Physiological roles of prolactin in the adrenocortical response to acute restraint stress

Effects of different winter paddock management of Thoroughbred weanlings and yearlings in the cold region of Japan on physiological function, endocrine function and growth

Effects of different winter paddock management of Thoroughbred weanlings and yearlings in Hokkaido, Japan, which is extremely cold in winter, on physiological function, endocrine function and growth were investigated. They were divided into two groups; those kept outdoors for 22 hr in the paddock (22hr group) and those kept outdoors for 7 hr in daytime with walking exercise for 1 hr using the horse-walker (7hr+W group), and the changes in daily distance travelled, body temperature (BT), heart rate (HR), HR variability (HRV), endocrine function and growth parameters were compared between the two groups from November at the year of birth to January at 1 year of age. The 7hr+W group could travel almost the same distance as the 22hr group by using the horse-walker. The 22hr group had a lower rate of increase in body weight than the 7hr+W group in January. In addition, lower in BT and HR were observed, and HRV analysis showed an increase in high frequency power spectral density, indicating that parasympathetic nervous activity was dominant. And also, changes in circulating cortisol and thyroxine were not observed despite cold environment. On the other hand, the 7hr+W group had higher prolactin and insulin like growth factor than the 22hr group in January, and cortisol and thyroxine were also increased. Physiological and endocrinological findings from the present study indicate that the management of the 7hr+W group is effective in promoting growth and maintaining metabolism during the winter season.

The role of prolactin in the suppression of the response to restraint stress in the lactating mouse

Suppression of the hypothalamic-pituitary-adrenal (HPA) axis is a well-characterised maternal adaptation that limits the exposure of the offspring to maternally-derived stress hormones. This current study has investigated the possible involvement of the lactogenic hormone, prolactin, in this physiologically important adaptation. As expected, circulating prolactin levels were higher in unstressed lactating mice compared to their virgin counterparts. Interestingly however, the ability of an acute period of restraint stress to further elevate prolactin levels was diminished in the former group. The stress-induced rise in prolactin levels in the virgin animals was concurrent with an increase in prolactin receptor activation within the adrenal cortical cells. This adrenal response was not seen in either the stressed or control lactation group, an observation that may be in part explained by the observed downregulation of prolactin receptor mRNA expression within this tissue. Further evidence of suppression of the HPA axis during lactation was revealed using in situ hybridisation to demonstrate that while acute restraint stress increased corticotrophin releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus in both virgin and lactating mice, the magnitude of this response was reduced in the latter group. This potentially adaptive response did not, however, appear to result from the altered prolactin profile during lactation because it was not affected by the pharmacological suppression of prolactin secretion from the pituitary. This study therefore suggests that during lactation the response of the HPA axis to stress is suppressed at multiple physiological levels which are mediated by both prolactin-dependent and prolactin-independent mechanisms.

The endocrine control of reproductive suppression in an aseasonally breeding social subterranean rodent, the Mahali mole-rat (Cryptomys hottentotus mahali)

Cooperative behaviour, sociality and reproductive suppression in African mole-rats have been extensively studied. Nevertheless, endocrine correlates of some species of social mole-rats have been neglected, and these species may hold the key to understanding the behavioural and physiological complexity that allows the maintenance of social groups in African mole-rats. In this study, we investigated endocrine correlates implicated in the suppression of reproduction and cooperative behaviours, namely glucocorticoids (a stress-related indicator) through faecal glucocorticoid metabolites (fGCMs), plasma testosterone (an indicator of aggression) and plasma prolactin in the Mahali mole-rat (Cryptomys hottentotus mahali) across reproductive classes (breeding females and males, non-breeding females and males) and season (wet and dry). Breeders possessed higher levels of testosterone than non-breeders. In reproductively suppressed non-breeding females, fGCMs were significantly higher than in breeders. Furthermore, an adrenocorticotropic hormone stimulation test (ACTH challenge test) on both male and female non-breeders revealed that female non-breeders show a more significant response to the ACTH challenge than males. At the same time, plasma prolactin levels were equally elevated to similar levels in breeding and non-breeding females. Chronically high levels of prolactin and fGCM are reported to cause reproductive suppression and promote cooperative behaviours in non-breeding animals. Furthermore, there was a negative relationship between plasma prolactin and progesterone in non-breeding females. However, during the wet season, a relaxation of suppression occurs through reduced prolactin which corresponds with elevated levels of plasma progesterone in non-breeding females. Therefore, prolactin is hypothesised to be the primary hormone controlling reproductive suppression and cooperative behaviours in non-breeding females. This study provides new endocrine findings for the maintenance of social suppression in the genus Cryptomys.

Stress Adaptation and the Brainstem with Focus on Corticotropin-Releasing Hormone

Stress adaptation is of utmost importance for the maintenance of homeostasis and, therefore, of life itself. The prevalence of stress-related disorders is increasing, emphasizing the importance of exploratory research on stress adaptation. Two major regulatory pathways exist: the hypothalamic–pituitary–adrenocortical axis and the sympathetic adrenomedullary axis. They act in unison, ensured by the enormous bidirectional connection between their centers, the paraventricular nucleus of the hypothalamus (PVN), and the brainstem monoaminergic cell groups, respectively. PVN and especially their corticotropin-releasing hormone (CRH) producing neurons are considered to be the centrum of stress regulation. However, the brainstem seems to be equally important. Therefore, we aimed to summarize the present knowledge on the role of classical neurotransmitters of the brainstem (GABA, glutamate as well as serotonin, noradrenaline, adrenaline, and dopamine) in stress adaptation. Neuropeptides, including CRH, might be co-localized in the brainstem nuclei. Here we focused on CRH as its role in stress regulation is well-known and widely accepted and other CRH neurons scattered along the brain may also complement the function of the PVN. Although CRH-positive cells are present on some parts of the brainstem, sometimes even in comparable amounts as in the PVN, not much is known about their contribution to stress adaptation. Based on the role of the Barrington’s nucleus in micturition and the inferior olivary complex in the regulation of fine motoric—as the main CRH-containing brainstem areas—we might assume that these areas regulate stress-induced urination and locomotion, respectively. Further studies are necessary for the field.

