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

Neurokinin-2 receptor negatively modulates substance P responses by forming complex with Neurokinin-1 receptor

BACKGROUND

Tachykinins and their cognate receptors, neurokinin receptors (NKs) including NK1, NK2, and NK3 play vital roles in regulating various physiological processes including neurotransmission, nociception, inflammation, smooth muscle contractility, and stimulation of endocrine and exocrine gland secretion. Their abnormal expression has been reported to be associated with neurological disorders, inflammation, and cancer. Even though NKs are expressed in the same cells with their expression being inversely correlated in some conditions, there is no direct evidence to prove their interaction. Understanding the functional crosstalk between NKs in mediated downstream signaling and cellular responses may elucidate the roles of each receptor in pathophysiology.

RESULTS

In this study, we showed that NKs were co-expressed in some cells. However, different from NK3, which only forms homodimerization, we demonstrated a direct interaction between NK1 and NK2 at the protein level using co-immunoprecipitation and NanoBiT-based protein interaction analysis. Through heterodimerization, NK2 downregulated substance P-stimulated NK1 signals, such as intracellular Ca2+ mobilization and ERK phosphorylation, by enhancing β-arrestin recruitment, even at the ligand concentration that could not activate NK2 itself or in the presence of NK1 specific antagonist, aprepitant. In A549 cells with receptors deleted and reconstituted, NK2 exerted a negative effect on substance P/NK1-mediated cell migration.

CONCLUSION

Our study has provided the first direct evidence of an interaction between NK1 and NK2, which highlights the functional relevance of their heterodimerization in cellular responses. Our findings demonstrated that through dimerization, NK2 exerts negative effects on downstream signaling and cellular response mediated by NK1. Moreover, this study has significant implications for understanding the complexity of GPCR dimerization and its effect on downstream signaling and cellular responses. Given the important roles of tachykinins and NKs in pathophysiology, these insights may provide clues for developing NKs-targeting drugs.

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.

Expression and function of human hemokinin-1 in human and guinea pig airways

Background

Human hemokinin-1 (hHK-1) and endokinins are peptides of the tachykinin family encoded by the TAC4 gene. TAC4 and hHK-1 expression as well as effects of hHK-1 in the lung and airways remain however unknown and were explored in this study.

Methods

RT-PCR analysis was performed on human bronchi to assess expression of tachykinin and tachykinin receptors genes. Enzyme immunoassay was used to quantify hHK-1, and effects of hHK-1 and endokinins on contraction of human and guinea pig airways were then evaluated, as well as the role of hHK-1 on cytokines production by human lung parenchyma or bronchi explants and by lung macrophages.

Results

In human bronchi, expression of the genes that encode for hHK-1, tachykinin NK₁-and NK₂-receptors was demonstrated. hHK-1 protein was found in supernatants from explants of human bronchi, lung parenchyma and lung macrophages. Exogenous hHK-1 caused a contractile response in human bronchi mainly through the activation of NK₂-receptors, which blockade unmasked a NK₁-receptor involvement, subject to a rapid desensitization. In the guinea pig trachea, hHK-1 caused a concentration-dependant contraction mainly mediated through the activation of NK₁-receptors. Endokinin A/B exerted similar effects to hHK-1 on both human bronchi and guinea pig trachea, whereas endokinins C and D were inactive. hHK-1 had no impact on the production of cytokines by explants of human bronchi or lung parenchyma, or by human lung macrophages.

Conclusions

We demonstrate endogenous expression of TAC4 in human bronchi, the encoded peptide hHK-1 being expressed and involved in contraction of human and guinea pig airways.

Psychosocial stress and liver disease status

"Psychosocial stress" is an increasingly common concept in the challenging and highly-demanding modern society of today. Organic response to stress implicates two major components of the stress system, namely the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Stress is anamnestically reported by patients during the course of disease, usually accompanied by a decline in their overall health status. As the mechanisms involving glucocorticoids and catecholamines have been deciphered, and their actions on immune cell function deeper understood, it has become clear that stress has an impact on hepatic inflammatory response. An increasing number of articles have approached the link between psychosocial stress and the negative evolution of hepatic diseases. This article reviews a number of studies on both human populations and animal models performed in recent years, all linking stress, mainly of psychosocial nature, and the evolution of three important liver-related pathological entities: viral hepatitis, cirrhosis and hepatocellular carcinoma.

