60 YEARS OF NEUROENDOCRINOLOGY: The structure of the neuroendocrine hypothalamus: the neuroanatomical legacy of Geoffrey Harris

History of the Development of Knowledge about the Neuroendocrine Control of Ovulation-Recent Knowledge on the Molecular Background

The physiology of reproduction has been of interest to researchers for centuries. The purpose of this work is to review the development of our knowledge on the neuroendocrine background of the regulation of ovulation. We first describe the development of the pituitary gland, the structure of the median eminence (ME), the connection between the hypothalamus and the pituitary gland, the ovarian and pituitary hormones involved in ovulation, and the pituitary cell composition. We recall the pioneer physiological and morphological investigations that drove development forward. The description of the supraoptic-paraventricular magnocellular and tuberoinfundibular parvocellular systems and recognizing the role of the hypophysiotropic area were major milestones in understanding the anatomical and physiological basis of reproduction. The discovery of releasing and inhibiting hormones, the significance of pulse and surge generators, the pulsatile secretion of the gonadotropin-releasing hormone (GnRH), and the subsequent pulsatility of luteinizing (LH) and follicle-stimulating hormones (FSH) in the human reproductive physiology were truly transformative. The roles of three critical neuropeptides, kisspeptin (KP), neurokinin B (NKB), and dynorphin (Dy), were also identified. This review also touches on the endocrine background of human infertility and assisted fertilization.

Age-related ciliopathy: Obesogenic shortening of melanocortin-4 receptor-bearing neuronal primary cilia

Obesity is often associated with aging. However, the mechanism of age-related obesity is unknown. The melanocortin-4 receptor (MC4R) mediates leptin-melanocortin anti-obesity signaling in the hypothalamus. Here, we discovered that MC4R-bearing primary cilia of hypothalamic neurons progressively shorten with age in rats, correlating with age-dependent metabolic decline and increased adiposity. This "age-related ciliopathy" is promoted by overnutrition-induced upregulation of leptin-melanocortin signaling and inhibited or reversed by dietary restriction or the knockdown of ciliogenesis-associated kinase 1 (CILK1). Forced shortening of MC4R-bearing cilia in hypothalamic neurons by genetic approaches impaired neuronal sensitivity to melanocortin and resulted in decreased brown fat thermogenesis and energy expenditure and increased appetite, finally developing obesity and leptin resistance. Therefore, despite its acute anti-obesity effect, chronic leptin-melanocortin signaling increases susceptibility to obesity by promoting the age-related shortening of MC4R-bearing cilia. This study provides a crucial mechanism for age-related obesity, which increases the risk of metabolic syndrome.

Advances in steroid research from the pioneering neurosteroid concept to metabolomics: New insights into pregnenolone function

Advances in neuroendocrinology have led to major discoveries since the 19th century, identifying adaptive loops for maintaining homeostasis. One of the most remarkable discoveries was the concept of neurosteroids, according to which the brain is not only a target but also a source of steroid production. The identification of new membrane steroid targets now underpins the neuromodulatory effects of neurosteroids such as pregnenolone, which is involved in functions mediated by the GPCR CB1 receptor. Structural analysis of steroids is a key feature of their interactions with the phospholipid membrane, receptors and resulting activity. Therefore, mass spectrometry-based methods have been developed to elucidate the metabolic pathways of steroids, the ultimate approach being metabolomics, which allows the identification of a large number of metabolites in a single sample. This approach should enable us to make progress in understanding the role of neurosteroids in the functioning of physiological and pathological processes.

Functional and developmental heterogeneity of pituitary lactotropes in medaka

In fish, prolactin-producing cells (lactotropes) are located in the anterior part of the pituitary and play an essential role in osmoregulation. However, small satellite lactotrope clusters have been described in other parts of the pituitary in several species. The functional and developmental backgrounds of these satellite clusters are not known. We recently discovered two distinct prolactin-expressing cell types in Japanese medaka (Oryzias latipes), a euryhaline species, using single cell transcriptomics. In the present study, we characterize these two transcriptomically distinct lactotrope cell types and explore the hypothesis that they represent spatially distinct cell clusters, as found in other species. Single cell RNA sequencing shows that one of the two lactotrope cell types exhibits an expression profile similar to that of stem cell-like folliculo-stellate cell populations. Using in situ hybridization, we show that the medaka pituitary often develops additional small satellite lactotrope cell clusters, like in other teleost species. These satellite clusters arise early during development and grow in cell number throughout life regardless of the animal's sex. Surprisingly, our data do not show a correspondence between the stem cell-like lactotropes and these satellite lactotrope clusters. Instead, our data support a scenario in which the stem cell-like lactotropes are an intrinsic stage in the development of every spatially distinct lactotrope cluster. In addition, lactotrope activity in both spatially distinct lactotrope clusters decreases when environmental salinity increases, supporting their role in osmoregulation. However, this decrease appears weaker in the satellite lactotrope cell clusters, suggesting that these lactotropes are regulated differently.

