-injury NMDA antagonist treatment on long-term Fos expression and hyperalgesia in a model of chronic neuropathic pain.

Chronic constriction injury (CCI) of the sciatic nerve results in persistent mechanical hyperalgesia together with Fos protein expression in the lumbar spinal cord. We have examined the relationship between mechanical hyperalgesia and Fos expression within the lumbar spinal cord on days 14, 35 and 55 after either CCI or sham operation. To determine the role of NMDA receptor mechanisms in the maintenance of hyperalgesia and Fos expression, the NMDA antagonist MK-801 (0.3 mg kg-1 s.c.) was administered daily on days 28 to 34 after operation. CCI animals developed unilateral hind limb hyperalgesia that persisted unchanged from days 14 to 55 of the study. MK-801 treatment reduced hyperalgesia by 57% (p=0.02) on day 35 in CCI animals but did influence hyperalgesia at day 55. In the spinal cord, Fos positive cells were present bilaterally throughout laminae 3-10 at all time points examined in both CCI and sham group animals. Fos counts ipsilateral to the side of injury in laminae 3-10 correlated significantly with hyperalgesia scores in the CCI but not sham animals. MK-801 treatment resulted in a suppression of Fos expression in ipsilateral laminae 3-4 (p=0.0017) and laminae 5-10 (p=0.0026) of CCI animals on day 35. Fos expression in sham group animals was not inhibited by MK-801 treatment at day 35. These results indicate that Fos expression is maintained by differing mechanisms following nerve injury or sham operation. The functional consequences of Fos expression following nerve injury and sham operation are discussed.

Animals↗
PubMed1999

Endogenously produced substance P contributes to lymphocyte proliferation induced by dendritic cells and direct TCR ligation.

Substance P (SP) is an immunoregulatory tachykinin which augments antigen- and mitogen-induced lymphocyte proliferation via signaling through the neurokinin-1 receptor (NK1-R). Non-neuronal cells of the immune system such as monocytes, T lymphocytes and eosinophils can be a source of SP. We have investigated if antigen-presenting dendritic cells (DC) produce SP. DC were grown from bone marrow precursors using a cocktail of GM-CSF, IL-4 and Flt-3 ligand. Reverse transcriptase-PCR amplification using primers for the mouse preprotachykinin-A gene and direct DNA sequencing of amplified products from purified DC demonstrated the presence of the gamma-transcript of the gene, coding for SP and neurokinin A. At the protein level, mouse DC expressed SP as determined by an enzyme immunoassay and confirmed by immunostaining. The functional role of endogenous SP release was determined. During the interaction with syngeneic or allogeneic DC, the addition of a specific NK1-R antagonist partly reduced proliferation in responding T lymphocytes. This was confirmed by using responders derived from NK1-R-deficient mice. In the absence of DC, proliferation of T cells induced by direct TCR ligation and soluble CD28 was partly dependent on signaling through NK1-R, revealing an autocrine effect of SP production by T cells. In conclusion, these results demonstrate that endogenously produced SP contributes to T cell proliferation induced by DC or TCR / CD28 stimulation.

Animals↗
PubMed1999

Substance P receptor (neurokinin-1)-expressing neurons in lamina I of the spinal cord encode for the intensity of noxious stimulation: a c-Fos study in rat.

The substance P receptor neurokinin-1 is expressed by a subset of neurons in the rat spinal cord. We have combined immunostaining for Fos, a marker of noxious peripheral stimulation, and neurokinin-1 to examine whether nociceptive signals from particular peripheral tissues (skin, muscle or knee joint) or activity generated by nerve injury or formalin-induced inflammation are preferentially modulated by substance P. Our results indicate that superficial and deep spinal neurokinin-1-positive neurons process nociceptive information in markedly different ways. In lamina I, the number of double-labelled neurons was positively correlated with the intensity of the stimulus (defined by the total Fos count) and was not directly related to any particular peripheral target. However, in the deeper layers of the spinal cord (V-X), there was no such correlation, and stimulation of joint nociceptors and formalin-induced inflammation produced the greatest proportion of Fos/neurokinin-1 co-localization, suggesting a particular role for substance P in the mediation of joint pain and inflammatory hyperalgesia. Thus, lamina I neurokinin-1 receptor-bearing neurons appear to be involved in intensity discriminative aspects of pain, whereas the deep neurokinin-1 cells are involved in spatial localization or the detection of particular nociceptive submodalities.

Animals↗
PubMed1999

A role for spinal lamina I neurokinin-1-positive neurons in cold thermoreception in the rat.

Lamina I neurons of the spinal cord convey specific nociceptive activity to the brain. A subpopulation of lamina I cells bears substance P receptors (neurokinin-1) and recent studies have shown that these neurons encode for the intensity of noxious peripheral stimulation. Here, we report that cool thermal stimuli, applied to the hindpaw of anaesthetized rats, induce Fos expression in lamina I neurokinin-1 neurons that is graded with respect to the intensity of the thermal stimulus. Thus, as the temperature of the stimulus was reduced, both the total number of neurokinin-l-positive neurons expressing Fos and the proportion of Fos nuclei present within neurokinin-1 cells showed a significant increase. These data show that lamina I neurokinin-1 cells encode the intensity of noxious cooling of the skin. In laminae III and IV, although there was no correlation between neurokinin-1 cell activation and stimulus intensity, the total Fos count in these layers was inversely related to the depth of cooling. Thus, neurons in laminae III and IV may also play a role in thermoreception.

Animals↗