Desensitization to intrathecal substance P in mice: possible involvement of opioids

The role of peptides in central sensitization

Peptides released in the spinal cord from the central terminals of nociceptors contribute to the persistent hyperalgesia that defines the clinical experience of chronic pain. Using substance P (SP) and calcitonin gene-related peptide (CGRP) as examples, this review addresses the multiple mechanisms through which peptidergic neurotransmission contributes to the development and maintenance of chronic pain. Activation of CGRP receptors on terminals of primary afferent neurons facilitates transmitter release and receptors on spinal neurons increases glutamate activation of AMPA receptors. Both effects are mediated by cAMP-dependent mechanisms. Substance P activates neurokinin receptors (3 subtypes) which couple to phospholipase C and the generation of the intracellular messengers whose downstream effects include depolarizing the membrane and facilitating the function of AMPA and NMDA receptors. Activation of neurokinin-1 receptors also increases the synthesis of prostaglandins whereas activation of neurokinin-3 receptors increases the synthesis of nitric oxide. Both products act as retrograde messengers across synapses and facilitate nociceptive signaling in the spinal cord. Whereas these cellular effects of CGRP and SP at the level of the spinal cord contribute to the development of increased synaptic strength between nociceptors and spinal neurons in the pathway for pain, the different intracellular signaling pathways also activate different transcription factors. The activated transcription factors initiate changes in the expression of genes that contribute to long-term changes in the excitability of spinal and maintain hyperalgesia.

Pharmacological characterization of desensitization in scratching behavior induced by intrathecal administration of hemokinin-1 in the rat

Desensitization is induced by the repeated administration of high doses of substance P (SP) or hemokinin-1 (HK-1). However, little information is available about the mechanisms involved in the induction of desensitization by these peptides. Thus, to characterize this desensitization, we examined the dose-dependent effect of these peptides, the effect of pretreatment with neurokinin 1(NK1) receptor antagonists, and the effect of pretreatment with inhibitors of protein kinases such as protein kinase A (PKA), protein kinase C (PKC), calcium/calmodulin kinase II (CaMKII) and mitogen-activated protein kinase kinase (MEK). The number of scratchings induced by 10(-3)M SP or HK-1 decreased following pretreatment with 10(-11)-10(-3)M SP or HK-1 with a marked reduction at 10(-3) and 10(-6)M SP or HK-1. The effect of NK1 receptor antagonists on desensitization induced by pretreatment with 10(-6)M SP was marked, whereas there was little effect of pretreatment with these antagonists on 10(-6)M HK-1-induced desensitization. Additionally, 10(-6)M SP- and HK-1-induced desensitization was attenuated by pretreatment with PKA, PKC and MEK inhibitors, except a CaMKII inhibitor that inhibited SP-induced desensitization. These results indicate that the receptor and kinases involved in HK-1-induced desensitization are partially different from those of SP.

The common carboxyl-terminal region of novel tachykinin peptides contributes to induce desensitization in scratching behavior of rats

Some novel tachykinin peptides exhibiting homology with known members of the tachykinin family have been recently reported; however, little is known about the function of these peptides. Repeated intrathecal administration of substance P (SP) causes desensitization by binding SP to neurokinin 1 (NK1) receptor. Thus, to clarify the characteristics of the receptors involved in these novel peptides, we investigated whether desensitization is induced by intrathecal administration of these peptides in rats since desensitization is induced by binding these peptides to the receptor. Intrathecal administration of 10(-3) M hemokinin-1 (HK-1) and 10(-3) M decapeptide common in the carboxyl-terminal region of endokinin A and endokinin B (EKA/B) as well as SP evoked scratching behavior. When each peptide was administered twice with an interval of 15 min, remarkable desensitization of scratching behavior was produced. Furthermore, the first administration of EKA/B or SP produced clear cross-desensitization to SP, EKA/B and HK-1, whereas the first administration of HK-1 demonstrated weak cross-desensitization to EKA/B and SP. These results suggest that EKA/B and SP may bind to both the NK1 receptor and HK-1-preferred receptor, and HK-1 may preferentially bind to its preferred receptor.

