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

Effect of endogenous substance P on visceral afferent signal integration in the nucleus tractus solitaries of rat brainstem slices

In the first synapse of the blood-pressure-regulating pathway, a neurokinin (NK) family peptide substance P (SP) is release with an excitatory neurotransmitter, glutamate, to enhance the sensitivity of the baroreflex responses. However, the underlying mechanisms of action are not yet well understood. The effects of NK receptor antagonists and agonists on solitary tract stimulation-evoked excitatory postsynaptic responses were recorded using whole-cell patch-clamp recordings of neurons in the medial portion of the nucleus tractus solitarius (mNTS) in the brainstem. SP reduced the amplitude of the evoked excitatory postsynaptic currents (eEPSCs) and shifted the holding current inward, in a dose-dependent manner. The concentrations of SP needed to induce such responses were different between capsaicin-sensitive unmyelinated (C-type) and capsaicin-resistant myelinated (A-type) neurons. The perfusion of a NK1 receptor antagonist, sendide, reduced the amplitude of eEPSCs in all tested neurons but did not affect the levels of the holding current. A Neurokinin type 1 receptor (NK1 receptor) agonist, [Sar9, Met(O2)11]-SP, reduced the amplitude of the eEPSCs and shifted the holding current inward in capsaicin-resistant neurons; however, it failed to induce any significant changes in the capsaicin-sensitive neurons. Furthermore, a selective Neurokinin type 3 receptor (NK3 receptor) antagonist, SB223412, failed to induce any changes in any tested neuron. In current-clamp experiments, sendide reduced solitary tract (ST)-stimulation evoked firing of action potentials in both A- and C-type neurons. [Sar9, Met(O2)11]-SP suppressed the firing of the action potentials in C-type but not A-type neurons. In spontaneous synaptic recordings, SP reduced frequency of the sEPSCs in CAP sensitive neuron but NK1 agonist reduced at capsaicin resistant neurons. Taken together, the findings show that ST activation leads to the co-transmission of SP and glutamate and enhances baroreflex sensitivity by potentiating the amplitude of eEPSC in an NK1 receptor activity-dependent manner.

Several neuropeptides involved in parkinsonian neuroprotection modulate the firing properties of nigral dopaminergic neurons

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The surviving nigral dopaminergic neurons display altered spontaneous firing activity in Parkinson's disease. The firing rate of nigral dopaminergic neurons decreases long before complete neuronal death and the appearance of parkinsonian symptoms. A mild stimulation could rescue dopaminergic neurons from death and in turn play neuroprotective effects. Several neuropeptides, including cholecystokinin (CCK), ghrelin, neurotensin, orexin, tachykinins and apelin, within the substantia nigra pars compacta play important roles in the modulation of spontaneous firing activity of dopaminergic neurons and therefore involve motor control and motor disorders. Here, we review neuropeptide-induced modulation of the firing properties of nigral dopaminergic neurons. This review may provide a background to guide further investigations into the involvement of neuropeptides in movement control by modulating firing activity of nigral dopaminergic neurons in Parkinson's disease.

Mechanisms of Transmission and Processing of Pain: A Narrative Review

Knowledge about the mechanisms of transmission and the processing of nociceptive information, both in healthy and pathological states, has greatly expanded in recent years. This rapid progress is due to a multidisciplinary approach involving the simultaneous use of different branches of study, such as systems neurobiology, behavioral analysis, genetics, and cell and molecular techniques. This narrative review aims to clarify the mechanisms of transmission and the processing of pain while also taking into account the characteristics and properties of nociceptors and how the immune system influences pain perception. Moreover, several important aspects of this crucial theme of human life will be discussed. Nociceptor neurons and the immune system play a key role in pain and inflammation. The interactions between the immune system and nociceptors occur within peripheral sites of injury and the central nervous system. The modulation of nociceptor activity or chemical mediators may provide promising novel approaches to the treatment of pain and chronic inflammatory disease. The sensory nervous system is fundamental in the modulation of the host's protective response, and understanding its interactions is pivotal in the process of revealing new strategies for the treatment of pain.

Inhibition of itch by neurokinin 1 receptor (Tacr1) -expressing ON cells in the rostral ventromedial medulla in mice

The rostral ventromedial medulla (RVM) is important in descending modulation of spinal nociceptive transmission, but it is unclear if the RVM also modulates spinal pruriceptive transmission. RVM ON cells are activated by noxious algesic and pruritic stimuli and are pronociceptive. Many RVM-spinal projection neurons express the neurokinin-1 receptor (Tacr1), and ON-cells are excited by local administration of substance P (SP). We hypothesized that Tacr1-expressing RVM ON cells exert an inhibitory effect on itch opposite to their pronociceptive action. Intramedullary microinjection of SP significantly potentiated RVM ON cells and reduced pruritogen-evoked scratching while producing mild mechanical sensitization. Chemogenetic activation of RVM Tacr1-expressing RVM neurons also reduced acute pruritogen-evoked scratching. Optotagging experiments confirmed RVM Tacr1-expressing neurons to be ON cells. We conclude that Tacr1-expressing ON cells in RVM play a significant role in the modulation of pruriceptive transmission.

Substance P Increases the Excitability of Dorsal Motor Nucleus of the Vagus Nerve via Inhibition of Potassium Channels

Increases in the substance P (SP) concentration in the medial portion of the dorsal motor nucleus of the vagus nerve (mDMV) in the brainstem are closely associated with chemotherapy induced nausea and vomiting (CINV). However, the underlying cellular and molecular mechanisms of action are not well understood. In this study, we investigated the effects of SP on mDMV neurons using whole-cell patch-clamp recordings from rat brainstem slices. Application of different concentrations of SP induced tonic and phasic responses. Submicromolar concentrations of induced an inward shift of the holding current by increasing membrane input resistance. The response was mimicked by acidification of the extracellular solution and inhibited by a neurokinin type 1 receptor antagonist. These responses have equilibrium potentials close to the K⁺ equilibrium potential. In addition, a TWIK-related acid-sensitive K⁺ channel 3 (TASK-3) inhibitor, PK-THPP, induced responses similar to those produced by submicromolar SP concentrations. Micromolar concentrations of SP facilitated γ-aminobutyric acid (GABA) release but diminished glutamate release; these changes were blocked by a GABA_B receptor antagonist and a neurokinin type 3 receptor antagonist, respectively. In current-clamp recordings, submicromolar SP concentrations increased neuronal excitability by depolarizing membrane potentials. However, neither the increase in SP concentration to the micromolar range nor the addition of GABA_A and ionotropic glutamate receptor antagonists affected neuronal excitability. Thus, SP increases the excitability of mDMV neurons by inhibiting K⁺ conductance.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Substance P: A neuropeptide involved in the psychopathology of anxiety disorders

