Hot and cold cognitive disturbances in antidepressant-free patients with major depressive disorder: a NeuroPharm study.

BACKGROUND: Cognitive disturbances are common and disabling features of major depressive disorder (MDD). Previous studies provide limited insight into the co-occurrence of hot (emotion-dependent) and cold (emotion-independent) cognitive disturbances in MDD. Therefore, we here map both hot and cold cognition in depressed patients compared to healthy individuals. METHODS: We collected neuropsychological data from 92 antidepressant-free MDD patients and 103 healthy controls. All participants completed a comprehensive neuropsychological test battery assessing hot cognition including emotion processing, affective verbal memory and social cognition as well as cold cognition including verbal and working memory and reaction time. RESULTS: The depressed patients showed small to moderate negative affective biases on emotion processing outcomes, moderate increases in ratings of guilt and shame and moderate deficits in verbal and working memory as well as moderately slowed reaction time compared to healthy controls. We observed no correlations between individual cognitive tasks and depression severity in the depressed patients. Lastly, an exploratory cluster analysis suggested the presence of three cognitive profiles in MDD: one characterised predominantly by disturbed hot cognitive functions, one characterised predominantly by disturbed cold cognitive functions and one characterised by global impairment across all cognitive domains. Notably, the three cognitive profiles differed in depression severity. CONCLUSION: We identified a pattern of small to moderate disturbances in both hot and cold cognition in MDD. While none of the individual cognitive outcomes mapped onto depression severity, cognitive profile clusters did. Overall cognition-based stratification tools may be useful in precision medicine approaches to MDD.

Oral contraceptives and the serotonin 4 receptor: a molecular brain imaging study in healthy women.

OBJECTIVE: Sex steroid hormones potently shape brain functions, including those critical to maintain mental health such as serotonin signaling. Use of oral contraceptives (OCs) profoundly changes endogenous sex steroid hormone levels and dynamics. Recent register-based studies show that starting an OC is associated with increased risk of developing depression. Here, we investigate whether use of OCs in healthy women is associated with a marker of the serotonin system in terms of serotonin 4 receptor (5-HT4R) brain imaging. METHODS: [11C]SB207145-PET imaging data on 53 healthy women, of whom 16 used OCs, were available from the Cimbi database. We evaluated global effects of OC use on 5-HT4R binding in a latent variable model based on 5-HT4R binding across cortical and subcortical regions. RESULTS: We demonstrate that OC users have 9-12% lower global brain 5-HT4R binding potential compared to non-users. Univariate region-based analyses (pallidostriatum, caudate, hippocampus, amygdala, anterior cingulate cortex, and neocortex) supported the global effect of OC use with the largest difference present in the hippocampus (-12.8% (95% CI [-21.0; -3.9], Pcorrected = 0.03). CONCLUSION: We show that women who use OCs have markedly lower brain 5-HT4R binding relative to non-users, which constitutes a plausible molecular link between OC use and increased risk of depressive episodes. We propose that this reflects a reduced 5-HT4R gene expression, possibly related to a blunted ovarian hormone state among OC users.

Genome-wide gene expression in a pharmacological hormonal transition model and its relation to depressive symptoms.

OBJECTIVES: Sensitivity to sex-steroid hormone fluctuations may increase risk for perinatal depression. We aimed to identify genome-wide biological profiles in women demonstrating sensitivity to pharmacological sex-hormone manipulation with gonadotrophin-releasing hormone agonist (GnRHa). METHODS: Longitudinal gene expression (Illumina Human HT12.v4) and DNA methylation data (Infinium HumanMethylation450K BeadChip) from 60 women (30 GnRHa, 30 placebo) were generated (Trial ID: NCT02661789). Differences between baseline and two follow-up points (initial stimulation- and subsequent early suppression phase) in the biphasic ovarian hormone response to GnRHa were assessed using linear mixed effects models. RESULTS: Genome-wide analysis revealed 588 probes differentially expressed from GnRHa intervention to first stimulatory phase follow-up (intervention group × time) after 10% fdr multiple testing correction. Of these, 54% genes were also significantly associated with estradiol changes over time (proxy for GnRHa response magnitude), 9.5% were associated with changes in depressive symptoms, and 38% were associated with changes in neocortical serotonin transporter binding. The genes were implicated in TGF beta signaling, adipogenesis, regulation of actin cytoskeleton, and focal adhesion pathways and enriched for DNA methylation changes (P = 0.006). CONCLUSIONS: These findings point toward an altered peripheral blood transcriptomic landscape in a pharmacological model of sex-hormone-induced depressive symptoms.

