Interaction of the tachykinin NK3 receptor agonist senktide with behavioral effects of cocaine in marmosets (Callithrix penicillata)

How does neurokinin 3 receptor agonism affect pathological and cognitive impairments in an Alzheimer's disease-like rat model?

Alzheimer's disease (AD) is accepted as a form of progressive dementia. Cholinergic systems are commonly affected in AD. Neurokinin 3 receptor (NK3R) is involved in learning memory-related processes. It is known that the activation of NK3R affects the release of many neurotransmitters. The aim of this project was to investigate the effects of NK3R agonist senktide administration on neurobehavioral mechanisms in the experimental AD-like rat model. 50 male Wistar albino rats were divided into Control (C), AD, Control + NK3R agonist (CS), AD + NK3R agonist (ADS), AD + NK3Ragonist + antagonist groups (ADSO). We designed AD-like model by intrahippocampal administration of Aβ1-42. After NK3R agonist + antagonist injections, open field (OF), Morris water maze (MWM) tests were applied. Cholinergic mechanism analysis from hippocampus-cortex tissues was performed by ELISA and catecholamine analysis from brain stem tissue were performed by HPLC method. The transitions from edge to center, rearing, grooming parameters were found to be reduced in final values of OF. While the group-time interaction was significant in the OF test findings, there was no significant difference between the groups. In MWM test, ADS group showed a learning level close to control group and animals in AD and ADSO groups could not learn target quadrant in MWM test. The brain stem NA and DA concentrations were not statistically significant. Hippocampal AChE-ChAT levels were supported by positive effects of senktide on learning via the cholinergic mechanisms. As a result, NK3R agonists were found to be effective in improving cognitive functions in rats with AD pathology. In the experimental AD model, positive effects of NK3R on learning memory may be mediated by cholinergic mechanisms.

Tacr3/NK3R: Beyond Their Roles in Reproduction

The Tacr3 gene encodes tachykinin receptor 3 (NK3R), which belongs to the tachykinin receptor family. This family of proteins includes typical G protein-coupled receptors and belongs to the rhodopsin subfamily. NK3R functions by binding to its high-affinity ligand, neurokinin B(NKB). The role of Tacr3/NK3R in growth and reproduction has been extensively studied, but Tacr3/NK3R is also widely expressed in the nervous system from the spinal cord to the brain and is involved in both physiological and pathological processes in the nervous system, including mood disorders, chronic pain, learning and memory deficiencies, Alzheimer's disease, Parkinson's disease, addiction-related processes, hypoxic-ischemic encephalopathy, body fluid management, neural development, and schizophrenia. Here, we summarize the structure of NK3R/NKB and its cellular signaling as well as the expression of Tacr3/NK3R in the nervous system, and we provide a comprehensive summary of the role of Tacr3/NK3R in neurological diseases, including reproduction-related disorders and other neurological diseases. At the end of this review, we propose the hypothesis that Tacr3/NK3R mediates a variety of brain functions by affecting the excitability of different neurons with specific functions. On the basis of this "excited or not" hypothesis, more studies related to Tacr3 should be carried out in other nervous system diseases in order to better understand the biological roles of Tacr3.

Neurokinin receptors in drug and alcohol addiction

The neurokinins are a class of peptide signaling molecules that mediate a range of central and peripheral functions including pain processing, gastrointestinal function, stress responses, and anxiety. Recent data have linked these neuropeptides with drug-related behaviors. Specifically, substance P (SP) and neurokinin B (NKB), have been shown to influence responses to alcohol, cocaine, and/or opiate drugs. SP and NKB preferentially bind to the neurokinin-1 receptor (NK1R) and neurokinin-3 receptor (NK3R), respectively, but do have some affinity for all classes of neurokinin receptor at high concentrations. NK1R activity has been shown to influence reward and reinforcement for opiate drugs, stimulatory and neurochemical responses to cocaine, and escalated and stress-induced alcohol seeking. In reinstatement models of relapse-like behavior, NK1R antagonism attenuates stress-induced reinstatement for all classes of drugs tested to date. The NK3R also influences alcohol intake and behavioral/neurochemical responses to cocaine, but less research has been performed in regard to this particular receptor in preclinical models of addiction. Clinically, agents targeting these receptors have shown some promise, but have produced mixed results. Here, the preclinical findings for the NK1R and NK3R are reviewed, and discussion is provided to interpret clinical findings. Additionally, important factors to consider in regards to future clinical work are suggested.

