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)