Use of selective antagonists to dissociate the central cardiovascular and behavioural effects of tachykinins on NK1 and NK2 receptors in the rat

The role of neuropeptides in adverse myocardial remodeling and heart failure

In addition to traditional neurotransmitters of the sympathetic and parasympathetic nervous systems, the heart also contains numerous neuropeptides. These neuropeptides not only modulate the effects of neurotransmitters, but also have independent effects on cardiac function. While in most cases the physiological actions of these neuropeptides are well defined, their contributions to cardiac pathology are less appreciated. Some neuropeptides are cardioprotective, some promote adverse cardiac remodeling and heart failure, and in the case of others their functions are unclear. Some have both cardioprotective and adverse effects depending on the specific cardiac pathology and progression of that pathology. In this review, we briefly describe the actions of several neuropeptides on normal cardiac physiology, before describing in more detail their role in adverse cardiac remodeling and heart failure. It is our goal to bring more focus toward understanding the contribution of neuropeptides to the pathogenesis of heart failure, and to consider them as potential therapeutic targets.

Substance P receptor antagonism: a potential novel treatment option for viral-myocarditis

Viral-myocarditis is an important cause of heart failure for which no specific treatment is available. We previously showed the neuropeptide substance P (SP) is associated with the pathogenesis of murine myocarditis caused by encephalomyocarditis virus (EMCV). The current studies determined if pharmacological inhibition of SP-signaling via its high affinity receptor, NK1R and downstream G-protein, Ras homolog gene family, member-A (RhoA), will be beneficial in viral-myocarditis. Aprepitant (1.2 mg/kg), a SP-receptor antagonist, or fasudil (10 mg/kg), a RhoA inhibitor, or saline control was administered daily to mice orally for 3 days, prior to, or 5 days following, intraperitoneal infection with and without 50 PFU of EMCV, following which disease assessment studies, including echocardiogram and cardiac Doppler were performed in day 14 after infection. Pretreatment and posttreatment with aprepitant significantly reduced mortality, heart and cardiomyocyte size, and cardiac viral RNA levels (P < 0.05 all, ANOVA). Only aprepitant pretreatment improved heart functions; it significantly decreased end systolic diameter, improved fractional shortening, and increased peak aortic flow velocity (P < 0.05 all, ANOVA). Pre- or posttreatment with fasudil did not significantly impact disease manifestations. These findings indicate that SP contributes to cardiac-remodeling and dysfunction following ECMV infection via its high affinity receptor, but not through the Rho-A pathway. These studies suggest that SP-receptor antagonism may be a novel therapeutic-option for patients with viral-myocarditis.

Are biological actions of neurokinin A in the adult brain mediated by a cross-talk between the NK1 and NK2 receptors?

Mice lacking the NK(1) receptor (NK(1)R-/- mice) and selective, high-affinity, non-peptide, NK(1), NK(2) and NK(3) receptor antagonists were used to identify the tachykinin receptor subtype(s) mediating the central responses induced by neurokinin A (NKA). The peptides, substance P (SP), NKA and senktide and the antagonists were injected intracerebroventricularly (ICV) through an implanted cannula. NKA (50 pmol) was as potent as SP (50 pmol) in inducing grooming behaviour (face washing and hind limb grooming) in wild-type mice, but both peptides failed to induce behavioural responses in NK(1)R-/- mice. In wild-type mice, the NK(1) receptor antagonist, RP 67580 (2 nmol), effectively inhibited grooming behaviour elicited by SP, but was inactive against grooming induced by NKA, which in turn was abolished after pre-treatment with the selective NK(2) receptor agonist, SR 48968 (2 nmol). Unlike NKA, the selective NK(2) receptor agonists, (β Ala(8)) NKA 4-10 and (NLeu(10)) NKA 4-10, injected ICV at doses of 50 or 100 pmol did not elicit any behavioural response in wild-type mice. The NK(3) receptor antagonist, SR 142801, inhibited behaviours induced by the NK(3) receptor agonist, senktide, but did not alter behavioural responses to either SP or NKA in wild-type mice. The present findings demonstrate that central biological actions of SP and senktide are mediated by activation of NK(1) and NK(3) receptors, respectively. Our results also indicate that NK(1) receptors are essential for generating central actions induced by NKA, which are most probably mediated by a cross-talk between the NK(1) and NK(2) receptors.

Compensatory mechanisms to maintain blood pressure in paraplegic rats: implication of central tachykinin NK-1 and NK-3 receptors?

People with high level spinal cord injury (SCI) suffer from both hypotension and spontaneous hypertension due to loss of supraspinal control of spinal sympathetic outflow. Few reports have addressed whether any changes occur in central regulation of blood pressure (BP) and heart rat (HR) at the supraspinal level. Central tachykinin NK-1 and NK-3 receptors are located in many cardiovascular areas in the brain and are known to modulate BP and HR. This study examined the intracerebroventricular (i.c.v.) effects of the selective NK-1 receptor agonist [Sar(9), Met(O(2))(11)]SP (65pmol, n=6) and NK-3 receptor agonist senktide (650pmol, n=6) on mean arterial pressure (MAP) and HR before and after complete spinal cord transection at thoracic level 4 (T4). [Sar(9), Met(O(2))(11)]SP evoked increases in MAP and HR which were still present 4days after the T4 SCI. Further analysis using the beta(1)-adrenoceptor antagonist atenolol (10mgkg(-1)) revealed an increased contribution of HR in the MAP increase after SCI. For senktide, 2 and 5weeks after T4 SCI, the rise in MAP induced by senktide was significantly increased in magnitude and was similar to a normal response at 8weeks. These effects were accompanied by a bradycardia, which was still present and amplified at 8weeks. Our results reveal a transient potentiation of the senktide-mediated MAP effect and a greater contribution of the HR in MAP increase by [Sar(9), Met(O(2))(11)]SP in T4 transected rats. Although the significance of these changes remains to be established. This suggest a reorganization of supraspinal mechanisms regulating BP and HR after a high level SCI. Central NK-1 and NK-3 receptors might therefore contribute to the maintenance of MAP following high thoracic SCI.

