Gender and age affect NK1 receptors in the human brain - a positron emission tomography study with [18F]SPA-RQ

Green Light Exposure Elicits Anti-inflammation, Endogenous Opioid Release and Dampens Synaptic Potentiation to Relieve Post-surgical Pain

Light therapy improves multiple conditions such as seasonal affective disorders, circadian rhythm dysregulations, and neurodegenerative diseases. However, little is known about its potential benefits in pain management. While current pharmacologic methods are effective in many cases, the associated side effects can limit their use. Non-pharmacological methods would minimize drug dependence, facilitating a reduction of the opioid burden. Green light therapy has been shown to be effective in reducing chronic pain in humans and rodents. However, its underlying mechanisms remain incompletely defined. In this study, we demonstrate that green light exposure reduced postsurgical hypersensitivity in rats. Moreover, this therapy potentiated the antinociceptive effects of morphine and ibuprofen on mechanical allodynia in male rats. Importantly, in female rats, GLED potentiated the antinociceptive effects of morphine but did not affect that of ibuprofen. We showed that green light increases endogenous opioid levels while lessening synaptic plasticity and neuroinflammation. Importantly, this study reveals new insights into how light exposure can affect neuroinflammation and plasticity in both genders. Clinical translation of these results could provide patients with improved pain control and decrease opioid consumption. Given the noninvasive nature of green light, this innovative therapy would be readily implementable in hospitals. PERSPECTIVE: This study provides a potential additional therapy to decrease postsurgical pain. Given the safety, availability, and the efficacy of green light therapy, there is a significant potential for advancing the green light therapy to clinical trials and eventual translation to clinical settings.

Sex Differences in Exercise-Induced Bronchoconstriction in Athletes: A Systematic Review and Meta-Analysis

Exercise-induced bronchoconstriction (EIB) is a common complication of athletes and individuals who exercise regularly. It is estimated that about 90% of patients with underlying asthma (a sexually dimorphic disease) experience EIB; however, sex differences in EIB have not been studied extensively. With the goal of better understanding the prevalence of EIB in males and females, and because atopy has been reported to occur at higher rates in athletes, in this study, we investigated sex differences in EIB and atopy in athletes. A systematic literature review identified 60 studies evaluating EIB and/or atopy in post-pubertal adult athletes (n = 7501). Collectively, these studies reported: (1) a 23% prevalence of EIB in athletes; (2) a higher prevalence of atopy in male vs. female athletes; (3) a higher prevalence of atopy in athletes with EIB; (4) a significantly higher rate of atopic EIB in male vs. female athletes. Our analysis indicates that the physiological changes that occur during exercise may differentially affect male and female athletes, and suggest an interaction between male sex, exercise, and atopic status in the course of EIB. Understanding these sex differences is important to provide personalized management plans to athletes with underlying asthma and/or atopy.

[18F]SPA-RQ/PET Study of NK1 receptors in the Whole Body of Guinea Pig and Rat

There is a substantial interest in the development of NK1 substance P antagonists as potential treatments for various neuropsychiatric and somatic disorders. The aim of this study was to determine whether [¹⁸F]SPA-RQ can be utilized as a tool for studying the whole body distribution and function of NK1 receptors in preclinical settings. The compound was injected into guinea pigs with or without premedication with a NK1 receptor antagonist (NK1A-2). For comparison, we included two rats in the study, as the affinity of antagonists for NK1 receptors is known to vary between species. The whole body biodistribution of the tracer was determined at several time points. The tracer showed specific binding in organs compatible with the known location of NK1-receptors. Premedication with a NK1 antagonist led to an inhibited uptake of [¹⁸F]SPA-RQ in several organs of guinea pigs, notably intestine, pancreas, urinary bladder, uterus, skin and lung. Specific binding was also seen in both cortex and striatum. In contrast, negligible specific binding was observed in the rat brain with [¹⁸F]SPA-RQ, whereas the tracer uptake in peripheral tissues was similar to that seen in guinea pigs. We conclude that [¹⁸F]SPA-RQ/PET is a useful tool to study the distribution and function of peripherally located NK1 receptors e.g. in different disease models.

