Quantitative autoradiographic localization of [125I-Tyr8]bradykinin receptor binding sites in the rat spinal cord: effects of neonatal capsaicin, noradrenergic deafferentation, dorsal rhizotomy and peripheral axotomy

Hypersensitivity Induced by Intrathecal Bradykinin Administration Is Enhanced by N-oleoyldopamine (OLDA) and Prevented by TRPV1 Antagonist

Transient receptor potential vanilloid 1 (TRPV1) channels contribute to the development of several chronic pain states and represent a possible therapeutic target in many painful disease treatment. Proinflammatory mediator bradykinin (BK) sensitizes TRPV1, whereas noxious peripheral stimulation increases BK level in the spinal cord. Here, we investigated the involvement of spinal TRPV1 in thermal and mechanical hypersensitivity, evoked by intrathecal (i.t.) administration of BK and an endogenous agonist of TRPV1, N-oleoyldopamine (OLDA), using behavioral tests and i.t. catheter implantation, and administration of BK-induced transient thermal and mechanical hyperalgesia and mechanical allodynia. All these hypersensitive states were enhanced by co-administration of a low dose of OLDA (0.42 µg i.t.), which was ineffective only under the control conditions. Intrathecal pretreatment with TRPV1 selective antagonist SB366791 prevented hypersensitivity induced by i.t. co-administration of BK and OLDA. Our results demonstrate that both thermal and mechanical hypersensitivity evoked by co-administration of BK and OLDA is mediated by the activation of spinal TRPV1 channels.

Sensitization of neonatal rat lumbar motoneuron by the inflammatory pain mediator bradykinin

Bradykinin (Bk) is a potent inflammatory mediator that causes hyperalgesia. The action of Bk on the sensory system is well documented but its effects on motoneurons, the final pathway of the motor system, are unknown. By a combination of patch-clamp recordings and two-photon calcium imaging, we found that Bk strongly sensitizes spinal motoneurons. Sensitization was characterized by an increased ability to generate self-sustained spiking in response to excitatory inputs. Our pharmacological study described a dual ionic mechanism to sensitize motoneurons, including inhibition of a barium-sensitive resting K⁺ conductance and activation of a nonselective cationic conductance primarily mediated by Na⁺. Examination of the upstream signaling pathways provided evidence for postsynaptic activation of B₂ receptors, G protein activation of phospholipase C, InsP3 synthesis, and calmodulin activation. This study questions the influence of motoneurons in the assessment of hyperalgesia since the withdrawal motor reflex is commonly used as a surrogate pain model.

DOI:http://dx.doi.org/10.7554/eLife.06195.001

When we accidentally place our hand on a hot stove, we normally experience a painful sensation that starts with the sensory nerves under our skin. These nerves respond by transmitting electrical impulses to our brain, where the painful sensation is then processed. At the same time, these impulses are also transmitted to the motor nerves that control the muscles in our hand to trigger an immediate reflex to withdraw the hand from the hot stove. Pain therefore has a useful role as it can reduce how bad an injury is.

People with a condition called hyperalgesia have an increased sensitivity to pain. This condition can result from a chemical called bradykinin ‘sensitizing’ the sensory nerves, causing them to transmit more electrical impulses in response to pain than normal. This makes the injury feel much more painful, and can make the pain last for longer than is beneficial.

It was less clear whether bradykinin also affects motor nerves and so triggers a withdrawal reflex. By recording the electrical activity of motor nerve cells taken from the spinal cords of newborn rats, Bouhadfane et al. now show that these motor nerves become more active when exposed to bradykinin.

Nerve cells generate electrical signals when ions—such as potassium, sodium, and calcium ions—move through channels in the membranes of the cell. Therefore, to investigate how bradykinin influences the electrical activity of motor nerves, Bouhadfane et al. exposed the cells to drugs that inhibit particular ion channels. This revealed that bradykinin sensitizes the motor nerves by blocking a type of potassium ion channel and activating another ion channel that mainly transports sodium ions. Furthermore, Bouhadfane et al. were able to identify the signaling pathways that allow bradykinin to affect the motor nerve cells.

The study implies that the neuronal circuitry for pain does not rely exclusively on sensory nerve cells but should also integrate motor nerve cells. A future challenge remains in developing a protocol to resolve the contribution of motor nerve cells to hyperalgesia assessed by reflex withdrawal.

DOI:http://dx.doi.org/10.7554/eLife.06195.002

Dose-depending effect of intracerebroventricularly administered bradykinin on nociception in rats

BACKGROUND

The effect of small and high doses of intracerebroventricularly (icv) applied bradykinin (BK) on nociception produced by mechanical stimuli and the participation of B1 and B2 receptors in this nociception were investigated in rats.

RESULTS

BK at the lowest dose (0.06 μg) produced hyperalgesia whereas at the higher doses (6 and 12 μg) antinociception. This effect was abolished by B1 or B2 receptor antagonists, des-Arg(10)-HOE140 and HOE140 (1 pmol icv), respectively.