The NK1 receptor mediates both the hyperalgesia and the resistance to morphine in mice lacking noradrenaline

Noradrenaline (NA), a key neurotransmitter of the endogenous pain inhibitory system, acutely inhibits nociceptive transmission (including that mediated by substance P), potentiates opioid analgesia, and underlies part of the antinociceptive effects of the widely prescribed tricyclic antidepressants. Lesions of noradrenergic neurons, however, result in either normal or reduced pain behavior and variable changes in morphine antinociception, undermining the proposed association between noradrenaline (NA) deficiency and chronic pain (hyperalgesia). We used mice lacking the gene coding for dopamine beta-hydroxylase, the enzyme responsible for synthesis of NA from dopamine, to reexamine the consequences of a lack of NA on pain behavior. Here, we show that absence of NA in the central nervous system results in a substance P-mediated chronic hyperalgesia (decreased nociceptive threshold) to thermal, but not mechanical, stimuli and decreased efficacy of morphine. Contrary to studies that show substance P-mediated hyperalgesia requires intense stimuli, we found that even a mild stimulus is sufficient to evoke substance P-dependent hyperalgesia in the NA-deficient mice. Restoring central NA normalized both the nociceptive threshold and morphine efficacy, which is consistent with a tonic inhibitory effect of NA on nociceptive transmission. Unexpectedly, however, antagonists to the substance P receptor (the NK1 receptor) could achieve the same effect as NA replacement. We conclude that when unopposed by NA, substance P acting at the NK1 receptor causes chronic thermal hyperalgesia, and that the reduced opioid efficacy associated with a lack of NA is due to increased NK1-receptor stimulation.

Simultaneous activation of N-methyl-D-aspartate and neurokinin-1 receptors modulates c-Fos and Zif/268 expression in the rat trigeminal nucleus caudalis

We examined the acute expression of c-Fos or Zif/268 by simultaneous activation of N-methyl-D-aspartate receptor and neurokinin-1 receptor of the trigeminal nucleus caudalis in anesthetized rats. A selective N-methyl-D-aspartate receptor agonist, N-methyl-D-aspartate, and/or a selective neurokinin-1 receptor agonist, substance P, was applied topically to the dorsal surface of the spinal trigeminal tract. Immunohistochemically stained nuclei for c-Fos and Zif/268 at laminae I and II of the trigeminal nucleus caudalis were counted. Ipsilateral c-Fos and Zif/268 were increased significantly dose-dependently by N-methyl-D-aspartate (at 136 and 340 microM, and at 68, 136 and 340 microM, respectively). On the contralateral side, only Zif/268 increased significantly (at 68, 136 or 340 microM). These increases were abolished by D-2-amino-5-phosphonovaleric acid (at 25 mM), a selective N-methyl-D-aspartate receptor antagonist. Substance P (at 3.7 or 7. 4 microM) significantly increased dose-dependently ipsilateral c-Fos and Zif/268. On the contralateral side, only c-Fos was significantly increased (at 3.7 and 7.4 microM). These increases were abolished by D-2-amino-5-phosphonovaleric acid (at 25 mM) and L-703,606 (at 10 microM), a selective neurokinin-1 receptor antagonist. The combined application of N-methyl-D-aspartate 340 microM + substance P (at 0.74 or 3.7 microM) significantly increased ipsilateral c-Fos compared to either agent alone. Combined application of N-methyl-D-aspartate 340 microM + substance P at 0.74, 3.7 or 7.4 microM significantly increased ipsilateral Zif/268 expression compared to either drug alone. Other combinations did not increase c-Fos and Zif/268. Our results indicate that activation of N-methyl-D-aspartate or neurokinin-1 receptor of the trigeminal nucleus caudalis contributes to the acute induction of both c-Fos and Zif/268 on the ipsilateral superficial layer of this nucleus and simultaneous activation of both receptors by their agonists with specific concentrations produces a marked expression of these proteins. Simultaneous activation of N-methyl-D-aspartate and neurokinin-1 receptors under some specific conditions may augment synaptic transmission, contributing to long-term neuronal change.

Sympathetic nervous system function in fibromyalgia

This review focuses on studies of the sympathetic nervous system in fibromyalgia (FM). First, a brief review of the sympathetic system, and its relationship to the human stress response, is outlined. Then various studies of functional assessment of sympathetic function in FM are highlighted. Certain methods of assessment (eg, heart rate variability, biochemical, and psychophysical responses to various stressors) that we believe to be of specific importance for future research are discussed in greater detail. Finally, findings on autonomic function in related disorders--specifically, chronic fatigue syndrome, irritable bowel syndrome, and migraine--will be briefly presented.

