Differences in neurokinin receptor pharmacology between rat and guinea-pig superior cervical ganglia

Electrophysiological effects of tachykinin agonists on sympathetic ganglia of spontaneously hypertensive rats

This study investigated the cellular basis for the enhanced ganglionic responsiveness to NK1 agonists in the spontaneously hypertensive rat (SHR) in comparison to their normotensive counterpart, the Wistar-Kyoto (WKY) rat. Rats for in vivo studies were anesthetized with pentobarbital and treated with chlorisondamine (10.5 micromol/kg). Extracellular recordings from the external carotid nerve showed a greater responsiveness of decentralized SHR superior cervical ganglia (SCG) to intravenous injection of SP (32 nmol/kg). Blood pressure and heart rate were increased in SHRs, whereas WKY rats responded with a decrease in blood pressure and only slight tachycardia. Membrane properties of SCG neurons, as shown by intracellular microelectrode recordings, were similar between strains. Picospritzer application of the NK1 agonist GR-73632 (100 microM, 1 s) evoked slow depolarization and increased neuron excitability. Spontaneous firing was evoked only in some neurons. Depolarization amplitudes were similar between strains; however, the NK1 agonist depolarized a greater number of neurons in hypertensive rats. In conclusion, SHRs are more responsive to ganglion stimulation by NK1 agonists due to a greater number of responsive cells within the SCG rather than an enhanced responsiveness of individual neurons.

Increased ganglionic responses to substance P in hypertensive rats due to upregulation of NK(1) receptors

Intravenous injection of substance P (SP) increases renal nerve firing and heart rate in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) by stimulating sympathetic ganglia. Blood pressure is increased in SHRs but lowered in WKYs. This study assesses the role of neurokinin-1 (NK(1)) receptors in mediating the ganglion actions of SP. Rats for functional studies were anesthetized and then treated with chlorisondamine. Renal nerve, blood pressure, and heart rate responses to intravenous injection of the NK(1) receptor agonist GR-73632 were similar but less than those to equimolar doses of SP in SHRs. GR-73632 only slightly increased renal nerve firing and heart rate and lowered blood pressure in WKYs. The NK(1) receptor antagonist GR-82334 (200 nmol/kg iv) blocked the ganglionic actions of GR-73632 and the pressor response to SP in SHRs. It reduced the renal nerve and heart rate responses by 52 and 35%. This suggests that the pressor response to SP is mediated by ganglionic NK(1) receptors and that NK(1) receptors also have a prominent role in mediating the renal nerve and heart rate responses to SP. Quantitative autoradiography showed that NK(1) receptors are more abundant in the superior cervical ganglia of SHRs. RT-PCR showed increased abundance of NK(1) receptor mRNA in SHRs as well. These observations suggest that the greater ganglionic stimulation caused by SP in SHRs is due to upregulation of NK(1) receptors.

Central and peripheral expression of neurokinin-1 and neurokinin-3 receptor and substance P-encoding messenger RNAs: peripheral regulation during formalin-induced inflammation and lack of neurokinin receptor expression in primary afferent sensory neurons

The neurokinin-1 receptor and its tachykinin neuropeptide ligand substance P are associated with the mediation of nociception. Substance P released from primary afferent sensory neurons activates neurokinin receptors on both central and peripheral targets that mediate specific aspects of central sensitization and inflammatory function; however, an autoreceptor function for the neurokinin-1 receptor remains highly controversial. Activation of the neurokinin-1 receptor by substance P during chronic nociception increases neurokinin-1 receptor gene expression in the spinal cord. Similarly, neurokinin-3 receptors on peripheral or target tissues or neurons could play an important role in the sensitization of sensory neurons. Therefore, this study (i) mapped the steady-state levels of substance P-encoding preprotachykinin, neurokinin-1 and neurokinin-3 receptor messenger RNAs in central and peripheral tissues including sensory ganglia, and (ii) investigated whether formalin-evoked nociception altered the quantity or location of neurokinin-1 or neurokinin-3 receptor messenger RNAs in the sensory ganglia or inflamed peripheral targets for substance P. Solution hybridization-nuclease protection assays quantified neurokinin receptor messenger RNA levels in central and peripheral tissues from normal and formalin-inflamed rats. High concentrations of the neurokinin-1 receptor were found in whole brain, spinal cord, and peripheral target organs innervated by substance P-containing neurons. Measurable levels of neurokinin-3 receptor messenger RNA were found only in brain, spinal cord and urinary bladder. Results also show that neither neurokinin-1 nor neurokinin-3 receptor messenger RNAs were detectable in primary afferent sensory neurons in the dorsal root ganglia of normal or formalin-inflamed rats. Neurokinin-1 receptor messenger RNA levels were, however, significantly increased in hindpaw tissues inflamed by formalin for 6 h. These results indicate that the plasticity of neurokinin-1 receptor gene expression in non-neuronal peripheral cells could regulate sensitivity to substance P in a manner similar to that in the spinal cord dorsal horn. Altered neurokinin-1 receptor gene expression provides a useful marker of long-term nociceptive activation and may mediate peripheral mechanisms of hyperalgesia and cellular sensitization during inflammation. Importantly, inflammation does not induce a phenotypic change in afferent sensory neurons providing neurokinin receptor targets for the direct sensitization of these neurons by substance P.

