Galanin in the bed nucleus of the stria terminalis and medial amygdala of the rat: lack of sexual dimorphism despite regulation of gene expression across puberty

Responsiveness of pituitary to galanin throughout the reproductive cycle of male European sea bass (Dicentrarchus labrax)

The neuropeptide galanin (Gal) is a putative factor regulating puberty onset and reproduction through its actions on the pituitary. The present study investigated the pituitary responsiveness to galanin and the patterns of galanin receptors (Galrs) expression throughout the reproductive cycle of two years old male European sea bass (Dicentrarchus labrax), an important aquaculture species. Quantitative analysis of pituitary and hypothalamus transcript expression of four galr subtypes revealed differential regulation according to the testicular developmental stage, with an overall decrease in expression from the immature stage to the mid-recrudescence stage. Incubation of pituitary cells with mammalian 1-29Gal peptide induced significant changes in cAMP concentration, with sensitivities that varied according to the testicular development stages. Furthermore 1-29Gal was able to stimulate both follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) release from pituitary cell suspensions. The magnitude of the effects and effective concentrations varied according to reproductive stage, with generalized induction of Fsh and Lh release in animals sampled in January (full spermiation). The differential expression of galrs in pituitary and hypothalamus across the reproductive season, together with the differential effects of Gal on gonadotropins release in vitro strongly suggests the involvement of the galaninergic system in the regulation the hypothalamus-pituitary-gonad axis of male sea bass. This is to our knowledge the first clear evidence for the involvement of galanin in the regulation of reproduction in non-mammalian vertebrates.

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.

Neonatal MeCP2 is important for the organization of sex differences in vasopressin expression

Several neurodevelopmental disorders are marked by atypical Methyl-CpG-binding protein 2 (MeCP2) expression or function; however, the role of MeCP2 is complex and not entirely clear. Interestingly, there are sex differences in some of these disorders, and it appears that MeCP2 has sex-specific roles during development. Specifically, recent data indicate that a transient reduction in MeCP2 within developing amygdala reduces juvenile social play behavior in males to female-typical levels. These data suggest that MeCP2 within the amygdala is involved in programming lasting sex differences in social behavior. In the present study, we infused MeCP2 or control siRNA into the amygdala of male and female rats during the first three days of postnatal life in order to assess the impact of a transient reduction in MeCP2 on arginine vasopressin (AVP), a neural marker that is expressed differentially between males and females and is linked to a number of social behaviors. The expression of AVP, as well as several other genes, was measured in two-week old and adult animals. Two-week old males expressed more AVP and galanin mRNA in the amygdala than females, and a transient reduction in MeCP2 eliminated this sex difference by reducing the expression of both gene products in males. A transient reduction in MeCP2 also decreased androgen receptor (AR) mRNA in two-week old males. In adulthood, control males had more AVP-immunoreactive (AVP-ir) cells than females in the centromedial amygdala (CMA), bed nucleus of the stria terminalis (BST) and in the fibers that project from these cells to the lateral septum (LS). A transient reduction in MeCP2 eliminated this sex difference. Interestingly, there were no lasting differences in galanin or AR levels in adulthood. Reducing MeCP2 levels during development did not alter estrogen receptorα, neurofilament or Foxg1. We conclude that a transient reduction in MeCP2 expression in the developing male amygdala has a transient impact on galanin and AR expression but a lasting impact on AVP expression, highlighting the importance of MeCP2 in organizing sex differences in the amygdala.

Differential activity by polymorphic variants of a remote enhancer that supports galanin expression in the hypothalamus and amygdala: implications for obesity, depression and alcoholism

The expression of the galanin gene (GAL) in the paraventricular nucleus (PVN) and in the amygdala of higher vertebrates suggests the requirement for highly conserved, but unidentified, regulatory sequences that are critical to allow the galanin gene to control alcohol and fat intake and modulate mood. We used comparative genomics to identify a highly conserved sequence that lay 42 kb 5' of the human GAL transcriptional start site that we called GAL5.1. GAL5.1 activated promoter activity in neurones of the PVN, arcuate nucleus and amygdala that also expressed the galanin peptide. Analysis in neuroblastoma cells demonstrated that GAL5.1 acted as an enhancer of promoter activity after PKC activation. GAL5.1 contained two polymorphisms; rs2513280(C/G) and rs2513281(A/G), that occurred in two allelic combinations (GG or CA) where the dominant GG alelle occurred in 70-83 % of the human population. Intriguingly, both SNPs were found to be in LD (R(2) of 0.687) with another SNP (rs2156464) previously associated with major depressive disorder (MDD). Recreation of these alleles in reporter constructs and subsequent magnetofection into primary rat hypothalamic neurones showed that the CA allele was 40 % less active than the GG allele. This is consistent with the hypothesis that the weaker allele may affect food and alcohol preference. The linkage of the SNPs analysed in this study with a SNP previously associated with MDD together with the functioning of GAL5.1 as a PVN and amygdala specific enhancer represent a significant advance in our ability to understand alcoholism, obesity and major depressive disorder.

