Testosterone regulates galanin gene expression in the bed nucleus of the stria terminalis

Galanin isoforms by alternative splicing: Structure, expression, and immunohistochemical location in the gonads of European sea bass

Galanin (Gal) is a neuropeptide with multiple functions that is widely expressed in the central and peripheral nervous systems of vertebrates. Anatomical and functional evidence suggests a possible role in regulating reproduction in fishes. To test this possibility, we have isolated and characterized two gal alternative transcripts in European sea bass (Dicentrarchus labrax) that encode two prepropeptides, respectively of 29 (gal_MT853221) and 53 (gal_MT853222) amino acids. The two gal transcripts are highly expressed in brain, pituitary and gonads, and appear to be differentially regulated in males and females. In males, gal_MT853222 in the hypothalamus and gal_MT853221 in the pituitary were downregulated with the progression of spermatogenesis (stages I-III). Both transcripts are downregulated in testicles of 1-year (precocious) and 2-year spermiating males compared to immature fish of the same age. Gal peptides and receptors are expressed throughout ovarian development in the hypothalamic-pituitary-gonadal (HPG) axis of females. In the testis, immunoreactive Gal-29 and Gal-53 peptides were detected in blood vessels and Leydig cells during the spermatogenesis stages I-III but Gal immunostaining was barely undetected in more advanced stages. In the ovary, both peptides localized in interstitial cells and blood vessels and in theca cells surrounding the maturing oocytes. The immunolocalization of galanin in Leydig and theca cells suggests a possible role in steroid production regulation. The different pattern of gal expression and Gal localization in the testis and ovary may suggest the possibility that androgens and estrogens may also regulate Gal gene transcription and translation. Altogether, this study showed evidence for the possible involvement of locally produced Gal in gametogenesis and that its production is differentially regulated in male and female gonads.

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.

Effects of neural androgen receptor disruption on aggressive behavior, arginine vasopressin and galanin systems in the bed nucleus of stria terminalis and lateral septum

In the present study, we investigated the role of the androgen receptor (AR) in the nervous system in the regulation of aggressive behavior and arginine vasopressin and galanin systems by testosterone. For this purpose, we used a conditional mouse line selectively lacking AR gene in the nervous system, backcrossed onto the C57BL/6J strain. Adult males were gonadectomized and supplemented with similar amounts of testosterone. When tested on two consecutive days in the resident intruder paradigm, fewer males of the mutant group exhibited aggressive behavior compared to their control littermates. In addition, a high latency to the first offensive attack was observed for the few animals that exhibited fighting behavior. This alteration was associated with a normal anogenital chemoinvestigation of intruder males. In olfactory discrimination tasks, sexual experience enhanced preference towards female-soiled bedding rather than male-soiled bedding and estrus females rather than intact males, regardless of genotype. This indicated that the behavioral alteration induced by neural AR mutation occurs in brain areas located downstream from the olfactory bulb. Quantification of the sexually dimorphic cell populations expressing preprovasopressin and galanin mRNAs in the bed nucleus of stria terminalis (BNST) and vasopressin-neurophysin 2 and galanin immunoreactivity in the lateral septum showed no significant differences between the two genotypes. The present findings indicate that the neural AR is required in the expression of aggressive behavior but not in the sexual differentiation of AVP and galanin cell number in the BNST and fiber immunoreactivity in the lateral septum. They also suggest that AR in the nervous system could mediate activational effects of testosterone in the regulation of aggressive behavior during adulthood.

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.

