Reinforcing effects of neurokinin substance P in the ventral pallidum: mediation by the tachykinin NK1 receptor

Nucleus Accumbens Tac1-Expressing Neurons Mediate Stress-Induced Anhedonia-like Behavior in Mice

Major depressive disorder (MDD) presents with two primary symptoms: depressed mood and anhedonia, which suggests that distinct neuronal circuits may regulate MDD. However, the underlying circuits of these individual symptoms linked to depression remain elusive. Herein, we identify a discrete circuit of tachykinin precursor 1 (Tac1)-expressing neurons in the nucleus accumbens (NAc) lateral shell, which project to ventral pallidum and contribute to stress-induced anhedonia-like behavior. Selective inhibition and activation of Tac1^NAc neurons bidirectionally modulate stress susceptibility, revealing that Tac1 neurons in the NAc are critical for regulating anhedonia-like behaviors. We find that a subpopulation of VP neurons receives inhibitory inputs from Tac1^NAc neurons and exhibits decreased excitability in susceptible mice. Furthermore, the inhibition of the neurokinin 1 receptor promotes susceptibility to social stress. Overall, our study reveals a discrete circuit regulating anhedonia-like behavior in mice.

Effects of Electrical Stimulation of NAc Afferents on VP Neurons' Tonic Firing

Afferents from the nucleus accumbens (NAc) are a major source of input into the ventral pallidum (VP). Research reveals that these afferents are GABAergic, however, stimulation of these afferents induces both excitatory and inhibitory responses within the VP. These are likely to be partially mediated by enkephalin and substance P (SP), which are also released by these afferents, and are known to modulate VP neurons. However, less is known about the potentially differential effects stimulation of these afferents has on subpopulations of neurons within the VP and the cellular mechanisms by which they exert their effects. The current study aimed to research this further using brain slices containing the VP, stimulation of the NAc afferents, and multi-electrode array (MEA) recordings of their VP targets. Stimulation of the NAc afferents induced a pause in the tonic firing in 58% of the neurons studied in the VP, while 42% were not affected. Measures used to reveal the electrophysiological difference between these groups found no significant differences in firing frequency, coefficient of variation, and spike half-width. There were however significant differences in the pause duration between neurons in the dorsal and ventral VP, with stimulation of NAc afferents producing a significantly longer pause (0.48 ± 0.06 s) in tonic firing in dorsal VP neurons, compared to neurons in the ventral VP (0.21 ± 0.09 s). Pauses in the tonic firing of VP neurons, as a result of NAc afferent stimulation, were found to be largely mediated by GABA_A receptors, as the application of picrotoxin significantly reduced their duration. Opioid agonists and antagonists were found to have no significant effects on the pause in tonic activity induced by NAc afferent stimulation. However, NK-1 receptor antagonists caused significant decreases in the pause duration, suggesting that SP may contribute to the inhibitory effect of NAc afferent stimulation via activation of NK-1 receptors.

Emerging targets for addiction neuropharmacology: From mechanisms to therapeutics

Drug abuse represents a considerable burden of disease and has enormous economic impacts on societies. Over the years, few medications have been developed for clinical use. Their utilization is endowed with several limitations, including partial efficacy or significant side effects. On the other hand, the successful advancement of these compounds provides an important proof of concept for the feasibility of drug development programs in addiction. In recent years, a wealth of information has been generated on the psychological mechanisms, genetic or epigenetic predisposing factors, and neurobiological adaptations induced by drug consumption that interact with each other to contribute to disease progression. It is now clear that addiction develops through phases, from initial recreational use to excessive consumption and compulsive drug seeking, with a shift from positive to negative reinforcement driving motivated behaviors. A greater understanding of these mechanisms has opened new vistas in drug development programs. Researchers' attention has been shifted from investigation of classical targets associated with reward to biological substrates responsible for negative reinforcement, impulse loss of control, and maladaptive mechanisms resulting from protracted drug use. From this research, several new biological targets for the development of innovative therapies have started to emerge. This chapter offers an overview of targets currently under scrutiny for the development of new medications for addiction. This work is not exhaustive but rather it provides a few examples of how this research has advanced in recent years by virtue of studies carried out in our laboratory.

The pharmacology of neurokinin receptors in addiction: prospects for therapy

Addiction is a chronic disorder in which consumption of a substance or a habitual behavior becomes compulsive and often recurrent, despite adverse consequences. Substance p (SP) is an undecapeptide and was the first neuropeptide of the neurokinin family to be discovered. The subsequent decades of research after its discovery implicated SP and its neurokinin relatives as neurotransmitters involved in the modulation of the reward pathway. Here, we review the neurokinin literature, giving a brief historical perspective of neurokinin pharmacology, localization in various brain regions involved in addictive behaviors, and the functional aspects of neurokinin pharmacology in relation to reward in preclinical models of addiction that have shaped the rational drug design of neurokinin antagonists that could translate into human research. Finally, we will cover the clinical investigations using neurokinin antagonists and discuss their potential as a therapy for drug abuse.

Anxiolytic effect of neurotensin microinjection into the ventral pallidum

Neurotensin (NT) acts as a neurotransmitter and neuromodulator in the central nervous system. NT is involved in reward and memory processes, drug addiction and also in the regulation of anxiety. The ventral pallidum (VP) receives neurotensinergic innervation from the ventral striatopallidal pathway originating from the nucleus accumbens. Positive reinforcing effects of NT in the VP had been shown recently, however the possible effects of NT on anxiety have not been examined yet. In our present experiments, the effects of NT on anxiety were investigated in the VP. In male Wistar rats bilateral microinjections of 100 ng or 250 ng NT were delivered in the volume of 0.4 μl into the VP, and elevated plus maze (EPM) test was performed. In another groups of animals, 35 ng NT-receptor 1 (NTR1) antagonist SR 48,692 was applied by itself, or microinjected 15 min before 100 ng NT treatment. Open field test (OPF) was also conducted. The 100 ng dose of NT had anxiolytic effect, but the 250 ng NT did not influence anxiety. The antagonist pretreatment inhibited the effect of NT, while the antagonist itself had no effect. In the OPF test there was no difference among the groups. Our present results show that microinjection of NT into the VP induces anxiolytic effect, which is specific to the NTR1 receptors because it can be eliminated by a specific NTR1 antagonist. It is also substantiated that neither the NT, nor the NTR1 antagonist in the VP influences locomotor activity.