Substance P (SP) is the most widely distributed neuropeptide in central nervous system (CNS) where it participates in numerous physiological and pathophysiological processes including stress and anxiety related behaviors. In line with this notion, brain areas that are thought to be involved in anxiety regulation contains SP and its specific NK1 receptors. SP concentration in different brain regions alters with the exposure of stressful stimulus and affected NK1 receptor binding is observed. SP is released in response to a stressor, which produces anxiogenic effects via activation of hypothalamic-pituitary-adrenal (HPA) axis, resulting in the liberation of cortisol. Moreover, SP is also involved in the activation of the sympathetic nervous system via stimulation of locus coeruleus (LC). This sympathetic surge initiates cortisol discharge by activation of HPA axis, representing the indirect anxiogenic effect of SP. Besides the aforementioned regions, SP also has an impact on other brain regions known to be involved in stress and anxiety mechanisms, including amygdala, lateral septum (LS), periaqueductal gray (PAG), ventromedial nucleus of the hypothalamus (VMH), and bed nucleus of stria terminalis (BNST). Thus, SP acts as an important neuromodulator in various brain regions in stress and anxiety response. Consistent with the above statement, SP makes a robust link in the psychopathology of anxiety disorders. As SP concentration is found elevated in stressed conditions, several studies have reported that the pharmacological antagonism or genetic depletion of NK-1 receptors results in the anxiolytic response making them a suitable therapeutic target for the treatment of stress and anxiety related disorders.

Sexual Dimorphic Distribution of Hypothalamic Tachykinin1 Cells and Their Innervations to GnRH Neurons in the Zebrafish

Substance P (SP) and neurokinin A (NKA), encoded by TAC1/Tac1 gene are members of the tachykinin family, which exert their neuromodulatory roles in vertebrate reproduction. In mammals, SP and NKA have been shown to regulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion via kisspeptin neurons. On the other hand, the role of SP/NKA in the regulation of reproduction in non-mammalian vertebrates is not well known. In the present study, we first localized expression of tac1 mRNA in the brain of male and female zebrafish, Danio rerio. Next, using an antibody against zebrafish tachykinin1 (Tac1), we examined the neural association of SP/NKA neural processes with GnRH3 neurons, and with kisspeptin (kiss2) neurons, in the brains of male and female zebrafish. In situ hybridization showed an apparent male-dominant tac1 expression in the ventral telencephalic area, the anterior and posterior parts of the parvocellular preoptic nucleus, and the suprachiasmatic nucleus. On the other hand, there was female-dominant tac1 expression in the ventral periventricular hypothalamus. Confocal images of double-labeled zebrafish Tac1 and GnRH3 showed associations between Tac1-immunoreactive processes and GnRH3 neurons in the ventral telencephalic area. In contrast, there was no apparent proximity of Tac1 processes to kiss2 mRNA-expressing neurons in the hypothalamus. Lastly, to elucidate possible direct action of SP/NKA on GnRH3 or Kiss2 neurons, expression of SP/NKA receptor, tacr1a mRNA was examined in regions containing GnRH3 or Kiss2 neurons by in situ hybridization. Expression of tacr1a mRNA was seen in several brain regions including the olfactory bulb, preoptic area and hypothalamus, where GnRH3 and Kiss2 cells are present. These results suggest that unlike in mammals, Tac1 may be involved in male reproductive functions via direct action on GnRH3 neurons but independent of kisspeptin in the zebrafish.

Neuroanatomical relationship between the cholinergic and tachykininergic systems in the adult human brainstem: An immunohistochemical study

The cholinergic system plays an important role in brain homeostasis and interacts with the neuropeptidergic systems, and the functional relationships between both systems are well known. However, in the brainstem the possible physiological interactions between neurokinins and acetylcholine are unknown, although both substances have been detected in the same brainstem nuclei and have been implicated in similar functions controlled from brainstem regions such as some cranial motor nuclei. The aim of this work is to determine whether these possible physiological interactions might have a neuroanatomical basis by means of the double immunohistochemical detection of neurokinins (NK) and the enzyme choline acetyl-transferase (ChAT) in the human brainstem. No double-labelled structures were detected, although both NK and ChAT were observed in cell bodies and fibers of the same brainstem nuclei. The distribution of immunoreactive fibers is widespread, and NK and ChAT were observed in several motor cranial nerves as well as in the substantia nigra. The results obtained in the present work provide a neuroanatomical basis for possible physiological interactions between NK and ChAT that may be carried out by volume-transmission mechanisms. These interactions might participate in motor regulation or in limbic pathways as well as influence on other neurotransmitter systems such as the dopaminergic system.

DNA methylation of the Tacr2 gene in a CUMS model of depression

Tacr2, the gene encoding the NK2 receptor, belongs to G protein-coupled receptors. Accumulating evidence has indicated that the tachykinin receptors may contribute to the pathophysiology of depression. During the last decade, some studies have shown that Tacr2 activation is involved in the modulation of emotional processes. However, the extent, to which stress impacts Tacr2 expression remains unclear. The molecular mechanisms underlying depression also remain poorly understood. In this study, we subjected adult male Sprague Dawley (SD) rats to chronic unpredictable mild stress (CUMS) to induce a depression-like phenotype. We then measured the body weight and performed the sucrose preference test, forced swimming test (FST) and open field test to detect the effects of stress on anhedonia and activity. Western blotting and real-time PCR were used to study the protein and mRNA expression levels of Tacr2, respectively, in the hypothalamus. To explore DNA methylation of the Tacr2 gene, we used methylated DNA immunoprecipitation sequencing (MeDIP-seq). Additionally, we used the bisulfite sequencing PCR (BSP) to further verify the DNA methylation levels of the Tacr2 receptor gene in rats. We found that the CUMS-sensitive rats exhibited a decrease in body weight and sucrose preference, a decrease in the distance traveled, rearing frequency and velocity in the open field test, and an increase in immobility time in the FST. Compared with the expression in the control rats, Tacr2 protein and mRNA expression in the hypothalamus significantly increased in the CUMS-sensitive rats; however, the DNA methylation levels of the Tacr2 gene were significantly lower than in the control rats. In summary, according to our findings, the stress-induced increase in Tacr2 expression in the hypothalamus correlated with a specific decrease in DNA methylation of the Tacr2 gene. These results may enrich the understanding of the pathological processes of depression and provide insights into therapeutic approaches for its treatment.

