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

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 Regulation in Epilepsy

Background:

Epilepsy is a common neurological disease characterized by abnormal temporary discharge of neurons in the central nervous system. In recent years, studies have revealed the localization and changes in the density of neuropeptides, such as substance P (SP) in the pathogenesis of epilepsy. This review is a concise overview of SP and their physiologic and pathologic functions on regulating epilepsy, and the underline mechanisms.

Methods:

We research and collect relative online content for reviewing the effects of SP in Epilepsy.

Results:

The SP/NK-1 receptor system may induce seizures and play an important role in status epilepticus and in experimental animal models of epilepsy. Newest studies show that several mechanisms may explain the excitatory effects of the SP/NK-1 receptor signaling pathway in epilepsy. By binding to the NK-1 receptor, NK-1 receptor antagonists may block the pathophysiological effects of SP, and further studies are needed to confirm the possible anti-epileptic activity of NK-1 receptor antagonists.

Conclusion:

SP plays crucial roles on through binding with NK-1 receptor during epilepsy pathologic processing, and the NK-1 receptor is receiving a great attention as a therapeutic target for treating epilepsy. Thus, the use of NK-1 receptor antagonists for the treatment of epilepsy should be investigated in further studies.

Role of substance P in the cardiovascular system

This article provides an overview of the structure and function of substance P signalling system and its involvement in the cardiovascular regulation. Substance P is an undecapeptide originating from TAC1 gen and belonging to the tachykinin family. The biological actions of substance P are mainly mediated through neurokinin receptor 1 since substance P is the ligand with the highest affinity to neurokinin receptor 1. Substance P is widely distributed within the central and peripheral nervous systems as well as in the cardiovascular system. Substance P is involved in the regulation of heart frequency, blood pressure and in the stretching of vessels. Substance P plays an important role in ischemia and reperfusion and cardiovascular response to stress. Additionally, it has been also implicated in angiogenesis, pain transmission and inflammation. The substance P/neurokinin receptor 1 receptor system is involved in the molecular bases of many human pathological processes. Antagonists of neurokinin receptor 1 receptor could provide clinical solutions for a variety of diseases. Neurokinin receptor 1 antagonists are already used in the prevention of chemotherapy induced nausea and vomiting.

Brain kinin B1 receptor is upregulated by the oxidative stress and its activation leads to stereotypic nociceptive behavior in insulin-resistant rats

Kinin B1 receptor (B1R) is virtually absent under physiological condition, yet it is highly expressed in models of diabetes mellitus. This study aims at determining: (1) whether B1R is induced in the brain of insulin-resistant rat through the oxidative stress; (2) the consequence of B1R activation on stereotypic nocifensive behavior; (3) the role of downstream putative mediators in B1R-induced behavioral activity. Sprague-Dawley rats were fed with 10% D-glucose in their drinking water or tap water (controls) for 4 or 12 weeks, combined either with a standard chow diet or a diet enriched with α-lipoic acid (1 g/kg feed) for 4 weeks. The distribution and density of brain B1R binding sites were assessed by autoradiography. Behavioral activity evoked by i.c.v. injection of the B1R agonist Sar-[D-Phe(8)]-des-Arg(9)-BK (10 μg) was measured before and after i.c.v. treatments with selective antagonists (10 μg) for kinin B1 (R-715, SSR240612), tachykinin NK1 (RP-67580) and glutamate NMDA (DL-AP5) receptors or with the inhibitor of NOS (L-NNA). Results showed significant increases of B1R binding sites in various brain areas of glucose-fed rats that could be prevented by the diet containing α-lipoic acid. The B1R agonist elicited head scratching, grooming, sniffing, rearing, digging, licking, face washing, wet dog shake, teeth chattering and biting in glucose-fed rats, which were absent after treatment with α-lipoic acid or antagonists/inhibitors. Data suggest that kinin B1R is upregulated by the oxidative stress in the brain of insulin-resistant rats and its activation causes stereotypic nocifensive behavior through the release of substance P, glutamate and NO.

Brain kinin B₁ receptor contributes to the onset of stereotypic nocifensive behavior in rat

While brain kinin B(1) receptor (B(1)R) is virtually absent in control rats, it contributes to hypertension via a midbrain dopaminergic (DA) mechanism in spontaneously hypertensive rat (SHR) and Angiotensin II (Ang II)-induced hypertension. This study aims at determining whether B(1)R can also affect stereotypic nocifensive behavior through DA and/or other neuromediators in the same models. The selective B(1)R agonist Sar[D-Phe(8)][des-Arg(9)]BK was injected i.c.v. (1 μg/site) to freely behaving SHR (16 weeks), Ang II-hypertensive rats (200 ng/kg/min × 2 weeks, s.c.) and control Wistar-Kyoto rats (WKY). Behavioral activity to the agonist was measured before and after treatment with receptor antagonists (10 μg/site i.c.v. or otherwise stated) for B(1) (SSR240612), tachykinin NK(1) (RP67580), glutamate NMDA (DL-AP5), DA D(1) (SCH23390, 0.2mg/kg s.c.) and D(2) (Raclopride, 0.16 mg/kg s.c.). Other studies included inhibitors (10 μg/site) of NOS (l-NNA) and iNOS (1400W). The possible desensitisation of B(1)R upon repeated intracerebral stimulation was also excluded. B(1)R expression was measured by qRT-PCR in selected areas and by immunohistochemistry in the ventral tegmental area. Results showed that the B(1)R agonist had no effect in WKY, yet it induced nocifensive behavioral manifestations in both models of hypertension (face washing, sniffing, head scratching, rearing, teeth chattering, grooming, digging, licking, wet-dog shakes). These responses were prevented by all antagonists and inhibitors tested, but 1400 W had a less inhibitory effect on most behaviors. Compared with WKY, B(1)R mRNA levels were markedly enhanced in hypothalamus, ventral tegmental area and nucleus accumbens of SHR and Ang II-treated rats. B(1)R was detected on DA neuron of the ventral tegmental area in SHR. Data suggest that kinin B(1)R is upregulated in midbrain DA system in hypertensive rats and its i.c.v. activation induced stereotypic nocifensive behavior that is mediated by several mediators, notably substance P, glutamate, DA and NO.

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.

Mapping of alpha-neo-endorphin- and neurokinin B-immunoreactivity in the human brainstem

We have studied the distribution of alpha-neo-endorphin- or neurokinin B-immunoreactive fibres and cell bodies in the adult human brainstem with no prior history of neurological or psychiatric disease. A low density of alpha-neo-endorphin-immunoreactive cell bodies was only observed in the medullary central gray matter and in the spinal trigeminal nucleus (gelatinosa part). Alpha-neo-endorphin-immunoreactive fibres were moderately distributed throughout the human brainstem. A high density of alpha-neo-endorphin-immunoreactive fibres was found only in the solitary nucleus (caudal part), in the spinal trigeminal nucleus (caudal part), and in the gelatinosa part of the latter nucleus. Neurokinin B-immunoreactive cell bodies (low density) were found in the periventricular central gray matter, the reticular formation of the pons and in the superior colliculus. The distribution of the neurokinin-immunoreactive fibres was restricted. In general, for both neuropeptides the density of the immunoreactive fibres was low. In the human brainstem, the proenkephalin system was more widely distributed than the prodynorphin system, and the preprotachykinin A system (neurokinin A) was more widely distributed than the preprotachykinin B system (neurokinin B).