Tachykinin-induced responses via neurokinin-1 and -3 receptors in hamster submandibular ganglion neurones

Both substance P and neurokinin A are known as neurotransmitters of the submandibular ganglion cell. In this study, the effects of neurokinin (NK) receptor-subtype agonists on hamster submandibular ganglion cells were investigated using the whole-cell patch-clamp technique. Membrane currents evoked by a ramp pulse from +50 to -100 mV (-150 mV/1000 msec) were compared in both the absence and presence of NK receptor agonist. The NK-1 receptor agonist [Sar9, Met (O2)11]-substance P, the NK-2 receptor agonist [Ala5, beta-Ala8]-alpha-neurokinin fragment 4-10, and the NK-3 receptor agonist senktide were used. The three agonists dose-dependently increased the amplitude of the inward current with a reversal potential near 0 mV. Their rank order was NK-1 = NK-3 > NK-2. Even when the external solution was replaced with Cs+ or N-methyl-D-glucamine+ instead of Na+, the NK receptor agonists also increased the amplitude of the inward current. Thus, NK-1 and NK-3 receptors are apparently coupled with non-selective cation channels in submandibular ganglion cells.

Expression of B1 and B2 bradykinin receptor mRNA and their functional roles in sympathetic ganglia and sensory dorsal root ganglia neurones from wild-type and B2 receptor knockout mice

Bradykinin has been implicated in nociception and inflammation. To examine the relative significance of B1 and B2 bradykinin receptor subtypes in sympathetic and sensory ganglia, the electrophysiological effects of bradykinin analogues and the expression of receptor subtype mRNA were examined in wild-type and "B2 knockout" mice from which the B2 receptor gene had been deleted. In wild-type mice the B2 receptor agonist bradykinin depolarized superior cervical ganglia (SCG) and activated inward currents in dorsal root ganglia (DRG) neurones. Responses to the B1 receptor agonist, [des-Arg10]-kallidin, were seen only in SCG that had been pre-treated with interleukins and the peptidase inhibitor captopril, but not in DRG neurones. The up-regulation of responses to [des-Arg10]-kallidin and substance P were blocked by indomethacin and, thus, were dependent upon cyclo-oxygenase activity. The effects of bradykinin were abolished in SCG and DRG's from B2 knockout mice and this was correlated with the absence of B2 receptor mRNA in ganglia from these animals. However, despite the presence of B1 receptor mRNA in interleukin treated SCG from B2 knockout mice, no depolarizing effects of the B1 receptor agonist [des-Arg10]-kallidin were observed. The successful elimination of bradykinin responses and B2 mRNA in sympathetic and sensory ganglia from B2 knockout mice, confirms that B2 receptors are the predominant functional bradykinin receptor subtype in these tissues and that B1 receptor mRNA is expressed in both sympathetic and sensory ganglia from these animals.

Temperature and agonist dependency of tachykinin NK1 receptor antagonist potencies in rat isolated superior cervical ganglion