Opioid activity of sendide, a tachykinin NK1 receptor antagonist

Sendide, a tachykinin NK1 receptor antagonist, was tested for antagonism against scratching, biting and licking responses elicited by intrathecal (i.t.) injections of various tachykinin receptor agonists, N-methyl-D-aspartate (NMDA), somatostatin and bombesin, in mice. Tachykinin NK1 receptor agonists, substance P, physalaemin and septide, produced a characteristic behavioural response, consisting of scratching, biting and licking. The substance P-induced response was reduced by small doses (0.0625-1.0 pmol) of sendide in a dose-dependent manner. The behavioural response elicited by other tachykinin NK1 receptor agonists, physalaemin and septide, was also reduced significantly by a small dose (1.0 pmol) of sendide. The inhibitory effect of sendide (1.0 pmol) was not affected by pretreatment with the opioid receptor antagonist, naloxone, at doses up to 4.0 mg/kg. Higher doses of sendide were needed to reduce the behavioural response to neurokinin A, a tachykinin NK2 receptor agonist, neurokinin B, a tachykinin NK3 receptor agonist and eledoisin, a tachykinin NK2/NK3 receptor agonist. Pretreatment with naloxone (2.0 mg/kg, i.p.) significantly antagonized sendide (1024 pmol)-induced inhibition of the behavioural responses to neurokinin A, neurokinin B and eledoisin. The behaviours elicited by i.t. injection of NMDA, somatostatin or bombesin were also reduced by a higher dose (1024 pmol) of sendide and this sendide effect was reversed by naloxone. These findings suggest that sendide at higher doses may possess opioid activity in addition to an antagonistic action at tachykinin NK1 receptors in the spinal cord.

Characterization and regulation of neurokinin1 receptors in primary cultures of rat neonatal spinal neurons

Neurokinin1 receptors are the primary target of substance P released from neurons during neural transmission, yet little is known regarding the regulation of neurokinin1 receptors on neurons. 125I-Bolton-Hunter-substance P was used in the present studies to determine whether primary cultures of rat neonatal spinal cord express neurokinin1 receptors and, therefore, can be used as a model to explore regulation of neuronal neurokinin1 receptors. 125I-Bolton-Hunter-substance P bound to a single site in neuron-enriched cultures with an affinity of 256 nM, which is comparable to its high affinity binding on adult rat spinal cord. Treatment of neuron-enriched cultures with 10 nM substance P resulted in a 47% decrease in 125I-Bolton-Hunter-substance P binding at 24 h which was due to a decrease in affinity of the receptor. However, at 48 h after treatment with substance P, 125I-Bolton-Hunter-substance P binding increased by 44%. The increase in binding was due to a two-fold increase in receptor density. These changes occurred in the presence of 0.5 microM tetrodotoxin, decreasing the likelihood that the changes in binding were secondary to the release of transmitters by substance P. Furthermore, substance P1-7, a metabolite of substance P that has putative physiological effects, did not alter 125I-Bolton-Hunter-substance P binding. These data provide evidence that neuronal neurokinin1 receptors are under homologous regulation in primary cultures of neonatal rat spinal cord and suggest that a similar mechanism occurs in vivo. Furthermore, the data suggest that a decrease in affinity of the neurokinin1 receptor may contribute, in part, to tachyphylaxis to substance P.

Central cardiovascular and behavioral effects of carboxy- and amino-terminal fragments of substance P in conscious rats

The central cardiovascular and behavioral effects of carboxy- (SP 5-11, SP 6-11, SP 7-11, SP 8-11) and amino- (SP 1-7, SP 1-9) terminal substance P (SP) fragments were compared with those of SP 1-11 in conscious rats. In addition, the ability of these SP-fragments to induce desensitization of the central NK1 receptor was investigated. SP 1-11 (50 pmol) injected i.c.v. induced an increase in mean arterial blood pressure (MAP), heart rate (HR) and a typical behavioral response consisting of face washing (FW), hindquarter grooming (HQG) and wet-dog shakes (WDS). The cardiovascular and behavioral responses to equimolar doses of SP 5-11 and SP 6-11 were similar to those of SP 1-11, however, only SP 5-11 induced exactly the same behavioral pattern as SP 1-11. SP 6-11 was more potent in inducing FW and WDS than SP 1-11 or SP 5-11. The carboxy-terminal SP-fragments, SP 7-11 and SP 8-11, and the amino-terminal SP-fragments, SP 1-7, SP 1-9, did not elicit any significant cardiovascular or behavioral responses. Pretreatment with SP 1-11 reduced the cardiovascular and behavioral responses to subsequent injections of SP 1-11. Of all SP-fragments tested, only SP 5-11 was able to attenuate the cardiovascular and behavioral responses to SP 1-11. Our results demonstrate that SP 6-11 represents the shortest carboxy-terminal amino acid sequence, that after i.c.v. injection, elicits the same cardiovascular response as SP 1-11, but fails to desensitize the NK1 receptor. The carboxy-terminal fragment, SP 5-11, is the shortest amino acid sequence which produces the same pattern of central cardiovascular and behavioral responses as SP 1-11 and also retains the ability to desensitize the NK1 receptor like SP 1-11.