Blockade of tachykinin NK1/NK2 receptors in the brain attenuates the activation of corticotrophin-releasing hormone neurones in the hypothalamic paraventricular nucleus and the sympathoadrenal and pituitary-adrenal responses to formalin-induced pain in the rat

Evidence from pharmacological studies has implicated substance P (SP), a natural ligand of tachykinin NK(1) receptors which can also interact with NK(2) receptors, in the generation of pressor and tachycardic responses to stress. Using selective blockade of brain NK(1) and NK(2) receptors, we tested in conscious rats the hypothesis that SP initiates, within the neuronal brain circuits, the sympathoadrenal, hypothalamic-pituitary-adrenal (HPA) and behavioural responses to noxious stimuli. Formalin injected s.c. through a chronically implanted catheter in the area of the lower leg was used as a pain stimulus. Rats were pretreated i.c.v. with vehicle or the selective, nonpeptide antagonists of tachykinin NK(1) and NK(2) receptors, RP 67580 and SR 48968, respectively. Ten minutes thereafter, formalin was injected s.c. and the cardiovascular responses were recorded, plasma concentrations of catecholamines, adrenocorticotrophic hormone (ACTH) and corticosterone were determined and the expression of the inducible transcription factor c-Fos in the paraventricular (PVN) and supraoptic nuclei was detected to identify neurones which were activated during pain stimulation. Blockade of NK(1) and NK(2) receptors attenuated the formalin-induced increases in mean arterial pressure and heart rate, adrenaline and ACTH concentrations in plasma, and completely abolished the pain-induced c-Fos expression in corticotrophin-releasing hormone neurones localised in the parvocellular division of the PVN. The results obtained provide pharmacological evidence that tachykinins, most probably SP, act as mediators within the neuronal circuits linked to the initiation and control of the cardiovascular, sympathoadrenal, HPA and behavioural responses to pain stimuli and provide an excitatory input to corticotrophin-releasing hormone neurones in the PVN to activate the HPA axis. Our data demonstrating the inhibition of the complex response pattern to noxious stimuli and stress are consistent with the proposed anxiolytic and antidepressant activity of NK(1) and NK(2) receptor antagonists.

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.

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.

Intraventricular injections of tachykinin NK3 receptor agonist reduce the gain of the baroreflex in unrestrained rats

The tachykinin neuropeptides acting at NK3 receptors affect mean arterial pressure (MAP) through both neuroendocrine and neural mechanisms. NK3 receptors are found in brainstem nuclei that mediate the baroreflex, but the effects of NK3 receptor stimulation on baroreflex function are unknown. The present study tests the effects of intraventricular injections of senktide, a selective NK3 receptor agonist, on the sensitivity of the baroreflex in three stains of rats: Charles River Laboratory, Long-Evans, and Brattleboro rats, which lack the ability to synthesize vasopressin. Rats with lateral ventricle cannulas were administered injections of isotonic saline, 100 ng, or 200 ng senktide, and 5 min later arterial baroreceptor-heart rate (HR) function was examined by constructing full-range blood pressure-HR curves using alternating doses (5-20 microg kg min) of phenylephrine and nitroprusside to raise and decrease blood pressure approximately 50 mm Hg over a period of 1 min, respectively. Intraventricular injections of 200 ng senktide had no significant effect on baseline MAP, but significantly decreased the gain of the baroreflex in all three rat strains whereas the 100 ng dose had no effect on the baroreflex. These results show that NK3 receptor stimulation modulates the baroreflex that is independent of any action of vasopressin.

A 25 year adventure in the field of tachykinins

Several aspects of our 25 year adventure in the field of tachykinins will be successively described. They concern: substance P (SP) synthesis and release in the basal ganglia, the identification and pharmacological characterization of central tachykinin NK(1), NK(2) and NK(3) binding sites and their topographical distribution, the description of some new biological tests for corresponding receptors, the identification of tachykinin NK(1) receptor subtypes or conformers sensitive to all endogenous tachykinins (substance P, neurokinin A (NKA), neurokinin B (NKB), neuropeptide gamma (NP gamma) and neuropeptide K (NPK)) and finally, the functional involvement of these receptors and their subtypes in tachykinin-induced regulations of dopamine and acetylcholine release in the striatum.

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.

Diencephalic neurons producing melanin-concentrating hormone are influenced by local and multiple extra-hypothalamic tachykininergic projections through the neurokinin 3 receptor

As melanin-concentrating hormone (MCH) neurons express the neurokinin 3 receptor (NK3) in the rat diencephalon, their innervation by tachykininergic fibers, the origin of this innervation and the effect of a NK3 agonist on MCH mRNA expression were researched. The obtained results show that the tachykininergic system develops complex relationships with MCH neurons. Overall, MCH cell bodies appeared targeted by both NKB- and SP-inputs. These afferents have multiple hypothalamic and extra-hypothalamic origins, but a local (intra-lateral hypothalamic area) origin from small interneurons was suspected as well. MCH cell bodies do not express NK1, but around 2.7% of the MCH neurons contained SP after colchicine injection. Senktide, a NK3 agonist, produced an increase of the MCH mRNA expression in cultured hypothalamic slices. This effect was reversed by two NK3 antagonists. Tachykinins enhance MCH mRNA expression, and, thus, may modulate the effect of MCH in functions such as feeding and reproductive behaviors in which this peptide has been experimentally involved.

Autoradiographic distribution of tachykinin NK2 binding sites in the rat brain: comparison with NK1 and NK3 binding sites

The autoradiographic distribution of tachykinin NK(2) binding sites was determined in the adult rat brain using [(125)I]neurokinin A in the presence of either senktide (NK(3) agonist) and [Pro(9)]substance P (NK(1) agonist) or senktide and SR 140333 (NK(1) antagonist). Indeed, this radioligand labels two subtypes of NK(1) binding sites (which present a high affinity not only for SP but also for neurokinin A, neuropeptide K and neuropeptide gamma) as well as NK(3) binding sites. The distribution of NK(2) binding sites was also compared with those of NK(1) and NK(3) binding sites, these sites being labeled with [(125)I]Bolton and Hunter substance P and [(125)I]Bolton and Hunter eledoisin, respectively. In agreement with our results obtained with membranes from various brain structures, NK(2)-sensitive [(125)I]neurokinin A labeling was mainly observed in few structures including the dorsal and ventral hippocampus, the septum, the thalamus and the prefrontal cortex. The density of NK(2) binding sites was weak when compared with those of NK(1) and NK(3) binding sites. Marked differences were observed in the distributions of NK(1), NK(2) and NK(3) binding sites. These results are discussed taking into consideration differences or similarities between the distributions of NK(2)-sensitive [(125)I]neurokinin A binding sites and of their endogenous ligands (neurokinin A, neuropeptide K and neuropeptide gamma) but also local NK(2) agonist responses blocked by NK(2) antagonists. Insights on the roles of endogenous tachykinins in several brain functions are also discussed on the basis of the respective distributions of different neurokinin binding sites.