An Introductory Guide to Organizational Neuroscience

The time is ripe for a renewed and interdisciplinary approach to organizational research that incorporates neuroscientific techniques. Like all methods, they have methodological, analytical, and interpretational limitations; however, the potential gains from using these techniques are far more considerable. We have therefore assembled a succinct yet authoritative collection of articles on the topic of neuroscience in organizational research, to serve as a solid introduction to the methods of neuroscience and what they can accomplish. The special topic is organized into two parts. The first includes a set of accessible reviews of the palette of brain imaging, mapping, and stimulation techniques (fMRI, fNIRS, EEG, MEG, and NIBS) as well as examples of the application of neuroscience methods to various disciplines including economics, marketing, finance, organizational behavior, neuroethology, as well an integrative translational critique on a variety of applications. The second is a collection of articles resulting from a competitive call for submissions that cover various neuroscience topics but also address important methodological and philosophical issues. The articles lay out a roadmap for the effective integration of neuroscientific methods into organizational research.

The Amphibious Mudskipper: A Unique Model Bridging the Gap of Central Actions of Osmoregulatory Hormones Between Terrestrial and Aquatic Vertebrates

Body fluid regulation, or osmoregulation, continues to be a major topic in comparative physiology, and teleost fishes have been the subject of intensive research. Great progress has been made in understanding the osmoregulatory mechanisms including drinking behavior in teleosts and mammals. Mudskipper gobies can bridge the gap from aquatic to terrestrial habitats by their amphibious behavior, but the studies are yet emerging. In this review, we introduce this unique teleost as a model to study osmoregulatory behaviors, particularly amphibious behaviors regulated by the central action of hormones. Regarding drinking behavior of mammals, a thirst sensation is aroused by angiotensin II (Ang II) through direct actions on the forebrain circumventricular structures, which predominantly motivates them to search for water and take it into the mouth for drinking. By contrast, aquatic teleosts can drink water that is constantly present in their mouth only by reflex swallowing, and Ang II induces swallowing by acting on the hindbrain circumventricular organ without inducing thirst. In mudskippers, however, through the loss of buccal water by swallowing, which appears to induce buccal drying on land, Ang II motivates these fishes to move to water for drinking. Thus, mudskippers revealed a unique thirst regulation by sensory detection in the buccal cavity. In addition, the neurohypophysial hormones, isotocin (IT) and vasotocin (VT), promote migration to water via IT receptors in mudskippers. VT is also dipsogenic and the neurons in the forebrain may mediate their thirst. VT regulates social behaviors as well as osmoregulation. The VT-induced migration appears to be a submissive response of subordinate mudskippers to escape from competitive and dehydrating land. Together with implications of VT in aggression, mudskippers may bridge the multiple functions of neurohypophysial hormones. Interestingly, cortisol, an important hormone for seawater adaptation and stress response in teleosts, also stimulates the migration toward water, mediated possibly via the mineralocorticoid receptor. The corticosteroid system that is responsive to external stressors can accelerate emergence of migration to alternative habitats. In this review, we suggest this unique teleost as an important model to deepen insights into the behavioral roles of these hormones in relation to osmoregulation.

The special relationship: glia-neuron interactions in the neuroendocrine hypothalamus

Natural fluctuations in physiological conditions require adaptive responses involving rapid and reversible structural and functional changes in the hypothalamic neuroendocrine circuits that control homeostasis. Here, we discuss the data that implicate hypothalamic glia in the control of hypothalamic neuroendocrine circuits, specifically neuron-glia interactions in the regulation of neurosecretion as well as neuronal excitability. Mechanistically, the morphological plasticity displayed by distal processes of astrocytes, pituicytes and tanycytes modifies the geometry and diffusion properties of the extracellular space. These changes alter the relationship between glial cells of the hypothalamus and adjacent neuronal elements, especially at specialized intersections such as synapses and neurohaemal junctions. The structural alterations in turn lead to functional plasticity that alters the release and spread of neurotransmitters, neuromodulators and gliotransmitters, as well as the activity of discrete glial signalling pathways that mediate feedback by peripheral signals to the hypothalamus. An understanding of the contributions of these and other non-neuronal cell types to hypothalamic neuroendocrine function is thus critical both to understand physiological processes such as puberty, the maintenance of bodily homeostasis and ageing and to develop novel therapeutic strategies for dysfunctions of these processes, such as infertility and metabolic disorders.