The ventral tegmental area as a putative target for tachykinins in cardiovascular regulation

Tachykinin receptor agonists and antagonists were microinjected into the ventral tegmental area (VTA) to study the relative participation of the three tachykinin receptors in cardiovascular regulation in freely behaving rat. Selective agonists (1-100 pmol) for NK1 ([Sar9, Met (O2)11]SP), NK2 ([beta-Ala8]NKA (4-10)) and NK3 (senktide) receptors evoked increases in blood pressure, heart rate (HR) along with behavioural manifestations (face washing, sniffing, head scratching, rearing, wet dog shake). At 1 pmol, NK1 and NK3 agonists did not affect behaviour and blood pressure but only HR. Tachykinin agonists-induced cardiovascular responses were selectively and reversibly blocked by the prior injection of antagonists for NK1 receptors (LY 303870 ((R)-1-[N-(2-methoxybenzyl)acetylamino]-3-(1H-indol-3-yl)-2-[N-(2-(4-(piperidin-1-yl)piperidin-1-yl)acetyl)amino]propane), 5 nmol), NK2 receptors (SR 48968 ([(S)-N-methyl-N-[4-acetylamino-4-phenylpiperidino-2-(3,4-dichlorophenyl)butyl]benzamide]), 250 pmol) and NK3 receptors (SB 235375 ((-)-(S)-N-(alpha-ethylbenzyl)-3-(carboxymethoxy)-2-phenylquinoline-4-carboxamide), 25 nmol). With the exception of the NK2 agonist, most behavioural effects were also blocked by antagonists. Tachykinin agonists-induced cardiovascular responses were inhibited by intravenous (i.v.) treatments with antagonists for D1 dopamine receptor (SCH23390, 0.2 mg kg(-1)) and beta1-adrenoceptor (atenolol, 5 mg kg(-1)) but not for D2 dopamine receptor (raclopride, 0.16 mg kg(-1)). Behavioural responses were blocked by SCH23390 only. The present study provides the first pharmacological evidence that the three tachykinin receptors in the rat VTA can affect the autonomic control of blood pressure and HR by increasing midbrain dopaminergic transmission. This mechanism may be involved in the coordination of behavioural and cardiovascular responses to stress and noxious stimulation.

Behavioral effects of local microinfusion of pituitary adenylate cyclase activating polypeptide (PACAP) into the paraventricular nucleus of the hypothalamus (PVN)

Pituitary adenylate cyclase activating polypeptide (PACAP) has been implicated in the regulation of several autonomic and neuroendocrine functions. In the hypothalamic paraventricular nucleus (PVN), for example, PACAP-immunoreactive fibers densely innervate corticotropin-releasing hormone (CRH)-containing neurons in the medial parvocellular region, suggesting that PACAP acts to mediate stress responses. Therefore, we examined the behavioral effects of an intra-PVN PACAP injection (25 pmol) in combination with a mild stressor. PACAP or artificial cerebrospinal fluid (aCSF) was microinjected into the PVN (0.25 l) and then animals were restrained or placed in their home cage for 5 min. Exploratory activity (total distance traveled) and scored behaviors (face washing, body grooming, wet dog shakes, and rearing) were observed in a familiar open field for 10 min. In animals receiving aCSF, there were no behavioral differences between restrained and unrestrained groups. For the entire 10-min observation period, animals receiving PACAP, whether restrained or not, displayed elevated face washing and body grooming with decreased locomotor activity and rearing. Among PACAP-injected animals, restrained animals displayed increased body grooming compared to unrestrained animals during the first 2 min in the open field suggesting a summation of the effects of peptide injection and stressor. The observed elevation in grooming is consistent with previous studies reporting similar increases following electrical-, NMDA-, CRH-, or stressor-induced activation of the PVN. Thus, at the level of the PVN, PACAP may act as an excitatory neuropeptide and augment behavioral responses to stressors.

Pituitary adenylate cyclase-activating polypeptide (PACAP) mimics neuroendocrine and behavioral manifestations of stress: Evidence for PKA-mediated expression of the corticotropin-releasing hormone (CRH) gene

The physiologic response to stress is highly dependent on the activation of corticotropin-releasing hormone (CRH) neurons by various neurotransmitters. A particularly rich innervation of hypophysiotropic CRH neurons has been detected by nerve fibers containing the neuropeptide PACAP, a potent activator of the cAMP-protein kinase A (PKA) system. Intracerebroventricular (icv) injections of PACAP also elevate steady-state CRH mRNA levels in the paraventricular nucleus (PVN), but it is not known whether PACAP effects can be associated with acute stress responses. Likewise, in cell culture studies, pharmacologic activation of the PKA system has stimulated CRH gene promoter activity through an identified cAMP response element (CRE); however, a direct link between PACAP and CRH promoter activity has not been established. In our present study, icv injection of 150 or 300 pmol PACAP resulted in robust phosphorylation of the transcription factor CREB in the majority of PVN CRH neurons at 15 to 30 min post-injection and induced nuclear Fos labeling at 90 min. Simultaneously, plasma corticosterone concentrations were elevated in PACAP-injected animals, and significant increases were observed in face washing, body grooming, rearing and wet-dog shakes behaviors. We investigated the effect of PACAP on human CRH promoter activity in alphaT3-1 cells, a PACAP-receptor expressing cell line. Cells were transiently transfected with a chloramphenicol acetyltransferase (CAT) reporter vector containing region - 663/+124 of the human CRH gene promoter then treated for with PACAP (100 nM) or with the adenylate cyclase activating agent, forskolin (2.5 muM). Both PACAP and forskolin significantly increased wild-type hCRH promoter activity relative to vehicle controls. The PACAP response was abolished in the CRE-mutant construct. Pretreatment of transfected cells with the PKA blocker, H-89, completely prevented both PACAP- and forskolin-induced increases in CRH promoter activity. Furthermore, CREB overexpression strongly enhanced PACAP-mediated stimulation of hCRH promoter activity, an effect which was also lost with mutation of the CRE. Thus, we demonstrate that icv PACAP administration to rats under non-stressed handling conditions leads to cellular, hormonal and behavioral responses recapitulating manifestations of the acute stress response. Both in vivo and in vitro data point to the importance of PACAP-mediated activation of the cAMP/PKA signaling pathway for stimulation of CRH gene transcription, likely via the CRE.

