Dopamine transporters participate in the physiological regulation of prolactin

Peony-Glycyrrhiza Decoction for Antipsychotic-Related Hyperprolactinemia in Patients with Schizophrenia: A Randomized Controlled Trial

Background

Most antipsychotic drugs are dopamine receptor antagonists that usually lead to abnormal increases in prolactin concentrations and the development of hyperprolactinemia (HPRL), which in turn causes sexual dysfunction in patients. Peony-Glycyrrhiza Decoction (PGD) enhanced dopamine D2 receptors (DRD2) and dopamine transporter (DAT) and significantly reversed the expression of DRD2 and DAT. Therefore, we hypothesized that PGD might effectively improve hyperprolactinemia and alleviate sexual dysfunction in patients.

Methods

We performed an 8-week randomized controlled study on 62 subjects with schizophrenia who were randomized into two groups. The experimental group was treated with the PGD intervention, and the control group did not receive treatment. The primary outcome indicators were the levels of sex hormones and the total Arizona Sexual Experience Scale (ASEX) score.

Results

There was a significant difference in PRL levels between the two groups at weeks 4 and 8. From the beginning to the end of the experiment, there was a significant increase in PRL levels in the control group, while there was no significant change in the experimental group. The ASEX scale assessed sexual function in both groups, and patients in the experimental group showed an improvement in sexual function at week 8. During the experiment, the two groups found no differences between Positive and Negative Syndrome Scale (PANSS) scores and Treatment Emergent Symptom Scale (TESS) scores.

Conclusion

PGD significantly improved the patient's sexual function but was less effective in reducing prolactin levels and may prevent further increases in prolactin levels.

Neuroimmunoendocrine Link Between Chronic Kidney Disease and Olfactory Deficits

Chronic kidney disease (CKD) is a multifactorial pathology that progressively leads to the deterioration of metabolic functions and results from deficient glomerular filtration and electrolyte imbalance. Its economic impact on public health is challenging. Mexico has a high prevalence of CKD that is strongly associated with some of the most common metabolic disorders like diabetes and hypertension. The gradual loss of kidney functions provokes an inflammatory state and endocrine alterations affecting several systems. High serum levels of prolactin have been associated with CKD progression, inflammation, and olfactory function. Also, the nutritional status is altered due to impaired renal function. The decrease in calorie and protein intake is often accompanied by malnutrition, which can be severe at advanced stages of the disease. Nutrition and olfactory functioning are closely interconnected, and CKD patients often complain of olfactory deficits, which ultimately can lead to deficient food intake. CKD patients present a wide range of deficits in olfaction like odor discrimination, identification, and detection threshold. The chronic inflammatory status in CKD damages the olfactory epithelium leading to deficiencies in the chemical detection of odor molecules. Additionally, the decline in cognitive functioning impairs the capacity of odor differentiation. It is not clear whether peritoneal dialysis and hemodialysis improve the olfactory deficits, but renal transplants have a strong positive effect. In the present review, we discuss whether the olfactory deficiencies caused by CKD are the result of the induced inflammatory state, the hyperprolactinemia, or a combination of both.

Patterns of prolactin secretion

Prolactin is pleotropic in nature affecting multiple tissues throughout the body. As a consequence of the broad range of functions, regulation of anterior pituitary prolactin secretion is complex and atypical as compared to other pituitary hormones. Many studies have provided insight into the complex hypothalamic-pituitary networks controlling prolactin secretion patterns in different species using a range of techniques. Here, we review prolactin secretion in both males and females; and consider the different patterns of prolactin secretion across the reproductive cycle in representative female mammals with short versus long luteal phases and in seasonal breeders. Additionally, we highlight changes in the pattern of secretion during pregnancy and lactation, and discuss the wide range of adaptive functions that prolactin may have in these important physiological states.

A pharmacogenetic study of patients with schizophrenia from West Siberia gets insight into dopaminergic mechanisms of antipsychotic-induced hyperprolactinemia

BACKGROUND

Hyperprolactinemia (HPRL) is a classical side effect of antipsychotic drugs primarily attributed to blockade of dopamine D2 receptors (DRD2s) on the membranes of lactotroph cells within the pituitary gland. Certain antipsychotic drugs, e.g. risperidone, are more likely to induce HPRL because of relative accumulation within the adenohypophysis. Nevertheless, due to competition for pituitary DRD2s by high dopamine levels may limit antipsychotic-induced HPRL. Moreover, the activity of prolactin-producing lactotrophs also depends on other hormones which are regulated by the extra-pituitary activity of dopamine receptors, dopamine transporters, enzymes of neurotransmitter metabolism and other factors. Polymorphic variants in the genes coding for these receptors and proteins can have functional significance and influence on the development of hyperprolactinemia.

METHODS

A set of 41 SNPs of genes for dopamine receptors DRD1, DRD2, DRD3, DRD4, the dopamine transporter SLC6A3 and dopamine catabolizing enzymes MAOA and MAOB was investigated in a population of 446 Caucasians (221 males/225 females) with a clinical diagnosis of schizophrenia (according to ICD-10: F20) with and without HPRL who were treated with classical and/or atypical antipsychotic drugs. Additive genetic model was tested and the analysis was carried out in the total group and in subgroup stratified by the use of risperidone/paliperidone.

RESULTS

One statistically significant association between polymorphic variant rs1799836 of MAOB gene and HPRL in men was found in the total group. Furthermore, the rs40184 and rs3863145 variants in SLC6A3 gene appeared to be associated with HPRL in the subgroup of patients using the risperidone/paliperidone, but not with HPRL induced by other antipsychotic drugs.

