Estrogen stimulates galanin expression within luteinizing hormone-releasing hormone-immunoreactive (LHRH-i) neurons via estrogen receptor-beta (ERbeta) in the female rat brain

The regulative effect of galanin family members on link of energy metabolism and reproduction

It is essential for the species survival that an efficient coordination between energy storage and reproduction through endocrine regulation. The neuropeptide galanin, one of the endocrine hormones, can potently coordinate energy metabolism and the activities of hypothalamic-pituitary-gonadal reproductive axis to adjust synthesis and release of metabolic and reproductive hormones in animals and humans. However, few papers have summarized the regulative effect of the galanin family members on the link of energy storage and reproduction as yet. To address this issue, this review attempts to summarize the current information available about the regulative effect of galanin, galanin-like peptide and alarin on the metabolic and reproductive events, with special emphasis on the interactions between galanin and hypothalamic gonadotropin-releasing hormone, pituitary luteinizing hormone and ovarian hormones. This research line will further deepen our understanding of the physiological roles of the galanin family in regulating the link of energy metabolism and reproduction.

Plasma galanin is a biomarker for severity of major depressive disorder

OBJECTIVE

This study investigated the association between plasma galanin level and depression severity.

METHODS

The severity of depression symptoms of 79 patients with major depressive disorder (MDD; 52 women and 27 men, 71 patients in onset, 8 in remission) was assessed using the 17-item Hamilton Depression Rating Scale. Venous fasting blood samples (5 mL) were taken from the 79 MDD patients, 35 healthy siblings, and 19 healthy controls, and plasma samples were prepared. Galanin levels in the plasma were measured by radioimmunoassay.

RESULTS

Plasma galanin in MDD patients was significantly higher than that of remission patients, healthy siblings, or healthy controls (P < 0.05) There was no significant difference between the healthy sibling and healthy control groups (P = 0.924). Plasma galanin of remission patients was also significantly higher than that of healthy controls (P < 0.05). There was no significant correlation between age and galanin levels in the 79 patients (r = 0.053, P = 0.646), nor was there a correlation between age and galanin levels when patients were stratified by gender (P > 0.05). There was a significant positive correlation between plasma galanin levels and depression severity in women MDD patients (r = 0.329, df = 42, P = 0.020), but not in men patients.

CONCLUSIONS

Plasma galanin levels may be an important biomarker for depression severity, especially in female patients.

Stimulation of food intake after central galanin is associated with arcuate nucleus activation and does not differ between genetically selected low and high body weight lines of chickens

Galanin, a 29 residue peptide found in the hypothalamus, causes orexigenic effects in a variety of species. In the present study, we investigated appetite-associated effects of galanin in chicks from lines which have been selected from a common founder population for either low or high body weight. The low line consists of some anorexic individuals and there are obese individuals in the high line. Central galanin caused increased food intake in both lines with the magnitude of response similar in both lines. We also quantified the number of c-Fos immunoreactive cells in several hypothalamic nuclei that are associated with appetite. Only the arcuate nucleus had an increase in the number of reactive cells, a response that was similar for both lines. From these results we concluded that selection for body weight likely did not affect galanin function on induction of feeding in either lines, and that the effect of galanin is associated with arcuate nucleus activation in chicks.

Co-localisation of kisspeptin with galanin or neurokinin B in afferents to mouse GnRH neurones

