Correlation of neurokinin (NK) 1 receptor occupancy in gerbil striatum with behavioral effects of NK1 antagonists

Role of the basal ganglia in innate and learned behavioural sequences

Integrating individual actions into coherent, organised behavioural units, a process called chunking, is a fundamental, evolutionarily conserved process that renders actions automatic. In vertebrates, evidence points to the basal ganglia - a complex network believed to be involved in action selection - as a key component of action sequence encoding, although the underlying mechanisms are only just beginning to be understood. Central pattern generators control many innate automatic behavioural sequences that form some of the most basic behaviours in an animal's repertoire, and in vertebrates, brainstem and spinal pattern generators are under the control of higher order structures such as the basal ganglia. Evidence suggests that the basal ganglia play a crucial role in the concatenation of simpler behaviours into more complex chunks, in the context of innate behavioural sequences such as chain grooming in rats, as well as sequences in which innate capabilities and learning interact such as birdsong, and sequences that are learned from scratch, such as lever press sequences in operant behaviour. It has been proposed that the role of the striatum, the largest input structure of the basal ganglia, might lie in selecting and allowing the relevant central pattern generators to gain access to the motor system in the correct order, while inhibiting other behaviours. As behaviours become more complex and flexible, the pattern generators seem to become more dependent on descending signals. Indeed, during learning, the striatum itself may adopt the functional characteristics of a higher order pattern generator, facilitated at the microcircuit level by striatal neuropeptides.

Blocking NK1 receptors disrupts the sequential and temporal organization of chain grooming in rats

The basal ganglia are a group of sub-cortical structures believed to play a critical role in action selection and sequencing. The striatum is the largest input structure of the basal ganglia and contains the neuropeptide substance P in abundance. Recent computational work has suggested that substance P could play a critical role in action sequence performance and acquisition, but this has not been tested experimentally before. The aim of the present study was to test how blocking substance P's main NK1-type receptors affected the sequential and temporal organization of spontaneous behavioral patterns. We did this in rats by focusing on the grooming chain, an innate and highly stereotyped ordered sequence. We performed an open field experiment in which the NK1 receptor antagonist L-733,060 was injected intraperitoneally in rats at two doses (2 and 4 mg/kg/ml), in a within-subject counterbalanced design. We used first order transition probabilities, Variable Length Markov Models, entropy metrics and T-pattern analysis to evaluate the effects of L-733,060 on sequential and temporal aspects of spontaneously ordered behavioral sequences. Our results suggest that blocking NK1 receptors made the transitions between the grooming chain elements significantly more variable, the transition structure of the grooming bouts simpler, and it increased the probability of transitioning from active to inactive states. Overall, this suggest that blocking substance P receptors led to a general break down in the fluency of spontaneous behavioral sequences, suggesting that substance P could be playing a key role in the implementation of sequential patterns.

Neurokinin-1 antagonist orvepitant for EGFRI-induced pruritus in patients with cancer: a randomised, placebo-controlled phase II trial

OBJECTIVE

To evaluate the efficacy of orvepitant (10 or 30 mg given once daily, orally for 4 weeks), a neurokinin-1 receptor antagonist, compared with placebo in reducing the intensity of epidermal growth factor receptor inhibitor (EGFRI)-induced intense pruritus.

DESIGN

Randomised, double-blind, placebo-controlled clinical trial.

SETTING

15 hospitals in Italy and five hospitals in the UK.

PARTICIPANTS

44 patients aged ≥18 years receiving an EGFRI for a histologically confirmed malignant solid tumour and experiencing moderate or intense pruritus after EGFRI treatment.

INTERVENTION

30 or 10 mg orvepitant or placebo tablets once daily for 4 weeks (randomised 1:1:1).

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary endpoint was change from baseline in mean patient-recorded numerical rating scale (NRS) score (over the last three recordings) at week 4. Secondary outcome measures were NRS score, verbal rating scale score, Skindex-16 and Leeds Sleep Evaluation Questionnaire at each study visit (baseline, weeks 1, 4, 8); rescue medication use; EGFRI dose reduction; and study withdrawal because of intense uncontrolled pruritus.

RESULTS

The trial was terminated early because of recruitment challenges; only 44 of the planned 90 patients were randomised. All patients were analysed for efficacy and safety. Mean NRS score change from baseline to week 4 was -2.78 (SD: 2.64) points in the 30 mg group, -3.04 (SD: 3.06) points in the 10 mg group and -3.21 (SD: 1.77) points in the placebo group; the difference between orvepitant and placebo was not statistically significant. No safety signal was detected. Adverse events related to orvepitant (asthenia, dizziness, dry mouth, hyperhidrosis) were all of mild or moderate severity.

CONCLUSIONS

Orvepitant was safe and well tolerated. No difference in NRS score between the orvepitant and placebo groups was observed at the week 4 primary endpoint. A number of explanations for this outcome are possible.

TRIAL REGISTRATION NUMBER

EudraCT2013-002763-25.

Design, optimization, and in vivo evaluation of a series of pyridine derivatives with dual NK1 antagonism and SERT inhibition for the treatment of depression

A series of substituted pyridines, ether linked to a phenylpiperidine core were optimized for dual NK(1)/SERT affinity. Optimization based on NK(1)/SERT binding affinities, and minimization of off-target ion channel activity lead to the discovery of compound 44. In vivo evaluation of 44 in the gerbil forced swim test (a depression model), and ex-vivo NK(1)/SERT receptor occupancy data support the potential of a dual acting compound for the treatment of depression.