Implication of nigral tachykinin NK3 receptors in the maintenance of hypertension in spontaneously hypertensive rats: a pharmacologic and autoradiographic study

1. The role of nigral tachykinin NK(1), NK(2) and NK(3) receptors in central cardiovascular regulation was studied by measuring the effects of selective agonists and antagonists on mean arterial pressure (MAP) and heart rate (HR) after bilateral microinjection into the substantia nigra of spontaneously hypertensive rats (SHR). Quantitative in vitro autoradiography was also performed in the midbrain of SHR and Wistar-Kyoto (WKY) with the NK(3) receptor ligand [(125)I]-HPP-Senktide. 2. Tachycardia was elicited by the NK(1) ([Sar(9),Met(O(2))(11)]SP) and NK(2) ([betaAla(8)]NKA(4-10)) agonists at 25 and 100 pmol while the NK(3) agonist (senktide, 50 and 100 pmol) had no significant effect. The three agonists had no effect on behaviour, and increases in MAP were elicited by the NK(1) agonist only. 3. Whereas antagonists at NK(1) (RP 67580, 500 pmol) and NK(2) (SR 48968, 500 pmol) receptors had no significant effect on MAP and HR, the NK(3) antagonist (R-820, 500 pmol) reduced MAP for over 3 h in SHR. That anti-hypertensive effect did not occur after intracerebroventricular or intravenous injection of R-820. Also, R-820 had no cardiovascular effect in WKY. 4. The affinity (K(D): 0.7 nM) and densities of specific NK(3) receptor binding sites measured in the substantia nigra, ventral tegmental area, hippocampus and amygdala were not significantly different in SHR and WKY. 5. It is concluded that endogenous tachykinins exert a tonic activity on NK(3) receptors in the substantia nigra of SHR to maintain high blood pressure. Hence, nigral tachykinin NK(3) receptors may represent a promising therapeutic target in the treatment of arterial hypertension.

Developmental pattern of tachykinins during aging in several organs: effect of exogenous melatonin

Mammalian neurokinin A (NKA) and substance P (SP) are neuropeptides widely distributed in the body; they are potential regulators of the basal blood flow and therefore of the function of many organs and tissues. In the present investigation, we studied the age-dependent changes in NKA and SP in ovary, liver, pancreas and spleen as well as the role of exogenous melatonin on these changes. Female rats of 5, 15 or 25 months of age were studied. In the ovary, NKA concentrations did not change during aging. SP concentrations in the control group were significantly higher (P<0.01) in old rats than in the other two age groups studied. Melatonin treatment resulted in reduced concentrations as compared with those of the control old rats. In the pancreas, NKA and SP concentrations increased during aging, the young rats showing significantly lower values (P<0.01) than middle-aged and old rats for NKA and significantly lower (P<0.01) than the old rats for SP. After melatonin treatment the differences in NKA concentrations disappeared and SP decreased in middle-aged as compared with those in old rats. In the liver, NKA and SP concentrations in the control and melatonin-treated groups did not differ significantly for the three age groups studied. Splenic NKA in control and melatonin-treated groups increased from young to middle-age up to old ages. SP concentrations showed similar values at all ages except in melatonin-treated old rats; in these animals there were significantly higher concentrations than in young melatonin-treated rats. The effect of melatonin was mainly observed on the ovary and pancreas in old rats, with a reduction in the concentrations as compared with those observed in the young groups.

Role of supraspinal serotonin receptors for micturition in normal conscious rats

Serotonin (5-HT) receptors are widely distributed in the central nervous system, including several areas involved in the control of micturition reflex pathways. However, the roles of the different subtypes of 5-HT receptors are not well known. We studied in normal, conscious rats, the effects on the cystometrogram of intracerebroventricular (i.c.v.) administration of 5-HT, 8-hydroxy-2-(di-N-propylaminotetralin) (8-OH-DPAT; agonist at 5-HT(1A) receptors), alpha-methyl-5-hydroxytryptamine maleate (agonist at 5-HT(2) receptors), 2-methyl-5-hydroxytryptamine hydrochloride (agonist at 5-HT(3) receptors), and 1-(4-amino-5-chloro-2methoxyphenyl)-3-(1-n-butyl-4piperidinyl)-1-propanone hydrochloride (RS67506; agonist at 5-HT(4) receptors). Female Sprague-Dawley rats, weighing approximately 230 g, were used. A polyethylene catheter was inserted into the bladder through the dome for cystometric investigations. For administration of drugs, a catheter was implanted into the right cerebral ventricle. Three days after implantation of the bladder catheter, continuous cystometry was performed. Administration of 5-HT (6 nmol/kg i.c.v.), 8-OH-DPAT (6 nmol/kg), alpha-methyl-5-hydroxytryptamine maleate (6 nmol/kg), or RS67506 hydrochloride (6 nmol/kg) significantly (P < 0.05) increased micturition pressure and decreased bladder capacity and micturition volume. The effects increased in a dose-dependent manner (18, 60 nmol/kg). Intracerebroventricular administration of 2-methyl-5-hydroxytryptamine hydrochloride (60 nmol/kg) caused no change in the cystometric parameters. The results suggest that in normal conscious rats, at the supraspinal level, 5-HT (via 5-HT(1A), 5-HT(2), and 5-HT(4) receptors) can enhance the micturition reflex induced by bladder filling. Whether this means that 5-HT(1A), 5-HT(2), and 5-HT(4) receptors can be targets for drugs meant for treatment of bladder hyperactivity, should be explored.

Ophidian envenomation strategies and the role of purines

Snake envenomation employs three well integrated strategies: prey immobilization via hypotension, prey immobilization via paralysis, and prey digestion. Purines (adenosine, guanosine and inosine) evidently play a central role in the envenomation strategies of most advanced snakes. Purines constitute the perfect multifunctional toxins, participating simultaneously in all three envenomation strategies. Because they are endogenous regulatory compounds in all vertebrates, it is impossible for any prey organism to develop resistance to them. Purine generation from endogenous precursors in the prey explains the presence of many hitherto unexplained enzyme activities in snake venoms: 5'-nucleotidase, endonucleases (including ribonuclease), phosphodiesterase, ATPase, ADPase, phosphomonoesterase, and NADase. Phospholipases A(2), cytotoxins, myotoxins, and heparinase also participate in purine liberation, in addition to their better known functions. Adenosine contributes to prey immobilization by activation of neuronal adenosine A(1) receptors, suppressing acetylcholine release from motor neurons and excitatory neurotransmitters from central sites. It also exacerbates venom-induced hypotension by activating A(2) receptors in the vasculature. Adenosine and inosine both activate mast cell A(3) receptors, liberating vasoactive substances and increasing vascular permeability. Guanosine probably contributes to hypotension, by augmenting vascular endothelial cGMP levels via an unknown mechanism. Novel functions are suggested for toxins that act upon blood coagulation factors, including nitric oxide production, using the prey's carboxypeptidases. Leucine aminopeptidase may link venom hemorrhagic metalloproteases and endogenous chymotrypsin-like proteases with venom L-amino acid oxidase (LAO), accelerating the latter. The primary function of LAO is probably to promote prey hypotension by activating soluble guanylate cyclase in the presence of superoxide dismutase. LAO's apoptotic activity, too slow to be relevant to prey capture, is undoubtedly secondary and probably serves principally a digestive function. It is concluded that the principal function of L-type Ca(2+) channel antagonists and muscarinic toxins, in Dendroaspis venoms, and acetylcholinesterase in other elapid venoms, is to promote hypotension. Venom dipeptidyl peptidase IV-like enzymes probably also contribute to hypotension by destroying vasoconstrictive peptides such as Peptide YY, neuropeptide Y and substance P. Purines apparently bind to other toxins which then serve as molecular chaperones to deposit the bound purines at specific subsets of purine receptors. The assignment of pharmacological activities such as transient neurotransmitter suppression, histamine release and antinociception, to a variety of proteinaceous toxins, is probably erroneous. Such effects are probably due instead to purines bound to these toxins, and/or to free venom purines.