Cardiovascular and behavioural effects induced by naloxone-precipitated morphine withdrawal in rat: characterization with tachykinin antagonists

This study examined the intracerebroventricular (i.c.v.) effects of three selective tachykinin receptor antagonists on the cardiovascular and behavioural responses induced by naloxone-precipitated morphine withdrawal in rats. I.c.v. injection of naloxone (10 microg) to morphine pre-treated rats (i.c.v. for 5 days) induced an immediate increase in blood pressure ( approximately 10 mmHg) and behavioural activity (sniffing > rearing > face washing approximately grooming approximately wet dog shake) without causing significant heart rate changes. The prior i.c.v. injection of the NK(1) receptor antagonist (6.5 nmol LY306740) reduced face washing and grooming during morphine withdrawal. NK(2) and NK(3) receptor antagonists (6.5 nmol SR48968 and R820) did not affect behavioural effects, yet the co-injection of the three tachykinin antagonists reduced all behavioural activity. The pressor response was not affected by the selective inhibition of NK(1) and NK(3) receptors while both blood pressure and heart rate were markedly enhanced by SR48968 during morphine withdrawal. The potentiating effect of SR48968 was prevented following simultaneous blockade of the three tachykinin receptors. In addition to confirming the involvement of central tachykinins in behavioural manifestations to morphine withdrawal, data suggest a modulatory function for tachykinins, especially the NK(2) receptor, in brain autonomic control of blood pressure and heart rate in supraspinal noloxone-precipitated withdrawal.

Stereospecific blockade of marble-burying behaviour in mice by selective, non-peptidergic neurokinin1 (NK1) receptor antagonists

By analogy with the selective serotonin reuptake inhibitor, fluvoxamine, and the tricyclic agent, clomipramine, the novel, selective, non-peptidergic NK(1) receptor antagonist, GR205,171, dose-dependently and completely blocked marble-burying behaviour in mice: Inhibitory Dose(50)s (ID(50)s), 4.5, 4.8 and 7.6 mg/kg, respectively. In contrast to GR205,171, its isomer, GR226,206, which displays substantially lower affinity for NK(1) receptors, was inactive (> 40.0 mg/kg). By analogy with GR205,171, a further, selective NK(1) antagonist, RP67,580, abolished marble-burying behaviour with an ID(50) of 11.9 mg/kg. At doses significantly reducing marble-burying behaviour, GR205,171 and RP67,580 little influenced motor behaviour. In conclusion, like fluvoxamine and clomipramine, selective, non-peptidergic NK(1) receptor antagonists block marble-burying in mice. Although the biological bases of this behaviour remain unclear, these observations underpin the contention that NK(1) receptors may be implicated in affective disorders.

Presence of NK2 binding sites in the rat brain

Attempts were made to label tachykinin NK2 binding sites in the adult rat brain using [125I]neurokinin A (NKA) as ligand in the presence of NK1 and NK3 agonist or antagonist to avoid labelling of NK1 and NK3 binding sites, respectively. A high-affinity, specifically NK2-sensitive, [125I]NKA-binding, temperature-dependent, reversible, sensitive to GTPgammaS and correspondence to a single population of binding sites (K(D) and B(max) values: 2.2 nM and 7.3 fmol/mg protein) was demonstrated on hippocampal membranes. Competition studies performed with tachykinins and tachykinin-related compounds indicated that the pharmacological properties of these NK2-sensitive [125I]NKA binding sites were identical to those identified in the rat urinary bladder and duodenum. NKA, neuropeptide K, and neuropeptide gamma, as well as the potent and selective NK2 antagonists SR 144190, SR 48968 and MEN 10627, presented a nanomolar affinity for these sites. The regional distribution of these NK2-sensitive [125I]NKA binding sites differs markedly from those of NK1 and NK3 binding sites, with the largest labeling being found in the hippocampus, the thalamus and the septum. Binding in other brain structures was low or negligible. A preliminary autoradiographic analysis confirmed [125I]NKA selective binding in hippocampal CA1 and CA3 areas, particularly, and in several thalamic nuclei.

Neurokinin(1) receptor antagonists as potential antidepressants

Selective, nonpeptide antagonists for tachykinin receptors first became available ten years ago. Of the three known tachykinin receptors, drug development has focused most intensively on the substance P-preferring receptor, neurokinin(1) (NK(1)). Although originally studied as potential analgesic compounds, recent evidence suggests that NK(1) receptor antagonists may possess antidepressant and anxiolytic properties. If confirmed by further controlled clinical studies, this will represent a mechanism of action distinct from all existing antidepressant agents. As reviewed in this chapter, the existing preclinical and clinical literature is suggestive of, but not conclusive, concerning a role of substance P and NK(1) receptors in the pathophysiology of depression and/or anxiety disorders. The ongoing clinical trials with NK(1) receptor antagonists have served as an impetus for much needed, basic research in this field.