The ventral pallidum: Subregion-specific functional anatomy and roles in motivated behaviors

The ventral pallidum (VP) plays a critical role in the processing and execution of motivated behaviors. Yet this brain region is often overlooked in published discussions of the neurobiology of mental health (e.g., addiction, depression). This contributes to a gap in understanding the neurobiological mechanisms of psychiatric disorders. This review is presented to help bridge the gap by providing a resource for current knowledge of VP anatomy, projection patterns and subregional circuits, and how this organization relates to the function of VP neurons and ultimately behavior. For example, ventromedial (VPvm) and dorsolateral (VPdl) VP subregions receive projections from nucleus accumbens shell and core, respectively. Inhibitory GABAergic neurons of the VPvm project to mediodorsal thalamus, lateral hypothalamus, and ventral tegmental area, and this VP subregion helps discriminate the appropriate conditions to acquire natural rewards or drugs of abuse, consume preferred foods, and perform working memory tasks. GABAergic neurons of the VPdl project to subthalamic nucleus and substantia nigra pars reticulata, and this VP subregion is modulated by, and is necessary for, drug-seeking behavior. Additional circuits arise from nonGABAergic neuronal phenotypes that are likely to excite rather than inhibit their targets. These subregional and neuronal phenotypic circuits place the VP in a unique position to process motivationally relevant stimuli and coherent adaptive behaviors.

Gut-brain peptides in corticostriatal-limbic circuitry and alcohol use disorders

Peptides synthesized in endocrine cells in the gastrointestinal tract and neurons are traditionally considered regulators of metabolism, energy intake, and appetite. However, recent work has demonstrated that many of these peptides act on corticostriatal-limbic circuitry and, in turn, regulate addictive behaviors. Given that alcohol is a source of energy and an addictive substance, it is not surprising that increasing evidence supports a role for gut-brain peptides specifically in alcohol use disorders (AUD). In this review, we discuss the effects of several gut-brain peptides on alcohol-related behaviors and the potential mechanisms by which these gut-brain peptides may interfere with alcohol-induced changes in corticostriatal-limbic circuitry. This review provides a summary of current knowledge on gut-brain peptides focusing on five peptides: neurotensin, glucagon-like peptide 1, ghrelin, substance P, and neuropeptide Y. Our review will be helpful to develop novel therapeutic targets for AUD.

Involvement of substance P and the NK-1 receptor in human pathology

The peptide substance P (SP) shows a widespread distribution in both the central and peripheral nervous systems, but it is also present in cells not belonging to the nervous system (immune cells, liver, lung, placenta, etc.). SP is located in all body fluids, such as blood, cerebrospinal fluid, breast milk, etc. i.e. it is ubiquitous in human body. After binding to the neurokinin-1 (NK-1) receptor, SP regulates many pathophysiological functions in the central nervous system, such as emotional behavior, stress, depression, anxiety, emesis, vomiting, migraine, alcohol addiction, seizures and neurodegeneration. SP has been also implicated in pain, inflammation, hepatitis, hepatotoxicity, cholestasis, pruritus, myocarditis, bronchiolitis, abortus, bacteria and viral infection (e.g., HIV infection) and it plays an important role in cancer (e.g., tumor cell proliferation, antiapoptotic effects in tumor cells, angiogenesis, migration of tumor cells for invasion, infiltration and metastasis). This means that the SP/NK-1 receptor system is involved in the molecular bases of many human pathologies. Thus, knowledge of this system is the key for a better understanding and hence a better management of many human diseases. In this review, we update the involvement of the SP/NK-1 receptor system in the physiopathology of the above-mentioned pathologies and we suggest valuable future therapeutic interventions involving the use of NK-1 receptor antagonists, particularly in the treatment of emesis, depression, cancer, neural degeneration, inflammatory bowel disease, viral infection and pruritus, in which that system is upregulated.

Stress-related neuropeptides and addictive behaviors: beyond the usual suspects

Addictive disorders are chronic, relapsing conditions that cause extensive disease burden. Genetic factors partly account for susceptibility to addiction, but environmental factors such as stressful experiences and prolonged exposure of the brain to addictive drugs promote its development. Progression to addiction involves neuroadaptations within neurocircuitry that mediates stress responses and is influenced by several peptidergic neuromodulators. While corticotrophin releasing factor is the prototypic member of this class, recent work has identified several additional stress-related neuropeptides that play an important role in regulation of drug intake and relapse, including the urocortins, nociceptin, substance P, and neuropeptide S. Here, we review this emerging literature, discussing to what extent the properties of these neuromodulators are shared or distinct and considering their potential as drug targets.

Cocaine sensitization does not alter SP effects on locomotion or excitatory synaptic transmission in the NAc of rats

Substance P (SP) and cocaine employ similar mechanisms to modify excitatory synaptic transmission in the nucleus accumbens (NAc), a region implicated in substance abuse. Here we explored, using NAc slices, whether SP effects on these synaptic responses were altered in rats that have been sensitized to cocaine and whether SP could mimic cocaine in triggering increased locomotion in sensitized rats. Intraperitoneal (IP) injection of naïve rats with cocaine (15 mg/kg) caused increased locomotion by 408.5 ± 85.9% (n = 5) which further increased by 733.1 ± 157.8% (n = 5) following a week of cocaine sensitization. A similar challenge with 10 mg/kg of SP after cocaine sensitization did not produce significant changes in locomotion (170.6 ± 61.0%; n = 4). In contrast to cocaine, IP injection of rats with SP or SP(5-11) (10-100 mg/kg) with or without phosphoramidon did not elicit changes in locomotion. In electrophysiological studies, both cocaine and SP depressed evoked NMDA and non-NMDA receptor-mediated excitatory synaptic currents (EPSCs) in slices obtained from naïve rats. In slices derived from cocaine-sensitized rats, cocaine but not SP produced a more profound decrease in non-NMDA compared to NMDA responses. Similar to that in naïve rats, cocaine's effect on the EPSCs in these sensitized rats occluded those of SP. Thus, although SP and cocaine may employ similar mechanisms to depress EPSCs in the NAc, IP injection of SP does not mimic cocaine-induced hyperlocomotion indicating that not all of cocaine's effects are mimicked by SP. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Deficits in substance P mRNA levels in the CeA are inversely associated with alcohol-motivated responding