Modulation of cardiac activity by tachykinins in the rat substantia nigra

1. The effects of tachykinin NK(1), NK(2) and NK(3) receptor agonists and antagonists were measured on blood pressure (MAP) and heart rate (HR) after bilateral microinjection into the substantia nigra (SN) of awake, unrestrained rats. 2. Increasing doses (25 pmol - 1 nmol) of selective agonists at NK(1) ([Sar(9),Met(O(2))(11)]SP), NK(2) ([beta-Ala(8)]NKA(4 - 10)) and NK(3) (senktide) receptors into the SN produced tachycardia which was selectively and reversibly blocked by the prior injection of tachykinin antagonists at NK(1) (RP67580, 250 pmol), NK(2) (SR48968, 250 pmol) and NK(3) (R-820, 500 pmol) receptor. A rapid fall in MAP followed by a pressor response was seen with 1 nmol of [Sar(9),Met(O(2))(11)]SP. Behavioural activity was elicited by 1 nmol of [Sar(9),Met(O(2)(11)]SP (sniffing > face washing = grooming) and senktide (sniffing > wet dog shake > rearing = locomotion). Tachykinin antagonists had no direct cardiovascular or behavioural effects. 3. The tachycardia produced by 100 pmol of [beta-Ala(8)]NKA(4 - 10) or senktide was abolished by an i.v. treatment with atenolol (beta(1)-adrenoceptor antagonist, 5 mg kg(-1)) while that evoked by [Sar(9),Met(O(2))(11)]SP was reduced. A combination of atenolol (5 mg kg(-1)) and atropine (muscarinic antagonist, 1 mg kg(-1)) blocked the response evoked by [Sar(9),Met(O(2))(11)]SP. 4. These data suggest that the SN is a potential site of modulation of cardiac activity by tachykinins. In addition to the withdrawal of the cardiovagal activity by NK(1) receptor, the three tachykinin receptors appear to increase the sympatho/adrenal drive to the heart. This occurs independently of changes in MAP and behaviour. Hence, this study highlights a new central regulatory mechanism of cardiac autonomic activity.

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.

C-FOS expression in the rat brain in response to substance P and neurokinin B

Substance P, the principal neurokinin peptide in the mammalian brain and the natural ligand for the NK(1) tachykinin receptor, plays an integrative role in the regulation of cardiovascular, neuroendocrine and behavioural responses to stress. In rats, stimulation of periventricular NK(1) receptors in the forebrain induces a distinct pattern of cardiovascular responses which is accompanied by intense grooming behaviour. Ligands for NK(3) receptors induce a different pattern of cardiovascular and behavioural responses which comprises an increased release of vasopressin from the posterior pituitary and wet-dog shakes behaviour. To define the brain areas in the rat which respond to stimulation of forebrain NK(1) and NK(3) receptors and participate in the generation of these responses, the induction of c-Fos immunoreactivity was examined in brains following intracerebroventricular injections of substance P and neurokinin B in conscious rats. Stimulation of central NK(1) receptors by substance P (25, 100 and 500 pmol) injected into the lateral ventricle elicited grooming behaviour (face washing and hind limb grooming) and resulted in a marked c-Fos expression in the paraventricular, dorsomedial and parabrachial nuclei and in the medial thalamus. At 25 pmol, substance P did not significantly increase c-Fos expression, at 100 pmol, maximal c-Fos activation was induced in all four brain regions which responded to the peptide. Intracerebroventricular pretreatment of rats with the selective and high-affinity, non-peptide NK(1) receptor antagonist, RP 67580 (500 pmol), but not with its inactive enantiomer, RP 68651, completely abolished the behavioural response to substance P and reduced the substance P-induced c-Fos expression in all brain areas to nearly control levels. Intracerebroventricular injection of the natural ligand for NK(3) receptors, neurokinin B (500 pmol), elicited wet-dog shakes behaviour and activated c-Fos expression in localized regions of the forebrain including the organum vasculosum laminae terminalis, subfornical organ, median preoptic nucleus, paraventricular, supraoptic and anterior hypothalamic nuclei, medial thalamus and in the ventral tegmental area. These results demonstrate that the neurokinins, substance P and neurokinin B, induce specific and different patterns of c-Fos expression in distinct regions of the rat brain. Brain areas which selectively responded to substance P have been traditionally linked to the central regulation of cardiovascular and neuroendocrine reactions to stress or involved in the processing of nociceptive responses. On the other side, brain areas activated by neurokinin B are known to be involved in the central regulation of blood pressure, water and salt homeostasis or control of behaviour.

Respiratory actions of tachykinins in the nucleus of the solitary tract: characterization of receptors using selective agonists and antagonists

1. The respiratory response to microinjection of tachykinins and analogues into the commissural nucleus of the solitary tract (cNTS) of urethane-anaesthetized rats was investigated in the presence and absence of selective tachykinin NK(1), NK(2) and NK(3) antagonists (RP 67580, SR 48968 and SR 142801, respectively). 2. All tachykinins, except for the selective NK(2) agonist, [Nle(10)]-NKA(4-10), increased tidal volume (VT). The rank potency order of naturally-occurring tachykinins was neurokinin A (NKA)> or =substance P (SP)>>NKB, whereas the rank order for selective analogues was senktide> or = septide>> [Sar(9),Met(O(2))(11)]-SP>>[Nle(10)]-NKA(4-10). Septide (NK(1)-selective) and senktide (NK(3)-selective) were 22 fold more potent (pD(2) approximately 12) at stimulating VT than SP (pD(2) approximately 10.5). 3. Tachykinin agonists produced varying degrees of respiratory slowing, independent of changes in VT. At doses producing maximum stimulation of VT, agonists induced either a mild (<10 breaths min(-1) decrease; SP and septide), moderate (10 - 25 breaths min(-1) decrease; NKA, NKB and [Sar(9),Met(O(2)]-SP) or severe ( approximately 40 breaths min(-1) decrease; senktide) bradypnoea. [Nle(10)]-NKA(4-10) produced a dose-dependent bradypnoea without affecting VT. 4. RP 67580 significantly attenuated the VT response to SP (33 pmol) and NKA (10 pmol) but not NKB (100 pmol). In the presence of RP 67580, the mild bradypnoeic response to NKB was significantly enhanced whereas SP and NKA induced a bradyapnea which was not observed in the absence of RP 67580. SR 48968 had no effect on the VT response to SP or NKB, markedly enhanced the VT response to NKA and completely blocked the bradypnoeic response to [Nle(10)]-NKA(4-10). Only SR142801 attenuated the VT response to NKB. 5. The present data suggest that all three tachykinin receptors (NK(1), NK(2) and NK(3)) are present in the cNTS and are involved in the central control of respiration.

The involvement of tachykinin NK2 and NK3 receptors in central sensitization of a spinal withdrawal reflex in the decerebrated, spinalized rabbit

Repetitive electrical stimulation of the sural nerve at a strength sufficient to excite C-fibres results in prolonged (> 20 min) increases in the reflex responses of gastrocnemius motoneurones evoked by stimulation of myelinated axons in the sural nerve. We have tested the susceptibility of this effect to blockade of tachykinin NK2 and NK1 receptors. In the control state, iterative stimulation of sural nerve C fibres increased gastrocnemius reflexes to a peak of between 200 and 400% of pre-stimulus levels, an effect that recovered to baseline values over 23-30 min. Pre-treatment with selective antagonists for NK2 (SR 48968, 1 mg/kg i.v.) or NK3 (SR 142801, 0.1 and 1 mg/kg i.v.) receptors failed to alter the peak facilitation resulting from sural nerve stimulation. However, both drugs significantly reduced the duration of enhancement of reflexes, to 18 min after SR 48968 and to 5 min after SR 142801. The inactive enantiomers of these compounds (SR 48965 and SR 142806, both 1 mg/kg i.v.) did not reduce facilitation of reflexes after sural nerve stimulation. We conclude that activation of tachykinin NK3 receptors is a major factor in maintaining central sensitization of the sural-gastrocnemius reflex after electrical stimulation of sural nerve C-fibres. The effects of SR 48968 were surprisingly weak and may have resulted from an effect of this compound at NK3 receptors.