Stress, visceral obesity, and metabolic complications

Stress is a state of threatened homeostasis or disharmony caused by intrinsic or extrinsic adverse forces and is counteracted by an intricate repertoire of physiologic and behavioral responses that aim to reestablish the challenged body equilibrium. The adaptive stress response depends upon an elaborate neuroendocrine, cellular, and molecular infrastructure, the stress system. Crucial functions of the stress system response are mediated by the hypothalamic-pituitary-adrenal (HPA) axis and the central and peripheral components of the autonomic nervous system (ANS). The integrity of the HPA axis and the ANS and their precise interactions with other CNS components are essential for a successful response to the various stressors. Chronic stress represents a prolonged threat to homeostasis by persistent or frequently repeated stressors and may lead to manifestations that characterize a wide range of diseases and syndromes. Such states progressively lead to a deleterious overload with complications caused by both the persistent stressor and the detrimental prolongation of the adaptive response. The metabolic syndrome can be described as a state of deranged metabolic homeostasis characterized by the combination of central obesity, insulin resistance, dyslipidemia, and hypertension. The incidence of both obesity and the metabolic syndrome in modern Western societies has taken epidemic proportions over the past decades and often correlates with indices of stress in the affected populations. Stress, primarily through hyperactivation of the HPA axis, appears to contribute to the accumulation of fat tissue, and vice versa, obesity itself seems to constitute a chronic stressful state and may cause HPA axis dysfunction. In addition, the description of obesity as a systemic low grade inflammatory condition that contributes to the derangement of the metabolic equilibrium implies that the proinflammatory cytokines which are secreted by the adipocytes hold a potentially important pathogenetic role. In this article we describe the physiology of the stress system response, with emphasis on metabolism, and review the recent data that implicate several neuroendocrine and inflammatory mechanisms mobilized during chronic stress in the development of the metabolic complications that characterize central obesity and the metabolic syndrome.

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.

Characterization of tachykinin receptors in the uterus of the oestrogen-primed rat

1 The aim of our study was to characterize the tachykinin receptor population in the oestrogen-primed rat uterus. For this purpose, we investigated the receptor type(s) responsible for tachykinin-induced contraction of longitudinally-arranged smooth muscle layer. The effects of substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and several of their analogues with well-defined selectivities for tachykinin NK1, NK2 and NK3 receptors were studied and their inhibition by the selective nonpeptide tachykinin receptor antagonists (S)1-(2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)pip eridin-3-yl]ethyl)-4-phenyl- -azoniabicyclo[2.2.2]octane chloride (SR 140333, NK1-selective), (S)-N-methyl-N[4-(4acetylamino-4-phenylpiperidino)-2-(3,4-dichloro phenyl)butyl]benzamide (SR 48968, NK2-selective) and (R)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)prop yl)-4-phenylpiperidin-4-yl)-N- methyla-cetamide (SR 142801, NK3-selective) was evaluated. Additionally, expression of tachykinin receptor mRNA was examined by using the reverse transcription-polymerase chain reaction (RT-PCR). 2 SP, NKA, [Nle10]-NKA(4-10), the analogue with selectivity at the tachykinin NK2 receptor type, and NKB elicited concentration-dependent contractions of the rat uterus. The pD2 values were 5.95+/-0.19; 6.73+/-0.21; 7.53+/-0.12 and 5.76+/-0.21, respectively. The selective agonist for the tachykinin NK1 receptor [Sar9Met(O2)11]-SP produced a small phasic response in the nanomolar concentration range. The selective tachykinin NK3 receptor agonist [MePhe7]-NKB failed to induce any significant contraction. 3 In the presence of the neutral endopeptidase inhibitor phosphoramidon (1 microM), the log concentration-response curves to exogenous tachykinins and their analogues were shifted significantly leftwards. The pD2 values were 6.12+/-0.10, 8.04+/-0.07, 7.89+/-0.03 and 6.59+/-0.07 for SP, NKA, [Nle10]-NKA(4-10) and NKB, respectively. In the presence of phosphoramidon (1 microM), [Sar9Met(O2)11]-SP (1 nM - 0.3 microM) induced concentration-dependent contractions of increasing amplitude when only one concentration of drug was applied to each uterine strip and the pD2 value was 7.61+/-0.89. [MePhe7]-NKB induced small, inconsistent contractions and, therefore, a pD2 value could not be calculated. 4 In experiments performed in the presence of phosphoramidon (1 microM), SR 48968 (3 nM - 0.1 microM) caused parallel and rightward shifts in the log concentration-response curves of NKA. The calculated pKB value was 9.16+/-0.08 and the slope of the Schild regression was 1.28+/-0.24. SR 48968 (0.1 microM) also antagonized responses to SP with an apparent pKB value of 7.63+/-0.13. SR 48968 (0.1 microM) inhibited contractions elicited by NKB (1 nM - 3 microM) and [Nle10]-NKA(4-10) (0.1 nM - 3 microM) but had no effect on the response evoked by [Sar9Met(O2)11]-SP (0.1 microM). 5 SR 140333 (0.1 microM) inhibited responses to SP with an apparent pKB value of 7.19+/-0.22. This compound did not significantly affect responses to NKA, [Nle10]-NKA(4-10) and NKB, but suppressed [Sar9Met(O2)11]-SP (0.1 microM)-induced contraction. SR 142801 (0.1 microM) had no effect on responses to natural tachykinins or their analogues. 6 Total RNA was extracted from some of the uteri used in functional studies. RT-PCR assays revealed single bands corresponding to the expected product sizes encoding cDNA for tachykinin NK1 (587 base pairs) and NK2 receptors (491 base pairs) (n=6 different animals). A very low abundance transcript corresponding to the 325 base pairs product expected for the tachykinin NK3 receptor was detected. 7 The present data show that functionally active tachykinin NK1 and NK2 receptors are expressed in the oestrogen-primed rat uterus. The NK2 receptor type seems to be the most important one involved in the contractile responses elicited by tachykinins. NK3 receptors are present in trace amounts and seem not to be involved in tachykinin-induced contractions.