Influence of exercise and emotional stresses on secretion of prolactin and growth hormone in Thoroughbred horses

The secretion of prolactin and growth hormone in response to exercise and emotional stresses was investigated in Thoroughbreds. Two experiments were performed: one with loading of only exercise stress and one with simultaneous loading of exercise and emotional stresses. Exercise stress was loaded in 4 steps using a treadmill for horses: pre-exercise period (5 min), walking period (6.5 min), galloping period (3 min), and cooling down period (10 min). Emotional stress was loaded by showing a loud video of an audience at a racetrack during the walking period. The results clearly demonstrated that exercise stress rapidly increased the secretion of prolactin and growth hormone and that secretion of them persisted for a specific period after the exercise. In addition, emotional stress promoted prolactin secretion.

Conscious rat PET imaging with soft immobilization for quantitation of brain functions: comprehensive assessment of anesthesia effects on cerebral blood flow and metabolism

BACKGROUND

Animal brain functions evaluated by in vivo imaging under anesthesia can be affected by anesthetic agents, resulting in incorrect assessment of physiological brain function. We therefore performed dynamic positron emission tomography (PET) imaging of conscious rats using recently reported soft immobilization to validate the efficacy of the immobilization for brain function assessments. We also determined the effects of six anesthetic agents-a mixed anesthetic agent (MMB), ketamine + xylazine (KX), chloral hydrate (Chloral), pentobarbital (PTB), propofol (PF), and isoflurane (IFL)-on brain function by comparison with conscious rats.

RESULTS

The immobilization enabled 45-min dynamic [¹⁸F]FDG-PET acquisition with arterial blood sampling using conscious rats without the use of special techniques or invasive surgery. The spatial resolution and quantitativity of [¹⁸F]FDG-PET were not significantly lower for conscious rats than for anesthetized rats. While MMB, Chloral, PTB, and PF showed ubiquitous reduction in the cerebral metabolic rates of glucose (CMR_glu) in brain regions, KX and IFL showed higher reductions in cerebellum and interbrain, and cerebellum, respectively. Cerebral blood flow (CBF) was reduced by MMB, KX, PTB, and PF; increased by IFL; and unaltered by Chloral. The magnitude of decrease in CMR_glu and CBF for MMB were not larger than for other five anesthetic agents, although blood glucose levels and body temperature can be easily affected by MMB.

CONCLUSION

The six anesthetic agents induced various effects on CMR_glu and CBF. The immobilization technique presented here is a promising tool for noninvasive brain functional imaging using conscious rats to avoid the effects of anesthetic agents.

Growth hormone receptor in dopaminergic neurones regulates stress-induced prolactin release in male mice

Arcuate nucleus (ARH) dopaminergic neurones regulate several biological functions, including prolactin secretion and metabolism. These cells are responsive to growth hormone (GH), although it is still unknown whether GH action on ARH dopaminergic neurones is required to regulate different physiological aspects. Mice carrying specific deletion of GH receptor (GHR) in tyrosine hydroxylase (TH)- or dopamine transporter (DAT)-expressing cells were produced. We investigated possible changes in energy balance, glucose homeostasis, fertility, pup survival and restraint stress-induced prolactin release. GHR deletion in DAT- or TH-expressing cells did not cause changes in food intake, energy expenditure, ambulatory activity, nutrient oxidation, glucose tolerance, insulin sensitivity and counter-regulatory response to hypoglycaemia in male and female mice. In addition, GHR deletion in dopaminergic cells caused no gross effects on reproduction and pup survival. However, restraint stress-induced prolactin release was significantly impaired in DAT- and TH-specific GHR knockout male mice, as well as in pegvisomant-treated wild-type males, whereas an intact response was observed in females. Patch clamp recordings were performed in ARH DAT neurones and, in contrast to prolactin, GH did not cause acute changes in the electrical activity of DAT neurones. Furthermore, TH phosphorylation at Ser40 in ARH neurones and median eminence axonal terminals was not altered in DAT-specific GHR knockout male mice during restraint stress. In conclusion, GH action in dopaminergic neurones is required for stress-induced prolactin release in male mice, suggesting the existence of sex differences in the capacity of GHR signalling to affect prolactin secretion. The mechanism behind this regulation still needs to be identified.

The Impact of Psychosis on Sexual Functioning: A Systematic Review

BACKGROUND

Sexual dysfunction among psychotic patients is highly prevalent. However, most research has focused on antipsychotic side effects on sexual functioning.

AIM

To provide evidence by means of a systematic review of the literature about the impact of psychosis on sexual functioning among unmedicated patients.

METHODS

Systematic search of MEDLINE (PubMed), Scopus, and Google Scholar for studies that reported sexual functioning among psychotic patients, who were drug-naïve or drug-free for at least 3 weeks before the study. Studies were published in English language between January 1994 and October 2019. We used the approach recommended by PRISMA, and the selection process was carried out by 2 reviewers.

OUTCOMES

The outcome measures were sexual function and sexual dysfunctions.

RESULTS

A total of 734 articles were obtained, 658 were obtained after duplicates were removed, 612 were excluded after reading the title and abstract, and 46 were included for a complete review of the articles. 5 papers were finally included. A total of 770 cases were included in the systematic review. The prevalence of sexual dysfunction in psychosis varied from 16.8% to 70% and in ultra-high state was 50%. It is noteworthy that those ultra-high-risk (prodromal) patients who develop psychosis had higher rates of sexual impairment. Therefore, we found higher rates of sexual dysfunction among untreated patients, both psychotic and ultra-high risk patients, than healthy controls.

CLINICAL IMPLICATIONS

The assessment of sexual behavior should be a part of routine psychiatric examination not only in psychotic but also in ultra-high-risk patients.

STRENGTHS & LIMITATIONS

This is the first systematic review about the impact of psychosis on sexual functioning among unmedicated patients. However, scarce and heterogeneous studies were identified.

