Endocrine factors in the hypothalamic regulation of food intake in females: a review of the physiological roles and interactions of ghrelin, leptin, thyroid hormones, oestrogen and insulin.

Controlling energy homeostasis involves modulating the desire to eat and regulating energy expenditure. The controlling machinery includes a complex interplay of hormones secreted at various peripheral endocrine endpoints, such as the gastrointestinal tract, the adipose tissue, thyroid gland and thyroid hormone-exporting organs, the ovary and the pancreas, and, last but not least, the brain itself. The peripheral hormones that are the focus of the present review (ghrelin, leptin, thyroid hormones, oestrogen and insulin) play integrated regulatory roles in and provide feedback information on the nutritional and energetic status of the body. As peripheral signals, these hormones modulate central pathways in the brain, including the hypothalamus, to influence food intake, energy expenditure and to maintain energy homeostasis. Since the growth of the literature on the role of various hormones in the regulation of energy homeostasis shows a remarkable and dynamic expansion, it is now becoming increasingly difficult to understand the individual and interactive roles of hormonal mechanisms in their true complexity. Therefore, our goal is to review, in the context of general physiology, the roles of the five best-known peripheral trophic hormones (ghrelin, leptin, thyroid hormones, oestrogen and insulin, respectively) and discuss their interactions in the hypothalamic regulation of food intake.

Oestrogens in the mammalian brain: from conception to adulthood--a review.

Environmental and plant oestrogens have been identified as compounds that when ingested, disrupt the physiological pathways of endogenous oestrogen actions and thus, act as agonists or antagonists of oestrogen. Although the risks of exposure to exogenous oestrogens (ExEs) are subject to scientific debate, the question of how ExE exposure affects the central nervous system remains to be answered. We attempt to summarise the mechanisms of oestrogenic effects in the central nervous tissue with the purpose to highlight the avenues potentially used by ExEs. The genomic and rapid, non-genomic cellular pathways activated by oestrogen are listed and discussed together with the best known interneuronal mechanisms of oestrogenic effects. Because the effects of oestrogen on the brain seem to be age dependent, we also found it necessary to put the age-dependent oestrogenic effects in parallel to their intra- and intercellular mechanisms of action. Finally, considering the practical risks of human ExE exposure, we briefly discuss the human significance of this matter. We believe this short review of the topic became necessary because recent data suggest new fields and pathways for endogenous oestrogen actions and have generated the concern that the hidden exposure of humans and domestic animal species to ExEs may also exert its beneficial and/or adverse effects through these avenues.

Immunolocalization of ecto-nucleoside triphosphate diphosphohydrolase 3 in rat brain: implications for modulation of multiple homeostatic systems including feeding and sleep-wake behaviors.

Three anti-peptide antisera were raised against three distinct amino acid sequences of ecto-nucleoside triphosphate diphosphohydrolase 3 (NTPDase3), characterized by Western blot analyses, and used to determine the distribution of NTPDase3 protein in adult rat brain. The three antisera all yielded similar immunolocalization data, leading to increased reliability of the results obtained. Unlike NTPDase1 and NTPDase2, NTPDase3 immunoreactivity was detected exclusively in neurons. Immunoreactivity was localized primarily to axon-like structures with prominent staining of presynaptic elements. Specific perikaryal immunostaining was detected primarily in scattered neurons near the lateral hypothalamic area and the perifornical nucleus. High densities of immunoreactive axon-like fibers were present in midline regions of the forebrain and midbrain. Highly scattered NTPDase3 positive fibers were observed in the cerebral cortex, the hippocampal formation, and the basal ganglia. Moreover, very high densities of immunostained fibers were detected in the mediobasal hypothalamus, with the overall mesencephalic pattern of staining associated closely with hormone responsive nuclei. High densities of NTPDase3 positive terminals were also associated with noradrenergic neurons. However, co-immunolocalization studies revealed clearly that NTPDase3 immunoreactivity was not localized within the noradrenaline cells or terminals. In contrast, nearly all of the NTPDase3 immunopositive hypothalamic cells, and most fibers in the mid- and hindbrain, also expressed hypocretin-1/orexin-A. The overall pattern of expression and co-localization with hypocretin-1/orexin-A suggests that NTPDase3, by regulating the extracellular turnover of ATP, may modulate feeding, sleep-wake, and other behaviors through diverse homeostatic systems.

Estradiol affects axo-somatic contacts of neuroendocrine cells in the arcuate nucleus of adult rats.

It has been shown that gonadal steroids have the capacity to induce synaptic plasticity in certain areas of the nervous system. Previously we have demonstrated that due to the effect of estradiol there is a transient decrease in the number of GABAergic axo-somatic synapses in the arcuate nucleus. By using systemic application of the tracer Fluorogold we retrogradely labeled a subpopulation of arcuate neurons that project to the median eminence. We than applied the disector method for synapse quantification and found that these "hypophysiotropic neurons" receive less axo-somatic inputs. We found that 17beta-estradiol induced a decrease in the numerical density of axo-somatic contacts of these retrogradely-labeled neoroendocrine cells. Our data support the hypothesis that the hormonally driven morphological synaptic plasticity is neuron specific within the arcuate nucleus and plays a decisive role in the regulation of anterior pituitary.

