Localization of Fos-like immunoreactivity induced by the NK3 tachykinin receptor agonist, senktide, in the guinea-pig brain

Ionic signalling mechanisms involved in neurokinin-3 receptor-mediated augmentation of fear-potentiated startle response in the basolateral amygdala

The tachykinin peptides include substance P (SP), neurokinin A and neurokinin B, which interact with three G-protein-coupled neurokinin receptors, NK1Rs, NK2Rs and NK3Rs, respectively. Whereas high densities of NK3Rs have been detected in the basolateral amygdala (BLA), the functions of NK3Rs in this brain region have not been determined. We found that activation of NK3Rs by application of the selective agonist, senktide, persistently excited BLA principal neurons. NK3R-elicited excitation of BLA neurons was mediated by activation of a non-selective cation channel and depression of the inwardly rectifying K+ (Kir) channels. With selective channel blockers and knockout mice, we further showed that NK3R activation excited BLA neurons by depressing the G protein-activated inwardly rectifying K+ (GIRK) channels and activating TRPC4 and TRPC5 channels. The effects of NK3Rs required the functions of phospholipase Cβ (PLCβ), but were independent of intracellular Ca2+ release and protein kinase C. PLCβ-mediated depletion of phosphatidylinositol 4,5-bisphosphate was involved in NK3R-induced excitation of BLA neurons. Microinjection of senktide into the BLA of rats augmented fear-potentiated startle (FPS) and this effect was blocked by prior injection of the selective NK3R antagonist SB 218795, suggesting that activation of NK3Rs in the BLA increased FPS. We further showed that TRPC4/5 and GIRK channels were involved in NK3R-elicited facilitation of FPS. Our results provide a cellular and molecular mechanism whereby NK3R activation excites BLA neurons and enhances FPS. KEY POINTS: Activation of NK3 receptors (NK3Rs) facilitates the excitability of principal neurons in rat basolateral amygdala (BLA). NK3R-induced excitation is mediated by inhibition of GIRK channels and activation of TRPC4/5 channels. Phospholipase Cβ and depletion of phosphatidylinositol 4,5-bisphosphate are necessary for NK3R-mediated excitation of BLA principal neurons. Activation of NK3Rs in the BLA facilitates fear-potentiated startle response. GIRK channels and TRPC4/5 channels are involved in NK3R-mediated augmentation of fear-potentiated startle.

Inhibition of substance P-induced defensive behavior via neurokinin-1 receptor antagonism in the central and medial but not basolateral nuclei of the amygdala in male Wistar rats

RATIONALE

The production of unconditioned defensive behaviors has been related to the amygdala, a key component of the encephalic aversion system. Microinjection of the neuropeptide substance P (SP) in the amygdala elicits defensive behaviors via the activation of type 1 neurokinin (NK-1) receptors. However, no studies have investigated whether intra-amygdala SP/NK-1 mechanisms can elicit other types of defensive responses, such as antinociception and ultrasonic vocalizations (USVs).

METHODS

The present study investigated the effects of SP-induced activation of the neurokininergic system in three main nuclei of the amygdala-basolateral (BLA), central (CeA), and medial (MeA) nuclei-in rats that were subjected to the elevated plus maze (EPM), tail-flick test, and USV recording. The effects of SP in these amygdaloid nuclei were challenged with combined injections of the NK-1 receptor antagonist spantide.

RESULTS

The present study showed that SP injections in the CeA and MeA but not BLA exerted anxiogenic-like effects. In contrast to the CeA, the anxiogenic-like effects of SP in the MeA were not dependent on NK-1 mechanisms. In the tail-flick test, SP microinjections produced antinociceptive effects only in the MeA through NK-1 receptor activation. No USV emissions were detected after the SP microinjections.

CONCLUSIONS

The present study showed that NK-1 receptors in the CeA and MeA but not BLA are involved in defensive reactions to conditions of fear. The present results may provide a better understanding of the neurochemical mediation of fear states.

