Glial cell line-derived neurotrophic factor sensitized the mechanical response of muscular thin-fibre afferents in rats

BACKGROUND

The role of glial cell line-derived neurotrophic factor (GDNF) in pain and muscular nociceptor activities is not well understood. We examined pain-related behaviour and mechanical response of muscular thin-fibre afferents after intramuscular injection of GDNF in rats.

METHODS

GDNF and antagonist to transient receptor potential V1 or acid-sensing ion channels were injected into rat gastrocnemius muscle and muscular mechanical hyperalgesia was assessed with a Randall-Selitto analgesiometer. Activities of single C- (conduction velocity < 2.0 m/s) and Aδ-fibres (conduction velocity 2.0-12.0 m/s) were recorded from extensor digitorum longus muscle-nerve preparations in vitro. The changes in the responses to mechanical stimuli before and after GDNF injection were recorded.

RESULTS

Mechanical hyperalgesia was observed from 1 h to 1 day after GDNF (0.03 μM, 20 μL) injection. The decreased withdrawal threshold was temporarily reversed after intramuscular injection of amiloride (50 mM, 20 μL), but not capsazepine (50 μM, 20 μL). In single-fibre recordings, both phosphate buffered saline (PBS) and GDNF failed to induce any significant discharges. GDNF significantly enhanced the mechanical response when compared with the PBS group, but only in Aδ-fibre afferents. C-fibres were not affected. Significantly lowered threshold and increased response magnitude to mechanical stimuli were observed 30 or 60-120 min after injection. These times are compatible with the timing of the onset of the hyperalgesic effect of GDNF.

CONCLUSIONS

These results suggest that GDNF increased the response of muscular Aδ-fibre afferents to mechanical stimuli, resulting in muscular mechanical hyperalgesia.

Decreased nerve growth factor upregulation is a mechanism for reduced mechanical hyperalgesia after the second bout of exercise in rats

Delayed onset muscle soreness (DOMS) is reduced when the same exercise is repeated after a certain interval. However, the mechanism for this adaptation, called a repeated bout effect, is still not well understood. Recently, we showed that upregulated nerve growth factor (NGF) triggered by B2 bradykinin receptor (B2R) activation in exercised muscle was responsible for DOMS. In this study, we investigated whether NGF upregulation was reduced after repeated bouts of exercise in rats, and if so, whether this change occurred upstream of B2R. A bout of 500 lengthening contractions (LC) was applied on day 0 and again 5 days later. DOMS was evaluated by the mechanical withdrawal threshold of the exercised extensor digitorum longus (EDL) muscle. Mechanical hyperalgesia and NGF mRNA upregulation in EDL were observed after the first LC, but not after the second LC. We then injected HOE140, a B2R antagonist with effects lasting only several hours, once before the first LC. This blocked the development of mechanical hyperalgesia and NGF mRNA upregulation not only after the first LC but also after the second LC. This suggests that adaptation occurred upstream of B2R, as the influence of the first LC was limited to that area by HOE140.

Role of mitogen-activated protein kinases in influenza virus induction of prostaglandin E2 from arachidonic acid in bronchial epithelial cells

BACKGROUND

Influenza virus (IV) infection causes airway inflammation; however, it has not been determined whether IV infection could catabolize arachidonic acid cascade in airway epithelial cells. In addition, the responsible intracellular signalling molecules that catabolize arachidonic acid cascade have not been determined.

OBJECTIVE

In the present study, to clarify these issues, we examined the cyclooxygenase (COX) expression, cytosolic phospholipase A2 (cPLA2) phosphorylation and prostaglandin E2 (PGE2) release in human bronchial epithelial cells (BEC) upon IV infection, and the role of mitogen-activated protein kinase (MAPK) including extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun-NH2-terminal kinase (JNK) in catabolizing arachidonic acid cascade in BEC.

METHODS

COX-2 expression, phosphorylation of cPLA2 and phosphorylation of ERK, JNK and p38 MAPK were determined by Western blot. The concentrations of PGE2 were determined by ELISA. PD 98059 as a specific inhibitor of MAPK kinase-1 (MEK-1), an up-stream kinase of ERK, SB 203580 as a specific inhibitor of p38 MAPK and CEP-11004 as a specific inhibitor of JNK cascade were used to investigate the role of ERK, p38 MAPK and JNK in catabolizing arachidonic acid cascade in BEC.

RESULTS

The results showed that (1) IV infection increases COX-2 expression, cPLA2 phosphorylation and PGE2 release, (2) ERK, p38 MAPK and JNK were phosphorylated, (3) CEP-11004 and PD 98059 predominantly attenuated COX-2 expression and cPLA2 phosphorylation, respectively, (4) SB 203580 did not remarkably affect COX-2 expression and cPLA2 phosphorylation, and (5) each inhibitor dose-dependently attenuated PGE2 release by various extents.

CONCLUSION

These results indicate that IV infection activates three distinct MAPKs, ERK, p38 MAPK and JNK, to participate to various extents in the induction of PGE2 synthesis from arachidonic acid in BEC.

Effects of PGE(2) on neurons from rat dorsal root ganglia in intact and adjuvant-inflamed rats: role of NGF on PGE(2)-induced depolarization

The effects of prostaglandin E(2) (PGE(2)) on primary afferent neurons were studied by intracellular recording from small (<30 microm) dorsal root ganglion (DRG) neurons cultured for up to 3 days. PGE(2) (10(-9)-10(-5) M) depolarized 4-10% of neurons cultured with nerve growth factor (NGF) in intact rats. The percentage of neurons depolarized increased in a concentration dependent manner, while the average amplitude of the depolarization did not change with concentration. The threshold to evoke an action potential was decreased by PGE(2) (10(-9)-10(-5) M) with the maximum percentage at 10(-9) M, and this effect was also observed in neurons not depolarized by PGE(2). Whether a neuron was depolarized by PGE(2) was not related with its capsaicin (CAP) sensitivity. In addition, we examined whether NGF influences the PGE(2) response of neurons in adjuvant-inflamed young adult animals. Removal of NGF from culture medium did not change the percentage of neurons depolarized by PGE(2) in intact rats (20 and 18% for neurons cultured without or with NGF for 2-3 days, respectively). Adjuvant induced inflammation increased the percentage of neurons depolarized by PGE(2) to 38%, but this was not reversed by an addition of anti-NGF antibody to the culture medium, suggesting that NGF does not play a substantial role in the increase in sensitivity to be depolarized by PGE(2).

