Galanin mRNA Levels Research Articles

Vasopressin and galanin expression in the hypothalamus of two African rodents, Taterillus gracilis and Steatomys caurinus, subjected to water-restriction

The expression of arginine-vasopressin (AVP) and galanin (GAL) was studied by immunohistochemistry and in situ hybridization in the hypothalamus of two species of African rodents. In the wild, these animals experience successive arid and wet seasons that alternately stimulate their antidiuretic and diuretic systems. In this study, animals were subjected to both standardized laboratory conditions and to eight days of water-restriction. Under both sets of conditions, AVP and GAL were detected in the supraoptic nucleus (SON), paraventricular nucleus (PVN), and median eminence (ME). AVP and GAL responses to water-restriction differed in the two species, as did behavioral adaptations to the hot-dry season. In Taterillus gracilis, AVP- and GAL-LI (like immunoreactivity) peptide and mRNA levels increased in the SON. AVP-LI peptide and mRNA levels increased in the PVN, whereas only AVP-LI peptide levels increased in the ME. Pituitary gland AVP pools were unchanged by water deprivation, whereas urinary AVP levels and osmolality increased. The AVP response is typical of that of desert rodents, favoring survival under conditions of water-restriction. In Steatomys caurinus, which estivates, AVP and GAL-LI peptide levels decreased in the hypothalamus, as they did in the laboratory rat. In the SON, AVP, and GAL mRNA levels increased, whereas, in the PVN, only AVP mRNA levels increased. Pituitary gland AVP levels decreased, whereas urinary AVP levels and osmolality increased. In both species, the changes in the amount of GAL-LI peptide appeared to be closely linked to changes in AVP levels, suggesting that this peptide is involved in the osmoregulatory response to water-restriction.

Galanin peptide levels in hippocampus and cortex of galanin-overexpressing transgenic mice evaluated for cognitive performance

Galanin-overexpressing transgenic mice (GAL-tg) generated on a dopamine β-hydroxylase promoter were previously shown to express high levels of galanin mRNA in the locus coeruleus, and to perform poorly on challenging cognitive tasks. The present study employed radioimmunoassay to quantitate the level of galanin peptide overexpression in two brain regions relevant to learning and memory, the hippocampus and cerebral cortex. Approximately 4-fold higher levels of galanin were detected in the hippocampus of GAL-tg as compared to WT. Approximately 10-fold higher levels of galanin were detected in the frontal cortex of GAL-tg as compared to WT. A second cohort of GAL-tg and WT again showed high levels of galanin overexpression in GAL-tg as compared to WT in both brain regions. Correlation analyses were conducted between galanin peptide concentrations and behavioral scores on four learning and memory tasks: the Morris water maze, social transmission of food preference, standard delay fear conditioning, and trace fear conditioning. While some significant correlations were detected, neither hippocampal nor cortical galanin levels in the two cohorts of GAL-tg consistently correlated with performance across these diverse cognitive tasks. Several interpretations of these findings are discussed, including the possibility that a threshold level of galanin overexpression is sufficient to impair performance on learning and memory tasks in mice.

Perinatal nicotine attenuates the hypoxia-induced up-regulation of tyrosine hydroxylase and galanin mRNA in locus ceruleus of the newborn mouse.

The effect of perinatal nicotine exposure on the hypoxic response in the newborn mouse was examined, with special reference to the catecholaminergic system. We studied transcripts for the catecholamine synthesizing enzyme tyrosine hydroxylase (TH) and the neuropeptide galanin (GAL) in locus ceruleus (LC) and adrenal medulla at different times after birth and postnatal hypoxia. We thereafter investigated how perinatal nicotine affected these mRNA levels, as well as the ability of the newborn to survive severe hypoxia. TH mRNA levels increased postnatally in both LC and adrenals, reaching peak values at 24 h postnatally and thereafter stabilizing at lower levels. GAL mRNA also increased in the LC but did not decrease after 24 h. Acute hypoxia (5% O(2) for 60 min) elicited increases in TH and GAL mRNA levels in the LC after 24 h. However, TH mRNA levels in the adrenals did not change. Perinatal nicotine exposure increased mortality after hypoxia (from 0% to 16.9%). Moreover, hypoxia-induced increases in TH and GAL mRNA levels in the LC were not observed in nicotine-treated pups. Nicotine also decreased basal TH mRNA levels in the adrenals. The present results suggest (1) that the postnatal increases in adrenal TH mRNA levels are not directly due to hypoxia at birth, and (2) that the increased mortality seen after hypoxia in nicotine pups concurs with a perturbed LC function in these animals. A deficient catecholamine synthesis in the adrenals may also contribute to the detrimental effect of prenatal exposure to nicotine on the response to hypoxia.