Tachykinin NK1 receptor antagonist L-733,060 and substance P deletion exert neuroprotection through inhibiting oxidative stress and cell death after traumatic brain injury in mice

Substance P (SP) is believed to play a role in traumatic brain injury (TBI), and the inhibition of binding of SP to the tachykinin neurokinin-1 receptor (NK1R) using NK1R antagonists had made favorable effects on TBI. Our current study addresses the functional roles and underlying mechanisms of SP and NK1R antagonist L-733,060 following TBI. Adult male wild type C57BL/6 J and SP knock out (SPKO) mice received a controlled cortical impact and outcome parameters were assessed. The results showed that TBI-induced motor and spatial memory deficits, lesion volume, brain water content and blood-brain barrier disruption were alleviated both in L-733,060-treated C57BL/6 J mice and vehicle-treated SPKO mice. L-733,060 treatment and SP deletion inhibited TBI-induced the release of cytochrome c from mitochondria to cytoplasm, activation of caspase-3, oxidative stress and neuroinflammation. Higher SP levels in serum and cortex were observed in wild type mice undergoing TBI relative to wild type sham group, but very little expression of cortical SP was detected in the SP-/- mice either TBI or not. Upregulation of NK1R expression after TBI was observed, and there was no significant difference between wild type and SPKO groups. in vitro, L-733,060 and SP deletion inhibited scratch injury-induced cell death, loss of mitochondrial membrane potential and reactive oxygen species (ROS) production following TBI. Together, the results of this study implicate a functional role for NK1-R antagonist L-733,060 and deletion of SP in TBI-induced neurological outcome, oxidative damage, neuroinflammation and cell death. Upregulation of NK1R maybe a consequence of TBI, independent of the levels of substance P. This study raises the possibility that targeting SP through its receptor NK1R or genetic deletion may have therapeutic efficacy in TBI.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.

Salt formation improved the properties of a candidate drug during early formulation development

The purpose of this study was to investigate if AZD5329, a dual neurokinin NK1/2 receptor antagonist, is a suitable candidate for further development as an oral immediate release (IR) solid dosage form as a final product. The neutral form of AZD5329 has only been isolated as amorphous material. In order to search for a solid material with improved physical and chemical stability and more suitable solid-state properties, a salt screen was performed. Crystalline material of a maleic acid salt and a fumaric acid salt of AZD5329 were obtained. X-ray powder diffractiometry, thermogravimetric analysis, differential scanning calorimetry and dynamic vapor sorption were used to investigate the physicochemical characteristics of the two salts. The fumarate salt of AZD5329 is anhydrous, the crystallization is reproducible and the hygroscopicity is acceptable. Early polymorphism assessment work using slurry technique did not reveal any better crystal modification or crystallinity for the fumarate salt. For the maleate salt, the form isolated originally was found to be a solvate, but an anhydrous form was found in later experiments; by suspension in water or acetone, by drying of the solvate to 100-120 °C or by subjecting the solvate form to conditions of 40 °C/75%RH for 3 months. The dissolution behavior and the chemical stability (in aqueous solutions, formulations and solid-state) of both salts were also studied and found to be satisfactory. The compound displays sensitivity to low pH, and the salt of the maleic acid, which is the stronger acid, shows more degradation during stability studies, in line with this observation. The presented data indicate that the substance fulfils basic requirements for further development of an IR dosage form, based on the characterization on crystalline salts of AZD5329.

The Roles of Neurokinins and Endogenous Opioid Peptides in Control of Pulsatile LH Secretion

Work over the last 15 years on the control of pulsatile LH secretion has focused largely on a set of neurons in the arcuate nucleus (ARC) that contains two stimulatory neuropeptides, critical for fertility in humans (kisspeptin and neurokinin B (NKB)) and the inhibitory endogenous opioid peptide (EOP), dynorphin, and are now known as KNDy (kisspeptin-NKB-dynorphin) neurons. In this review, we consider the role of each of the KNDy peptides in the generation of GnRH pulses and the negative feedback actions of ovarian steroids, with an emphasis on NKB and dynorphin. With regard to negative feedback, there appear to be important species differences. In sheep, progesterone inhibits GnRH pulse frequency by stimulating dynorphin release, and estradiol inhibits pulse amplitude by suppressing kisspeptin. In rodents, the role of KNDy neurons in estrogen negative feedback remains controversial, progesterone may inhibit GnRH via dynorphin, but the physiological significance of this action is unclear. In primates, an EOP, probably dynorphin, mediates progesterone negative feedback, and estrogen inhibits kisspeptin expression. In contrast, there is now compelling evidence from several species that kisspeptin is the output signal from KNDy neurons that drives GnRH release during a pulse and may also act within the KNDy network to affect pulse frequency. NKB is thought to act within this network to initiate each pulse, although there is some redundancy in tachykinin signaling in rodents. In ruminants, dynorphin terminates GnRH secretion at the end of pulse, most likely acting on both KNDy and GnRH neurons, but the data on the role of this EOP in rodents are conflicting.

Sleep-inducing effect of substance P-cholera toxin A subunit in mice

Evidence indicates that the neuropeptide substance P (SP) can act through neurokinin receptors to alter sleep and/or non-rapid eye movement (NREM) sleep slow-wave activity. Consequently, drugs acting on SP receptors could potentially be used as a novel treatment for sleep-related disorders. In the present study, we used SP conjugated with cholera toxin A subunit (SP-CTA), which enhances its duration of activity on SP receptor-expressing cells, to determine the effects of selectively activating SP receptor-expressing brain cells on sleep regulation in mice. Herein, we found that intracerebroventricular administration of SP-CTA enhanced amounts of NREM sleep which was highly fragmented. This result suggests that the activation of SP receptor-expressing cells in the brain can produce not only arousal effects as shown in previous studies but also sleep-inducing effects.

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.