CONCLUSION

Depending on the dose used, BK produces pro- or anti-nociceptive action. Both B1 and B2 receptors are involved in the action of icv applied BK.

Kinin receptor antagonists as potential neuroprotective agents in central nervous system injury

Injury to the central nervous system initiates complex physiological, cellular and molecular processes that can result in neuronal cell death. Of interest to this review is the activation of the kinin family of neuropeptides, in particular bradykinin and substance P. These neuropeptides are known to have a potent pro-inflammatory role and can initiate neurogenic inflammation resulting in vasodilation, plasma extravasation and the subsequent development of edema. As inflammation and edema play an integral role in the progressive secondary injury that causes neurological deficits, this review critically examines kinin receptor antagonists as a potential neuroprotective intervention for acute brain injury, and more specifically, traumatic brain and spinal cord injury and stroke.

Role of kinin B1 and B2 receptors in a rat model of neuropathic pain

Kinin B1 and B2 receptor (R) gene expression (mRNA) is increased in the sensory system after peripheral nerve injury. This study measured the densities of B1R and B2R binding sites in the spinal cord and dorsal root ganglia (DRG) by quantitative autoradiography, and evaluated the effects of two selective non-peptide antagonists at B1R (LF22-0542) and B2R (LF16-0687) on pain behavior after partial ligation of the left sciatic nerve. Increases of B1R binding sites were seen in superficial laminae of the ipsi- and contralateral spinal cord at 2 and 14 days while B2R binding sites were increased on the ipsilateral side at 2 days and on both sides at 14 days. In DRG, B1R and B2R binding sites were significantly increased at 2 days (ipsilateral) and 14 days on both sides. Whereas tactile allodynia started to develop progressively from 2 to 25 days post-ligation, the occurrence of cold allodynia and thermal hyperalgesia became significant from day 8 and day 14 post-ligation, respectively. At day 21 after sciatic nerve ligation, thermal hyperalgesia was blocked by LF22-0542 (10 mg/kg, s.c.) and LF16-0687 (3 mg/kg, s.c.), yet both antagonists had no effect on tactile and cold allodynia. Data highlight the implication of both kinin receptors in thermal hyperalgesia but not in tactile and cold allodynia associated with peripheral nerve injury. Hence LF22-0542 and LF16-0687 present therapeutic potential for the treatment of some aspects of neuropathic pain.

Bradykinin produces pain hypersensitivity by potentiating spinal cord glutamatergic synaptic transmission

Bradykinin, an inflammatory mediator, sensitizes nociceptor peripheral terminals reducing pain threshold. We now show that the B2 kinin receptor is expressed in rat dorsal horn neurons and that bradykinin, a B2-specific agonist, augments AMPA- and NMDA-induced, and primary afferent-evoked EPSCs, and increases the frequency and amplitude of miniature EPSCs in superficial dorsal horn neurons in vitro. Administration of bradykinin to the spinal cord in vivo produces, moreover, an NMDA-dependent hyperalgesia. We also demonstrate that nociceptive inputs result in the production of bradykinin in the spinal cord and that an intrathecal B2-selective antagonist suppresses behavioral manifestations of central sensitization, an activity-dependent increase in glutamatergic synaptic efficacy. Primary afferent-evoked central sensitization is, in addition, reduced in B2 receptor knock-out mice. We conclude that bradykinin is released in the spinal cord in response to nociceptor inputs and acts as a synaptic neuromodulator, potentiating glutamatergic synaptic transmission to produce pain hypersensitivity.

Effects of alpha-lipoic acid on kinin B1 and B2 receptor binding sites in the spinal cord of chronically angiotensin-treated rats

A quantitative autoradiographic study was performed to determine whether kinin receptors are altered in the rat spinal cord in an experimental model of arterial hypertension under antioxidant therapy with alpha-lipoic acid. Sprague-Dawley rats were fed for 4 weeks with a normal chow diet or with an alpha-lipoic acid supplemented diet (1000 mg/kg feed), and treated for the last 2 weeks with angiotensin II (AT II) (200 ng/kg/min with an osmotic pump implanted s.c.). Control rats received either diet but not AT II. A 2-week administration of AT II increased significantly systolic blood pressure, the production of superoxide anion in the aorta and B1 receptor binding sites in the thoracic spinal dorsal horn. This treatment did not affect spinal B2 receptor binding sites, glycemia and insulinemia. The diet supplemented with alpha-lipoic acid reduced significantly the increase in systolic blood pressure, the production of aortic superoxide anion and prevented the increases of B1 receptor binding sites. Results show an association between the oxidative stress and the increases of B1 receptors and arterial blood pressure induced by AT II. Data also exclude the possibility that arterial hypertension is a primary mechanism leading to an increase of B2 receptor binding sites in the rat spinal cord.