Mental distress and personality in women undergoing GnRH agonist versus GnRH antagonist protocols for assisted reproductive technology.

STUDY QUESTION: Do mental distress and mood fluctuations in women undergoing GnRH agonist and GnRH antagonist protocols for assisted reproductive technology (ART) differ depending on protocol and the personality trait, neuroticism? SUMMARY ANSWER: ART treatment did not induce elevated levels of mental distress in either GnRH antagonist or agonist protocols but neuroticism was positively associated with increased mental distress, independent of protocols. WHAT IS KNOWN ALREADY: ART treatment may increase mental distress by mechanisms linked to sex hormone fluctuations. General psychological characteristics, such as personality traits indexing negative emotionality, e.g. neuroticism, are likely to affect mental distress during ART treatment. STUDY DESIGN, SIZE, DURATION: A total of 83 women undergoing their first ART cycle were consecutively randomized 1:1 to GnRH antagonist (n = 42) or GnRH agonist (n = 41) protocol. The study population was a subgroup of a larger ongoing Danish clinical randomized trial and was established as an add-on in the period 2010-2012. PARTICIPANTS/MATERIALS, SETTING, METHODS: Women in the GnRH antagonist protocol received daily injections with recombinant follicle-stimulating hormone, Puregon(®) and subcutaneous injections with GnRH antagonist, Orgalutran(®). Women in the GnRH agonist protocol received nasal administration of the GnRH agonist, Synarela(®) and subcutaneous injections with FSH, Puregon(®). The study design did not allow for a blinding procedure. All women self-reported the Profile of Mood States, the Perceived Stress Scale, the Symptom Checklist-92-Revised, and the Major Depression Inventory questionnaires, at baseline, at ART cycle day 35, on the day of oocyte pick-up, and on the day of hCG testing. Also, a series of Profile of Mood States were reported daily during pharmacological treatment to monitor mood fluctuations. The personality trait Neuroticism was assessed at baseline by the self-reported NEO-PI-R questionnaire. MAIN RESULTS AND THE ROLE OF CHANCE: ART did not induce within- or between-protocol changes in any of the applied measures of mental distress. However, the GnRH antagonist protocol was associated with more pronounced median mood fluctuations during the stimulation phase (antagonist, 11.0 SD, [IQR = 21.1-6.1]; agonist, 8.9 SD, [IQR = 11.3-5.7], P = 0.025). This association became non-significant after applying a Bonferroni-Holm correction. Neuroticism was highly positively associated with increased levels of mental distress throughout treatment independent of protocols (all P-values <0.006), and cross-sectional analysis revealed that women with high or low Neuroticism scores at baseline showed a significant trend towards lower chances of a positive pregnancy test (P-value =0.028). LIMITATIONS, REASONS FOR CAUTION: Information on prognostic factors such as preceding length of infertility, number of retrieved oocytes and number of prior insemination treatments was not accounted for in the analyses. The stratification of protocols by age in the subgroups of women included in this study was suboptimal. Women with prior or current use of antidepressant medication were excluded from our study. WIDER IMPLICATIONS: Our results imply that mental distress emerging during ART treatment is not causally linked to hypogonadism per se or to the choice of protocol. Rather, our data highlight the potential importance of (i) rapid increases in ovarian steroids and (ii) addressing personality traits indexing negative emotionality, i.e. Neuroticism, in women undergoing ART treatment, to optimize both emotional adjustment and, possibly, the chances of obtaining pregnancy. STUDY FUNDING/COMPETING INTERESTS: The Danish Research Council for Independent Research and MSD, Denmark kindly supported the study. The authors declare no competing financial interests. TRIAL REGISTRATION NUMBER: EudraCT - 2008-005452-24.

Central 5-HT4 receptor binding as biomarker of serotonergic tonus in humans: a [11C]SB207145 PET study.