The Significance of NK1 Receptor Ligands and Their Application in Targeted Radionuclide Tumour Therapy

To date, our understanding of the Substance P (SP) and neurokinin 1 receptor (NK1R) system shows intricate relations between human physiology and disease occurrence or progression. Within the oncological field, overexpression of NK1R and this SP/NK1R system have been implicated in cancer cell progression and poor overall prognosis. This review focuses on providing an update on the current state of knowledge around the wide spectrum of NK1R ligands and applications of radioligands as radiopharmaceuticals. In this review, data concerning both the chemical and biological aspects of peptide and nonpeptide ligands as agonists or antagonists in classical and nuclear medicine, are presented and discussed. However, the research presented here is primarily focused on NK1R nonpeptide antagonistic ligands and the potential application of SP/NK1R system in targeted radionuclide tumour therapy.

Evaluation of aprepitant and fosaprepitant in pediatric patients

BACKGROUND

Single-dose i.v. fosaprepitant has been approved as an alternative to 3 day oral aprepitant, a neurokinin-1 receptor antagonist, and improves prevention of chemotherapy-induced nausea and vomiting (CINV). Because fosaprepitant has shown similar efficacy to aprepitant in adult patients only, this study compared the efficacy and safety of aprepitant and fosaprepitant in pediatric patients.

METHODS

Children younger than 18 years who received aprepitant or fosaprepitant to manage CINV between January 2015 and March 2018 at the National Cancer Center Hospital (Tokyo) were recruited to this study. The primary endpoint was complete response (CR; no vomiting/rescue medication) between 0 and 120 h after the start of chemotherapy. Secondary endpoints were safety based on the frequency of severe adverse events, and evaluation of patient characteristics as risk factors (effect of age and sex).

RESULTS

A total of 125 chemotherapy cycles were evaluated. In the aprepitant group, CR was observed in 36 of 80 treatment cycles (45.0%), whereas in the fosaprepitant group, it was observed in 19 of 45 cycles (42.2%; P = 0.852). No treatment-related severe adverse events were observed in either group. The number of non-CR was greater than that of CR in patients aged 6-14 years. The difference in CR rate between male and female patients was not statistically significant (47.1% vs 40.0%, respectively; P = 0.471).

CONCLUSIONS

Aprepitant and fosaprepitant were safely used and may be equally useful for pediatric patients receiving highly emetogenic chemotherapy. CR rate may be associated with patient age.

Brain neurokinin-1 receptor availability in never-medicated patients with major depression - A pilot study

BACKGROUND

Neurotransmitter substance P (SP) and its preferred neurokinin-1 receptor (NK1R) have been implicated in the treatment of affective and addiction disorders. Despite promising preclinical data on antidepressant action, the clinical trials of NK1R antagonists in major depression have been disappointing. There are no direct in vivo imaging studies on NK1R characteristics in patients with a major depressive disorder (MDD).

METHODS

In this cross-sectional case-control study, we recruited nine never-medicated patients with moderate to severe MDD and nine matched healthy controls. NK1R availability (NK1R binding potential, BP_ND) was measured with in vivo 3-D positron emission tomography and a specific NK1 receptor tracer [¹⁸F]SPA-RQ. Clinical symptoms were assessed with the 17-item Hamilton Rating Scale for Depression (HAM-D17).

RESULTS

NK1R-BP_ND did not differ statistically significantly between patients with MDD and healthy controls. HAM-D17 total scores (range 21-32) correlated positively with NK1R-BP_ND in cortical and limbic areas. HAM-D17 subscale score for anxiety symptoms correlated positively with NK1R-BP_ND in specific brain areas implicated in fear and anxiety.

LIMITATIONS

Small sample size. Low variability in the clinical HAM-D subscale ratings may affect the observed correlations.

CONCLUSIONS

Our preliminary results do not support a different baseline expression of NK1Rs in a representative sample of never-medicated patients with MDD during a current moderate/severe depressive episode. The modulatory effect of NK1Rs on affective symptoms is in line with early positive results on antidepressant action of NK1 antagonists. However, the effect is likely to be too weak for treatment of MDD with NK1R antagonists alone in clinical practice.