Characterization and regulation of tachykinin receptors in the nucleus tractus solitarius

1. The characteristics, localization and regulation of tachykinin receptors in the rat nucleus tractus solitarius (NTS) involved in respiratory control were investigated using a combination of in vivo microinjection and in vitro autoradiographic techniques. 2. Microinjection of receptor-selective tachykinin agonists and antagonists into the NTS of urethane-anaesthetized rats suggests that stimulation of NK1 and NK3 receptors increases tidal volume, whereas NK2 and NK3 receptor activation produces a bradypnoea. 3. Depletion of NK1 receptors in the NTS due to either ageing or acute hypoxia correlates with a markedly reduced respiratory response to substance P. In contrast, chemical ablation of sensory neurons by neonatal capsaicin administration dramatically increases the respiratory response to a variety of NK1, NK2 and NK3 agonists. 4. These studies suggest that all three tachykinin receptors are present in the rat NTS and that these receptors are subject to both acute and chronic regulation.

Characterization of central and peripheral effects of septide with the use of five tachykinin NK1 receptor antagonists in the rat

1. Effects of two tachykinin NK1 receptor selective agonists (septide and [Sar9, Met(O2)11]SP) were compared on the increases in mean arterial pressure (MAP), heart rate (HR) and motor behaviour following intracerebroventricular (i.c.v.) administration in unanaesthetized rat, and on the vascular permeability increases to intradermal (i.d.) injection in the anaesthetized rat. Moreover, five tachykinin NK1 receptor selective antagonists (LY303870, LY306740, LY303241, SR140333 and RP67580) were tested against the two agonists to compare their pharmacological profile. 2. [Sar9, Met(O2)11]SP and septide (10-100 pmol per rat, i.c.v.) were equipotent in increasing MAP and HR, yet they had dissimilar time-course. Both agonists increased dose-dependently face washing and sniffing while [Sar9, Met(O2)11]SP was the sole to produce grooming, septide was more potent than [Sar9, Met(O2)11]SP (6.5-650 pmol) in increasing vascular permeability. 3. For most centrally mediated responses, LY303870 and RP67580 were significantly more potent in inhibiting septide than [Sar9, Met(O2)11]SP. In some parameters, greater blockade was achieved when antagonists (particularly LY306740) were given 1 h instead of 10 min prior to i.c.v. septide. 4. All antagonists except LY303241 blocked dose-dependently the increases in vascular permeability to equipotent doses of [Sar9, Met(O2)11]SP and septide. LY303870 and LY306740 were more potent against septide. 5. The antagonism afforded by LY303870, LY306740 and LY303241 was stereoselective and only SR140333 was found to cause central and peripheral non specific effects. 6. The data confirm a distinct pharmacological profile for septide in vivo. RP67580 and LY306740 are currently the most valuable tachykinin NK1 receptor antagonists for in vivo studies in rat.

Respiratory action of capsaicin microinjected into the nucleus of the solitary tract: involvement of vanilloid and tachykinin receptors

1. The respiratory response to microinjection of capsaicin into the commissural nucleus of the solitary tract (cNTS) of urethane-anaesthetized rats was investigated in the absence and presence of the competitive vanilloid (capsaicin) antagonist, capsazepine, and selective tachykinin NK1, NK2 and NK3 antagonists (RP 67580, SR 48968 and SR 142801, respectively). 2. Microinjection of capsaicin reduced respiratory frequency but not tidal volume (VT), leading to an overall reduction in minute ventilation (VE). The effect was dose-dependent between 0.5 and 2 nmol capsaicin. Doses greater than 2 nmol produced apnoea. Tachyphylaxis was observed following repeated injection of capsaicin (1 nmol, 30 min apart). 3. Capsazepine (1 nmol) had no effect on frequency or VT when injected alone but completely blocked the respiratory response to capsaicin (1 nmol). 4. RP 67580 (1 but not 5 nmol) alone depressed frequency and VT slightly. Moreover, RP 67580 appeared to potentiate the bradypnoeic effect of capsaicin. In contrast, SR 48968 and SR 142801 (1 and 5 nmol) alone had no significant effect on respiration. However, both agents significantly attenuated the reduction in frequency produced by capsaicin. 5. In conclusion, microinjection of capsaicin into the cNTS decreases overall ventilation, primarily by reducing frequency. The action of capsaicin appears from the data to be mediated by vanilloid receptors since it is blocked by the competitive vanilloid antagonist capsazepine and is subject to tachyphylaxis. However, since NK2 (SR 48968) and NK3 (SR 142801) receptor antagonists block the actions of capsaicin, we propose that capsaicin acts also by releasing tachykinins from central afferent terminals in the cNTS.

Facilitation of striatal acetylcholine release by dopamine D1 receptor stimulation: involvement of enhanced nitric oxide production via neurokinin-2 receptor activation

The regulation of striatal cholinergic function by dopamine D1 receptor activation was examined in vivo in urethane-anaesthetized rats with microdialysis probes. Extracellular acetylcholine levels were enhanced by activation of D1 receptors either directly by a striatal application of the D1 receptor agonist (+)-SKF-38393 (3 microM) or indirectly by the release of dopamine evoked by striatal application of neurotensin (0.1 microM) under D2 receptor blockade. SR 144190, a new potent and selective non-peptide neurokinin-2 receptor antagonist (0.03-1 mg/kg, i.p.), dose-dependently reduced the acetylcholine release induced by (+)-SKF-38393 or neurotensin. Furthermore, intrastriatal application of SR 144190 (1 nM) blocked the increase in acetylcholine release induced by the local application of (+)-SKF-38393 (3 microM), neurokinin A (1 microM) or substance P (1 microM). Finally, a role for nitric oxide in mediating the effects of D1 neurokinin-2 receptor activation on acetylcholine release is proposed since local infusion of the competitive inhibitor of nitric oxide synthase, N(G)-monomethyl-L-arginine (0.01-10 microM), blocked the increase in acetylcholine release induced by (+)-SKF-38393 (3 microM), neurotensin (0.1 microM) or neurokinin A (1 microM) without affecting the enhancing effect of the neurokinin-1 agonist septide (0.1 microM).