Increases of spinal kinin receptor binding sites in two rat models of insulin resistance

An autoradiographic study was conducted to determine whether kinin receptors are altered in the rat spinal cord in two experimental models of chronic hyperglycemia and insulin resistance. Sprague-Dawley rats were given 10% d-glucose in their drinking water alone or with insulin (9 mU/kg/min with osmotic pumps) for 4 weeks. Both groups and control rats were treated either with a normal chow diet or with an alpha-lipoic acid-supplemented diet as antioxidant therapy. After 4 weeks of treatment, glycemia, insulinemia, blood pressure, insulin resistance index, the production of superoxide anion in the aorta and the density of B2 receptor binding sites in the dorsal horn were significantly increased in the two models. These effects were prevented or attenuated by alpha-lipoic acid. In contrast, B2 receptor binding sites of most spinal cord laminae were increased in the glucose group only and were not affected by alpha-lipoic acid. Results show that chronic hyperglycemia associated with insulin resistance increases B1 and B2 receptor binding sites in the rat spinal cord through distinct mechanisms, including the oxidative stress for the B1 receptor.

Autoradiographic distribution and alterations of kinin B2 receptors in the brain and spinal cord of streptozotocin-diabetic rats

This study investigates whether bradykinin (BK) B(2) receptor binding sites are increased in the brain and thoracic spinal cord of streptozotocin (STZ)-diabetic rats at 2, 7, and 21 days posttreatment by in vitro autoradiography with the radioligand [(125)I]HPP-Hoe 140. In control and diabetic rats, specific binding sites for B(2) receptors were detected in the brain and in various laminae of the spinal cord, predominantly in superficial laminae (K(d)=34 pM). In diabetic rats, B(2) receptor densities were significantly increased in lamina l of the dorsal horn (+35% at 7 and 21 days), spinal trigeminal nucleus (+70% at 7 and 21 days) and nucleus tractus solitarius (+100% at 2 and 7 days). B(2) receptor analogues D-Arg[Hyp(3),Thi(5),D-Tic(7),Oic(8)]-BK (Hoe 140), 3-(4 hydroxyphenyl)propionyl-Hoe 140 (HPP-Hoe 140), LF16-0687 mesylate ((2-Pyrrolidinecarboxamide, N-[3-[[4-aminoiminomethyl)benzoyl]amino]propyl]-1-[[2,4-dichoro-3-[[(2,4-dimethyl-8-quinolinyl)oxy]methyl]phenyl]sulfonyl]-(2S)-(9Cl)), and BK decreased binding of [(125)I]-HPP-Hoe 140 in the spinal dorsal horn, with K(i) values of 0.5, 1.5, 3.2, and 3.7 nM, respectively. These values were not significantly different in diabetic rats at 7 days (0.5 (Hoe 140), 0.7 (HPP-Hoe 140), 1.2 (BK), and 1.7 (LF16-0687) nM). While des-Arg(10)-Hoe 140 was three orders of magnitude less potent than Hoe 140, B(1) receptor agonist (des-Arg(9)-BK) and antagonist (AcLys[D-betaNal(7),Ile(8)]des-Arg(9)-BK, R-715) did not affect [(125)I]-HPP-Hoe 140 binding at 1 microM concentration. Data suggest a very discrete and temporal increase of B(2) receptor density (without affinity changes) in the spinal cord and hindbrain of STZ-diabetic rats. This contrasts with the early induction and over-expression of B(1) receptors reported in the brain and spinal cord of STZ-diabetic rats.

Effect of sumatriptan in different models of pain in rats

The effect of sumatriptan in two standard algesimetric tests and in a model of cephalalgia was evaluated in rats. The pain threshold was measured by the hot-plate and the writhing tests; cephalalgia was produced by injecting bradykinin (10 microg in a volume of 10 microl) into a common carotid artery. Sumatriptan was subcutaneously (s.c.) injected at the doses of 4, 8, 24 or 42 mg/kg; morphine (5 or 10 mg/kg s.c.) and indomethacin (5 or 10 mg/kg s.c) were used as standard analgesic drugs. Sumatriptan had no analgesic activity either in the hot-plate test or in the writhing test. On the other hand, at 24 and 42 mg/kg it dose-dependently reduced the response to the intracarotid injection of bradykinin (vocalization and tachypnea), this effect being prevented by the 5-HT(1B) receptor antagonist, isamoltane. The 5-HT(1D) receptor antagonist BRL15572 prevented the effect of sumatriptan on bradykinin-induced tachypnea, but not the effect of sumatriptan on bradykinin-induced vocalization. These data demonstrate that sumatriptan is significantly effective in a reliable animal model of cephalalgia, while having no systemic analgesic activity.