CONCLUSIONS

Our results indicate that genetic variants of MAOB and SLC6A3 may have consequences on the modulation of prolactin secretion. A further search for genetic markers associated with the development of antipsychotic-related hyperprolactinemia in schizophrenic patients is needed.

GIRK Channel Activity in Dopamine Neurons of the Ventral Tegmental Area Bidirectionally Regulates Behavioral Sensitivity to Cocaine

Dopamine (DA) neurons of the VTA have been widely implicated in the cellular and behavioral responses to drugs of abuse. Inhibitory G protein signaling mediated by GABA_B receptors (GABA_BRs) and D₂ DA receptors (D₂Rs) regulates the excitability of VTA DA neurons, DA neurotransmission, and behaviors modulated by DA. Most of the somatodendritic inhibitory effect of GABA_BR and D₂R activation on DA neurons reflects the activation of G protein-gated inwardly rectifying K⁺ (GIRK) channels. Furthermore, GIRK-dependent signaling in VTA DA neurons can be weakened by exposure to psychostimulants and strengthened by phasic DA neuron firing. The objective of this study was to determine how the strength of GIRK channel activity in VTA DA neurons influences sensitivity to cocaine. We used a Cre-dependent viral strategy to overexpress the individual GIRK channel subunits in VTA DA neurons of male and female adult mice, leading to enhancement (GIRK2) or suppression (GIRK3) of GIRK channel activity. Overexpression of GIRK3 decreased somatodendritic GABA_BR- and D₂R-dependent signaling and increased cocaine-induced locomotor activity, whereas overexpression of GIRK2 increased GABA_BR-dependent signaling and decreased cocaine-induced locomotion. Neither manipulation impacted anxiety- or depression-related behavior, despite the link between such behaviors and DA signaling. Together, these data show that behavioral sensitivity to cocaine in mice is inversely proportional to the strength of GIRK channel activity in VTA DA neurons and suggest that direct activators of the unique VTA DA neuron GIRK channel subtype (GIRK2/GIRK3 heteromer) could represent a promising therapeutic target for treatment of addiction.SIGNIFICANCE STATEMENT Inhibitory G protein signaling in dopamine (DA) neurons, including that mediated by G protein-gated inwardly rectifying K⁺ (GIRK) channels, has been implicated in behavioral sensitivity to cocaine. Here, we used a viral approach to bidirectionally manipulate GIRK channel activity in DA neurons of the VTA. We found that decreasing GIRK channel activity in VTA DA neurons increased behavioral sensitivity to cocaine, whereas increasing GIRK channel activity decreased behavioral sensitivity to cocaine. These manipulations did not alter anxiety- or depression-related behaviors. These data highlight the unique GIRK channel subtype in VTA DA neurons as a possible therapeutic target for addiction.

Dopamine Release Dynamics in the Tuberoinfundibular Dopamine System

The relationship between neuronal impulse activity and neurotransmitter release remains elusive. This issue is especially poorly understood in the neuroendocrine system, with its particular demands on periodically voluminous release of neurohormones at the interface of axon terminals and vasculature. A shortage of techniques with sufficient temporal resolution has hindered real-time monitoring of the secretion of the peptides that dominate among the neurohormones. The lactotropic axis provides an important exception in neurochemical identity, however, as pituitary prolactin secretion is primarily under monoaminergic control, via tuberoinfundibular dopamine (TIDA) neurons projecting to the median eminence (ME). Here, we combined electrical or optogenetic stimulation and fast-scan cyclic voltammetry to address dopamine release dynamics in the male mouse TIDA system. Imposing different discharge frequencies during brief (3 s) stimulation of TIDA terminals in the ME revealed that dopamine output is maximal at 10 Hz, which was found to parallel the TIDA neuron action potential frequency distribution during phasic discharge. Over more sustained stimulation periods (150 s), maximal output occurred at 5 Hz, similar to the average action potential firing frequency of tonically active TIDA neurons. Application of the dopamine transporter blocker, methylphenidate, significantly increased dopamine levels in the ME, supporting a functional role of the transporter at the neurons' terminals. Lastly, TIDA neuron stimulation at the cell body yielded perisomatic release of dopamine, which may contribute to an ultrafast negative feedback mechanism to constrain TIDA electrical activity. Together, these data shed light on how spiking patterns in the neuroendocrine system translate to vesicular release toward the pituitary and identify how dopamine dynamics are controlled in the TIDA system at different cellular compartments.SIGNIFICANCE STATEMENT A central question in neuroscience is the complex relationship between neuronal discharge activity and transmitter release. By combining optogenetic stimulation and voltammetry, we address this issue in dopamine neurons of the neuroendocrine system, which faces particular spatiotemporal demands on exocytotic release; large amounts of neurohormone need to be secreted into the portal capillaries with precise timing to adapt to physiological requirements. Our data show that release is maximal around the neurons' default firing frequency. We further provide support for functional dopamine transport at the neurovascular terminals, shedding light on a long-standing controversy about the existence of neuroendocrine transmitter reuptake. Finally, we show that dopamine release occurs also at the somatodendritic level, providing a substrate for an ultrashort autoregulatory feedback loop.