A role for Tac2, NkB, and Nk3 receptor in normal and dysregulated fear memory consolidation

The centromedial amygdala (CeM), a subdivision of the central amygdala (CeA), is believed to be the main output station of the amygdala for fear expression. We provide evidence that the Tac2 gene, expressed by neurons specifically within the CeM, is required for modulating fear memories. Tac2 is colocalized with GAD65 and CaMKIIα but not with PKCd and Enk neurons in the CeM. Moreover, the Tac2 product, NkB, and its specific receptor, Nk3R, are also involved in the consolidation of fear memories. Increased Tac2 expression, through a stress-induced PTSD-like model, or following lentiviral CeA overexpression, are sufficient to enhance fear consolidation. This effect is blocked by the Nk3R antagonist osanetant. Concordantly, silencing of Tac2-expressing neurons in CeA with DREADDs impairs fear consolidation. Together, these studies further our understanding of the role of the Tac2 gene and CeM in fear processing and may provide approaches to intervention for fear-related disorders.

Neurokinin B causes acute GnRH secretion and repression of GnRH transcription in GT1-7 GnRH neurons

Genetic studies in human patients with idiopathic hypogonadotropic hypogonadism (IHH) identified mutations in the genes that encode neurokinin B (NKB) and the neurokinin 3 receptor (NK3R). However, determining the mechanism whereby NKB regulates gonadotropin secretion has been difficult because of conflicting results from in vivo studies investigating the luteinizing hormone (LH) response to senktide, a NK3R agonist. NK3R is expressed in a subset of GnRH neurons and in kisspeptin neurons that are known to regulate GnRH secretion. Thus, one potential source of inconsistency is that NKB could produce opposing direct and indirect effects on GnRH secretion. Here, we employ the GT1-7 cell model to elucidate the direct effects of NKB on GnRH neuron function. We find that GT1-7 cells express NK3R and respond to acute senktide treatment with c-Fos induction and increased GnRH secretion. In contrast, long-term senktide treatment decreased GnRH secretion. Next, we focus on the examination of the mechanism underlying the long-term decrease in secretion and determine that senktide treatment represses transcription of GnRH. We further show that this repression of GnRH transcription may involve enhanced c-Fos protein binding at novel activator protein-1 (AP-1) half-sites identified in enhancer 1 and the promoter, as well as chromatin remodeling at the promoter of the GnRH gene. These data indicate that NKB could directly regulate secretion from NK3R-expressing GnRH neurons. Furthermore, whether the response is inhibitory or stimulatory toward GnRH secretion could depend on the history or length of exposure to NKB because of a repressive effect on GnRH transcription.

In vitro and in vivo characterization of the non-peptide NK3 receptor antagonist SB-223412 (talnetant): potential therapeutic utility in the treatment of schizophrenia

Neurokinin-3 (NK3) receptors are concentrated in forebrain and basal ganglia structures within the mammalian CNS. This distribution, together with the modulatory influence of NK3 receptors on monoaminergic neurotransmission, has led to the hypothesis that NK3 receptor antagonists may have therapeutic efficacy in the treatment of psychiatric disorders. Here we describe the in vitro and in vivo characterization of the highly selective NK3 receptor antagonist talnetant (SB-223412). Talnetant has high affinity for recombinant human NK3 receptors (pKi 8.7) and demonstrates selectivity over other neurokinin receptors (pKi NK2 = 6.6 and NK1<4). In native tissue-binding studies, talnetant displayed high affinity for the guinea pig NK3 receptor (pKi 8.5). Functionally, talnetant competitively antagonized neurokinin B (NKB)-induced responses at the human recombinant receptor in both calcium and phosphoinositol second messenger assay systems (pA2 of 8.1 and 7.7, respectively). In guinea pig brain slices, talnetant antagonized NKB-induced increases in neuronal firing in the medial habenula (pKB = 7.9) and senktide-induced increases in neuronal firing in the substantia nigra pars compacta (pKB = 7.7) with no diminution of maximal agonist efficacy, suggesting competitive antagonism at native NK3 receptors. Talnetant (3-30 mg/kg i.p.) significantly attenuated senktide-induced 'wet dog shake' behaviors in the guinea pig in a dose-dependent manner. Microdialysis studies demonstrated that acute administration of talnetant (30 mg/kg i.p.) produced significant increases in extracellular dopamine and norepinephrine in the medial prefrontal cortex and attenuated haloperidol-induced increases in nucleus accumbens dopamine levels in the freely moving guinea pigs. Taken together, these data demonstrate that talnetant is a selective, competitive, brain-penetrant NK3 receptor antagonist with the ability to modulate mesolimbic and mesocortical dopaminergic neurotransmission and hence support its potential therapeutic utility in the treatment of schizophrenia.