CONCLUSIONS

Impaired sexual functioning is common in the onset of psychosis (or during ultra-high-risk state) and prior to the beginning of treatment. This suggests that psychotic symptoms and sexual dysfunction may have common etiological pathways at the psychosocial and neurobiological levels. Vargas-Cáceres S, Cera N, Nobre P, et al. The Impact of Psychosis on Sexual Functioning: A Systematic Review. J Sex Med 2021;18:457-466.

Potential mechanisms linking psychological stress to bone health

Chronic psychological stress affects many body systems, including the skeleton, through various mechanisms. This review aims to provide an overview of the factors mediating the relationship between psychological stress and bone health. These factors can be divided into physiological and behavioural changes induced by psychological stress. The physiological factors involve endocrinological changes, such as increased glucocorticoids, prolactin, leptin and parathyroid hormone levels and reduced gonadal hormones. Low-grade inflammation and hyperactivation of the sympathetic nervous system during psychological stress are also physiological changes detrimental to bone health. The behavioural changes during mental stress, such as altered dietary pattern, cigarette smoking, alcoholism and physical inactivity, also threaten the skeletal system. Psychological stress may be partly responsible for epigenetic regulation of skeletal development. It may also mediate the relationship between socioeconomic status and bone health. However, more direct evidence is required to prove these hypotheses. In conclusion, chronic psychological stress should be recognised as a risk factor of osteoporosis and stress-coping methods should be incorporated as part of the comprehensive osteoporosis-preventing strategy.

Investigating the Role of Prolactin as a Potential Biomarker of Stress in Castrated Male Domestic Dogs

Prolactin has been recently regarded as a potential biomarker of both acute and chronic stress in several species. Since only few studies until now have focussed on domestic dogs, this study was aimed at evaluating whether prolactin, cortisol and stress behaviour correlated with each other in sheltered dogs. Both cortisol and prolactin analysis were performed in serum samples through a hormone-specific ELISA kit. For each dog, a stress score was calculated by summing the number of occurrences of stress-related behaviours. The presence/absence of fear during the time spent in the collection room was also scored for each individual. Results revealed a weak negative correlation between cortisol and prolactin levels. Neither of the hormones was correlated with the stress score, nor did their values seem to be influenced by showing fear in the collection room. The weak negative correlation found between cortisol and prolactin values agrees with results obtained in other studies, indicating that prolactin response might be an alternative to cortisol response. This, together with the high serum prolactin levels compared to those reported by other authors for healthy domestic dogs, may indicate that prolactin might be a good biomarker of chronic stress, and although further studies are needed to better understand the potential role of prolactin in the evaluation of canine welfare.

Plasma prolactin levels are associated with the severity of illness in drug-naive first-episode psychosis female patients

Patients with schizophrenia frequently present hyperprolactinemia as a consequence of antipsychotic treatment. However, an increase in circulating prolactin levels has also been shown in patients without previous treatment. Our objective was to compare prolactin levels between antipsychotic-naive first-episode psychosis (AN-FEP) patients and healthy controls (HC). As part of an FEP program (Programa Asistencial Fases Iniciales de Psicosis [PAFIP]), 270 AN-FEP patients and 153 HC were eligible for this study. Serum prolactin levels were measured by an automated immunochemiluminescent assay. Subjects' sex and having an AN-FEP diagnosis both had an effect on prolactin levels, with higher levels in women than in men, and in AN-FEP patients than in HC. Moreover, plasma prolactin levels showed a negative correlation with the SAPS scores in AN-FEP female patients. AN-FEP patients have increased levels of prolactin, which might be stress-induced. This, together with the association of higher prolactin with a lower severity of the disease, suggests that prolactin might play a neuroprotective role, especially in women.

The median eminence detects and responds to circulating prolactin in the male mouse

In addition to its established lactational roles, prolactin acts on multiple target tissues and its circulating levels are responsive to a range of physiological stimuli. The present study used immunohistochemistry to demonstrate that systemic administration of prolactin activates target cells in the arcuate nucleus and median eminence of the male mouse. Prolactin receptor stimulation results in the phosphorylation and thus activation of the signal transducer and activator of transcription (STAT)5 pathway. Interestingly, although, in the arcuate nucleus, this response was localised to cell nuclei, the median eminence displayed both nuclear and diffuse, non-nuclear, phospho-STAT5 (pSTAT5) staining. Dual-label immunostaining demonstrated that, although the majority of nuclear pSTAT5 within the median eminence was located within vimentin-positive tanycytes, the non-nuclear staining occurred primarily in neuronal (βIII tubulin immunoreactive) elements. This conclusion was supported by the marked reduction of this signal in prolactin-treated mice lacking neuronal prolactin receptors. A smaller reduction was also seen in animals lacking prolactin receptors on GABAergic but not glutamatergic neurones. These findings identify a new prolactin target tissue and, in doing so, support the proposal that the median eminence has a sensory role in addition to its established secretory function. The physiological significance of this prolactin response is unknown, although its rapidity (maximum within 2 minutes of i.p. injection) suggests that it may enable the early detection of an increase in circulating prolactin. It is also possibile that non-nuclear prolactin-generated pSTAT5 in the median eminence may have a local, non-transcriptional, action. To this end, we used Evans Blue dye to demonstrate that elevated prolactin appears to reduce median eminence permeability and also that this effect is lost in animals lacking neuronal prolactin receptors.

Serum prolactin level and its correlation with psychopathology in drug free/drug naïve schizophrenia a case control study

BACKGROUND

There is a discrepancy in literature regarding level of prolactin in drug free/ drug naïve patients with non-affective psychosis. Few earlier studies have found low levels of prolactin whereas recent studies have found high levels of prolactin when compared to controls. Most of these studies have not considered the possible confounding factors. Also ours is the first study that evaluated the correlation between psychopathology & prolactin levels after considering the confounding agents.

