Neuroendocrine thymus and beta-adrenergic responsiveness in aging mice

It has previously been shown that thymus exerts a regulatory influence on the beta-adrenergic system, controlling, in particular, DNA synthesis in submandibular glands following injection with isoproterenol (IPR). A decreased peak of response found in old mice can be corrected by grafting a neonatal thymus into old animals. In order to clear whether its restoring action needs mutual interrelationships with other control systems or, alternatively, whether even some thymic factor can be effective, the IPR response mentioned above was also assayed in old animals treated with a thymic extract (TME). Among the numerous thymic factors, this extract was chosen due to the effect that it was prepared on the basis of non-immunological tests and had already been shown to be effective in correcting some alterations observed in old rats. Results show that TME is capable of partially restoring the impaired response found in old mice. The location of the peak of thymidine incorporation, however, is shifted towards the right with respect the peak time observed in young, old and thymus-grafted old mice. Without additional studies, it cannot be decided whether the shift and the only partial recovery is due to the particular dose and duration of the treatment or represents a weaker action of the extract with respect to that of thymic graft.     

Neuroendocrine physiology of the early and late menopause.

Hormonal integration of the reproductive system is dramatically affected by reproductive aging. The progressive loss of ovarian follicles with normal aging is accompanied by an initial decrease in inhibin B and a concomitant increase in follicle-stimulating hormone. Subsequently, inhibin A and progesterone decrease, where as estradiol levels are maintained and often increase. In the late reproductive stage, cycles remain regular whereas the early and late menopausal transition are characterized by irregular cycles and often dramatic swings in estradiol and gonadotropin levels. Studies in younger and older postmenopausal women suggest that there are age-related changes in the neuroendocrine axis that are independent of the changing ovarian hormonal milieu of the menopausal transition but may contribute to the end of reproductive life.     

Neuroendocrine control of growth hormone in fish

The biological actions of growth hormone (GH) are pleiotropic, including growth promotion, energy mobilization, gonadal development, appetite, and social behavior. Accordingly, the regulatory network for GH is complex and includes many endocrine and environmental factors. In fish, the neuroendocrine control of GH is multifactorial with multiple inhibitors and stimulators of pituitary GH secretion. In fish, GH release is under a tonic negative control exerted mainly by somatostatin. Sex steroid hormones and nutritional status influence the level of brain expression and effectiveness of some of these GH neuroendocrine regulatory factors, suggesting that their relative importance differs under different physiological conditions. At the pituitary level, some, if not all, somatotropes can respond to multiple regulators. Therefore, ligand- and function-specificity, as well as the integrative responses to multiple signals must be achieved at the level of signal transduction mechanisms. Results from investigations on a limited number of stimulatory and inhibitory GH-release regulators indicate that activation of different but convergent intracellular pathways and the utilization of specific intracellular Ca(2+) stores are some of the strategies utilized. However, more work remains to be done in order to better understand the integrative mechanisms of signal transduction at the somatotrope level and the relevance of various GH regulators in different physiological circumstances.     

Hyperplasia of the thymus gland in children: physiology or pathology?

A critical analysis of the literature data and of the results of clinicoroentgenological, hormonal and immunological studies in children with thymomegaly makes it possible to regard hyperplasia of the thymus gland at early childhood as a sign of functional incompetence of the thymus and of the secondary immunodeficient state.     

Neuroendocrine control of physiological color change in Chameleo gracilis

Color changes in Chameleo gracilis are under neuroendocrine control. Denervation of the limbs, by removal of the sciatic or brachial nerves, does not interfere with the normal color changes in the affected limbs. Denervated skins, placed back onto C. gracilis, show color changes in synchrony with the rest of the animal. Pieces of isolated skin turn very dark or black in alpha-melanophore stimulating hormone (alpha-MSH) and green in adrenaline, but do not show any color changes in physiological saline. Hypophysectomized animals turn green but never turn dark. Injections of alpha-MSH cause intact or hypophysectomized animals to turn dark or black, while injections of adrenaline cause them to turn light green. Injections of physiological saline have no effect. Crude pituitary extracts cause darkening of isolated skins or of intact animals injected with such extracts. Similar treatment with crude extracts of adrenal glands causes the skins to become light green. Electrical stimulation of transected spinal cord leads to localized lightening of the skin but never to darkening of the same. Light, temperature, darkness, and color of the surroundings influence color change. Color change to green at night and to darker colors in the daytime suggests a possible circadian rhythm in the phenomenon.     

Neuroendocrine control of GH release during acute aerobic exercise

GH secretion declines with aging and is decreased in conditions such as obesity. Several physiologic factors alter pulsatile GH secretion, including age, gender, body composition, regional distribution of fat and in particular abdominal visceral fat, sleep, nutrition, exercise and serum concentrations of gonadal steroids, insulin and IGF-I. Acute aerobic exercise is a powerful stimulus to GH release. Available studies suggest that intensity and duration of acute exercise, fitness, and training state may all influence, in part, the GH response to exercise. Intensity of exercise plays a key role in GH response to exercise. In the present paper we will discuss the GH response during acute aerobic exercise with a focus on exercise intensity and GH release. We will also provide an overview of the neuroendocrine control of exercise-induced GH release. Finally, information related to the effects of aging and gender on the GH response to exercise will be provided.     