Cisplatin causes over-expression of tachykinin NK(1) receptors and increases ERK1/2- and PKA- phosphorylation during peak immediate- and delayed-phase emesis in the least shrew (Cryptotis parva) brainstem

Scant information is available regarding the effects of cisplatin on the expression profile of tachykinin NK(1) receptors and downstream signaling during cisplatin-induced emesis. Cisplatin causes peak early- and delayed-phase emesis in the least shrew at 1-2 and 33 h post-injection. To investigate the expression profile of NK(1) receptor during both emetic phases, we cloned the cDNA corresponding to a ~700 base pairs of mRNA flanked by two stretches of nucleotides conserved among different species and demonstrated that the shrew NK(1) receptor nucleotide sequence shares ~90% sequence identity with the human NK(1) receptor. Of the 12 time-points tested, significant increases in expression levels of NK(1) receptor mRNA in the shrew brainstem occurred at 2 and 28 h post-cisplatin injection, whereas intestinal NK(1) receptor mRNA was increased at 28 h. Shrew brainstem and intestinal substance P mRNA levels also tended to increase during the two phases. Furthermore, expression levels of NK(1) receptor protein were significantly increased in the brainstem at 2, 8, and 33 h post-cisplatin. No change in brainstem 5-HT(3) receptor protein expression was observed. The temporal enhancements in NK(1) receptor protein expression were mirrored by significant increases in the phosphorylation status of the brainstem ERK1/2 at 2, 8, and 33 h post-cisplatin. Phosphorylation of PKA significantly increased at 33rd and 40th hour. Our results indicate associations between cisplatin's peak immediate- and delayed-phase vomiting frequency with increased: (1) expression levels of NK(1) receptor mRNA and its protein level, and (2) downstream NK(1) receptor-mediated phosphorylation of ERK1/2 and PKA signaling.

In vitro and in vivo pharmacological characterization of the novel NK₁ receptor selective antagonist Netupitant

The novel NK(1) receptor ligand Netupitant has been characterized in vitro and in vivo. In calcium mobilization studies CHO cells expressing the human NK receptors responded to a panel of agonists with the expected order of potency. In CHO NK(1) cells Netupitant concentration-dependently antagonized the stimulatory effects of substance P (SP) showing insurmountable antagonism (pK(B) 8.87). In cells expressing NK(2) or NK(3) receptors Netupitant was inactive. In the guinea pig ileum Netupitant concentration-dependently depressed the maximal response to SP (pK(B) 7.85) and, in functional washout experiments, displayed persistent (up to 5h) antagonist effects. In mice the intrathecal injection of SP elicited the typical scratching, biting and licking response that was dose-dependently inhibited by Netupitant given intraperitoneally in the 1-10mg/kg dose range. In gerbils, foot tapping behavior evoked by the intracerebroventricular injection of a NK(1) agonist was dose-dependently counteracted by Netupitant given intraperitoneally (ID(50) 1.5mg/kg) or orally (ID(50) 0.5mg/kg). In time course experiments in gerbils Netupitant displayed long lasting effects. In all the assays Aprepitant elicited similar effects as Netupitant. These results suggest that Netupitant behaves as a brain penetrant, orally active, potent and selective NK(1) antagonist. Thus this molecule can be useful for investigating the NK(1) receptor role in the control of central and peripheral functions. Netupitant has clinical potential in conditions such as chemotherapy induced nausea and vomiting, in which the blockade of NK(1) receptors has been demonstrated valuable for patients.

Potentiation of brain stimulation reward by morphine: effects of neurokinin-1 receptor antagonism

RATIONALE

The abuse potential of opioids may be due to their reinforcing and rewarding effects, which may be attenuated by neurokinin-1 receptor (NK1R) antagonists.

OBJECTIVE

This study was conducted to measure the effects of opioid and NK1R blockade on the potentiation of brain stimulation reward (BSR) by morphine using the intracranial self-stimulation method.

METHODS

Adult male C57BL/6J mice (n = 15) were implanted with unipolar stimulating electrodes in the lateral hypothalamus and trained to respond for varying frequencies of rewarding electrical stimulation. The BSR threshold (θ(0)) and maximum response rate (MAX) were determined before and after intraperitoneal administration of saline, morphine (1.0-17.0 mg/kg), or the NK1R antagonists L-733,060 (1.0-17.0 mg/kg) and L-703,606 (1.0-17.0 mg/kg). In morphine antagonism experiments, naltrexone (0.1-1.0 mg/kg) or 10.0 mg/kg L-733,060 or L-703,606 was administered 15 min before morphine (1.0-10.0 mg/kg) or saline.

RESULTS

Morphine dose-dependently decreased θ(0) (maximum effect = 62% of baseline) and altered MAX when compared to saline. L-703,606 and L-733,060 altered θ(0); 10.0 mg/kg L-733,060 and L-703,606, which did not affect θ(0) or MAX, attenuated the effects of 3.0 and 10.0 mg/kg morphine, and 1.0 and 0.3 mg/kg naltrexone blocked the effects of 10.0 mg/kg morphine. Naltrexone given before saline did not affect θ(0) or MAX.

CONCLUSIONS

The decrease in θ(0) by morphine reflects its rewarding effects, which were attenuated by NK1R and opioid receptor blockade. These results demonstrate the importance of substance P signaling during limbic reward system activation by opioids.

In vitro and ex vivo autoradiography of the NK-1 antagonist [³H]-LY686017 in Guinea pig brain

NK-1 receptor antagonists have shown potential for the clinical treatment of chemotherapy-induced nausea and vomiting, depression and alcoholism. In a recent study, we disclosed the potential for the NK-1 antagonist, LY686017, to treat alcoholism in a clinical population. To assess whether this compound could be utilized as a platform for a brain imaging ligand, we evaluated the binding of [³H]-LY686017 to sections of guinea pig in vitro. In these studies, [³H]-LY686017 bound with a distribution and pharmacology consistent with the NK-1 receptor. Using sections through the region of the caudate nucleus, we obtained a K(d) of 0.34 nM and a B(max) of 31.37 fmoles/mg tissue. Based on its high potency and low nonspecific binding in vitro, we initiated studies to evaluate the radioligand as a tool to measure in vivo receptor occupancy. In initial studies, 25 microCi of [³H]-LY686017 was administered via an indwelling jugular catheter and accumulation of radioactivity in the caudate (NK-1 containing tissue) and cerebellum (low NK-1 expression) were assessed. The ratios of caudate to cerebellum radioactivity were optimal 2 h after radioligand administration so this time point was used for subsequent studies. To assess the pharmacological specificity of the radioactivity accumulation, we administered various doses of Aprepitant, a potent NK-1 antagonists 1h prior to intravenous administration of [³H]-LY686017. Aprepitant produced a dose-dependent reduction in radioactivity in the caudate with an approximate 70% reduction at 10 mg/kg. To image NK-1 receptors, 100 microCi of [³H]-LY686017 was administered and the brains sectioned for autoradiography. In these studies, a characteristic distribution on NK-1 receptors was observed. Based on these results, LY686017 should serve as a suitable chemical platform for future imaging ligand development.