Neuroanatomical projections of the species-specific tyrosine hydroxylase-immunoreactive cells of the male prairie vole bed nucleus of the stria terminalis and medial amygdala

The principal nucleus of the bed nucleus of the stria terminalis (BSTpr) and posterodorsal part of the medial amygdalar nucleus (MEApd) are densely interconnected sites transmitting olfactory information to brain areas mediating sociosexual behaviors. In male prairie voles (Microtus ochrogaster), the BSTpr and MEApd contain hundreds of cells densely immunoreactive for tyrosine hydroxylase (TH). Such tremendous numbers of TH-immunoreactive (TH-ir) cells do not exist in other rodents examined, and studies from our laboratory suggest these cells may be part of a unique chemical network necessary for monogamous behaviors in prairie voles. To obtain information about how these TH-ir cells communicate with other sites involved in social behaviors, we first used biotinylated dextran amine (BDA) to determine sites that receive BSTpr efferents and also contain TH-ir fibers. Only in the medial preoptic area (MPO) and MEApd did we find considerable comingling of BDA-containing and TH-ir fibers. To examine if these sites receive input specifically from BSTpr TH-ir cells, the retrograde tracer Fluorogold was infused into the MPO or MEApd. Almost 80% of TH-ir projections to the MPO originated from the BSTpr or MEApd, involving about 40% of all TH-ir cells in these sites. In contrast, the MEApd received almost no input from TH-ir cells in the BSTpr, and received it primarily from the ventral tegmental area. Retrograde tracing from the BSTpr itself revealed substantial input from MEApd TH-ir cells. Thus, the male prairie vole brain contains a species-specific TH-ir network involving the BSTpr, MEApd, and MPO. By connecting brain sites involved in olfaction, sociality and motivation, this network may be essential for monogamous behaviors in this species.

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.

The bed nucleus of the stria terminalis in the Syrian hamster (Mesocricetus auratus): absence of vasopressin expression in standard and wild-derived hamsters and galanin regulation by seasonal changes in circulating sex steroids

The bed nucleus of the stria terminalis (BNST) is a nucleus of the forebrain highly sensitive to sex steroids and containing vasopressin neurons implicated in several social- and reproduction-related behaviours such as scent-marking, aggression, pair bonding and parental behaviour. Sexually dimorphic vasopressin expression in BNST neurons has been reported in almost all rodents, with the notable exception of the Syrian hamster. In this species, vasopressin expression is completely absent in the BNST. Because almost all Syrian hamsters used in research are derived from a very small breeding stock captured in 1930, we compared commercially available Syrian hamsters with a recently captured, wild-derived breeding stock. We checked for vasopressin expression using in situ hybridization and immunohistochemistry. Vasopressin expression in BNST neurons was completely absent in both breeding stocks, confirming the absence of BNST vasopressin expression in Mesocricetus auratus and ruling out a breeding artefact. Because vasopressin expression in BNST neurons appears to be strictly dependent on circulating sex steroids, the absence of vasopressin expression in Syrian hamster BNST neurons might be due to an insensitivity of these neurons to sex steroids. BNST vasopressin neurons also express galanin. Although galanin expression in the BNST is not sexually dimorphic in the Syrian hamster, it appears to be regulated by sex steroids. In the Djungarian hamster, photoperiodically driven seasonal variations of circulating sex steroids result in a seasonal rhythm of galanin expression in BNST neurons. We analysed the sex steroid dependence of galanin expression in the Syrian hamster. Castration and short photoperiod-induced sexual quiescence both resulted in downregulation of galanin mRNA in cell bodies (BNST) and immunoreactivity in the fibres (lateral septum). Testosterone supplementation of short photoperiod-adapted animals was able to restore galanin expression. Thus Syrian hamster BNST neurons respond to circulating sex steroids and their seasonal variations as observed in other rodent species.

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.

[Characteristics of galanin and vasoactive intestinal peptide immunoreactivity in the rat amygdala complex]

INTRODUCTION

Morphological features and morphometric parameters of galanin (GAL) and vasoactive intestinal peptide (VIP) immunoreactive neurons and neuronal fibres were studied in all nuclei of adult male rat amygdala.

MATERIAL AND METHODS

After perfusion and fixation, rat brains were immunohistochemically stained with antibodies against GAL and VIP and then visualized by avidin-biotin-peroxidase complex.