B2 receptor-mediated enhanced bradykinin sensitivity of rat cutaneous C-fiber nociceptors during persistent inflammation

Bradykinin (BK), which has potent algesic and sensitizing effect on nociceptors, is of current interest in understanding the mechanisms of chronic pain. BK response is mediated by B2 receptor in normal conditions; however, findings that B1 receptor blockade alleviated hyperalgesia in inflammation have been highlighting the role of B1 receptor in pathological conditions. It has not yet been clear whether nociceptor activities are modified by B1 receptor agonists or antagonists during inflammation. In addition, previous studies reported the change in BK sensitivity of nociceptors during short-lasting inflammation, and data in persistent inflammation are lacking. Therefore we investigated whether an experimentally induced persistent inflammatory state modulates the BK sensitivity of nociceptors and which receptor subtype plays a more important role in this condition. Complete Freund's adjuvant was injected into the rat-tail and after 2-3 wk, persistent inflammation developed, which was prominent in the ankle joint. Using an in vitro skin-saphenous nerve preparation, single-fiber recordings were made from mechano-heat sensitive C-fiber nociceptors innervating rat hairy hindpaw skin, and their responses were compared with those obtained from C-fibers tested similarly in normal animals. BK at 10(-8) M excited none of the 10 C-fibers in normal animals while it excited 5 of 11 (45%) C-fibers of inflamed animals, and at 10(-6) M BK excited all of the 11 inflamed C-fibers (or 94% of 36 tested C-fibers) but only 4 of 10 (or 45% of 58 tested C-fibers) in normal animals. Thus the concentration-response curves based on the incidence of BK induced excitation, and the total number of impulses evoked in response to BK were significantly shifted to the left. Moreover, an increased percentage of the inflamed C-fibers responded to 10(-6) M BK with bursting or high-frequency discharges. Thirty-percent of inflamed C-fibers had spontaneous activity, and these fibers showed comparatively less tachyphylaxis to consecutive second and third 10(-6) M BK stimulation. A B2 receptor antagonist (D-Arg-[Hyp3, Thi5,8,D-phe7]-BK) completely eliminated BK responses in inflamed rats, while B1 receptor antagonists (B 9958 and Des-Arg9-[Leu8]-BK) had no effect. Selective B1 receptor agonist (Des-Arg10-Kallidin) excited 46% (n = 13) of inflamed C-fibers at 10(-5) M concentration, which is 1,000 times higher than that of BK needed to excite the same percentage of inflamed C-fibers. We conclude that in chronically inflamed tissue, sensitivity of C-fiber nociceptors to BK, which is B2 receptor mediated, is strongly increased and that B1 receptor may not be important to a persistent inflammatory state, at least at the primary afferent level.

Differences between the Lewis and Sprague-Dawley rats in chronic inflammation induced norepinephrine sensitivity of cutaneous C-fiber nociceptors

We investigated whether there are any differences between the Lewis and Sprague-Dawley (SD) rats in chronic inflammation-induced norepinephrine (NE) sensitivity of nociceptors. Activities of C-fiber nociceptors innervating rat hairy hindpaw skin were recorded in an in vitro skin-nerve preparation. Sixty-five percent of C-fibers from inflamed Lewis rats were excited by NE (10 microM), against only 38% of C-fibers from inflamed SD rats. The average of the total impulses evoked in response to NE was also significantly higher in Lewis rats. The alpha2-adrenoceptor antagonist CH 38083 (10 microM) and yohimbine (10 microM) consistently blocked the NE-excitation of both strains. These results show that after chronic inflammation, C-fiber nociceptors of Lewis strain rats have a stronger sensitivity to NE, and that alpha2-adrenoceptors are predominately involved in the NE-sensitivity of inflamed rats in both strains.

Effects of lowering barometric pressure on guarding behavior, heart rate and blood pressure in a rat model of neuropathic pain

We investigated whether lowering barometric pressure by 20 mmHg (LP) aggravates the guarding behavior suggestive of spontaneous pain following sciatic nerve chronic constriction injury (CCI) in rats. Systemic blood pressure (BP) and heart rate (HR) of unrestrained rats were recorded telemetrically during LP both before and after the CCI surgery. CCI rats showed guarding posture in normopressure conditions, and LP increased the cumulative time of this behavior. Baseline BP but not HR was increased following CCI. LP increased BP and HR of the rats only before the CCI surgery. Animals after CCI surgery showed variable (BP, HR) and transient (HR) responses to LP. These results indicate that (1) LP aggravated spontaneous pain and increased BP and HR in the CCI rats, and (2) CCI surgery influenced BP and HR of rats.

Increase in spontaneous action potentials and sensitivity in response to norepinephrine in dorsal root ganglion neurons of adjuvant inflamed rats

To gain an understanding of the cellular mechanisms of hyperalgesia and spontaneous pain in adjuvant-induced chronic inflammation, we investigated the effects of nerve growth factor (NGF), which is known to increase in inflamed tissues and to cause hyperalgesia, on the spontaneous activities and norepinephrine-induced excitation of dorsal root ganglion (DRG) neurons. Intracellular recordings were obtained from freshly dissociated and cultured DRG neurons (<30 microm) from intact and adjuvant inflamed (AI) rats. Of more than 100 freshly dissociated DRG neurons from the intact rats, none produced spontaneous action potentials, whereas 23% of the neurons from the AI rats did. Spontaneous activities were induced in 34% neurons from intact rats when cultivated for one day with NGF. No neurons from the intact rats responded to norepinephrine (NE), irrespective of whether they were freshly dissociated or cultured with NGF. In contrast, 11% of neurons from the AI rats, both freshly dissociated and cultured without NGF, had a small depolarization in response to NE. The present results suggest that, in AI rats NGF plays an important role in inducing spontaneous activities in DRG neurons, but not in inducing sensitivity to NE.

