Estrogen regulation of the dopamine-activated GIRK channel in pituitary lactotrophs: implications for regulation of prolactin release during the estrous cycle

Sex differences in pituitary corticotroph excitability

Stress-related illness represents a major burden on health and society. Sex differences in stress-related disorders are well documented, with women having twice the lifetime rate of depression compared to men and most anxiety disorders. Anterior pituitary corticotrophs are central components of the hypothalamic-pituitary-adrenal (HPA) axis, receiving input from hypothalamic neuropeptides corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), while regulating glucocorticoid output from the adrenal cortex. The dynamic control of electrical excitability by CRH/AVP and glucocorticoids is critical for corticotroph function; however, whether corticotrophs contribute to sexually differential responses of the HPA axis, which might underlie differences in stress-related disorders, is very poorly understood. Using perforated patch clamp electrophysiology in corticotrophs from mice expressing green fluorescent protein under the control of the Pomc promoter, we characterized basal and secretagogue-evoked excitability. Both male and female corticotrophs show predominantly single-spike action potentials under basal conditions; however, males predominantly display spikes with small-amplitude (<20 mV) afterhyperpolarizations (B-type), whereas females displayed a mixture of B-type spikes and spikes with a large-amplitude (>25 mV) afterhyperpolarization (A-type). In response to CRH, or CRH/AVP, male cells almost exclusively transition to a predominantly pseudo-plateau bursting, whereas only female B-type cells display bursting in response to CRH±AVP. Treatment of male or female corticotrophs with 1 nM estradiol (E2) for 24-72 h has no effect on the proportion of cells with A- or B-type spikes in either sex. However, E2 results in the cessation of CRH-induced bursting in both male and female corticotrophs, which can be partially reversed by adding a BK current using a dynamic clamp. RNA-seq analysis of purified corticotrophs reveals extensive differential gene expression at the transcriptional level, including more than 71 mRNAs encoding ion channel subunits. Interestingly, there is a two-fold lower level (p < 0.01) of BK channel pore-forming subunit (Kcnma1) expression in females compared to males, which may partially explain the decrease in CRH-induced bursting. This study identified sex differences at the level of the anterior pituitary corticotroph ion channel landscape and control of both spontaneous and CRH-evoked excitability. Determining the mechanisms of sex differences of corticotroph and HPA activity at the cellular level could be an important step for better understanding, diagnosing, and treating stress-related disorders.

Therapeutic potential of targeting G protein-gated inwardly rectifying potassium (GIRK) channels in the central nervous system

G protein-gated inwardly rectifying potassium channels (Kir3/GirK) are important for maintaining resting membrane potential, cell excitability and inhibitory neurotransmission. Coupled to numerous G protein-coupled receptors (GPCRs), they mediate the effects of many neurotransmitters, neuromodulators and hormones contributing to the general homeostasis and particular synaptic plasticity processes, learning, memory and pain signaling. A growing number of behavioral and genetic studies suggest a critical role for the appropriate functioning of the central nervous system, as well as their involvement in many neurologic and psychiatric conditions, such as neurodegenerative diseases, mood disorders, attention deficit hyperactivity disorder, schizophrenia, epilepsy, alcoholism and drug addiction. Hence, GirK channels emerge as a very promising tool to be targeted in the current scenario where these conditions already are or will become a global public health problem. This review examines recent findings on the physiology, function, dysfunction, and pharmacology of GirK channels in the central nervous system and highlights the relevance of GirK channels as a worthful potential target to improve therapies for related diseases.

Cross-generational impact of a male murine pheromone 2-sec-butyl-4,5- dihydrothiazole in female mice

The current understanding of the activity of mammalian pheromones is that endocrine and behavioural effects are limited to the exposed individuals. Here, we demonstrate that the nasal exposure of female mice to a male murine pheromone stimulates expansion of mammary glands, leading to prolonged nursing of pups. Subsequent behavioural testing of the pups from pheromone-exposed dams exhibited enhanced learning. Sialic acid components in the milk are known to be involved in brain development. We hypothesized that the offspring might have received more of this key nutrient that promotes brain development. The mRNA for polysialyltransferase, which produces polysialylated neural cell adhesion molecules related to brain development,was increased in the brain of offspring of pheromone-exposed dams at post-natal day 10, while it was not different at embryonic stages, indicating possible differential brain development during early post-natal life.

Pheromone-induced cell proliferation in the murine subventricular zone

Enhancement of adult neurogenesis in female mice was previously demonstrated through exposure to soiled bedding from males, although the identity of relevant chemosignals has remained unknown. The farnesenes and SBT (2-sec-butyl-4,5-dihydrothiazole) are male murine pheromones that dominant males secrete at higher levels. Previous studies have shown that they induce oestrus in female mice. We have recently shown that these pheromones strongly increase cell proliferation in the SVZ (subventricular zone) of adult female mice. In addition, we found that a female murine pheromone, 2,5-dimethylpyrazine, facilitates similar changes in males. 2,5-dimethylpyrazine is a female pheromone that is secreted when females are housed in large groups and it was originally found to suppress oestrus in females. We found that it does not have suppressive effect on the cell proliferation in the SVZ of females. Similarly, male murine pheromones, SBT and the farnesenes, do not show a suppressive effect on the cell proliferation in the SVZ of males. Our results demonstrated that pheromonal communication between males and females has strong stimulatory effect on both the reproductive physiology and brain cell proliferation, but intrasex pheromonal exchanges do not reduce progenitor proliferation in these brain regions.