Localization of B1 bradykinin receptor mRNA in the primate brain and spinal cord: an in situ hybridization study

The bradykinin 1 and 2 receptors (B1R, B2R) are important mediators of cardiovascular homeostasis, inflammation, and nociception. While B2R is constitutively expressed in many tissues, B1R expression is thought to be absent, but induced under proinflammatory conditions. However, recent data from knockout mice have indicated that B1R acts centrally to mediate nociception, a finding that suggests the constitutive presence of B1R in brain and/or spinal cord. The purpose of the present study was to further elucidate the physiological role of B1R by evaluating the localization of B1R mRNA in the nonhuman primate brain and spinal cord with in situ hybridization. Cryostat sections from monkey brain and spinal cord were hybridized with a [(35)S]-labeled riboprobe complementary to B1R mRNA, stringently washed, and apposed to film and emulsion. The results of these studies revealed the presence of B1R mRNA throughout the rostral-caudal extent of the brain and spinal cord. In particular, labeled cells were seen in the cerebral and entorhinal cortex, dentate gyrus, and pyramidal neurons of the hippocampus, in the thalamus, hypothalamus, amygdala, pontine nuclei, spinal cord, and dorsal root ganglion. Together the present findings offer detailed information about the distribution of B1R mRNA in the primate brain and spinal cord and demonstrate a basal level of expression in the primate nervous system. Moreover, these data provide a foundation for understanding the central actions of kinins and their putative role in mediating a number of processes, including pain and nociception.

Autoradiographic analysis of rat brain kinin B1 and B2 receptors: normal distribution and alterations induced by epilepsy

Kindling-induced seizures constitute an experimental model of human temporal lobe epilepsy that is associated with changes in the expression of several inflammatory proteins and/or their receptors in distinct brain regions. In the present study, alterations of kinin receptors in the brain of amygdaloid-kindled rats were assessed by means of in vitro autoradiography, using (125)I-labeled 3-4 hydroxyphenyl-propionyl-desArg(9)-D-Arg degrees -[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin (B(1) receptors) and (125)I-labeled 3-4 hydroxyphenyl-propionyl-D-Arg degrees -[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin (B(2) receptors) as ligands. Results demonstrate that B(2) receptors are widely distributed throughout the brain of control rats. The highest densities were observed in lateral septal nucleus, median preoptic nucleus, dentate gyrus, amygdala, spinal trigeminal nucleus, mediovestibular nucleus, inferior cerebellar peduncles, and in most of cortical regions (0.81-1.4 fmol/mg tissue). In contrast, very low densities of B(1) receptors were detected in all analyzed areas from control rats (0.18-0.26 fmol/mg tissue). When assessed in kindled rats, specific binding sites for B(2) receptors were significantly decreased (41 to 76%) in various brain areas. Conversely, B(1) receptor binding sites were markedly increased in kindled rats, especially in hippocampus (CA2 congruent with CA1 congruent with CA3), Amy and entorhinal, peririnal/piriform, and occipital cortices (152-258%). Data show for the first time that kindling-induced epilepsy results in a significant decline of B(2) receptor binding sites, accompanied by a striking increase of B(1) receptor labeling in the rat brain. An altered balance between B(1) and B(2) receptor populations may play a pivotal role in the onset and/or maintenance of epilepsy.

Chronic effects of angiotensin-converting enzyme inhibition on kinin receptor binding sites in the rat spinal cord

With the use of in vitro receptor autoradiography, this study aims at determining whether the higher level of kinin B(2) receptor density in the spinal cord of the spontaneously hypertensive rat (SHR) is secondary to arterial hypertension and whether chronic treatment with angiotensin I-converting enzyme inhibitors (ACEI) can regulate neuronal B(1) and B(2) receptors. SHR received, from the age of 4 wk, one of the two ACEI (lisinopril or zofenopril, 10 mg x kg(-1) x day(-1)) or for comparison, the selective AT(1) antagonist (losartan, 20 mg x kg(-1) x day(-1)) in their drinking water for a period of 4, 12, and 20 wk. Age-matched untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. B(2) receptor binding sites in most laminae were higher in SHR than in WKY from the age of 8 to 24 wk. Whereas B(1) receptor binding sites were significantly present in young SHR and WKY, they were barely detectable in adult rats. ACEI (16 and 24 wk) and AT(1) antagonist (24 wk) enhanced the number of B(2) without changing B(1) receptor binding sites. However, at 8 wk the three treatments significantly increased B(1) and decreased B(2) receptors in lamina I. It is concluded that 1) the higher density of B(2) receptors in the spinal cord of SHR is not due to hypertension, 2) kinin receptors are regulated differently by ACEI in neuronal and vascular tissues, and 3) aging may have a profound impact on levels of B(1) and B(2) receptors in the rat spinal cord.

Kinin B2 receptor localization and expression in the hypothalamo-pituitary-adrenal axis of spontaneously hypertensive rats

OBJECTIVE

An enhanced hypothalamo-pituitary-adrenocortical (HPA) activity has been demonstrated during onset of high blood pressure in spontaneously hypertensive rats (SHR). Furthermore, compared to normotensive Wistar-Kyoto (WKY) rats, SHR show hypersensitivity to bradykinin (BK)-induced pressor responses which may be caused by an upregulation of B(2) receptor expression in the brain.

METHODS

We performed an immunohistochemical localization and measured gene expression of B(2) receptors in the hypothalamus, pituitary and adrenal glands of SHR at three ages corresponding to the development of hypertension, i.e. prehypertensive phase, onset of hypertension and established hypertension. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot technique, B(2) receptor mRNA and protein levels, respectively, were measured.