The Role of Substance P in Secondary Pathophysiology after Traumatic Brain Injury

It has recently been shown that substance P (SP) plays a major role in the secondary injury process following traumatic brain injury (TBI), particularly with respect to neuroinflammation, increased blood–brain barrier (BBB) permeability, and edema formation. Edema formation is associated with the development of increased intracranial pressure (ICP) that has been widely associated with increased mortality and morbidity after neurotrauma. However, a pharmacological intervention to specifically reduce ICP is yet to be developed, with current interventions limited to osmotic therapy rather than addressing the cause of increased ICP. Given that previous publications have shown that SP, NK1 receptor antagonists reduce edema after TBI, more recent studies have examined whether these compounds might also reduce ICP and improve brain oxygenation after TBI. We discuss the results of these studies, which demonstrate that NK1 antagonists reduce posttraumatic ICP to near normal levels within 4 h of drug administration, as well as restoring brain oxygenation to near normal levels in the same time frame. The improvements in these parameters occurred in association with an improvement in BBB integrity to serum proteins, suggesting that SP-mediated increases in vascular permeability significantly contribute to the development of increased ICP after acute brain injury. NK1 antagonists may therefore provide a novel, mechanistically targeted approach to the management of increased ICP.

Do Substance P and Neurokinin A Play Important Roles in the Control of LH Secretion in Ewes?

There is now general agreement that neurokinin B (NKB) acts via neurokinin-3-receptor (NK3R) to stimulate secretion of GnRH and LH in several species, including rats, mice, sheep, and humans. However, the roles of two other tachykinins, substance P (SP) and neurokinin A, which act primarily via NK1R and NK2R, respectively, are less clear. In rodents, these signaling pathways can stimulate LH release and substitute for NKB signaling; in humans, SP is colocalized with kisspeptin and NKB in the mediobasal hypothalamus. In this study, we examined the possible role of these tachykinins in control of the reproductive axis in sheep. Immunohistochemistry was used to describe the expression of SP and NK1R in the ovine diencephalon and determine whether these proteins are colocalized in kisspeptin or GnRH neurons. SP-containing cell bodies were largely confined to the arcuate nucleus, but NK1R-immunoreactivity was more widespread. However, there was very low coexpression of SP or NK1R in kisspeptin cells and none in GnRH neurons. We next determined the minimal effective dose of these three tachykinins that would stimulate LH secretion when administered into the third ventricle of ovary-intact anestrous sheep. A much lower dose of NKB (0.2 nmol) than of neurokinin A (2 nmol) or SP (10 nmol) consistently stimulated LH secretion. Moreover, the relative potency of these three neuropeptides parallels the relative selectivity of NK3R. Based on these anatomical and pharmacological data, we conclude that NKB-NK3R signaling is the primary pathway for the control of GnRH secretion by tachykinins in ewes.

Expanding the Role of Tachykinins in the Neuroendocrine Control of Reproduction

Reproductive function is driven by the hormonal interplay between the gonads and brain-pituitary axis. Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner, which is critical for the attainment and maintenance of fertility, however, GnRH neurons lack the ability to directly respond to most regulatory factors, and a hierarchical upstream neuronal network governs its secretion. We and others proposed a model in which Kiss1 neurons in the arcuate nucleus (ARC), so called KNDy neurons, release kisspeptin (a potent GnRH secretagogue) in a pulsatile manner to drive GnRH pulses under the coordinated autosynaptic action of its cotransmitters, the tachykinin neurokinin B (NKB, stimulatory) and dynorphin (inhibitory). Numerous genetic and pharmacological studies support this model; however, additional regulatory mechanisms (upstream of KNDy neurons) and alternative pathways of GnRH secretion (kisspeptin-independent) exist, but remain ill defined. In this aspect, attention to other members of the tachykinin family, namely substance P (SP) and neurokinin A (NKA), has recently been rekindled. Even though there are still major gaps in our knowledge about the functional significance of these systems, substantial evidence, as discussed below, is placing tachykinin signaling as an important pathway for the awakening of the reproductive axis and the onset of puberty to physiological GnRH secretion and maintenance of fertility in adulthood.

The ventromedial hypothalamus oxytocin induces locomotor behavior regulated by estrogen

Our previous studies demonstrated that excitation of neurons in the rat ventromedial hypothalamus (VMH) induced locomotor activity. An oxytocin receptor (Oxtr) exists in the VMH and plays a role in regulating sexual behavior. However, the role of Oxtr in the VMH in locomotor activity is not clear. In this study we examined the roles of oxytocin in the VMH in running behavior, and also investigated the involvement of estrogen in this behavioral change. Microinjection of oxytocin into the VMH induced a dose-dependent increase in the running behavior in male rats. The oxytocin-induced running activity was inhibited by simultaneous injection of Oxtr-antagonist, (d(CH2)5(1), Try(Me)(2), Orn(8))-oxytocin. Oxytocin injection also induced running behavior in ovariectomized (OVX) female rats. Pretreatment of the OVX rats with estrogen augmented the oxytocin-induced running activity twofold, and increased the Oxtr mRNA in the VMH threefold. During the estrus cycle locomotor activity spontaneously increased in the dark period of proestrus. The Oxtr mRNA was up-regulated in the proestrus afternoon. Blockade of oxytocin neurotransmission by its antagonist before the onset of the dark period of proestrus decreased the following nocturnal locomotor activity. These findings demonstrate that Oxtr in the VMH is involved in the induction of running behavior and that estrogen facilitates this effect by means of Oxtr up-regulation, suggesting the involvement of oxytocin in the locomotor activity of proestrus female rats.

Mapping the binding pocket of a novel, high-affinity, slow dissociating tachykinin NK3 receptor antagonist: biochemical and electrophysiological characterization

The NK3 receptor is a GPCR that is prominently expressed in limbic areas of the brain, many of which have been implicated in schizophrenia. Phase II clinical trials in schizophrenia with two selective NK3 antagonists (osanetant and talnetant) have demonstrated significant improvement in positive symptoms. The objective of this study was to characterize the properties of a novel dual NK2/NK3 antagonist, RO5328673. [(3)H]RO5328673 bound to a single saturable site on hNK2, hNK3 and gpNK3 with high-affinity. RO5328673 acted as an insurmountable antagonist at both human and guinea-pig NK3 receptors in the [(3)H]IP accumulation assay. In binding kinetic analyses, [(3)H]RO5328673 had fast association and dissociation rates at hNK2 while it had a fast association rate and a remarkably slow dissociation rate at gp and hNK3. In electrophysiological recordings of gp SNpc, RO5328673 inhibited the senktide-induced potentiation of spontaneous activity of dopaminergic neurons with an insurmountable mechanism of action. RO5328673 exhibited in-vivo activity in gerbils, robustly reversing the senktide-induced locomotor activity. The TM2 residue gpNK3-A114(2.58) (threonine in all other species) was identified as the critical residue for the RO5328673's slower dissociation kinetics and stronger insurmountable mode of antagonism in the guinea-pig as compared to hNK3-T139(2.58). Using site-directed mutagenesis, [(3)H]RO5328673 binding and rhodopsin-based modeling, the important molecular determinants of the RO5328673-binding pocket of hNK3 were determined. A comparison of the RO5328673-binding pocket with that of osanetant showed that two antagonists have similar contact sides on hNK3 binding crevice except for three mutations V95L(1.42), Y247W(5.38), V255I(5.46), which behaved differently between interacting modes of two antagonists in hNK3.