Effects of lowering ambient temperature on pain-related behaviors in a rat model of neuropathic pain

To clarify the mechanism by which changes in chronic pain are induced by cold environments, rats rendered neuropathic by a chronic constriction injury (CCI) to the sciatic nerve were exposed to low ambient temperature (LT; 7 degrees C decrease from 22 degrees C) in a climate-controlled room. LT exposure aggravated pain-related behaviors in CCI rats, i.e., decreased the threshold to von Frey hair and paw pressure stimulation, prolonged the duration of foot withdrawal to pinprick stimulation, and increased the cumulative duration of guarding posture. Lumbar sympathectomy (SYX) did not inhibit LT-induced augmentations of pain-related behaviors in CCI rats. LT exposure decreased the skin temperatures of both hind paws to the same degree in the sham-operated control and SYX rats, while in the CCI and SYX+CCI rats it caused a larger temperature decrease in the injured paw than in the uninjured one. These results indicate that LT exposure augments abnormalities in pain-related behaviors of neuropathic rats, and also suggest that sympathetic nervous activity is not a predominant factor in the augmenting mechanism.

Possible contribution of protein kinase C in the effects of histamine on the visceral nociceptor activities in vitro

To clarify the possible contribution of protein kinase C activation in histamine-induced excitation and sensitization of the heat response of testicular polymodal receptors, the effects of staurosporine, a protein kinase C inhibitor, and phorbol 12,13-dibutyrate, a protein kinase C activating phorbol ester, were studied in visceral polymodal receptors. Single polymodal receptor activities were recorded in vitro from testis-spermatic nerve preparations obtained from deeply anesthetized dogs (pentobarbital sodium, 30 mg/kg, i.v.). Histamine (10 microM)-induced excitation and facilitation of the heat response of polymodal receptors were both suppressed by staurosporine (1 microM), suggesting that activation of protein kinase C is involved in both these effects of histamine. Application of phorbol 12,13-dibutyrate (0.1 microM) mixed with histamine increased the histamine-induced excitation, whereas a 5 min application of phorbol 12,13-dibutyrate before histamine suppressed it. These results suggest that phorbol 12,13-dibutyrate-activated protein kinase C has inactivation as well as activation effects on the intracellular cascade connected to histamine receptors, and that the former has a slower time course.

Endogenous nerve growth factor increases the sensitivity to bradykinin in small dorsal root ganglion neurons of adjuvant inflamed rats

To examine the cellular mechanisms of hyperalgesia observed in an adjuvant-induced chronic inflammation, the role of nerve growth factor (NGF) in the response to bradykinin (BK) in small neurons from dorsal root ganglia (DRG) was studied via intracellular recordings. After 2 days of cultivation in the absence of NGF, the percentage of neurons from adjuvant-inflamed (AI) rats which were depolarized by BK (53%) was significantly higher than that in neurons from intact rats (13%). This higher percentage in AI rat neurons was significantly reduced after culturing with anti-NGF (17%), but was not influenced by the addition of NGF (57%). The present result demonstrated that sensitivity to BK of DRG neurons from AI rats is increased due to the action of endogenous NGF, suggesting that plastic change in primary afferent neurons caused by NGF may be one of the mechanisms involved in hyperalgesia.

Lowering barometric pressure aggravates mechanical allodynia and hyperalgesia in a rat model of neuropathic pain

To examine the effects of meteorological change on the pain-related behaviors of neuropathic rats, animals with a chronic constriction injury (CCI) to the sciatic nerve were exposed to low barometric pressure (LP), 20 mmHg below the natural atmospheric pressure in a climate-controlled room. CCI caused a decreased hindpaw withdrawal threshold to von Frey hair (VFH) stimulation (mechanical allodynia) and prolonged duration of hindpaw withdrawal in response to pinprick stimulation (mechanical hyperalgesia). When the CCI rats were exposed to LP, both these pain-related behaviors were aggravated, whereas no change was seen in a group of controls. In the CCI rats sympathectomy inhibited this LP-induced augmentation of pain-related behaviors. These results show that LP intensifies the abnormalities in the pain-related behaviors of neuropathic rats, and that sympathetic activity contributes to the LP effect.

Potentiation and suppression of the histamine response by raising and lowering the temperature in canine visceral polymodal receptors in vitro

It is well known that itch and inflammatory pain are enhanced when tissue is warmed, while they are suppressed when tissue is cooled. To see whether these changed sensations are based on the changed response of sensory receptors, the temperature dependency of the excitation of polymodal receptors induced by histamine, which plays an important role both in itch and inflammatory pain, was studied. Single nerve activities of polymodal receptors were recorded from canine testis-spermatic nerve preparations in vitro. Raising the temperature from 34 to 40 degrees C, a temperature below the threshold for the heat response of polymodal receptors, facilitated the histamine-induced nerve discharge to 268% of that at 34 degrees C, while lowering the temperature to 28 degrees C decreased it to 25%. Facilitation of the histamine response was also observed in the noxious temperature range (48 and 51 degrees C). These results suggest that the potentiation of the histamine-induced sensation by increasing the tissue temperature, as well as its suppression by lowering tissue temperature, can be explained by a temperature-dependent response of peripheral sensory receptors to histamine. However, the suppression of itch by noxious heat reported by Bickford (Bickford, R.G., Experiments relating to the itch sensation, its peripheral mechanism, and central pathways, Clin. Sci. Incorp. Heart, 3 (1937) 377-386) cannot be explained by the noxious heat-induced facilitation of the peripheral receptor response reported in this paper.

Nerve growth factor increases sensitivity to bradykinin, mediated through B2 receptors, in capsaicin-sensitive small neurons cultured from rat dorsal root ganglia

To examine the effects of nerve growth factor (NGF) on the response to bradykinin (BK) of primary afferent neurons, intracellular recordings were obtained from small (< 30 microm) and large (> or = 35 microm) neurons in rat dorsal root ganglia (DRG). The response to BK in the small neurons was tested in 23 freshly dissociated neurons (dissociated group), 37 neurons cultured in the absence of NGF (no-NGF group) and 117 neurons in the presence of NGF (NGF group). Application of BK (10(-7) or 10(-5) M) induced a depolarization in a small number of neurons in the freshly dissociated (13%) and the no-NGF (11%) groups. After cultivation with NGF, the percentage of neurons that were depolarized by BK significantly increased to 46% after 2 days of cultivation. In the NGF group, the percentage of neurons sensitive to BK was significantly greater among capsaicin (CAP)-sensitive than among CAP-insensitive neurons (48 vs 20%). This BK-induced depolarization was completely blocked by a B2 receptor antagonist, but not a B1 receptor antagonist. With large neurons, in contrast, NGF did not increase the percentage that were BK-sensitive (9% in the dissociated group vs 0% after being cultured 2 days with NGF). These results demonstrate that NGF increases sensitivity to BK, mediated through B2 receptors only, in capsaicin-sensitive small neurons cultured from rat DRGs.