Impact of Triclosan on Female Reproduction through Reducing Thyroid Hormones to Suppress Hypothalamic Kisspeptin Neurons in Mice

Triclosan (TCS), a broad-spectrum antimicrobial agent, is widely used in clinical settings and various personal care products. The aim of this study was to evaluate the influence of TCS on reproductive endocrine and function. Here, we show that the exposure of adult female mice to 10 or 100 mg/kg/day TCS caused prolongation of diestrus, and decreases in antral follicles and corpora lutea within 2 weeks. TCS mice showed decreases in the levels of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone, and gonadotrophin-releasing hormone (GnRH) mRNA with the lack of LH surge and elevation of prolactin (PRL). TCS mice had lower kisspeptin immunoreactivity and kiss1 mRNA in anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). Moreover, the estrogen (E2)-enhanced AVPV-kisspeptin expression was reduced in TCS mice. In addition, the serum thyroid hormones (triiodothyronine (T3) and thyroxine (T4)) in TCS mice were reduced with increases in levels of thyroid stimulating hormone (TSH) and thyroid releasing hormone (TRH). In TCS mice, the treatment with Levothyroxine (L-T4) corrected the increases in PRL, TSH and TRH; the administration of L-T4 or type-2 dopamine receptors agonist quinpirole inhibiting PRL release could rescue the decline of kisspeptin expression in AVPV and ARC; the treatment with L-T4, quinpirole or the GPR45 agonist kisspeptin-10 recovered the levels of serum LH and FSH and progesterone, and GnRH mRNA. Furthermore, TCS mice treated with L-T4 or quinpirole resumed regular estrous cycling, follicular development and ovulation. Together, these results indicate that exposing adult female mice to TCS (≥10 mg/kg) reduces thyroid hormones causing hyperprolactinemia that then suppresses hypothalamic kisspeptin expression, leading to deficits in reproductive endocrine and function.

Incomplete concordance of dopamine transporter Cre (DATIREScre)-mediated recombination and tyrosine hydroxylase immunoreactivity in the mouse forebrain

Co-localization of the expression of the dopamine transporter (DAT) with the catecholamine synthesising enzyme tyrosine hydroxylase (TH) has been investigated using transgenic mice expressing Cre recombinase (Cre) dependent green fluorescent protein (GFP) under the control of the DAT promoter (DAT^IREScre/GFP). Brain sections from adult female mice were stained for Cre-induced GFP and TH using immunohistochemistry, revealing a high degree of co-expression in the midbrain dopaminergic neurons (A8-10) with the exception of the periaqueductal and dorsal raphe nuclei where dual-labelling was notably lower. In contrast, most of the rostral groups of TH-expressing neurons in the forebrain (A11, A13 - A15) showed little or no co-localization with Cre-induced GFP. Interestingly, a subpopulation of about 30% of the TH-immunoreactive neurons in the arcuate nucleus (A12) also express GFP staining. This observation supports the proposal that this hypothalamic cluster of dopaminergic neurons is neurochemically, and thus potentially functionally, heterogeneous. This study extends earlier literature focusing primarily on DAT expression in midbrain structures to demonstrate a heterogeneity of DAT and TH co-localization in forebrain neurons, particularly those in the hypothalamus. It also highlights the importance of carefully selecting and validating transgenic mouse lines when studying dopaminergic neurons.

Conditional Deletion of the Prolactin Receptor Reveals Functional Subpopulations of Dopamine Neurons in the Arcuate Nucleus of the Hypothalamus

Tuberoinfundibular dopamine (TIDA) neurons, known as neuroendocrine regulators of prolactin secretion from the pituitary gland, also release GABA within the hypothalamic arcuate nucleus. As these neurons express prolactin receptors (Prlr), prolactin may regulate GABA secretion from TIDA neurons, potentially mediating actions of prolactin on hypothalamic function. To investigate whether GABA is involved in feedback regulation of TIDA neurons, we examined the physiological consequences of conditional deletion of Prlr in GABAergic neurons. For comparison, we also examined mice in which Prlr were deleted from most forebrain neurons. Both neuron-specific and GABA-specific recombination of the Prlr gene occurred throughout the hypothalamus and in some extrahypothalamic regions, consistent with the known distribution of Prlr expression, indicative of knock-out of Prlr. This was confirmed by a significant loss of prolactin-induced phosphorylation of STAT5, a marker of prolactin action. Several populations of GABAergic neurons that were not previously known to be prolactin-sensitive, notably in the medial amygdala, were identified. Approximately 50% of dopamine neurons within the arcuate nucleus were labeled with a GABA-specific reporter, but Prlr deletion from these dopamine/GABA neurons had no effect on feedback regulation of prolactin secretion. In contrast, Prlr deletion from all dopamine neurons resulted in profound hyperprolactinemia. The absence of coexpression of tyrosine hydroxylase, a marker for dopamine production, in GABAergic nerve terminals in the median eminence suggested that rather than a functional redundancy within the TIDA population, the dopamine/GABA neurons in the arcuate nucleus represent a subpopulation with a functional role distinct from the regulation of prolactin secretion.

SIGNIFICANCE STATEMENT

Using a novel conditional deletion of the prolactin receptor, we have identified functional subpopulations in hypothalamic dopamine neurons. Although commonly considered a uniform population of neuroendocrine neurons involved in the control of prolactin secretion, we have shown that approximately half of these neurons express GABA as well as dopamine, but these neurons are not necessary for the feedback regulation of prolactin secretion. The absence of tyrosine hydroxylase in GABAergic nerve terminals in the median eminence suggests that only the non-GABAergic dopamine neurons are involved in the control of pituitary prolactin secretion, and the GABAergic subpopulation may function as interneurons within the arcuate nucleus to regulate other aspects of hypothalamic function.

A molecular census of arcuate hypothalamus and median eminence cell types

The hypothalamic arcuate-median eminence complex (Arc-ME) controls energy balance, fertility, and growth through molecularly distinct cell types, many of which remain unknown. To catalog cell types in an unbiased way, we profiled gene expression in 20,921 individual cells in and around the adult mouse Arc-ME using Drop-seq. We identify 50 transcriptionally distinct Arc-ME cell populations, including a rare tanycyte population at the Arc-ME diffusion barrier, a novel leptin-sensing neuronal population, multiple AgRP and POMC subtypes, and an orexigenic somatostatin neuronal population. We extended Drop-seq to detect dynamic expression changes across relevant physiological perturbations, revealing cell type-specific responses to energy status, including distinctly responsive subtypes of AgRP and POMC neurons. Finally, integrating our data with human GWAS data implicates two previously unknown neuronal subtypes in the genetic control of obesity. This resource will accelerate biological discovery by providing insights into molecular and cell type diversity from which function can be inferred.