Modular distribution of vasoactive intestinal polypeptide in the rat barrel cortex: changes induced by neonatal removal of vibrissae.

The distribution of vasoactive intestinal polypeptide-immunoreactive neuronal structures in the barrel cortex (posteromedial barrel subfield) of adult rats was analysed after unilateral removal of the vibrissal follicles of row C in neonatal rats. The hypothesis was tested whether the distribution of vasoactive intestinal polypeptide-immunoreactive structures depends on the normal anatomical organization of the specific sensory input. After three months survival the distribution of the vasoactive intestinal polypeptide-immunoreactive structures was morphometrically evaluated. This approach revealed alterations in the contralateral posteromedial barrel subfield, where the disappearance of barrel row C and a substantial increase in size mainly of barrel row D, but also of other rows could be detected. Increase in row D included both barrels and the interspace (septal segments between barrels in one row). As vasoactive intestinal polypeptide immunoreactivity of the barrel field was found previously to be localized in synaptic boutons involved in symmetric synapses, our present findings suggest that (i) the interspace is enriched in inhibitory vasoactive intestinal polypeptide-immunoreactive synapses as opposed to the excitatory thalamocortical input reaching the barrel hollow, (ii) the spatial distribution of the vasoactive intestinal polypeptide system in the barrel cortex is closely associated with the neuronal organization of the sensory input and reacts with a considerable plasticity to lesion-induced changes of the input, and (iii) the compensatory barrel hypertrophy in a row neighbouring the deafferented row involves an increasing number of vasoactive intestinal polypeptide-immunoreactive synapses per barrel.

Oestrogen-induced changes in the synaptology of the monkey (Cercopithecus aethiops) arcuate nucleus during gonadotropin feedback.

To assess their role in the regulation of gonadotropin secretion in primates, we determined the number of synaptic connections on gondotropin releasing hormone (GnRH)- and non-GnRH neurones of the arcuate nucleus of ovariectomized (OVX) and OVX plus oestradiol benzoate-treated African green monkeys. After 24 h (day 1), 48 h (day 2) and 8 days (day 8), we performed immunostaining for GnRH. Using electron microscopy, synapses on GnRH- and randomly selected non-GnRH neurones were counted and characterized according to the classification of Gray (symmetric/inhibitory or asymmetric/excitatory). Serum concentrations of oestradiol (OVX) needed to 232 pg/ml on day 1, 63 pg/ml on day 2 and 45 pg/ml on day 8. Concentrations of luteinizing hormone (LH) fell after ovariectomy to 9 microg/ml on day 1, surged to 93 microg/ml on day 2 and declined again by day 8. (a) Ten days after ovariectomy, there were no synapses on GnRH neurones, whereas non-GnRH cells received substantial inhibitory innervation and moderate excitatory input. (b) On day 1, GnRH neurones had highest numbers of inhibitory synapses, while inhibitory synapses on non-GnRH neurones decreased, whereas numbers of excitatory synapses remained relatively unchanged compared to OVX monkeys. (c) By day 2, synapses on GnRH neurones decreased, while synapses increased on non-GnRH cells compared to day 1. (d) On day 8, the most pronounced alteration on GnRH cells was an elevated inhibitory input while non-GnRH neurones received the fewest synapses compared to day 2. We conclude that during an oestrogen-induced LH surge, synapses on GnRH- and mixed non-GnRH neurones are differentially regulated. These findings suggest that oestrogen modulation of arcuate nucleus synapses may be important in the regulation of gonadotropin secretion in monkeys.

Estrogen effects on tyrosine hydroxylase-immunoreactive cells in the ventral mesencephalon of the female rat: further evidence for the two cell hypothesis of dopamine function.

The present study was undertaken to examine the differential effect of estrogen (E) on the expression of tyrosine hydroxylase (TH) in the substantia nigra compacta (SNc) and in two subdivisions of the ventral tegmental area in ovariectomized (ovx) and ovx plus estradiol benzoate (ovx+E)-treated female rats. Cell counting of TH-immunoreactive perikarya of the SNc, paranigral (PN) and interfascicular (IF) nucleus was performed and compared. Our findings demonstrate that E eliminated TH immunoreactivity from a number of midbrain neurons, while it seemingly did not affect it in others. This signifies a differential effect of E on ventral mesencephalic dopaminergic neurons.

Identification of a developmental gradient of estrogen receptor expression and cellular localization in the developing and adult female rat primary somatosensory cortex.