METHOD

It was a cross sectional, hospital based case control study. Purposive sampling was done to identify the cases of schizophrenia. 59 cases and 59 controls fulfilling inclusion and exclusion criteria were taken for the study after taking consent. Socio-demographic and other relevant clinical data were collected. Scores of PANSS AND BPRS were collected on the day of admission. Blood samples were collected from 8 to 10 am in the morning. Samples were centrifuged and the serum was stored in sterile vials at minus 80° centigrade. Serum Prolactin, free T3, freeT4, Thyroid Stimulating Hormone & Cortisol levels were evaluated for both cases and controls and correlation between them and with psychopathology of cases was seen.

RESULTS

Our study showed that prolactin level was increased in drug free/naïve cases of schizophrenia. Significant difference was found between T4 levels of cases and controls. No correlation was found between prolactin and psychopathology.

CONCLUSION

Prolactin is increased in drug free/ drug naïve patients of schizophrenia and this is not related to confounding factors. There was no significant correlation between prolactin and psychopathology.

Stress-Induced Hyperprolactinemia: Pathophysiology and Clinical Approach

While prolactin is most well known for its role in lactation and suppression of reproduction, its physiological functions are quite diverse. There are many etiologies of hyperprolactinemia, including physiologic as well as pathologic causes. Physiologic causes include pregnancy, lactation, sleep-associated, nipple stimulation and sexual orgasm, chest wall stimulation, or trauma. Stress is also an important physiologic cause of hyperprolactinemia, and its clinical significance is still being explored. This review will provide an overview of prolactin physiology, the role of stress in prolactin secretion, as well as the general clinical approach to hyperprolactinemia.

Hyperprolactinemia and insulin resistance in drug naive patients with early onset first episode psychosis

BACKGROUND

Hyperprolactinemia and glucose and lipid metabolism abnormalities are often found in patients with schizophrenia and are generally considered secondary to the use of antipsychotic drugs. More recent studies have shown these same neuroendocrine and metabolic abnormalities in antipsychotic naïve patients with first episode psychosis (FEP), rising the hypothesis that schizophrenia itself may be related to an abnormal regulation of prolactin secretion and to impaired glucose tolerance. The aim of this study was to compare prolactin levels, glycometabolism parameters and lipid profile between a sample of 31 drug-naive adolescents in the acute phase of FEP and a control group of 23 subjects at clinical high risk (CHR) of developing psychosis.

METHODS

The assessment involved anthropometric data (weight, height, BMI index, pubertal stage) and blood tests (levels of glucose, glycated hemoglobin, serum insulin, triglycerides, total and fractionated cholesterol, prolactin). Insulin resistance (IR) was calculated through the homeostatic model of assessment (HOMA-IR), assuming a cut-off point of 3.16 for adolescent population. FEP patients and CHR controls were compared by using Student's t-distribution (t-test) for parametric data. P < 0.05 was considered significant.

RESULTS

Significant higher level of prolactin was found in FEP group than in CHR group (mean = 28.93 ± 27.16 vs 14.29 ± 7.86, P = 0.009), suggesting a condition of hyperprolactinemia (HPRL). Patients with FEP were more insulin resistant compared to patients at CHR, as assessed by HOMA-IR (mean = 3.07 ± 1.76 vs 2.11 ± 1.11, P = 0.043). Differences of fasting glucose (FEP = 4.82 ± 0.71, CHR = 4.35 ± 0.62, P = 0.016) and HbA1c (FEP = 25.86 ± 13.31, CHR = 33.00 ± 2.95, P = 0.013), were not clinically significant as the mean values were within normal range for both groups. No significant differences were found for lipid profile. A BMI value within the range of normal weight was found for both groups, with no significant differences.

CONCLUSION

We suggested that HPRL, increase in HOMA-IR, and psychotic symptoms may be considered different manifestations of the acute onset of schizophrenia spectrum psychosis, with a common neurobiological vulnerability emerging since adolescence. The influence of age and gender on clinical manifestations of psychotic onset should be considered for early prevention and treatment of both schizophrenia spectrum psychosis and neuroendocrine-metabolic dysfunctions.

Effects of Pup Separation on Stress Response in Postpartum Female Rats

There is a complex collection of neuroendocrine function during the postpartum period. Prolactin (PRL) released by suckling stimulus and its PRL receptors (PRL-R) in the central nervous system (CNS) are involved in hyporesponsiveness of the hypothalamic-pituitary-adrenal (HPA) axis in lactating mammals including rodents and humans. It is not clear how long it takes to reestablish the attenuated HPA axis activity of lactating rats to a pre-pregnancy state after pup separation. We first tested the hypothesis that HPA axis activity in response to an acute stress in postpartum rats would return to a pre-pregnancy state after pup separation. Restraint stress for 30 min was performed at the end of pup separation as an acute stressor. Plasma levels of corticosterone (CORT) were measured following restraint stress or no-stress (control) in virgin rats and postpartum rats housed with their pups or with pup removal for different periods of time of one hour, 24 h, or eight days. We then tested the hypothesis that circulating PRL level and CNS PRL-R gene expression were involved in mediating the acute stress response in postpartum rats. Plasma levels of PRL and PRL-R mRNA levels in the choroid plexus of the CNS were determined in both no-stress and stress, virgin rats, and postpartum rats housed with their pups or with pup removal for various periods, and their correlation with plasma CORT levels was assessed. The results demonstrated that PRL levels declined to virgin state in all postpartum rats separated from their pups, including the dams with one-hour pup separation. Stress-induced HPA activity dampened in lactating rats housed with pups, and returned to the pre-pregnancy state after 24 h of pup separation when both circulating PRL level and CNS PRL-R expression were restored to a pre-pregnancy state. Additionally, basal plasma CORT and CNS PRL-R expression were significantly correlated in rats with various pup status. This study suggested that stress-induced HPA activation occurred when PRL-R expression was similar to the level of virgin females, indicating that PRL-R upregulation contributes to an attenuated HPA response to acute stress. Understanding neuroendocrine responses to stress during the postpartum period is critical to understand postpartum-related neuropsychiatric illnesses and to maintain mental health in postpartum women.