Using rat isolated superior cervical ganglion we have further characterised tachykinin NK1 receptors and investigated the possible existence of tachykinin NK1 receptor subtypes. At 37 degrees C, tachykinin NK1 receptor antagonists GR82334 ([D-Pro9[spiro-gamma- lactam]Leu10,Trp11]physalaemin-1(1-11)), CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine) and (+/-)-RP67580 (7,7-diphenyl-2[1-imino-2(2-methoxy- phenyl)-ethyl]perhydroisoindol-4-one (3aR,7aR)) antagonised more potently depolarisation responses evoked by GR73632 (delta Ava]L-Pro9,N-MeLeu10]SP-(7-11)), septide ([pGlu6,Pro9]SP-(6-11)) and neurokinin A than those evoked by substance P, substance P O-methyl ester and [Sar9,Met(O2)11]substance P. GR73632 and substance P O-methyl ester evoked depolarisation responses of similar magnitude, unaffected by addition of tetrodotoxin, but which cross-desensitised. At 22 degrees C, the ability of GR82334 and (+/-)-RP67580 to inhibit substance P O-methyl ester-evoked but not GR73632-evoked responses was enhanced greatly. These results suggest a single population of tachykinin NK1 receptors in this preparation. The agonist and temperature dependency of tachykinin NK1 receptor antagonist potency in rat isolated superior cervical ganglion may reflect different conformational changes in the tachykinin NK1 receptor induced by partial or full sequence substance P analogues.

The mammalian tachykinin receptors

The tachykinins (TKs) are a family of small peptides which share the common C-terminal sequence Phe-X-Gly-Leu-MetNH2. Three peptides of this family, substance P, neurokinin A and neurokinin B, have an established role as neurotransmitters in mammals. 2. Three receptors for TKs have been cloned: they are G-protein coupled receptors with seven putative transmembrane spanning segments and have been termed NK1 (substance P-preferring), NK2 (neurokinin A-preferring) and NK3 (neurokinin B-preferring). 3. Synthetic agonists are available to selectively stimulate only one receptor, while natural TKs can act as full agonist at each one of the three receptors, albeit at different concentrations. 4. A number of potent and selective antagonists, both peptide and nonpeptide in nature, have recently been developed. 5. The introduction of these ligands has revealed an unforeseen pharmacological heterogeneity of NK1, NK2 and NK3 receptors which appears largely, if not exclusively, linked to the existence of species homologues of the three receptors.

Tachykinins as mediators of slow EPSPs in guinea-pig gall-bladder ganglia: involvement of neurokinin-3 receptors

1. The effects of endogenous tachykinins and related peptides on intact guinea-pig gall-bladder neurones were investigated with single-electrode voltage- and current-clamp recording techniques. 2. Pressure ejection of substance P (100 microM) caused a long lasting membrane depolarization that was associated with a decrease in input resistance. In cells that were voltage-clamped to their resting membrane potential, substance P activated an inward current. 3. The reversal potentials of the substance P-induced depolarization and inward current were congruent to 0 mV. In a low-Na+ solution, the substance P-induced depolarization and inward current were reduced in amplitude. 4. Substance P increased the excitability of neurones, as evidenced by a greater anodal break activity and an increase in the number of action potentials generated during a depolarizing current pulse. 5. Substance P, neurokinin A (NKA) and neurokinin B (NKB) were applied by superfusion to determine the relative potencies of these tachykinins. NKB was the most potent, with an EC50 of 24 nM. The EC50 values for NKA and substance P were 47.8 and 281 nM, respectively. 6. The neurokinin-3 (NK-3) receptor agonist senktide depolarized neurones with an EC50 of 6.3 nM. Neither the NK-1 receptor agonist [Sar9,Met(O2)11]-substance P nor the NK-2 receptor agonist [beta-Ala8]-NKA(4-10) caused a measurable depolarization. 7. The NK-3 antagonist [Trp7,beta-Ala8]-NKA (4-10) inhibited the responsiveness of gall-bladder neurones to substance P with a KB (dissociation constant of receptor antagonist) of 49 nM, and depressed both capsaicin-induced depolarizations and stimulus-evoked slow EPSPs. 8. These data indicate that tachykinins mediate slow EPSPs in guinea-pig gall-bladder ganglia by activating NK-3 receptors on gall-bladder neurones. It is proposed that in response to inflammation or high intraluminal pressure, tachykinins may be released within ganglia by sensory fibres and act directly on intrinsic neurones to facilitate ganglionic transmission.