Morphological characterization of substance P receptor-immunoreactive neurons in the rat spinal cord and trigeminal nucleus caudalis

Although there is considerable evidence that primary afferent-derived substance P contributes to the transmission of nociceptive messages at the spinal cord level, the population of neurons that expresses the substance P receptor, and thus are likely to respond to substance P, has not been completely characterized. To address this question, we used an antibody directed against the C-terminal portion of the rat substance P receptor to examine the cellular distribution of the receptor in spinal cord neurons. In a previous study, we reported that the substance P receptor decorates almost the entire dendritic and somatic surface of a subpopulation of spinal cord neurons. In the present study we have taken advantage of this labeling pattern to identify morphologically distinct subpopulations of substance P receptor-immunoreactive neurons throughout the rostral-caudal extent of the spinal cord. We observed a dense population of fusiform substance P receptor-immunoreactive neurons in lamina I at all segmental levels. Despite having the highest concentration of substance P terminals, the substantia gelatinosa (lamina II) contained almost no substance P receptor-immunoreactive neurons. Several distinct populations of substance P receptor-immunoreactive neurons were located in laminae III-V; many of these had a large, dorsally directed dendritic arbor that traversed the substantia gelatinosa to reach the marginal layer. Extensive labeling was also found in neurons of the intermediolateral cell column. In the ventral horn, we found that labeling was associated with clusters of motoneurons, notably those in Onuf's nucleus in the sacral spinal cord. Finally, we found no evidence that primary afferent fibers express the substance P receptor. These results indicate that relatively few, but morphologically distinct, subclasses of spinal cord neurons express the substance P receptor. The majority, but not all, of these neurons are located in regions that contain neurons that respond to noxious stimulation.

Substance P and neurokinin A induced desensitization to cardiovascular and behavioral effects: evidence for the involvement of different tachykinin receptors

Desensitization and cross-desensitization to the cardiovascular and behavioral effects elicited by intracerebroventricular (i.c.v.) substance P (SP) and neurokinin A (NKA) injections were examined in conscious, freely moving rats. The cardiovascular responses to equimolar doses of both peptides were identical, however, the pattern of the behavioral responses differed. Relative to SP, NKA was weaker in eliciting hindquarter grooming but more effective in eliciting wet dog shakes. SP pretreatment (50 pmol) desensitized the cardiovascular and behavioral responses to both, subsequent injections of SP (50 pmol) as well as of NKA (50 or 500 pmol) injected 30 or 60 min after SP, indicating cross-desensitization. NKA pretreatment (50 pmol) partly reduced the cardiovascular but not the behavioral responses to subsequent equimolar doses of NKA. The cardiovascular responses to SP (50 pmol) were reduced only 30 min but not 60 min after pretreatment with a 10 times higher dose of NKA (500 pmol). Of all behavioral manifestations to i.c.v. SP, only hindquarter grooming was attenuated by pretreatment with either dose of NKA. The equal potency of SP and NKA in eliciting the cardiovascular effects but different pattern of behavioral responses to these peptides suggest an involvement of different types of tachykinin receptors in mediating the central effects of the two peptides. The fact that NKA induced cross-desensitization selectively to one type of behavioral manifestations elicited by SP, indicates the existence of two subtypes of SP (NK1) receptors in the rat brain.