Restraint stress increases prolactin-mediated phosphorylation of signal transducer and activator of transcription 5 in the hypothalamus and adrenal cortex in the male mouse

Prolactin is a pleiotropic peptide hormone produced by the lactotrophs in the anterior pituitary. Its rate of secretion is primarily regulated by a negative-feedback mechanism where prolactin stimulates the activity of the tuberoinfundibular dopaminergic (TIDA) neurones, increasing their release of dopamine, which accesses the pituitary via the median eminence to suppress further prolactin secretion. In addition to its well established role in lactation, circulating prolactin is secreted in response to stress, although the mechanism by which this is achieved or its cellular targets remains unknown. In the present study, we show that 15 minutes of restraint stress causes an approximately seven-fold increase in circulating prolactin concentration in male mice. Monitoring prolactin receptor activation, using immunohistochemistry to determine the level and distribution of tyrosine phosphorylated signal transducer and activator of transcription 5 (pSTAT5), we show that this stress-induced increase in prolactin interacts with both central and peripheral targets. Restraint stress for 15 minutes significantly increased pSTAT5 staining in the arcuate nucleus, median eminence and the zona fasciculata of the adrenal cortex. In each case, this response was prevented by pretreating the animals with bromocriptine to block prolactin secretion from the pituitary. Interestingly, in contrast to many cells in the arcuate nucleus, stress reduced pSTAT5 staining of the TIDA neurones (identified by dual-labelling for tyrosine hydroxylase). This suggests that there is reduced prolactin signalling in these cells and thus potentially a decline in their inhibitory influence on prolactin secretion. These results provide evidence that prolactin secreted in response to acute stress is sufficient to activate prolactin receptors in selected target tissues known to be involved in the physiological adaptation to stress.

Acute stress diminishes M-current contributing to elevated activity of hypothalamic-pituitary-adrenal axis

Acute stress stimulates corticotrophin-releasing hormone (CRH)-expressing neurons in the hypothalamic paraventricular nucleus (PVN), which is an essential component of hypothalamic-pituitary-adrenal (HPA) axis. However, the cellular and molecular mechanisms remain unclear. The M-channel is a voltage-dependent K⁺ channel involved in stabilizing the neuronal membrane potential and regulating neuronal excitability. In this study, we tested our hypothesis that acute stress suppresses expression of Kv7 channels to stimulate PVN-CRH neurons and the HPA axis. Rat PVN-CRH neurons were identified by expressing enhanced green fluorescent protein driven by Crh promoter. Acute restraint stress attenuated the excitatory effect of Kv7 blocker XE-991 on the firing activity of PVN-CRH neurons and blunted the increase in plasma corticosterone (CORT) levels induced by microinjection of XE-991 into the PVN. Furthermore, acute stress significantly decreased the M-currents in PVN-CRH neurons and reduced PVN expression of Kv7.3 subunit in the membrane. In addition, acute stress significantly increased phosphorylated AMP-activated protein kinase (AMPK) levels in the PVN tissue. Intracerebroventricular injection of the AMPK inhibitor dorsomorphin restored acute stress-induced elevation of CORT levels and reduction of membrane Kv7.3 protein level in the PVN. Dorsomorphin treatment increased the M-currents and reduced the firing activity of PVN-CRH neurons in acutely stressed rats. Collectively, these data suggest that acute stress diminishes Kv7 channels to stimulate PVN-CRH neurons and the HPA axis potentially via increased AMPK activity.

Prolactin concentrations in antipsychotic-naïve patients with schizophrenia and related disorders: A meta-analysis

OBJECTIVE

The use of dopaminergic antagonist antipsychotics is associated with hyperprolactinemia, but some studies have found increased prolactin concentrations in antipsychotic-naive patients with schizophrenia and related disorders. We conducted a systematic review and meta-analysis of studies of prolactin in antipsychotic-naïve patient with these disorders (PRISMA No. CRD42015016337).

DATA SOURCES

PubMed (Medline), PsycInfo, and Web of Science were searched for articles from 1950 to the present in English.

STUDY SELECTION

Seven studies of males (N=141 for patients, N=191 for control subjects) and five studies of females (N=67 and N=116) met criteria for inclusion: data on blood prolactin concentrations for both control subjects and antipsychotic-naive patients with schizophrenia or a related disorder, with data available separately for males and females.

DATA EXTRACTION

Data was extracted from the papers by one author and independently verified by a second.

RESULTS

The mean effect size for males was 1.02 (95% CI, 0.77, 1.26; p<0.001) and 0.43 for females (95% CI 0.11, 0.76; p<0.01). Meta-regression analyses for age, smoking, body mass index (BMI), year of publication, and cortisol were not significant. Funnel plots did not suggest the presence of a publication bias.

CONCLUSIONS

Our meta-analyses found significantly increased prolactin levels in both male and female antipsychotic-naïve patients with schizophrenia and related disorders. The small number of studies and limited matching for potentially confounding variables in some of the studies were limitations of this analysis. Prolonged hyperprolactinemia may lead to sexual dysfunction and osteoporosis, and some antipsychotics cause additional elevation of prolactin concentrations.

Different effects of an extended photoperiod treatment on growth, gonadal function, and condition of hair coats in Thoroughbred yearlings reared under different climate conditions

One- to two-year-old Thoroughbred colts and fillies being reared in Miyazaki (warm climate) and Hidaka (cold climate), Japan, were administered extended photoperiod (EP) treatment between December 20 and the following April 10, and its effect on growth, endocrine changes, gonadal activation, and hair coat condition was investigated. In colts reared in Miyazaki, no effect of EP treatment was noted on the growth indices, including body weight (BW), height at withers (HW), girth, and cannon circumference (CC), whereas the BWs and CCs of fillies were significantly higher in the EP treatment group than the control. In Hidaka, the BWs and HWs of colts and HWs of fillies were significantly higher in the EP treatment group. Gonadal activation characterized by an increase in circulating hormone concentrations was earlier in the EP treatment group for fillies reared in Miyazaki [luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17β (E2)] and in colts (LH, testosterone, and E2) and fillies (LH, FSH, P4, and E2) reared in Hidaka. Regardless of sex and climate, prolactin was significantly higher in the EP treatment group, whereas insulin-like growth factor (IGF-I) was not. Initial ovulation occurred before April in more of the EP treatment group than the control regardless of the climate. Molting of the hair coat, examined in March, was advanced in the EP treatment group regardless of sex and climate. These results suggest that EP treatment may promote growth and gonadal activation in fillies reared in Miyazaki and in colts and fillies reared in Hidaka and that the effect may be mediated by prolactin.