The gonadotrophin-releasing hormone (GnRH) secreting neurones, which form the final common pathway for the central regulation of reproduction, are directly targeted by kisspeptin (KP) via the G protein-coupled receptor, GPR54. In these multiple labelling studies, we used ovariectomised mice treated with 17β-oestradiol (OVX + E(2)) or vehicle (OVX + oil) to determine: (i) the ultrastructural characteristics of KP-immunoreactive (IR) afferents to GnRH neurones; (ii) their galanin or neurokinin B (NKB) content; and (iii) the co-expression of galanin or NKB with KP in the two major subpopulations of KP neurones located in the rostral periventricular area of the third ventricle (RP3V) and the arcuate nucleus (Arc). Electron microscopic investigation of the neuronal juxtapositions revealed axosomatic and axodendritic synapses; these showed symmetrical or asymmetrical characteristics, suggesting a phenotypic diversity of KP afferents. Heterogeneity of afferents was also demonstrated by differential co-expression of neuropeptides; in OVX + E(2) mice, KP afferents to GnRH neurones showed galanin-immunoreactivity with an incidence of 22.50 ± 2.41% and NKB-immunoreactivity with an incidence of 5.61 ± 2.57%. In OVX + oil animals, galanin-immunoreactivity in the KP afferents showed a major reduction, appearing in only 5.78 ± 1.57%. Analysis for co-localisation of galanin or NKB with KP was extended to the perikaryal level in animal models, which showed the highest KP incidence; these were OVX + E(2) females for the RP3V and OVX + oil females for the ARC. In the RP3V of colchicine-treated OVX + E(2) animals, 87.84 ± 2.65% of KP-IR neurones were galanin positive. In the Arc of the colchicine-treated OVX + oil animals, galanin immunoreactivity was detected in only 12.50 ± 1.92% of the KP expressing neurones. By contrast, the incidence of co-localisation with NKB in the Arc of those animals was 98.09 ± 1.30%. In situ hybridisation histochemistry of sections from OVX + E(2) animals identified galanin message in more than a third of the KP neurones in the RP3V (38.67 ± 11.57%) and in the Arc (42.50 ± 12.52%). These data suggest that GnRH neurones are innervated by chemically heterogeneous KP cell populations, with a small proportion deriving from the Arc group. The presence of galanin within KP axons innervating GnRH neurones and the oestrogen-dependent regulation of that presence add a new dimension to the roles played by galanin in the central regulation of reproduction.

Foetal hypothalamic and pituitary expression of gonadotrophin-releasing hormone and galanin systems is disturbed by exposure to sewage sludge chemicals via maternal ingestion

Animals and humans are chronically exposed to endocrine disrupting chemicals (EDCs) that are ubiquitous in the environment. There are strong circumstantial links between environmental EDC exposure and both declining human/wildlife reproductive health and the increasing incidence of reproductive system abnormalities. The verification of such links, however, is difficult and requires animal models exposed to 'real life', environmentally relevant concentrations/mixtures of environmental contaminants (ECs), particularly in utero, when sensitivity to EC exposure is high. The present study aimed to determine whether the foetal sheep reproductive neuroendocrine axis, particularly gondotrophin-releasing hormone (GnRH) and galaninergic systems, were affected by maternal exposure to a complex mixture of chemicals, applied to pasture, in the form of sewage sludge. Sewage sludge contains high concentrations of a spectrum of EDCs and other pollutants, relative to environmental concentrations, but is frequently recycled to land as a fertiliser. We found that foetuses exposed to the EDC mixture in utero through their mothers had lower GnRH mRNA expression in the hypothalamus and lower GnRH receptor (GnRHR) and galanin receptor (GALR) mRNA expression in the hypothalamus and pituitary gland. Strikingly, this, treatment had no significant effect on maternal GnRH or GnRHR mRNA expression, although GALR mRNA expression within the maternal hypothalamus and pituitary gland was reduced. The present study clearly demonstrates that the developing foetal neuroendocrine axis is sensitive to real-world mixtures of environmental chemicals. Given the important role of GnRH and GnRHR in the regulation of reproductive function, its known role programming role in utero, and the role of galanin in the regulation of many physiological/neuroendocrine systems, in utero changes in the activity of these systems are likely to have long-term consequences in adulthood and represent a novel pathway through which EC mixtures could perturb normal reproductive function.