RESULTS AND DISCUSSION

The greatest number of galanin-immunoreactive neurons were identified in the medial part of the central nucleus and in the dorsal part of the medial nucleus. In the first case, most neurons were bipolar (37%), and in the second, they were ovoid (45%). GAL-immunoreactive fibers were identified in the medial nucleus, "bed nucleus" of the accessory olfactory tract, fiontal cortical nucleus, amygdalo-hippocampal area and basolateral nucleus. VIP-immunoreactive neurons were diffusely distributed in more nuclei than the previous, mostly in the lateral, basolateral, and basomedial nucleus. They were mostly ovoid (40%). VIP-immunoreactive fibers were observed in the lateral part oJ'the central nucleus, while long and radially oriented fibers were present in the frontal and dorsal cortical nucleus.

CONCLUSION

By distribution analysis of GAL and VIP immunoreactive neurons and fibers, and according to literature data, it can be assumed that the medial part of the central nucleus receives VIP fibers from other parts of the amygdaloid body, and then sends GAL fibers to the medial nucleus.

Androgens regulate the sexually dimorphic production of co-contained galanin and cholecystokinin in lumbar laminae VII and X neurons

A population of rat lumbar laminae VII and X putative spinothalamic (STT) neurons that co-contain cholecystokinin-8 (CCK) and galanin (GAL) are sexually dimorphic. Males have a significantly greater number of these neurons, as well as having greater optical densities for both neuropeptides than females. Optical densities for GAL and CCK immunoreactivities in these lumbar neurons in rats that have the testicular feminization mutation (Tfm) are not significantly different from females; however, the number of these lumbar neurons in Tfm rats is significantly smaller than in females. These data suggest that androgens, as well as functional androgen receptors (that Tfm rats lack), are necessary for the establishment of these sexual dimorphisms. Functionally, these CCK- and GAL-containing neurons in the deep lumbar laminae may contribute to the establishment of known sex differences in the affective component of somatic and visceral nociception, as well as the sexually dimorphic nature of some pelvic diseases, e.g., irritable bowel syndrome or cystitis.

Targeting steroid receptor coactivator-1 expression with locked nucleic acids antisense reveals different thresholds for the hormonal regulation of male sexual behavior in relation to aromatase activity and protein expression

Steroid receptors such as the androgen and estrogen receptors require the presence of several proteins, known as coactivators, to enhance the transcription of target genes. The first goal of the present study was to define the role of SRC-1 on the steroid-dependent expression of the aromatase protein and its activity in male Japanese quail. The second goal was to analyze the rapid plasticity of the POM following antisense treatment interruption. We confirm here that the inhibition of SRC-1 expression by daily intracerebroventricular injections of locked nucleic acid antisense oligonucleotides in the third ventricle at the level of the preoptic area-hypothalamus (HPOA) significantly reduces testosterone-dependent male sexual behavior. In the first experiment, aromatase protein expression in HPOA was inhibited in SRC-1-depleted males but the enzymatic activity remained at the level measured in controls. We observed in the second experiment a recovery of the behavioral response to testosterone treatment after interruption of the antisense injection. However, several morphological characteristics of the POM were not different between the control group, the antisense-treated birds and antisense-treated birds in which treatment had been discontinued 3 days earlier. Antisense was also less effective in knocking-down SRC-1 in the present experiments as compared to our previous study. An analysis of this variation in the degree of knock-down of SRC-1 expression suggests dissociation among different aspects of steroid action on brain and behavior presumably resulting from the differential sensitivity of behavioral and neurochemical responses to the activation by testosterone and/or its estrogenic metabolites.

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.

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.