The search for new biomarkers for cognition in schizophrenia

The search for biomarkers in cognition has been the focus of a large part of the research on patients suffering from schizophrenia. The scientific literature is heterogeneous, and few studies establishing an integrative model of pathogenesis and therapeutic response are available in this field. In this review, we aimed to summarize three essential aspects correlated with cognitive performance: 1) the relationship between inflammation and cognition in schizophrenia, 2) the role of prolactin in cognition, and 3) the association between cognition and neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF). Several studies support the association of inflammatory markers with cognitive status in schizophrenia. In recent decades, the development of effective therapies for cognitive impairment in schizophrenia has focused on the search for anti-inflammatory and immunomodulatory medications. Conversely, the implications of prolactin and its functions in cognition, the transition to psychosis and the diagnosis and prognosis of schizophrenia have been established independent of antipsychotic treatment. With regard to neurotrophic factors, a recent study has correlated BDNF levels with cognitive recovery in schizophrenic patients treated with cognitive remediation. We conclude that although there is a diversity of biomarkers focused on cognitive function in schizophrenia, BDNF is the biomarker that has accumulated the vast majority of evidence in the current literature.

Prolactin serum levels correlate with inflammatory status in drug-naïve first-episode schizophrenia

OBJECTIVES

The present study was to examine the relationship between serum levels of prolactin and the inflammatory status in drug-naïve, first-episode schizophrenia patients with normal weight.

METHODS

Patients with normal weight, drug-naïve, first-episode schizophrenia and healthy controls were enrolled in the study. Serum levels of prolactin (PRL) were measured using electrical chemiluminescence immunoassay. Serum levels of interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were examined using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Sixty patients with normal weight, drug-naïve, first-episode schizophrenia and 60 healthy controls were enrolled. The schizophrenia group had higher serum levels of PRL, IL-1β, IL-6 and TNF-α compared with the control group. There was a gender difference of hyperprolactinemia in schizophrenia group. There were positive relationships between serum levels of PRL and serum levels of IL-1β, IL-6 and TNF-α within the schizophrenia group. Within the schizophrenia group, TNF-α was the strongest predictor among the three cytokines for serum levels of prolactin after controlling for gender, age, education, smoking status and disease duration.

CONCLUSIONS

Patients with normal weight, drug-naïve, first-episode schizophrenia present elevated serum levels of PRL, which might be related to the up-regulated inflammatory status in this patient population.

Prolactin serum levels in first-episode neuroleptic-naive patients with pituitary microadenoma and comorbid psychosis

This study was designed to explore the relationship between pituitary microadenoma and psychosis and to evaluate the role that prolactin plays in pituitary microadenoma and comorbid psychosis. In this study, the prolactin serum levels were compared between 74 first-episode drug-naive patients with a pituitary microadenoma with psychosis (PMP), and 58 patients with a pituitary microadenoma with no psychosis (PMNP). Patients with PMP had significantly higher prolactin serum levels; male patients with PMP had a mean [S.D.] prolactin level of 705.4 uIU/ml [226.1] vs. 433.1 uIU/ml [58.4] for male patients with PMNP, while female patients with PMP had a mean prolactin level of 1890.1 uIU/ml [1138.7] vs. 978.6 uIU/ml [657.9] for female patients with PMNP. The size of microadenoma in the patients with PMP was larger than those in the patients with PMNP, regardless of sex. Our data suggested that a higher prolactin serum level is a characteristic of first-episode neuroleptic-naive patients with PMP.

Prolactin administration during early postnatal life decreases hippocampal and olfactory bulb neurogenesis and results in depressive-like behavior in adulthood

Tight regulation of hormone and neurochemical milieu during developmental periods is critical for adequate physiological functions. For instance, activation of peptide systems during early life stress induces morphological changes in the brain resulting in depression and anxiety disorders. Prolactin (PRL) exerts different actions within the brain; it regulates neurogenesis and modulates neuroendocrine functions in the adult. However, PRL effects during early postnatal life are hardly known. Therefore, we examined whether neonatal administration of PRL influences cell survival in the hippocampal dentate gyrus (DG) and in the olfactory bulb (OB) and whether such influence results in behavioral consequences in adulthood. PRL-treated rat pups (13 mg/kg; PND1 to PND14), injected with BrdU at postnatal day 5 (PND5), showed a decrease in the density of DG BrdU/DCX and BrdU/NeuN-positive cells that survive at PND15. Similarly, PRL treatment decreased the density of BrdU+ cells in the OB compared with VEH. Fluorojade B analysis showed no significant changes in the amount of cell death in the DG between the groups. Postnatal PRL administration induced a passive coping strategy in the forced swimming test in male and female adult rats when compared with control and vehicle groups. Corticosterone endogenous levels at PND12 were not affected by PRL or VEH treatment. Altogether, these results suggest that opposed to its effects in the adult, postnatal PRL treatment affects neurogenesis and results in psychopathology later in life. High PRL levels, as observed in neonates under several pathological states, might contribute to detrimental effects on the developing brain.