Central injection of senktide, an NK3 receptor agonist, or neuropeptide Y inhibits LH secretion and induces different patterns of Fos expression in the rat hypothalamus

Arcuate neurokinin B (NKB) neurons express estrogen receptor-alpha and are strongly modulated by gonadal steroids. Although numerous studies suggest that NKB neurons participate in the reproductive axis, there is no information on the regulation of luteinizing hormone (LH) secretion by NKB or its receptor, NK3. In the present study, we determined if central injection of senktide, a selective NK3 receptor agonist, would alter serum LH in ovariectomized, estrogen-primed rats. The effects of senktide were compared to neuropeptide Y (NPY), a well-characterized modulator of LH secretion. Saline, senktide, or NPY was injected into the lateral ventricle of unanesthetized rats and serial blood samples were collected for LH radioimmunoassay. The rats were sacrificed 90 min after injection and the brains were removed and processed for Fos immunocytochemistry. A significant inhibition of serum LH was observed from 30 to 90 min after injection of senktide relative to saline controls. In the senktide-injected rats, the inhibition of serum LH was accompanied by increased Fos expression in the medial preoptic area and arcuate nucleus--two reproductive control centers. Senktide also induced Fos in the paraventricular nuclei (PVN) and supraoptic nuclei (SON). Injection of NPY also inhibited serum LH but increased Fos expression only in the PVN and SON. This study provides the first demonstration of alterations in LH secretion by an NK3 receptor agonist. These data, combined with the induction of Fos in medial preoptic and arcuate neurons, strongly support the hypothesis that NKB neurons play a role in the regulation of gonadotropin secretion.

Cigarette smoke increases mucosal permeability in guinea pig trachea via tachykinin NK2 receptor activation

We investigated whether exposure to cigarette smoke increases the mucosal permeability in guinea pig trachea and if this effect could be mediated by tachykinin NK2 receptor activation. Guinea pigs were exposed to either three different doses of cigarette smoke or room air. Mucosal permeability was measured by monitoring the rate of appearance in the circulation of horseradish peroxidase (HRP) that had been instilled into the isolated tracheal segment. Exposure to 20 and 30 puffs but not 10 puffs of cigarette smoke increased the tracheal mucosal permeability. Pretreatment with the tachykinin NK2 receptor antagonist SR48,968 [(S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzamide] completely inhibited the increase in the permeability of the tracheal mucosa induced by exposure to cigarette smoke, whereas the tachykinin NK1 receptor antagonist SSR240,600 [(R)-2-(1-{2-[4-{2-[3,5-bis(trifluoromethyl)phenyl]acetyl}-2-(3,4-dichlorophenyl)-2-morpholinyl]ethyl}-4-piperidinyl)-2-methylpropanamide] and the tachykinin NK3 receptor antagonist SR142,801 [(S)-(N)-(1-[3-(1-benzoyl-3(3,4-dichlorophenyl)piperidine-3-yl)propyl]-4-phenylpiperidin-4-yl)-N-methyl-acetamide] had no effect. It is concluded that endogenous tachykinins via NK2 receptor activation mediate the increase in the permeability of the tracheal mucosa induced by exposure to cigarette smoke in guinea pigs.