Possible role of the N-terminus of substance P in kainic acid-induced toxicity in rats

Subcutaneously administered kainic acid (KA) in the rat results in brain damage accompanied by a behavioral response characterized by wet dog shakes (WDS), seizures and brain damage, an effect that is potentiated by opioids. Based on the potentiative effect of the N-terminus of substance P (SP) on the ability of KA to induce behavioral responses in mice, we tested the hypothesis that the N-terminus of SP also plays a role in KA-induced neurotoxicity in rats. Pretreatment i.p. with 1 or 10 nmol of SP(1-7), a major N-terminal metabolite of the undecapeptide SP, 15 min before administration of 12 mg/kg of KA potentiated the incidence of WDS. In contrast, after administration of 1 nmol of [D-Pro2, D-Phe7]SP(1-7) (D-SP(1-7)), the D-isomer of SP(1-7) and a substance P N-terminal antagonist, the intensity of KA-induced WDS was no different from those in either the KA- or saline-injected rats. However, pretreatment with D-SP(1-7) completely blocked the potentiative effect of SP(1-7) on the KA-induced WDS. While the severity of KA-induced lesions was not significantly altered by pretreatment with 1 nmol of SP(1-7), the effect of KA was not significantly different from that in control rats when administered with 1 nmol of D-SP(1-7). These results suggest a possible involvement of endogenous SP N-terminal activity in the effects following subcutaneous (s.c.) administration of KA.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P-(1-7), a substance P metabolite, inhibits withdrawal jumping in morphine-dependent mice

Substance P has been previously shown to inhibit the intensity of the morphine abstinence syndrome in mice. In view of the rapid degradation of substance P after its release from nerve terminals, we hypothesized that this inhibition is mediated by the N-terminus of substance P and its metabolites rather than via the C-terminus interacting with neurokinin receptors. Intrathecal injection of substance P-(1-7) (1 nmol) 30 min prior to naloxone challenge, in mice that had received 25 micrograms of morphine sulfate intrathecally once daily for three days, caused a dose-related attenuation of withdrawal jumping. In contrast, administration of the substance P-(1-7) antagonist, [D-Pro2,D-Phe7]substance P-(1-7), 15 min prior to naloxone increased withdrawal jumping behaviors. Equimolar doses of morphine and naloxone at 30 min had no effect. From these data, it appears that substance P N-terminal metabolites modulate withdrawal behaviors in morphine-dependent mice.

Substance P receptor desensitization in the dorsal horn: possible involvement of receptor-G protein complexes

The repeated administration of a high dose of substance P (SP) onto the spinal cord has been shown to attenuate behavioral responses to an intense heat (tail-flick) or noxious mechanical stimulus (paw pressure). Studies performed to investigate the action of spinal SP have suggested that changes in behavioral responses involve endogenous opiate or neurokinin systems. This study was performed to investigate whether the binding characteristics of SP receptors in the dorsal horn are altered following successive administration of SP. Two populations of [3H]-SP binding sites were distinguished on the basis of their binding affinity. Gpp(NH)p, a stable analogue of GTP, decreased the size and affinity of the high affinity binding component selectively labelled with [125I]-Bolton Hunter-SP. Repeated intrathecal administration of SP (15 micrograms) which reduced behaviors also reduced the number and affinity of high affinity binding sites. Thus, attenuated behaviors in response to repeated administration of SP are paralleled by an alteration of SP binding in the dorsal horn. The altered agonist affinity seen under desensitizing conditions raises the possibility that SP receptor desensitization involves an uncoupling of receptor-G protein complexes.

Identification of a novel receptor mediating substance P-induced behavior in the mouse

To determine whether opioid receptors or the more recently characterized naloxone-sensitive substance P (SP) N-terminal binding sites play a role in desensitization to the behavioral effects of SP, we assessed the effects of selective antagonists at mu-(naloxonazine and beta-funaltrexamine), delta- (naltrindole) and kappa- (nor-binaltorphimine) opioid receptors, as well as the effect of [D-Pro2,D-Leu7]SP-(1-7) D-SP-(1-7) (D-SP (1-7)), an inhibitor of [3H]SP-(1-7) binding, on behaviors induced by intrathecally administered SP in mice. Whereas naloxone, a non-selective opioid antagonist, inhibited the development of behavioral desensitization to SP, the response to repeated SP administration remained unaffected by pretreatment with selective opioid antagonists. Like naloxone, however, the SP-(1-7) antagonist inhibited SP-induced desensitization. The protection against desensitization to SP by D-SP-(1-7), but not by selective antagonists of mu, delta or kappa receptors, suggests that desensitization to the behavioral effects of SP does not appear to be mediated by an action at an opioid receptor but by an action at the SP-(1-7) binding site.