Anxiolytic-like effects of the neurokinin 1 receptor antagonist GR-205171 in the elevated plus maze and contextual fear-potentiated startle model of anxiety in gerbils

Gerbils show a neurokinin (NK)1 receptor pharmacological profile, which is similar to that observed in humans, and thus have become a commonly used species to test efficacy of NK1 receptor antagonists. The aim of this study was to determine whether systemic administration of the NK1 receptor antagonist GR-205171 produced anxiolytic-like effects in the elevated plus maze and in a novel contextual conditioned fear test using fear-potentiated startle (FPS). On the elevated plus maze, treatment with GR-205171 at 0, 0.3, 1.0, and 5.0 mg/kg doses, 30 min before testing produced anxiolytic-like effects in an increasing dose-response manner as measured by the percentage of open arm time and percentage of open arm entries. For contextual fear conditioning, gerbils were given 10 unsignaled footshocks (0.6 mA) at a 2-min variable interstimulus interval in a distinctive training context. Twenty-four hours after training, gerbils received treatment of GR-205171 at 0, 0.3, 1.0, and 5.0 mg/kg doses, 30 min before testing in which startle was elicited in the same context in which they were trained. Contextual FPS was defined as an increase in startle over pretraining baseline values. All drug dose levels (0.3, 1.0, and 5.0 mg/kg) significantly attenuated contextual FPS when compared with the vehicle control group. A control group, which received testing in a different context, showed little FPS. These findings support other evidence for anxiolytic activity of NK1 receptor antagonists and provide a novel conditioned fear test that may be an appropriate procedure to test other NK1 antagonists for preclinical anxiolytic activity in gerbils.

S41744, a dual neurokinin (NK)1 receptor antagonist and serotonin (5-HT) reuptake inhibitor with potential antidepressant properties: a comparison to aprepitant (MK869) and paroxetine

Though neurokinin(1) (NK(1)) receptors are implicated in depressed states and their treatment, selective antagonists have disappointed in clinical trials. Accordingly, we designed a novel ligand, S41744 (2-piperazin-1-yl-indan-2-carboxylic-acid-(3-chloro-5-fluoro-benzyl)-methyl-amide), which both blocks NK(1) receptors and interferes with serotonin (5-HT) reuptake. S41744 mimicked the selective antagonist aprepitant in binding human (h)NK(1) receptors and in antagonising Substance-P-mediated Extracellular-Regulated-Kinase phosphorylation (pK(B), 7.7). Further, it dose-dependently (0.63-40.0 mg/kg, i.p.) displaced ex vivo [(3)H]-[Sar(9),Met(O(2))(11)]-Substance P binding to gerbil striatum, attenuated formalin-induced hind-paw licking in gerbils, and antagonised locomotion induced by i.c.v. administration of the NK(1) agonist GR73632 to guinea pigs. Like paroxetine, S41744 recognised h5-HT transporters, reduced synaptosomal uptake of 5-HT (pK(B), 7.9), and dose-dependently (0.63-10.0 mg/kg) elevated dialysis levels of 5-HT in the hippocampus and frontal cortex of freely-moving guinea pigs. Further, S41744 increased extracellular levels of 5-HT in frontal cortex and hippocampus of rats to a greater extent than paroxetine, and its inhibitory influence upon serotonergic perikarya was blunted relative to its affinity for 5-HT transporters. S41744 more potently blocked stress-induced vocalizations in guinea pigs than aprepitant and paroxetine, and it was active in forced-swim and marble-burying procedures of putative antidepressant properties in mice. While aprepitant displayed anxiolytic actions in stress-induced foot-tapping and social interaction tests in gerbils, paroxetine was anxiogenic and S41744 "neutral", reflecting balanced NK(1) antagonism and suppression of 5-HT reuptake. Moreover, S41744 shared anxiolytic actions of aprepitant in the rat Vogel Conflict Test. In conclusion, S41744 is an innovative NK(1) antagonist/5-HT reuptake inhibitor justifying further evaluation for treatment of stress-related disorders.

NK1 (TACR1) receptor gene 'knockout' mouse phenotype predicts genetic association with ADHD

Mice with functional genetic ablation of the Tacr1 (substance P-preferring receptor) gene (NK1R-/-) are hyperactive. Here, we investigated whether this is mimicked by NK1R antagonism and whether dopaminergic transmission is disrupted in brain regions that govern motor performance. The locomotor activity of NK1R-/- and wild-type mice was compared after treatment with an NK1R antagonist and/or psychostimulant (d-amphetamine or methylphenidate). The inactivation of NK1R (by gene mutation or receptor antagonism) induced hyperactivity in mice, which was prevented by both psychostimulants. Using in vivo microdialysis, we then compared the regulation of extracellular dopamine in the prefrontal cortex (PFC) and striatum in the two genotypes. A lack of functional NK1R reduced (>50%) spontaneous dopamine efflux in the prefrontal cortex and abolished the striatal dopamine response to d-amphetamine. These behavioural and neurochemical abnormalities in NK1R-/- mice, together with their atypical response to psychostimulants, echo attention deficit hyperactivity disorder (ADHD) in humans. These findings prompted genetic studies on the TACR1 gene (the human equivalent of NK1R) in ADHD patients in a case-control study of 450 ADHD patients and 600 screened supernormal controls. Four single-nucleotide polymorphisms (rs3771829, rs3771833, rs3771856, and rs1701137) at the TACR1 gene, previously known to be associated with bipolar disorder or alcoholism, were strongly associated with ADHD. In conclusion, our proposal that NK1R-/- mice offer a mouse model of ADHD was borne out by our human studies, which suggest that DNA sequence changes in and around the TACR1 gene increase susceptibility to this disorder.

Cellular and behavioural profile of the novel, selective neurokinin1 receptor antagonist, vestipitant: a comparison to other agents

This study characterized the novel neurokinin (NK)(1) antagonist, vestipitant, under clinical evaluation for treatment of anxiety and depression. Vestipitant possessed high affinity for human NK(1) receptors (pK(i), 9.4), and potently blocked Substance P-mediated phosphorylation of Extracellular-Regulated-Kinase. In vivo, it occupied central NK(1) receptors in gerbils (Inhibitory Dose(50), 0.11 mg/kg). At similar doses, it abrogated nociception elicited by formalin in gerbils, and blocked foot-tapping and locomotion elicited by the NK(1) agonist, GR73632, in gerbils and guinea pigs, respectively. Further, vestipitant attenuated fear-induced foot-tapping in gerbils, separation-induced distress-vocalizations in guinea pigs, marble-burying behaviour in mice, and displayed anxiolytic actions in Vogel conflict and fear-induced ultrasonic vocalization procedures in rats. These actions were mimicked by CP99,994, L733,060 and GR205,171 which acted stereoselectively vs its less active isomer, GR226,206. In conclusion, vestipitant is a potent NK(1) receptor antagonist: its actions support the utility of NK(1) receptor blockade in the alleviation of anxiety and, possibly, depression.