Pharmacological manipulation of brain galaninergic system and sexual behavior in male mice.

Available data suggest a complex role for the brain galaninergic system in male sexual behavior; however, the results so far obtained in animals with either galanin or galanin antagonists are conflicting. To define the better influence of galanin on male sexual behavior by studying, in mice, (i) the effect of galanin and of the chimeric galanin peptide M40 on the copulatory performance, and (ii) galanin mRNA levels in hypothalamic arcuate and dorso-medial nuclei. For the behavioral testing, only sexually sluggish male mice were used. Galanin mRNA levels were studied in both sexually potent and impotent mice by means of in situ hybridization. Standard behavioral parameters for sexual behavior were recorded or calculated. Synthetic galanin (0.05, 0.1 or 1 microg/mouse) and M40 (5 or 20 microg/mouse) were intracerebroventricularly (ICV) injected, 15 min before the copulatory test. Galanin mRNA levels were evaluated. In sexually sluggish male mice, both galanin (0.1 and 1 microg/mouse ICV) and M40 (20 microg/mouse ICV), significantly increased intromission frequency and ejaculation latency; M40 also improved copulatory efficacy. On the other hand, in the hypothalamic arcuate and dorso-medial nuclei, the levels of galanin mRNA were not significantly different in sexually potent and impotent male mice. These results show that in sexually sluggish male mice the ICV injection of either galanin or the chimeric analogue M40 greatly prolongs the duration of the copulation; without a reduction of the sexual drive or of the copulatory performance. On the other hand, the hybridization experiments seem to rule out an important physiological role of the brain galaninergic system in the regulation of male sexual behavior, at least in mice.

Decreased galanin mRNA levels in growth hormone-releasing hormone neurons after perinatally induced growth retardation.

Intrauterine growth retardation (IUGR) is associated with persistent postnatal growth retardation accompanied by dysfunction of the hypothalamic components of the growth hormone (GH) axis. At the adult stage, this is reflected by increased somatostatin (SS) and decreased neuropeptide Y (NPY) mRNA levels, whereas the GH-releasing hormone (GHRH) mRNA levels are normal and the output of GH remains unchanged. To extend our insight into the hypothalamic control of GH secretion in growth retarded rats, we determined galanin (GAL) mRNA levels at the adult stage of perinatally malnourished (i.e. IUGR and early postnatally food restricted) rats. Analyses included comparison of GAL mRNA levels in GHRH neurons in perinatally malnourished adult rats using a semi-quantitative double labeling in situ hybridization technique. We report that IUGR is accompanied by a 60% decrease in GAL mRNA levels in all GHRH neurons in the male IUGR group whereas a tendency towards a decrease was observed in the male early postnatally food restricted (FR) group. These effects became more pronounced when the analysis was restricted to GHRH neurons coexpressing GAL mRNA i.e. decreased GAL mRNA levels were seen in both male and female IUGR rats and in FR males. These data show that GAL mRNA levels in GHRH neurons are persistently decreased after perinatal malnutrition. Taking these results together with our previous data on SS, NPY and GHRH mRNA levels, we can conclude that IUGR leads to a reprogramming of the hypothalamic regulation of GH secretion.