Acute restraint stress induces rapid and prolonged changes in erythrocyte and hippocampal redox status

The onset and consequential changes in reduction-oxidation (redox) status that take place in response to short-term stress have not been well defined. This study utilized erythrocytes and neural tissue from male Wistar rats to demonstrate the rapid redox alterations that occur following an acute restraining stress. Serial blood samples collected from catheterized animals were used to measure prolactin, corticosterone, glucose, general oxidative status, and glutathione/glutathione disulfide ratios. Restraint increased prolactin concentration by approximately 300% at 30 min and rapidly returned to baseline values by 120 min of stress. Baseline blood glucose and corticosterone increased during stress exposure by approximately 25% and 150% respectively. Over the experimental period, the erythrocytic oxidative status of restrained animals increased by approximately 10% per hour which persisted after stress exposure, while changes in the glutathione redox couple were not observed until 120 min following the onset of stress. Application of restraint stress increased hippocampal oxidative status by approximately 17% while no change was observed in the amygdala. It was concluded that while endocrine and metabolic markers of stress rapidly increase and habituate to stress exposure, redox status continues to change following stress in both peripheral and neural tissue. Studies with longer post-restraint times and the inclusion of several brain regions should further elucidate the consequential redox changes induced by acute restraint stress.

Role of sex steroids in progesterone and corticosterone response to acute restraint stress in rats: sex differences

Adrenal progesterone secretion increases along with corticosterone in response to stress in male and female rats to modulate some stress responses. Here we investigated the role of sex steroids in sex differences in the progesterone response to 60 min of restraint stress in adult male and female rats. Comparisons between males and females in the progesterone response were evaluated in parallel with corticosterone responses. From day 5 to 7 after gonadectomy, female and male rats were treated with estradiol or testosterone, respectively (OVX-E and ORCH-T groups), or oil (OVX and ORCH groups). Female rats in proestrus, intact and 7 d adrenalectomized (ADX) male rats were also studied. At 10:00 h, blood samples were withdrawn via an implanted jugular cannula before (-5 min), during (15, 30, 45, 60 min) and after (90 and 120 min) restraint stress to measure plasma progesterone and corticosterone concentrations by radioimmunoassay. Intact male and proestrus female rats exhibited similar progesterone responses to stress. Gonadectomy did not alter the amount of progesterone secreted during stress in female rats but decreased secretion in male rats. Unlike corticosterone, the progesterone response to stress in females was not influenced by estradiol. In males, testosterone replacement attenuated the progesterone and corticosterone responses to stress. Basal secretion of progesterone among intact, ORCH and ADX males was similar, but ADX-stressed rats secreted little progesterone. Hence, the gonads differently modulate adrenal progesterone and corticosterone responses to stress in female and male rats. The ovaries enhance corticosterone but not progesterone secretion, while the testes stimulate progesterone but not corticosterone secretion.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Changes in prolactin secretion in the short- and long-term after adrenalectomy

OBJECTIVE: To evaluate the modulation of the hypothalamus-pituitary-adrenal axis (HPA) on prolactin secretion in rats after adrenalectomy (ADX). MATERIALS AND METHODS: Plasma corticosterone, ACTH, and prolactin concentrations were measured by radioimmunoassay in rats after bilateral ADX in the short- (3 hours and 1day) and long-term (3, 7, and 14 days). RESULTS: Animals that underwent ADX showed undetectable corticosterone levels and a triphasic ACTH response with a transient increase (3h), a decrease (1d), and further increase in the long-term after ADX. Sham animals showed a marked increase in corticosterone and ACTH levels three hours after surgery, with a decrease to basal levels thereafter. Plasma prolactin levels were not changed after ADX. CONCLUSION: There are different points of equilibrium in the HPA axis after the glucocorticoid negative feedback is removed. Prolactin plasma secretion is not altered in the short or long- term after ADX, suggesting that the peptidergic neurons essential for prolactin release are not activated after ADX.

Prolactin concentrations in newly diagnosed, antipsychotic-naïve patients with nonaffective psychosis

BACKGROUND

Previous studies have found increased prolactin concentrations in antipsychotic-naïve patients with schizophrenia. However, the roles of other hormones, and of potentially confounding variables such as gender and smoking, have not been considered.

METHODS

Blood from newly diagnosed, antipsychotic-naïve patients with nonaffective psychosis (13 women and 20 men) and matched controls (12 women and 21 men) was assayed for prolactin, as well as three other hormones that impact prolactin concentrations: thyrotropin-stimulating hormone (TSH), ghrelin, and cortisol.

RESULTS

Patients had significantly higher prolactin concentrations: female patients had a mean [SD] of 37.1 ng/mL [24.9] vs. 13.5 ng/mL [7.2] for female control subjects (p=.001), while male patients had a mean of 15.3 ng/mL [9.5] vs. 7.6 ng/mL [2.2] for male control subjects (p=.006). Patients and control subjects did not differ on concentrations of TSH, ghrelin, or cortisol. The group differences could not be attributed to differences in age, gender, smoking, body mass index, ethnicity, or the socioeconomic status of the family of origin.

CONCLUSIONS

Increased prolactin concentrations in antipsychotic-naïve patients do not appear to be due to important confounding variables, or to the effects of elevated TSH, ghrelin, or cortisol.

Prolactin in response to acute psychosocial stress in healthy men and women

BACKGROUND

Serum levels of the anterior pituitary hormone prolactin have been reported to increase in response to different types of psychological stressors in humans. However, experimental laboratory stress studies investigating the acute response of prolactin to psychological stress show inconsistent results as increased, as well as decreased or unchanged levels of prolactin have been reported.

OBJECTIVE

The aim of this study was to investigate the effect of acute psychosocial stress on serum concentrations of prolactin in healthy men and women and possible sex differences.

METHOD

Thirty men and 15 women (age 30-50 years) underwent Trier Social Stress Test (TSST), a tool for investigating psychobiological stress responses in a laboratory setting. Blood samples were collected before and directly after the stress test and after 30 min of recovery.

RESULTS

We observed significantly elevated prolactin levels - along with significantly increased plasma adrenocorticotropic hormone (ACTH), serum cortisol, heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) - in response to the stressor. The prolactin response pattern did not differ between men and women, but there was some indication that women might have higher magnitude of response. Large individual differences regarding the magnitude of response were seen in general. The magnitude of the prolactin response was significantly related to the magnitude of the response of the hypothalamic-pituitary-adrenal (HPA) axis and, to some extent, the cardiovascular responses, indicating that individual differences in prolactin response in healthy men and women are dependent on the general physiological stress activation. In women, the magnitude of response was also related to estradiol level.