Sex-specific patterns of galanin, cholecystokinin, and substance P expression in neurons of the principal bed nucleus of the stria terminalis are differentially reflected within three efferent preoptic pathways in the juvenile rat

Neurons in the principal bed nucleus of the stria terminalis (BSTp) integrate hormonal and sensory information associated with reproduction and transmit this information to hypothalamic nuclei that regulate neuroendocrine and behavioral functions. The neuropeptides galanin (GAL), cholecystokinin (CCK), and substance P (SP) are highly expressed in BSTp neurons and are differentially regulated by sex steroids. The current experiments investigated whether developmental or peripubertal hormone-mediated changes in GAL, CCK, and SP expression are reflected within efferent pathways to the preoptic structures that regulate gonadotropin secretion and sexual behavior. Anterograde labeling of projections from the BSTp of male and female juvenile rats combined with immunohistochemical labeling of GAL-, CCK-, and SP-containing fibers in the anteroventral periventricular preoptic nucleus (AVPV) and the central and medial divisions of the medial preoptic nucleus (MPNc, MPNm, respectively) revealed unique sex differences in each region. In the AVPV, Phaseolus vulgaris leucoagglutinin-labeled fibers were seen at a greater density in males than in females, and higher percentages of these fibers contained GAL in males than in females. In contrast, fibers projecting from the BSTp to the MPNc were more likely to contain SP in females than in males. Treatment of gonadectomized, peripubertal males and females with exogenous testosterone and estradiol did not alter the densities of GAL-, CCK-, or SP-containing fibers in any of the three brain areas examined. Collectively, these results suggest that patterns of neuropeptide expression in BSTp projections are established during development, resulting in a distinct, stable, and sex-specific chemoarchitectural profile for each projection pathway.

Opioid receptor modulation of a metabolically sensitive ion channel in rat amygdala neurons

We have used single-channel patch-clamp recordings to study opiate receptor effects on freshly dissociated neurons from the rat amygdalohippocampal area (also called the posterior nucleus of the amygdala), an output nucleus of the amygdala implicated in appetitive behaviors. Dissociated cells included a distinct subpopulation that was 30-40 micrometer in diameter, multipolar or pyramidal in shape, and immunoreactive for neuron-specific enolase, mu opioid receptors, and galanin. In whole-cell perforated-patch recordings, these cells responded to low concentrations of mu opioid agonists with a hyperpolarization. In cell-attached single channel recordings, these cells expressed a large variety of K(+)-permeable ion channels, including 20-100 pS inward rectifiers and 150-200 pS apparent Ca(2+)-activated K(+) channels, none of which appeared sensitive to the presence of opioid drugs. In contrast, a 130 pS inwardly rectifying channel was selectively activated by mu opioid receptors in this same subpopulation of cells and was active only in the presence of opioid agonists, and inhibited in the presence of antagonists. Channels identical to the 130 pS channel in conductance and voltage sensitivity were activated in the absence of opioids, when the cells were treated with glucose-free medium or with the metabolic inhibitor rotenone. The sulfonylurea drug tolbutamide inhibited 130 pS channel openings elicited by opioids. Thus, a subpopulation of amygdala projection neurons expresses a metabolically sensitive ion channel that is selectively modulated by opiate receptors. This mechanism may allow opioid neurotransmitters to regulate ingestive behaviors, and thus, opiate drugs to influence reward pathways.

Invited review: Estrogens effects on the brain: multiple sites and molecular mechanisms

Besides their well-established actions on reproductive functions, estrogens exert a variety of actions on many regions of the nervous system that influence higher cognitive function, pain mechanisms, fine motor skills, mood, and susceptibility to seizures; they also appear to have neuroprotective actions in relation to stroke damage and Alzheimer's disease. Estrogen actions are now recognized to occur via two different intracellular estrogen receptors, ER-alpha and ER-beta, that reside in the cell nuclei of some nerve cells, as well as by some less well-characterized mechanisms. In the hippocampus, such nerve cells are sparse in number and yet appear to exert a powerful influence on synapse formation by neurons that do not have high levels of nuclear estrogen receptors. However, we also find nonnuclear estrogen receptors outside of the cell nuclei in dendrites, presynaptic terminals, and glial cells, where estrogen receptors may couple to second messenger systems to regulate a variety of cellular events and signal to the nuclear via transcriptional regulators such as CREB. Sex differences exist in many of the actions of estrogens in the brain, and the process of sexual differentiation appears to affect many brain regions outside of the traditional brain areas involved in reproductive functions. Finally, the aging brain is responsive to actions of estrogens, which have neuroprotective effects both in vivo and in vitro. However, in an animal model, the actions of estrogens on the hippocampus appear to be somewhat attenuated with age. In the future, estrogen actions over puberty and in pregnancy and lactation should be further explored and should be studied in both the hypothalamus and the extrahypothalamic regions.