Effect of Peripheral Nerve Lesion and Lumbar Sympathectomy on Peptide Regulation in Dorsal Root Ganglia in the NGF-Overexpressing Mouse

Galanin is a peptide normally expressed at low levels both in sensory and in sympathetic neurons. It is strongly upregulated after peripheral nerve lesions, and it has been proposed that nerve growth factor (NGF) plays a role in this regulation. In the present study the effect of both sciatic nerve transection and lumbar sympathectomy on galanin in lumbar dorsal root ganglia (DRGs) was examined in mice overexpressing NGF (NGFOE) in the skin under the keratin promoter. The superior cervical ganglia (SCG) were also studied. In the DRG pericellular baskets containing tyrosine hydroxylase- (TH) and galanin-like immunoreactivity (LI) were found, mostly in the same fibers. Galanin-positive baskets were also found in the trigeminal ganglia. However, only single neuropeptide Y (NPY)-positive baskets were observed within the DRGs. No marked difference in number of galanin-positive neurons was seen between wild-type and NGFOE mice. After sciatic nerve transection galanin was upregulated in DRG neurons to about the same extent in NGFOE mice as in wild-type mice. Galanin-, but not TH-LIs decreased in the pericellular baskets. After lumbar sympathectomy both galanin- and TH-immunoreactive baskets disappeared, suggesting a sympathetic origin. In the SCG the very low galanin mRNA levels were strongly increased after lesion of the carotid nerves, both in wild-type and in NGFOE mice. However, whereas NPY mRNA levels decreased in the SCG after axotomy in the wild-type mice, there was a distinct increase in the NGFOE mice. Our results show that high NGF levels in skin induce formation of pericellular baskets in DRGs expressing galanin- and TH-LI and that galanin in these baskets is strongly influenced by peripheral axotomy. However, overexpression of NGF did not markedly influence galanin expression in DRG neurons, neither normally nor after nerve lesions. Finally, expression of NPY in sympathetic ganglia is differently regulated in NGFOE compared to wild-type mice.

Long-Lasting Regulation of Galanin, Opioid, and Other Peptides in Dorsal Root Ganglia and Spinal Cord during Experimental Polyarthritis

Mechanisms involved in transition from acute to chronic pain are still not well understood and our means to therapeutically influence this transition are limited. Moreover, very little is known about long-lasting consequences of prolonged exposure to painful stimuli with regard to phenotypic changes and pain experience. In this study we have analyzed long term behavioral and neurochemical effects of intradermal tail injection of heat-killed mycobacterium butyricum suspended in complete Freund's adjuvant. Calcitonin gene-related peptide (CGRP) and galanin mRNA levels were investigated in dorsal root ganglia of polyarthritic rats during the acute (21-) and the remission stage (79 days postinjection), and opioid peptide mRNAs and receptors were studied in the spinal cord. Most of the increases in peptide mRNA levels observed during the acute stage of arthritis were still present in the remission stages. Thus, CGRP and galanin mRNAs in DRGs, and opioid peptide mRNAs and opioid receptors in the spinal cord were still strongly up-regulated, when animals do not exhibit spontaneous pain behavior and inflammation. Hot-plate test in the presence of naloxone, performed in the remission stage, indicated that opiates participate in pain threshold regulation after prolonged painful condition. Finally, X-ray examination revealed a complete destruction of joint structure, thus suggesting a parallel lesion of peripheral nerve endings. These results suggest that in the remission stage of chronic joint inflammation several types of mechanisms are activated aiming at counteracting both inflammatory and neuropathic pain. Thus, opioid systems in the dorsal horn as well as galanin in DRG neurons are upregulated, both alternating pain.

In vitro effects of oestradiol on galanin gene expression in rat anterior pituitary cells.

While the pituitary galanin gene is highly responsive to oestrogen stimulation in vivo, in vitro effects of oestrogens on pituitary galanin gene expression have been less studied. We therefore examined the short-term effects of 17beta-oestradiol on galanin synthesis by dispersed rat anterior pituitary cell cultures and investigated the mechanisms by which oestrogens may modulate galanin gene expression. 17beta-oestradiol increased galanin mRNA expression in a dose-dependent manner, with a maximal increase observed at a concentration of 10-7 M. The 17beta-oestradiol (10-7 M)-induced increase in galanin mRNA expression varied from 3- to 20-fold (average 12-fold) depending upon the experiments and was also time-dependent, reaching significance after 6 h. A 1-h exposure of anterior pituitary cells to 17beta-oestradiol was sufficient to induce markedly galanin mRNA expression after 24 h (by 16-fold) and 48 h (by 25-fold). Tamoxifen administered simultaneously with or following 17beta-oestradiol treatment completely abolished the oestrogen-induced increase of galanin mRNA levels. Cycloheximide (10 microg/ml), a protein synthesis inhibitor, also blocked 17beta-oestradiol-induced galanin gene expression. Using transcription blockade by actinomycin D, we observed similar decreases of pituitary galanin mRNA concentrations, in the presence and absence of 17beta-oestradiol, implying no oestrogen effect on mRNA stability. We conclude that oestrogens stimulate rat pituitary galanin gene expression, mainly through a transcriptional mechanism, and that this effect requires persistent binding of the hormone to its nuclear receptor and newly synthesized protein intermediates.