Behavioral and pharmacological validation of the gerbil forced-swim test: effects of neurokinin-1 receptor antagonists

Several studies have suggested that neurokinin-1 (NK1) receptor antagonists may have therapeutic potential as novel antidepressant drugs. To test these compounds preclinically, gerbils have become one of the preferred species in that they demonstrate close NK1 receptor homology with humans and bind NK1 antagonists with higher affinity than rats and mice. The intent of the present study was to determine whether the forced-swim test (FST), one of the most commonly used animal tests of antidepressant-like activity, could be adapted for use with the gerbil. Critical factors in the establishment of this assay included swim tank diameter, weight, and sex of the animals tested. Pharmacological validation of the FST using standard antidepressant compounds (eg fluoxetine, paroxetine, desipramine) resulted in decreased immobility time during the test, indicative of an antidepressant-like effect. Similar to results reported for the rat and mouse FST, the antipsychotic drug haloperidol increased immobility, whereas the psychostimulant, amphetamine decreased immobility, and anxiolytic drugs (eg buspirone) had no effect. Investigation into the locomotor effects of all compounds tested was consistent with previous reports in other species, with the exception of paroxetine, which produced hyperactivity at therapeutically effective doses in gerbils. In addition to standard antidepressants, NK1 antagonists (L-733060, MK-869, and CP-122721) all reduced immobility in the gerbil FST without affecting locomotor activity. Overall, these results suggest that the gerbil is an ideal species for use in the FST, and that this paradigm may have predictive validity for identifying novel antidepressant compounds.

Utilization of the least shrew as a rapid and selective screening model for the antiemetic potential and brain penetration of substance P and NK1 receptor antagonists

Substance P (SP) is thought to play a cardinal role in emesis via the activation of central tachykinin NK1 receptors during the delayed phase of vomiting produced by chemotherapeutics. Although the existing supportive evidence is significant, due to lack of an appropriate animal model, the evidence is indirect. As yet, no study has confirmed that emesis produced by SP or a selective NK1 receptor agonist is sensitive to brain penetrating antagonists of either NK1, NK2, or NK3 receptors. The goals of this investigation were to demonstrate: 1) whether intraperitoneal (i.p.) administration of either SP, a brain penetrating (GR73632) or non-penetrating (e.g. SarMet-SP) NK1 receptor agonist, an NK2 receptor agonist (GR64349), or an NK3 receptor agonist (Pro7-NKB), would induce vomiting and/or scratching in the least shrew (Cryptotis parva) in a dose-dependent manner; and whether these effects are sensitive to the above selective receptor antagonists; 2) whether an exogenous emetic dose of SP (50 mg/kg, i.p.) can penetrate into the shrew brain stem and frontal cortex; 3) whether GR73632 (2.5 mg/kg, i.p.)-induced activation of NK1 receptors increases Fos-measured neuronal activity in the neurons of both brain stem emetic nuclei and the enteric nervous system of the gut; and 4) whether selective ablation of peripheral NK1 receptors can affect emesis produced by GR73632. The results clearly demonstrated that while SP produced vomiting only, GR73632 caused both emesis and scratching behavior dose-dependently in shrews, and these effects were sensitive to NK1-, but not NK2- or NK3-receptor antagonists. Neither the selective, non-penetrating NK1 receptor agonists, nor the selective NK2- or NK3-receptor agonists, caused a significant dose-dependent behavioral effect. An emetic dose of SP selectively and rapidly penetrated the brain stem but not the frontal cortex. Systemic GR73632 increased Fos expression in the enteric nerve plexi, the medial subnucleus of nucleus tractus solitarius, and the dorsal motor nucleus of the vagus, but not the area postrema. Ablation of peripheral NK1 receptors attenuated the ability of GR73632 to induce a maximal frequency of emesis and shifted its percent animals vomiting dose-response curve to the right. The NK1-ablated shrews exhibited scratching behavior after systemic GR73632-injection. These results, for the first time, affirm a cardinal role for central NK1 receptors in SP-induced vomiting, and a facilitatory role for gastrointestinal NK1 receptors. In addition, these data support the validation of the least shrew as a specific and rapid behavioral animal model to screen concomitantly both the CNS penetration and the antiemetic potential of tachykinin NK1 receptor antagonists.

TRPV1-mediated protection against endotoxin-induced hypotension and mortality in rats

This study was designed to test the hypothesis that the transient receptor potential vanilloid type 1 (TRPV1) channel, expressed primarily in sensory nerves, and substance P (SP), released by sensory nerves, play a protective role against lipopolysaccharide (LPS)-induced hypotension. LPS (10 mg/kg iv) elicited tachycardia and hypotension in anesthetized male Wistar rats, which peaked at 10 min and gradually recovered 1 h after the injection. Blockade of TRPV1 with its selective antagonist capsazepine (CAPZ, 3 mg/kg iv) impaired recovery given that the fall in mean arterial pressure (MAP) was greater 1 h after CAPZ plus LPS injections compared with LPS injection alone (45 +/- 5 vs. 25 +/- 4 mmHg, P < 0.05). Blockade of the neurokinin 1 (NK1) receptor with its selective antagonists RP-67580 (5 mg/kg iv) or L-733,060 (4 mg/kg iv) prevented recovery, considering that falls in MAP were not different 1 h after injections of NK1 antagonists plus LPS from their peak decreases (66 +/- 9 vs. 74 +/- 5 mmHg or 60 +/- 7 vs. 69 +/- 3 mmHg, respectively, P > 0.05). LPS increased plasma SP, norepinephrine (NE), and epinephrine (Epi) levels compared with vehicles, and the increases in plasma SP, NE, and Epi were significantly inhibited by CAPZ or RP-67580. The survival rate at 24 or 48 h after LPS injection (20 mg/kg ip) was lower in conscious rats pretreated with CAPZ or RP-67580 compared with rats treated with LPS alone (P < 0.05). Thus our results show that the TRPV1, possibly via triggering release of SP which activates the NK1 and stimulates the sympathetic axis, plays a protective role against endotoxin-induced hypotension and mortality, suggesting that TRPV1 receptors are essential in protecting vital organ perfusion and survival during the endotoxic condition.