Neuropeptides in learning and memory

Dementia conditions and memory deficits of different origins (vascular, metabolic and primary neurodegenerative such as Alzheimer's and Parkinson's diseases) are getting more common and greater clinical problems recently in the aging population. Since the presently available cognitive enhancers have very limited therapeutical applications, there is an emerging need to elucidate the complex pathophysiological mechanisms, identify key mediators and novel targets for future drug development. Neuropeptides are widely distributed in brain regions responsible for learning and memory processes with special emphasis on the hippocampus, amygdala and the basal forebrain. They form networks with each other, and also have complex interactions with the cholinergic, glutamatergic, dopaminergic and GABA-ergic pathways. This review summarizes the extensive experimental data in the well-established rat and mouse models, as well as the few clinical results regarding the expression and the roles of the tachykinin system, somatostatin and the closely related cortistatin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate-cyclase activating polypeptide (PACAP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), opioid peptides and galanin. Furthermore, the main receptorial targets, mechanisms and interactions are described in order to highlight the possible therapeutical potentials. Agents not only symptomatically improving the functional impairments, but also inhibiting the progression of the neurodegenerative processes would be breakthroughs in this area. The most promising mechanisms determined at the level of exploratory investigations in animal models of cognitive disfunctions are somatostatin sst4, NPY Y2, PACAP-VIP VPAC1, tachykinin NK3 and galanin GALR2 receptor agonisms, as well as delta opioid receptor antagonism. Potent and selective non-peptide ligands with good CNS penetration are needed for further characterization of these molecular pathways to complete the preclinical studies and decide if any of the above described targets could be appropriate for clinical investigations.

Concurrent modulation of extracellular levels of noradrenaline and cAMP during stress and by anxiogenic- or anxiolytic-like neuropeptides in the prefrontal cortex of awake rats

The purpose of this study was to examine the effects of stress and the role of locally infused anxiogenic-like neuropeptides galanin, CCK-8, vasopressin, substance P and neurokinin A, and anxiolytic-like peptides NPY, nociceptin/orphanin FQ, somatostatin and neurotensin, on modulation of noradrenaline (NA) and cAMP efflux monitored simultaneously by microdialysis in the medial prefronatal cortex of awake rats. Concentrations of cAMP were determined by a newly developed method based on derivatization of cAMP with 2-chloroacetaldehyde followed by HPLC with fluorescence detection. Local infusion of forskolin (10 and 30 μM) dose-dependently increased the cAMP levels to 417% and 1050% of the control group, respectively. Similarly, local infusion of NA (10 μM) increased the cAMP to the peak level of 168%. A 5-min tail pinch and a 10-min swim stress rapidly increased the NA and cAMP levels to 167% and 203% (NA) and 141% and 161% (cAMP), respectively. Infusion of galanin and CCK-8 (0.5 nmol, and 1.5 nmol/0.5 μl) dose-dependently increased NA to the peak levels of 191% and 179% and cAMP levels to 174% and 166%, respectively. The peak levels following infusions of vasopressin, substance P and neurokinin A were 91%, 135% and 86% for NA and 131%, 83% and 76% for cAMP, respectively. Infusions of anxiolytic-like peptides at highest concentrations significantly increased (NPY, 136%) or decreased (nociceptin, 71%; somatostatin, 86%) the NA levels, whereas neurotensin had no effect. The cAMP levels decreased to 86% (NPY, neurotensin), 78% (nociceptin), somatostatin infusion was without effect. The present findings confirmed a close correlation between the stress-induced increases in prefrontal cortical NA and cAMP levels, as well as, concurrent changes in NA and cAMP levels following infusions of galanin and CCK-8 (increased levels) and nociceptin/orphanin FQ (decreased levels). Infusions of other neuropeptides showed a more complex pattern of NA and cAMP responses.

Changes in response properties of rostral ventromedial medulla neurons during prolonged inflammation: modulation by neurokinin-1 receptors

Activation of neurokinin-1 (NK-1) receptors in the rostral ventromedial medulla (RVM) can facilitate pain transmission in conditions such as inflammation, and thereby contribute to hyperalgesia. Since blockade of NK-1 receptors in the RVM can attenuate hyperalgesia produced by prolonged inflammation, we examined the role of NK-1 receptors in changes of response properties of RVM neurons following four days of hind paw inflammation with complete Freund's adjuvant. Recordings were made from functionally identified ON, OFF and NEUTRAL cells in the RVM. Spontaneous activity and responses evoked by a series of mechanical (10, 15, 26, 60, 100, and 180 g) and heat (34-50 °C) stimuli applied to the inflamed and non-inflamed hind paws were determined before and at 15 and 60 min after injection of the NK-1-antagonist L-733,060 or vehicle into the RVM. Prolonged inflammation did not alter the proportions of functionally-identified ON, OFF and NEUTRAL cells. ON cells exhibited enhanced responses to mechanical (60-100g) and heat (48-50 °C) stimuli applied to the inflamed paw, which were attenuated by L-733,060 but not by vehicle. Inhibitory responses of OFF cells evoked by mechanical stimuli applied to the inflamed paw were also inhibited by L-733,060, but responses evoked by stimulation of the contralateral paw were increased. Heat-evoked responses of OFF cells were not altered by L-733,060. Also, neither L-733,060 nor vehicle altered spontaneous ongoing discharge rate of RVM neurons. These data indicate that NK-1 receptors modulate excitability of ON cells which contribute to both mechanical and heat hyperalgesia, whereas NK-1 modulation of OFF cells contributes to mechanical hyperalgesia during prolonged inflammation.

Trigeminal-rostral ventromedial medulla circuitry is involved in orofacial hyperalgesia contralateral to tissue injury

BACKGROUND

Our previous studies have shown that complete Freund's adjuvant (CFA)-induced masseter inflammation and microinjection of the pro-inflammatory cytokine interleukin-1β (IL-1β) into the subnucleus interpolaris/subnucleus caudalis transition zone of the spinal trigeminal nucleus (Vi/Vc) can induce contralateral orofacial hyperalgesia in rat models. We have also shown that contralateral hyperalgesia is attenuated with a lesion of the rostral ventromedial medulla (RVM), a critical site of descending pain modulation. Here we investigated the involvement of the RVM-Vi/Vc circuitry in mediating contralateral orofacial hyperalgesia after an injection of CFA into the masseter muscle.