Short-term glucocorticoid administration decreases both hypothalamic and pituitary galanin synthesis in the adult male rat

Galanin (GAL) is a peptide that has been implicated in the regulation of the growth axis. It is generally accepted that GAL can increase serum growth hormone (GH) levels, although the underlying mechanism for this increase is unknown. It is well known that long-term glucocorticoid treatment alters in vivo GH secretion, since there is a decrease in serum GH in response to stimuli. It has previously been shown in our laboratory that administration of GAL can overcome the effects of glucocorticoid administration on GH secretion. The aim of the present study was to determine the effects of long-term glucocorticoid administration on the regulation of hypothalamic and pituitary GAL mRNA levels. Adult male rats were treated for 72 hours with the synthetic glucocorticoid dexamethasone ([DEX] 40 μg/kg/d intraperitoneal injections). RNase protection assays were performed on both the hypothalamus and pituitary for the presence of GAL mRNA. As expected, DEX significantly decreased somatic growth, as evidenced by a decrease (50%) in the weight gain of glucocorticoid-treated versus control animals. It was also demonstrated that in both the hypothalamus and pituitary, glucocorticoid treatment reduced the level of GAL mRNA (to 11% and 6.5%, respectively) compared with the control condition. We conclude that the decrease in GAL mRNA may lead to a decrease in GAL secretion, which in turn may be involved in the glucocorticoid-induced inhibition of GH secretion.

Galanin expression is decreased by cAMP-elevating agents in cultured sympathetic ganglia.

Galanin expression is co-regulated in peripheral neurons with that of vasoactive intestinal peptide (VIP) under a variety of conditions. For example, the expression of both increase after explantation of adult rat superior cervical ganglia (SCG). Because VIP participates in a positive feedback loop regulating its own expression, we examined whether VIP also increases galanin expression. Galanin mRNA and peptide are nearly undetectable in the SCG in vivo, but increase dramatically after 24-48 h in organ culture. Addition of VIP or forskolin to the culture medium reduced galanin mRNA expression by 75% and 77%, respectively, and reduced galanin peptide expression by 76% and 82%, respectively, compared with ganglia cultured in control medium. In contrast, isoproterenol stimulation did not significantly alter levels of galanin mRNA or peptide, consistent with previous observations that isoproterenol exerts its effect on SCG non-neuronal cells, but not on neurons. The results indicate that galanin and VIP are differentially regulated in sympathetic neurons by cAMP- elevating agents.

Disruption of neural signaling within the hypothalamic ventromedial nucleus upregulates galanin gene expression in association with hyperphagia: an in situ hybridization analysis

Hypothalamic neuropeptides play critical roles in the regulation of appetite and body weight. We recently reported that disruption of neural signaling in the ventromedial nucleus (VMN) by microinjection of the neurotoxin, colchicine (COL), produced transient hyperphagia with attendant body weight gain lasting for 4 days. The neural mechanism(s) underlying this temporary shift in energy homeostasis is still unknown. Galanin (GAL) is produced in several hypothalamic nuclei and since microinjection of GAL into these sites stimulates feeding, we tested the hypothesis that galaninergic signaling is upregulated in COL-treated rats. COL (4 μg in 0.5 μl saline) or saline alone was microinjected into the VMN of adult male rats and GAL mRNA was evaluated in the basal hypothalamus by ribonuclease protection assay on day 1, day 2 and day 4 after injection. Whereas in saline-treated rats body weight and GAL mRNA remained unaffected, they were significantly increased in COL-injected rats through the period of observation. To identify the specific neuronal subpopulations involved, GAL mRNA levels were analyzed in feeding-related hypothalamic nuclei using semiquantitative in situ hybridization histochemistry on day 4 after microinjection of COL or saline into the VMN. In COL-treated rats, GAL mRNA levels increased dramatically over controls in the supraoptic nucleus, paraventricular nucleus (PVN), dorsomedial nucleus (DMN), arcuate nucleus (ARC) and lateral hypothalamic area (LHA); no significant change was observed in the central nucleus of amygdala. These results indicated that disruption of neurotransmission in the VMN upregulated GAL gene expression in those hypothalamic sites (PVN, DMN, LHA and ARC) that are implicated in regulation of feeding, and since GAL stimulates feeding, this neurochemical rearrangement may contribute to the over-eating in these animals. These results also suggest that, normally, neurons in the VMN may suppress GAL neurotransmission in feeding-regulating hypothalamic neural circuits.