Bradykinin receptors in mouse and rat isolated superior cervical ganglia

1. The ability of bradykinin and its analogues to depolarize rat and mouse superior cervical ganglia was studied by use of in vitro grease-gap recording techniques, and the ability of antagonists selective for bradykinin receptor subtypes to block their effects was examined. 2. Bradykinin (3 microM) depolarized ganglia from both species, although the magnitude of the maximal response was less in mouse (15 +/- 5%, n = 7) than rat tissue (33 +/- 6%, n = 7), relative to muscarine (1 microM). 3. Interleukin 1 beta (30 u ml-1 for 18 h at 37 degrees C) increased the depolarization caused by bradykinin (3 microM) in mouse ganglia from 15% to 54% (P < 0.001, n = 12). Responses to the B1 receptor agonist, [des-Arg10]-kallidin (3 microM) were similarly potentiated but this was only detected after inhibition of peptidase activity with 10 microM captopril (4% to 35%, n = 5). 4. In ganglia from both species the rank order of agonist potency was bradykinin = [Lys0]-bradykinin >> [des-Arg10]-kallidin. However, like responses to [des-Arg10]-kallidin in mouse tissue, both the potency of bradykinin and the maximal depolarization achieved (EC50 = 912 nM; 80%, n = 11) was enhanced following inhibition of angiotensin converting enzyme with 10 microM captopril (EC50 = 50 nM; 135%, n = 4). 5. Responses to bradykinin were selectively antagonized by the B2 receptor antagonist, Hoe 140 but not by the B1 antagonist, [Leu8]-bradykinin1-8. From Schild analysis the pA2 value for Hoe 140 in mouse tissue was 9.65, although the slope of the regression line was significantly greater than unity, indicating non-competitive kinetics (slope = 1.88 +/- 0.18, n = 9). The depolarization caused by [Lys0]-bradykinin was also antagonized by Hoe 140 (3 nM).6. Thus the predominant bradykinin receptor in mouse superior cervical ganglia is compatible with a B2 subtype. Furthermore the depolarizations caused by B1 and B2 agonists in this tissue can be increased following exposure to interleukin l beta, and by blocking peptide degradation with captopril.

Differences in the effects of tachykinin NK1 receptor antagonists: neuronal versus smooth muscle tissues

The effects of three tachykinin NK1 receptor antagonists (L-668,169, (+/-)-RP 67580, and (+/-)-CP 96.345) were examined for their ability to antagonise responses evoked by substance P O-methyl ester (a selective NK1 receptor agonist) in isolated neuronal tissue (rat superior cervical ganglia and guinea-pig locus coeruleus) and smooth muscle tissues (rat urinary bladder and guinea-pig ileum longitudinal muscle/myenteric plexus). (+/-)-RP 67580 was similarly effective in antagonising responses in both rat superior cervical ganglia and urinary bladder (estimated pKa value = 7.4 for both tissues); however, (+/-)-CP 96,345 was 50-fold less effective in antagonising responses in guinea-pig locus coeruleus than in ileum longitudinal muscle/myenteric plexus (estimated pKa values = 7.6 and 9.3 respectively). It is suggested that the differential effects of (+/-)-CP 96,345 may reflect the existence of a population of NK1 receptors within guinea-pig locus coeruleus that are less sensitive to the effects of this NK1 receptor antagonist.

Electrophysiological effects of tachykinins and capsaicin on guinea-pig bronchial parasympathetic ganglion neurones

1. We evaluated the effects of neurokinins, tachykinin analogues, or capsaicin on passive membrane properties of guinea-pig bronchial parasympathetic neurones using intracellular recording techniques. 2. Substance P (SP) and the tachykinin analogue, acetyl-[Arg6,Sar9,Met(O2)11]-SP(6-11) (ASMSP), at concentrations selective for the neurokinin (NK)-1 receptor subtype, depolarized the resting potential (3 and 5 mV, respectively) with no change in input resistance. Neurokinin A and beta Ala8NKA(4-10), at concentrations selective for the NK-2 receptor subtype (0.1 microM), were without effect. 3. Neurokinin B (NKB) and [Asp5,6,methyl-Phe8]SP(5-11) (senktide analogue), at concentrations selective for NK-3 receptor subtype, elicited maximum depolarizations of 16 +/- 2 mV for both agonists. The peak of the depolarization was associated with an decrease in membrane resistance (35 +/- 4 and 50 +/- 7%, respectively). 4. Capsaicin (1 microM) elicited a 3-24 mV depolarization of the resting potential of thirteen of eighteen bronchial ganglion neurones and decreased the input resistance of seven of thirteen of these neurones. The effects of capsaicin were reduced by desensitization with senktide analogue at a concentration selective for the NK-3 receptor subtype, whereas a non-peptide NK-1 receptor antagonist had no effect. 5. Using voltage clamp analysis, capsaicin and senktide analogue evoked an inward current and an increase in membrane conductance at the resting membrane potential. The reversal potential for senktide analogue was estimated to be + 4 mV. 6. These data support the hypothesis that neurokinin-containing nerve terminals are localized within guinea-pig bronchial parasympathetic ganglia and, when released, the predominant effect of the neurokinins is by activation of NK-3 receptors.