Axon terminals containing CGRP-immunoreactivity form synapses with CRF- and Met-enkephalin-immunopositive neurons in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The lateral division of the bed nucleus of the stria terminalis (BSTL) is an important forebrain structure that relays information between limbic structures and the hypothalamus. The BSTL displays a very dense calcitonin gene-related peptide-immunoreactive (-ir) fiber terminal network, and contains a substantial number of the corticotropin releasing factor (CRF)-ir neurons. Several Met-enkephalin-ir perikarya have also been observed in the BSTL. The distributions of CRF- and Met-enkephalin-ir neurons and that of the calcitonin gene-related peptide (CGRP)-ir axon terminals overlap within the BSTL, suggesting synaptic connections between CRF- and Met-enkephalin-ir neurons and axon terminals immunoreactive for CGRP. Double staining immunohistochemistry revealed that CGRP-ir axon terminals were within close proximity to dendrites or perikarya of corticotropin releasing factor and Met-enkephalin-ir neurons. When viewed at the electron microscopic level, axodendritic or axosomatic synapses between CGRP-ir fiber terminals and neurons immunoreactive for CRF and Met-enkephalin were detected. Most of the CRF-ir neurons project to brainstem centers, which modulate the physiological changes accompanying stress, whereas the Met-enkephalin-ir perikarya are most likely interneurons that often colocalize with GABA. The parabrachial nucleus, a vital autonomic center, is the primary source of CGRP-ir fiber terminals to the BSTL. The synaptic contacts between the CGRP axon terminals and CRF- and Met-enkephalin-ir neurons underlie the importance of connections between autonomic brainstem centers and BSTL, which can be fundamental in the modulatory control of endocrine, physiological and behavioral responses during stress.

Sex differences in the response of postnatal rat lumbar lamina X neurons to exogenously applied galanin recorded in vitro

Intracellular recording techniques were used in a horizontal slice preparation of postnatal rat lumbar spinal cord to compare the responses of male and female lamina X neurons to exogenously applied galanin. Although there was no significant sex difference in the resting membrane potential or input resistance of neurons, superfusion of galanin 1-16 (1 microM) produced a membrane hyperpolarization that averaged -5.3 mV in males and only -2.0 mV in females. The galanin-induced membrane hyperpolarization of lamina X neurons was accompanied by an inconsistent and varied change in input resistance. No depolarizing effect of galanin was detected in either sex. Galanin did not significantly alter the spike shape, amplitude, after hyperpolarization or locally evoked synaptic responses. The more than 2.5 fold significant sex difference in response to galanin occurred at a developmental timepoint at which lamina X expressed a comparably higher amount of galanin-like immunoreactivity in males compared to females. These results provide the first indication of a sex difference in the response of lamina X neurons to any neuropeptide. Given the antinociceptive role of galanin in the spinal cord, these results raise the possibility for the presence of distinct physiological and anatomical substrates for sex-dependent differences in nociceptive processing in lamina X of the lumbosacral spinal cord.

Expression of GalR1 and GalR2 galanin receptor messenger ribonucleic acid in proopiomelanocortin neurons of the rat arcuate nucleus: effect of testosterone

Previous studies have shown that galanin-containing fibers make synaptic contacts with POMC neurons in the arcuate nucleus. However, the ability of POMC neurons to express galanin receptors has never been assessed. The present study was designed to investigate whether POMC neurons express galanin receptor messenger RNA (mRNA) and whether testosterone could modulate galanin receptor gene expression. A dual-labeling in situ hybridization histochemistry, using 35S-labeled (galanin receptors GalR1 or GalR2) and digoxigenin-labeled (POMC) riboprobes, was performed on brain sections from intact, castrated, and testosterone-replaced adult male rats. For analysis, the arcuate nucleus was divided into four rostro-caudal areas. The results revealed that both GalR1 and GalR2 mRNAs were expressed in POMC neurons. Most POMC neurons expressing galanin receptor mRNAs were found in the rostral parts of the nucleus. Castration reduced the labeling density of galanin receptor mRNAs in POMC neurons, and testosterone prevented the effects of castration in all rostro-caudal subdivisions of the arcuate nucleus. Taken together, these data indicate that galanin can directly modulate the activity of POMC neurons, via an action on GalR1 or GalR2 receptors, particularly in the rostral-arcuate nucleus. In addition, testosterone can modulate the expression of GalR1 and GalR2. Because POMC neurons located in the rostral part of the nucleus are known to project preferentially to the preoptic area, POMC neurons expressing the galanin receptor genes may play an important role in the regulation of the GnRH neuroendocrine axis.