Stress-induced C-fos expression in the rat locus coeruleus is dependent on neurokinin 1 receptor activation

These experiments examined the role of substance P-selective neurokinin 1 receptors in the restraint-induced activation of the rat locus coeruleus. Immunohistochemistry revealed high levels of neurokinin 1 receptor expression in the plasma membrane of tyrosine hydroxylase-positive locus coeruleus neurons. The selective neurokinin 1 receptor antagonists, RP 67580 (5 nmol) and L-760,735 (3.4 nmol), were administered intracerebroventricularly prior to restraint stress, and c-fos protein was measured as an index of locus coeruleus activation. Both antagonists attenuated the restraint-induced increase in locus coeruleus c-fos expression, whereas their inactive enantiomers were ineffective. These results suggest that neurokinin 1 receptors may mediate activation of locus coeruleus neurons during stress. Neurokinin 1 receptor antagonists may prove to be novel therapeutic compounds in the treatment of anxiety and depression.

Role of supraspinal tachykinins for volume- and L-dopa-induced bladder activity in normal conscious rats

To clarify the roles of tachykinins in volume-induced micturition and in bladder hyperactivity, presumed to originate from supraspinal structures, normal, female Sprague-Dawley rats were investigated cystometrically before and after intracerebroventricular (i.c.v) administration of RP 67,580, a selective antagonist of NK-1 receptors, and/or SR 48,968, a selective antagonist of NK-2 receptors. The effects of RP 67,580 and SR 48,968 on intra-peritoneal (i.p.) L-dopa-induced bladder hyperactivity were also investigated. I.c.v. administration of RP 67,580 (20 nmol) SR 48,968 (20 nmol) suppressed micturition. Combination of i.c.v. RP 67, 580 (2 nmol) and SR 48,968 (2 nmol) significantly decreased micturition pressure (18%), and increased bladder capacity (26%), micturition volume (18%), and residual volume (223%). In rats pretreated with i.p. carbidopa 50 mg/kg, i.p. L-dopa 50 mg/kg caused bladder hyperactivity that was attenuated by the combination of i.c. v. RP 67,580 (2 nmol) and SR 48,968 (2 nmol). The results suggest that tachykinins, via stimulation of NK receptors in supraspinal structures, are involved in both volume and L-dopa-induced stimulation of bladder activity. This may imply that tachykinins can influence both the supraspinal and spinal control of the urinary bladder. It also implies that supraspinal NK receptors are a possible target for drugs aimed for elimination of bladder hyperactivity mediated via these pathways. Neurourol. Urodynam. 19:101-109, 2000.

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.

Age and species-dependent differences in the neurokinin B system in rat and human brain

Neurokinin B and its cognate neurokinin-3 receptor are expressed more in the forebrain than in brain stem structures but little is known about the primary function of this peptide system in the central processing of information. In general, few studies have specifically addressed age-related changes of tachykinins, notably the changes in number and/or distribution of the neurokinin B-expressing and neurokinin-3 receptor-bearing neurons. Data on functions and changes of neurokinins in physiological aging are limited and apply mainly to the substance P/neurokinin-1 receptor system. In the present study, we analyzed neurokinin B/neurokinin-3 receptor system in young (5 months) versus middle aged (15 months) and old rats (23-25 months) and also in aging human brains. For the majority of the immunohistochemically examined regions of the rat brain, there was no statistically significant change in neuronal number and size of the neurokinin B and neurokinin-3 receptor staining. In the adult human brain, there was no age-associated change of the number or size of neurokinin-B-positive neurons. However, we found a major decline in number of neurokinin-3 receptor-expressing neurons between young/middle aged (30 years to 69 years) versus old (70 years and older) adults. Interestingly, numbers of neurokinin-3 receptor-positive microglia increased whereas the neurokinin-3 receptor-positive astrocytes remained unchanged in both aging rat and human brains. Finally, in addition to assessing the morphological and quantitative changes of the neurokinin B/neurokinin-3 receptor system in the rat and human brain, we discuss functional implications of the observed interspecies differences.

Further evidence that central tachykinin NK-1 receptors mediate the inhibitory effect of tachykinins on angiotensin-induced drinking in rats

The order of potency of tachykinin (TK) receptor agonists suggests that TK NK-1 receptors mediate their inhibitory effect on water intake induced by intracerebroventricular (i.c.v.) injection of angiotensin II (AngII) in rats. The present study was aimed at further evaluating which TK receptor subtype mediates the effect, using selective antagonists for the TK receptor subtypes. Pulse i.c.v. injection of the TK agonist neuropeptide gamma (NP gamma), 31-250 ng/rat, markedly inhibited AngII-induced water intake. The i.c.v. injection of the NK-1 receptor antagonist SR14033, 0.5 microgram/rat, significantly reduced, while 1 microgram/rat completely abolished the inhibitory effect of NP gamma, 125 ng/rat. The selective NK-2 receptor antagonist SR48968 and the selective NK-3 receptor antagonist R820 were devoid of any effect up to the i.c.v. dose of 2 micrograms/rat. On the other hand, i.c.v. injection of SR140333, 1 microgram/rat, did not increase drinking induced by i.c.v. injection of AngII, 0.1-10 ng/rat, and did not increase drinking in water sated or water deprived rats. The results of the present study confirm that central TKergic mechanisms inhibit AngII-induced drinking in rats, and provide further evidence that TK NK-1 receptors mediate the effect. Failure of i.c.v. injected SR 140333 to increase AngII-induced drinking, as well as water intake in sated or deprived rats suggests that brain NK-1 receptor mechanisms apparently do not exert a tonic control on AngII-induced drinking and, in general, on water intake in rats. From a pharmacological point of view, the inhibitory effect of TKs on the dipsogenic action of AngII can represent a functional test for activity at central NK-1 receptors in rats.

In vitro and in vivo characterization of NK3 receptors in the rabbit eye by use of selective non-peptide NK3 receptor antagonists