NK-3 receptor activation depolarizes and induces an after-depolarization in pyramidal neurons in gerbil cingulate cortex

The involvement of tachykinins in cortical function is poorly understood. To study the actions of neurokinin-3 (NK3) receptor activation in frontal cortex, whole cell patch clamp recordings were performed from pyramidal neurons in slices of cingulate cortex from juvenile gerbils. Senktide (500nM), a selective NK3 receptor agonist, induced a transient increase in spontaneous EPSPs in layer V pyramidal neurons, accompanied by a small depolarization ( approximately 4 mV). EPSPs during senktide had a larger amplitude and faster 10-90% rise time than during control. Senktide induced a transient depolarization in layer II/III pyramidal neurons, which often reached threshold for spikes. The depolarization ( approximately 6 mV) persisted in TTX, and was accompanied by an increase in input resistance. Senktide also transiently induced a slow after-depolarization, which appeared following a depolarizing pulse. The slow after-depolarization persisted in TTX. These data suggest that activation of NK3 receptors on layer II/III pyramidal neurons induce post-synaptic depolarization and an after-depolarization, which could be mediated by blockade of a leak potassium conductance and a non-selective cation conductance, respectively.

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

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

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Permissive role of neurokinin NK(3) receptors in NK(1) receptor-mediated activation of the locus coeruleus revealed by SR 142801

The present experiments investigated the role of neurokinin-1 (NK(1)) and neurokinin-3 (NK(3)) receptors on the activity of the locus coeruleus (LC)-noradrenergic system by using a dual probe microdialysis technique in anesthetized guinea pigs. The local application in the LC of the selective NK(1) receptor agonists [SAR(9),Met(O(2))(11)]-SP (10 microM) and septide (1 microM) as well as the selective NK(3) receptor agonist senktide (1 microM), enhanced the extracellular norepinephrine (NE) levels in the prefrontal cortex. The enhancing effect of [SAR(9),Met(O(2))(11)]-SP was completely blocked by the peripheral administration of the selective non peptide NK(1) and NK(3) receptor antagonists, GR 205171 (1 mg/kg, i.p.) and SR 142801 (0.1 mg/kg, i.p.), respectively, whereas SR 142806 (0.1 mg/kg, i.p.) the inactive enantiomer of SR 142801 had no effect. Moreover, the [SAR(9),Met(O(2))(11)]-SP-induced increase in LC DOPAC concentrations, is only antagonized by GR 205171. In contrast, only SR 142801 (0.3 mg/kg, i.p.) could block stereoselectively the senktide-evoked increase in NE levels. Both [SAR(9),Met(O(2))(11)]-SP and senktide effects were blocked by local infusion into the LC of SR 142801 (10(-9) M). These results demonstrate that stimulation of NK(1) and NK(3) receptors located in the LC area modulates the activity of the LC-NE system, and that the excitatory effects of NK(1) receptor agonists require NKB/NK(3) receptor activation in the LC.

Role of tachykinin receptors in the central processing of afferent input from the acid-threatened rat stomach

Noxious challenge of the rat gastric mucosa by hydrochloric acid (HCl) is signalled via vagal afferent neurons to several brain nuclei in which tachykinins and tachykinin receptors are present. Therefore, we tested whether tachykinin receptor antagonists would modify the central transmission of input from the acid-threatened stomach. Neuronal excitation was visualized by in situ hybridization autoradiography (ISH) of c-fos messenger ribonucleic acid (mRNA) 45 min after intragastric (IG) administration of HCl (0.5 M; 10 ml/kg). This stimulus has previously been shown to cause neurons in the nucleus tractus solitarii (NTS), lateral parabrachial nucleus (LPB), paraventricular (Pa) nuclei, supraoptic (SO) nucleus, central amygdala (CeA), area postrema (AP), subfornical organ (SFO) and habenula (Hb) to express c-fos mRNA. Intraperitoneal (IP) pretreatment with the NK1 receptor antagonist GR-205,171 (3 mg/kg) attenuated the acid-induced transcription of c-fos mRNA in NTS and augmented it in SFO. The NK2 receptor antagonist SR-144,190 (0.1 mg/kg, IP) had no effect. Subcutaneous administration of the NK3 receptor antagonist SB-222,200 (20 mg/kg) reduced the c-fos mRNA response in AP and SFO and enhanced it in Hb. These data show that the transmission of input from the acid-threatened stomach in distinct brain nuclei involves tachykinins acting at NK1 and NK3 receptors, but not NK2 receptors.