RESULTS

A specific immunostaining for B(2) receptors was observed in the hypothalamic nuclei paraventricularis (PVN) and supraopticus (SON). In the pituitary and adrenal glands, a strong immunostaining was observed in neurohypophysis (NH) and adrenal medulla, respectively. At all ages tested, B(2) receptor mRNA and protein levels were higher in the hypothalamus and adrenal glands of SHR compared to age-matched WKY rats. Among SHR, the mRNA level was increased in neurohypophysis with age, and no difference was found in the adenohypophysis (AH) between SHR and WKY rats.

CONCLUSION

The data demonstrate a specific localization and an upregulation of B(2) receptor expression in the hypothalamus and adrenal glands of SHR, providing an anatomical and molecular basis for a possible contributory role to bradykinin-induced hypersensitivity of cardiovascular responses. The increased B(2) receptor expression in the hypothalamus and adrenal glands may also play a role in the abnormalities of the HPA axis in SHR during the development of hypertension.

Autoradiographic detection of kinin receptors in the human medulla of control, hypertensive, and diabetic donors

Kinins have been elected to the status of central neuromediators. Their effects are mediated through the activation of two G-protein-coupled receptors, denoted B, and B2. Functional and binding studies suggested that B1 and B2 receptors are upregulated in the medulla and spinal cord of hypertensive and diabetic rats. The aim of this study was to localize and quantify kinin receptors in post-mortem human medulla obtained from normotensive, hypertensive, and diabetic subjects, using in vitro receptor autoradiography with the radioligands [125I]HPP-HOE140 (B2 receptor) and [125I]HPP[des-Arg10]-HOE140 (B1 receptor). Data showed specific binding sites for B2 receptor (0.4-1.5 fmol/mg tissue) in 11 medullary nuclei from 4 control specimens (paratrigeminal > ambiguus > cuneate, gelatinous layer of the caudal spinal trigeminal nucleus > caudal and interpolar spinal trigeminal, external cuneate, solitary tract > hypoglossal > gracile > inferior olivary nuclei). Increased density of B2 receptor binding sites was observed in seven medullary nuclei of four hypertensive specimens (paratrigeminal > external cuneate > interpolar and caudal spinal trigeminal, gracile, inferior olivary > hypoglossal nuclei). B2 receptor binding sites were seemingly increased in the same medullary nuclei of two diabetic specimens. Specific binding sites for B1 receptor (1.05 and 1.36 fmol/mg tissue) were seen only in the inferior olivary nucleus in two out of the ten studied specimens. The present results support a putative role for kinins in the regulation of autonomic, nociceptive, and motor functions at the level of the human medulla. Evidence is also provided that B2 receptors are upregulated in medullary cardiovascular centers of subjects afflicted of cardiovascular diseases.

Pharmacologic and autoradiographic evidence for an up-regulation of kinin B(2) receptors in the spinal cord of spontaneously hypertensive rats

1. The effects of intrathecally (i.t.) injected kinin B(1) and B(2) receptor agonists and antagonists were measured on mean arterial pressure (MAP) and heart rate (HR) of conscious unrestrained spontaneously hypertensive rats (SHR of 16 weeks old) and age-matched normotensive Wistar Kyoto (WKY). Quantitative in vitro autoradiographic studies were also performed on the thoracic spinal cord of both strains with specific radioligands for B(2) receptors, [(125)I]-HPP-Hoe 140, and B(1) receptors, [(125)I]-HPP-[des-Arg(10)]-Hoe140. 2. Bradykinin (BK) (0.81 - 810 pmol) increased MAP dose-dependently with increases or decreases of HR. The pressor response to BK was significantly greater in SHR. The cardiovascular response to 8.1 pmol BK was reversibly blocked by 81 pmol Hoe 140 (B(2) antagonist) but not by 81 - 810 pmol [des-Arg(10)]-Hoe 140 (B(1) antagonist) in both strains. 3. The B(1) receptor agonist, des-Arg(9)-BK (8100 pmol) produced either no effects or increased MAP with variable effects on HR. These responses were similar in both strains and were reversibly blocked by 81 pmol Hoe 140. Inhibition with 8100 pmol [des-Arg(10)]-Hoe 140 was not specific to B(1) agonist-mediated responses. 4. [(125)I]-HPP-Hoe 140 specific binding sites were predominantly located to superficial laminae of the dorsal horn and were significantly higher in SHR. Low levels of [(125)I]-HPP-[des-Arg(10)]-HOE 140 specific binding sites were found in all laminae of both strains. 5. It is concluded that the hypersensitivity of the cardiovascular response to BK is due to an increased number of B(2) receptors in the spinal cord of SHR and that B(1) receptors are unlikely involved in spinal cardiovascular regulation in SHR.