Immunohistochemistry was used to investigate the spatiotemporal distribution of estrogen receptor alpha and beta (ER alpha, ER beta) in the posteromedial barrel subfield (PMBS) of the cerebral cortex in developing and adult female rats. Counting of immunopositive cells in predefined areas from each layer of the PMBS showed that at PN3, ER alpha immunoreactivity (IR) was present in every cell, whereas ER beta-IR was not detected. At PN6, about 59% of the cells were ER alpha immunopositive and low levels of ER beta-IR were observed in scattered cells. At PN18 the proportion of ER alpha-IR cells decreased to 49%; however, ER beta-IR became widespread and was detected in 39% of cells. By PN25 only faint ER alpha-IR was observed and in the adults ER alpha-IR was not detected. In contrast, at PN25 and in adults, ER beta-IR was detected in about half the cells of the PMBS. Regarding the cellular localization of ER-IR, at PN3 an outside-in gradient of cytoplasmic to nuclear localization of ER alpha-IR was observed. At PN18 and in adults ER beta-IR was preferentially localized to the nucleus of principal neurons, and to the cytoplasm of small, stellate-shaped interneurons. Together, these observations reveal a developmental transition of ER expression in the PMBS; ER alpha is expressed during early development, ER alpha and ER beta are co-expressed at later developmental times, and only ER beta is expressed in adults. These changes in ER expression and localization suggest that ER alpha and ER beta may play important, but different roles in the formation and function of the PMBS region of the primary somatosensory cortex.

Retarded myelination in the lumbar spinal cord of piglets born with spread-leg syndrome.

Piglets born with spread-leg syndrome, a congenital weakness of the hindlimb adductors, were investigated to determine the site of lesion leading to limb impairment. Histological and immunohistochemical studies of the motor neuron unit showed no alterations but quantitative analysis revealed a reduction of axonal diameter and myelin sheath-thickness of the fibres innervating the adductors of the affected limbs. In the lumbar spinal cord a lack of myelination was observed in the tracts descending to the lower motor neurons. Recovery from the syndrome was accompanied by a catching-up of myelination with that of the controls. The spread-leg syndrome is due to a nutritional deficiency in the sow; thus it is assumed that the deficient maternal substances, mainly choline and methionine, are essential for the normal myelin production by spinal white matter oligodendrocytes of the fetus.

Estrogenic actions in the brain: estrogen, phytoestrogens, and rapid intracellular signaling mechanisms.

The endogenous gonadal steroid 17beta-estradiol (E2) plays an important role in the development, maturation, and function of a wide variety of reproductive and nonreproductive tissues, including those of the nervous system. The actions of E2 at target tissues can be divided into 1) long-term "genomic" actions that are mediated by intracellular estrogen receptor-induced changes in gene expression and 2) rapid actions that modulate a diverse array of intracellular signal transduction cascades. Environmental estrogens are compounds present in the environment that can mimic, and in some cases antagonize, the effects of endogenous estrogens. As a result of these actions, there is currently much interest within the scientific community regarding the relative benefits or threats associated with exposure to different environmental estrogens. Within the general public there is considerable acceptance of the benefits associated with increased use of "natural" estrogens as a component of a healthy diet and in postmenopausal women as an alternative to estrogen replacement therapies. First, this review will focus attention on the role of estrogens in the central nervous system by briefly discussing some of the known mechanisms through which estrogen's effects are mediated, focusing on rapid intracellular signaling mechanisms during neurodevelopment. Second, with the hope of bringing attention to an area of study that until recently has received little consideration, we will briefly discuss phytoestrogens and suggest that these compounds have the potential to influence rapid E2-induced mechanisms in the nervous system in ways that may result in modified brain functions.

Meningeal allografts of the 6-day-old rat pineal: a model for a pineal deprived of intracerebral innervation.

Pineals from 6-day-old rats were transplanted into an incised bed of the parietal cortex of adult rats, of which 29 survived 4-5 weeks after transplantation. The pinealocytes and capillaries in the grafts were comparable in structure to those in the control. Grafts were demarcated from the host cortical tissue by a double, meninx plus gland-capsule sheath through which no nerve ingrowth was seen into the graft from the host brain. On the other hand, sympathetic nerves originating from the cervical ganglia reached the grafted pineal along the perivascular spaces of blood vessels, as is the case in situ. On this basis. the present meningeal graft is thought to be a model of the pineal gland surviving without its intracerebral neural control.

AMPA receptors colocalize with neuropeptide-Y- and galanin-containing, but not with dopamine, neurons of the female rat arcuate nucleus: a semiquantitative immunohistochemical colocalization study.

It is well established that excitatory amino acid (EAA) neurotransmission is an essential component in the regulation of the gonadotropin-releasing hormone (GnRH) delivery system. However, the morphological interconnection of these systems is not fully understood. The objective of the present study was to determine whether or not alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors--as indicators of aspartate/glutamatergic innervation--are present in the major neuronal populations, such as the neuropeptide-Y-(NPY), galanin- (GAL) and tyrosine-hydroxylase- (TH) containing neurons of the arcuate nucleus (AN) of the female rat. Colocalization experiments using the "mirror" technique demonstrated that: (1) AN neurons containing GluR1 are also immunoreactive (IR) for GluR2/3; (2) 38.32% of AMPA-IR cells contain NPY and 31.72% of AMPA-containing neurons are also IR for GAL; in turn, 79.41% of NPY- and 56.19% of GAL-containing neurons are IR for AMPA receptors; none of the neurons are IR for both AMPA receptors and TH. These data suggest that an excitatory aspartate/glutamatergic input is implicated in the regulation of the examined neuropeptide-containing AN neurons but not in that of TH-IR cells of the same area.