What are the roles of substance P and neurokinin-1 receptors in the control of negative chronotropic or negative dromotropic vagal motoneurons? A physiological and ultrastructural analysis

Recent data indicate that there is a cardiotopic organization of negative chronotropic and negative dromotropic neurons in the nucleus ambiguus (NA). Negative dromotropic neurons are found in the rostral ventrolateral NA (rNA-VL), negative chronotropic neurons are found in the caudal ventrolateral NA (cNA-VL), and both types of neurons are found in an intermediate level of the ventrolateral NA (iNA-VL). Substance P (SP) immunoreactive nerve terminals synapse upon negative chronotropic vagal motoneurons in the iNA-VL, and SP microinjections in the NA cause bradycardia. In the present report we have attempted to: (1) define the type of tachykinin receptor which mediates the negative chronotropic effect of SP microinjections into the iNA-VL; (2) define the physiological effect of microinjections of a selective SP agonist into the rNA-VL on atrioventricular (AV) conduction: and (3) find ultrastructural evidence for synaptic interactions of SP-immunoreactive nerve terminals with negative dromotropic vagal motoneurons in the rNA-VL. Microinjections of the excitatory amino acid glutamate (Glu) into the iNA-VL to activate all local vagal preganglionic neurons caused both bradycardia and a decrease in the rate of AV conduction. Injections of the selective neurokinin-1 (NK-1) receptor agonist drug GR-73632 also caused bradycardia, however the rapid onset of agonist induced desensitization prevented an evaluation of potential effects on AV conduction in the iNA-VL. These data suggest that the SP-induced bradycardia which can be elicited from the NA is mediated, at least in part, by NK-1 receptors. Microinjections of Glu into the rNA-VL caused a decrease in AV conduction without an effect on cardiac rate. On the other hand, GR-73632 microinjections into rNA-VL did not affect AV conduction. Following injections of the beta subunit of cholera toxin conjugated to horseradish peroxidase (CTB-HRP) into the left atrial fat pad ganglion which selectively mediates changes in AV conduction, retrogradely labeled neurons were histochemically visualized in the rNA-VL. These tissues were subsequently processed for the simultaneous immunocytochemical visualization of SP, and examined by electron microscopy. Histochemically labeled neurons were large, multipolar, with abundant cytoplasm containing large masses of rough endoplasmic reticulum, and exhibited distinctive dendritic and somatic spines. Unlabeled nerve terminals were noted to form either asymmetric or symmetric synapses with dendrites, dendritic spines, and perikarya of histochemically labeled neurons. SP-immunoreactive nerve terminals were also detected in the rNA-VL. SP terminals typically contained numerous small pleomorphic vesicles, multiple large dense core vesicles, and several mitochondria, and they synapsed upon unlabeled dendritic profiles. A total of 154 SP-immunoreactive nerve terminals were observed on photomicrographs of tissues which also contained histochemically labeled profiles. None made an identifiable synapse with a retrogradely labeled profile on the sections examined. In summary, both physiological and ultrastructural data indicate that SP terminals in the iNA-VL do modify the output of negative chronotropic vagal motoneurons. This effect is mediated by NK-1 receptors. On the other hand both physiological and ultrastructural data indicate that SP terminals in the rNA-VL do not modify the output of negative dromotropic vagal motoneurons. Therefore different mechanisms (neurotransmitters or receptors) mediate the central vagal control of cardiac rate and AV conduction.

Intracerebroventricular responses to neuropeptide gamma in the conscious rat: characterization of its receptor with selective antagonists

1. The cardiovascular and behavioural effects elicited by the intracerebroventricular (i.c.v.) administration of neuropeptide gamma (NP gamma) in the conscious rat were assessed before and 5 min after i.c.v. pretreatment with antagonists selective for NK1 (RP 67,580), NK2 (SR 48,968) and NK3 (R 820) receptors. In addition, the central effects of NP gamma before and after desensitization of the NK1 and NK2 receptors with high doses of substance P (SP) and neurokinin A (NKA) were compared. 2. Intracerebroventricular injection of NP gamma (10-780 pmol) evoked dose- and time-dependent increases in mean arterial blood pressure (MAP), heart rate (HR), face washing, head scratching, grooming and wet-dog shake behaviours. Similar injection of vehicle or 1 pmol NP gamma had no significant effect on those parameters. 3. The cardiovascular and behavioural responses elicited by NP gamma (25 pmol) were significantly and dose-dependently reduced by pretreatment with 650 pmol and 6.5 nmol of SR 48,968. No inhibition of NP gamma responses was observed when 6.5 nmol of RP 67,580 was used in a similar study. Moreover, the prior co-administration of SR 48,968 (6.5 nmol) and RP 67,580 (6.5 nmol) with or without R 820 (6.5 nmol) did not reduce further the central effects of NP gamma and significant residual responses (30-50%) remained. 4. No tachyphylaxis to NP gamma-induced cardiovascular and behavioural changes was observed when two consecutive injections of 25 pmol NP gamma were given 24 h apart. 5. Simultaneous NK1 and NK2 receptor desensitization reduced significantly central effects mediated by 25 pmol NP gamma. However, significant residual responses persisted as seen after pretreatment with SR 48,968. 6. The results suggest that the central effects of NP gamma are mediated partly by NK2 receptors and by another putative tachykinin receptor subtype (NP gamma receptor?) that appears to be different from NK1 and NK3 receptors.