Psychological and physiological changes during isolation and confinement: I. Group dynamics and member interaction

The isolated and confined environment of a laboratory setting was used as one of the analogous environments of long-term manned spaceflight. This setting has more advantages than the natural one in that the behavioral variables can be easily controlled. Thus, a hyperbaric chamber was used in this experiment. The subjects were five men from 22- to 26-years old who had never met before the experiment. Over a total 5-day isolation and confinement period as well as 2-day pre- and post-isolation periods, the subjects were given different kinds of physiological and psychological tasks. During these periods their behavior and communications were recorded in order to observe when the formation of a group begins and how it forms and functions. The formation of a sub-group of three men was observed on the third day of isolation, showing strong reciprocal connections among these subjects who developed bonds that were quite stable. It is, however, not known how this sub-group functioned within the large group, since the experimental period was possibly too short.

Examination of colocalization of calcitonin gene-related peptide- and substance P-like immunoreactivity in the knee joint of the dog

It is generally assumed that the majority of substance P (SP)-containing afferents are also immunoreactive for calcitonin gene-related peptide (CGRP). In order to determine whether this is also the case in articular afferents where the contents of these peptides are low, we carried out a double labeling study using Fast Blue (FB) as a retrograde tracer injected into the center of the knee joint cavity of the dog together with immunohistochemistry for SP and CGRP. After 7-36 days of survival, dorsal root ganglia (DRGs, L4-S1) were removed. Labeled cells were found mainly (94%) in L5 - 6 DRGs, and SP- and CGRP-like immunoreactivity was found in about 17 and 29% of FB-labeled cells, respectively. The coexistence of SP and CGRP was observed in 10.4% of articular afferents and only 62.7% of SP-positive articular neurons contained CGRP, a much lower ratio than in other afferents of the dog such as testicular afferents. Our data suggest that these peptides are not always released together and that they do not always work together in the joint under normal conditions.

Evidence that protein kinase C activation is involved in the excitatory and facilitatory effects of bradykinin on canine visceral nociceptors in vitro

The involvement of protein kinase (PK) C activation in the effects of bradykinin (BK) on peripheral nociceptors, polymodal receptors, was examined using canine testis-spermatic nerve preparations in vitro. Phorbol 12,13-dibutyrate 0.1 microM, which activates PKC, suppressed the BK-induced excitation when applied for 3-5 min prior to BK application, but facilitated it when applied simultaneously with BK. Neither effect was induced by an inactive phorbol ester, 4alpha-phorbol 12, 13-didecanoate, demonstrating that both effects were mediated through the activation of PKC. In addition, staurosporine 1 microM, a PK inhibitor, suppressed both BK-induced excitation and facilitation of the heat response of testicular polymodal receptors without influencing on-going activities and the heat response itself. These results suggest that PKC activation is involved in the excitatory and facilitatory effects of BK on peripheral nociceptors.

Peripheral mechanism of hyperalgesia--sensitization of nociceptors

The peripheral mechanism of hyperalgesia is considered to be the result of nociceptor sensitization. As possible agents causing nociceptor sensitization, bradykinin, histamine, prostaglandin (PG)s, protons and nerve growth factor are evaluated with respect to their release into the injured tissue, their sensitizing potencies. Whether blocking these agents suppresses sensitization was also evaluated. In addition, the intracellular mechanisms by which bradykinin, histamine and PGs cause sensitization are reviewed.

Calcitonin gene-related peptide- and substance P-like immunoreactive fibers in the spermatic nerve and testis of the dog

In order to determine if calcitonin gene-related peptide (CGRP) and substance P (SP) coexist in peripheral spermatic nerve fibers, we carried out a double-staining immunofluorescence study using confocal microscopy and fluorescence microscopy. CGRP- and SP-like immunoreactivity (LI) coexisted in the spermatic nerve trunk and in the single fibers running along the surface of the testis. The great majority of the SP-containing fibers also held CGRP-LI, although some fibers contained CGRP-LI without SP-LI. These observations are consistent with previous observations on testicular dorsal root ganglion neurons. Additionally, we carried out an immunogold silver staining for CGRP and found CGRP-containing nerve bundles, single nerve fibers and their nerve terminals. Some CGRP-containing nerve terminals were located very superficially in the tunica albuginea (<5 microm from the surface).

[A survival case of intraoperative pulmonary embolism diagnosed early by transesophageal echocardiography]

An otherwise healthy 36-year-old housewife was diagnosed with advanced cancer of the stomach 5 months after her third parturition. Surgery was performed with the patient under total intravenous anesthesia combined with continuous epidural anesthesia. The course of anesthesia and the operative course were uneventful until the abdominal skin was sutured, when unexplained severe circulatory collapse developed. A widely dissociated PETCO2- PaCO2 suggested pulmonary embolism, and the findings of transesophageal echocardiography corroborated the diagnosis. Infusion of 480,000 units of urokinase in 30 minutes was immediately started via a Swan-Ganz catheter, and intravenous heparin 10,000 units in 24 hours, was administrated continuously. The pulmonary circulation was restored 30 minutes after the start of therapy, resulting in rapid recovery of the patient's systemic circulatory and acid-base status. The patient was safely extubated 19 hours postoperatively.

H1-receptor-mediated excitation and facilitation of the heat response by histamine in canine visceral polymodal receptors studied in vitro

1. We examined excitation and the facilitatory effect on the heat responses induced by histamine in visceral polymodal receptors with the use of the canine testis-spermatic nerve preparation in vitro. 2. The proportion of units that showed excitation (> 10 impulses 1 min after application of histamine was initiated) increased roughly with higher concentrations of histamine: 7% at 1 microM, 26% at 10 microM, 79% at 100 microM, and 61% at 1,000 microM. The discharge rate also increased with the concentration. 3. Histamine (100 and 1,000 microM) responses > 0.5 imp/s were observed only in units with conduction velocities (CVs) of < or = 10 m/s, but not in those with CVs faster than 10 m/s. On average, histamine-induced discharges were significantly greater in units with CVs of < or = 10 m/s at all concentrations > or = 10 microM. Thus units studied in this experiment were empirically divided into slow-CV (< or = m/s) and fast-CV (> 10 m/s) groups. 4. Histamine significantly facilitated the heat responses of the slow-CV group from 10 microM, and also facilitated the fast-CV group from 100 microM. This sensitizing effect was observed irrespective of the precedent histamine-induced excitation. The magnitude of sensitization tended to increase with an increase in histamine concentration. 5. For studying the histamine receptor subtype involved in excitation and facilitation, we used D-chlorpheniramine maleate (5 microM) (an H1 receptor antagonist), famotidine (20 microM) (an H2 receptor antagonist), and thioperamide maleate (20 microM) (an H3 receptor antagonist). The magnitude of histamine-induced excitation of the slow-CV group was significantly suppressed by the H1 receptor antagonist but not by other antagonists. 6. The facilitatory effect of histamine on the heat response was also suppressed by the H1 receptor antagonist in both slow- and fast-CV groups. 7. These results strongly suggested that both excitation and facilitation of the heat response induced by histamine are mediated through the H1 receptor.