Endogenous peripheral oxytocin measures can give insight into the dynamics of social relationships: a review

The neuropeptide, oxytocin, receives increasing attention due to its role in stress regulation and promoting affiliative social behavior. Research across mammals points to a complex pattern whereby social context and individual differences moderate the central release of oxytocin as well as moderate the effects that exogenous administration of oxytocin has on social behavior. In addition, it is becoming evident that measuring endogenous peripheral oxytocin levels is an informative tool. This is particularly so when oxytocin can be measured from non-invasively collected samples, such as in urine. Although it is still debated as to whether peripheral measures of oxytocin relate to central measures of oxytocin, anatomical and functional evidence indicate a link between the two. We argue that non-invasive measures of peripheral oxytocin hold several research and potential therapeutic advantages. Principally, study subjects can be sampled repeatedly in different social contexts where social history between interaction partners can be taken into account. Several hormones can be measured simultaneously allowing examination of the influence of oxytocin interactions with other hormones on motivational states. Valence of relationships as well as changes in relationship quality over time can be measured through endocrine responses. Also, the approach of identifying natural social contexts that are associated with endogenous oxytocin release offers the potential of behavioral therapy as an addition or alternative to chemical therapy in the field of mental health.

Expression of estradiol receptor, GPR30, in bovine anterior pituitary and effects of GPR30 agonist on GnRH-induced LH secretion

G-protein - coupled receptor 30 (GPR30) is an estradiol receptor located on the plasma membrane, and it initiates several rapid, non-genomic signaling events. GPR30 has recently been identified in rat anterior pituitary (AP); however, little is known about the role of GPR30 in controlling luteinizing hormone (LH) secretion from gonadotropes in animals. To fill this research gap, we hypothesized that GPR30 is expressed in bovine AP and mediates estradiol inhibition of gonadotropin-releasing hormone (GnRH)-induced LH release. We confirmed the expressions of GPR30 mRNA and protein by RT-PCR, western blotting, and immunohistochemistry. We cultured bovine AP cells (n=8) for 3 days in steroid-free conditions and then treated them with increasing concentrations (0.001nM, 0.01nM, 0.1nM, 1nM, and 10nM) of estradiol or a GPR30-specific agonist, G1, for 5min before GnRH stimulation. As expected, estradiol at 0.001-0.1nM inhibited the GnRH-stimulated LH secretion. However, we found also that G1 at 0.001nM was able to inhibit this secretion (P<0.05). In contrast, both estradiol and G1 at higher doses were less efficient in suppressing the GnRH-stimulated LH secretion. Neither estradiol nor G1 suppressed GnRH-stimulated follicle-stimulating hormone secretion. In separate experiments, fluorescent immunohistochemistry and immunocytochemistry revealed that approximately 50% of GPR30-positive cells express LH, and about 30% of LH-positive cells express GPR30. In conclusion, GPR30 is expressed in bovine gonadotropes and other AP cells and may partially contribute to rapid negative estradiol feedback of GnRH-induced LH secretion.

Molecular basis of the facilitation of the heterooligomeric GIRK1/GIRK4 complex by cAMP dependent protein kinase

G-protein activated inwardly rectifying K⁺ channels (GIRKs) of the heterotetrameric GIRK1/GIRK4 composition mediate I_K + ACh in atrium and are regulated by cAMP dependent protein kinase (PKA). Phosphorylation of GIRK1/GIRK4 complexes promotes the activation of the channel by the G-protein Gβγ-dimer (“heterologous facilitation”). Previously we reported that 3 serines/threonines (S/Ts) within the GIRK1 subunit are phosphorylated by the catalytic subunit of PKA (PKA-cs) in-vitro and are responsible for the acute functional effects exerted by PKA on the homooligomeric GIRK1^F137S (GIRK1^⁎) channel. Here we report that homooligomeric GIRK4^WT and GIRK4^S143T (GIRK4^⁎) channels are clearly regulated by PKA phosphorylation. Heterooligomeric channels of the GIRK1^{S385CS401CT407C}/GIRK4^WT composition, where the GIRK1 subunit is devoid of PKA mediated phosphorylation, exhibited reduced but still significant acute effects (reduction during agonist application was ≈ 49% compared to GIRK1^WT/GIRK4^WT). Site directed mutagenesis of truncated cytosolic regions of GIRK4 revealed four serines/threonines (S/Ts) that were heavily phosphorylated by PKA-cs in vitro. Two of them were found to be responsible for the acute effects exerted by PKA in vivo, since the effect of cAMP injection was reduced by ≈ 99% in homooligomeric GIRK4^{⁎T199CS412C} channels. Coexpression of GIRK1^WT/GIRK4^T199CS412C reduced the acute effect by ≈ 65%. Only channels of the GIRK1^{S385CS401CT407C}/GIRK4^T199CS412C composition were practically devoid of PKA mediated effects (reduction by ≈ 97%), indicating that both subunits contribute to the heterologous facilitation of I_K + ACh.