Structure–activity relationship study on senktide for development of novel potent neurokinin-3 receptor selective agonists

A potent neurokinin-3 receptor (NK3R) selective agonist with resistance to proteolytic digestion was developed.

Sensitization of hypervigilance effects of cocaine can be induced by NK3 receptor activation in marmoset monkeys

BACKGROUND

Cocaine is a widely abused drug which can result in the establishment of addiction. The neurokinin3-receptor (NK3-R) has been linked to cocaine addiction by genetic, epigenetic, and pharmacological studies suggesting that a cocaine-induced increase in NK3-R signaling may contribute to the establishment of cocaine addiction-related behaviors.

METHODS

Here we measured cocaine-induced sensitization of vigilance- and locomotor behaviors in marmoset monkeys (Callithrix penicillata) in an open field.

RESULTS

We found a sensitization of vigilance-related, but not locomotor behaviors after repeated cocaine (7mg/kg, i.p.) treatment. There was a cross-sensitization for scan frequency, but not of glance frequency, both vigilance-related behaviors, after repeated treatment with the NK3-R agonist senktide (0.2mg/kg, i.p.) given for 7 days, after a cocaine challenge (5mg/kg, i.p.).

CONCLUSIONS

These data suggest that in marmoset monkeys, repeated cocaine treatment leads to a sensitization of vigilance-related behaviors, which have a prominent role in spontaneously expressed activities in this species, but not of locomotor activity. Repeated activation of NK3-Rs can mimic some of the behavioral sensitization effect and may thus contribute to the establishment of cocaine related behaviors.

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.

NK-3 receptor antagonism prevents behavioral sensitization to cocaine: a role of glycogen synthase kinase-3 in the nucleus accumbens

Repeated administration of cocaine induces heightened behavioral hyperactivity termed sensitization. Although NK-3 receptors have been shown to modulate acute cocaine-induced behaviors, their role in behavioral sensitization is unknown. The present study investigated whether NK-3 receptor blockade altered behavioral sensitization to cocaine. Additionally, glycogen synthase kinase-3 (GSK3) has been shown to be involved in dopamine receptor signaling and in development of sensitization; therefore regulation of GSK3 activity in the nucleus accumbens was also investigated. Administration of the NK-3 receptor antagonist SB 222200 (5 mg/kg, s.c.) prior to repeated cocaine (20 mg/kg, i.p.) prevented the development of sensitized responses after a cocaine challenge. Pre-treatment with SB 222200 before a cocaine challenge also blocked expression of sensitization. Decrease in GSK3 activity demonstrated by increased phosphorylation of GSK3α and GSK3β was detected 20 mins after an acute cocaine injection. In contrast, a cocaine challenge failed to alter phosphorylation of GSK3α and GSK3β in sensitized mice. SB 222200 prior to repeated cocaine resulted in increased phosphorylation of GSK3α and GSK3β akin to changes following acute cocaine. Collectively, these findings demonstrate the involvement of NK-3 receptors in development and expression of behavioral sensitization and in regulation of GSK3 activity in the nucleus accumbens after repeated cocaine.

Blockade of neurokinin-3 receptors modulates dopamine-mediated behavioral hyperactivity

Acute activation or blockade of neurokinin-3 (NK-3) receptors has been shown to alter dopamine-mediated function and behaviors, however long-term effects of NK-3 receptor blockade remain largely unknown. The present study investigated whether acute and repeated administration of the NK-3 receptor antagonist SB 222200 altered hyperactivity induced by cocaine, and examined its effects on dopamine D1 receptor density in the striatum. Adult male CD-1 mice received either vehicle or SB 222200 (2.5 or 5 mg/kg, s.c.) 30 min before a cocaine injection (20 mg/kg, i.p.) and behavioral responses were recorded. Mice that were administered SB 222200 had an attenuated stereotypic response to cocaine compared to vehicle treated mice. Mice were also injected once daily with either vehicle or SB 222200 (5 mg/kg, s.c.) for 5 days, and after a 7-day drug-free period they were challenged with either saline, cocaine or the dopamine D1 receptor agonist SKF 82958 (0.125 or 0.25 mg/kg, i.p.). Mice injected with SB 222200 had significantly enhanced hyperactivity when challenged with cocaine or a low dose of SKF 82958 (0.125 mg/kg, i.p.) compared to control mice. Brains of mice administered vehicle or SB 222200 for 5 days were harvested after a 7-day drug-free period for dopamine D1 receptor quantification by radioligand binding. [(3)H] SCH 23390 homogenate binding studies showed a 19.7% increase in dopamine D1 receptor density in the striatum of SB 222200 treated mice. These data suggest that repeated blockade of NK-3 receptors enhances subsequent dopamine-mediated behaviors possibly resulting from dopamine D1 receptor up-regulation in the striatum.