Opposite effects of increased intracellular cyclic AMP on the heat and bradykinin responses of canine visceral polymodal receptors in vitro

To clarify the validity of the long standing hypothesis that effects of E series prostaglandin (PG)S are mediated by cyclic AMP (cAMP), we studied the effects of increases in intracellular cAMP on the heat and bradykinin responses of testicular polymodal receptors. Polymodal receptor activities were recorded in vitro from testis-spermatic nerve preparations excised from dogs anesthetized with pentobarbital (30 mg/kg, i.v.). Increases in intracellular cAMP induced by either forskolin (5 or 10 microM), an adenylyl cyclase activator, or a mixture of dibutyryl cAMP (20-100 microM), a membrane permeable cAMP analog, and 3-isobutyl-1-methyl xanthine (20-100 microM), an inhibitor of the cAMP degrading enzyme, significantly augmented the response to heat (42-48 degrees C). In contrast, these substances failed to facilitate the response to bradykinin (0.1 or 1 microM) and instead suppressed it. Dideoxyforskolin (10 microM), an inactive analog of forskolin, had no effects on both the heat and bradykinin responses. These results demonstrate that an increase in intracellular cAMP induces opposite effects on the heat and bradykinin responses. Possible involvement of intracellular cAMP in the facilitatory effects of PGE2 on both responses was discussed in connection with the PGE receptor subtypes involved in the sensitization of the bradykinin and heat responses.

Coexistence of calcitonin gene-related peptide- and substance P-like immunoreactivity in retrogradely labeled superior spermatic neurons in the dog

The coexistence of calcitonin gene-related peptide (CGRP) and substance P (SP) was determined in primary afferent neurons of the superior spermatic nerve of the dog. Testicular afferent neurons were visualized by retrograde labeling with the fluorescent dye fast blue. CGRP-like immunoreactivity (LI) was found in about 80% of testicular L1 and L2 dorsal root ganglion cells, and 81% of CGRP-positive neurons also contained SP. Conversely, SP-LI was found in 66% of testicular afferents, and 96% of SP-positive neurons simultaneously contained CGRP. Both CGRP- and SP-LI were observed in the whole size range of the testicular afferent neurons. No significant difference in the diameter was detected between CGRP- and SP-positive testicular afferent neurons. In contrast, the diameter of SP-positive cells was significantly smaller than that of CGRP-positive cells in the whole population of dorsal root ganglion (DRG) neurons. Compared to skin and muscle afferents, a larger population of the testicular afferents contain these peptides. This is considered to be one of the characteristic features of visceral afferents. Coexistence of CGRP and SP in testicular afferent neurons suggest a close functional relationship between these two neuropeptides in the sensory nervous system.

EP receptor subtypes implicated in the PGE2-induced sensitization of polymodal receptors in response to bradykinin and heat

1. Our previous studies, in which we used in vitro canine testispermatic nerve preparations, showed that prostaglandin E2 (PGE2) augments both bradykinin (BK)- and heat-induced discharges of polymodal receptors. However, the PGE2 concentration required to augment the BK responses were 100 times lower than those necessary for the heat responses, suggesting that different receptors are involved in these phenomena. We studied which receptors for E series of prostaglandins (EP receptors) were responsible, using the antagonist and agonists for three subtypes of EP receptors. 2. PGE2-induced augmentation of the BK responses was unaffected when treated with an antagonist for the EP1 receptor, AH6809. 3. An agonist for the EP3 receptor, M&B28767, at > or = 10 nM, significantly augmented the BK responses in a concentration-dependent manner that mimics the PGE2-induced effect. An agonist for the EP1 receptor, 17-phenyl trinor PGE2 (17-phen PGE2), at the high concentrations of 0.1 and 1 microM, augmented the BK responses in two and four of nine cases tested, respectively. However, this augmentation was not suppressed by the antagonist for the EP1 receptor, AH6809. In addition, an agonist for the EP2 receptor, butaprost, did not affect the BK responses even when applied at 10 microM. 4. In contrast, butaprost at > or = 10 nM significantly augmented the heat responses in a concentration-dependent manner. M&B28767 and 17-phen PGE2, respectively, augmented the heat responses at higher concentrations of 100 nM and 1 microM. 5. These results indicate that the EP3 and EP2 receptor subtypes are differentially implicated in the respective PGE2-induced augmentation of BK responses and heat responses of polymodal receptors.

Segmental distribution of afferent neurons innervating the canine testis

To clarify the afferent innervation of the canine scrotal contents, retrograde labeling of neurons in the dorsal root ganglia (DRG) has been carried out using two methods: (1) horseradish peroxidase (HRP) injection into the surface of the testis and epididymis; and (2) exposure of the superior spermatic nerve to a fluorescent dye (Fast blue; FB). Injections of HRP resulted in labeling of DRG cells located predominantly from T10 to L4 (87%) and, to a lesser extent, at S1-S3 (13%). Transection of the vas deferens previous to testicular injections eliminated labeling in the S1-S3 DRG, but not at thoracolumbar levels. These findings indicated that primary afferent fibers of the testis and epididymis project mainly to the DRG at higher than L4 through the superior spermatic nerve, but an additional population of the fibers also projects the sacral level through the inferior spermatic nerve. Exposure of the superior spermatic nerve to FB resulted in a similar distribution of labeled cells as compared with testicular injections of HRP after vasectomy. Labeled cells (8.1%) were also observed in the contralateral T13-L3 DRG. In both FB and HRP groups, the major part of the labeled cells was located in L1 and L2. The sizes of HRP- and FB-labeled cells were smaller than those of unlabeled cells in the L1 and L2 DRG. The cumulative frequency distribution histogram for the diameter of HRP- and FB-labeled cells could be fitted by a normal distribution.