1. Inhibition of NK3 receptor agonist-induced contraction in the rabbit isolated iris sphincter muscle was used to assess the in vitro functional activity of three 2-phenyl-4-quinolinecarboxamides, members of a novel class of potent and selective non-peptide NK3 receptor antagonists. In addition, an in vivo correlate of this in vitro response, namely NK3 receptor agonist-induced miosis in conscious rabbits, was characterized with some of these antagonists. 2. In vitro senktide (succinyl-[Asp9,MePhe8]-substance P (6-11) and [MePhe7]-neurokinin B ([MePhe7]-NKB) were potent contractile agents in the rabbit iris sphincter muscle but exhibited quite different profiles. Senktide produced monophasic log concentration-effect curves with a mean pD2=9.03+/-0.06 and mean nH=1.2+/-0.02 (n=14). In contrast, [MePhe7]-NKB produced shallow log concentration-effect curves which often appeared biphasic (nH=0.54+/-0.04, n=8), preventing the accurate determination of pD2 values. 3. The contractile responses to the NK3 receptor agonist senktide were antagonized in a surmountable and concentration-dependent manner by SB 223412 ((-)-(S)-N-(alpha-ethylbenzyl)-3-hydroxy-2-phenylquinoline-4-ca rboxamide; 3-30 nM, pA2=8.4, slope=1.8+/-0.3, n=4). SB 222200 ((-)-(S)-N-(alpha-ethylbenzyl)-3-methyl-2-phenylquinoline-4-car box amide; 30-300 nM, pA2=7.9, slope=1.4+/-0.06, n=4) and SB 218795 ((-)-(R)-N-(alpha-methoxycarbonylbenzyl)-2-phenylquinoline-4-carboxamide; 0.3 and 3 microM apparent pKB=7.4+/-0.06, n=6). 4. Contractile responses to the NK3 receptor agonist [MePhe7]-NKB in the rabbit iris sphincter muscle were unaffected by SB 218795 (0.3 and 3 microM, n=8). In contrast, SB 223412 (30 and 300 microM n=4) and SB 222200 (0.3 and 3 microM, n=4) inhibited responses to low concentrations (< or = 1 nM), to a greater extent than higher concentrations (> 1 nM) of [MePhe7]-NKB. Furthermore, log concentration-effect curves to [MePhe7]-NKB became steeper and monophasic in the presence of each antagonist. 5. SB 218795 (3 microM, n=4) had no effect on contractions induced by transmural nerve stimulation (2 Hz) or substance P, exemplifying the selectivity of this class of antagonist for functional NK3 receptors over NK1 receptors in the rabbit. 6. In vivo, senktide (1, 10 and 25 microg i.v., i.e. 1.2, 11.9 and 29.7 nmol, respectively) induced concentration-dependent bilateral miosis in conscious rabbits (maximum pupillary constriction=4.25+/-0.25 mm; basal pupillary diameter 7.75+/-0.48 mm; n=4). The onset of miosis was within 2-5 min of application of senktide and responses lasted up to 30 min. Responses to two i.v. administrations of 25 microg senktide given 30 min apart revealed no evidence of tachyphylaxis. Topical administration of atropine (1%) to the eye enhanced pupillary responses to 25 microg senktide. This was probably due to the mydriatic effect of atropine since it significantly increased baseline pupillary diameter from 7.0+/-0.4 mm to 9.0+/-0.7 mm (n=4), thereby increasing the maximum capacity for miosis. Senktide-induced miosis was inhibited by SB 222200 (1 and 2 mg kg[-1], i.v., i.e. 2.63 and 5.26 micromol kg[-1]; maximum inhibition 100%; n=3-4), SB 223412 (0.5 and 1 mg kg[-1], i.v., i.e. 1.31 and 2.61 micromol kg[-1]; maximum inhibition 100%; n=3), SB 218795 (0.5 and 1 mg kg[-1] i.v., i.e. 1.26 and 2.52 micromol kg-1; maximum inhibition 78%; n=3), and the structurally distinct NK3 receptor antagonist SR 142801 ((S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)propyl)-4-phenylepipiperidin-4-yl)-N-methylacetamide; 1.5mg kg-1, i.v., i.e. 2.47micromol kg-1, maximum inhibition 92%; n=3). 7. Topical administration of senktide (25microg; 29.7nmol) to the eye induced unilateral miosis in the treated eye only. At this dose there was no significant difference (P<0.05) between pupillary constriction obtained by topical or i.v. senktide, and topically administered atropine had no significant effect on responses to topical senktide (n=4). 8. [MePhe7]-NKB (125, 250 and 500microg, i.v., i.e. 98.31, 196.62 and 393.24nmol, respectively) also induced bilateral miosis in conscious rabbits (maximum pupillary constriction=4.13+/-0.30mm; n=4), but in contrast to in vitro studies this agonist was approximately 100 fold less potent than senktide. [MePhe7]-NKB-induced miosis was inhibited by SB 222200 (5mg kg-1, i.v., i.e. 13.14micromol kg-1; maximum inhibition 69%; n=3). 9. In summary, SB 223412, SB 222200 and SB 218795 are potent and selective antagonists of NK3 receptor-mediated contraction in the rabbit isolated iris sphincter muscle. In addition, NK3 receptor agonist-induced miosis in conscious rabbits is a good in vivo correlate of the in vitro rabbit iris sphincter muscle preparation and appears to be a useful model for characterizing the pharmacodynamic profile and efficacy of structurally distinct NK3 receptor antagonists, such as SB 222200, SB 223412, SB 218795 and SR 142801.

Biochemical and pharmacological activities of SR 144190, a new potent non-peptide tachykinin NK2 receptor antagonist

(R)-3-(1-[2-(4-benzoyl-2-(3,4-difluorophenyl)-morpholin-2-yl)- ethyl]-4-phenylpiperidin-4-yl)-1-dimethylurea (SR 144190) is a new non-peptide antagonist of tachykinin NK2 receptors. SR 144190 potently and selectively inhibited neurokinin A binding to NK2 receptors from various species, including humans. In in vitro functional assays, it was a potent, selective and competitive antagonist of NK2 receptors with apparent affinities (pA2 values) between 9.08 and 10.10. In vivo, SR 144190 blocked [Nle10]neurokinin A-(4-10)-induced bronchoconstriction in guinea pigs (ID50 = 21 micrograms kg-1 i.v. and 250 micrograms kg-1 i.d.) and [beta Ala8]neurokinin A-(4-10)-induced urinary bladder contraction in rats (ID50 = 11 micrograms kg-1 i.v. and 190 micrograms kg-1 i.d.). It prevented citric acid-induced cough and airway hyperresponsiveness to acetylcholine in guinea pigs (1 mg kg-1 i.p.) as well as castor oil-induced diarrhoea in rats (0.01-10 micrograms kg-1 s.c. or p.o). Finally, it blocked the turning behaviour induced by intrastriatal injections of [Nle10]neurokinin A-(4-10) in mice (ID50 = 3 micrograms kg-1 i.v. and 16 micrograms kg-1 p.o.).

Cardiovascular and behavioural effects of intracerebroventricularly administered tachykinin NK3 receptor antagonists in the conscious rat