Peony-Glycyrrhiza Decoction for Antipsychotic-Related Hyperprolactinemia in Women With Schizophrenia: A Randomized Controlled Trial

OBJECTIVES

An herbal preparation called peony-glycyrrhiza decoction (PGD) may have the potential in reducing antipsychotic-related hyperprolactinemia (hyperPRL). This double-blind, randomized placebo-controlled study aimed to reevaluate the efficacy of PGD against antipsychotic-related hyperPRL.

METHODS

Ninety-nine schizophrenic women who were under antipsychotic therapy and had symptomatic hyperPRL were randomly assigned to additional treatment with placebo (n = 50) or PGD (n = 49, 45 g/d) for 16 weeks. The severity of hyperPRL, psychosis, and abnormal involuntary movements was assessed at baseline and weeks 8 and 16 using standard instruments including the Prolactin Related Adverse Event Questionnaire. Blood levels of prolactin (PRL) and related pituitary and sex hormones were measured at the same time points.

RESULTS

Peony-glycyrrhiza decoction treatment produced a significantly greater reduction of the Prolactin Related Adverse Event Questionnaire score at weeks 8 and 16 and a greater improvement on abnormal involuntary movements at end point compared with placebo, without altering the severity of psychosis. The group treated with PGD showed significantly higher proportion of having overall improvement on hyperPRL symptoms (χ = 4.010, P = 0.045) and menstrual resumption (χ = 4.549, P = 0.033) at week 8 than placebo. Serum PRL levels were similar in the 2 groups.

CONCLUSIONS

Peony-glycyrrhiza decoction is effective in reducing antipsychotic-related hyperPRL and abnormal involuntary movement symptoms, but no reduction in blood PRL concentrations was observed. The underlying mechanisms of PGD's effects need further investigation (trial registration of NCT01852331 at www.clinicaltrials.gov).

Dopamine Autoreceptor Regulation of a Hypothalamic Dopaminergic Network

How autoreceptors contribute to maintaining a stable output of rhythmically active neuronal circuits is poorly understood. Here, we examine this issue in a dopamine population, spontaneously oscillating hypothalamic rat (TIDA) neurons, that underlie neuroendocrine control of reproduction and neuroleptic side effects. Activation of dopamine receptors of the type 2 family (D2Rs) at the cell-body level slowed TIDA oscillations through two mechanisms. First, they prolonged the depolarizing phase through a combination of presynaptic increases in inhibition and postsynaptic hyperpolarization. Second, they extended the discharge phase through presynaptic attenuation of calcium currents and decreased synaptic inhibition. Dopamine reuptake blockade similarly reconfigured the oscillation, indicating that ambient somatodendritic transmitter concentration determines electrical behavior. In the absence of D2R feedback, however, discharge was abolished by depolarization block. These results indicate the existence of an ultra-short feedback loop whereby neuroendocrine dopamine neurons tune network behavior to echoes of their own activity, reflected in ambient somatodendritic dopamine, and also suggest a mechanism for antipsychotic side effects.

TIDAL WAVES: Network mechanisms in the neuroendocrine control of prolactin release

Neuroendocrine tuberoinfundibular dopamine (TIDA) neurons tonically inhibit pituitary release of the hormone, prolactin. Through the powerful actions of prolactin in promoting lactation and maternal behaviour while suppressing sexual drive and fertility, TIDA neurons play a key role in reproduction. We summarize insights from recent in vitro studies into the membrane properties and network behaviour of TIDA neurons including the observations that TIDA neurons exhibit a robust oscillation that is synchronized between cells and depends on intact gap junction communication. Comparisons are made with phasic firing patterns in other neuronal populations. Modulators involved in the control of lactation - including serotonin, thyrotropin-releasing hormone and prolactin itself - have been shown to change the electrical behaviour of TIDA cells. We propose that TIDA discharge mode may play a central role in tuning the amount of dopamine delivered to the pituitary and hence circulating prolactin concentrations in different reproductive states and pathological conditions.

Water Extract of Fructus Hordei Germinatus Shows Antihyperprolactinemia Activity via Dopamine D2 Receptor

Objective. Fructus Hordei Germinatus is widely used in treating hyperprolactinemia (hyperPRL) as a kind of Chinese traditional herb in China. In this study, we investigated the anti-hyperPRL activity of water extract of Fructus Hordei Germinatus (WEFHG) and mechanism of action. Methods. Effect of WEFHG on serum prolactin (PRL), estradiol (E2), progesterone (P), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and hypothalamus protein kinase A (PKA) and cyclic adenosine monophosphate (cAMP) levels of hyperPRL rats were investigated. And effect of WEFHG on PRL secretion, D2 receptors, and dopamine transporters (DAT) was studied in MMQ, GH3, and PC12 cells, respectively. Results. WEFHG reduced the secretion of PRL in hyperPRL rats effectively. In MMQ cell, treatment with WEFHG at 1–5 mg/mL significantly suppressed PRL secretion and synthesis. Consistent with a D2-action, WEFHG did not affect PRL in rat pituitary lactotropic tumor-derived GH3 cells that lack the D2 receptor expression but significantly increased the expression of D2 receptors and DAT in PC12 cells. In addition, WEFHG reduced the cAMP and PKA levels of hypothalamus in hyperPRL rats significantly. Conclusions. WEFHG showed anti-hyperPRL activity via dopamine D2 receptor, which was related to the second messenger cAMP and PKA.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.