Association between amygdala neurokinin-1 receptor availability and anxiety-related personality traits

Animal studies indicate that substance P (SP) and its preferred neurokinin-1 (NK1) receptor modulate stress and anxiety-related behavior. Alterations in the SP-NK1 system have also been observed in human anxiety disorders, yet little is known about the relation between this system and individual differences in personality traits associated with anxiety propensity and approach-avoidance behavior, including trait anxiety, neuroticism, and extraversion. Exploring this relation could provide important insights into the neurobiological underpinnings of human anxiety and the etiology of anxiety disorders, as anxious traits are associated with increased susceptibility to develop psychopathological conditions. Here we examined the relationship between central NK1 receptor availability and self-rated measures of trait anxiety, neuroticism, and extraversion. The amygdala was chosen as the primary region of interest since this structure has been suggested to mediate the effect of the SP-NK1 system on anxiety. Anxious traits and NK1 receptor availability, determined with positron emission tomography and the radiotracer [¹¹C]GR205171, were measured in 17 healthy individuals. Voxel-wise analyses showed a significant positive correlation between bilateral amygdala NK1 receptor availability and trait anxiety, and a trend in similar direction was observed for neuroticism. Conversely, extraversion was found to be negatively associated with amygdala NK1 receptor availability. Extraversion also correlated negatively with the NK1 measure in the cuneus/precuneus and fusiform gyrus according to exploratory whole-brain analyses. In conclusion, our findings indicate that amygdala NK1 receptor availability is associated with anxiety-related personality traits in healthy subjects, consistent with a modulatory role for the SP-NK1 system in human anxiety.

Age Differences in the Time Course and Magnitude of Changes in Circulating Neuropeptides After Pain Evocation in Humans

This study tested the hypothesis that older adults would have a stronger response for substance P (facilitatory) but weaker response to β-endorphin (inhibitory), in magnitude as well as time course. Eight younger and 9 older adults underwent 3 experimental sessions using well validated laboratory pain models: cold pressor task, contact heat pain, and a nonpainful control. Blood was collected through an indwelling catheter at baseline and 3, 15, 30, 45, and 60 minutes after stimuli administration. Older adults had higher baseline levels of both neuropeptides suggesting increased peripheral activity compared with younger adults. After the cold pressor task, older adults demonstrated a quick and strong release of substance P with dramatic recovery, whereas young adults maintained a constant low-grade response. Unlike substance P, β-endorphin increased between 3 and 15 minutes for both groups with the upsurge substantially higher for older adults. After heat pain, younger adults had an immediate surge in circulating substance P and β-endorphin that was more pronounced than among older adults. However, levels of substance P for younger adults slowly tapered whereas they continued to climb for the older adults through 30 minutes. β-endorphin peaked at 30 minutes for both groups and returned to baseline. No changes were observed during the nonpainful control session.

PERSPECTIVE

Older adults had higher baseline levels of substance P and β-endorphin suggesting increased peripheral activity compared with younger adults. After pain evocation, older adults demonstrated a more intense early response for both neuropeptides suggesting peripheral mechanisms involved in the response to pain may change with age.

Overlapping expression of serotonin transporters and neurokinin-1 receptors in posttraumatic stress disorder: a multi-tracer PET study

The brain serotonergic system is colocalized and interacts with the neuropeptidergic substance P/neurokinin-1 (SP/NK1) system. Both these neurochemical systems have independently been implicated in stress and anxiety, but interactions between them might be crucial for human anxiety conditions. Here, we examined the serotonin and substance P/neurokinin-1 (SP/NK1) systems individually as well as their overlapping expression in 16 patients with posttraumatic stress disorder (PTSD) and 16 healthy controls. Participants were imaged with the highly selective radiotracers [(11)C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile (DASB) and [(11)C]GR205171 assessing serotonin transporter (SERT) and NK1 receptor availability, respectively. Voxel-wise analyses in the amygdala, our a priori-defined region of interest, revealed increased number of NK1 receptors, but not SERT in the PTSD group. Symptom severity, as indexed by the Clinician-administered PTSD Scale, was negatively related to SERT availability in the amygdala, and NK1 receptor levels moderated this relationship. Exploratory, voxel-wise whole-brain analyses revealed increased SERT availability in the precentral gyrus and posterior cingulate cortex of PTSD patients. Patients, relative to controls, displayed lower degree of overlapping expression between SERT and NK1 receptors in the putamen, thalamus, insula and lateral orbitofrontal gyrus, lower overlap being associated with higher PTSD symptom severity. Expression overlap also explained more of the symptomatology than did either system individually, underscoring the importance of taking interactions between the neurochemical systems into account. Thus, our results suggest that aberrant serotonergic-SP/NK1 couplings contribute to the pathophysiology of PTSD and, consequently, that normalization of these couplings may be therapeutically important.