Axon terminals containing tyrosine hydroxylase- and dopamine-beta-hydroxylase immunoreactivity form synapses with galanin immunoreactive neurons in the lateral division of the bed nucleus of the stria terminalis in the rat

Catecholaminergic projections from brainstem sources to the bed nucleus of the stria terminalis play a central role in the neurochemically mediated modulation/regulation of stress response. The lateral division of the bed nucleus of the stria terminalis (BSTL) exhibits several galanin immunoreactive (ir) neurons that are also central in the modulatory control of acute stress responses. The distribution of galaninergic nervous structures overlaps with that of the dopaminergic and noradrenergic axon terminals in the BSTL. Since both monoamines and galanin regulate/modulate the central regulatory pathways of endocrine, behavioral and physiological responses during stress, the aim of this study was to demonstrate synaptic interaction between galanin-ir nervous structures and fiber terminals immunopositive for dopamine or noradrenaline in the BSTL, thereby providing morphological data to understand better the significance of catecholamine-galanin interactions in brain areas responding to stressful stimuli. Double-labeling immunohistochemistry applied both at light and electron microscopic levels made it possible to demonstrate synaptic interactions between galanin-ir nervous structures and axon terminals immunopositive for either dopamine or noradrenaline. The dopaminergic fiber terminals innervated galanin-ir cells and dendrites in the laterodorsal division of the bed nucleus of the stria terminalis (BST), whereas the noradrenergic axons contacted galaninergic neurons and dendrites in the lateroventral BST. In this study, interactions between monoamines and galanin-ir structures were demonstrated in the BSTL which can be central in the modulatory control of the major stress regulatory pathway of the limbic-hypothalamo-pituitary-adrenal axis.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

Effects of estrous cyclicity on the expression of the galanin receptor Gal-R1 in the rat preoptic area: a comparison with the male

Variations in the number of galanin receptor (Gal-R1)-expressing cells and levels of Gal-R1 messenger RNA (mRNA) were determined in the preoptic area in intact female rats throughout the phases of the estrous cycle and compared with those in the male. Female and male Wistar rats were fixed by perfusion with 4% paraformaldehyde. Cryostat sections were hybridized with a 35S-labeled antisense Gal-R1 riboprobe. The number of Gal-R1 mRNA-expressing cells was lower in the rostral preoptic area than in the medial preoptic area. During the estrous cycle, the highest number of Gal-R1 mRNA-expressing cells in the rostral preoptic region was detected at 0800 h on proestrus, whereas in the medial preoptic area, the maximum number was observed at 1800 h on estrus. Gal-R1 mRNA levels in individual cells were low during diestrus and increased at estrus in both areas. In the male, the number of mRNA-expressing cells and the hybridization signal were significantly lower than those in females during estrus. The results demonstrate that Gal-R1 gene expression in the preoptic area varies during the estrous cycle and is low in males. Short term treatment of ovariectomized rats with estradiol plus progesterone caused significantly decreased preoptic Gal-R1 mRNA levels compared with those after treatment with estrogen only. These observations suggest that in the preoptic area, expression of Gal-R1 is influenced by progesterone. The variation in Gal-R1 expression is likely to influence the extent to which galanin can influence the preoptic cells implicated in the control of neighboring GnRH cells.

Vasopressin and galanin mRNAs coexist in the nucleus of the horizontal diagonal band: a novel site of vasopressin gene expression

Vasopressin (VP) neurons have been identified in several brain regions where VP has been hypothesized to act as a neurotransmitter or neuromodulator. In many sites, VP is colocalized with the neuropeptide galanin (GAL). Here, using single in situ hybridization histochemistry, we have identified a novel group of neurons within the nucleus of the horizontal diagonal band of Broca (HDB) that express the VP gene and have assessed the distribution of these cells in adult male and female rats (90 days old, n = 7/group). VP mRNA-expressing neurons were scattered throughout the rostrocaudal extent of the HDB, and the number of VP neurons detected unilaterally ranged from 1 to 17 cells per 20 microns section. Using double in situ hybridization histochemistry on alternate sections, we have assessed the number of cells expressing VP and/or GAL mRNA in the diagonal band and have determined the extent of their colocalization. Approximately 50% of all VP-expressing neurons in the HDB coexpressed GAL mRNA, and 33% of GAL-expressing neurons in this region coexpressed VP mRNA. No sex differences were detected in the number of neurons expressing either VP or GAL mRNA or in the incidence of coexpression of VP and GAL mRNAs in this region. VP neurons in the HDB exhibited a low level of expression, and cellular VP mRNA content did not differ between male and female rats. However, sex differences were present in the bed nucleus of the stria terminalis (BNST) of these same rats.(ABSTRACT TRUNCATED AT 250 WORDS)