1,2,3-Triazoles

Rapid progress in the synthetic application of benzotriazole derivatives in the last 20 years has resulted in over 1000 scientific papers on the subject. This fact is reflected in Section 5.01.7, which involves almost a half of the volume of this chapter. The section is arranged according to hybridization of the C-α atom and atomic numbers of the atoms in positions β and γ to allow an easy access to the material of interest. Recent discovery of copper catalysis in [3+2] cycloadditions of azides to acetylenes, the so-called ‘click chemistry’, which boosted application of the 1,2,3-triazole derivatives, especially in medicinal chemistry, is presented in Section 5.01.9. From the point of view of practical applications, Section 5.01.11 is organized according to the number, position, and combination of the substituents at the aromatic rings. Another novel feature that has no precedence in the previous editions of Comprehensive Heterocyclic Chemistry is an addition of triazole and benzotriazole complexes with various transitions metals to Section 5.01.4.

[3H]GR205171 displays similar NK1 receptor binding profile in gerbil and human brain

1 In this study, [(3)H]GR205171 (3(S)-(2-methoxy-5-(5-trifluoromethyltetrazol-1-yl)-phenylmethylamino)-2(S)-phenylpiperidine), a potent and selective NK1 receptor antagonist, was characterised in autoradiographic studies in gerbil brain and in binding experiments on homogenates from gerbil and human brain cortex and striatum. 2 In autoradiographic studies in gerbil brain, highest levels of [(3)H]GR205171 binding sites were observed in caudate putamen, nucleus accumbens, medial and cortical nuclei of the amygdala and intermediate levels were detected in the hypothalamus, basolateral amygdala, septum, and cortex. 3 Saturation experiments in homogenates of brain striatum from gerbil showed that [(3)H]GR205171 binds to a single receptor population with a pK(d) value of 10.8+/-0.2 and a B(max) value of 607+/-40 fmol mg(-1). A lower number of NK1 receptor sites was found in cortex, where a B(max) of 94+/-6 fmol mg(-1) protein was obtained. Saturation experiments performed on homogenates from brain striatum of two human subjects and brain cortex of three human subjects showed that [(3)H]GR205171 binds with pK(d) values not different from gerbil and B(max) values ranging from 318+/-51 to 432+/-27 fmol mg(-1) protein in striatum and from 59+/-1 to 74+/-21 fmol mg(-1) protein in cortex. The natural ligand [(3)H]Substance P (SP) bound with sub-nanomolar affinity to 15 and 6% sites compared to [(3)H]GR205171 in gerbil and human striatum, respectively. 4 In competition binding experiments, GR205171 and the NK1 receptor antagonists aprepitant (MK-869), L-733,060 and NKP-608 bound with similar pK(i) values in gerbil and human striatum, irrespective of the use of [(3)H]GR205171 or [(3)H]SP as radioligand. The following rank order was found in terms of pK(i) values: GR205171>aprepitant> or =L-733,060>NKP-608. In homologous displacement experiments in gerbil and human striatum, SP showed nanomolar affinity, whereas in [(3)H]GR205171 competition experiments SP bound with pIC(50) values in the micromolar range and Hill slopes significantly lower than one. 5 It is concluded that the similarities of [(3)H]GR205171 binding characteristics and pharmacology between gerbil and human in cortex and striatum support the use of gerbil in preclinical models to study the effects of NK1 receptor antagonists in the central nervous system.

Neurokinin 1 Receptor Antagonists: Correlation between in Vitro Receptor Interaction and in Vivo Efficacy

We compared the neurokinin 1 receptor (NK(1)R) antagonists aprepitant, CP-99994 [(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine], and ZD6021 [3-cyano-N-((2S)-2-(3,4-dichlorophenyl)-4-[4-[2-(methyl-(S)-sulfinyl)phenyl]piperidino]butyl)-N-methyl]napthamide]] with respect to receptor interactions and duration of efficacy in vivo. In Ca(2+) mobilization assays (fluorometric imaging plate reader), antagonists were applied to human U373MG cells simultaneously with or 2.5 min before substance P (SP). In reversibility studies, antagonists were present for 30 min before washing, and responses to SP were repeatedly measured afterward. The compounds were administered i.p. to gerbils, and the gerbil foot tap (GFT) response was monitored at various time points. The NK(1)R receptor occupancy for aprepitant was determined in striatal regions. Levels of compound in brain and plasma were measured. Antagonists were equipotent at human NK(1)R and acted competitively with SP. After preincubation, aprepitant and ZD6021 attenuated the maximal responses, whereas CP-99994 only shifted the SP concentration-response curve to the right. The inhibitory effect of CP-99994 was over within 30 min, whereas for ZD6021, 50% inhibition still persisted after 60 min. Aprepitant produced maximal inhibition lasting at least 60 min. CP-99994 (3 micromol/kg) inhibited GFT by 100% 15 min after administration, but the effect declined rapidly together with brain levels thereafter. The efficacy of ZD6021 (10 micromol/kg) lasted 4 h and correlated well with brain levels. Aprepitant (3 micromol/kg) inhibited GFT and occupied striatal NK(1)R by 100% for >48 h despite that brain levels of compound were below the limit of detection after 24 h. Slow functional reversibility is associated with long-lasting in vivo efficacy of NK(1)R antagonists, whereas the efficacy of compounds with rapid reversibility is reflected by their pharmacokinetics.