1. In the conscious rat, three tachykinin NK3 receptor antagonists, namely SR142801 ((S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)pro pyl)-4-phenylpiperidin-4-yl)-N-methylacetamide), R820 (3-indolylcarbonyl-Hyp-Phg-N(Me)-Bzl) and R486 (H-Asp-Ser-Phe-Trp-beta-Ala-Leu-Met-NH2) were assessed against the intracerebroventricular (i.c.v.) effects induced by senktide, a selective NK3 receptor agonist, on mean arterial blood pressure (MAP), heart rate (HR) and motor behaviour. 2. Senktide (10-650 pmol per animal; i.c.v; n = 4-16) at the lowest dose caused a significant fall in MAP (-10 +/- 6 mmHg), while at the highest doses (100 and 650 pmol), senktide caused a rise in MAP (9 +/- 3 and 12 +/- 1 mmHg, respectively) when compared to vehicle. The intermediate doses (25 and 65 pmol) had no effect on MAP. The highest two doses caused a tachycardia of 62 +/- 15 and 88 +/- 8 beats min(-1), respectively. The dose of 65 pmol had a biphasic effect on HR, an initial bradycardia of 47 +/- 12 beats min(-1) followed by a tachycardia of 46 +/- 14 beats min(-1). The lowest doses caused either a rise of 52 +/- 10 beats min(-1) (25 pmol) or no effect (10 pmol) on HR. All doses of senktide caused similar increases in face washing, sniffing and wet dog shakes except at the dose of 100 pmol, when wet dog shakes were more than double those observed with the other doses. 3. The antagonist SR142801 (100 pmol -65 nmol per animal; i.c.v.; n = 6-8) caused increases in MAP at the highest two doses (6.5 and 65 nmol) while HR, dose-dependently, increased (23 +/- 6 to 118 +/- 26 beats min[-1]) and the onset dose-dependently decreased. The (R)-enantiomer, SR142806 (100 pmol - 65 nmol per animal; i.c.v.; n = 6-8) only caused rises in MAP (13 +/- 2 mmHg) and HR (69 +/- 11 beats min[-1]) at the highest dose. These drugs had no apparent effect on behaviour, except for the highest dose of SR142801 which increased sniffing. The antagonist R820 (650 pmol - 6.5 nmol per animal; i.c.v.; n = 6) had no effect on MAP or HR and only increased sniffing behaviour at 6.5 nmol. At 650 pmol (n = 6), R486 had no effect on any variable, but at 3.25 nmol, i.c.v. (n = 4) a delayed tachycardia and a significant increase in all behavioural variables were observed. 4. The cardiovascular responses induced by 6.5 nmol SR142801 and 25 pmol senktide were inhibited by R820 (6.5 nmol, 5 min earlier i.c.v.). In contrast, R820 failed to affect the central cardiovascular and behavioural responses induced by 10 pmol [Sar9, Met(O2)11]substance P, a NK1 receptor selective agonist. The senktide-induced behavioural changes were not inhibited by R820 (6.5 nmol, i.c.v.) while R486 (650 pmol, i.c.v.) blocked both the cardiovascular and behavioural responses to 25 pmol senktide. A mixture of antagonists for NK1 (RP67580; 6.5 nmol) and NK2 (SR48968; 6.5 nmol) receptors injected i.c.v. did not affect the cardiovascular response to SR142801. Cross-desensitization was shown between the central responses to SR142801 and senktide, but not between SR142801 and [Sar9, Met(O2)11]substance P. 5. The antagonists SR142801 and SR142806 (6.5-650 nmol kg(-1); n = 5-7), given i.v., did not evoke any cardiovascular or behavioural changes, except a delayed bradycardia for SR142806 (650 nmol kg[-1]), and also failed to inhibit the increase in MAP evoked by senktide (4 nmol kg(-1), i.v.). However, at the highest dose, both drugs slightly reduced the senktide-induced tachycardia. 6. Although the present data are consistent with the in vitro pharmacological bioassays and binding data, showing that SR142801 is a poor antagonist at rat peripheral NK3 receptors, they suggest that SR142801 has a partial agonist action at these receptors centrally. A separation of the cardiovascular and behavioural effects mediated by central NK3 receptor activation was achieved with SR142801 and R820 but not with R486. These results could be explained by the existence of NK3 receptor subtypes in the rat or by the differential activation and inhibition of the same receptor protein linked to the production of different second messengers. Differences in the pharmacokinetic or pharmacodynamic properties of the antagonists cannot be excluded at this time.

Renal effects of intrathecally injected tachykinins in the conscious saline-loaded rat: receptor and mechanism of action

1. The effects of intrathecally (i.t.) injected substance P (SP), neurokinin A (NKA), [beta-Ala8]NKA (4-10) and [MePhe7]neurokinin B (NKB) at T13 thoracic spinal cord level were investigated on renal excretion of water, sodium and potassium in the conscious saline-loaded rat. Antagonists selective for NK1 (RP 67580), NK2 (SR 48968) and NK3 (R 820; 3-indolylcarbonyl-Hyp-Phg-N(Me)-Bzl) receptors were used to characterize the spinal effect of SP on renal function. 2. Saline gavage (4.5% of the body weight) enhanced renal excretion of water, sodium and potassium over the subsequent hour of measurement. Whereas these renal responses were not affected by 0.65 nmol SP, the dose of 6.5 nmol SP blocked the natriuretic response (aCSF value 3.9 +/- 0.8; SP value 0.7 +/- 0.3 micromol min(-1), P<0.01) as well as the renal excretion of water (aCSF value 48.9 +/- 5.8; SP value 14.5 +/- 4.0 microl min(-1), P<0.01) and potassium (aCSF value 4.8 +/- 0.6; SP value 1.5 +/- 0.6 micromol min(-1), P<0.01) at 30 min post-injection. SP had no significant effect on urinary osmolality. The SP-induced renal inhibitory effects during the first 30 min were abolished in rats subjected to bilateral renal denervation 1 week earlier or in rats injected i.t. 5 min earlier with 6.5 nmol RP 67580. In contrast, the co-injection of SR 48968 and R 820 (6.5 nmol each) did not affect the inhibitory responses to SP. On their own, these antagonists had no direct effect on renal excretion function. Since SP induced only transient changes in mean arterial blood pressure (-18.8 +/- 3.8 mmHg at 1 min and +6.3 +/- 2.4 mmHg at 5 min post-injection), it is unlikely that the renal effects of SP are due to systemic haemodynamic changes. 3. NKA (6.5 nmol but not 0.65 nmol) produced a transient drop in renal excretion of water (aCSF value 31.2 +/- 5.1; NKA value 11.3 +/- 4.2 microl min(-1), P<0.05), sodium (aCSF value 1.7 +/- 0.8; NKA value 0.4 +/- 0.2 micromol min(-1), P<0.05) and potassium (aCSF value 4.1 +/- 0.7; NKA value 1.5 +/- 0.4 micromol min(-1), P<0.05) at 15 min post-injection. However, the same doses (6.5 nmol) of selective agonists for tachykinin NK2 ([beta-Ala8]NKA(4-10)) and NK3 ([MePhe7]NKB) receptors were devoid of renal effects. 4. This study provided functional evidence that tachykinins may be involved in the renal control of water and electrolyte excretion at the level of the rat spinal cord through the activation of NK1 receptors and the sympathetic renal nerve.

Renal effects of intracerebroventricularly injected tachykinins in the conscious saline-loaded rat: receptor characterization

1. The effects of intracerebroventricularly (i.c.v.) injected substance P (SP), neurokinin A (NKA) and [MePhe7]neurokinin B (NKB) were investigated on renal excretion of water, sodium and potassium in the conscious saline-loaded rat. The central effects of [MePhe7]NKB were characterized with selective tachykinin antagonists for NK1 (RP 67580), NK2 (SR 48968) and NK3 (R 820) receptors. 2. Whereas SP or NKA (65 or 650 pmol) failed to modify the renal responses, [MePhe7]NKB (65-6500 pmol) produced dose-dependent and long-lasting (30-45 min) decreases in renal excretion of water (maximal reduction at 65 pmol: from 66.14 +/- 7.62 to 21.07 +/- 3.79 microliters min-1), sodium (maximal reduction at 65 pmol: from 10.19 +/- 2.0 to 1.75 +/- 0.48 mumol min-1) and potassium (maximal reduction at 65 pmol: from 4.31 +/- 1.38 to 0.71 +/- 0.27 mumol min-1). While 650 pmol [MePhe7]NKB elevated urinary osmolality, neither 65 pmol nor 6.5 nmol [MePhe7]NKB altered this parameter. 3. Both the antidiuresis and antinatriuresis induced by [MePhe7]NKB (65 pmol) were significantly blocked by the prior i.c.v. injection of R 820 (1.3 nmol, 5 min earlier), although the potassium excretion was only partially reduced. However, R 820 did not affect the antidiuresis and antinatriuresis elicited by endothelin-1 (1 pmol, i.c.v.). On its own, R 820 decreased renal potassium excretion with no effect on urinary osmolality and renal excretion of water and sodium. The i.c.v. co-injection of RP 67580 and SR 48968 (6.5 nmol each, 5 min earlier) failed to modify the renal responses to [MePhe7]NKB in a similar study. 4. The central effects of [MePhe7]NKB (65 pmol) on renal excretion were blocked by the prior i.v. administration of a linear peptide vasopressin V2 receptor antagonist (50 micrograms kg-1, 5 min earlier). 5. These results suggest that the central NK3 receptor, probably located in the hypothalamus, is implicated in the renal control of water and electrolyte homeostasis through the release of vasopressin in the conscious saline-loaded rat.