In the present study, in vitro and in vivo studies were conducted to determine the relationship between innate substance P (SP) levels and alcohol-motivated behavior in alcohol-preferring (P) and nonpreferring (NP) rat lines. In Experiment 1, in situ hybridization and quantitative autoradiography were used to detect and measure SP mRNA levels in discrete brain loci of the P and NP rats. The results indicated significantly lower SP mRNA levels in the central nucleus of the amygdala (CeA) of P compared with those of NP rats. Experiment 2 evaluated the effects of SP, microinfused into the CeA, on alcohol (10%, v/v) and sucrose (2%, w/v) motivated responding in the P rat. The results revealed that, when infused into the CeA (1-8 microg), SP reduced alcohol responding by 48-85% of control levels, with no effects on sucrose responding. Neuroanatomical control infusions (1-8 microg) into the caudate putamen (CPu) also failed to significantly alter alcohol- or sucrose-motivated behaviors. Given the selective reductions on alcohol (compared to sucrose) responding by direct intracranial infusion of SP, the data suggest that deficits in SP signaling within the CeA (an anxiety regulating locus) are inversely associated with alcohol-motivated behaviors. Activation of SP receptors in the CeA may reduce anxiety-like behavior in the P rat and contribute to reductions on alcohol responding. The SP system may be a suitable target for the development of drugs to reduce alcohol-drinking behavior in humans.

Neuronal pathways linking substance P to drug addiction and stress

Accumulating evidence suggests that the neuropeptide substance P (SP) and its principal receptor neurokinin 1 (NK1) play a specific role in the behavioral response to opioids and stress that may help to initiate and maintain addictive behavior. In animal models, the NK1 receptor is required for opioids to produce their rewarding and motivational effects. SP neurotransmission is also implicated in the behavioral response to stress and in the process of drug sensitization, potentially contributing to vulnerability to addiction or relapse. However, SP neurotransmission only plays a minor role in opioid-mediated antinociception and the development of opioid tolerance. Moreover, the effects of SP on addiction-related behavior are selective for opioids and evidence supporting a role in the response to cocaine or psychostimulants is less compelling. This review will summarize the effects of SP neurotransmission on opioid-dependent behaviors and correlate them with potential contributing neural pathways. Specifically, SP neurotransmission within components of the basal forebrain particularly the nucleus accumbens and ventral pallidum as well as actions within the ascending serotonin system will be emphasized. In addition, cellular- or network-level interactions between opioids and SP signaling that may underlie the specificity of their relationship will be reviewed.

Cocaine and amphetamine-regulated transcript-containing neurons in the nucleus accumbens project to the ventral pallidum in the rat and may inhibit cocaine-induced locomotion

We have previously demonstrated that cocaine- and amphetamine-regulated transcript (CART) peptide colocalizes with GABA, dynorphin, D1 receptors, and substance P in some neurons in the nucleus accumbens (NAcc). One of the main nuclei that receive accumbal efferents is the ventral pallidum (VP), and both dynorphin and substance P have been shown to be present in the cell bodies and terminals of this projection. Thus, we investigated whether CART peptide is also present in the VP in terminals that originate in the accumbens. The anterograde tracer Phaseolus vulgaris leukoagglutinin (PHA-L) colocalized with CART in neuronal processes in the VP when injected into the NAcc. Also, CART colocalized with the retrograde tracer r-BDA in accumbens cell bodies after the tracer was injected into the VP. Using electron microscopic immunocytochemistry, we examined CART terminals in the VP and found that CART-immunoreactive terminals formed symmetric synapses consistent with inhibitory GABAergic synapses. These synapses closely resemble GABAergic synapses in the substantia nigra pars reticulata (SNr), another nucleus that receives some CART-containing accumbal efferents. Lastly, we found that intra-pallidal injection of CART 55-102 inhibited cocaine-induced locomotion, indicating that CART peptide in the VP can have functional effects.

Neurokinin3 receptor modulation of the behavioral and neurochemical effects of cocaine in rats and monkeys

Neurokinin3 (NK3) receptors and their endogenous ligands (e.g. the neuropeptide substance P and its C-terminal fragment) have been implicated in psychomotor activity and reinforcement mechanisms. We review here recent findings on the involvement of NK3 receptors in the behavioral and neurochemical effects of cocaine. Although NK3 receptors can modulate dopamine (DA) activity in the brain, recent results suggest that this modulation does not occur during spontaneous behavioral activity. However, NK3 receptors play a role in the regulation of cocaine-induced DA responses in the nucleus accumbens core and shell subregions. NK3 receptor agonism as well as antagonism potentiate cocaine's effects on nucleus accumbens DA subregions specifically, and modulate the acute behavioral effects of cocaine in rats and non-human primates (Callithrix penicillata). However, conditioned place preference studies in rats have, so far, failed to provide evidence for an involvement of NK3 receptors in the reinforcing effects of cocaine.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Neurokinin 3 receptor activation potentiates the psychomotor and nucleus accumbens dopamine response to cocaine, but not its place conditioning effects