Amine oxidase activity of β-amyloid precursor protein modulates systemic and local catecholamine levels

The catecholamines dopamine (DA), norepinephrine (NE) and epinephrine (E) are neurotransmitters and hormones that mediate stress responses in tissues and plasma. The expression of β-amyloid precursor protein (APP) is responsive to stress and is high in tissues rich in catecholamines. We recently reported that APP is a ferroxidase, subsuming, in neurons and other cells, the iron-export activity that ceruloplasmin mediates in glia. Here we report that, like ceruloplasmin, APP also oxidizes synthetic amines and catecholamines catalytically (K(m) NE=0.27 mM), through a site encompassing its ferroxidase motif and selectively inhibited by zinc. Accordingly, APP knockout mice have significantly higher levels of DA, NE and E in brain, plasma and select tissues. Consistent with this, these animals have increased resting heart rate and systolic blood pressure as well as suppressed prolactin and lymphocyte levels. These findings support a role for APP in extracellular catecholaminergic clearance.

Not only dopamine D2 receptors involved in Peony-Glycyrrhiza Decoction, an herbal preparation against antipsychotic-associated hyperprolactinemia

Clinical studies have demonstrated the effectiveness of an herbal preparation called Peony-Glycyrrhiza Decoction (PGD) in alleviating antipsychotic-induced hyperprolactinemia (hyperPRL). In the present study, we further examined the pharmacological action of PGD on prolactin (PRL) secretion using in vitro and in vivo models, with specific attention to the role of dopaminergic mediators and other sex hormones. Treatment with PGD at 1-5mg/ml significantly suppressed PRL secretion and synthesis in MMQ cells, a model of hyperPRL derived from pituitary adenoma cells. The suppressive effects were completely abolished by pretreatment with 10μM haloperidol, a dopamine D(2) receptor antagonist. Consistent with a D(2)-action, PGD did not affect PRL in rat pituitary lactotropic tumor-derived GH3 cells that lack the D(2) receptor expression but significantly increased the expression of D(2) receptors and dopamine transporters (DAT) in PC12 cells. In a rat model of hyperPRL, produced by repeated injection of the dopamine blocker metoclopramide (MCP), chronic PGD (2.5-10g/kg daily) significantly reduced elevated serum PRL. The reduction in magnitude was similar to that elicited by bromocriptine (BMT), a dopamine D(2) receptor agonist currently used for treatment of hyperPRL. Neither PGD nor BMT altered serum estradiol, but PGD reversed decreased serum progesterone to control level, whereas BMT did not. These results indicate that the anti-hyperPRL effects of PGD are associated not only with D(2) receptor and DAT modulation, but also with a normalization of other sex hormone dysfunction. This experimental evidence supports clinical use of PGD as an effective treatment of antipsychotic-induced hyperPRL.

A Review of the Incidence and Coincidence of Uterine and Mammary Tumors in Wistar and Sprague-Dawley Rats Based on the RITA Database and the Role of Prolactin

Wistar rats are frequently selected for use in carcinogenicity studies because of their advantageous survival rate, which is more favorable than other strains such as the Sprague-Dawley (SD) strain. Uterine and mammary tumors are relatively common spontaneous neoplasms of both strains. We examined the incidence and coincidence of uterine tumors and mammary tumors in control animals of both strains within the RITA database. There was a strong inverse relationship between these tumor types in Wistar rats ( p < .001). A less strong relationship was present in SD rats ( p = .057). This association is likely to be related to prolactin. A short review of the role of prolactin in rats is given. These results are also discussed in the background of nonspecific toxicity at high dose levels in carcinogenicity studies above MTD levels resulting in reduction in body weights of >10%.

GPR30 differentially regulates short latency responses of luteinising hormone and prolactin secretion to oestradiol

Rapid, nongenomic actions of 17beta-oestradiol (E(2)) on hypothalamic neurones that may be relevant to reproductive function were described decades ago. The orphan G protein-coupled receptor, GPR30, was recently shown to bind oestrogens and to trigger rapid signalling in vitro, and is expressed in several rat and human brain regions, including the hypothalamus. We used two complementary approaches to investigate the role of GPR30 in hypothalamic responses to E(2) that are relevant to reproductive physiology. Serial blood sampling after the acute administration of the selective GPR30 agonist G1 was used to assess the role of GPR30 in short latency negative-feedback inhibition of luteinising hormone (LH) secretion and facilitation of prolactin secretion in ovariohysterectomised female rats. In vivo RNA interference (RNAi), mediated by adeno-associated virus-expressing small hairpin RNA (shRNA) infused into the mediobasal hypothalamus, was used to study the effects of GPR30 knockdown on these rapid responses to E(2). Longer-term actions of E(2) on female sexual behaviour (lordosis) were also examined in female rats subjected to in vivo RNAi. Administration of E(2) or G1 triggered a short latency surge of prolactin secretion, and animals subjected to GPR30 RNAi showed significantly less E(2)-dependent prolactin release than animals receiving control virus. G1 did not mimic E(2) negative-feedback inhibition of LH secretion, and GPR30 RNAi did not interfere with E(2) suppression of LH or facilitation of lordosis behaviour. These findings suggest that activation of GPR30 promotes short latency prolactin secretion but does not mediate E(2) negative-feedback inhibition of LH secretion or E(2) facilitation of female reproductive behaviour.