Gonadotropin-positive pituitary tumors accompanied by ovarian tumors in aging female ERbeta-/- mice

At 2 years of age, 100% (23/23) of ERbeta(-/-) female mice have developed large pituitary and ovarian tumors. The pituitary tumors are gonadotropin-positive and the ovarian tumors are sex cord (less differentiated) and granulosa cell tumors (differentiated and estrogen secreting). No male mice had pituitary tumors and no pituitary or ovarian tumors developed in ERalpha(-/-) mice or in ERalphabeta(-/-) double knockout mice. The tumors have high proliferation indices, are ERalpha-positive, ERbeta-negative, and express high levels of nuclear phospho-SMAD3. Mice with granulosa cell tumors also had hyperproliferative endometria. The cause of the pituitary tumors appeared to be excessive secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus resulting from high expression of NPY. The ovarian phenotype is similar to that seen in mice where inhibin is ablated. The data indicate that ERbeta plays an important role in regulating GnRH secretion. We suggest that in the absence of ERbeta, the proliferative action of FSH/SMAD3 is unopposed and the high proliferation leads to the development of ovarian tumors. The absence of tumors in the ERalphabeta(-/-) mice suggests that tumor development requires the presence of ERalpha.

Galanin and the neuroendocrine axes

Galanin has diverse physiological functions, including nociception, arousal/sleep regulation, cognition, and many aspects of neuroendocrine activities that are associated with feeding, energy metabolism, thermoregulation, osmotic and water balance, and reproduction. This review will provide a brief overview of galanin action in some major neuroendocrine processes. Most of the recent data are about the role of galanin in the central regulation of food intake and energy metabolism, and to some extent, in the regulation of reproduction. It seems that galanin plays a modulatory role rather than a regulatory one in the central and peripheral branches of the neuroendocrine systems. In the hypothalamus, it functions as a neurotransmitter/ neuromodulator. In the pituitary and the peripheral endocrine glands, it acts via its receptors in a paracrine/autocrine fashion. The development of new, selective, and potent antagonists of GALRs should keep advancing our knowledge not only in the physiology of galanin but also in its pathophysiology.

Polymorphisms in the galanin gene are associated with symptom-severity in female patients suffering from panic disorder

BACKGROUND

Galanin (GAL) is a neuropeptide, which is expressed primarily in limbic nuclei in the brain and mediates miscellaneous physiological processes and behaviors. In animal studies, both the application of GAL and antagonism of its receptors have been shown to affect anxiety-like and depression-related behavior. In humans, intravenous administration of the neuropeptide galanin has been reported to have fast antidepressant efficacy. Furthermore, GAL is involved in hypothalamic-hypophysiotropic signalling and cosecreted with luteinizing hormone-releasing hormone (LHRH), possibly acting as a mediator of estrogen action.

METHODS

In this study six single nucleotide polymorphisms (SNPs) within the gene coding for GAL were analyzed for possible associations with diagnosis and severity of symptoms in 121 male and female patients suffering from panic disorder (PD).

RESULTS

Our results suggest an association between genetic variations in the GAL-gene and severity of PD-symptoms in female patients. The most pronounced effects could be observed for two haplotypes containing the closely linked, non-protein-coding SNPs rs948854 and rs4432027. Both polymorphisms are located within CpG-dinucleotides in the promoter region of GAL and thus might be involved in epigenetic regulation of the GAL-gene.

LIMITATIONS

A relatively small patient sample was analyzed in this study, the herein presented results need to be validated in independent studies.

CONCLUSIONS

The results of this study underline the potential of further genetic research concerning GAL and a possible role of this neuropeptide in the pathogenesis of female PD. In this regard, GAL and its receptors appear to be a promising target for pharmacological therapy of anxiety and affective disorders.

Differential Modulation of Gonadotropin Secretion by Selective Estrogen Receptor 1 and Estrogen Receptor 2 Agonists in Ovariectomized Ewes1