Metabolism, Pharmacokinetics, and Excretion of the Substance P Receptor Antagonist CP-122,721 in Humans: Structural Characterization of the Novel Major Circulating Metabolite 5-Trifluoromethoxy Salicylic Acid by High-Performance Liquid Chromatography-Tandem Mass Spectrometry and NMR Spectroscopy

The metabolism, pharmacokinetics, and excretion of a potent and selective substance P receptor antagonist, CP-122,721 [(+)-(2S,3S)-3-(2-methoxy-5-trifluoromethoxybenzylamino)-2-phenylpiperidine], have been studied in six healthy male human subjects [four extensive metabolizers (EMs) and two poor metabolizers (PMs) of CYP2D6) following oral administration of a single 30-mg dose of [14C]CP-122,721. Approximately 84% of the administered radioactivity was recovered from the urine and feces of the subjects over a period of 312 h. Approximately 80% of the dose for EM subjects was recovered within 48 h. PM subjects, however, excreted only about 45% of the dose in 48 h and required the full 312 h to achieve nearly 80% recovery. Absorption of CP-122,721 was rapid in both extensive and poor metabolizers, as indicated by the rapid appearance of radioactivity in serum. The serum concentrations of total radioactivity were always much greater than those of unchanged drug indicating early formation of metabolites. The average CP-122,721 t1/2 was 6.7 h and 45.0 h for EM and PM subjects, respectively. The serum concentrations of CP-122,721 reached a peak of 7.4 and 69.8 ng/ml for extensive and poor metabolizers, respectively. The major metabolic pathways of CP-122,721 were due to O-demethylation, aromatic hydroxylation, and indirect glucuronidation. The minor metabolic pathways included aliphatic oxidation at the piperidine moiety, O-dealkylation of the trifluoromethoxy group, N-dealkylation, and oxidative deamination. In addition to the major human circulating metabolite 5-trifluoromethoxy salicylic acid (TFMSA), all other circulating metabolites of CP-122,721 were glucuronide conjugates of oxidized metabolites. TFMSA was identified using high pressure liquid chromatography/tandem mass spectrometry and NMR and mechanisms were proposed for its formation. There are no known circulating active metabolites of CP-122,721.

In vivo mapping of substance P receptors in brains of laboratory animals by high-resolution imaging systems

Neurotransmission mediated by substance P (SP) and NK(1) receptor has been implicated in the pathophysiology of analgesia, emesis and diverse neuropsychiatric conditions including depression and anxiety disorder. Several lines of clinical trials using NK(1) receptor antagonists have been conducted to date, and the efficiency of preclinical assessments for proof of concept and dose optimization could be greatly increased by configuring an in vivo analytical system that permits quantitative mapping of NK(1) receptors in the brains of small-size laboratory animals expressing "human-like" NK(1) receptors. Hence, we investigated the applicability of experimental animals, ranging from rodents to primates, to positron emission tomographic (PET) measurements with [(18)F]fluoroethyl-SPA-RQ, a modification of a recently established radioligand for NK(1) receptors. A pharmacokinetic assay could be performed for a rhesus monkey in an awake condition, which allows the circumvention of influences of anesthesia on SP neurotransmission. Coregistration of PET and magnetic resonance images acquired by small-animal-dedicated devices enabled detailed localization of NK(1) receptors in the gerbil and marmoset brains. The present study also revealed the potentials of SDZ NKT 343 as an antagonist for central NK(1) receptors. In conjunction with additional in vitro and ex vivo autoradiographic observations, our in vivo results have demonstrated a similarity in the binding pattern among the animals examined, justifying cross-species extrapolation of PET findings on the SP-NK(1) pathway.

Comparison of lorazepam [7-chloro-5-(2-chlorophenyl)-1,3-dihydro-3-hydroxy-2H-1,4-benzodiazepin-2-one] occupancy of rat brain gamma-aminobutyric acid(A) receptors measured using in vivo [3H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester) binding and [11C]flumazenil micro-positron emission tomography

The occupancy by lorazepam of the benzodiazepine binding site of rat brain GABA(A) receptors was compared when measured using either in vivo binding of [(3)H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester) in terminal studies or [(11)C]flumazenil binding in anesthetized animals assessed using a small animal positron emission tomography (PET) scanner (micro-PET). In addition, as a bridging study, lorazepam occupancy was measured using [(3)H]flumazenil in vivo binding in rats anesthetized and dosed under micro-PET conditions. Plasma lorazepam concentrations were also determined, and for each occupancy method, the concentration required to produce 50% occupancy (EC(50)) was calculated because this parameter is independent of the route of lorazepam administration. For the in vivo binding assay, lorazepam was dosed orally (0.1-10 mg/kg), whereas for the micro-PET study, lorazepam was given via the i.v. route as a low dose (0.75 mg/kg bolus) and then a high dose (0.5 mg/kg bolus then 0.2 mg/ml infusion). The lorazepam plasma EC(50) in the [(11)C]flumazenil micro-PET study was 96 ng/ml [95% confidence intervals (CIs) = 74-124 ng/ml], which was very similar to the [(3)H]flumazenil micro-PET simulation study (94 ng/ml; 95% CI = 63-139 ng/ml), which in turn was comparable with the [(3)H]flumazenil in vivo binding study (134 ng/ml; 95% CI = 119-151 ng/ml). These data clearly show that despite the differences in dosing (i.v. in anesthetized versus orally in conscious rats) and detection (in vivo dynamic PET images versus ex vivo measurements in filtered and washed brain homogenates), [(11)C]flumazenil micro-PET produces results similar to [(3)H]flumazenil in vivo binding.

Molecular cloning, mutations and effects of NK1 receptor antagonists reveal the human-like pharmacology of gerbil NK1 receptors

The present study investigates the pharmacology of the cloned neurokinin 1 receptor from the gerbil (gNK(1)R), a species claimed to have human-like NK(1)R (hNK(1)R) pharmacology. The amino acid sequence of NK(1)R was cloned. The hNK(1)R, rat NK(1)R (rNK(1)R), gNK(1)R and mutants of the gNK(1)R were expressed in CHO cells. The affinity and potency of NKR agonists and the NK(1)R antagonists CP99994 and RP67580 (NK(1)R-selective) and ZD6021 (NK1/2R) were assessed in vitro by monitoring [(3)H]-SarMet SP binding and substance P-evoked mobilization of intracellular Ca(2+). The gerbil foot tap (GFT) method was used to assess the potency of the antagonists in vivo. The gNK(1)R coding sequence displayed an overall 95% and 97% homology with hNK(1)R and rNK(1)R, respectively. The affinity of the NK(1)R-selective agonist (3)H-SarMet SP for human and gerbil NK(1)R was similar (2.0 and 3.1 nM) but lower for rNK(1)R (12.4 nM). The rank order potency of the agonists for NK(1)R was SP > or = ASMSP > or = NKA >>> pro7NKB in all species. The NK(1)R antagonists, ZD6021 and CP99994, had comparable affinity and potency for gerbil and human NK(1)R, but were 1000-fold less potent for rNK(1)R. In contrast, RP67580 had comparable affinity and potency for all three species. Mutations in positions 116 and 290 did not affect agonist potency at the gNK(1)R while the potency of the antagonists ZD6021 and CP99994 were markedly decreased (10-20-fold). It is concluded that gNK(1)R has similar antagonist pharmacology as the human-like orthologue and that species differences in antagonist function depend on key residues in the coding sequence and antagonist structure.