Excitation and sensitization of the heat response induced by a phorbol ester in canine visceral polymodal receptors studied in vitro

To clarify the possible involvement of protein kinase (PK) C activation in the excitation and sensitization of polymodal receptors (PMRs), the effects of phorbol 12,13-dibutyrate (PDBu) on PMRs were studied in canine testis-spermatic nerve preparations in vitro. Application of PDBu (10(-7), 10(-6), AND 10(-5) M) for 5 min evoked a significant increase in the ongoing activity of the PMRs within 15 min. PDBu (10(-8) to 10(-5) M) significantly augmented the subsequent heat responses of the PMRs. Staurosporine (10(-6) M), a PK inhibitor, attenuated the effect of PDBu on heat responses. These data suggest that activation of PKC contributes to the activities of PMRs.

Influence of histamine on the bradykinin response of canine testicular polymodal receptors in vitro

Effects of histamine on the testicular polymodal receptors were studied in vitro using canine testis-spermatic nerve preparations. Histamine induced distinct increase in the discharge rate in 6 out of 17 units tested (high responders), while it only weakly excited the remaining 11 units (low responders). The bradykinin response of low responders tended to be slightly facilitated by pretreatment with histamine, while that of high responders tended to be suppressed. Significant correlation was observed between the magnitude of histamine-induced discharges and the magnitude of change in the bradykinin responses.

Incomplete suppressive effects of acetylsalicylic acid on the heat sensitization of canine testicular polymodal receptor activities

1. Using canine testis-spermatic nerve preparations in vitro, we studied the effects of acetylsalicylic acid (ASA), an inhibitor of cyclooxygenase, on the polymodal receptor response to heat stimulation itself and on the sensitizing effects on the heat and bradykinin responses induced by strong heat stimulation (55 degrees C for 30 s). 2. Greater heat responses tended to be strongly suppressed by ASA (550 microM), with a significant correlation observed between the response magnitude and the magnitude of the suppression (r = 0.88 for the response at 45 degrees C; r = 0.83 for the response at 48 degrees C). The change in the heat response at 48 degrees C from 1.18 +/- 0.19 to 0.62 +/- 0.11 imp/s was statistically significant (n = 21, P < 0.01). 3. After stimulation at 55 degrees C in the presence of ASA, resting discharges at 34 degrees C appeared in only 2 of the 21 units tested. The responses at 45 and 48 degrees C, however, were significantly potentiated after this stimulation (those at 45 degrees C from 0.12 +/- 0.05 to 2.19 +/- 0.51 imp/s, mean +/- SE; those at 48 degrees C from 0.62 +/- 0.11 to 2.42 +/- 0.49 imp/s; P < 0.01, n = 21 for both). Sensitization was observed up to 50 min after stimulation at 55 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible involvement of the EP2 receptor subtype in PGE2-induced enhancement of the heat response of nociceptors

Prostaglandin E2 augments bradykinin- and heat-induced discharges of polymodal receptors as studied in vitro preparations. Our previous study revealed the involvement of the EP3 receptor subtype in the PGE2 induced enhancement of the BK response [Brain Res. 632 (1993) 321-324]. The agonist for EP2 (butaprost; 10(-8) M) significantly augmented heat responses, but did not augment the BK responses at concentrations from 10(-8) to 10(-5) M; however, the agonist for EP3 (M&B28767) or EP1 (17-phenyl-trinor-PGE2) at 10(-7) M did not affect the heat responses. These findings indicate the involvement of the EP2 receptor subtype in the augmenting effect of PGE2 on heat responses.

Histamine-induced sensitization of the heat response of canine visceral polymodal receptors

In elucidating the possible involvement of histamine (His) in hyperalgesia to heat, the effects of His on the heat response of testicular polymodal receptors were studied in vitro in canine testis-spermatic nerve preparations. His (100 and 1000 microM) induced discharges > 0.5 impulses/s (high-responders) in about one third of units tested. His (> or = 10 microM) facilitated the heat response irrespective of whether His alone induced substantial excitation, and the magnitude of facilitation at 100 microM did not differ between high- and low-responders (His-induced discharges < or = 0.5 impulses/s). Conduction velocity of high-responders at 100 microM (2.2 +/- 0.9 m/s, n = 5) was slower on average than that of low-responders (12.9 +/- 1.6 m/s, n = 9). The sensitizing effect of His reported in this paper suggests that His plays a role in hyperalgesia.

Forskolin does not augment the bradykinin response of canine visceral polymodal receptors in vitro

In clarifying the possible involvement of cyclic AMP (cAMP) in prostaglandin (PG) E2-induced sensitization of the bradykinin response of canine testicular polymodal receptors, the effects of forskolin, an activator of adenylyl cyclase, were studied in the presence and absence of acetylsalicylic acid (ASA, 550 microM) which blocks PG production. Forskolin (10 microM) seldom induced discharges in polymodal receptors. An unexpected outcome of this study was that forskolin induced no facilitation of the bradykinin (0.1 microM) response, both in the absence and presence of ASA. A slight yet significant suppression of the bradykinin response was instead observed in the absence of ASA. These results suggest that intracellular cAMP may be related with PG E2-induced sensitization of the bradykinin response through its decrease.

Involvement of EP3 subtype of prostaglandin E receptors in PGE2-induced enhancement of the bradykinin response of nociceptors

Prostaglandin E2 augments bradykinin-induced discharges of polymodal receptors as studied in vitro preparations. The antagonist and agonists for three subtypes of EP receptors were used to determine which subtype is involved in this phenomenon. The agonist for EP3 (M&B28767) simulated the PGE2-induced effect but not for EP2 (butaprost). The antagonist for EP1 (AH6809) did not suppress the effect. These findings indicate the involvement of the EP3 receptor subtype in the effect.

Augmenting effects of cyclic AMP on the heat response of canine testicular polymodal receptors

It has long been thought that the augmenting effects of E series prostaglandins (PG) are mediated by cyclic AMP (cAMP). In clarifying the validity of this hypothesis, we studied the effects of increases in intracellular cAMP on the heat response of testicular polymodal receptors. Recordings were obtained from testis-spermatic nerve preparations excised from dogs anesthetized with pentobarbital (30 mg/kg, i.v.). Induction of increases in intracellular cAMP by either forskolin, an adenylyl cyclase activator, or a mixture of dibutyryl cAMP (10(-4) M) and 3-isobutyl-1-methyl xanthine (10(-4) M) significantly and reversibly augmented the heat response. These results support the notion that cAMP is involved in the augmenting effect of PG E2 on the heat response of nociceptors.