Stimulation of anterior pituitary galanin and prolactin gene expression in suckling rats.

Recent evidence suggests that galanin may regulate prolactin (PRL) secretion during lactation. In this article, we describe the regulation of anterior pituitary galanin and PRL gene expression during pregnancy and after parturition in the rat. Expression of galanin and PRL in the anterior pituitary were significantly higher at d 20 of pregnancy compared to diestrus. One day after parturition, galanin mRNA levels increased a further 4.5-fold. This post partum increase in gene expression was not observed for PRL. The increase in galanin gene expression was maintained above the diestrous level for at least 10 d after parturition. PRL mRNA expression, on the other hand, was largely unchanged after parturition. Although the increase in galanin gene expression 1 d after parturition was independent of suckling, subsequently, galanin gene expression was significantly higher in nursing mothers. Anterior pituitary galanin gene expression was 12-fold higher in nursing mothers compared with those that were not, 3 d after parturition. Similarly, PRL gene expression was significantly lower in mothers who were not suckling their pups 3 d after parturition. Initiation of suckling alone was insufficient to stimulate galanin and PRL expression. Despite suckling for 2 d, removal of the suckling stimulus subsequently resulted in a rapid decrease in galanin gene expression. Hence, the stimulatory effect of suckling on galanin expression requires a sustained suckling stimulus. In conclusion, the data support the hypothesis that anterior pituitary galanin plays an important role during lactation, likely acting to amplify lactotroph stimulation through paracrine and autocrine mechanisms.

Galanin in normal and hyperplastic anterior pituitary cells. From pituitary tumor cell lines to transgenic mice.

Studies on the regulation of galanin expression in the epithelial cells of the anterior pituitary gland have provided a wealth of insight into the cellular and molecular biology of this unique peptide. Galanin is localized within subpopulations of specific pituitary cell types, and hypothalamic as well as gonadal factors including dopamine, somatostatin, thyrotropin-releasing hormone, growth hormone-releasing hormone (GHRH), estrogen, and progesterone dynamically regulate its expression and release. Galanin gene expression and peptide secretion are markedly increased in estrogen-induced prolactinomas, wherein galanin serves as both an autocrine and paracrine hormone regulating prolactin secretion. Galanin mRNA and peptide levels are also dramatically elevated in somatotroph adenomas of human GHRH transgenic mice. Moreover, galanin secretion is increased from the hyperplastic somatotrophs of hGHRH transgenic mice. However, not all pituitary adenomas are associated with increased galanin gene expression; galanin synthesis is repressed in 131I-induced thyrotroph adenomas. Thus, galanin acts locally to regulate pituitary hormone secretion and appears to act as a mitogenic factor to increase the proliferation of pituitary cells in a cell-type specific manner.

Anorectic effect of pituitary adenylate cyclase activating polypeptide (PACAP) in rats: lack of evidence for involvement of hypothalamic neuropeptide gene expression.

We investigated the effect of centrally administered pituitary adenylate cyclase activating polypeptide (PACAP) on feeding in rats, and the involvement of hypothalamic neuropeptide gene expression using in situ hybridization. Intracerebroventricular injection of PACAP (1000 pmol/rat) significantly decreased food intake in a dose-dependent manner. In PACAP-treated rats, neuropeptide Y (NPY) mRNA levels in the arcuate nucleus and galanin mRNA levels in the paraventricular nucleus increased, and corticotropin-releasing hormone (CRH) mRNA levels in the paraventricular nucleus decreased. In rats fasted for 72 h, NPY mRNA levels increased, and CRH mRNA levels decreased, but galanin mRNA levels were unchanged. These results indicate that the anorectic function of PACAP is not mediated by NPY or CRH, and that PACAP increases galanin synthesis.