RESULTS

Microinjection of the IL-1 receptor antagonist (5 nmol, n=6) into the ipsilateral Vi/Vc attenuated the CFA-induced contralateral hyperalgesia but not the ipsilateral hyperalgesia. Intra-RVM post-treatment injection of the NK1 receptor antagonists, RP67580 (0.5-11.4 nmol) and L-733,060 (0.5-11.4 nmol), attenuated CFA-induced bilateral hyperalgesia and IL-1β induced bilateral hyperalgesia. Serotonin depletion in RVM neurons prior to intra-masseter CFA injection prevented the development of contralateral hyperalgesia 1-3 days after CFA injection. Inhibition of 5-HT(3) receptors in the contralateral Vi/Vc with direct microinjection of the select 5-HT(3) receptor antagonist, Y-25130 (2.6-12.9 nmol), attenuated CFA-induced contralateral hyperalgesia. Lesions to the ipsilateral Vc prevented the development of ipsilateral hyperalgesia but did not prevent the development of contralateral hyperalgesia.

CONCLUSIONS

These results suggest that the development of CFA-induced contralateral orofacial hyperalgesia is mediated through descending facilitatory mechanisms of the RVM-Vi/Vc circuitry.

Are biological actions of neurokinin A in the adult brain mediated by a cross-talk between the NK1 and NK2 receptors?

Mice lacking the NK(1) receptor (NK(1)R-/- mice) and selective, high-affinity, non-peptide, NK(1), NK(2) and NK(3) receptor antagonists were used to identify the tachykinin receptor subtype(s) mediating the central responses induced by neurokinin A (NKA). The peptides, substance P (SP), NKA and senktide and the antagonists were injected intracerebroventricularly (ICV) through an implanted cannula. NKA (50 pmol) was as potent as SP (50 pmol) in inducing grooming behaviour (face washing and hind limb grooming) in wild-type mice, but both peptides failed to induce behavioural responses in NK(1)R-/- mice. In wild-type mice, the NK(1) receptor antagonist, RP 67580 (2 nmol), effectively inhibited grooming behaviour elicited by SP, but was inactive against grooming induced by NKA, which in turn was abolished after pre-treatment with the selective NK(2) receptor agonist, SR 48968 (2 nmol). Unlike NKA, the selective NK(2) receptor agonists, (β Ala(8)) NKA 4-10 and (NLeu(10)) NKA 4-10, injected ICV at doses of 50 or 100 pmol did not elicit any behavioural response in wild-type mice. The NK(3) receptor antagonist, SR 142801, inhibited behaviours induced by the NK(3) receptor agonist, senktide, but did not alter behavioural responses to either SP or NKA in wild-type mice. The present findings demonstrate that central biological actions of SP and senktide are mediated by activation of NK(1) and NK(3) receptors, respectively. Our results also indicate that NK(1) receptors are essential for generating central actions induced by NKA, which are most probably mediated by a cross-talk between the NK(1) and NK(2) receptors.

Cortical nNOS neurons co-express the NK1 receptor and are depolarized by Substance P in multiple mammalian species

We have previously demonstrated that Type I neuronal nitric oxide synthase (nNOS)-expressing neurons are sleep-active in the cortex of mice, rats, and hamsters. These neurons are known to be GABAergic, to express Neuropeptide Y (NPY) and, in rats, to co-express the Substance P (SP) receptor NK1, suggesting a possible role for SP in sleep/wake regulation. To evaluate the degree of co-expression of nNOS and NK1 in the cortex among mammals, we used double immunofluorescence for nNOS and NK1 and determined the anatomical distribution in mouse, rat, and squirrel monkey cortex. Type I nNOS neurons co-expressed NK1 in all three species although the anatomical distribution within the cortex was species-specific. We then performed in vitro patch clamp recordings in cortical neurons in mouse and rat slices using the SP conjugate tetramethylrhodamine-SP (TMR-SP) to identify NK1-expressing cells and evaluated the effects of SP on these neurons. Bath application of SP (0.03–1 μM) resulted in a sustained increase in firing rate of these neurons; depolarization persisted in the presence of tetrodotoxin. These results suggest a conserved role for SP in the regulation of cortical sleep-active neurons in mammals.

Differential modulation of neurons in the rostral ventromedial medulla by neurokinin-1 receptors

The rostral ventromedial medulla (RVM) is part of descending circuitry that modulates nociceptive processing at the level of the spinal cord. RVM output can facilitate pain transmission under certain conditions such as inflammation, and thereby contribute to hyperalgesia. Evidence suggests that substance P and activation of neurokinin-1 (NK-1) receptors in the RVM are involved in descending facilitation of nociception. We showed previously that injection of NK-1 receptor antagonists into the RVM attenuated mechanical and heat hyperalgesia produced by intraplantar injection of capsaicin. Furthermore, intraplantar injection of capsaicin excited ON cells in the RVM and inhibited ongoing activity of OFF cells. In the present studies, we therefore examined changes in responses of RVM neurons to mechanical and heat stimuli after intraplantar injection of capsaicin and determined the role of NK-1 receptors by injecting a NK-1 receptor antagonist into the RVM prior to capsaicin. After capsaicin injection, excitatory responses of ON cells and inhibitory responses of OFF cells evoked by mechanical and heat stimuli applied to the injected, but not contralateral, paw were increased. Injection of the NK-1 antagonist L-733,060 did not alter evoked responses of ON or OFF cells but attenuated the capsaicin-evoked enhanced responses of ON cells to mechanical and heat stimuli with less of an effect on the enhanced inhibitory responses of OFF cells. These data support the notion that descending facilitation from RVM contributes to hyperalgesia and that NK-1 receptors, presumably located on ON cells, play an important role in initiating descending facilitation of nociceptive transmission.