Neurokinin(3) receptors (NK(3)-Rs) have been implicated in psychomotor activity and reinforcement mechanisms. Recently, we showed that NK(3)-R antagonism blocked the psychostimulant properties of cocaine both in rats and in primates. Here, using in vivo microdialysis in the nucleus accumbens (NAc) of freely moving rats, we investigated the effect of the NK(3)-R agonist senktide (0.2 and 0.4 mg/kg s.c.) on the cocaine-evoked increase in dopamine. Cocaine (10 mg/kg i.p.) increased dopamine levels to 404 and 480% of baseline in the core and shell of the NAc, respectively. Pretreatment with senktide at a dose of 0.2 mg/kg potentiated this effect to 666 (core) and 869% (shell) of baseline, without having any effect on dopamine when given alone. Behavioural measurements revealed that 0.2 mg/kg senktide also potentiated the cocaine-induced increase in horizontal and vertical activity. Senktide alone induced a short-lasting increase in activity that was not accompanied by any alterations of the neurochemical parameters. In conditioned place preference (CPP) experiments, senktide pretreatment did not alter CPP induced by cocaine (5 and 10 mg/kg i.p.), and had no effect when given alone. Likewise, cocaine-conditioned locomotor activity was not affected by the NK(3)-R agonist. However, as in the microdialysis studies, cocaine-induced (5 and 10 mg/kg i.p.) hyperactivity was potentiated by senktide, and there was evidence for a facilitation of sensitization to the hyperlocomotor effects of cocaine by senktide. These data provide evidence that NK(3)-Rs are involved in the control of the hyperlocomotor and NAc DA response to cocaine, but not in cocaine-induced CPP.

Reinstatement of episodic-like memory in rats by neurokinin-1 receptor antagonism

We previously showed that a systemic administration of the selective non-peptide neurokinin-1-receptor (NK-1-R) antagonist SR140333 increases hippocampal acetylcholine levels and facilitates long term memory. In the present study, we investigated whether systemic SR140333 has beneficial effects on episodic-like memory for unique experiences. Rats received either no injection, a vehicle injection or SR140333 at doses of 1, 3 and 9 mg/kg (i.p.) prior to the acquisition of an object memory for what, where and when. In line with previous results, untreated rats showed episodic-like memory, while vehicle-injected rats were impaired. A low dose of 1mg/kg SR140333 reinstated episodic-like memory. This result might be related to the effects of SR140333 on hippocampal cholinergic transmission and/or on the stress-response elicited by the injection procedure. Higher doses of SR140333 (3 and 9 mg/kg) induced psychomotor effects, including stereotypic behaviors and arched posture. Since NK-1-R antagonists have anxiolytic and promestic properties and induce hippocampal acetylcholine release at lower doses, they might be effective in the alleviation of the cognitive deficits and increased anxiety seen in early stages of Alzheimer's disease.

Assessment of antidepressant and anxiolytic properties of NK1 antagonists and substance P in Wistar Kyoto rats

In an attempt to explore the involvement of substance P in depression and anxiety and its' potential therapeutic effects, we measured basal plasma and hypothalamic levels of substance P in a well-studied animal model of depression--adult male Wistar Kyoto (WKY) rats and their controls, Wistar rats. We also studied the influence of a substance P receptor (NK1) antagonist (SPA) on "anxiety-like" and "depressive-like" behaviors exhibited by the WKY rats in the open field and swim test paradigms, compared to controls. WKY rats exhibited lower levels of substance P compared to controls in the hypothalamus. Though the WKY strain exhibited less rearing behavior in the open field compared to controls, SPA did not influence this pattern of behavior. In contrast, SPA had a significant effect on a depressive-like behavior exhibited by the WKY strain--it reduced significantly the immobility duration of WKY rats in the swim test. Thus it seems that depression involves alterations in levels of substance P, and that NK1 antagonists may be effective in the relief of depressive, but not anxiety symptoms.

Neurokinin receptor antagonism attenuates cocaine's behavioural activating effects yet potentiates its dopamine-enhancing action in the nucleus accumbens core

Several lines of evidence indicate a role for neurokinin3 receptors (NK3-Rs) in behavioural activation and mechanisms governing reinforcement processes. In this study we investigated the effect of pretreatment with the NK3-R antagonist, SR142801, (0.2 and 2.0 mg/kg) on the cocaine-induced (10.0 mg/kg i.p.) increase in extracellular dopaminergic activity in the nucleus accumbens (NAc). In vivo microdialysis in the NAc of freely moving rats showed that cocaine increased concentrations of dopamine (DA) to approximately 350% in the core and approximately 450% in the shell. Pre-treatment with SR142801 significantly potentiated this effect in the core (to approximately 550%), whereas this effect was not found in the shell. We also investigated the effects of NK3-Rs antagonism on cocaine-induced hyperactivity and conditioned place preference. SR142801 blocked the hyperactivity, but neither the conditioned place preference nor the conditioned locomotor activity induced by cocaine, although there was a slight tendency towards a reduced place preference. When given alone, SR142801 had no effects on behaviour or extracellular dopamine concentrations in any of the structures investigated. These data provide evidence for a contribution of NK3-Rs in the acute behavioural and neurochemical effects of cocaine, involving dopaminergic activity in the core of the nucleus accumbens.

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.

Effects of central neurokinin-1 receptor antagonism on cocaine- and opiate-induced locomotor activity and self-administration behaviour in rats

The neuropeptide substance P (SP) and its preferred receptor, the neurokinin-1 (NK-1) receptor, have been implicated in some of the reward-related behavioural effects of abused drugs, including psychostimulants and opiates. The first objective of the present series of experiments was to assess the role of the NK-1 receptor in two reward-related behavioural effects of cocaine: locomotor activity and self-administration. In tests for locomotor activity, rats were given intracerebroventricular (ICV) infusions of the selective NK-1 receptor antagonist, GR82334 (0, 10, 50 pmol), prior to systemic injections of cocaine. In self-administration experiments, rats were trained to self-administer cocaine on a fixed-ratio 5 (FR5) schedule of reinforcement. Following acquisition of stable responding, animals were pretreated with GR82334 (0, 2, 10, 50 pmol; ICV) prior to subsequent self-administration sessions. Based on evidence suggesting a potentially selective role for NK-1 receptors in opiate reward, we also examined the effects of GR82334 on morphine-induced locomotor activity and heroin self-administration. Results showed that GR82334 had no effect on cocaine-induced locomotor activity or cocaine self-administration, but attenuated morphine-induced locomotor activity and increased heroin self-administration. These findings suggest that endogenous activity at NK-1 receptors may play a specific role in opiate-induced, but not cocaine-induced, locomotor activation and reinforcement.