Neuroendocrine control of maternal behavior in non-human and human mammals

Mammalian parental care is essentially provided by the mother and it occupies most of the reproductive period for female. The synchronization of maternal behavior with parturition and lactation ensures that the mother responds to the needs of the young at the appropriate time. This temporal synchrony is accomplished by hormonal changes that underly both the onset of maternal behavior and of parturition and lactation. The aim of this review is to describe and compare the hormonal mechanisms that regulate the onset of maternal behavior across a variety of mammals, including humans, that represent different behavioral strategies. Are involved the steroid hormones, estradiol and progesterone synthesized by the ovaries which primed the future mother to repond maternally. In response to these steroids, oxytocin release induced by vaginocervical stimulation and prolactin release affect the maternal brain. The medial preoptic area integrates the hormonal signals to regulate maternal behavior. The hormonal cocktail that stimulates maternal behavior varies across mammalian species. Because most of the studies in humans are correlative and because human environment is complex, direct causality between hormones and maternal behavior is unclear. However, one can reasonably think that hormones create a positive bias towards the baby increasing the occurrence of maternal behavior.     

Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis

In the freshwater snail Lymnaea stagnalis the anterior mantle region, which mainly consists of large numbers of special glycogen-storing cells, is an important depot for the energy reserves of this snail. In organ culture experiments the central nervous system (CNS), in contrast to other tissues, both inhibits glycogen synthesis (measured as incorporation of [14C]glucose into glycogen) and stimulates glycogen breakdown in anterior mantle tissue (measured as a decreased retention of prelabeled glycogen). These effects are dose dependent, with saturation at the highest doses tested. High-potassium Ringer solution stimulates the secretion of a CNS factor which induces glucose release by anterior mantle tissue. This glucose-release-stimulating effect of the CNS is also dose dependent, but saturation of the response was not achieved. It is concluded that inhibition of glycogen synthesis and stimulation of glycogen breakdown and glucose release are probably effects of a single neurohormone which controls glycogen mobilization from the storage cells in the mantle. Like similar factors in other animal phyla, this putative neurohormone is referred to as a hyperglycemic factor.     

Neuroendocrine control by kisspeptins: role in metabolic regulation of fertility

The neurohormonal control of reproduction involves a hierarchical network of central and peripheral signals in the hypothalamic-pituitary-gonadal (HPG) axis. Development and function of this neuroendocrine system is the result of a lifelong delicate balance between endogenous regulators and environmental cues, including nutritional and metabolic factors. Kisspeptins are the peptide products of KISS1, which operate via the G-protein-coupled receptor GPR54 (also known as Kiss1R). These peptides have emerged as essential upstream regulators of neurons secreting gonadotropin-releasing hormone (GnRH), the major hypothalamic node for the stimulatory control of the HPG axis. They are potent elicitors of gonadotropin secretion in various species and physiological settings. Moreover, Kiss1 neurons in the hypothalamus participate in crucial features of reproductive maturation and function, such as brain-level sex differentiation, puberty onset and the neuroendocrine regulation of gonadotropin secretion and ovulation. Cotransmitters of Kiss1 neurons, such as neurokinin B, with roles in controlling the HPG axis have been identified by genetic, neuroanatomical and physiological studies. In addition, a putative role has been proposed for Kiss1 neurons in transmitting metabolic information to GnRH neurons, although the precise mechanisms are as yet unclear. In this Review, we present the major reproductive features of kisspeptins, especially their interplay with neurokinin B and potential roles in the metabolic control of puberty and fertility, and suggest new avenues for research.     

Neuroendocrine ageing

Abstract. Ageing is followed by an involution of neuroendocrine functions, resulting in a decreased secretion of sex steroids and growth hormone. In addition, Cortisol secretion may be inadequately elevated upon stress challenges, due to deficient braking functions by central glucocorticoid receptors. In combination, these endocrine perturbations will probably result in changes in psychological factors such as energy and well-being, altered body composition, and insulin resistance, as well as other risk factors for diseases characteristic of the ageing human, such as cardiovascular disease, non-insulin-dependent diabetes mellitus and stroke. This cluster of phenomena is frequently seen before the period of normal ageing, indicating premature ageing processes. The background factors in these conditions probably include psychosocial stressors, which are perceived differently depending on individual coping abilities. Socio-economic and other environmental factors, such as smoking and alcohol abuse, may well be responsible for the expression of this syndrome of premature ageing. Preventive and therapeutic trials with hormonal substitution therapy to treat these aberrations have been promising, and encourage further studies aimed at elucidating potential risks in relation to potential improvement of quality of life and, perhaps, longevity.     

Neuroendocrine tumours

Neuroendocrine tumours are a heterogeneous group including, for example, carcinoid, gastroenteropancreatic neuroendocrine tumours, pituitary tumours, medullary carcinoma of the thyroid and phaeochromocytomas. They have attracted much attention in recent years, both because they are relatively easy to palliate and because they have indicated the chronic effect of the particular hormone elevated. As neuroendocrine phenotypes became better understood, the definition of neuroendocrine cells changed and is now accepted as referring to cells with neurotransmitter, neuromodulator or neuropeptide hormone production, dense-core secretory granules, and the absence of axons and synapses. Neuroendocrine markers, particularly chromogranin A, are invaluable diagnostically. Study of several neuroendocrine tumours has revealed a genetic etiology, and techniques such as genetic screening have allowed risk stratification and prevention of morbidity in patients carrying the particular mutation. Pharmacological therapy for these often slow-growing tumours, e.g. with somatostatin analogues, has dramatically improved symptom control, and radiolabelled somatostatin analogues offer targeted therapy for metastatic or inoperable disease. In this review, the diagnosis and management of patients with carcinoid, gut neuroendocrine tumours, multiple endocrine neoplasia types 1 and 2, and isolated phaeochromocytoma are evaluated.