The objectives of this study were to determine whether activation of estrogen receptor 1 (ESR1; also known as ERalpha), or estrogen receptor 2 (ESR2; also known as ERbeta), or both are required to: 1) acutely inhibit secretion of LH, 2) induce the preovulatory-like surge of LH, and 3) inhibit secretion of FSH in ovariectomized (OVX) ewes. OVX ewes (n = 6) were administered intramuscularly 25 micrograms estradiol (E2), 12 mg propylpyrazoletriol (PPT; a subtype-selective ESR1 agonist), 21 mg diaprylpropionitrile (DPN; a subtype-selective ESR2 agonist), or PPT + DPN. Like E2, administration of PPT, DPN, or combination of the two rapidly decreased (P < 0.05) secretion of LH. Each agonist induced a gradual, prolonged rise in secretion of LH after the initial inhibition, but neither agonist alone nor the combined agonists was able to induce a "normal" preovulatory-like surge of LH similar to that induced by E2. Compared with E2-treated ewes, the beginning of the increase in secretion of LH occurred earlier (P < 0.01) in DPN-treated ewes, later (P < 0.05) in PPT-treated ewes, and at a similar interval in ewes receiving the combined agonist treatment. Like E2, PPT decreased (P < 0.05) secretion of FSH, but the duration of suppression was much longer in PPT-treated ewes. DPN did not alter secretion of FSH in this study. Modulation of the number of GnRH receptors by PPT and DPN was examined in primary cultures of ovine pituitary cells. In our hands, both PPT and DPN increased the number of GnRH receptors, but the dose of DPN required to stimulate synthesis of GnRH receptors was 10 times higher than that of PPT. We conclude that in OVX ewes: 1) ESR1 and ESR2 mediate the negative feedback of E2 on secretion of LH at the level of the pituitary gland, 2) ESR1 and ESR2 do not synergize or antagonize the effects of each other; however, they do interact to synchronize the beginning of the stimulatory effect of E2 on secretion of LH, 3) ESR1 and ESR2 may mediate at least partially the positive feedback of E2 on LH secretion by increasing the number of GnRH receptors, and 4) only ESR1 appears to be involved in the negative feedback of E2 on secretion of FSH.

Sexually dimorphic immunoreactivity of galanin and colocalization with arginine vasotocin in the chicken brain (Gallus gallus domesticus)

The bed nucleus of the stria terminalis medialis (BSTM) of adult chickens (Gallus gallus domesticus) was previously shown to synthesize arginine vasotocin (AVT) in males only and coincides spatially and temporally with steroid activity regulating male reproductive behavior. Galanin has been shown to be a potent modulator of the behavioral and neuroendocrine responses in the mammalian BSTM and in other sexually dimorphic brain regions. In the present study of adult chickens the morphological relationship of AVT and galanin was examined by immunohistochemical analysis of two limbic structures, the BSTM and the lateral septum (SL). The analysis also included the hypothalamic nuclei supraopticus (SON) and paraventricularis (PVN). In males galanin and AVT were both synthesized in the BSTM, while in females neither galanin nor AVT was present. Furthermore, in the males galanin and AVT were colocalized in the majority of neurons within BSTM and in fibers of the SL. In both sexes galanin neurons in the PVN were scattered between the distinct clusters of AVT neurons and there was no colocalization of galanin and AVT in single PVN neurons. Furthermore, AVT immunoreactivity was significantly higher in the SON than in the PVN in both sexes. In the SON, galanin was colocalized with AVT in significantly more neurons in hens than in males (P </= 0.05%). These results demonstrate that the distributions of galanin and AVT are sexually dimorphic not only in the limbic BSTM but also in the hypothalamic SON. It is tempting to speculate that galanin in the SON is involved in regulation of oviposition as an AVT-dependent female-specific function.

Galanin and its receptors: introduction to the Third International Symposium, San Diego, California, USA, 21-22 October 2004

The Third Galanin Symposium presented many different and exciting results on galanin research reflecting a major progress since the previous symposium in 1998. A major impression was the many possible relationships of galaninergic mechanisms to important brain functions such as development, cognition and ageing as well as many aspects related to a wide spectrum of diseases, including Alzheimer's disease, anxiety/depression, addiction, obesity, pain and tumour growth. These studies were based on an extensive armament of methodologies including various strains of transgenic mice. Unfortunately, the pharmaceutical industry had only a minor participation. Nevertheless, exciting developments in the generation of agonists and antagonists are emerging, providing hope that we at the next symposium will be able to validitate many of the challenging hypotheses concerning galanin and disease with the help of pharmacological tools.