Prostaglandin E2-induced sensitization of the heat response of canine visceral polymodal receptors in vitro

The sensitizing effect of prostaglandin (PG) E2 on the heat response of testicular polymodal receptors was studied in vitro by recording single polymodal receptor activities from the testis-spermatic nerve preparations excised from deeply anesthetized dogs. PG E2 at 10(-7) M had no significant influence on the heat response. PG E2 at 10(-6) and 10(-5) M did not induce substantial increases in discharge rates, yet it significantly augmented the heat response. The concentration necessary for augmenting the heat response is thus 100 times greater than that (10(-8) M) previously reported for bradykinin [Naunyn-Schmiedebergs Arch. Pharmacol., 344 (1991) 368-376].

Spinal termination patterns of canine identified A-delta and C spermatic polymodal receptors traced by intracellular labeling with Phaseolus vulgaris-leucoagglutinin

The spinal projection patterns of spermatic polymodal receptors were studied by intracellular labeling of functionally identified canine dorsal root ganglion (DRG) neurons with Phaseolus vulgaris-leucoagglutinin (PHA-L). The processes of 2 C-fiber and 1 A-delta-fiber spermatic polymodal receptor neurons were labeled well enough to trace their central terminations. The labeled C-fiber DRG neurons were of medium size (mean diameter 36.8 and 40.7 microns). On entering the spinal cord, axons of the C-polyclonal receptors divided into rostral and caudal main branches that extended over 3 spinal segments (20 and 25 mm, respectively), and issued a total of 16 and 15 collaterals, respectively. The majority of collaterals ran in or along the lateral surface, but both neurons had 1 or 2 collaterals or terminal branches running through the middle, or along the medial surface of the dorsal horn. Terminal swellings and en passant enlargements were observed mainly in laminae I, V, and VII. Some C-fiber terminations appeared in lamina II and the adjacent lateral column. The A-delta polymodal receptor had a termination pattern similar to that of the C-fiber units with the exception of a shorter distance over which its 13 identified collaterals were issued (10 mm), and continuation of the rostral main branch into Lissauer's tract (traced for 3.6 mm) after all branches appeared. Two terminal branches were found running just above the central canal in another A-delta neuron in which termination could be only partially traced.(ABSTRACT TRUNCATED AT 250 WORDS)

Strong heat stimulation sensitizes the heat response as well as the bradykinin response of visceral polymodal receptors

1. Hyperalgesia after thermal injury is a common phenomenon, but its mechanism is poorly understood. As a step toward understanding the mechanism for heat sensitization, we searched conditions that would induce sensitization consistently and studied changes in polymodal receptors in their responses to heat (45 and 48 degrees C) and to bradykinin. Experiments were conducted in vitro, with the use of testis-superior spermatic nerve preparations excised from anesthetized dogs. 2. Stimulation at 55 degrees C for 30 s induced clear augmentation of the responses to stimulations at 45 and 48 degrees C when tested within 10 min in 22 out of 24 testicular polymodal units. In the remaining two units, weak or delayed augmenting tendencies were observed. The response to stimulation at 45 degrees C increased from 0.28 +/- 0.08 to 2.99 +/- 0.46 (SE) imp/s, whereas at 48 degrees C it increased from 1.08 +/- 0.16 to 4.60 +/- 0.63 imp/s (P < 0.001, n = 24). A low-level ongoing discharge appeared in about one-half of the units studied. 3. Despite frequent rinsing of the receptive field, augmentation of the heat response observed after stimulation at 55 degrees C continued for up to approximately 3 h. 4. The response to bradykinin (94 nM) was also potentiated: the net mean discharge rate (NMDR) during a 1-min application period of bradykinin as well as the total number of impulses induced by one bradykinin application significantly increased from 0.91 +/- 0.27 to 1.97 +/- 0.32 imp/s and from 213.9 +/- 42.3 to 433.5 +/- 58.7 impulses, respectively (P < 0.001, n = 15).(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitizing effects of bradykinin on the heat responses of the visceral nociceptor

1. Whether bradykinin (BK), which is known as an endogenous pain-producing substance, induces augmentation of the discharges of polymodal receptors evoked by heat stimulation was investigated in in vitro canine testis-superior spermatic nerve preparations. 2. The heat response was significantly augmented by pretreatments with BK at concentrations greater than 0.094 nM, whereas BK induced significant increases in the mean discharge rates at concentrations above 9.4 nM. Both effects increased in a concentration-dependent manner. The augmenting effect of BK on the heat response diminished within 10 min after application of BK, regardless of concentration. 3. When 9.4 nM BK was applied in a mixture with 940 nM NPC349, a B2 receptor antagonist, the averaged mean discharge rate evoked by BK and the averaged augmenting effect were both significantly suppressed compared with those induced by BK given alone. 4. The augmenting effect of BK on the heat response of polymodal receptors could be observed even in the absence of BK-evoked discharges per se in several cases in which low concentrations of BK or BK plus B2 antagonists were given. 5. These findings suggest that the augmenting effects of BK on the heat response depend on B2 receptor-mediated intracellular processes acting in parallel to, but not directly on, the impulse-generation mechanism of the heat response of the polymodal receptor.

Comparison of the effects of prostaglandins E2 and I2 on testicular nociceptor activities studied in vitro

Effects of exogenous prostaglandin (PG) E2 and PGI2 on testicular polymodal receptor activities were compared in in vitro recordings of single- or multi-fiber discharges from canine testis-spermatic nerve preparations. PGI2 up to 1.4 x 10(-6) mol/l (cumulative method) or 1.0 x 10(-5) mol/l (non-cumulative method) excited only weakly some of the receptors, and similar observations were made with PGE2. Both PGs applied cumulatively or non-cumulatively at concentrations above 1.4 x 10(-8) mol/l augmented the response to bradykinin (9.4 x 10(-8) mol/l) in more than half of the cases tested. The augmenting effect of PGE2 lasted longer than that of PGI2 both with the cumulative and the non-cumulative method. The degree of augmentation tended to increase dependent on concentration, but some cases showed no further increase or rather a decrease in augmentation by PGs at a ten times higher concentration, especially when PGs were applied cumulatively. A second challenge by PG after a short interval (2 min) did not induce augmentation. These phenomena were considered to be tachyphylaxis to PGs. Cross-tachyphylaxis to PGE2 and PGI2 was also observed. There was not much difference in excitatory and augmenting potencies between these two PGs, but there was a clear difference in the concentrations of the PGs necessary to induce excitation of polymodal receptors and to facilitate their response to bradykinin.