Sex differences in serotonergic but not gamma-aminobutyric acidergic (GABA) projections to the rat ventromedial nucleus of the hypothalamus

Hormonal conditions that elicit lordosis in female rats are ineffective in males, suggesting that this behavior is actively suppressed in males. Previous studies theorize that serotonergic and gamma-aminobutyric acidergic (GABA) inputs to the ventrolateral division of the ventromedial nucleus of the hypothalamus (VMNvl) may contribute to lordosis inhibition in males. Using triple-label immunofluorescent techniques, the present studies explored potential sex differences in the density of these projections within three hypothalamic sites: the VMNvl, the arcuate nucleus (ARC), and the dorsomedial nucleus of the hypothalamus. Antibodies directed against HuC/D, estrogen receptor (ER)-alpha and either serotonin (5-HT) or the gamma-aminobutyric acid synthetic enzyme glutamic acid decarboxylase-65 were used to compare the densities of glutamic acid decarboxylase (GAD)-65- and 5-HT-containing fibers in each brain area, the percentage of VMNvl HuC/D immunoreactive (ir) neurons that contained ERalpha, and the percentage of HuC/D and ERalpha double-labeled cells receiving apparent contacts from 5-HT fibers between adult, gonadectomized male and female rats. The densities of VMNvl and ARC 5-HT immunolabeled fibers were significantly higher in the males, and the percentage of VMNvl HuC/D-ir neurons containing ERalpha was significantly higher in the females. The percentage of HuC/D-ir cells contacted by 5-HT fibers was significantly higher in the males, compared with the females, but there was no sex difference in the proportion of those cells receiving contacts that were ERalpha-ir. Neonatal administration of estradiol but not genistein masculinized 5-HT content in the adult female VMNvl, but the percentage of HuC/D-ir cells colabeled with ERalpha was not significantly affected by treatment. A similar, but not statistically significant, pattern was observed in the ARC. These findings suggest that the development of serotonergic inputs to the male VMNvl is orchestrated by neonatal estradiol exposure. The hormone-dependent organization of these 5-HT projection patterns may be an important developmental mechanism accounting for sex-specific behaviors in adulthood.

The 3' part of the dopamine transporter gene DAT1/SLC6A3 is associated with withdrawal seizures in patients with alcohol dependence

BACKGROUND

Some studies have reported that the A9 allele of the variable nucleotide tandem repeat (VNTR) of the gene which encodes the dopamine transporter (DAT1/SLC6A3) is associated with alcoholism withdrawal symptoms such as alcohol withdrawal seizures (WSs), whereas others did not. We investigated whether polymorphisms within the DAT1 gene are associated with WS taking into account some of the confounding factors such as the severity of alcohol dependence.

METHODS

To further assess the role of this gene in WS, we genotyped the VNTR and 7 single nucleotide polymorphisms (SNPs) encompassing the DAT1 gene in a sample of 250 alcohol-dependent subjects (175 men and 75 women), of whom 24% exhibited WSs, taking into account the severity of alcohol dependence.

RESULTS

The VNTR is associated with an increased risk of WSs (odd ratio = 3.5; p = 0.019), even when controlling for confounding factors (p = 0.031). As 2 SNPs, in roughly the same location of the gene (namely rs27072 and rs27048), are also associated with WSs, it is possible that the initial association of the VNTR polymorphism was tagging a specific haplotype of this gene. Indeed, in our sample of alcohol-dependent patients, 2 haplotypes were associated with a significantly different risk of WSs.

CONCLUSIONS

The present study adds evidence for a significant role of the 3' part of the DAT1 gene in WS of alcohol-dependent patients, not only because it is in accordance with previous work, but also because of larger statistical power (as relying on a sample over sampled with the studied phenotype), as it gives a more precise analysis of different SNPs within the DAT1 gene, and as it confirms the association when major potentially confounding factors are taken into account in a logistical regression analysis.

Plasma progesterone levels and cocaine-seeking in freely cycling female rats across the estrous cycle

Previous studies have reported sex and estrous cycle-dependent differences in the reinstatement of cocaine-seeking triggered by cocaine injections or drug-paired cues. However, the relationship between estradiol or progesterone levels and cocaine-seeking in a reinstatement model of relapse has not been explored. Thus, we examined changes in plasma hormone levels during cocaine-taking and -seeking behaviors in gonadally intact female rats. Rats self-administered cocaine (0.5mg/kg infusion) during daily 2-h sessions, followed by extinction. For reinstatement, cocaine (0, 5, or 10mg/kg, i.p.) was administered 30 min prior to testing. Vaginal smears and blood samples were collected prior to and during chronic cocaine self-administration, extinction, and reinstatement testing. Relative to non-estrous females, females in estrus showed greater responding during self-administration, extinction, and during cocaine-primed reinstatement. The highest progesterone levels were noted at the time of lowest cocaine-seeking (proestrus) and the lowest levels of progesterone occurred at the time of highest cocaine-seeking (estrus). In contrast, plasma estradiol levels did not show any clear pattern with cocaine-seeking. These data from an animal model of relapse supports recent clinical evidence that progesterone reduces subjective craving in cocaine-dependent women. Overall, these results suggest that progesterone administration may be a useful intervention for reducing the incidence of relapse.