Identification of a biomarker that can inform on extracellular serotonin (5-HT) levels in the brains of living humans would enable greater understanding of the way brain circuits are modulated by serotonergic neurotransmission. Substantial evidence from studies in animals and humans indicates an inverse relationship between central 5-HT tonus and 5-HT type 4 receptor (5-HT4R) density, suggesting that 5-HT4R receptor density may be a biomarker marker for 5-HT tonus. Here, we investigated whether a 3-week administration of a selective serotonin reuptake inhibitor, expected to increase brain 5-HT levels, is associated with a decline in brain 5-HT4R binding. A total of 35 healthy men were studied in a placebo-controlled, randomized, double-blind study. Participants were assigned to receive 3 weeks of oral dosing with placebo or fluoxetine, 40 mg per day. Brain 5-HT4R binding was quantified at baseline and at follow-up with [(11)C]SB207145 positron emission tomography (PET). Three weeks of intervention with fluoxetine was associated with a 5.2% reduction in brain 5-HT4R binding (P=0.017), whereas placebo intervention did not change 5-HT4R binding (P=0.52). Our findings are consistent with a model, wherein the 5-HT4R density adjusts to changes in the extracellular 5-HT tonus. Our data demonstrate for the first time in humans that the imaging of central 5-HT4R binding may be used as an in vivo biomarker of the central 5-HT tonus.

Does Harm Avoidance mediate effects of recollected parental bonding on mental distress in adulthood?

BACKGROUND: Adverse early life conditions such as perceived low quality of parental bonding increase vulnerability to stress and psychopathology in adulthood. However, the mechanisms by which perceptions of parental bonding translate into vulnerability are unclear and remain sparsely investigated in healthy populations. We proposed a model, in which the personality trait Harm Avoidance would mediate effects of recollected parental bonding during the first sixteen years of life on measures of perceived stress and mental distress severity in adulthood. METHOD: Five-hundred-eighteen adults (65.1 % women), aged 18-53years, completed questionnaires of parental bonding, perceived stress, trait Harm Avoidance, and severity of mental distress. Direct and indirect effects mediated through trait Harm Avoidance were examined in a structural equation model. RESULTS: Under the causal assumptions of our proposed model, indirect effects of trait Harm Avoidance mediated the relationship between parental overprotection and severity of mental distress, while significantly attenuating the direct effects of parental care on severity of mental distress. Moreover, indirect effects of trait Harm Avoidance significantly attenuated the direct effects of parental overprotection and care on perceived stress. CONCLUSION: In this large sample of mentally healthy adults, recollected parental bonding was significantly associated with levels of perceived stress and severity of mental distress. The results from our proposed model further suggest that trait Harm Avoidance may be a developmental link, by which the quality of recollected parental bonding in childhood translates into adult vulnerability to stress and mental distress.

No association between peripheral serotonin-gene-related DNA methylation and brain serotonin neurotransmission in the healthy and depressed state.

BACKGROUND: Methylation of serotonin-related genes has been proposed as a plausible gene-by-environment link which may mediate environmental stress, depressive and anxiety symptoms. DNA methylation is often measured in blood cells, but little is known about the association between this peripheral epigenetic modification and brain serotonergic architecture. Here, we evaluated the association between whole-blood-derived methylation of four CpG sites in the serotonin transporter (SLC6A4) and six CpG sites of the tryptophan hydroxylase 2 (TPH2) gene and in-vivo brain levels of serotonin transporter (5-HTT) and serotonin 4 receptor (5-HT4) in a cohort of healthy individuals (N = 254) and, for 5-HT4, in a cohort of unmedicated patients with depression (N = 90). To do so, we quantified SLC6A4/TPH2 methylation using bisulfite pyrosequencing and estimated brain 5-HT4 and 5-HTT levels using positron emission tomography. In addition, we explored the association between SLC6A4 and TPH2 methylation and measures of early life and recent stress, depressive and anxiety symptoms on 297 healthy individuals. RESULTS: We found no statistically significant association between peripheral DNA methylation and brain markers of serotonergic neurotransmission in patients with depression or in healthy individuals. In addition, although SLC6A4 CpG2 (chr17:30,236,083) methylation was marginally associated with the parental bonding inventory overprotection score in the healthy cohort, statistical significance did not remain after accounting for blood cell heterogeneity. CONCLUSIONS: We suggest that findings on peripheral DNA methylation in the context of brain serotonin-related features should be interpreted with caution. More studies are needed to rule out a role of SLC6A4 and TPH2 methylation as biomarkers for environmental stress, depressive or anxiety symptoms.