Role of substance P in stress-derived degranulation of dermal mast cells in mice

BACKGROUND

The interaction between nerves and mast cells can effect regulation of the immune system and inflammatory responses. Recent studies have shown that various stressors can induce degranulation of dermal mast cells in animals.

OBJECTIVES

This study was conducted to confirm that substance P (SP) was involved in the degranulation of dermal mast cells in stress conditions.

METHODS

Using a communication box system, foot shock stress (FS) and psychological stress (PS) were administered to mice and the degranulation rate of dermal mast cells, the number of SP-positive nerve fibers and changes in SP content were determined. The inhibitory effect of a non-peptide NK1-receptor antagonist on these changes was investigated.

RESULTS

Both FS and PS significantly enhanced the degranulation of dermal mast cells and increased the number of SP-positive nerve fibers. FS significantly decreased dermal SP content whereas SP was increased by PS. These changes were inhibited by intraperitoneal injection of NK(1) receptor antagonist.

CONCLUSIONS

It was considered that SP released from the nerve ending, had an important role in the degranulation of dermal mast cells. Results of this study suggest that the tachykinin receptor antagonist exhibited an inhibitory effect on aggravated stress-induced dermatitis.

Activation of central neurokinin-1 receptors induces reinstatement of cocaine-seeking behavior

A number of neurochemical systems have been implicated in mediating relapse to drug-seeking behavior. Substance P (SP) is a neuropeptide that interacts with some of these systems, suggesting a possible role for SP and its preferred receptor, the neurokinin-1 (NK-1) receptor, in the mediation of relapse. In this study, we examined whether selective activation of NK-1 receptors induces reinstatement of cocaine-seeking behavior, and whether endogenous activity at these receptors is involved in mediating cocaine-induced reinstatement. For each experiment, rats were trained to self-administer cocaine for 8--10 days, and following a period of extinction, tests for reinstatement were given. To examine the effects of NK-1 receptor activation on reinstatement of cocaine-seeking behavior, animals received an intracerebroventricular (ICV) infusion of the selective NK-1 receptor agonist, [Sar(9)Met(O(2))(11)]-SP (0, 1, 3 microg), immediately prior to the test session. To examine the role of endogenous NK-1 receptor activity on cocaine-induced reinstatement, rats were pretreated with ICV infusions of the selective NK-1 receptor antagonists, RP 67580 (0, 0.1, 0.5, 2.5 nmol) or GR 82334 (0, 2, 10, 50 pmol), prior to systemic priming injections of cocaine (10mg/kg or 20mg/kg; i.p.). The results showed that [Sar(9)Met(O(2))(11)]-SP induced reinstatement of cocaine-seeking behavior, but that RP 67580 and GR 82334 had no effect on cocaine-induced reinstatement. These findings suggest that while activation of NK-1 receptors is capable of inducing reinstatement of cocaine-seeking behavior, endogenous activity at these receptors is not involved in mediating the priming effects of cocaine on reinstatement of drug-seeking behavior.

Substance P receptor antagonists in psychiatry: rationale for development and therapeutic potential

Increasing evidence suggests that substance P (SP) and its receptor (neurokinin [NK]-1 receptor [NK1R]) might play an important role in the modulation of stress-related, affective and/or anxious behaviour. First, SP and NK1R are expressed in brain regions that are involved in stress, fear and affective response (e.g. amygdala, hippocampus, hypothalamus and frontal cortex). Second, the SP content in these areas changes upon application of stressful stimuli. Third, the central administration of SP produces a range of fear-related behaviours. In addition, the SP/NK1R system shows significant spatial overlap with neurotransmitters such as serotonin and noradrenaline (norepinephrine), which are known to be involved in the regulation of stress, mood and anxiety. Therefore, it was hypothesised that blockade of the NK1R might have anxiolytic as well as antidepressant effects. Preclinical studies investigating the effects of genetic or pharmacological NK1R inactivation on animal behaviour in assays relevant to depression and anxiety revealed that the behavioural changes resemble those seen with reference antidepressant or anxiolytic drugs. Furthermore, antagonism or genetic inactivation of the NK1R causes alterations in serotonin and norepinephrine neuronal transmission that are likely to contribute to the antidepressant/anxiolytic activity of NK1R antagonists but that are--at least partially--distinct from those produced by established antidepressant drugs. This underlines the conceivable unique mechanism of action of this new class of compounds. In three independent clinical trials with three different compounds (aprepitant [MK-869], L-759274 and CP-122721), an antidepressant effect of NK1R antagonists could be demonstrated. These results, however, have been challenged by recent failed studies with aprepitant. There are numerous indications from preclinical studies that, in addition to SP and NK1R, other neurokinins and/or neurokinin receptors might also be involved in the modulation of stress-related behaviour and that exclusive blockade of the NK1R might not be sufficient to produce consistent anxiolytic and antidepressant effects. One such candidate is the neurokinin-2 receptor (NK2R), and clinical trials to assess the antidepressant effects of NK2R antagonists are currently underway. Of special interest might also be substances that block more than one receptor type such as NK1/2R antagonists or NK1/2/3R antagonists. These compounds may be more efficacious in antagonising the effects of SP than compounds that only block the NK1R.