Comparative behavioural profile of centrally administered tachykinin NK1, NK2 and NK3 receptor agonists in the guinea-pig

1. The NK1 tachykinin receptor agonists, septide, [Sar9,Met(O2)11]SP and [Pro9]SP produced locomotor hyperactivity (10-20 min) when injected intracerebroventricularly (i.c.v.) in the guinea-pig. The most potent in eliciting this hyperactivity was septide (from 0.63 to 5 micrograms), compared to [Sar9,Met(O2)11]SP, which was active at 2.5 and 5 micrograms and [Pro9]SP which induced a non-significant increase even at 10 micrograms. 2. Wet-dog shakes were elicited by septide, [Sar9,Met(O2)11]SP and [Pro9]SP injected by the i.c.v. route in the guinea-pig. [Sar9,Met(O2)11]SP, active from 0.16 to 2.5 micrograms was more potent than septide (active at 1.25 micrograms) and [Pro9]SP (active at 0.63 micrograms) in eliciting such behaviour. To a lesser extent, grooming was also observed after injection of these agonists. 3. The NK2 tachykinin receptor agonist, [Lys5,MeLeu9,Nle10]NKA(4-10), up to the dose of 10 micrograms i.c.v. had no effect in the guinea-pig. It neither modified locomotor activity nor induced a characteristic behavioural response. At higher doses (20 micrograms), some toxic effects were noted. 4. The NK3 tachykinin receptor agonist, senktide, contrasts with the NK1 receptor agonists in that it elicited only wet-dog shakes, at doses ranging from 0.32 to 1.25 micrograms. It neither modified locomotor activity (1 microgram) nor induced grooming (up to 5 micrograms) in the guinea-pig. 5. To our knowledge, these results are the first demonstration that the guinea-pig could be useful to differentiate tachykinin agonists on the basis of their behavioural profile, distinct from those obtained in mice and rats.

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

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

Central tachykinins: mediators of defence reaction and stress reactions

The tachykinins substance P, neurokinin A, and neurokinin B are natural agonists for NK1, NK2, and NK3 receptors, respectively. Evidence from biochemical, neurophysiological, pharmacological, and molecular biology studies indicates that the tachykinin-containing pathways within the brain contribute to central cardiovascular and endocrine regulation and to the control of motor activity. The hypothalamus, which represents a site for the integration of central neuroendocrine and autonomic processes, is rich in tachykinin nerve endings and tachykinin receptors. Stimulation of periventricular or hypothalamic NK1 receptors in conscious rats induces an integrated cardiovascular, behavioural, and endocrine response. The cardiovascular response is associated with increased sympathoadrenal activity and comprises an increase in blood pressure and heart rate, mesenteric and renal vasoconstriction, and hind-limb vasodilatation. The behavioural response consists of increased locomotion and grooming behaviour. This response pattern is consistent with an integrated stress response to nociceptive stimuli and pain in rodents. Several studies have demonstrated rapid changes in substance P levels and its receptors in distinct brain areas following acute stress. These data indicate that substance P and other tachykinins, in addition to serving as nociceptive and pain transmitters in the spinal cord, may act in the brain as neurotransmitters--neuromodulators within the neuronal circuits mediating central stress responses.

Effects of the tachykinin NK1 receptor antagonist, RP 67580, on central cardiovascular and behavioural effects of substance P, neurokinin A and neurokinin B

1. We have investigated the effects of the non-peptide NK1 tachykinin receptor antagonist, RP 67580, and its inactive enantiomer, RP 68651, on the cardiovascular and behavioural responses to substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) injected intracerebroventricularly (i.c.v.) in conscious rats. 2. The SP and NKA (25 pmol)-induced increases in blood pressure (BP) and heart rate (HR) were of the same magnitude. The cardiovascular responses to both peptides were associated with excessive grooming behaviour and wet dog shakes (WDS). Relative to SP, NKA was weaker in inducing hindquarter grooming (HG), but more effective in eliciting WDS. The cardiovascular response to NKB (50 pmol) comprised an increase in BP and HR, while the behavioural response was weak. 3. RP 67580 (100 pmol), injected 10 or 30 min prior to SP, effectively inhibited the cardiovascular and behavioural responses to the peptide whereas lower doses were ineffective. Pretreatment with 500 pmol of RP 67580, 10 or 30 min prior to SP, reduced the BP response. Of the behavioural manifestations, only face washing was attenuated when the antagonist was injected 10 min before SP. At 2500 pmol, the antagonist exaggerated the BP response to the peptide without affecting the behavioural response. RP 68651 (100 or 2500 pmol) did not modify the central responses to SP. 4. Neither RP 67580 nor RP 68651 (100 pmol), affected the cardiovascular and behavioural responses to NKA or NKB. 5. Our results indicate that RP 67580 is a selective and high affinity antagonist at central NK1 tachykinin receptors in the rat.

Effects of substance P on cardiovascular regulation in the rabbit

The effect of substance P on blood pressure and aortic reflex was investigated in rabbits. Microinjections of substance P and Sar9, Met(O2)11-SP (a selective NK1-receptor agonist) into the floor of the fourth ventricle led to a dose-dependent increase of blood pressure and a sharp enhancement of the baroreflex. These effects were abolished by pretreatment with SR 140333 (a selective NK1-receptor antagonist). Intraventricular injection of the antagonist alone significantly decreased the amplitude of the aortic reflex. After bivagotomy, the amplitude of the parasympathetic component of the baroreflex decreased dramatically and substance P injections were no longer effective. Our results demonstrate that substance P activation of NK1 receptors plays a major role in the modulation of the parasympathetic component of the baroceptor reflex.