Cognitive processing of infant stimuli in pregnant women with and without affective disorders and the association to postpartum depression.

Pregnancy and childbirth are among the strongest risk factors for depression but the neurocognitive mechanisms underlying this enhanced risk are unknown. This study investigated emotional and non-emotional cognition in 57 pregnant women with or without an affective disorder during their third trimester, and the association between cognitive biases and subsequent postpartum depression (PPD). Of the pregnant women, 22 had a diagnosis of unipolar disorder (UD) and seven of bipolar disorder (BD) in full or partial remission, while 28 had no history of affective disorder. We included a control group of 29 healthy non-pregnant women. First, participants were interviewed, completed non-emotional and emotional cognitive tests and lastly filled out questionnaires. The participants were assessed two times after birth: at a home visit shortly after birth, and with a telephone interview to assess PPD in the first six months after birth. Healthy pregnant women rated infant cries less negatively than non-pregnant women, possibly reflecting preparation for motherhood. Pregnant women with UD exhibited a negative bias in ratings of infant cries, whereas pregnant women with BD showed a positive bias in ratings of infant happy faces and recognition of adult facial expressions. Across all pregnant women, more negative ratings of infant cries were associated with enhanced risk of PPD. Negatively biased perception of infant cries during pregnancy may thus signal vulnerability toward PPD.

Cerebral serotonin transporter binding is inversely related to body mass index.

Overweight and obesity is a health threat of increasing concern and understanding the neurobiology behind obesity is instrumental to the development of effective treatment regimes. Serotonergic neurotransmission is critically involved in eating behaviour; cerebral level of serotonin (5-HT) in animal models is inversely related to food intake and body weight and some effective anti-obesity agents involve blockade of the serotonin transporter (SERT). We investigated in 60 healthy volunteers body mass index (BMI) and regional cerebral SERT binding as measured with [(11)C]DASB PET. In a linear regression model with adjustment for relevant covariates, we found that cortical and subcortical SERT binding was negatively correlated to BMI (-0.003 to -0.012 BP(ND) unit per kg/m(2)). Tobacco smoking and alcohol consumption did not affect cerebral SERT binding. Several effective anti-obesity drugs encompass blockade of the SERT; yet, our study is the first to demonstrate an abnormally decreased cerebral SERT binding in obese individuals. Whether the SERT has a direct role in the regulation of appetite and eating behaviour or whether the finding is due to a compensatory downregulation of SERT secondary to other dysfunction(s) in the serotonergic transmitter system, such as low baseline serotonin levels, remains to be established.

Brain serotonin 2A receptor binding: relations to body mass index, tobacco and alcohol use.

Manipulations of the serotonin levels in the brain can affect impulsive behavior and influence our reactivity to conditioned reinforcers. Eating, tobacco smoking, and alcohol consumption are reinforcers that are influenced by serotonergic neurotransmission; serotonergic hypofunction leads to increased food and alcohol intake, and conversely, stimulation of the serotonergic system induces weight reduction and decreased food/alcohol intake as well as tobacco smoking. To investigate whether body weight, alcohol intake and tobacco smoking were related to the regulation of the cerebral serotonin 2A receptor (5-HT(2A)) in humans, we tested in 136 healthy human subjects if body mass index (BMI), degree of alcohol consumption and tobacco smoking was associated to the cerebral in vivo 5-HT(2A) receptor binding as measured with (18)F-altanserin PET. The subjects' BMI's ranged from 18.4 to 42.8 (25.2+/-4.3) kg/m(2). Cerebral cortex 5-HT(2A) binding was significantly positively correlated to BMI, whereas no association between cortical 5-HT(2A) receptor binding and alcohol or tobacco use was detected. We suggest that our observation is driven by a lower central 5-HT level in overweight people, leading both to increased food intake and to a compensatory upregulation of cerebral 5-HT(2A) receptor density.

Neuroticism modulates mood responses to pharmacological sex hormone manipulation in healthy women.