Galanin immunoreactivity in mouse basal forebrain: sex differences and discrete projections of galanin-containing cells beyond the blood-brain barrier

The distribution of galanin-immunoreactive (GAL-IR) cell bodies in the basal forebrain of mice was investigated. The overall pattern of staining for GAL in the area of brain analyzed was similar to that reported in other species with noticeable variations. Distinctive groups of GAL-IR cells were present in the bed nucleus of stria terminalis (BNST), supraoptic nucleus, retrochiasmatic supraoptic nucleus (SOR), magnocellular paraventricular nucleus, arcuate nucleus (ARC) and the nucleus circularis which is one of the cell groups belonging to the accessory magnocellular system. Comparison of the number of GAL-IR cells between the sexes indicated sexual dimorphism in the BNST, SOR and the ARC. As compared with female mice, the mean number of GAL-IR cells/section in the BNST and the SOR was higher and that in the ARC was lower in the males. Unlike in rats, the preoptic area contained mostly scattered GAL-IR cell bodies. Intraperitoneal injection of the retrograde tracer fluoro-gold in male mice resulted in uptake of fluoro-gold by selective GAL-IR cell groups in the basal forebrain suggesting that only some of these cell groups may project outside the blood-brain barrier whereas others may be involved in intracerebral neural transmission.

Absence of vasopressin expression by galanin neurons in the golden hamster: implications for species differences in extrahypothalamic vasopressin pathways

In golden hamsters, there is a complete absence of the small diameter vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BST) and medial amygdala (Me) which have been shown to exhibit steroid dependency and sexual dimorphism in many other rodent species. In rats, VP in the BST/Me is always colocalized with the neuropeptide galanin (GAL) and the sex difference in VP cell number appears to result from a sex difference in the number of GAL neurons which coexpress VP. Likewise, we reasoned that the species difference in extrahypothalamic VP pathways present in the golden hamster could result from a reduced coexpression of VP by GAL neurons in these regions. Here, we used in situ hybridization histochemistry to determine whether GAL mRNA expressing neurons are present in the BST and Me of golden hamsters despite the absence of VP expression in these regions. In addition, we have used slice binding and receptor autoradiography to identify specific GAL binding sites in the lateral septum, a probable target region of BST/Me neurons, and in situ hybridization to confirm that some of these binding sites correspond to the GALR1 GAL receptor subtype. Our findings indicate that the absence of VP expression in the BST/Me of golden hamsters results from a failure of extrahypothalamic GAL neurons to express the VP phenotype. Because GAL is expressed in the extended amygdaloid complex and GAL receptors are present in the septum of golden hamsters, GAL may play a role in modulating functions previously attributed to BST/Me pathways.

Regulation of galanin in memory pathways

Based on early immunocytochemical findings, galanin (GAL) was postulated to function as an inhibitory cotransmitter in rat cholinergic memory pathways. However, recent studies indicate that in the basal state GAL is not widely expressed by forebrain cholinergic neurons in rats. Inhibition of cholinergic transmission by cosecreted GAL may be enhanced under certain conditions, because GAL gene expression in the cholinergic basal forebrain is significantly increased prior to puberty and following nerve growth factor treatment. Other sources of GAL in rat septohippocampus that could interact with cholinergic pathways include noradrenergic neurons in the locus ceruleus and vasopressinergic neurons in the bed nucleus of the stria terminalis (BST) and medial amygdala (Me). GAL is extensively colocalized within these steroid-sensitive cell groups where its expression is upregulated by gonadal hormones. GAL, acting via the GALR1 receptor subtype, does not appear to directly regulate the activity of cholinergic neurons, but it may regulate the release of vasopressin and GAL into septohippocampus from BST/Me neurons.

Gonadal steroid-dependent GAL-IR cells within the medial preoptic nucleus (MPN) and the stimulatory effects of GAL within the MPN on sexual behaviors

More GAL-I cells exist within sexually dimorphic cell groups of the medial preoptic nucleus (MPN) in male rate than females, a large percentage of estrogen-concentrating cells within MPN cell groups are also GAL-immunoreactive (GAL-IR), and significantly more GAL-IR cells are visible with estrogen or its precursor, testosterone. Gonadal steroids also increase the size (diameter) of MPN GAL-IR cells and the number of GAL-IR cell processes within a portion of the MPN called the "GAL-IR MPOA plexus," which exists in males only. GAL microinjected into the MPN stimulated male-typical sexual behaviors, with more testosterone required in females than males. Immunoneutralization with anti-GAL serum inhibited male-typical sexual behavior, indicating a role for endogenous GAL within the MPN. Microinjection of GAL into the MPN also stimulated female-typical sexual behaviors in estrogen-treated females and males, and GAL within the MPN dramatically overrode an inhibition of lordosis by dihydrotestosterone in rats of both sexes.