Increased neurokinin-1 receptor availability in the amygdala in social anxiety disorder: a positron emission tomography study with [11C]GR205171

The neurokinin-1 (NK1) receptor is abundantly expressed in the fear circuitry of the brain, including the amygdala, where it modulates stress and anxiety. Despite its proposed involvement in psychopathology, only a few studies of NK1 receptor availability in human subjects with anxiety disorders exist. Here, we compared NK1 receptor availability in patients with social anxiety disorder (SAD; n = 17) and healthy controls (n = 17) using positron emission tomography and the radiotracer [11C]GR205171. The Patlak Graphical plot using a cerebellar reference region was used to model the influx parameter, Ki measuring NK1 receptor availability. Voxel-wise statistical parametric mapping analyses revealed increased NK1 receptor availability specifically in the right amygdala in SAD patients relative to controls. Thus, we demonstrate that exaggerated social anxiety is related to enhanced NK1 receptor availability in the amygdala. This finding supports the contribution of NK1 receptors not only in animal models of stress and anxiety but also in humans with anxiety disorders.

Sex and the migraine brain

The brain responds differently to environmental and internal signals that relate to the stage of development of neural systems. While genetic and epigenetic factors contribute to a premorbid state, hormonal fluctuations in women may alter the set point of migraine. The cyclic surges of gonadal hormones may directly alter neuronal, glial and astrocyte function throughout the brain. Estrogen is mainly excitatory and progesterone inhibitory on brain neuronal systems. These changes contribute to the allostatic load of the migraine condition that most notably starts at puberty in girls.

Netupitant PET imaging and ADME studies in humans

Netupitant is a new, selective NK1 receptor antagonist under development for the prevention of chemotherapy-induced nausea and vomiting. Two studies were conducted to evaluate the brain receptor occupancy (RO) and disposition (ADME) of netupitant in humans. Positron emission tomography (PET) imaging with the NK1 receptor-binding-selective tracer [(11) C]-GR205171 was used to evaluate the brain penetration of different doses of netupitant (100, 300, and 450 mg) and to determine the NK1 -RO duration. A NK1 -RO of 90% or higher was achieved with all doses in the majority of the tested brain regions at Cmax, with a long duration of RO. The netupitant minimal plasma concentration predicted to achieve a NK1 -RO of 90%, C90% , in the striatum was 225 ng/mL; after administration of netupitant 300 mg, concentrations exceeded the C90% . In the ADME study, a single nominal dose of [(14) C]-netupitant 300 mg was used to assess its disposition. Absorption was rapid and netupitant was extensively metabolized via Phase I and II hepatic metabolism. Elimination of >90% was predicted at day 29 and was principally via hepatic/biliary route (>85%) with a minor contribution of the renal route (<5%). In conclusion, these studies demonstrate that netupitant is a potent agent targeting NK1 receptors with long lasting RO. In addition, netupitant is extensively metabolized and is mainly eliminated through the hepatic/biliary route and to a lesser extent via the kidneys.