Analysis of dopamine transporter gene expression pattern -- generation of DAT-iCre transgenic mice

The dopamine transporter is an essential component of the dopaminergic synapse. It is located in the presynaptic neurons and regulates extracellular dopamine levels. We generated a transgenic mouse line expressing the Cre recombinase under the control of the regulatory elements of the dopamine transporter gene, for investigations of gene function in dopaminergic neurons. The codon-improved Cre recombinase (iCre) gene was inserted into the dopamine transporter gene on a bacterial artificial chromosome. The pattern of expression of the bacterial artificial chromosome-dopamine transporter-iCre transgene was similar to that of the endogenous dopamine transporter gene, as shown by immunohistochemistry. Recombinase activity was further studied in mice carrying both the bacterial artificial chromosome-dopamine transporter-iCre transgene and a construct expressing the beta-galactosidase gene after Cre-mediated recombination. In situ studies showed that beta-galactosidase (5-bromo-4-chloroindol-3-yl beta-D-galactoside staining) and the dopamine transporter (immunofluorescence) had identical distributions in the ventral midbrain. We used this animal model to study the distribution of dopamine transporter gene expression in hypothalamic nuclei in detail. The expression profile of tyrosine hydroxylase (an enzyme required for dopamine synthesis) was broader than that of beta-galactosidase in A12 to A15. Thus, only a fraction of neurons synthesizing dopamine expressed the dopamine transporter gene. The bacterial artificial chromosome-dopamine transporter-iCre transgenic line is a unique tool for targeting Cre/loxP-mediated DNA recombination to dopamine neurons for studies of gene function or for labeling living cells, following the crossing of these mice with transgenic Cre reporter lines producing fluorescent proteins.

Tyrosine hydroxylase and dopamine transporter expression in lactotrophs from postlactating rats: involvement in dopamine-induced apoptosis

Cessation of lactation causes a massive loss of surplus lactotrophs in the rat pituitary gland. The factors and mechanisms involved in this phenomenon have not yet been elucidated. Besides its inhibitory control on prolactin secretion and lactotroph proliferation, evidence suggests that dopamine (DA) may be a proapoptotic factor for lactotrophs. We therefore tested the proapoptotic effect of DA on pituitary glands from virgin, lactating, and postlactating rats. By measuring mitochondrial membrane potential loss, caspase-3 activation, and nuclear fragmentation, we show that DA induces apoptosis specifically in lactotrophs from postlactating rats. We then determined that this effect was partly mediated by the DA transporter (DAT) rather than the D(2) receptor, as corroborated by the detection of DAT expression exclusively in lactotrophs from postlactating rats. We also observed tyrosine hydroxylase (TH) expression in postlactating lactotrophs that was accompanied by an increase in DA content in the anterior pituitary gland of postlactating compared with virgin rats. Finally, we observed that cells expressing TH coexpressed DAT and cleaved caspase-3. These findings show that DA may play a role in lactotroph regression during the postlactation period by inducing apoptosis. The fact that this process requires DAT and TH expression by lactotrophs themselves suggests that it may be "autocrine" in nature.

Prolactin Levels in Workers Exposed to Chemical, Physical and Psycho‐Social Urban Stressors

The aim of this study was to evaluate whether traffic police officers exposed to chemical, physical and psycho-social stressors, are at risk for alterations in plasma levels of prolactin (PRL) compared to a control group. Plasma PRL levels were evaluated in 92 male and 51 female, non-smoker, traffic police officers exposed to urban stressors and in 92 male and 51 female controls, matched by sex, age and working life (mean, SD and distribution), after excluding workers with the principal extra-occupational confounding factors. Mean PRL levels were significantly higher than controls in non-smoker, male and female traffic police officers (respectively, p=0.000 and p=0.013). The number of non-smoker, male and female traffic police officers with PRL values outside the upper normal limit for our laboratory was higher than, but not significantly different from controls. Mean PRL levels were not significantly higher than controls in smoker, male and female traffic police officers. The number of smoker, male and female traffic police officers with PRL values outside the normal limit for our laboratory was not significantly different from controls. The results suggest that exposure to urban chemical and physical stressors, interacting with psychosocial factors, may have an influence on PRL levels in traffic police officers. The level of plasma PRL might be a useful early biological marker for workers exposed to urban stressors.

Estrogen mediated inhibition of dopamine transport in the striatum: regulation by G alpha i/o

In the current study, the interaction between estrogen priming and dopamine D2 receptor activation on dopamine uptake in the striatum of ovariectomized female rats was investigated. Basal ADP-[(32)P(i)]ribosylation of G(i/o) was examined in synaptosomal membranes prepared from ovariectomized, estrogen primed or N-p-(isothiocyanatophenethyl) spiperone (NIPS) treated rats. [(32)P(i)]-incorporation was significantly increased (141%) in tissue from NIPS treated animals but attenuated (57%) in tissue from estrogen primed animals. Dopamine uptake kinetics were measured in vivo following manipulation of the heterotrimeric G-protein by pertussis toxin (0.5 microg, 48 h). Pertussis toxin significantly inhibited dopamine uptake at all concentrations of dopamine examined. Co-treatment with estrogen and pertussis toxin resulted in a further attenuation of dopamine transport at high but not low dopamine concentrations. These data are consistent with an estrogen mediated alteration of G-protein activity and support the hypothesis that estrogen may alter transporter activity through a modulation of dopamine D2 autoreceptor/G alpha(i/o) protein coupling.

Immobilization stress-induced increase in plasma catecholamine levels is inhibited by a prolactoliberin (salsolinol) administration

Catecholamines (CAs) are significantly involved in the regulation of homeostasis of the organism at rest and especially during stressful situations. Stress induces increases in plasma CA (epinephrine and norepinephrine) levels and prolactin (PRL) release from the adenopituitary. We have recently observed that salsolinol, which is produced by the neuro-intermediate lobe of the pituitary gland and by the hypothalamus, can selectively release PRL. Salsolinol is therefore considered to be a putative endogenous PRL-releasing factor. Based on the similarity of CA and PRL responses to stressors, we investigated whether salsolinol plays a role in the regulation of plasma CA levels at rest and of CA release induced by immobilization stress (IMO). Salsolinol did not affect CA baseline levels; however, it did inhibit IMO-induced CA release. Thus, the present study shows for the first time that salsolinol is not only a PRL-releasing factor but is also a potent inhibitor of stress-induced release of epinephrine and norepinephrine.