Naloxone-reversible effect of spantide on the spinally mediated behavioural response induced by neurokinin-2 and -3 receptor agonists

[D-Arg1, D-Trp7,9, Leu11]-substance P (spantide) was tested for antagonism against the licking, biting and scratching response induced by various neurokinin (NK) receptor agonists and bombesin (Bom) in mice. When co-administered with substance P (SP) intrathecally, spantide reduced the SP-induced behavioural responses in a dose-dependent manner. The duration of this antagonistic effect was approximately 30 min. Behavioural responses induced by physalaemin (Phy), [pGlu6, L-Pro9]-SP (6-11) (septide), [pGlu6, D-Pro7]-SP (6-11) (D-septide) and eledoisin (Ele) were also dose-dependently decreased by relatively small doses of spantide. Higher doses of spantide were needed to reduce the behavioural responses induced by [Sar9, Met (O2)11]-SP, neurokinin A (NK A) and neurokinin B (NK B). No significant effect of spantide was observed against the behavioural responses elicited by Bom. Pretreatment with naloxone, an opioid antagonist, resulted in a reversible effect on the behavioural reduction of NK-2 and NK-3 receptor agonists produced by spantide. However, the effect of spantide on the NK-1 receptor agonist-induced response was unchanged by naloxone. In homogenates of mouse spinal cord, competition studies confirmed that the binding of the opioid ligand [3H]naloxone was displaced by spantide with a low but measurable affinity. These results suggest that the behavioural response to NK-2 and NK-3 receptor agonists may be partially inhibited by spantide through the activation of opioid system in the mouse spinal cord.

Opioid and neurokinin activities of substance P fragments and their analogs

Newly developed substance P (SP) analogs with altered N-terminal sequences which equalize the lipophilicity of the N-terminal and C-terminal elements and of their fusion product were examined using i.t. injection in mice. I.t. injection of either the full length analog or the C-terminal hexapeptide (CP) produced biting and scratching behavior similar to that elicited by SP. SPF was approximately 5-fold and CP 14-fold less potent than native SP. The N-terminal peptide (NP) was inactive by itself but inhibited CP-elicited behavior. Naloxone antagonized this action of NP and shifted the SPF dose-response curve 4-fold to the left. However, naloxone had no effect on the action of CP or on the action of any of the native neurokinins. The results are consistent with the hypothesis that N- and C-terminal analogs of SP can have opioid and SP-like actions, respectively, in the CNS of rodents. Furthermore, analogs of SP which include at least the terminal tetrapeptide retain neurokinin activity.

Neurokinin and NMDA antagonists (but not a kainic acid antagonist) are antinociceptive in the mouse formalin model

While much evidence implicates substance P (SP), an endogenous neurokinin (NK), as a primary sensory transmitter of acute pain in mammalian spinal cord, its role in continuous (tonic) pain is less clear. Although glutamate is co-localized with SP in dorsal root ganglion neurons, its role in nociceptive processing is uncertain. While antagonists of NKs and excitatory amino acids (EAAs) have been found to be antinociceptive in some acute assays, they have not been tested against tonic pain. We hypothesize that: (1) NKs and EAAs contribute to signaling of tonic chemogenic nociception; and (2) interaction between NK and EAA systems is important in determining the perceived intensity of a continuous noxious stimulus. We therefore evaluated two NK antagonists ([D-Pro2,D-Trp7,9] SP (DPDT-SP, 0.26-6.6 nmoles, non-specific) and [D-Pro4, D-Trp7,9,10,Phe11]-SP(4-11) (DPDTP-octa, 1.6-12.3 nmoles, somewhat NK-1 selective], as well as DL-2-amino-5-phosphonovalerate (DL-AP5, NMDA antagonist, 0.05-1 nmole) and urethane (a kainic acid (KA) antagonist at 2.5 mumoles) for antinociceptive activity in the mouse formalin model. Administered intrathecally (i.t.), DL-AP5 and both NK antagonists were significantly antinociceptive while urethane (2.5 mumoles) and naloxone (2.7 nmoles) were inactive. A50 values for mean % analgesia, nmoles/mouse i.t. (95% CLs) were: DPDT-SP, 1.1 (0.79-1.6); DPDTP-octa, 3.9 (2.4-6.1); DL-AP5, 0.29 (0.16-0.71). The antinociception associated with 1.3 nmoles of DPDT-SP was not reversed by co-administering 2.7 nmoles of naloxone. Co-administration of 0.1 nmoles of DL-AP5 with either 1.3 nmoles of DPDT-SP or 3.3 nmoles of DPDTP-octa did not lead to additive antinociception.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of substance P analogues on the scratching, biting and licking response induced by intrathecal injection of N-methyl-D-aspartate in mice