Acute NK₁ receptor antagonist administration affects reward incentive anticipation processing in healthy volunteers

The primary brain structures of reward processing are mainly situated in the mid-brain dopamine system. The nucleus accumbens (NAc) receives dopaminergic projections from the ventral tegmental area and works as a key brain region for the positive incentive value of rewards. Because neurokinin-1 (NK₁) receptor, the cognate receptor for substance P (SP), is highly expressed in the NAc, we hypothesized that the SP/NK₁ receptor system might play a role in positive reward processing in the NAc in humans. Therefore, we conducted a functional MRI (fMRI) study to assess the effects of an NK₁ receptor antagonist on human reward processing through a monetary incentive delay task that is known to elicit robust activation in the NAc especially during gain anticipation. Eighteen healthy adults participated in two series of an fMRI study, taking either a placebo or the NK₁ receptor antagonist aprepitant. Behavioural measurements revealed that there was no significant difference in reaction time, hit rate, or self-reported effort for incentive cues between the placebo and aprepitant treatments. fMRI showed significant decrease in blood oxygenation-level-dependent signals in the NAc during gain anticipation with the aprepitant treatment compared to the placebo treatment. These results suggest that SP/NK₁ receptor system is involved in processing of positive incentive anticipation and plays a role in accentuating positive valence in association with the primary dopaminergic pathways in the reward circuit.

Diminished neurokinin-1 receptor availability in patients with two forms of chronic visceral pain

Central sensitization and dysregulation of peripheral substance P and neurokinin-1 receptor (NK-1R) signaling are associated with chronic abdominal pain in inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). Although positron emission tomography (PET) has demonstrated that patients with injury-related chronic pain have diminished NK-1R availability in the brain, it is unknown whether these deficits are present in IBD and IBS patients, who have etiologically distinct forms of non-injury-related chronic pain. This study's aim was to determine if patients with IBD or IBS exhibit deficits in brain expression of NK-1Rs relative to healthy controls (HCs), the extent to which expression patterns differ across patient populations, and if these patterns differentially relate to clinical parameters. PET with [(18)F]SPA-RQ was used to measure NK-1R availability by quantifying binding potential (BP) in the 3 groups. Exploratory correlation analyses were performed to detect associations between NK-1R BP and physical symptoms. Compared to HCs, IBD patients had NK-1R BP deficits across a widespread network of cortical and subcortical regions. IBS patients had similar, but less pronounced deficits. BP in a subset of these regions was robustly related to discrete clinical parameters in each patient population. Widespread deficits in NK-1R BP occur in IBD and, to a lesser extent, IBS; however, discrete clinical parameters relate to NK-1R BP in each patient population. This suggests that potential pharmacological interventions that target NK-1R signaling may be most effective for treating distinct symptoms in IBD and IBS.

Substance P and vasoactive intestinal peptide levels in middle ear effusions of children

CONCLUSION

This is the first report demonstrating high levels of substance P (SP) that inversely correlate with vasoactive intestinal peptide (VIP) levels in middle ear effusions (MEEs) of patients with otitis media with effusion (OME). Increased SP and decreased VIP levels might play a role in the pathogenesis of chronic OME.

OBJECTIVE

The etiology of OME is multifactorial, and neurogenic inflammation may play a significant role. SP and VIP levels were not evaluated previously in MEEs of children with OME.

METHODS

Fifty patients aged 2-12 years (mean age 5.24 ± 2.64) were included in the study. MEEs were classified as mucoid or serous based on the gross appearance. SP and VIP levels were determined using ELISA.

RESULTS

High levels of SP were detected in MEEs. In addition SP levels were significantly higher in serous samples (2910.55 ± 307.96 vs 2218.55 ± 262.30 pg/ml). There were also age-dependent changes, such that SP levels were significantly higher in children aged 2-3 years compared with those who were 4-5 and 6-12 years old. VIP levels were undetectable in 30% of patients and the mean level of VIP was 50.91 ± 16.01 pg/ml in serous middle ear effusions and 54.86 ± 15.91 pg/ml in mucoid MEEs.

