Is it possible to modify serotonin receptor sensitivity?

It is possible to induce sub- and super-sensitivity of β-adrenergic receptors by long-term treatment with drugs acting on catecholamine systems. In contrast, analogous treatment with drugs acting on serotoninergic systems does not modify serotonin receptor sensitivity as measured by serotonin binding. Firstly, chronic 1-5HTP, the precursor amino acid, increases serotonin turnover but does not decrease serotonin binding. Secondly, chronic clomipramine, a predominantly serotonin uptake inhibitor also has no effect on serotonin binding. Thirdly, chronic metergoline, a selective serotonin antagonist in the cortex, does not induce supersensitivity.This apparent intractability of the serotonin receptor to changes after long-term treatment indicates a different post-synaptic regulatory mechanism than that found in catecholaminergic neurones. Furthermore, modification of serotonin receptor sensitivity is probably not relevant to the mode of action of antidepressant drugs. Rather, the response of pineal melatonin stimulation found after chronic clomipramine in these experiments implicates induction of β-receptor subsensitivity.     

Do testosterone declines during the transition to marriage and fatherhood relate to men's sexual behavior? Evidence from the Philippines

Testosterone (T) is thought to help facilitate trade-offs between mating and parenting in humans. Across diverse cultural settings married men and fathers have lower T than other men and couples' sexual activity often declines during the first years of marriage and after having children. It is unknown whether these behavioral and hormonal changes are related. Here we use longitudinal data from a large study in the Philippines (n = 433) to test this model. We show that among unmarried non-fathers at baseline (n = 153; age: 21.5 ± 0.3 years) who became newly married new fathers by follow-up (4.5 years later), those who experienced less pronounced longitudinal declines in T reported more frequent intercourse with their partners at follow-up (p < 0.01) compared to men with larger declines in T. Controlling for duration of marriage, findings were similar for men transitioning from unmarried to married (without children) (p < 0.05). Men who remained unmarried and childless throughout the study period did not show similar T-sexual activity outcomes. Among newly married new fathers, subjects who had frequent intercourse both before and after the transition to married fatherhood had more modest declines in T compared to peers who had less frequent sex (p < 0.001). Our findings are generally consistent with theoretical expectations and cross-species empirical observations regarding the role of T in male life history trade-offs, particularly in species with bi-parental care, and add to evidence that T and sexual activity have bidirectional relationships in human males.     

Short-term changes in fathers' hormones during father-child play: impacts of paternal attitudes and experience

Hormonal differences between fathers and non-fathers may reflect an effect of paternal care on hormones. However, few studies have evaluated the hormonal responses of fathers after interacting with their offspring. Here we report results of a 30-minute in-home experiment in which Filipino fathers played with their toddlers and consider whether paternal experience and men's perceptions of themselves as fathers affect hormonal changes. Fathers provided saliva and dried blood spot samples at baseline (B) and 30 (P30) and 60 (P60, saliva only) minutes after the interaction. We tested whether testosterone (T), cortisol (CORT), and prolactin (PRL) shifted after the intervention. In the total sample, T did not vary over the study period, while CORT declined from B to P30 and P60, and PRL also declined from B to P30. Fathers who spent more time in daily caregiving and men who thought their spouses evaluated them positively as parental caregivers experienced a larger decline in PRL (B to P30) compared to other fathers. First-time fathers also had larger declines in PRL compared to experienced fathers. Experienced fathers also showed a greater decline in CORT (B to P60) compared to first-time fathers. These results suggest that males' paternal experience and age of offspring affect hormonal responses to father–child play and that there is a psychobiological connection between men's perceptions of themselves as fathers and their hormonal responsivity to childcare.     

Phoenixin is negatively associated with anxiety in obese men

Phoenixin was recently identified in the rat hypothalamus and initially implicated in reproductive functions. A subsequent study described an anxiolytic effect of the peptide. The aim of the study was to investigate a possible association of circulating phoenixin with anxiety in humans. We therefore enrolled 68 inpatients with a broad spectrum of psychometrically measured anxiety (GAD-7). We investigated men since a menstrual cycle dependency of phoenixin has been assumed. Obese subjects were enrolled since they often report psychological comorbidities. In addition, we also assessed depressiveness (PHQ-9) and perceived stress (PSQ-20). Plasma phoenixin levels were measured using a commercial ELISA. First, we validated the ELISA kit performing a spike-and-recovery experiment showing a variance of 6.7 ± 8.8% compared to the expected concentrations over the whole range of concentrations assessed, while a lower variation of 1.6 ± 0.8% was observed in the linear range of the assay (0.07–2.1 ng/ml). We detected phoenixin in the circulation of obese men at levels of 0.68 ± 0.50 ng/ml. These levels showed a negative association with anxiety scores (r = −0.259, p = 0.043), while no additional associations with other psychometric parameters were observed. In summary, phoenixin is present in the human circulation and negatively associated with anxiety in obese men, a population often to report comorbid anxiety.