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

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

Localization of NK1 and NK3 receptors in guinea-pig brain

In this study the localizations of tachykinin neurokinin-1 (NK1) and neurokinin-3 (NK3) receptors in the guinea-pig brain are described. In agreement with studies in rat and human brain, the neurons that exhibited the most marked NK1 receptor immunoreactivity were found in the dorsomedial caudate putamen. NK1 receptors were also widely distributed in diencephalic structures and in the mid and hind brain. NK3 receptors were distributed in both superficial and deep layers of the cortex and many appeared to be located on cells with astrocyte-like morphology in the glia limitans. In several regions including the thalamus, hypothalamus, amygdala, periaqueductal gray, substantia nigra and area postrema, both NK1 and NK3 immunoreactivity were found. The present study revealed that tachykinin receptors are widely distributed in the guinea-pig central nervous system.

Detailed distribution of Neurokinin 3 receptors in the rat, guinea pig and gerbil brain: a comparative autoradiographic study

The neurokinin 3 (NK3) receptor is predominantly expressed in the central nervous system (CNS). Species differences in neurokinin 3 (NK3) receptor pharmacology have led to the preferential use of guinea pigs and gerbils in the characterization of non-peptide NK3 antagonists. Little is known about the central localization of NK3 receptors in the CNS of these species. To study this, [(3)H]senktide and [(3)H]SR 142801 were used in autoradiography experiments to visualize the NK3 receptors in the guinea pig and gerbil brain and compared to with the distribution of [(3)H]senktide binding sites in the rat brain. In the three species, the NK3 receptor was similarly distributed within the cerebral cortex, the zona incerta, the medial habenula, the amygdaloid complex, the superior colliculus and the interpeduncular nucleus. Outside of these structures, our study has revealed that each species displayed a specific distribution pattern of central NK3 receptors. The rat was the only species where NK3 receptors could be visualized in the striatum, the supraoptic nucleus and the paraventricular nucleus of the hypothalamus. The guinea pig differed mainly from the two other species by the absence of detectable binding sites in the substantia nigra pars compacta and the ventral tegmental area. A specific localization of NK3 receptors in the anterodorsal and anteroventral thalamic nuclei characterized the gerbil. This last species is also unique by in the higher level of NK3 receptors in the dorsal and median raphe nuclei. All these differences suggest that the NK3 receptor mediates different functions in different species.

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.

Localization of tachykinin receptors and Fos-like immunoreactivity induced by substance P in guinea-pig brain

1. In the present study, a comparison was made between the distribution of tachykinin NK1 and NK3 receptor immunoreactivity and the distribution of Fos-like immunoreactivity induced by the tachykinin agonist substance P (SP) in the guinea-pig brain. 2. In agreement with results from previous studies in rat brain, NK1 receptor-immunoreactive neurons were found to be widely distributed throughout the brain in the striatum and in diencephalic and mesencephalic structures, while NK3 receptor-immunoreactive neurons were mainly in telencephalic structures. Considerable overlap was observed between NK1 and NK3 receptor distributions. 3. Substance P induced Fos-like immunoreactivity (Fos-LI) in extensive areas of the guinea-pig brain. The induction of Fos-LI was markedly inhibited in many areas by pretreatment with the NK1 receptor antagonist SR 140333. The NK3 receptor antagonist SR 142801 reduced Fos-LI staining in fewer areas, although a reduction was observed in the cortex, striatum and hypothalamus. 4. In general, tachykinin receptors were located at sites corresponding to areas of functional activation by SP, as shown by Fos-LI. These results extend previous studies by adding a functional dimension to tachykinin receptor localization studies.

Distribution of Fos-like immunoreactivity within the rat brain following intraventricular injection of the selective NK(3) receptor agonist senktide