BACKGROUND: Women show increased risk of depressive symptoms during hormonal transition phases. The risk mechanisms may include changes in mood in response to fluctuating ovarian hormones moderated by predisposing risk factors for mood disorders, such as personality trait Neuroticism. METHODS: A pooled sample of 92 mentally healthy women (28.3 ± 7.1, mean age ± SD) from two independent cohorts run in our lab, using gonadotropin-releasing hormone agonist (GnRHa) experimentally (n = 28) compared to placebo (n = 27) and as part in vitro fertilization (n = 37), were extracted from the Center for Integrated Molecular Brain Imaging database. All women filled in questionnaires of trait Neuroticism from the NEO personality Inventory-Revised (NEO PI-R) at baseline and self-reported levels of mood disturbances with the Profile of Mood States (POMS) daily during 14 days of GnRHa intervention or placebo. Effects of intervention by trait Neuroticism on serial daily reports of mood disturbances were examined using mixed model analyses. RESULTS: Personality trait Neuroticism significantly modulated daily mood responses to GnRHa, but not placebo. Women with high and low scores on trait Neuroticism at baseline experienced more pronounced changes in mood when exposed to GnRHa, whereas women with medium trait Neuroticism scores remained relatively stable. CONCLUSIONS: The susceptibility to hormone-triggered mood changes appears to depend upon women's general tendency to experience distress and destabilization of mood, as captured by personality trait Neuroticism. This could aid clinicians evaluate hormone-related vulnerability for mood disorders in women and may guide targeted prevention in reproductive care.

Sex hormone manipulation slows reaction time and increases labile mood in healthy women.

BACKGROUND: Women show increased risk of depressive symptoms in life phases where ovarian steroid hormone levels fluctuate or decline rapidly. The risk mechanisms may include changes in mental state and affective cognition possibly mediated by serotonergic neurotransmission. METHODS: In a randomized controlled double-blinded trial, 61 healthy women (mean age 24.3±4.9 years) were tested with measures of affective verbal memory, reaction time, mental distress, and serotonin transporter binding at baseline and at follow-up after receiving gonadotropin-releasing hormone agonist (GnRHa) or placebo intervention. Women also reported daily mood profiles during intervention. We tested direct effects of intervention and indirect effects through changes in serotonin transporter binding on verbal affective memory, simple reaction time and self-reported measures of mental distress, and further effects of GnRHa on daily mood. RESULTS: GnRHa induced an increase in simple reaction time (p=0.03) and more pronounced fluctuations in daily self-reported mood in a manner dependent on baseline mood (p=0.003). Verbal affective memory recall, overall self-perceived mental distress, and serotonin transporter binding were not affected. CONCLUSIONS: In healthy women transient sex-steroid hormone fluctuations decrease speed of information processing and further produce more labile mood only in women with elevated levels of mood disturbances at baseline.

Evaluation of acute tryptophan depletion and sham depletion with a gelatin-based collagen peptide protein mixture.

Acute Tryptophan Depletion (ATD) is a dietary method used to modulate central 5-HT to study the effects of temporarily reduced 5-HT synthesis. The aim of this study is to evaluate a novel method of ATD using a gelatin-based collagen peptide (CP) mixture. We administered CP-Trp or CP+Trp mixtures to 29 healthy volunteers; 13 from a randomized, double-blinded crossover study and sixteen from a randomized, double-blinded study run in our laboratory. Plasma amino acids, mood, side effects, cortisol concentrations, mean arterial blood pressure and heart rate were measured at multiple time-points. Repeated measures analysis of variance and Wilcoxon or Mann-Whitney U non-parametric tests were used to analyze the effects of intervention. Intake of the CP-Trp mixture efficiently reduced plasma Trp; however, the CP+Trp mixture induced a large significant increase in plasma Trp. No other significant effects of CP-Trp compared to CP+Trp were observed. The transient increase in plasma Trp after CP+Trp may impair comparison to the CP-Trp and we therefore recommend in future studies to use a smaller dose of Trp supplement to the CP mixture.

Role of emotional processing in depressive responses to sex-hormone manipulation: a pharmacological fMRI study.