Effect of intrathecal pretreatment with the neurokinin receptor antagonist CP-99994 on the expression of naloxone-precipitated morphine withdrawal symptoms

In morphine-dependent rats pretreated with an intrathecal injection of saline (vehicle), intraarterial injection of 0.5 mg/kg of naloxone produced an immediate increase in blood pressure. Heart rate increased in most rats just after naloxone injection; however, the responses were transient, not lasting more than about 4 min after injection. Naloxone-precipitated behavioral changes were dominated by the appearance of body shakes and escape attempts that were strongly expressed during the first 10 min after naloxone. Pretreatment of morphine-dependent rats with an intrathecal injection of 100 nmol of the neurokinin-1 receptor antagonist CP-99994 significantly inhibited the magnitude and shortened the duration of the pressor response to naloxone. CP-99994 did ot reduce the expression of the associated withdrawal behaviors. Substance P significantly reversed the inhibitory effects of CP-99994 on the expression of the withdrawal-associated pressor response. Intrathecal pretreatment with CP-99994 also produced a dose-dependent inhibition of the expression of the pressor response to local spinal (intrathecal) injection of naloxone (60 micrograms) in morphine dependent rats without significant alteration of the expression of withdrawal-associated behaviors. These results indicate that spinal neurokinin-1 receptors mediate some of the cardiovascular signs of morphine withdrawal and suggest the possibility of developing a novel class of antiopiate withdrawal agents.

Effects of central administration of tachykinin receptor agonists and antagonists on plus-maze behavior in mice

This study assessed the effects of intracerebroventricular administration of selective agonists and antagonists for tachykinin NK1 and NK2 receptors on performance of mice in the elevated plus-maze, an ethological model of anxiety. Mice were treated with either vehicle (5 microliters) or 1, 10, 100 or 500 pmol of substance P, neurokinin A, the selective NK1 receptor agonist substance P methyl ester, or the selective NK2 receptor agonist, [beta-Ala8]neurokinin A-(4-10). Other mice received similar doses of FK 888, i.e., N2-[(4R)-4-hydroxy-1-(1-methyl-1 H-indol-3-y)carbonyl-L-prolyl]-N-methyl-N-phenylmethyl-3-(2-naphthyl)-L- alaninamide, or SR 48968, i.e., (S)-N-methyl-(N-[4-acetylamine-4-phenylpiperidine)-2-(3, 4-dichlorophenyl)buthyl]benzamide, selective antagonists of tachykinin NK1 and NK2 receptors, respectively. Injections of substance P, neurokinin A, substance P methyl ester or [beta-Ala8]neurokinin A-(4-10) significantly reduced the frequency of open arm entries, and [beta-Ala8]neurokinin A-(4-10) also enhanced the percentage of entries into enclosed arms. Conversely, the NK1 antagonist FK 888 and the NK2 antagonist SR 48968 each increased the time spent in the open arms, and SR 48968 also increased the frequency of entries into the open arms. None of the tachykinin receptor agonists or antagonists modified motor performance and coordination on the rotarod apparatus or ambulation in an activity cage. Together, these results suggest that centrally administered NK1 and NK2 receptor agonists and antagonists can modulate anxiety, as evaluated in the elevated plus-maze test in mice. Stimulation of either tachykinin NK1 or NK2 receptors induces anxiogenic-like responses, whereas the reverse occurs following their blockade. The anxiolytic-like profiles of action of both tachykinin NK1 and NK2 receptor antagonists suggest that central tachykinin mechanisms are tonically involved in the modulation of anxiety.

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.

Cardiovascular responses to intrathecal neuropeptide gamma in conscious rats: receptor characterization and mechanism of action

1. In the conscious rat, cardiovascular responses to intrathecally (i.t.) administered neuropeptide gamma (NP gamma) were studied prior to and after the i.t. pretreatment with selective antagonists at NK1 ((+/-)-CP 96345 and RP 67580), NK2 (SR 48968) and NK3 (R 486) receptors. Pretreatment with a mixture of peptidase inhibitors (phosphoramidon, captopril, bacitracin, phenanthroline) was also tested to ascertain whether or not the effect of NP gamma was mediated by a metabolite. The involvement of peripheral catecholamines was examined with intravenous injection of alpha-adrenoceptor (phentolamine) and beta-adrenoceptor (propranolol) antagonists. 2. NP gamma (0.078-78 nmol) induced dose-dependent increases in heart rate (HR) and mean arterial blood pressure (MAP). The highest dose of 78 nmol did not induce an increase of MAP greater than that with 7.8 nmol but was preceded by a transient decrease of MAP (1-3 min). No desensitization was observed when three injections of 7.8 nmol NP gamma were given at 90 min intervals. 3. Cardiovascular and behavioural (biting/scratching) effects evoked by 0.78 nmol NP gamma were significantly reduced by the NK1 antagonists, (+/-)-CP 96345 (65 nmol) or RP 67580 (7.8 and 78 nmol). However, cardiovascular responses to NP gamma were not affected by (+/-)-CP 96345 (6.5 nmol), SR 48968 (7.8 and 78 nmol) or R 486 (25 nmol). Pretreatment with peptidase inhibitors significantly enhanced the cardiovascular and behavioural responses to NP gamma. 4. The pressor response to 7.8 nmol NP gamma was converted to a vasodepressor response by pretreatment with phentolamine (2 mg kg-1, i.v.) while the chronotropic response was markedly reduced by propranolol (2 mg kg-1, i.v.). 5. These results suggest that the cardiovascular responses to i.t. NP gamma are mediated by NK1 receptors in the spinal cord leading to the peripheral release of catecholamines from sympathetic fibres or the adrenal medulla. It is unlikely that the spinal action of NP gamma results from its metabolic conversion into neurokinin A or another major metabolite.

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 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.

Functional interaction between losartan and central tachykinin NK3 receptors in the conscious rat

1. The cardiovascular and behavioural effects elicted by the intracerebroventricular (i.c.v.) injection of substance P (SP), neurokinin A (NKA), [MePhe7]neurokinin B ([MePhe7]NKB) or angiotensin II (AII) in the conscious rat were assessed before and 5 min after i.c.v. pretreatment with antagonists selective for angiotensin AT1 (losartan and its active metabolite EXP 3174), angiotensin AT2 (PD 123,319) or tachykinin NK3 (R 486) receptors. 2. I.c.v. administration of 25 pmol AII evoked an increase in mean arterial blood pressure (MAP) and water intake behaviour, accompanied by a transient bradycardia, whereas 25 pmol [MePhe7]NKB caused a transient increase in MAP and heart rate (HR) concurrently with marked wet dog shake behaviour. At the same dose, SP and NKA were more potent than [MePhe7]NKB in increasing MAP and HR, but did not produce water intake or wet dog shake behaviours. 3. Losartan (650 pmol, i.c.v.) reduced significantly the cardiovascular and behavioural responses to AII or [MePhe7]NKB, but not to SP or NKA. While 65 pmol losartan was inactive, 260 pmol inhibited selectively the central effects of AII. Whereas EXP 3174 (6.5 nmol) blocked both AII and [MePhe7]NKB-mediated responses, the dose of 650 pmol blocked only the responses to AII. 4. The central responses to AII and [MePhe7]NKB were not affected by PD 123,319 (650 pmol). On the other hand, the [MePhe7]NKB-induced central effects were significantly reduced by R 486 (650 pmol). The NK3-selective antagonist had no effect against AII. 5. This study provides functional evidence, to support earlier binding data, that losartan (and to some extent its active metabolite EXP 3174) interact with the tachykinin NK3 receptor in rat brain. However,the cardiovascular and behavioural responses induced by central tachykinin agonists (SP, NKA and[MePhe7]NKB) and All are mediated by unrelated mechanisms.

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.