The role of substance P in stress and anxiety responses

Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.

Comparison of in vivo and ex vivo [3H]flumazenil binding assays to determine occupancy at the benzodiazepine binding site of rat brain GABAA receptors

In the present study, the occupancy of flumazenil (Ro 15-1788; 1-30mg/kg p.o.) at the benzodiazepine site of rat brain GABA(A) receptors was compared using in vivo and ex vivo binding methodologies with [(3)H]flumazenil as the radioligand. Animals either received tracer quantities of [(3)H]flumazenil 3min before being killed for the in vivo binding, or were killed and brain homogenates incubated with 1.8nM [(3)H]flumazenil. The flumazenil dose required to inhibit in vivo binding of [(3)H]flumazenil by 50% (ID(50)) was 2.0mg/kg, which represents the most accurate measure of benzodiazepine site occupancy by flumazenil in vivo. Occupancy measured in crude brain homogenates using the ex vivo method was time dependent with a 3mg/kg dose giving occupancies of 77% and 12% using 0.5 or 60min ex vivo incubations times, respectively, presumably due to dissociation from the binding site during the ex vivo incubation. When incubation time was minimised (0.5min), and despite being under non-equilibrium conditions, the ex vivo method gave an ID(50) of 1.5mg/kg which was not too dissimilar from that observed using in vivo binding (2.0mg/kg). As expected, ex vivo binding can give an underestimation of receptor occupancy but this can be minimised by careful attention to the kinetics of unlabelled drug and radioligand.

Investigating the effect of bilateral amygdala lesions on fear conditioning and social interaction in the male Mongolian gerbil

Identification of the selective neurokinin NK(1) receptor antagonist, 2-(R)-(1-(R)-3,5-Bis(trifluromethyl)phenylethoxy)-3-(S)-(4-fluoro)phenyl-4-(3-oxo-1,2,4-triazol-5yl)methylmor-phine (MK-869), as a novel therapeutic approach for anxiety/depression has led to increased use of the Mongolian gerbil in behavioural studies since the gerbil NK(1) receptor pharmacology is similar to human, but not rat or mouse. Within this species, foot tapping and immobility elicited by aversive conditioning, as well as social interaction have been shown to be sensitive to clinically used anxiolytic and antidepressant agents and also NK(1) receptor antagonists. The high levels of NK(1) receptor binding in the amygdala as well as preclinical studies demonstrating increased release of substance P and corresponding internalisation of NK(1) receptors in the basolateral amygdala in response to stressful stimuli suggest that the BLA may represent a potential site of action for NK(1) receptor antagonists in anxiety and/or depression. Therefore, in the current study, we assessed the effect of bilateral BLA lesions in male Mongolian gerbils on footshock-induced foot tapping and immobility, social interaction, and NK(1)-agonist-induced foot tapping. Lesioned gerbils exhibited reduced immobility time during fear conditioning, a non-significant reduction in immobility time when re-exposed to the conditioned stimulus (CS) 24 h later, and increased social interaction in the gerbil social interaction task. In contrast, BLA lesions had no effect on NK(1)-agonist-induced foot tapping. These data provide further support that the gerbil BLA is a potential site for NK(1) receptor antagonists to attenuate anxiety-related behaviours.

Blockade of tachykinin NK1 receptors attenuates stress-induced rise of extracellular noradrenaline and dopamine in the rat and gerbil medial prefrontal cortex

Substance P receptor antagonists cause antidepressant- and anxiolytic-like effects in rodents that are thought to involve brain monoamines. In the present study, we examined the effects of the NK1 receptor antagonist GR-205,171 on basal and stress-induced rise of extracellular noradrenaline (NA) and dopamine (DA) in the medial prefrontal cortex (mPFC) of conscious rats and gerbils with the in vivo microdialysis technique. GR-205,171 given intraperitoneally to rats (10 and 30 mg/kg) and gerbils (0.3 and 1 mg/kg) did not affect extracellular NA in either species and increased extracellular DA in rats. Forty minutes of immobilization increased extracellular NA and DA by, respectively, 179% and 188% of baseline values in rats and 222% and 316% of baseline values in gerbils. At 10 mg/kg, GR-205,171 attenuated the stress-induced increase of extracellular NA in the rat. At 30 mg/kg, GR-205,171 suppressed the effect of stress on extracellular DA but had no effect on NA. A lower dose (1 mg/kg) attenuated the stress-induced rise of extracellular NA and DA in the mPFC of gerbils. The results show that blockade of NK1 receptors marginally increased basal extracellular DA in rats but had no effect in gerbils, whereas the stress-induced rise of extracellular NA and DA was markedly attenuated in both species. It is suggested that catecholamines may contribute to the functional effects of GR-205,171.

Neurokinin-1 receptor resensitization precedes receptor recycling

Following agonist binding, neurokinin-1 receptors undergo rapid desensitization followed by internalization and recycling. Desensitization requires receptor phosphorylation but does not require internalization, whereas resensitization is thought to require internalization and recycling. Our previous data, however, have suggested that, following activation and desensitization, the return of responsiveness to the neurokinin-1 agonist substance P (termed "resensitization") occurs hours before internalized receptors are recycled back to the plasma membrane. To further investigate this novel mechanism of neurokinin-1 receptor resensitization, we have studied the time courses of neurokinin-1 receptor responsiveness, recycling, and dephosphorylation by measuring cellular Ca(2+) responses, ligand-receptor binding, and receptor phosphorylation, respectively. Concentration-response curves and competition binding curves were obtained at various times following desensitization. The effects of the nonhydrolyzable GTP analog Gpp(NH)p on substance P binding were also studied to assess receptor-G protein coupling. After receptor activation and desensitization, Ca(2+) signaling in response to substance P occurred within 90 min, whereas the return of receptor binding required 240 min. Receptor dephosphorylation was greater than 90% complete 20 min after agonist washout. In addition, the return of substance P responsiveness coincided with a return in sensitivity of substance P binding to Gpp(NH)p, indicating a return in receptor-G protein coupling. These data show that the resensitization of responsiveness to substance P precedes receptor recycling. This may result from a conversion of nonfunctional neurokinin-1 receptors to functional receptors at the plasma membrane.