The source of origin of PACAP- and VIP-immunoreactive fibers in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The bed nucleus of the stria terminalis (BSTL), which is known to be involved in the modulation of stress responses, exhibits a dense network of pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) immunoreactive (ir) fibers. The origin of the PACAP-ir fibers is unknown, and the origin of the VIP-ir fibers remains uncertain. The most important brain regions connected to the BSTL are the amygdaloid nuclei, the paraventricular and ventromedial hypothalamic nuclei, mesencephalic periaqueductal grey, the dorsal and linear raphe nuclei, the parabrachial nucleus, and the dorsal vagal complex. After microinjecting cholera toxin B subunit (CTB) in the BSTL as a retrograde tracer, neurons were double labeled for CTB and PACAP or VIP immunohistochemistry and the cells from which the PACAP- and VIP-ir fiber networks in the BSTL originated were identified. Cholera toxin B subunit labeled and VIP-ir cells were found in the mesencephalic periaqueductal grey and the dorsal and linear raphe nuclei, but no double labeled cells were seen in the amygdaloid nuclei or the hypothalamic region. CTB- and PACAP-ir neurons were observed in the paraventricular nucleus and the dorsal vagal complex. No double labeled perikarya were seen in the parabrachial nucleus or in the amygdaloid nuclei.

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.

GALR1 galanin receptor mRNA is co-expressed by galanin neurons but not cholinergic neurons in the rat basal forebrain

The neuropeptide galanin (GAL) has been proposed to be an inhibitory modulator of cholinergic transmission in the hippocampus and may impair memory by directly affecting the activity of basal forebrain (BF) cholinergic neurons. Alternatively, GAL may act indirectly and modulate the activity of other neurotransmitter systems which, in turn, influence cholinergic transmission. We have used double in situ hybridization histochemistry to evaluate the co-expression of the GAL receptor subtype, GALR1, within cholinergic neurons in the medial septum/diagonal band of adult male rats. In alternate brain sections, we assessed the co-expression of GALR1 mRNA within another forebrain cell group implicated in memory functions, the neurons of the bed nucleus of the stria terminalis (BNST) and medial amygdala (AMe) which co-express vasopressin (VP) and GAL and project to septo-hippocampus. Despite the abundance of GALR1 mRNA-expressing neurons in the cholinergic BF, we found no evidence for the co-expression of this receptor subtype within cholinergic neurons in the medial septum/diagonal band. In contrast, we detected an extensive co-expression (95%) of GALR1 mRNA within extrahypothalamic VP/GAL neurons. These results do not support the idea that GAL, acting via the GALR1 receptor, directly impairs BF cholinergic neurons but suggest, instead, that non-cholinergic neurons in the BF may play a role in mediating the inhibitory actions of GAL on cholinergic function. However, our findings provide anatomical evidence that GAL could directly modulate the activity and/or secretion pattern of extrahypothalmic VP/GAL neurons into septo-hippocampal regions.

Axon terminals containing PACAP- and VIP-immunoreactivity form synapses with CRF-immunoreactive neurons in the dorsolateral division of the bed nucleus of the stria terminalis in the rat