Glutamate release from adult primary sensory neurons in culture is modulated by growth factors

The aim of this study was to examine possible modulatory effects of some trophic molecules, i.e. nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF), on potassium (K(+))-, bradykinin (BK)- or capsaicin (CAPS)-evoked release of glutamate (GLU) from dorsal root ganglion (DRG) neurons in vitro. BK (0.5 and 1 microM) induced a dramatic and significant increase in glutamate release. Neither CAPS nor K(+) (60 mM) produced any significant increase of GLU release vs. basal levels during a 5-min stimulation. The BK-evoked release of GLU was almost completely blocked by HOE 140, a selective BK2-receptor antagonist at high doses. Basal release of GLU was significantly reduced in cultures grown in the presence of bFGF, whereas BDNF and NGF had no significant effect. Incubation with growth factors generally decreased the BK-stimulated GLU release, an effect most pronounced for bFGF, which completely blocked BK-stimulated release. The rise in intracellular [Ca(2+)] following stimulation with BK (100 nM-1 microM), potassium (60 mM) or ATP (10 microM) was also studied using a Ca(2+)-sensitive indicator, Fura-2, in cultures grown in basal medium with or without bFGF. None of the bFGF-treated cells exhibited strong Ca(2+) responses to BK or ATP stimulation, while 10-20% of the responding cells grown in basal medium exhibited strong responses. The K(+)-induced increase of [Ca(2+)] did not vary between the different groups. The present findings suggest that sensory neurotransmission involving glutamate may be modulated by growth factors and that regulation of intracellular Ca(2+) homeostasis may be a contributing factor.

Kinin receptors in pain and inflammation

Kinins are among the most potent autacoids involved in inflammatory, vascular and pain processes. These short-lived peptides, including bradykinin, kallidin and T-kinin, are generated during tissue injury and noxious stimulation. However, emerging evidence also suggests that kinins are stored in neuronal elements of the central nervous system (CNS) where they are thought to play a role as neuromediators in various cerebral functions, particularly in the control of nociceptive information. Kinins exert their biological effects through the activation of two transmembrane G-protein-coupled receptors, denoted bradykinin B(1) and B(2). Whereas the B(2) receptor is constitutive and activated by the parent molecules, the B(1) receptor is generally underexpressed in normal tissues and is activated by kinins deprived of the C-terminal Arg (des-Arg(9)-kinins). The induction and increased expression of B(1) receptor occur following tissue injury or after treatment with bacterial endotoxins or cytokines such as interleukin-1 beta and tumor necrosis factor-alpha. This review summarizes the most recent data from various animal models which convey support for a role of B(2) receptors in the acute phase of the inflammatory and pain response, and for a role of B(1) receptors in the chronic phase of the response. The B(1) receptor may exert a strategic role in inflammatory diseases with an immune component (diabetes, asthma, rheumatoid arthritis and multiple sclerosis). New information is provided regarding the role of sensory mechanisms subserving spinal hyperalgesia and intrapleural neutrophil migration that occur upon B(1) receptor activation in streptozotocin-treated rats, a model of insulin-dependent diabetes mellitus in which the B(1) receptor seems to be rapidly overexpressed. Although it is widely accepted that the blockade of kinin receptors with specific antagonists could be of benefit in the treatment of somatic and visceral inflammation and pain, recent molecular and functional evidence suggests that the activation of B(1) receptors with an agonist may afford a novel therapeutic approach in the CNS inflammatory demyelinating disorder encountered in multiple sclerosis by reducing immune cell infiltration (T-lymphocytes) into the brain. Hence, the B(1) receptor may exert either a protective or detrimental effect depending on the inflammatory disease. This dual function of the B(1) receptor deserves to be investigated further.

Basal expression of bradykinin B(1) receptor in the spinal cord in humans and rats

The bradykinin B(1) receptor has been considered as a receptor induced by tissue injury and inflammation mainly in the peripheral tissues. In the present study, we have investigated whether there is a basal expression in the spinal cord by both reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical staining methods. Southern blotting of the DNA reverse-transcribed from human and rat spinal cord mRNA and amplified by polymerase chain reaction (PCR) showed a substantial basal B(1) receptor expression in both human and rat spinal cord. Immunohistochemical staining demonstrated B(1)-positive neurons in the spinal cord dorsal horn, suggesting that the B(1) receptor is constitutively expressed by spinal neurons.

Bradykinin B1 receptor is constitutively expressed in the rat sensory nervous system

Using immunocytochemistry with an antibody raised to a specific rat bradykinin B1 receptor sequence, we showed that the B1 receptor was expressed in the naive rat sensory nervous system. B1 immunoreactivity was seen in laminae 1 and 2 of the dorsal horn of the spinal cord, where primary afferents terminate, and on peripheral nerve terminals in the bladder. B1 receptor was co-expressed preferentially with IB4 positive, but not calcitonin gene-related peptide (CGRP) containing C-cell bodies in the dorsal root ganglion. B1 activation has an important role in the hyperalgesia associated with inflammation, but the site of action of B1 antagonists has generally been believed to be on peripheral, non-neuronal cells. The striking distribution of B1 receptors on sensory neurones suggests that a direct action of B1 activators on the nervous system may also contribute to hyperalgesia.