CONCLUSION

Prolactin does increase in response to psychosocial stress, however, with large individual variation in magnitude of response. The pattern of prolactin response does not differ between men and women. However, there was some indication that women might have higher magnitude of increase than men, and that the magnitude of response in women was dependent on estradiol levels, and this needs to be further studied.

Recent findings on neuroprotection against excitotoxicity in the hippocampus of female rats

Newborn mammals are totally dependent on maternal milk and care for survival. The mother's brain undergoes different behavioural, physiological and emotional adaptations that make the mother more likely to satisfy the demands of the offspring. Recent reports from our group show that, compared to nulliparous rats, lactation diminishes cell damage induced by excitotoxicity in the dorsal hippocampus of the dam after systemic or i.c. administration of kainic acid (KA) and the resulting motor seizures. Elevated levels of prolactin (PRL), oxytocin, progesterone and glucocorticoids are characteristics of lactation, and the pronounced fluctuation of these hormones occurring in this phase may play a role protecting the hippocampus. Indeed, PRL administration to ovariectomised rats significantly diminishes the deleterious effects of KA in the dorsal hippocampus and reduces the progression of KA-induced seizures. Thus, lactation is a natural model for neuroprotection because it effectively prevents acute and chronic cell damage of the hippocampus induced by excitotoxicity.

The CRH-R₁ receptor mediates luteinizing hormone, prolactin, corticosterone and progesterone secretion induced by restraint stress in estrogen-primed rats

Acute stress has been shown to modify hypothalamus-pituitary-gonadal (HPG) axis activity. Corticotropin-releasing hormone (CRH), the principal regulator of the hypothalamus-pituitary-adrenal (HPA) axis, has been implicated as a mediator of stress-induced effects on the reproductive axis. The role of the specific CRH receptor subtypes in this response is not completely understood. In the current study, we investigated the role of the CRH-R(1) receptor on luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), progesterone (P) and corticosterone (CT) secretion in stress-induced responses under the influence of estrogen (E(2)). Estrogen-primed ovariectomized rats (estradiol cypionate, 10 μg sc) received an i.v. administration of antalarmin (0.1 or 1mg/kg), a selective CRH-R(1) antagonist, or vehicle before restraint stress for 40 min. Seven blood samples were collected from two experimental groups (one from 10:00 h to 14:00 h and the other from 10:00 h to 18:00 h). An increase of plasma LH induced by restraint acute-stress was followed by alteration of the secretion pattern in the estrogen-induced afternoon surge. In a similar manner, we observed a suppression of the afternoon surge in plasma FSH, a delay of E(2)-induced PRL secretion, and an increase in plasma P and CT. Antalarmin attenuated stress-induce LH increase, decreased CT and P secretion and blocked the stress effects on PRL secretion. These findings suggest that CRH-R(1) mediates, at least in part, the restraint stress effects on the HPA, PRL, and reproductive axes.

Transcriptional control of adrenal steroidogenesis: novel connection between Janus kinase (JAK) 2 protein and protein kinase A (PKA) through stabilization of cAMP response element-binding protein (CREB) transcription factor

In the adrenal gland, adrenocorticotropin (ACTH) acting through the cAMP protein kinase (PKA) transduction pathway is the main regulator of genes involved in glucocorticoid synthesis. The prolactin (PRL) receptor is expressed in the adrenal cortex of most mammals, but experimental proof that PRL ensures direct control on glucocorticoid synthesis in rodents remains elusive. To unravel the physiological importance of PRL in adrenocortical functions, we measured steroidogenic capacity of Prlr-deficient mice (Prlr(-/-)) and explored the influence of JAK/STAT signaling, the major PRL transduction pathway, on the steroidogenic activity of adrenocortical cell cultures. We demonstrate that lack of Prlr does not affect basal (nor stress-induced) corticosterone levels in mice. PRL triggers JAK2/STAT5-dependent transcription in adrenal cells, but this does not influence corticosterone release. In contrast, pharmacological or siRNA-mediated inhibition of JAK2 reveals its essential role in both basal and ACTH/cAMP-induced steroidogenesis. We demonstrate that nuclear JAK2 regulates the amount of active transcription factor CREB (cAMP response element-binding protein) through tyrosine phosphorylation and prevention of proteasomal degradation, which in turn leads to transcriptional activation of the rate-limiting steroidogenic Star gene. Hence, we describe a novel link between PKA and JAK2 by which nuclear JAK2 signaling controls adrenal steroidogenesis by increasing the stability of CREB.

4-Nitrophenol isolated from diesel exhaust particles disrupts regulation of reproductive hormones in immature male rats

In previous studies, we found that 4-nitrophenol (PNP) isolated from diesel exhaust particles exhibited both estrogenic and anti-androgenic activities. This compound is also a degradation product of the insecticide parathion. Here, we investigated the in vivo effect of PNP on reproductive function in immature male rats. Twenty-eight-day-old rats were injected subcutaneously with PNP (0.01, 0.1, 1, or 10 mg/kg) daily for 14 days. Plasma concentrations of luteinizing hormone (LH) were significantly lower in all PNP dosage groups than in the control group, and follicle-stimulating hormone (FSH) was significantly decreased in rats treated with 0.1, 1, or 10 mg/kg PNP. However, plasma concentrations of testosterone were significantly increased by 10 mg/kg PNP, and plasma concentrations of immunoreactive (ir)-inhibin were also significantly increased in the 0.1, 1, and 10 mg/kg PNP groups. Plasma concentrations of prolactin were significantly increased by 10 mg/kg PNP, and plasma concentrations of corticosterone were significantly increased in all treatment groups. These findings clearly show that PNP influences the hypothalamic-pituitary-gonadal axis in immature male rats, with decreased secretion of LH and FSH and increased secretion of testosterone and inhibin. PNP, therefore, appears to disrupt endocrine activity in the immature male reproductive system.