Further localization of cardiovascular and behavioral actions of substance P in the rat brain

Cardiovascular and behavioral actions of substance P (SP) were examined after microinjection into the medial preoptic area (MPO), anterior hypothalamic area (AH), and ventral tegmental area (VTA) in conscious unrestrained rats. SP elicited marked increases in mean arterial pressure and heart rate as well as stereotyped behaviors of excessive grooming and exploring when injected into the MPO or AH. In the MPO, the latencies to the cardiovascular responses were observed after SP injection into the VTA. These results, together with our previous results, suggest that SP acts as transmitter or modulator in the rostral hypothalamic areas to elicit cardiovascular defense responses. In contrast, SP may not be involved in causing a defense reaction in the more caudal areas of the defense center.

Substance P is involved in the sensitization of the acoustic startle response by footshocks in rats

The acoustic startle response (ASR) can be enhanced by administration of footshocks (sensitization). The neural mechanisms underlying this effect are largely unknown. A previous electrophysiological study (Kungel et al., Brain Res., 643 (1994) 29-39) has shown that the neuropeptide substance P (SP) increases the responsiveness to acoustic stimuli of neurons in the caudal pontine reticular nucleus (PnC). Since the PnC is an important part of the primary acoustic startle circuit, we hypothesized that SP is involved in the enhancement of the ASR by electric footshocks. We tested this hypothesis in different experiments by locally injecting SP and SP-antagonists into the PnC of freely moving rats. The present data show that SP (0.5 pmol-1 nmol) locally injected into the PnC dose-dependently increases the amplitude of the ASR in rats. This effect was antagonized by pretreatment with the SP-antagonist CP-96,345. Furthermore, we show that the sensitization of the ASR by 0.6 mA-footshocks can be blocked by local microinjections of the SP-antagonists CP-96,345 (5 pmol-10 nmol) or CP-99,994 (0.5 nmol-100 nmol) into the PnC. Possible pathways relevant for the sensitization of the ASR are discussed.

Differential ability of tachykinin NK-1 and NK-2 agonists to produce scratching and grooming behaviours in mice

Potent and selective NK-1 and NK-2 agonists as well as compounds with lower selectivity and affinity for NK-1 binding sites were compared in their ability to produce scratching and grooming behaviours when injected intracerebroventricularly in mice. Septide, an agonist with a low affinity for NK-1 binding sites, [Sar9, Met(O2)11]SP and to a lesser extent [Pro9]SP, two potent and selective NK-1 agonists were the most effective drugs in stimulating these behaviours. Only high doses of [Apa9,10]SP and [Lys5, Tyr7, Pro8]NKA(4-10), two agonists with low affinity for NK-1 binding sites, produced scratching and grooming responses. Similarly, only high doses of [Lys5, MeLeu9, NLe10]NKA(4-10), a potent NK-2 agonist, produced grooming behaviour. When coinjected with the endopeptidase enzyme inhibitor phosphoramidon, the effects of [Apa9,10]SP, [Lys5, Tyr7, Pro8]NKA(4-10) and [Pro9]SP were markedly enhanced. Analyses of the potency of the different agents to displace 3H-SP binding in mouse subcortical structures revealed that the affinities of the agonists for NK-1 receptors are similar to those previously reported in rat brain. The efficacy of the agonists at producing behavioural responses was not equivalent to their potency to bind to central NK-1 receptors. These findings therefore suggest that a stimulation of NK-1 but also non classical NK-1 receptors are involved in the induction of scratching and grooming behaviours.

Pentagastrin infusions in patients with panic disorder. II. Neuroendocrinology

Cholecystokinin (CCK) has well-documented anxiogenic effects in animals and normal people, and panicogenic effects in patients with panic disorder, but little is known about its neuroendocrine profile. We examined neuroendocrine responses to intravenous infusions of pentagastrin, a selective CCK-B receptor agonist, in 10 patients with panic disorder and 10 normal control subjects. Pentagastrin potently activated the hypothalamic-pituitary-adrenal (HPA) axis, but did not release growth hormone or any of several vasoactive peptides (neurokinin A, substance P, vasoactive intestinal peptide). The HPA axis response was unrelated to increases in symptoms. Panic patients did not differ from controls in neuroendocrine responses to the CCK agonist. Differential sensitivity to novelty stress accounted for the only patient-control differences in neuroendocrine profiles. The data suggest that CCK may help modulate normal HPA axis activity, but its anxiogenic effects are unrelated to its stimulatory effects on the HPA axis. Pentagastrin provides a safe and readily available probe for further study of CCK receptor systems in humans.

Physiological and pharmacological characterization of the spinal tachykinin NK2 receptor

The goal of these investigations was to study the role of tachykinin NK2 receptors in neonatal spinal cords using the selective NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) and the new NK2 receptor antagonist GR 94800. Experiments were performed with superfused hemisected rat and gerbil spinal cords. Dorsal roots were electrically stimulated and the synaptically elicited responses and the DC-potentials were recorded extracellularly from the corresponding ventral roots. [beta-Ala8]neurokinin A-(4-10) depolarized ventral roots (0.01-10 microM) and increased their spontaneous activity in a concentration-dependent manner. These effects of [beta-Ala8]neurokinin A-(4-10) were reduced by GR 94800. The action of GR 94800 was selective because the depolarizing effects of similar magnitude evoked by the NK1 receptor agonist [Sar9,Met(O2)11]substance P were not affected by GR 94800. The pA2 values of GR 94800 amounted to 6.0 +/- 0.4 in the rat and 5.4 +/- 0.3 in the gerbil. The NK2 receptor agonist was more potent in the rat than in the gerbil. The estimated EC50 (mean +/- S.E.M.) was found to be 3.9 + 6.0/-1.3 microM in the rat and 2.4 + 2.9/-1.3 microM in the gerbil spinal cord. The NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) potentiated the monosynaptic reflex evoked by dorsal root stimulation. The potentiation manifested itself as an increase in the amplitude of the early component of the response. The receptor type mediating this effect could not be elucidated. The potentiation ranged between 30 +/- 27 and 110 +/- 36% (0.3 and 10 microM), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular and behavioural effects of centrally administered tachykinins in the rat: characterization of receptors with selective antagonists