Neurokinin3-R agonism in aged rats has anxiolytic-, antidepressant-, and promnestic-like effects and stimulates ACh release in frontal cortex, amygdala and hippocampus

Neurokinin-3 receptors (NK(3)-R) are localized in brain regions which have been implicated in processes governing learning and memory as well as emotionality. The effects of acute subcutaneous (s.c.) senktide (0.2 and 0.4 mg/kg), a NK(3)-R agonist, were tested in aged (23-25 month old) Wistar rats: (a) in an episodic-like memory test, using an object discrimination task (this is the first study to test for deficits in episodic-like memory in aged rats, since appropriate tests have only recently became available); (b) on parameters of anxiety in an open field test, (c) on indices of depression in the forced swimming test and (d) on the activity of cholinergic neurons of the basal forebrain, using in vivo microdialysis and HPLC. Neither the saline-, nor senktide-treated aged animals, exhibited episodic-like memory. However, the senktide-, but not the vehicle-treated group, exhibited object memory for spatial displacement, a component of episodic memory. Senktide injection also had anxiolytic- and antidepressant-like effects. Furthermore, the active doses of senktide on behavior increased ACh levels in the frontal cortex, amygdala and hippocampus, suggesting a relationship between its cholinergic and behavioral actions. The results indicate cholinergic modulation by the NK(3)-R in conjunction with a role in the processing of memory and emotional responses in the aged rat.

Contractile effect of tachykinins on rabbit small intestine

AIM

To study the role of the tachykinin receptors in spontaneous contractions of longitudinal and circular smooth muscle from rabbit small intestine and to determine the mechanism of action of Substance P (SP).

METHODS

Rabbit duodenum, jejunum and ileum segments were prepared. The spontaneous contractions of longitudinal and circular smooth muscle were recorded using a computer via an isometric force transducer. The specific agonists and antagonists of tachykinin receptors were added into the organ bath.

RESULTS

The agonists of tachykinin NK1 receptor (SP and [Sar9] SP), NK2 receptor (NKA and (β-Ala8)-NKA), and NK3 receptor (NKB and Senktide) all induced contractions in the small intestine. The contractions were diminished by NK1 receptor antagonist L-733,060, NK2 receptor antagonist GR-94800, and NK3 receptor antagonist SB 218795. Contractions caused by SP were also reduced by atropine, verapamil, PKC inhibitor staurosporine, and PLC inhibitor U73122.

CONCLUSION

Ttachykinin NK1, NK2, and NK3 receptors mediate the contractions of the smooth muscle in rabbit intestine. Furthermore, SP acts directly on smooth muscle cells through the tachykinin NK1 receptor.

Early development evaluation of AZD8081: a substrate for the NK receptors

The purpose of the present study was to find out if AZD8081, a dual neurokinin (NK)1/2 receptor antagonist, was suitable for development of an oral, solid immediate release (IR) formulation and in a further perspective also as an oral extended release (ER) formulation. AZD8081 is a base with pK(a) values <2.5 and about 8.5. The measured intrinsic solubility is about 0.1 mg/mL and the solubility in FaSSIF (fasted simulated small intestinal fluid) is about 3.2 mg/mL. Aqueous buffer solutions are stable for at least 1 month between pH 1-7 up to 37°C. In the solid-state, a mixture of amorphous and crystalline substance showed significant chemical instability in the initial stress testing studies. No degradation was, however, observed for highly crystalline material at similar conditions. It is concluded that the impurity profile and/or the present solid-state of the batches affect the stability of the substance. The amorphous contribution of the substance is the main cause to the observed degradation in solid-state. Crystalline AZD8081 is polymorphic with two known monotropic forms, form A and form B. Both forms are only slightly hygroscopic ansolvates with melting points of approximately 108°C and 117°C, respectively. Form B is the more stable of the two forms and is therefore most suited for further development. The candidate is suitable for development of standard IR formulations since no specific limitations of significance for formulation development were identified. In addition, the good stability in human intestinal fluid and in colon slurry makes AZD8081 a suitable candidate for ER formulation.

Involvement of neurokinin receptors in the control of pulsatile luteinizing hormone secretion in rats

It has recently been shown that neurokinin B, a tachykinin, is associated with GnRH pulse generation in sheep and goats. The aim of the present study was to clarify the role of tachykinin receptors in the control of LH secretion in rats. To this end, we evaluated the effect of CS-003, an antagonist for all three neurokinin receptors (NK1, NK2 and NK3 receptors), on pulsatile LH secretion in both sexes of rats with different routes of administration. Both oral and third ventricular administration of CS-003 suppressed LH secretion in both sexes of gonadectomized animals. Furthermore, intact male rats with oral administration of CS-003 showed decreased serum testosterone levels, which might be due to suppressed LH secretion. None of the three subtype-specific neurokinin receptor antagonists showed a significant effect on LH secretion in ovariectomized rats when each antagonist was singly administered. The present results suggest that neurokinins play a role in the control of pulsatile GnRH/LH secretion via multiple neurokinin receptors in both male and female rats.

Early development evaluation of AZD2738, a substrate for the NK receptors

The purpose of this study was to investigate whether AZD2738, a dual neurokinin NK1/2 receptor antagonist, is a suitable candidate for further development with an oral immediate release solid dosage form as a possible final product. The neutral form of AZD2738 has only been isolated as amorphous material. In order to search for a solid material with improved physical and chemical stability and more suitable solid-state properties, a salt screen was performed. Mostly crystalline material of fumarate, maleate and chloride salt of AZD2738 were obtained. X-ray powder diffractometry, thermogravimetric analysis, differential scanning calorimetry and dynamic vapor sorption were used to investigate the physicochemical characteristics of the salts. Based on the physicochemical properties, the chloride salt is preferred for continued product development. The chloride salt of AZD2738 is an anhydrate, the crystallization is reproducible, the hygroscopicity is acceptable and just one polymorph was obtained. Notably is that the two obtained polymorphs of the fumarate salt of AZD2738 are monotropically related, whereas the two identified polymorphs for the maleate salt of the compound are enantiotropic. The dissolution behavior and the stability (in aqueous solutions, formulations and solid state) of the salts were also studied and found to be satisfactory, at least at pH >3. Liquid formulations should preferable be stored frozen at pH >3.

Testicular toxicity induced by a triple neurokinin receptor antagonist in male dogs

Mechanism mediating the testicular toxicity induced by CS-003, a triple neurokinin receptor antagonist, was investigated in male dogs. Daily CS-003 administrations showed testicular toxicity, such as a decrease in the sperm number, motility and prostate weight; and an increase in sperm abnormality, accompanying histopathological changes in the testis, epididymis and prostate. A single CS-003 administration suppressed plasma testosterone and LH levels in intact and castrated males. The suppressed LH release was restored by GnRH agonist injection, suggesting that pituitary sensitivity to GnRH is not impaired by CS-003. Treatment with SB223412, a neurokinin 3 receptor antagonist, caused a similar effect to CS-003, such as toxicity in the testis, prostate and epididymis and decreased plasma level of LH and testosterone. In conclusion, CS-003-induced testicular toxicity is caused by the inhibition of neurokinin B/neurokinin 3 receptor signaling probably at the hypothalamic level in male dogs.