Age, sex and NK1 receptors in the human brain -- a positron emission tomography study with [¹¹C]GR205171

The substance P/neurokinin 1 (SP/NK1) system has been implicated in the processing of negative affect. Its role seems complex and findings from animal studies have not been easily translated to humans. Brain imaging studies on NK1 receptor distribution in humans have revealed an abundance of receptors in cortical, striatal and subcortical areas, including the amygdala. A reduction in NK1 receptors with increasing age has been reported in frontal, temporal, and parietal cortices, as well as in hippocampal areas. Also, a previous study suggests sex differences in cortical and subcortical areas, with women displaying fewer NK1 receptors. The present PET study explored NK1 receptor availability in men (n=9) and women (n=9) matched for age varying between 20 and 50years using the highly specific NK1 receptor antagonist [¹¹C]GR205171 and a reference tissue model with cerebellum as the reference region. Age by sex interactions in the amygdala and the temporal cortex reflected a lower NK1 receptor availability with increasing age in men, but not in women. A general age-related decline in NK1 receptor availability was evident in the frontal, temporal, and occipital cortices, as well as in the brainstem, caudate nucleus, and thalamus. Women had lower NK1 receptor availability in the thalamus. The observed pattern of NK1 receptor distribution in the brain might have functional significance for brain-related disorders showing age- and sex-related differences in prevalence.

Increased neurokinin-1 receptor availability in temporal lobe epilepsy: a positron emission tomography study using [(11)C]GR205171

PURPOSE

Activation of the neurokinin-1 (NK1) receptor by neuropeptide substance P (SP) induces and maintains epileptic activity in various experimental models of epilepsy. The primary objective of this study was to investigate whether neurobiological changes linked to NK1-SP receptor system are associated with hyperexcitability in patients with temporal lobe epilepsy (TLE). A secondary objective was to investigate the relationship between seizure frequency and NK1 receptor availability.

METHODS

A positron emission tomography study was conducted with the selective NK1 receptor antagonist [(11)C]GR205171 in nine patients with TLE and 18 healthy control participants. Parametric PET images were generated using the Patlak graphical method, with cerebellum as reference region. Data analyses including group comparisons were performed using statistical parametric mapping.

RESULTS

Patients with TLE showed increased NK1 receptor availability in both hemispheres with the most pronounced increase in anterior cingulate gyrus ipsilateral to seizure onset. A positive correlation between NK1 receptor availability and seizure frequency was observed in the medial temporal lobe and in the lentiform nucleus ipsilateral to the seizure onset.

CONCLUSION

Our results suggest that there is an intrinsic network using the NK1-SP receptor system for synaptic transmission and epileptiform activity in TLE.

Physiological and anatomical bases for sex differences in pain and nausea as presenting symptoms of acute coronary syndromes

Acute coronary syndromes (ACS) are common in both men and women. Studies show that women have longer times before diagnosis and treatment in the Emergency Department and worse outcomes than men, which may be related to the differing symptom presentations of men and women. Men are more likely to have chest pain, whereas women are more likely to have dyspnea or nausea. However, women tend to be older and more likely to have diabetes mellitus, hypertension, and peripheral neuropathies. Men and women also exhibit differences in the neural receptors and pathways involved in pain and noxious-stimuli perception. Moreover, men and women may have subtle differences in the locations and sites of their atherosclerotic lesions, all of which may affect symptom presentation. The purposes of this review are to present: (1) the physiology of two common symptoms associated with ACS, ie, pain and nausea; (2) how these symptoms differ between men and women; and (3) how different comorbidities may affect the presentation of these symptoms.

First evaluation of [11C]R116301 as an in vivo tracer of NK1 receptors in man

Purpose

NK1 receptors have been implicated in various neuropsychiatric and other disorders. R116301 is a selective NK1 receptor antagonist. In this pilot study, [¹¹C]R116301 was evaluated as a potential positron emission tomography (PET) ligand for the NK1 receptor.

Procedures

Two dynamic PET studies were performed in three normal volunteers before and after a blocking dose of aprepitant. Data were analyzed using striatum to cerebellum standardized uptake value (SUV) ratios.

Results

Baseline SUV ratios at 60–90 min after injection ranged from 1.22 to 1.70. Following aprepitant administration, this specific signal was completely blocked. Aprepitant administration did not significantly affect uptake in cerebellum, confirming the absence of NK1 receptors in cerebellum.

Conclusion

These preliminary results indicate that [¹¹C]R116301 has potential as a radioligand for in vivo assessment of NK1 receptors in the human brain.