The effects of substance P after central administration on the activity of the mesolimbic system of the rat brain as studied by microdialysis

In vivo microdialysis was used to study the effects of substance P on dopamine, dihydroxyphenylacetic acid, and homovanillic acid levels in the nucleus accumbens in rats. Each animal received sequential injections of physiological saline, 0.1 microg of substance P, and 1 microg of substance P into the lateral ventricle over three days. Dialysates showed increases in dopamine levels in response to neuropeptide, by 41% for the 0.1 microg dose and 71% for the 1 microg dose. The dynamics of these changes also depended on the concentration of the agent. Administration of 1 microg of substance P gave a peak dopamine level at 50 min; the neurotransmitter level remained significantly elevated 75 min after dosage with substance P. The dopamine level was increased only at 75 min when the 0.1 microg dose of neuropeptide was used. Changes in metabolite levels were also dose-dependent. After the 1 microg dose, the dihydroxyphenylacetic acid level increased by 28%, while the 0.1 microg dose produced no significant change in the level of this metabolite. The homovanillic acid level did not respond to administration of substance P at either dose. These data support the suggestion that the influence of substance P on the internal compensation system is to a significant extent mediated by dopaminergic mechanisms and provides a possible explanation for the effects of the neuropeptide seen in a conditioned place preference reflex.

Mutagenesis and knockout models: NK1 and substance P

Tachykinins play an important role as peptide modulators in the CNS. Based on the concentration and distribution of the peptides and their receptors, substance P (SP) and its cognate receptor neurokinin 1 (NK1R) seem to play a particularly important role in higher brain functions. They are expressed at high levels in the limbic system, which is the neural basis of emotional responses. Three different lines of evidence from physiological studies support such a role of SP in the regulation of emotionality: (1) stress is often associated with elevated level of SP in animals and humans; (2) systematic and local injections of SP influence anxiety levels in a dose-dependent and site-specific manner; (3) NK1 receptor antagonists show anxiolytic effects in different animal models of anxiety. Although these studies point to the NK1 receptor as a promising target for the pharmacotherapy of anxiety disorders, high affinity antagonists for the human receptors could not be studied in rats or mice due to species differences in the antagonist binding sites. However, studies on anxiety and depression-related behaviors have now been performed in mouse mutants deficient in NK1 receptor or SP and NKA. These genetic studies have shown that anxiety and depression-related phenotypes are profoundly affected by the tachykinin system. For example, NK1R-deficient mice seem to be less prone depression-related behaviors in models of depression, and one study also provided evidence for reduced anxiety levels. Mice deficient in SP and NKA behaved similarly as the NK1R knockouts. In animal models of anxiety they performed like wildtype mice treated with anxiolytic drugs. In behavioral paradigms related to depression they behaved like wildtype animals treated with antidepressants. In summary, the genetic studies clearly show that the SP/NK1 system plays an important role in the modulation of emotional behaviors.

Neurokinin-1 receptor antagonism by SR140333: enhanced in vivo ACh in the hippocampus and promnestic post-trial effects

Substance P (SP) has memory-promoting, reinforcing and anxiolytic-like effects when applied systemically or centrally. Such effects may be mediated by the neurokinin-1 (NK-1) receptor, since SP preferentially binds to this receptor. We measured the effects of a selective non-peptide NK-1 receptor antagonist, SR140333 (1, 3 and 9 mg/kg i.p.) on ACh levels in frontal cortex, amygdala and hippocampus by microdialysis and HPLC. Levels of ACh in the hippocampus increased dose-dependently immediately after treatment. The same doses of SR140333 given post-trial had minor facilitative effects on inhibitory avoidance learning and open-field habituation, but did not have reinforcing effects in a conditioned place preference (CPP) task. The selective action of NK-1 receptor antagonism on hippocampal ACh may be related to its positive influence on learning.

Analogs of WIN 62,577 define a second allosteric site on muscarinic receptors

WIN 51,708 (17-beta-hydroxy-17-alpha-ethynyl-5-alpha-androstano[3,2-b]pyrimido[1,2-a]benzimidazole) and WIN 62,577 (17-beta-hydroxy- 17-alpha-ethynyl-delta(4)-androstano[3,2-b]pyrimido[1,2-a]benzimidazole) are potent and centrally active antagonists at rat, but not human, NK(1) receptors. The interactions of these compounds and some analogs with [(3)H]N-methyl scopolamine ([(3)H]NMS) and unlabeled acetylcholine (ACh) at M(1)-M(4) muscarinic receptors have been studied using equilibrium and nonequilibrium radioligand binding methods. The results are consistent with the predictions of the allosteric ternary complex model. The WIN compounds have log affinities for the unliganded receptor in the range 5 to 6.7, and exhibit positive, negative, or neutral cooperativity with [(3)H]NMS and ACh, depending on the receptor subtype and nature of the interacting ligands. WIN 62,577 is an allosteric enhancer of ACh affinity at M(3) receptors. Although interacting allosterically, WIN 62,577 and WIN 51,708 do not affect [(3)H]NMS dissociation from M(3) receptors. Certain analogs have higher affinities than WIN 62,577, and truncated forms of WIN 62,577, including steroids, also act allosterically. One analog, 17-beta-hydroxy-17-alpha-Delta(4)-androstano[3,2-b]pyrido[2,3-b]indole (PG987), has the unique effect of speeding [(3)H]NMS dissociation; its largest effect, 2.5-fold, is at M(3) receptors. The interaction between PG987 and other allosteric agents on [(3)H]NMS dissociation from M(3) receptors indicate that PG987 binds reversibly to a site distinct from that to which gallamine and strychnine bind: in contrast, PG987 seems to bind to the same site on M(3) receptors as KT5720, staurosporine, and WIN 51,708. Therefore, in addition to the allosteric site that binds strychnine (and probably chloromethyl brucine, another allosteric enhancer) there is a second, nonoverlapping, pharmacologically distinct allosteric site on M(3) receptors that also supports positive cooperativity with ACh.