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

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

The tachykinin receptor 3 is associated with alcohol and cocaine dependence

BACKGROUND

A broad region on chromosome 4q was previously linked to the phenotype of alcohol dependence in the Collaborative Study on the Genetics of Alcoholism sample. A strong positional candidate gene was identified within this region: tachykinin receptor 3 gene (TACR3), which encodes tachykinin receptor 3 (NK3R), the receptor for the tachykinin 3 (neurokinin B) peptide. Pharmacological studies have provided evidence that the administration of NK3R agonists attenuates the intake of alcohol and NK3R can also mediate the acute and chronic behavioral effects of cocaine.

METHODS

Thirty SNPs were genotyped throughout TACR3. Family based association analysis was performed in 219 European American families to detect an association with alcohol dependence. Subsequent analyses were performed to evaluate the evidence of association with other definitions of alcohol dependence as well as cocaine dependence.

RESULTS

Seven of the 9 SNPs in the 3' region of TACR3 provided significant evidence of association with alcohol dependence (p <or= 0.05). Further analyses suggest that the evidence of association is strongest among those subjects with more severe alcohol dependence (defined by ICD-10) and those with co-morbid cocaine dependence. Haplotype analyses further strengthen the evidence of association in the 3' region of the gene.

CONCLUSIONS

These results indicate that sequence variations in TACR3 contribute to the variation in more severe alcohol dependent individuals and those who are also cocaine dependent.

Gender differences in zebrafish responses to cocaine withdrawal

The acute responses to cocaine and its withdrawal contribute to cocaine dependence and potentiate relapse, with gender being one of the genetic factors affecting the outcome. Here we report that in both male and female zebrafish (Danio rerio, AB strain), an initial low-dose cocaine treatment (1.5 muM, immersion) does not acutely change their behavior. The cocaine withdrawal, however, is associated with an anxiety-like state that develops earlier in female zebrafish but is more robust and persistent in males, and can be acutely attenuated by cocaine administration. This is not a result of gender differences in the expression of anxiety-like state, since behavioral responses to an anxiogenic drug, FG-7142, are similar in male and female zebrafish. The basal brain dopamine (DA) levels and the expression of dopamine transporter mRNA (zDAT) show no significant sexual dimorphism. Acute cocaine exposure does not significantly change DA or zDAT. Withdrawal from repeated cocaine administration results in an overall reduction in zDAT, as well as an increase in DA levels. Neither treatment leads to significant gender differences in brain DA or zDAT. The common and gender-specific effects of cocaine on zebrafish, a well-characterized model of vertebrate development and genetics, should help in understanding the mechanisms involved in the anxiety associated with cocaine withdrawal and provide new opportunities in search for therapeutic solutions.

Effects of acute systemic cocaine administration on the cortisol, ACTH and prolactin levels of black tufted-ear marmosets

The effect of acute systemic cocaine administration on total circulating cortisol, adrenocorticotropin hormone (ACTH) and prolactin levels of nine adult black tufted-ear marmoset monkeys (Callithrix penicillata) was investigated. For each subject, two blood samples were obtained after an i.p. injection of 10 and 20mg/kg of cocaine: one sample was drawn 30-min post-injection, while the second was following a 60-min interval. Blood samples were also obtained 0, 30 and 60 min following a saline injection. The 20 mg/kg dose of cocaine induced a significant decrease in ACTH levels 60 min after being administered. Circulating levels of cortisol, on the other hand, increased significantly 60 min after the 20 mg/kg dose. Prolactin concentrations decreased significantly 30 and 60 min after both doses of cocaine had been administered (10 and 20 mg/kg). Finally, the content of the three hormones analyzed remained constant 0, 30 and 60 min post-saline administrations. Therefore, an acute systemic cocaine challenge alters the basal circulating levels of ACTH, cortisol and prolactin of marmoset monkeys. A distinct response pattern was observed for each hormone analyzed, possibly related to specific negative feedback mechanisms and/or this species glucocorticoid-resistance. The use of this small neotropical primate may thus provide a unique opportunity to investigate cocaine-induced neuroendocrine effects.