Sex-hormone fluctuations may increase risk for developing depressive symptoms and alter emotional processing as supported by observations in menopausal and pre- to postpartum transition. In this double-blinded, placebo-controlled study, we used blood-oxygen level dependent functional magnetic resonance imaging (fMRI) to investigate if sex-steroid hormone manipulation with a gonadotropin-releasing hormone agonist (GnRHa) influences emotional processing. Fifty-six healthy women were investigated twice: at baseline (follicular phase of menstrual cycle) and 16 ± 3 days post intervention. At both sessions, fMRI-scans during exposure to faces expressing fear, anger, happiness or no emotion, depressive symptom scores and estradiol levels were acquired. The fMRI analyses focused on regions of interest for emotional processing. As expected, GnRHa initially increased and subsequently reduced estradiol to menopausal levels, which was accompanied by an increase in subclinical depressive symptoms relative to placebo. Women who displayed larger GnRHa-induced increase in depressive symptoms had a larger increase in both negative and positive emotion-elicited activity in the anterior insula. When considering the post-GnRHa scan only, depressive responses were associated with emotion-elicited activity in the anterior insula and amygdala. The effect on regional activity in anterior insula was not associated with the estradiol net decline, only by the GnRHa-induced changes in mood. Our data implicate enhanced insula recruitment during emotional processing in the emergence of depressive symptoms following sex-hormone fluctuations. This may correspond to the emotional hypersensitivity frequently experienced by women postpartum.

Cohort study of risk of fracture before and after surgery for primary hyperparathyroidism.

OBJECTIVES: To study whether fracture risk before and after surgery was increased in patients with primary hyperparathyroidism. DESIGN: Cohort study. SETTING: Three Danish university hospitals. PARTICIPANTS: 674 consecutive patients with primary hyperparathyroidism (median age 61, range 13-89 years) operated on during the period 1 January 1979 to 31 December 1997; 2021 age and sex matched controls from national patient register. MAIN OUTCOME MEASURE: Fractures. RESULTS: The cases had an increased relative rate of fractures compared with the controls before surgery (1.8, 95% confidence interval 1.3 to 2.3) but not after surgery (1.0, 0.8 to 1.3). The risk of fracture was increased for the vertebrae (3.5, 1.3 to 9.7), the distal part of the lower leg and ankles (2.3, 1.2 to 4.3), and the non-distal part of the forearm (4.0, 1.5 to 10.6) before surgery but not after. The increase in risk of fracture began about 10 years before surgery. Risk peaked 5-6 years before surgery and remained raised, although at a lower level, in the five years immediately before surgery. A small increase in risk of fracture of the distal forearm emerged more than 10 years after surgery (2.9, 1. 3 to 6.7). CONCLUSIONS: Risk of fracture is increased up to 10 years before surgery in patients with primary hyperparathyroidism. The risk returns to normal after surgery.

[Cohort study of fracture risk before and after surgery of primary hyperparathyroidism]. / Kohortestudie af frakturrisiko før og efter operation for primaer hyperparatyreoidisme.

We studied the risk of fracture in 674 patients operated on for primary hyperparathyroidism compared to 2,021 age- and gender-matched controls, matched for age and gender, randomly drawn from the background population. Before surgery, there was an increased risk of fracture (relative risk 1.8, 9% confidence interval 1.3-2.3), but after surgery the relative risk was normalised (RR = 1.0, 0.8-1.3). The increased risk began ten years before surgery and peaked five to six years before surgery. After surgery, there was a temporary increase in the first year, but in the following years the fracture risk was normalised, with a small rise in distal forearm fractures more than ten years after surgery. Primary hyperparathyroidism may have started up to ten years before surgery, and the fracture risk is normalised after surgery.

Gender and the use of hormonal contraception in women are not associated with cerebral cortical 5-HT 2A receptor binding.

Gender influences brain function including serotonergic neurotransmission, which may play a role in the well-known gender variations in vulnerability to mood and anxiety disorders. Even though hormonal replacement therapy in menopause is associated with globally increased cerebral 5-HT(2A) receptor binding it is not clear if gender or use of hormonal contraception exhibits associations with 5-HT(2A) receptor binding. We found no significant effect of gender on cortical 5-HT(2A) receptor binding (P=0.15, n=132). When adjusting for the personality trait neuroticism, known to be positively correlated to frontolimbic 5-HT(2A) receptor binding and to be more pronounced in women, again, the effect of gender was not significant (P=0.42, n=127). Also, the use of hormonal contraception (n=14) within the group of pre-menopausal women (total n=29) was not associated with cortical 5-HT(2A) receptor binding (P=0.31). In conclusion, neither gender, nor the use of hormonal contraception in premenopausal women was associated with cortical 5-HT(2A) receptor binding.