Human positron emission tomography studies of brain neurokinin 1 receptor occupancy by aprepitant

BACKGROUND

Aprepitant is a highly selective substance P (neurokinin 1 [NK(1)] receptor) antagonist that significantly improves the pharmacotherapy of acute and delayed highly emetogenic chemotherapy-induced nausea and vomiting, probably through an action in the brain stem region of the central nervous system. Here, we report the use of positron emission tomography imaging with the NK(1) receptor binding-selective tracer [(18)F]SPA-RQC to determine the levels of central NK(1) receptor occupancy achieved by therapeutically relevant doses of aprepitant in healthy humans.

METHODS

Two single-blind, randomized, placebo-controlled studies in healthy subjects were performed. The first study evaluated the plasma concentration-occupancy relationships for aprepitant dosed orally at 10, 30, 100, or 300 mg, or placebo (n = 12). The second study similarly evaluated oral aprepitant 30 mg and placebo (n = 4). In each study, dosing was once daily for 14 consecutive days. Data from both studies were combined for analyses. The ratio of striatal/cerebellar [(18)F]SPA-RQ (high receptor density region/reference region lacking receptors) was used to calculate trough receptor occupancy 24 hours after the last dose of aprepitant.

RESULTS

Brain NK(1) receptor occupancy increased after oral aprepitant dosing in both a plasma concentration-related (r =.97; 95% confidence interval [CI] =.94-1.00, p <.001) and a dose-related (r =.94; 95% CI =.86-1.00, p <.001) fashion. High (> or =90%) receptor occupancy was achieved at doses of 100 mg/day or greater. The plasma concentrations of aprepitant that achieved 50% and 90% occupancy were estimated as approximately 10 ng/mL and approximately 100 ng/mL, respectively.

CONCLUSIONS

Positron emission tomography imaging with [(18)F]SPA-RQ allows brain NK(1) receptor occupancy by aprepitant to be predicted from plasma drug concentrations and can be used to guide dose selection for clinical trials of NK(1) receptor antagonists in central therapeutic indications.

Aprepitant

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Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800–322–4349. The June 2003 monograph topics are aprepitant, gemifloxacin, desirudin for injection, gatifloxacin ophthalmic solution, and pegvisomant. The DUE is on aprepitant.

Centrally administered hemokinin-1 (HK-1), a neurokinin NK1 receptor agonist, produces substance P-like behavioral effects in mice and gerbils

Hemokinin-1 (HK-1) is a recently described mouse tachykinin peptide whose biological functions are not fully understood. To date, a unique receptor for HK-1 has not been identified. Recent studies suggest HK-1 may have a role in immunological functions, but there has been little characterization of HK-1's effects in the central nervous system (CNS). In the present studies, we confirm that HK-1 is an endogenous agonist at all of the known tachykinin receptors, and is selective for the NK1 receptor over the NK2 and NK3 subtypes. CHO cells transfected with the human NK1 receptor released intracellular calcium in response to HK-1. In addition, HK-1 competed with substance P (SP) for binding to mouse NK1 and human NK1 receptors. In vivo central administration of HK-1 to gerbils and mice induced foot-tapping and scratching behaviors, respectively, similar to those observed following central administration of SP or the NK1 receptor agonist, GR-73632. Furthermore, these behavioral effects were blocked by the selective NK1 receptor antagonist, MK-869. Finally, a comprehensive expression analysis of HK-1 demonstrated that HK-1 mRNA is much more broadly expressed than previously reported with expression observed in many brain regions. Together these data demonstrate that HK-1 is a functional agonist at NK1 receptors and suggest that HK-1 may function both centrally and peripherally.

Peripheral tachykinin receptors as potential therapeutic targets in visceral diseases

More than 10 years of intensive preclinical investigation of selective tachykinin (TK) receptor antagonists has provided a rationale to the speculation that peripheral neurokinin (NK)-1, -2 and -3 receptors may be involved in the pathophysiology of various human diseases at the visceral level. In the airways, despite promising effects in animal models of asthma, pilot clinical trials with selective NK-1 or -2 receptor antagonists in asthmatics have been ambiguous, whereas the potential antitussive effects of NK-1, -2 or -3 antagonists have not yet been verified in humans. In the gastrointestinal (GI) tract, irritable bowel syndrome (IBS) and pancreatitis are appealing targets for peripherally-acting NK-1 and -2 antagonists, respectively. In the genito-urinary tract, NK-1 receptor antagonists could offer some protection against nephrotoxicity and cytotoxicity induced by chemotherapeutic agents, whereas NK-2 receptor antagonists appear to be promising new agents for the treatment of neurogenic bladder hyperreflexia. Finally, there is preclinical evidence for hypothesising an effect of NK-3 receptor antagonists on the cardiovascular disturbance that characterises pre-eclampsia. Other more speculative applications are also mentioned.

NK1 receptors in the medial hypothalamus potentiate defensive rage behavior elicited from the midbrain periaqueductal gray of the cat

Defensive rage in the cat occurs naturally in response to a threat and is also elicited by electrical or chemical stimulation over the rostro-caudal extent of the medial hypothalamus and dorsolateral aspect of the periaqueductal gray (PAG). This behavior is mediated over a descending projection from the hypothalamus to the midbrain PAG. The underlying hypothesis for the present study was that medial hypothalamic defensive rage neurons are excited in two ways: by NK(1) receptors and by an ascending input from the PAG. The first aspect of this hypothesis was tested by eliciting defensive rage by electrical stimulation of the PAG and then microinjecting a selective NK(1) agonist and antagonist into the hypothalamus. Microinjections of 16 or 12 nmol/0.25 microl of the NK(1) agonist, GR 73632, resulted in facilitation of defensive rage. These facilitatory effects were then blocked by pretreatment with the NK(1) antagonist, GR 82334. However, microinjections of GR 82334 alone had no effect. The second aspect of the hypothesis was tested by stimulating defensive rage sites in the PAG and using immunohistochemical methods to test for the presence of c-Fos in the hypothalamus. The results revealed the presence of c-Fos immunoreactivity in the medial but not lateral hypothalamus. Overall, the findings indicate that NK(1) receptors in the medial hypothalamus facilitate defensive rage elicited from PAG neurons whose axons project back to the medial hypothalamus. The likely ethological significance of the ascending input is that it allows for potentiation and prolongation of defensive rage in response to a threatening stimulus.