Maze model to study spatial learning and memory in freely moving monkeys

Many types of mazes have been used in cognitive brain research and data obtained from those experiments, especially those from rodents' studies, support the idea that the hippocampus is related to spatial learning and memory. But the results from non-human primates researches regarding the role of the hippocampus in spatial learning and memory are controversial and inconsistent with those obtained in rodents. This might be due to the differences of the methods used in non-human primates and rodents. Several kinds of maze models including two-dimensional computerized visual maze models and three-dimensional maze models have been developed for non-human primates, but they all have some defects. Therefore, development of a maze model for non-human primates that is comparable with those used in rodents is necessary to solve the controversy. This paper describes a large-scale, three-dimensional outdoor maze model for non-human primates which can be used to study spatial learning and memory. Monkeys learn to use the maze quickly compared with two-dimensional computerized visual mazes. It has many advantages which could make up the limits of the existing three-dimensional mazes in non-human primates, and can be comparable with radial arm mazes used in rodents. Based on the results, we believe that the new maze model will be valuable in many research areas, especially in studies involving spatial learning and memory in freely moving monkeys.

Disruption of the neurokinin-3 receptor (NK3) in mice leads to cognitive deficits

RATIONALE

The structurally related neuropeptides, substance P, neurokinin A, and neurokinin B, belong to a family of molecules termed tachykinins and are widely distributed in the central and peripheral nervous systems. These peptides mediate their effects through three G protein coupled receptor subtypes, the neurokinin-1, neurokinin-2 and neurokinin-3 receptors, respectively.

OBJECTIVE

To study the physiological functions of NK3, a line of NK3 knockout mice were generated and characterized in a broad spectrum of well-established behavioral tests.

RESULTS

In several tests, including spontaneous locomotor activity, elevated plus maze, forced swim, and hot plate, wild-type and knockout mice performed similarly. However, in several cognition tests, including passive avoidance, acquisition of conditioned avoidance responding (CAR), and the Morris water maze, NK3 knockout mice displayed deficits compared to wild-type mice. Although NK3 wild-type and knockout mice performed similarly in the training phase of the passive avoidance test, knockout mice had shorter latencies to enter the dark compartment on days 3 and 4, suggesting impaired retention. In the acquisition phase of the conditioned avoidance responding assay, NK3 knockout mice acquired the CAR task at a slower rate than wild-type mice. Once the CAR test was acquired, both NK3 wild-type and knockout mice responded similarly to clozapine and risperidone, drugs which suppress responding in this test. In the Morris water maze, NK3 knockout mice showed increased latencies to find the escape platform on day 3 of training, suggesting a modest, but significant delay in acquisition compared to wild-type mice.

CONCLUSION

These studies suggest a role for NK3 in learning and memory in mice.

Anxiogenic effects of cocaine withdrawal in zebrafish

Continued usage of cocaine is determined by genetic, conditioned and homeostatic factors, while it is reinforced by drug-induced reward and the emotionally negative state of drug withdrawal, which includes anxiety. The molecular mechanisms of these long-term behavioral and physiological alterations have yet to be fully elucidated. Here we demonstrate that in zebrafish, a wide range of non-anesthetic cocaine doses, 0.015-15 muM, does not result in acute alterations in locomotor activity, in spite of the high brain cocaine levels induced (7-120 pg/microg protein). Conversely, cocaine withdrawal causes hyperactivity associated with stereotypy. The behavioral hyperactivity is progressively increased during the initial period of withdrawal (24-72 h) and is maintained for at least 5 days. Such effect of cocaine withdrawal is aggravated by environmental stimulation and attenuated in the home environment. Administration of cocaine (1.5 microM) or a non-sedative dose of diazepam (5 microM, immersion) acutely counteracts withdrawal-associated hyperactivity and stereotypy in zebrafish, with the magnitude of these effects positively correlating with the degree of prior increase in basal activity. Administration of an anxiogenic benzodiazepine inverse agonist, FG-7142, results in zebrafish behavior similar to that observed during cocaine withdrawal. Together, the results suggest that cocaine withdrawal produces long-lasting behavioral effects in zebrafish which are consistent with an anxiety-like state. Thus, zebrafish, a powerful model for the study of vertebrate genetics, could provide insights into the molecular mechanisms of drug withdrawal.

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

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

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.