Neurokinin B (NKB) is one member of an evolutionarily conserved family of neuropeptides, the tachykinins. Preferential binding of NKB to endogenous NK(3) receptors affects a variety of biological and physiological processes, including endocrine secretions, sensory transmission, and fluid and electrolyte homeostasis. In light of its widespread biological actions, immunohistochemical detection of the c-Fos protein product was used to study the distribution of neuronal activation in the rat brain caused by intraventricular (icv) injections of the selective NK(3) receptor agonist (succinyl-[Asp(6), N-Me-Phe(8)] substance P [6-11]), senktide. Quantitative analysis revealed that treatment with isotonic saline or 200 ng senktide resulted in the differential expression of Fos-like immunoreactivity (FLI) throughout the brain. Senktide induced the highest number of FLI neurons in the lateral septum, bed nucleus of the stria terminalis, amygdala, paraventricular nucleus of the hypothalamus, median preoptic nucleus, organum vasculosum of the lamina terminalis, supraoptic nucleus, periaqueductal gray, and medial nucleus of the solitary tract compared to isotonic saline controls. Additional regions that contained elevated FLI following icv injection of senktide, relative to saline injection, included the cerebral cortex, lateral hypothalamic nucleus, suprachiasmatic nucleus, ventral tegmental area, substantia nigra, inferior colliculus, locus coeruleus, zona incerta, and arcuate nucleus. Our data indicate that activation of NK(3) receptors induces the expression of FLI within circumscribed regions of the rat brain. This pattern of neuronal activation overlaps with nuclei known to regulate homeostatic processes, such as endocrine secretion, cardiovascular function, salt intake, and nociception.

Distribution of Fos-like immunoreactivity in guinea-pig brain following administration of the neurokinin-1 receptor agonist, [SAR9,MET(O2)11]substance P

The tachykinins are a family of peptides with putative neurotransmitter roles in the nervous system. They mediate their effects via neurokinin-1, neurokinin-2 and neurokinin-3 receptors. There has been increasing interest in the therapeutic application of the tachykinin neurokinin-1 receptor antagonists in the treatment of pain and emesis, and more recently in depression. However, the central role of neurokinin-1 receptors is not well understood. The aims of the present study were to determine the behavioural responses of guinea-pigs, and the distribution of Fos-like immunoreactivity in the guinea-pig brain, following intracerebroventricular administration of the neurokinin-1 receptor-selective agonist, [Sar9,Met(O2)11]substance P. The effects of pretreatment with the neurokinin-1 receptor antagonist, SR 140333, were also investigated. Administration of [Sar9,Met(O2)11]substance P induced increased locomotor activity, as well as face washing, grooming and wet-dog shake behaviours, all of which were inhibited by the neurokinin-1 receptor antagonist, SR 140333, indicating the involvement of neurokinin-1 receptors. In order to localize the brain regions activated by [Sar9,Met(O2)11]substance P, the distribution of neurons expressing Fos-like immunoreactivity was examined. [Sar9,Met(O2)11]substance P induced increased Fos-like immunoreactivity in widespread areas, including the frontal cortex, hippocampus, amygdala, thalamus, hypothalamus, periaqueductal gray, area postrema and nucleus of the solitary tract. SR 140333 reduced Fos-like immunoreactivity induced by [Sar9,Met(O2)11]substance P in most areas. Thus, brain regions associated with emotion, sensation, learning and memory, autonomic regulation and emesis were activated by stimulation of neurokinin-1 receptors. The present data have added a functional domain to previous neurokinin-1 receptor localization studies by describing the extensive regions of the CNS that may be activated by stimulation of these receptors, and the potential of neurokinin-1 receptor antagonists to inhibit activation of these regions.

Naloxone-induced changes in tachykinin NK3 receptor modulation of experimental anxiety in mice

This study investigates the influence of naloxone, an opioid antagonist, upon the effects of drugs acting on tachykinin NK3 receptor in the elevated plus-maze test. Mice were intracerebroventricularly (i.c.v.) injected either with vehicle, 10 pmol of senktide, an NK3 agonist, or 100 pmol of [Trp7beta-Ala8]NKA(4-10) or SR142801, NK3 antagonists. Senktide alone significantly increased the frequency of entries and the time spent in open arms, an anxiolytic-like effect, whereas the NK3 antagonists alone showed no effect at the dose used. Naloxone alone did not alter the behavior of the animals on the plus-maze apparatus. Nevertheless, animals pretreated with naloxone (2 mg/kg, i.p.) showed an increase in senktide's anxiolytic-like effect and a similar profile of action for [Trp7beta-Ala8]NKA(4-10), but not for SR142801, which presented an anxiogenic-like effect. Altogether, these findings indicate a putative neurokinin-opioid relationship in the modulation of experimental anxiety in mice.