Bidirectional Anticipation of Future Osmotic Challenges by Vasopressin Neurons

Ingestion of water and food are major hypo- and hyperosmotic challenges. To protect the body from osmotic stress, posterior pituitary-projecting, vasopressin-secreting neurons (VP_pp neurons) counter osmotic perturbations by altering their release of vasopressin, which controls renal water excretion. Vasopressin levels begin to fall within minutes of water consumption, even prior to changes in blood osmolality. To ascertain the precise temporal dynamics by which water or food ingestion affect VP_pp neuron activity, we directly recorded the spiking and calcium activity of genetically defined VP_pp neurons. In states of elevated osmolality, water availability rapidly decreased VP_pp neuron activity within seconds, beginning prior to water ingestion, upon presentation of water-predicting cues. In contrast, food availability following food restriction rapidly increased VP_pp neuron activity within seconds, but only following feeding onset. These rapid and distinct changes in activity during drinking and feeding suggest diverse neural mechanisms underlying anticipatory regulation of VP_pp neurons.

Electrophysiology of Hypothalamic Magnocellular Neurons In vitro: A Rhythmic Drive in Organotypic Cultures and Acute Slices

Hypothalamic neurohormones are released in a pulsatile manner. The mechanisms of this pulsatility remain poorly understood and several hypotheses are available, depending upon the neuroendocrine system considered. Among these systems, hypothalamo-neurohypophyseal magnocellular neurons have been early-considered models, as they typically display an electrical activity consisting of bursts of action potentials that is optimal for the release of boluses of the neurohormones oxytocin and vasopressin. The cellular mechanisms underlying this bursting behavior have been studied in vitro, using either acute slices of the adult hypothalamus, or organotypic cultures of neonatal hypothalamic tissue. We have recently proposed, from experiments in organotypic cultures, that specific central pattern generator networks, upstream of magnocellular neurons, determine their bursting activity. Here, we have tested whether a similar hypothesis can be derived from in vitro experiments in acute slices of the adult hypothalamus. To this aim we have screened our electrophysiological recordings of the magnocellular neurons, previously obtained from acute slices, with an analysis of autocorrelation of action potentials to detect a rhythmic drive as we recently did for organotypic cultures. This confirmed that the bursting behavior of magnocellular neurons is governed by central pattern generator networks whose rhythmic drive, and thus probably integrity, is however less satisfactorily preserved in the acute slices from adult brains.

60 YEARS OF NEUROENDOCRINOLOGY: Celebrating the brain's other output-input system and the monograph that defined neuroendocrinology

The brain's unimaginably complex operations are expressed in just two types of output: muscle activity and hormone release. These are the means by which the brain acts beyond its bony casing. Muscle-mediated actions (such as speaking, writing, pupillary reflexes) send signals to the outside world that may convey thoughts, emotions or evidence of neurological disorder. The outputs of the brain as a hormone secreting gland are usually less evident. Their discovery required several paradigm shifts in our understanding of anatomy. The first occurred in 1655. Exactly 300 years later, Geoffrey Harris' monograph Neural control of the pituitary gland launched the scientific discipline that is now known as neuroendocrinology. His hypotheses have stood the test of time to a remarkable degree. A key part of his vision concerned the two-way 'interplay between the central nervous system and endocrine glands'. Over the past 60 years, the importance of this reciprocity and the degree to which cerebral functions are influenced by the endocrine environment have become increasingly clear.

Contribution of GnIH Research to the Progress of Reproductive Neuroendocrinology

Since the discovery of gonadotropin-releasing hormone (GnRH) in mammals at the beginning of the 1970s, it was generally accepted that GnRH is the only hypothalamic neuropeptide regulating gonadotropin release in mammals and other vertebrates. In 2000, however, gonadotropin-inhibitory hormone (GnIH), a novel hypothalamic neuropeptide that actively inhibits gonadotropin release, was discovered in quail. Numerous studies over the past decade and a half have demonstrated that GnIH serves as a key player regulating reproduction across vertebrates, acting on the brain and pituitary to modulate reproductive physiology and behavior. In the latter case, recent evidence indicates that GnIH can regulate reproductive behavior through changes in neurosteroid, such as neuroestrogen, biosynthesis in the brain. This review summarizes the discovery of GnIH, and the contributions to GnIH research focused on its mode of action, regulation of biosynthesis, and how these findings advance our understanding of reproductive neuroendocrinology.