The effects of ventral tegmental administration of GABA(A), GABA(B), NMDA and AMPA receptor agonists on ventral pallidum self-stimulation

The ventral pallidum (VP) is a basal forebrain structure that is interconnected with motor and limbic structures and may be considered as an interface between motivational and effector neural signals. Results from a considerable number of studies suggest that this structure is critically involved in reward-related behavior. The VP shares reciprocal connections with other reward-implicated regions, such as the ventral tegmental area (VTA). This anatomy predicts that drug-induced neuronal alterations in the VTA could profoundly alter the function of the VP. Here, using the curve-shift intracranial self-stimulation method, we studied the effects of muscimol (GABA(A) agonist), baclofen (GABA(B) agonist), NMDA and AMPA, microinjected bilaterally into the VTA on the rewarding efficacy of VP self-stimulation. Central injections of the highest dose of muscimol (0.128 microg) resulted in significant elevations in VP self-stimulation thresholds, indicating a reduction in the rewarding efficacy of the stimulation. Elevations in VP self-stimulation thresholds were also evident after intrategmental injections of higher doses of baclofen (0.12, 0.48 microg). By contrast, intrategmental activation of NMDA and AMPA receptors did not affect reward thresholds. These findings suggest that GABAergic and glutamatergic transmission in the VTA activate different circuits that may mediate different functions. Thus, the VTA--VP projection activated by GABA modulates VP stimulation reward, while the projection activated by glutamate may be involved in reward-unrelated effects, rather than in the processing of reward. The decreased rewarding efficacy of VP self-stimulation following intrategmental injections of muscimol and baclofen may be due to GABAergic modulation of ventral tegmental dopaminergic and nondopaminergic neurons projecting to the VP.

Opposite effects of substance P fragments C (anxiogenic) and N (anxiolytic) injected into dorsal periaqueductal gray

Recent findings implicating neurokinins in the expression of anxiety-like behaviors have stimulated interest in the participation of these neuropeptides in the dorsal periaqueductal gray matter (dPAG), one of the main output regions of the brainstem for the expression of defense reaction. Studies on the behavior of rats submitted to the elevated plus-maze test in this laboratory have shown that microinjections of substance P into the dorsal periaqueductal gray produce anxiogenic-like effects. Now, we analyze what portion of the molecule of substance P is responsible for these effects through the examination of the action of its C- and N-terminus fragments (6-11 and 1-7) in the elevated plus-maze. We also investigated whether these effects are influenced by prior treatment with the tachykinin NK(1) receptor antagonist 17-beta-hydroxy-17-alpha-ethynyl-5alpha-androstanol[3,2-b]pyrimido[1,2-a]benzimidazole (WIN51,708). To this end, rats were implanted with a cannula in the dorsal periaqueductal gray and injected 1 week later with equimolar doses (17.5 and 35 pmol) of either C- or N-fragments of substance P and tested in the elevated plus-maze. The results show that the C-terminal fragment has an anxiogenic profile of effects, including reduction in the number of entries and time spent in the open arms of the maze, plus increases in scanning, stretched-attend posture, head dipping and flat-back approach. On the other hand, the N-terminal fragment produced opposite effects, namely, an increase in the number of entries and time spent in the open arms of the maze accompanied by an increase in end-arm activity, rearing and head dipping. The tachykinin NK(1) receptor antagonist WIN51,708 (20 mg/kg, i.p.) inhibited the effects of the carboxy-terminal of substance P while it did not change the effects of the N-terminal fragment. Microinjection of WIN51,708 (20 mg/kg, i.p.), by its own, did not produce any significant effects. Therefore, the results indicate that the anxiogenic effects of substance P injected into the dorsal periaqueductal gray are encoded by its carboxy-terminal sequence and due to its action on tachykinin NK(1) receptors.

Place aversion induced by microinjections of C-fragment of substance P into the dorsal periaqueductal gray of rats is mediated by tachykinin NK1 receptors

Neural circuits in the dorsal periaqueductal gray matter (dPAG) play an important role in the integration of defensive behavior. The neurokinin substance P causes conditioned place aversion when administered into this region. The present study examined whether these effects may be mimicked by its carboxy-terminal amino acid sequence and whether they are influenced by prior treatment with the tachykinin NK1 receptor antagonist WIN51,708. The behavioral testing apparatus is a circular open field consisting of 4 uniform quadrants that are equally preferred by the rats prior to drug treatments. For conditioning, rats received drug injections on three consecutive days and were placed into their assigned quadrant. The carboxy-terminal analog (17.5 pmol/0.2 microl) applied into the dPAG produced place aversion effects with reduced time spent in the drug-paired quadrant on the testing day. The effects of the carboxy-terminal analog was antagonized by pretreatment with WIN51,708 (20 mg/kg, i.p.). Microinjection of WIN51,708 (20 mg/kg, i.p.), by its own, did not produce significant effects. These findings suggest that previous reports showing conditioned place aversion effects of SP injected into the dPAG are encoded by its carboxy-terminal sequence and due to its action on tachykinin NK1 receptors.

Neurokinin(1) receptor antagonists as potential antidepressants

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

Involvement of substance P and central opioid receptors in morphine modulation of the CHS response

Morphine administration prior to challenge with the antigen 2,4-dinitro-fluorobenzene increases the contact hypersensitivity (CHS) response in rats. The present study extended these findings by showing that central, but not systemic, administration of N-methylnaltrexone antagonized the morphine-induced enhancement of the CHS response. The importance of the neuroimmune mediator substance P was shown via the attenuation of the morphine-induced enhancement following both systemic and topical administration of the NK-1 antagonist WIN51,708. Taken together, the findings of the present study provide new data showing that central opioid receptors and peripheral substance P are involved in the morphine-induced enhancement of the CHS response.