The bed nucleus of the stria terminalis (BST) is a highly heterogeneous forebrain structure, within which the median and lateral BST play distinct functional roles. The medial BST (BSTM) is thought to be related to sexual behavior, while the lateral BST (BSTL) may have a stress-related function. In the human brain, the BST shows marked sexual dimorphism in the distribution of vasoactive intestinal polypeptide (VIP) immunoreactive fibers and also contains a very high concentration of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactivity (ir). Using immunohistochemistry (IHC) to examine the rat brain, the present study found that both VIP and PACAP containing afferent fibers are abundant in the BSTLd (dorsolateral division of BST), but not in the BSTM. IHC did not reveal any apparent difference between the sexes in the size of distribution of either immunoreactivity. Double staining IHC showed that axonal terminals of both VIP and PACAP neurons were in close proximity to dendrites or perikarya of corticotropin releasing factor (CRF) neurons. At the electron microscopic level IHC revealed the presence of axodendritic or axosomatic synapses between VIP-ir and PACAP-ir axon terminals and CRF-ir neurons. Although the origin of PACAP-ir fibers in the BSTLd remains to be determined, these morphological findings suggest that PACAP and VIP regulate the activity of CRF neurons in the BSTLd as neurotransmitters or neuromodulators.

The rat galanin-gene promoter: response to members of the nuclear hormone receptor family, phorbol ester and forskolin

We have cloned a rat genomic DNA fragment of approximately 12.5 kb. Nine kb of the cloned fragment lie in the 5'-flanking region of the gene and contain the promoter elements, while the remaining 3.5 kb contain the first four complete exons, the first three introns, and part of the fourth intron of the rat galanin gene. We have partially analysed some of the elements within the proximal sequence of this promoter which may influence the transcriptional regulation of the rat galanin gene. The rat galanin-gene promoter contains many regions which share homology with both the human and the bovine galanin genes and certain cis-elements appear to be conserved among the three species. In an attempt to test whether some of these elements are functional in the rat gene, transient transfection studies were carried out in selected cell lines. Estrogen, thyroid hormone and retinoic acid all showed a minimal degree of promoter stimulation when the rat galanin-gene promoter was co-transfected with the appropriate hormone receptors in Neuro 2A cells, while co-transfection of the nuclear orphan receptor ELP1 was able to stimulate transcription of a galanin promoter-driven reporter-gene construct (-374 bp) by 35-fold. The galanin promoter mediated a 3-4-fold induction in response to forskolin or TPA. Deletion of a 5-bp element at -50 bp from the start of transcription was able to greatly reduce the forskolin response but not the TPA response. These results point to several elements that may be targets of transcription factors linked to extracellular stimuli.

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)

Galanin--10 years with a neuroendocrine peptide

Galanin is a 29/30 amino acids long neuropeptide which does not belong to any known peptide family. The N-terminal first 16 amino acids of the molecule are both necessary and sufficient for receptor recognition and receptor activation. The main pharmacophores of galanin in its central and pancreatic actions are Gly1, Trp2, Asn5 and Tyr9, respectively. The neuropeptide galanin has multiple effects in both the central and peripheral nervous systems. Centrally, galanin potently stimulates fat intake and impairs cognitive performance. Anoxic glutamate release in the hippocampus is inhibited by galanin and the noradrenergic tonus in the brain is influenced by a hyperpolarizing action of galanin in the locus coeruleus. In the spinal cord galanin inhibits spinal excitability and potentiates the analgesic effect of morphine. In the neuroendocrine system galanin acts in a stimulatory manner on the release of growth hormone and prolactin, and peripherally galanin inhibits glucose induced insulin release. Galanin also causes contraction of the jejunum. The galanin receptor is a Gi-protein-coupled, membrane-bound glycoprotein with an estimated molecular mass of 53 kDa. Several putative tissue specific galanin receptor subtypes have been proposed on a pharmacological basis. The distribution of galanin receptors and of galanin like immunoreactivity are overlapping in the CNS, both being high in areas such as the locus coeruleus, raphe nucleus and hypothalamus. Galanin receptor activation leads to a reduced intracellular Ca(2+)-concentration, either by direct action on voltage sensitive Ca(2+)-channels or indirectly via opening of K(+)-channels or via inhibition of adenylyl cyclase activity. The lowered intracellular Ca2+ level subsequently leads to a reduced PLC activity. Galanin also inhibits cGMP synthesis induced by depolarization. A number of synthetic high affinity galanin receptor antagonists of the peptide type were developed recently, which have enabled the elucidation of functional roles of endogenous galanin in several systems. Furthermore, putative subtypes of galanin receptors can be distinguished by the use of these new galanin receptor ligands.