Transporters in the neurohypophysial neuroendocrine system, with special reference to vesicular glutamate transporters (BNPI and DNPI): a review

Recent advances in gene technology have helped to identify novel proteins and allowed study of their distribution and functions in the mammalian brain. One class of these proteins is that of transporters, which exist in plasma and organellar membranes of neurons and other cells to move substances selectively across membranes. These transporters can be categorized further into subclasses by their structural property, substrate selectivity, and site of action. Some of them have been identified in the hypothalamus, which is the only brain site where a neural signal is converted to a humoral one, namely, a hormone for a target organ. This unique neural mechanism has long attracted attention as the neuroendocrine system, part of which has been extensively studied as the hypothalamic-neurohypophysial system involved in secretion of vasopressin and oxytocin. However, transporters in this system have been less well studied. A morphological examination of novel transporters would give us cues to a better understanding of the neuronal organization and function of the system. In this review, we first summarize recent findings on expression of transporter gene and immunoreactivity in the hypothalamus. In the second part, we explain our observations on two vesicular glutamate (inorganic phosphate) transporters (BNPI and DNPI) in the supraoptic and paraventricular nuclei and neurohypophysis. Further study of these and other transporters will provide a basis on which to reevaluate the organization and function of the hypothalamic-neurohypophysial system.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Dissociation of prolactin secretion from tuberoinfundibular dopamine activity in late pregnant rats

This study investigated whether the PRL surge that precedes parturition is accompanied by a decrease in activity of hypothalamic tuberoinfundibular dopamine (TIDA) neurons, as occurs during the PRL surges of early pregnancy. Serial blood samples were collected at regular intervals during early and late pregnancy via chronic indwelling jugular cannulae, and concentrations of plasma PRL were determined by RIA. In addition, pregnant rats were killed at either 1200 and 0300 h on different days throughout pregnancy. Levels of TIDA neuronal activity were estimated using concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence as an index of dopamine metabolism. During early pregnancy, plasma PRL concentrations showed characteristic diurnal and nocturnal surges peaking at 1700 and 0300 h, respectively, whereas during late pregnancy, there was a broad nocturnal surge throughout the night preceding parturition. During early pregnancy, DOPAC was elevated at 1200 h, associated with suppressed plasma PRL, whereas at 0300 h, during the nocturnal PRL surge, DOPAC was significantly reduced (P < 0.05). On the last day of pregnancy DOPAC levels were significantly reduced at both 1200 and 0300 h compared with those at 1200 h in early pregnancy regardless of the PRL concentration. This experiment was repeated with additional groups to further characterize the timing of the fall in TIDA activity during late pregnancy. DOPAC concentrations were elevated throughout the second half of pregnancy, then fell significantly between 0300-1200 h on day 21, approximately 36 h before parturition. As in the previous experiment, the timing of changes in DOPAC concentrations in the median eminence was dissociated from the antepartum PRL surge. These data indicate that the regulation of PRL secretion during late pregnancy is different from that of early pregnancy. Despite the prolonged reduction in activity of TIDA neurons during late pregnancy, PRL secretion still occurs as a nocturnal surge, suggesting that dopamine is not the only regulator of PRL secretion at this time.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Immunoneutralization of prolactin prevents stimulatory feedback of prolactin on hypothalamic neuroendocrine dopaminergic neurons

We have found that exogenous prolactin (PRL) stimulates all three populations of hypothalamic neuroendocrine dopaminergic neurons. In this study, we investigated the effects of immunoneutralization of endogenous PRL on the activity of these neurons. Injection of 17beta-estradiol (E2) (20 microg subcutaneously) 10 d after ovariectomy induced a proestrus-like increase in PRL in peripheral plasma the following afternoon. At 1000 h the day after E2 injection, rats received either rabbit antirat PRL antiserum (PRL-AS) (200 microL) or normal rabbit serum (NRS, 200 microL, controls) intraperitoneally. Groups of rats were then decapitated every 2 h from 1100 h to 2100 h. Trunk blood was collected and serum extracted with protein A to remove the PRL-AS/PRL complex, and the remaining free PRL was measured by radioimmunoassay. Sites of neuroendocrine dopaminergic nerve terminals, the median eminence (ME), and intermediate and neural lobes of the pituitary gland were excised and stored for determination of dopamine (DA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) concentrations by high-performance liquid chromatography electrochemical detection (EC). In addition, the anterior lobe of the pituitary gland, the locus of DA action, was collected. The concentration of PRL in NRS-treated animals increased by 1500 h, peaked by 1700 h, and returned to low levels by 2100 h. PRL-AS prevented the increase in PRL secretion in response to E2. The turnover of DA (DOPAC:DA ratio; an index of dopaminergic neuronal activity) in the ME of NRS-treated animals increased at 1500 h and rapidly returned to basal levels. Treatment with PRL-AS prevented the increase in DA turnover in the ME. DA turnover in the intermediate lobe increased coincident with the peak of PRL in serum of NRS-treated rats. PRL-AS administration prevented increased DA turnover in the intermediate lobe. The turnover of DA in the neural lobe increased by 1300 h and decreased steadily through 2100 h. However, administration of PRL-AS minimally suppressed the turnover of DA in the neural lobe. Moreover, administration of PRL-AS attenuated the rise of DA in the anterior lobe associated with the waning phase of the E2-induced PRL surge. These results clearly indicate that endogenous PRL regulates its own secretion by activating hypothalamic neuroendocrine dopaminergic neurons.