Neurokinin-1 receptor expression and function in human macrophages and brain: perspective on the role in HIV neuropathogenesis

Substance P (SP) is upregulated in HIV infection in adult men and women, as determined by increased plasma levels. There is a reciprocal and bidirectional relationship between substance P and HIV in HIV-infected monocyte-derived macrophages and cell lines (e.g., THP-1). Substance P up-regulates HIV and HIV up-regulates SP protein expression. Neurokinin-1 receptor (NK1R) antagonists inhibit HIV infectivity through downregulation of the chemokine receptor, CCR5, and downregulation of HIV LTR. Neurokinin-1 receptor is expressed in full-length and truncated forms. The full-length NK1R is capable of signaling, whereas the truncated NK1R primes the chemokine receptor CCR5. Both full-length and truncated NK1R are expressed in several brain regions in human autopsy brains. SP-NK1R interactions have regulatory roles in inflammation and infection. The differential expression of truncated and full-length NK1R has important biological consequences. These include receptor-receptor interaction (e.g., NK1R-CCR5); changes in expression during cell differentiation (e.g., THP-1 cells); and differences in regional tissue distribution (e.g., differences in different brain regions). NK1R-SP receptor pathways are important cell regulatory pathways.

Detection of full-length and truncated neurokinin-1 receptor mRNA expression in human brain regions

We have applied a newly developed SYBR green-based real-time RT-PCR assay for quantification of full-length and truncated neurokinin-1 receptor (NK1R) mRNA expression in nine regions of human brain tissues obtained from 23 subjects who died with no evidence of neurological or neurodegenerative disease. The following brain regions were examined: cingulate cortex, cerebellum, nucleus accumbens, caudate nucleus, putamen, pons, hippocampus, locus coeruleus, and basal ganglia. The SYBR green-based real-time PCR was more sensitive than TaqMan probe-based real-time PCR in amplifying both full-length and truncated NK1R mRNA. The real-time RT-PCR assay had excellent specificity and sensitivity, with a dynamic range of detection between 100 and 1,000,000 copies of the NK1R cDNA per reaction. The truncated NK1R mRNA levels were more abundant than those of the full-length NK1R in most of the regions examined and there was no significant difference in the truncated NK1R mRNA levels among the nine regions studied. There was, however, a significant difference in the expression of full-length NK1R mRNA levels among the nine regions (P=0.0024), and the putamen region expressed the highest full-length NK1R mRNA. Further studies are needed in order to examine the differences between full-length and truncated NK1R in signal transduction and functional consequences in order to delineate the significance of the co-presence of the two forms of NK1R in the human brain.

PET imaging of neurokinin-1 receptors with [(18)F]SPA-RQ in human subjects: assessment of reference tissue models and their test-retest reproducibility

[(18)F]SPA-RQ (substance P antagonist receptor quantifier) labels the substance P-preferring (NK(1)) receptor in human brain. A prior study showed that [(18)F]SPA-RQ brain uptake can be quantified with a reference tissue method and thereby avoid invasive blood sampling. The purposes of this study were to compare three different reference tissue methods and to assess test-retest reproducibility. Eight healthy subjects underwent two [(18)F]SPA-RQ scans. We calculated the binding potential (BP), which is proportional to receptor density, from both regional volume of interest and voxel-wise data. We compared three reference tissue methods: simplified reference tissue model, multilinear reference tissue model (MRTM), and its two-parameter version (MRTM2). The three methods generated equivalent values of regional BP, but MRTM2 was the most resistant to noise. Temporally stable values of BP were obtained with 240 min of imaging data. MRTM2 had excellent test-retest reproducibility, with high reliability (intraclass correlation > 0.9) and low variability (< 10%). In addition to regional volume of interest analysis, we also created parametric images of BP, variability, and reliability based on voxel-wise time-activity data. The reproducibility of parametric BP was also good, with variability < 20% and reliability > 0.7 in gray matter regions. In conclusion, a two-parameter reference tissue method (MRTM2) provided reproducible and reliable measurements of [(18)F]SPA-RQ brain uptake using 240 min of both regional and voxel-wise data.