Activation of galanin pathways across puberty in the male rat: assessment of regional densities of galanin binding sites

Galanin-like immunoreactivity and galanin messenger RNA levels increase across puberty in neurons of gonadal steroid-dependent brain nuclei. We hypothesized that this activation and the associated increase in endogenous galanin release would result in changes across puberty in both galanin binding density and the level of receptor occupancy. Here we have assessed the density of galanin binding sites in several brain regions of prepubertal and adult male rats with or without GTP to induce dissociation of endogenous galanin from its binding sites. The developmental changes in the level of receptor occupancy were used as an indirect measure of changes in neuropeptide release from galanin expressing neurons. In standard binding conditions (buffer preincubation), 125I-labeled galanin binding showed a generalized decline in adult brains (34-68%) compared with prepubertal levels in most regions of the telencephalon and diencephalon. Following preincubation with 10(-5) M GTP, galanin binding showed a dramatic increase in most regions of the adult (152-504%) and several regions of the prepubertal brain (132-245%) over their standard binding levels. However, this increase was greatest in adult animals. Finally, although preincubation of brain slices with GTP eliminated most of the apparent age-related differences observed in standard binding conditions, several brain regions of the adult brain continued to show a significant reduction (38-76%) in 125I-labeled galanin binding compared with prepubertal animals. Only one region, the lateral preoptic area, exhibited enhanced 125I-labeled galanin binding in adult (160%) compared with prepubertal brain after GTP preincubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of galanin pathways across puberty in the male rat: galanin gene expression in the bed nucleus of the stria terminalis and medial amygdala

Galanin and vasopressin are coexpressed in the bed nucleus of the stria terminalis and medial amygdala of the male rat. In adult males, the level of gene expression for both peptides in these regions is dependent on circulating levels of testosterone. We hypothesized that galanin messenger RNA levels would be enhanced in adult males compared with prepubertal males due to the rise in plasma testosterone levels. We used in situ hybridization and quantitative autoradiography to measure galanin messenger RNA in cells of the bed nucleus of the stria terminalis and medial amygdala of prepubertal and adult male rats. Our results show that significantly (P < or = 0.05) more galanin messenger RNA expressing neurons are detectable in the bed nucleus of the stria terminalis of adult compared with prepubertal male rats. In contrast, no differences were observed between the groups in the number of labeled neurons detected within the medial amygdala. However, the average labeling intensity was significantly enhanced in both the bed nucleus of the stria terminalis (P < or = 0.001) and medial amygdala (P < or = 0.001) of adult compared with prepubertal animals. The present findings are consistent with the hypothesis that gonadal hormones regulate galanin gene expression in some brain regions and suggest that the activation of the hypothalamic-pituitary-gonadal axis which occurs naturally with puberty is associated with activation of galanin pathways in the bed nucleus of the stria terminalis and medial amygdala.

Localization of androgen receptor within peptidergic neurons of the rat forebrain

This study tested for the presence of androgen receptor-immunoreactivity in somatostatin, galanin, vasopressin, corticotropin-releasing hormone, and oxytocin neurons in the rat forebrain. The brains of adult male Sprague-Dawley rats were fixed with 4% paraformaldehyde. Androgen receptor was visualized in coronal sections using nickel intensification of diaminobenzidine, and the neuropeptides were identified using a brown diaminobenzidine reaction product. Androgen receptor was localized to the nuclei of neurons in the septum, amygdala, cortex, hippocampus, and hypothalamus. The majority of somatostatin-containing neurons in the periventricular hypothalamic nucleus also contained androgen receptor. Androgen receptor was also found within galanin-expressing cells in the bed nucleus of the stria terminalis and in the amygdala. Androgen receptor was not observed in corticotropin-releasing hormone, vasopressin, or oxytocin neurons in all areas examined. The data suggest that androgens may be capable of directly regulating somatostatin-expressing neurons of the periventricular nucleus of the hypothalamus and galanin-containing neurons of the bed nucleus of the stria terminalis and amygdala.