Stress and Critical Illness: The Integrated Immune/Hypothalamic-Pituitary-Adrenal Axis Response

Critical illness leads to a coordinated reaction that is categorized as the stress response; activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system leads to metabolic and cardiovascular changes that are generally directed toward maintenance of homeostasis. The HPA axis and the sympathetic nervous system are linked via reciprocally activating brainstem pathways. The immune system acts via cytokines, which are hormones, to activate the HPA axis. Glucocorticoid secretion suppresses immune activity, thus completing an immune-HPA feedback loop. Restraint of immune activity may be a major function of glucocorticoids during stress, thus averting the potential for immune-mediated damage to healthy tissues. Cortisol also acts to produce adaptive metabolic, cardiovascular, and cognitive changes. Activation of the stress system is also associated with inhibition of thyroid, gonadal, and growth axes through neuroendocrine and peripheral mechanisms; such effects can be seen as directed toward conservation of energy. There is growing evidence that hyperfunction and hypofunction of the integrated stress system may lead to a variety of previously unexplained disorders. Recently, a more detailed understanding of the stress system combined with astute clinical observation of critically ill patients has led to promising new avenues for therapeutic investigation.

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.

Effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and concentrations of neuropeptides in the hippocampus in WKY and SHR rats

The effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and on hippocampal concentrations of neuropeptide Y, neurokinin A, substance P, galanin and vasoactive intestinal peptide (VIP)-like immunoreactivities were studied in WKY (wistar-Kyoto) and SHR (spontaneously hypertensive) rats. Significantly higher concentrations of substance P-like immunoreactivity, neurokinin A-like immunoreactivity and neuropeptide Y-like immunoreactivity were found in the hippocampus immediately after 3 weeks of treatment (electro-acupuncture and running), but not 1 week after the last (tenth) changes in neuropeptide concentrations were similar in the two rat strains. Open-field behaviour was significantly reduced during the treatment period in both strains. There were significant negative correlations between behaviour and neuropeptide concentrations in SHR rats, suggesting interdependency with sympathetic activity. It is proposed that the effects of electro-acupuncture and physical exercise in rats are related to increases in neuropeptide Y, neurokinin A and substance P in the hippocampus.

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.

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.