1. Intrathecal (i.t.) administration of N-methyl-D-aspartate (NMDA) elicited a dose-dependent behavioural response consisting of licking, biting and scratching in mice. 2. Repeated i.t. injections of 0.4 nmol NMDA, at 5 min intervals, resulted in the rapid development of desensitization to this NMDA-induced behavioural phenomenon. 3. The NMDA-induced response was dose-dependently inhibited by the simultaneous injection of a selective NMDA-receptor antagonist, D-2-amino-5-phosphonovaleric acid. 4. The substance P (SP) analogues [D-Pro2, D-Trp7,9] SP and [D-Arg1, D-Trp7,9, Leu11] SP (spantide) inhibited NMDA-induced behavioural responses in a dose-dependent manner. However, [D-Phe7, D-His9] SP (6-11), a SP analogue selective for neurokinin1 (NK1) receptors, failed to inhibit NMDA-induced responses even at a dose of 4.0 nmol. 5. These results indicate that NMDA-induced behavioural responses are mainly mediated through NMDA receptors without affecting NK1 receptors in the spinal cord.

Modulation of a peripheral inflammatory response to substance P by locally administered opioid receptor agonists

Using a blister model of inflammation in the rat hind footpad, the present study was undertaken to examine possible peripheral effects of specific mu (DAGO) and delta (DSLET) opioid receptor agonists on an inflammatory response induced by substance P, the putative mediator of neurogenic inflammation. When perfused over the blister base, SP induced both plasma extravasation and vasodilatation responses. These responses were significantly inhibited in the presence of either opioid receptor agonist in a naloxone reversible manner. DSLET inhibited SP responses in a dose dependent manner and was 100 times more potent than DAGO. The role of primary afferent sensory nerve terminals in these modulatory effects was investigated in rats pretreated as neonates with capsaicin. The ability of DAGO and DSLET to inhibit the inflammatory response in these rats was significantly less than that in controls. The data raises the possibility that the inhibitory effect of the opioid receptor agonists on the inflammatory response might reflect a role for opioids in modulating tachyphylaxis to SP.

Effects of urethane and ketamine on substance P- and excitatory amino acid-induced behavior in mice

Urethane and ketamine were tested for their ability to alter the caudally directed binding and scratching response elicited by the intrathecal (i.t.) injection of excitatory amino acids (EAAs) or substance P (SP). EAAs, such as N-methyl-D-aspartate (NMDA), kainate acid and quisqualic acid, but not SP, were inhibited by subanesthetic doses of urethane. In contrast, SP was more sensitive than NMDA to the inhibitory effect of (+)-ketamine. (-)-Ketamine produced much less inhibition of the SP-induced behaviors than the (+)isomer. These results have important implications regarding the use of urethane and ketamine as anesthetics for studies in which these excitatory compounds are potential mediators.

Interactions between substance P, calcitonin gene-related peptide, taurine and excitatory amino acids in the spinal cord

Using in vivo microdialysis in the dorsal spinal cord of the rat, we have previously observed increases in glutamate and aspartate during exposure to a noxious stimulus. The present investigation was designed to determine whether these increases may be mediated by substance P. Infusion of 1 mM of substance P in the dialysis fluid increased the concentrations of glutamate and aspartate, similar to the response seen during noxious stimulation. In addition, substance P also increased the concentrations of the inhibitory amino acids glycine and taurine. Calcitonin gene-related peptide, previously shown to enhance substance P-induced biting and scratching behavior, produced no effect on amino acid release by itself but potentiated the apparent release of taurine by substance P. To assess the importance of substance P-induced amino acid release in sensory processing, we examined the influence of taurine and of excitatory amino acid antagonists on the biting and scratching behavior produced by excitatory amino acids and substance P. Taurine selectively inhibited only substance P-induced biting and scratching while excitatory amino acid antagonists inhibited only excitatory amino acid-induced behavior. To further explore the ability of taurine to inhibit the substance P-induced behavior, 3 tests of nociception were then used. Pretreatment with taurine inhibited the nociceptive-related writhing behavior produced by an intraperitoneal injection of acetic acid in mice but failed to alter the latency of response in the hot plate or tail flick assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of substance P-induced desensitization with substance P amino terminal metabolites in the mouse spinal cord