Substance P induces the reversible formation of varicosities in the dendrites of rat brainstem neurons

This study investigated the ability of substance P (Sub P) to induce dendritic varicosities (DVs) or beads in neurons of the rostral ventromedial medulla (RVM) of the rat. Microinjection of 5-200 pmol Sub P in the RVM produced a concentration-dependent increase in the number of DVs in distal dendrites of RVM neurons that were immunoreactive for the neurokinin-1 receptor, but not serotonin. The effect was reversible, as DVs were essentially absent 2 and 4h after microinjection. Fluoro-Jade B labeled neurons were not evident in the RVM 4 days after microinjection of Sub P, although such neurons were present 4 days after microinjection of a neurotoxic dose of kainate. Bath application of Sub P to brainstem slices for a period as brief as 30s also produced DVs in neurokinin-1 immunoreactive RVM neurons. Prior exposure to L-703606 prevented the formation of DVs by Sub P, implicating the neurokinin-1 receptor, a Gq type of G protein coupled receptor, in the formation of DVs by Sub P. Finally, stabilization of microtubules by prior exposure to taxol also prevented the formation of DVs, consistent with the idea that increases in intracellular Ca(2+) lead to the formation of DVs secondary to a disruption of the linear arrays of microtubules in dendrites. These data establish a mechanistic basis for the formation of DVs by Sub P and support further studies to test the hypothesis that the formation of DVs is a morphological mechanism by which neurons can regulate their responses to inhibitory or excitatory inputs.

Spinal cord mechanisms mediating behavioral hyperalgesia induced by neurokinin-1 tachykinin receptor activation in the rostral ventromedial medulla

Hyperalgesia in animal injury models is linked to activation of descending raphespinal modulatory circuits originating in the rostral ventromedial medulla (RVM). A neurokinin-1 (NK-1) receptor antagonist microinjected into the RVM before or after inflammation produced by complete Freund's adjuvant (CFA) resulted in an attenuation of thermal hyperalgesia. A transient (acute) or a continuous infusion of Substance P (SP) microinjected into the RVM of non-inflamed animals led to similar pain hypersensitivity. Intrathecal pretreatment or post-treatment of a 5-HT3 receptor antagonist (Y-25130 or ondansetron) blocked the SP-induced hyperalgesia. The SP-induced hyperalgesia was both GABA(A) and NMDA receptor-dependent after pre- and post-treatment with selective antagonists at the spinal level. A microinjection of SP into the RVM also led to increased NMDA NR1 receptor subunit phosphorylation in spinal cord tissue. The GABA(A) receptor-mediated hyperalgesia involved a shift in the anionic gradient in dorsal horn nociceptive neurons and an increase in phosphorylated NKCC1 protein (isoform of the Na-K-Cl cotransporter). Following a low dose of SP infused into the RVM, intrathecal muscimol (GABA(A) agonist) increased SP-induced thermal hyperalgesia, phosphorylated NKCC1 protein expression, and NMDA NR1 subunit phosphorylation in the spinal cord. The thermal hyperalgesia was blocked by intrathecal gabazine, the GABA(A) receptor antagonist, and MK-801, the NMDA receptor channel blocker. These findings indicate that NK-1 receptors in the RVM are involved in SP-induced thermal hyperalgesia, this hyperalgesia is 5-HT3-receptor dependent at the spinal level, and involves the functional interaction of spinal GABA(A) and NMDA receptors.

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

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

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

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

Direct cellular peptidomics of supraoptic magnocellular and hippocampal neurons in low-density co-cultures

Genomic and proteomic studies of brain regions of specialized function provide evidence that communication among neurons is mediated by systems of diverse chemical messengers. These analyses are largely tissue- or population-based, whereas the actual communication is from cell-to-cell. To understand the complement of intercellular signals produced by individual neurons, new methods are required. We have developed a novel neuron-to-neuron, serum-free, co-culture approach that was used to determine the higher-level cellular peptidome of individual primary mammalian neurons. We isolated magnocellular neurons from the supraoptic nucleus of early postnatal rat and maintained them in serum-free low density cultures without glial support layers; under these conditions they required low-density co-cultured neurons. Co-culturing magnocellular neurons with hippocampal neurons permitted local access to individual neurons within the culture for mass spectrometry. Using direct sampling, peptide profiles were obtained for spatially distinct, identifiable neurons within the co-culture. We repeatedly detected 10 peaks that we assign to previously characterized peptides and 17 peaks that remain unassigned. Peptides from the vasopressin prohormone and secretogranin-2 are attributed to magnocellular neurons, whereas neurokinin A, peptide J, and neurokinin B are attributed to cultured hippocampal neurons. This approach enables the elucidation of cell-specific prohormone processing and the discovery of cell-cell signaling peptides.

Neurokinin-2 receptor antagonism in medial septum influences temporal-order memory for objects and forebrain cholinergic activity

In the mammalian brain the neurokinin NK(2) receptors are predominantly located in the hippocampus, thalamus, septum and frontal cortex. It has been shown that administration of the NK(2) receptor agonist, neurokinin A (NKA), into the medial septum of rats increases extracellular levels of acetylcholine (ACh) in the hippocampus and that NK(2) receptor antagonism blocks this increase. Therefore, given the prominent role of hippocampal ACh in information processing, we hypothesized that NK(2) receptor antagonism in the medial septum would negatively affect learning and memory via its influence on the cholinergic neurons of the basal forebrain. We investigated the action of local application of the peptidic NK(2) receptor antagonist, Bz-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH (1, 10 and 100pmol), into the medial septum on object memory for temporal order and spatial location using an object novelty paradigm. By means of in vivo microdialysis and HPLC analyses, we also examined the influence of NK(2) receptor antagonism in the medial septum on ACh in major cholinergic projection areas of the basal forebrain, namely, hippocampus, frontal cortex and amygdala.

RESULTS

Injection of vehicle alone into the medial septum impaired memory for temporal order and spatial location of objects. Application of 1pmol of the NK(2) receptor antagonist partially reversed this deficit by reinstating memory for temporal order. Injection of 10pmol of the NK(2) receptor antagonist into the medial septum decreased levels of ACh in the hippocampus (at 30min post-injection), and frontal cortex (at 30 and 80min post-injection) in comparison to vehicle. However, this apparent decrease was the result of the blockade of a saline-induced increase in ACh levels.