Increased mRNA expression of the B1 and B2 bradykinin receptors and antinociceptive effects of their antagonists in an animal model of neuropathic pain

We examined the role of B1 and B2 bradykinin receptors in promoting neuropathic hypersensitivity following peripheral nerve injury. Forty eight-hours following chronic constriction injury to a rat sciatic nerve there was an increased expression of B2 receptor mRNA in the lumbar dorsal root ganglia ipsilateral to the site of nerve injury. At 14 days following surgery there was also an ipsilateral increase of B1 receptor mRNA as well as a contralateral increased expression of B2 receptor mRNA. Increased expression of both receptors also coincided with analgesic effects of their antagonists. While HOE-140, a potent B2 receptor antagonist was analgesic at both time points tested, the B1 receptor antagonist des-Arg(9), [Leu(8)]-BK had an analgesic effect only at 14 days. The results support the concept that peripheral nerve injury is associated with local inflammation and that bradykinin, acting on both of its receptors promotes pain hypersensitivity.

Monoarticular antigen-induced arthritis leads to pronounced bilateral upregulation of the expression of neurokinin 1 and bradykinin 2 receptors in dorsal root ganglion neurons of rats

STATEMENT OF FINDINGS: This study describes the upregulation of neurokinin 1 and bradykinin 2 receptors in dorsal root ganglion (DRG) neurons in the course of antigen-induced arthritis (AIA) in the rat knee. In the acute phase of AIA, which was characterized by pronounced hyperalgesia, there was a substantial bilateral increase in the proportion of lumbar DRG neurons that express neurokinin 1 receptors (activated by substance P) and bradykinin 2 receptors. In the chronic phase the upregulation of bradykinin 2 receptors persisted on the side of inflammation. The increase in the receptor expression is relevant for the generation of acute and chronic inflammatory pain.

Centrally bradykinin B2-receptor-induced hypertensive and positive chronotropic effects are mediated via activation of the sympathetic nervous system

OBJECTIVE

The presence of bradykinin B2 receptors in the cardiovascular regulatory centres of the brain indicates that increase in mean arterial pressure (MAP) and heart rate after intracerebroventricular (i.c.v.) injections of bradykinin is mediated via stimulation of sympathetic nervous system.

METHODS

Adult Wistar- Kyoto (WKY) rats were instrumented chronically with an i.c.v. cannula, and the catheters were placed into the femoral artery and vein. Increasing doses of bradykinin (1 -300 pmol) were given i.c.v. and (i) MAP and heart rate, (ii) plasma dopamine, noradrenaline and adrenaline, and (iii) plasma arginine vasopressin (AVP) levels were determined. In addition, following blockade of peripheral alpha1 -adrenoceptors with prazosin (50 and 250 microg/kg i.v.) beta1-adrenoceptors with atenolol (10 mg/kg i.v.) or V1 -receptors with TMe-AVP (Manning compound) (10 microg/kg i.c.v. and 100 microg/kg i.v.) the effects of bradykinin (100 pmol i.c.v.) on MAP and heart rate were determined.

RESULTS

Bradykinin increased MAP and heart rate dose-dependently. The pressor effects of 100 pmol bradykinin i.c.v. were completely blocked by pretreatment with the specific B2 receptor antagonist Hoe 140 (3 pmol, i.c.v.). There was no change in plasma dopamine, noradrenaline, adrenaline or AVP levels after increasing doses of bradykinin. However, peripheral blockade of alpha1- and beta1-adrenoceptors reduced the bradykinin-induced increase in MAP and heart rate, whereas central and peripheral V1 receptor blockade did not alter the cardiovascular responses to i.c.v. bradykinin.

CONCLUSION

Our data suggest that the hypertensive and positive chronotropic effects induced by i.c.v. bradykinin are due to stimulation of sympathoneuronal rather than sympathoadrenal pathway in vivo.

Building blocks of pain: the regulation of key molecules in spinal sensory neurones during development and following peripheral axotomy

The pathways, synapses and molecules involved in pain processing in the newborn are not only required to trigger repair and recuperation but are also involved in the process of forming a mature nervous system. Sensory neurons in the dorsal root ganglion and dorsal horn express a phenomenal array of molecules which contribute to their structural and functional characteristics and many of these are developmentally regulated both pre- and postnatally. In order to understand nociceptive signalling and pain in the neonate we need a clear picture of that regulation. This review concentrates on the changing expression of selected key molecules, receptors and channels in the embryo, neonate and adult, which both characterise the sensory neuron and contribute to its response to painful stimuli in normal and pathological conditions.