Intrathecal injection of mice with substance P (SP) or its C-terminal fragments results in a behavioral syndrome characterized by reciprocal caudally directed biting and scratching. Repeated injection of SP, but not SP C-terminal fragments, results in a decrease in the intensity of, or desensitization to, these SP-induced behaviors. Peptidase inhibitors, phosphoramidon (PH), bacitracin (BAC), diprotin A (DPA) and angiotensin converting enzyme inhibitor (ACEI OR SQ20881), together with [3H]SP, were used to investigate the possible accumulation of tritiated N-terminal metabolites in the mouse spinal cord in vivo during the development of desensitization to SP. SP N-terminal metabolites in the spinal cord were quantified by reverse-phase HPLC. The magnitude of SP-induced desensitization correlated well (r = .95) with total SP N-terminal metabolites recovered from the spinal cords of the same mice studied in vivo. The magnitude of SP-induced desensitization was also found to be negatively correlated (r = .95) with total recovered intact [3H]SP. The rank order of potency of the peptidase inhibitors in decreasing the magnitude of SP-induced desensitization was BAC = PH much greater than ACEI greater than DPA. The order of potency for in vitro inhibition of SP metabolism using synaptic membrane-derived peptidases was BAC greater than PH much greater than ACEI. These results support the hypothesis that desensitization to SP-induced behaviors depends, at least in part, on the concentration of SP N-terminal metabolites in the spinal cord.

Effects of lysergic acid diethylamide (LSD) and adjuvant-induced inflammation on desensitization to and metabolism of substance P in the mouse spinal cord

We have previously shown that the caudally directed biting and scratching response to repeated intrathecal (i.t.) injections of substance P (SP) is decreased by the third injection of SP and that this apparent desensitization to SP is less pronounced in mice pretreated with Freund's adjuvant. This study was designed to study the mechanism of this desensitization to SP and to examine the effect of lysergic acid diethylamide tartrate (LSD) on desensitization. Our results indicate that while 25 micrograms of LSD/kg body weight i.p. in naive mice had no effect on the response to a single injection of SP, LSD decreased the development of desensitization to SP-induced behaviors. In contrast, identical injections of LSD in adjuvant-pretreated mice not only failed to prevent desensitization but enhanced the degree of apparent desensitization to SP. Tolerance developed to the effects of LSD on desensitization to SP-induced behaviors in both adjuvant- and saline-pretreated mice. When injected i.t. with SP, LSD failed to alter the degree of desensitization to SP-induced behaviors, suggesting that the effect of LSD is not produced at the spinal cord level. Separation and quantification of SP and its metabolites in the spinal cord using high performance liquid chromatography (HPLC) techniques indicated that either a single injection of LSD or pretreatment with Freund's adjuvant produced similar patterns of changes in the concentrations of SP-related peptides in mouse spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of [3H]DAGO binding by substance P (SP) and SP fragments in the mouse brain and spinal cord via MU1 interactions

Binding of [3H]DAGO to fresh, frozen or beta-funaltrexamine (beta-FNA) pretreated membranes of mouse brain and spinal cord was extensively studied using substance P (SP) or SP fragments as potential competitors and/or modulators. The objective was to determine whether SP exerts its analgesic effect by interacting with mu opioid receptors. The affinity of DAGO was reduced and binding capacity was increased in the presence of SP or the N-terminal SP fragments SP(1-9) and SP(1-4) but not the C-terminal SP fragment SP(5-11). Because sub-nanomolar concentrations of SP or N-terminal SP fragments displaced [3H] DAGO binding to a minor but detectable degree, it is suggested that SP interacts with mu 1 sites through its N-terminus portion. The effect of SP on DAGO binding was less in the spinal cord compared to the rest of the brain. Modulation of DAGO binding by SP was enhanced in the brain after pretreatment of membranes with the narcotic antagonist beta-FNA. These results suggest a novel mechanism for the analgesic action of SP.