Rett syndrome: review of biological abnormalities

The Rett syndrome (RS) is a peculiar, sporadic, atrophic disorder, almost entirely confined to females. After the first six months of life there is developmental slowing with reduced communication and head growth for about one year. This is followed by a rapid destructive stage with severe dementia and loss of hand skills (with frequent hand wringing), apraxia and ataxia, autistic features and irregular breathing with hyperventilation. Seizures often supervene. Subsequently there is some stabilization in a pseudo-stationary stage during the preschool to school years, associated with more emotional contact but also abnormalities of the autonomic and skeletal systems. After the age of 15-20 years, a late motor deterioration occurs with dystonia and frequent spasticity but seizures become milder. RS has generally been considered an X-linked disorder in which affected females represent a new mutation, with male lethality. Linkage studies suggested a critical region at Xq28. In 1999, mutations in the gene MECP2 encoding X-linked methyl cytosine-binding protein 2 (MeCP2) were found in a proportion of Rett girls. This protein can bind methylated DNA. Analyses are leading to much further investigation of mutants and their effects on genes. Neuropathological and electrophysiological studies of RS are described. Description of neurometabolic factors includes reduced levels of dopamine, serotonin, noradrenaline and choline acetyltransferase (ChAT) in brain, also estimation of nerve growth factors, endorphin, substance P, glutamate and other amino acids and their receptor levels. The results of neuroimaging are surveyed, including volumetric magnetic resonance imaging (MRI) and positron emission tomography (PET).

The psychopharmacology of tachykinin NK-3 receptors in laboratory animals

The present article reviews the studies so far published on the psychopharmacological effects mediated by tachykinin NK-3 receptors in laboratory animals. Central administration of NK-3 receptor agonists has been reported to attenuate alcohol intake in alcohol-preferring rats and to evoke conditioned place preference. These findings suggest that NK-3 receptors may affect reward processes to drugs of abuse. Anxiolytic-like and antidepressant-like effects have been previously reported for NK-1 receptor antagonists, and anxiolytic-like effects for NK-2 receptor antagonists. More recently, it has been shown that NK-3 receptor agonists have anxiolytic-like and antidepressant-like effects in mice and rats, while an NK-3 receptor antagonist was reported to be anxiogenic in mice. These findings indicate that different TK receptor subtypes may be involved in anxiolytic-like and antidepressant-like effects in laboratory animals and raise interest for the possible role of NK-3 receptors in the control of anxiety and depression in man.

Substance P and its role in neural mechanisms governing learning, anxiety and functional recovery

The neurokinin Substance P (SP) is widely distributed in the central nervous system and has been extensively studied in various functional aspects. This review focuses on the behavioral relevance of SP. Here we show that SP can have memory-promoting, reinforcing and anxiolytic-like effects when administered systemically or into the nucleus basalis of the ventral pallidum. These effects seem to be mediated via the SP-preferring NK(1)receptor and differentially related to N- versus C-terminal fragments of the undecapeptide. Secondly, SP injection into the ventral pallidum can lead to increases of acetylcholine in frontal cortex and dopamine in nucleus accumbens, suggesting that the hypermnestic, positively reinforcing and anxiolytic effects observed upon basal forebrain injection of SP are mediated by activation of the nucleus accumbens-ventral pallidum circuitry. Furthermore, SP and certain SP-fragments may not only be considered to have beneficial behavioral effects in normal animals, but can also prevent lesion-induced functional deficits and improve the speed of recovery. This indicates that SP agonists might also have a neuroprotective capacity in parallel with recovery-promoting actions.

Nociceptin/orphanin FQ and drugs of abuse

Nociceptin/orphanin FQ (NC) binds with high affinity to the opioid receptor-like1 (ORL1) receptor. NC has been reported to block opioid-induced supraspinal analgesia, and it has been proposed that it may represent a functional antiopioid peptide in the control of brain nociceptive processes. The wide distribution of NC and of its receptors in the central nervous system suggests, however, that it may be involved in the control of a variety of biologic functions. Increasing evidence indicates that it may influence the rewarding and reinforcing properties of drugs of abuse. NC has been shown to abolish the rewarding properties of ethanol and morphine in the place conditioning paradigm, to reduce ethanol consumption in alcohol-preferring rats and to inhibit stress-induced alcohol-seeking behavior. These findings suggest that drugs directed at central NC receptors may represent an interesting approach to the treatment of ethanol and opiate abuse.

Anxiolytic-like effects in rats produced by ventral pallidal injection of both N- and C-terminal fragments of substance P

Prior studies have shown that the neurokinin substance P (SP) has anxiolytic-like effects when administered into the nucleus basalis (NB) area of the rat ventral pallidum. The present work was performed to examine whether the anxiolytic effects of SP in the nucleus basalis can be assigned its amino (N)- or carboxy (C)-terminal moiety. Using the elevated plus-maze model of anxiety in combination with unilateral injection of N-terminal SP(1-7) or C-terminal SP(7-11) into the NB region, we found that the treatment with either SP-fragment increased the number of entries into and time spent on the open arms as well as excursions into the end of the open arms, indicative of an anxiolytic-like profile. Furthermore, the effective doses of SP(1-7) (0.67 ng) and SP(7-11) (0.45 ng) were equimolar to the dosage of the whole SP molecule (1 ng), which was effective to reduce anxiety. Thus, the results support earlier findings that ventral pallidal injection of SP has anxiolytic-like effects and provide new evidence that fragments of SP, representing the N- and C-terminal domain of the peptide can reduce fear-parameters at a concentration similar to that of the parent peptide.

The neurokinin-1 receptor antagonist WIN51,708 attenuates the anxiolytic-like effects of ventralpallidal substance P injection

We reported previously that the neurokinin substance P has anxiolytic-like effects when administered into the nucleus basalis of the rat ventral pallidum. The present study aimed to determine the possible involvement of the neurokinin-1 receptor in the anxiolytic action of intrabasalis substance P injection. Behavioral testing was performed in the rat elevated plus-maze model of anxiety. Microinjection of substance P (1 ng) into the nucleus basalis increased sojourn times on the open arms, excursions into the end of the open arms and scanning over the edge of an open arm, indicative of an anxiolytic-like profile. The non-peptide neurokinin-1 receptor antagonist WIN51,708, administered i.p. 20 min prior to intrabasalis substance P injection, antagonized the anxiolytic effects of the neurokinin in a dose-dependent manner. WIN51,708 at 10 mg/kg diminished, while at the higher dose of 20 mg/kg the antagonist completely blocked, the effect of substance P on anxiety-related behaviors. These findings suggest that the anxiolytic-like effects of substance P in the nucleus basalis are mediated through neurokinin-1 receptive sites.