Pre- and postsynaptic distribution of cannabinoid and mu opioid receptors in rat spinal cord

In vitro receptor binding and quantitative autoradiography were used to assess the pre- and postsynaptic distribution of cannabinoid receptors in the cervical dorsal horn of the rat spinal cord. An extensive unilateral dorsal rhizotomy was performed across seven or eight successive spinal segments from C3 to T1 or T2. The densities of cannabinoid and mu opioid receptors in the central (C6) spinal segment were assessed 2, 4, 8, and 16 days post rhizotomy and compared with those of untreated rats. Rhizotomy induced approximately a 50% ipsilateral loss in the [3H]CP55,940 binding to spinal cannabinoid receptors that was maximal at 8 days post-rhizotomy. By comparison, the binding of [3H][d-Ala2-MePhe4, Gly-ol5]enkephalin (DAMGO) to mu receptors was depleted approximately 60% in near-adjacent sections. By contrast, changes in [3H]CP55,940 binding contralateral to the deafferentation were largely absent at all post-lesion delays. These data suggest that under conditions in which a spinal segment is completely deafferented, approximately 50% of cannabinoid receptors in the cervical (C6) dorsal horn reside presynaptically on central terminals of primary afferents. The present data provide anatomical evidence for presynaptic as well as postsynaptic localization of cannabinoid receptors in the spinal dorsal horn.

Labelling of peptides with 1.4-nm gold particles to demonstrate their binding sites in the rat spinal cord

Recently we presented a method to label the neuropeptide substance P with a 1.4-nm gold particle covalently bound at the N-terminus that can be used for demonstrating its binding sites in histological sections. In this study we examined whether the peptides neuropeptide Y, somatostatin, calcitonin gene-related peptide and bradykinin can be labelled in the same way. Polyacrylamide gel electrophoresis revealed a reduction in mobility for peptide-gold conjugates over gold particles alone consistent with peptide binding. In cryostat sections of the rat lumbar spinal cord, the peptides showed a distinct binding pattern in the grey matter corresponding to data of studies using autoradiographic methods. Therefore, we conclude that this simple and fast method can be used for labelling peptides in general to demonstrate their binding sites in histological sections, provided the peptide binds by its C-terminus.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Lumbar but not cervical intrathecal DAMGO suppresses extrasegmental nociception in awake rats

he effect of intrathecally administered [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) on withdrawal latencies evoked by noxious heat applied to either cervical or lumbar dermatomes was studied in awake rats. Administration of DAMGO to the lumbar intrathecal space produces a dose-dependent suppression of withdrawals evoked by noxious thermal stimulation in either lumbar or cervical dermatomes. Administration of the same doses of DAMGO to the cervical spinal cord produces a suppression of withdrawals evoked by stimulation in cervical but not lumbar dermatomes. Control experiments provide evidence that the drugs administered intrathecally to either enlargement do not spread to the other enlargement.

Receptor localization in the mammalian dorsal horn and primary afferent neurons

The dorsal horn of the spinal cord is a primary receiving area for somatosensory input and contains high concentrations of a large variety of receptors. These receptors tend to congregate in lamina II, which is a major receiving center for fine, presumably nociceptive, somatosensory input. There are rapid reorganizations of many of these receptors in response to various stimuli or pathological situations. These receptor localizations in the normal and their changes after various pertubations modify present concepts about the wiring diagram of the nervous system. Accordingly, the present work reviews the receptor localizations and relates them to classic organizational patterns in the mammalian dorsal horn.

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Localization of bradykinin-like immunoreactivity in the rat spinal cord: effects of capsaicin, melittin, dorsal rhizotomy and peripheral axotomy

A putative role for bradykinin has been proposed in the processing of sensory information at the level of the spinal cord. Autoradiographic studies have demonstrated the presence of B2 kinin receptor binding sites in superficial laminae of the dorsal horn and a down-regulation of those receptors in rat models of pain injury. In this study, classical immunocytochemistry and confocal microscopy immunofluorescence were used first to localize bradykinin-like immunoreactivity in all major spinal cord segments of naive rats; second, to assess bradykinin-like immunoreactivity changes that occur in animals subjected to various chemical treatments and surgical lesions. High densities of bradykinin-like immunoreactivity were observed in motoneuron of the ventral horn, deeper laminae and nucleus dorsalis of the dorsal horn. Higher magnification of ventral horn showed strong immunostaining of motoneuron perikaryas and their proximal processes. Two types of bradykinin-like immunoreactivity immunostained cellular bodies were observed in deeper laminae of the dorsal horn. These interneurons, morphologically corresponding to islets and antenna-type cells project dendrites to adjacent laminae. Furthermore, numerous strongly marked dendrites, transversally cut, suggest the presence of projection neurons to higher cervical centres. Following unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesion of the sciatic nerve, important increases of bradykinin-like immunoreactivity were found in laminae III and IV of the ipsilateral dorsal horn. In contrast, significant decreases of immunodeposits were observed in both cell bodies and numerous dendrites of motoneuron surrounding neuropil. Specific destructions of sensory afferent fibres with capsaicin or selective activation of kallikreins with melittin caused increases of bradykinin-like immunoreactivity in both the dorsal and ventral horns of the spinal cord. These results which demonstrate the cellular localization of bradykinin-like immunoreactivity in both dorsal and ventral horns of the rat spinal cord, further reveal the plasticity of this non-sensory peptidergic system following various chemical and surgical treatments. Hence, these anatomical findings along with earlier functional and receptor autoradiographic studies reinforce the putative role of bradykinin in sensory function.