1. The effects of intracerebroventricular (i.c.v.) injection of selective and potent NK1 (RP 67580), NK2 (SR 48968) and NK3 (R 486, [Trp7, beta-Ala8]NKA(4-10)) receptor antagonists were assessed on the cardiovascular and behavioural responses elicited by the i.c.v. injection of substance P (SP), neurokinin A (NKA) or [MePhe7]neurokinin B ([MePhe7]NKB) in the conscious freely moving rat. 2. SP, NKA and [MePhe7]NKB (5-650 pmol) evoked dose-dependent increases in mean arterial blood pressure (MAP) and heart rate (HR) with the rank order of potency SP > NKA > [MePhe7]NKB. The cardiovascular responses were accompanied by excessive face washing, grooming and wet dog shakes. 3. The cardiovascular effects and face washing behaviour induced by SP (25 pmol) were significantly reduced by the pre-injection (i.c.v., 5 min earlier) of RP 67580 (6.5 nmol). However, this antagonist failed to affect the central effects of 25 pmol NKA or [MePhe7]NKB. 4. The cardiovascular and behavioural responses (except for wet dog shakes) elicited by NKA (25 pmol) were significantly reduced by 6.5 nmol SR 48968. However, the latter antagonist had no effect on the SP or [MePhe7]NKB-mediated responses. 5. Both cardiovascular and behavioural effects produced by either SP or NKA (25 pmol) were completely abolished when rats were pretreated with a combination of RP 67580 (6.5 nmol) and SR 48968 (6.5 nmol), yet this combination of antagonists failed to modify the central effects of [MePhe7]NKB. 6. R 486 (6.5 nmol) inhibited the cardiovascular effects as well as wet dog shakes produced by [MePhe7]NKB, but it was inactive against the responses induced by either SP or NKA. 7. None of the tachykinin receptor antagonists or agonists caused motor impairment or respiratory distress. All antagonists blocked in a reversible manner and were devoid of intrinsic activity except R486 (6.5 nmol) which produced a transient increase of MAP and HR.8. These results suggest that the central effects of SP, NKA and [MePhe7]NKB are primarily mediated by central NK1, NK2 and NK3 receptors, respectively. However, a minor activation of NK2 receptors bySP and NK1 receptors by NKA was seen during blockade of both receptors. This study therefore supports the existence of functional NK1, NK2 and NK3 receptors in the adult rat brain.

Cardiovascular and behavioural effects of centrally administered neuropeptide K in the rat: receptor characterization

1. The cardiovascular and behavioural responses to intracerebroventricularly (i.c.v.) administered neuropeptide K (NPK) were studied in conscious rats. The central effects of NPK were characterized by pretreatment (i.c.v.) with selective antagonists for the NK1 ((+/-)-CP 96345 and RP 67580), NK2 (SR 48968) and NK3 (R 487) receptors. 2. NPK (10-65 pmol) induced tachycardia and dose-dependent increases of mean arterial blood pressure. The cardiovascular responses reached a maximum within 3 min post-injection and lasted for more than 1 h. Concurrently, NPK produced dose-dependent increases of face washing, head scratching, grooming, walking and wet dog shakes. 3. A desensitization of most of the behavioural responses (except head scratching) but not of the cardiovascular response was shown when two consecutive injections of 25 pmol NPK were given 24 h apart. 4. Both the cardiovascular and behavioural responses (except the head scratching) to 25 pmol NPK were blocked by pre-administration (i.c.v.) of 6.5 nmol (+/-)-CP 96345 or RP 67580 given 5 min earlier. No inhibition of NPK responses was observed when 6.5 nmol SR 48968 or R 487 were used in a similar study. Additionally, NPK effects were significantly reduced 24 h after the prior injection of (+/-)-CP 96345 but not of RP 67580. 5. These results support the involvement of NK1 receptors in the cardiovascular and behavioural effects of i.c.v. NPK. Thus, this peptide may play a putative role in central cardiovascular regulation as it is the most potent endogenous tachykinin described centrally, to date.

Differential effects of selective tachykinin NK2 receptor antagonists in rat spinal cord

The effects of intrathecally (i.t.) injected selective tachykinin NK2 receptor antagonists, MEN 10,207, MEN 10,376 and R396, on the spinal effect of neurokinin A were studied in decerebrate, spinalized, unanesthetized rats. I.t. neurokinin A (7 pmol) briefly facilitated the flexor reflex, an effect that was dose dependently inhibited by pretreatment with MEN 10,207 and MEN 10,376 with similar and high potency. I.t. R396 itself caused strong facilitation of the flexor reflect. At lower doses, the effect of i.t. neurokinin A was potentiated by R396. R396 only exhibited moderate antagonism of neurokinin A-induced reflex facilitation even at very high doses. It has been proposed that the tachykinin NK2 receptor may be further classified into two subtypes, NK2A and NK2B, with MEN 10,207 and MEN 10,376 having high affinity for the former and R396 for the latter. Our results suggested that the tachykinin NK2 receptor in rat spinal cord which mediates the excitatory effect of neurokinin A may belong to the NK2A subpopulation of receptors.

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

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