Facilitatory effects of opioids on the discharges of visceral nociceptors

Effects of opioids on the activity of visceral nociceptors were tested using the in vitro testis-spermatic nerve preparations excised from deeply anesthetized dogs. Morphine, DADLE and dynorphin (10 microM) elicited discharges of polymodal receptors in approximately 1/3 of the tested cases. The incidence of the excitatory response of morphine increased at higher concentrations. The excitatory responses were quite variable among preparations and showed a strong tendency for tachyphylaxis. Similar increases in discharges were elicited when morphine was applied during the steady state of the response evoked by bradykinin (BK) or BK mixed with prostaglandin E2. Pretreatment of morphine for 5 min significantly augmented the subsequent BK responses for 30 min or more. Naloxone per se induced neither excitation nor augmentation of the subsequent BK response, however it reversed the augmenting effect of morphine on BK response. In contrast with previous reports proposing peripheral analgesic effects of opioids, suppressive effects on nociceptors were never observed in the present experiment. Peripheral effects of opioids were discussed.

Effects of ionic calcium on the responses of canine testicular polymodal receptors to algesic substances

1. To explore possible mechanisms of the responses to algesic substances (bradykinin, hypertonic saline, and high K+ solution) of polymodal receptors in the canine testis, the Ca2+ concentration was varied in vitro. 2. After 1 min in Ca2+-free media, the responses to both high K+ solution (60 mM K+) and hypertonic saline (0.6 M Na+) were significantly augmented and tended to increase further with time; return to normal Ca2+ concentration quickly reversed these changes. These augmenting effects were blocked by the substitution of Mg2+ for Ca2+. The excitation produced by 60 mM K+ was decreased by increasing Ca2+ in a concentration-dependent fashion. 3. Reducing the bath concentration of K+ decreased responses evoked by 9 X 10(-8) M bradykinin (BK), whereas increased K+ concentration had the opposite effect. 4. The excitatory effects of BK were significantly suppressed in extracellular Ca2+-free condition. The suppression was not affected by the addition of Mg2+. Prostaglandin E2, which has been known to be released by BK and to augment the BK response, failed to restore the suppressed response by either preapplication (2.8 X 10(-7) M) or simultaneous application in high concentration (1.4 X 10(-5) M). 5. On the basis of these observations, it was postulated that Ca2+ concentration-dependent changes of the responses to 60 mM K+ and 0.6 M Na+ results from Ca2+-dependent "membrane surface potential" changes. The suppressed response to BK by Ca2+ depletion may be explained by the intervention of Ca2+-dependent processes other than PG production.

Respiratory changes induced by activation of testicular afferents in dogs

Reportedly, more than 90% of the testicular afferents of the dog are of the polymodal type. The possible involvement of these afferents in modulation of respiration was studied using anesthetized dogs, which had been vagotomized and with both common carotid arteries ligated. Electrical stimulation of the superior spermatic nerve at an intensity of 1/5 Tc (Tc: threshold intensity for C-fiber activation) induced no substantial changes in respiration, while above 1/2 Tc it induced an increase in minute expiratory volume (VE), or a decrease followed by an increase in VE. The pattern of respiratory change was converted from the former to the latter by increasing the stimulation frequency while maintaining the same intensity. Mechanical stimulation of the testis through a stimulator with a tip of 1 cm in diameter caused an increase of VE at 200 g and a decrease followed by an increase of VE above 500 g. Intra-arterial injection of bradykinin (3 x 10(-6) M), hypertonic saline (1.5 M) and high K+ solution (180 mM) to the spermatic artery induced similar respiratory changes. Pneumograms showed a shift in end-expiratory position even at stimulus intensities without significant VE changes. Phrenic nerve recordings from some artificially ventilated dogs, revealed an prolongation of the first expiratory phase followed by augmentation of phrenic activity, mostly an increase in respiratory rate. Comparison between afferent activities and reflex respiratory changes suggests that above described two types of respiratory changes are brought about by the activities of testicular polymodal receptors.

Observations on electrophysiologically characterized receptive fields of thin testicular afferent axons: a preliminary note on the analysis of fine structural specializations of polymodal receptors

The sparse distribution of thin, principally unmyelinated sensory axons confined largely to the planar tunica vasculosa of the testis provides a suitable model for examining the fine structure of electrophysiologically characterized nerve fiber terminals. The marked sites of polymodal receptors of canine testis using the in vitro preparation devised by Kumazawa et al. (1987) were examined in serial sections traced to the terminal with the electron microscope, revealing the first micrographs of a characterized polymodal receptor ending. The inferred role of these terminals in nociception, their organelle content, and the problems encountered in interpreting our initial findings are considered in the context of the variety of morphological patterns and functional roles of thin sensory axons.

Effects of prostaglandins and other putative chemical intermediaries on the activity of canine testicular polymodal receptors studied in vitro

An in vitro testis-superior spermatic nerve preparation was used to evaluate the effects of chemical agents applied in the bathing solution. Both directly evoked discharges and responses to algesic solutions [bradykinin (BK) 9 X 10(-8) M, hypertonic saline 616 mM and high K+ solution 60 mM] of polymodal receptors were studied. Prostaglandin (PG)-E2 (1.4 X 10(-6)-1.4 X 10(-5) M) and serotonin (5-HT) (1.1 X 10(-6) to 1.4 X 10(-4) M) had only a weak excitatory effect. However, test responses to algesic substances were regularly greatly increased by PG-E2, -I2 and 5-HT. Concentrations of PG-E2 of 1.4 X 10(-8) M or greater augmented BK responses; higher concentrations and/or longer applications were needed to enhance responses to algesic salt solutions. Effective concentrations for the PGs and 5-HT were near those reported for inflamed tissues and exudate. Aspirin (ASA) (5.5 X 10(-4) M or greater, for more than 4 min) suppressed the responses to BK but not those evoked by hypertonic saline. The ASA effect on the BK response was largely restored by an addition of PG-E2. Substance P also had a weak excitatory effect on some polymodal receptors, but no significant enhancement of the response to BK was noted. These results further support a role of polymodal receptors in transmitting nociceptive information, of inflammatory origin.