Inducible galanin and GalR2 receptor system in motor neuron injury and regeneration.

Galanin has been ascribed several physiological roles that are thought to be mediated via multiple galanin receptors. Recently, two galanin receptors--galanin receptor-1 (GalR1) and galanin receptor-2 (GalR2)--have been cloned and characterized and shown to have differences in amino acid sequence, pharmacology, and second messenger signaling systems. Previous studies have demonstrated an up-regulation of galanin expression in damaged neurons of several different types. Using in situ hybridization histochemistry this study investigated whether adult cranial motor neurons express mRNAs encoding GalR1 and/or GalR2 and explored possible time-dependent changes in these transcripts following facial nerve injury. GalR2 mRNA levels were increased in the ipsilateral facial nucleus 3 (approximately 1.8-fold) and 7 days (approximately 3.7-fold) after unilateral facial nerve crush and had returned to levels equivalent to those in contralateral controls by 14-21 days. GalR1 mRNA was not detected in facial nuclei of naive, sham-operated, or operated rats but was present in adjacent reticular nuclei. Galanin mRNA levels were also increased eight- to 10-fold in the ipsilateral facial nucleus following nerve injury. These experiments confirm the putative importance of galanin signaling systems after nerve injury by demonstrating a differential response of galanin receptor subtypes and suggest an important "autoreceptor" role for the GalR2 receptor in these processes.

NGF and LIF both regulate galanin gene expression in primary DRG cultures.

Both target-derived and injury-induced factors could be involved in the axotomy-induced increases in galanin expression in dorsal root, ganglion (DRG) neurons. Galanin mRNA levels were studied in primary cultures of E13.5 embryos, grown for 14 days in culture, in response to two candidate molecules, nerve growth factor (NGF) and leukemia inhibitory factor (LIF). In these cultures, NGF withdrawal alone resulted in a significant increase in galanin mRNA. Addition of LIF onto NGF-containing cultures did not produce a significant increase, while addition of LIF to NGF-deprived cultures caused an upregulation of galanin mRNA which was significantly stronger than that of NGF withdrawal alone. Thus, NGF withdrawal and LIF increase act together to up-regulate galanin gene transcription in DRG neurons.

Temporal Patterns of Gonadotropin-Releasing Hormone (GnRH), c-fos, and Galanin Gene Expression in GnRH Neurons Relative to the Luteinizing Hormone Surge in the Rat

Gonadotropin-releasing hormone (GnRH) neurons increase their expression of Fos and galanin coincident with the luteinizing hormone (LH) surge in the female rat. To define the temporal relationships between the expression of these genes and the GnRH gene itself and to gain insight about the possible functional interactions of these processes, we compared levels of c-fos, galanin, and GnRH mRNA in GnRH neurons and plasma levels of LH in the rat, beginning 6 hr before and continuing for 24 hr after a sex steroid-induced LH surge. LH levels were increased significantly by 1600 hr. They increased twofold further by 1800 hr and then returned to baseline by 2400 hr. Using in situ hybridization, we determined that levels of c-fos mRNA in GnRH neurons were elevated significantly at 1600 hr only, whereas levels of galanin mRNA in GnRH neurons first increased twofold by 1800 hr, increased an additional twofold by 2400 hr, and remained elevated at all time points sampled thereafter. There were no significant changes in cellular levels of GnRH mRNA over the time points sampled. These results are consistent with the hypothesis that the induction of c-fos gene expression in GnRH neurons leads to an increase in galanin gene expression, and that the sustained increase in galanin mRNA levels in GnRH neurons reflects either the need to replenish galanin stores that are depleted at the time of the LH surge or the involvement of galanin with physiological events that occur on the day of estrus.

Hypothalamic Neuropeptide Y and Galanin in Overweight Rats Fed a Cafeteria Diet

Pedrazzi, P., L. Cattaneo, L. Valeriani, S. Boschi, D. Cocchi and M. Zoli. Hypothalamic neuropeptide Y and galanin in overweight rats fed a cafeteria diet. Peptides 19(1) 157–165, 1998.—We evaluated neuropeptide Y (NPY) and galanin (GAL) immunoreactivity (IR) and mRNA in the paraventricular and arcuate nucleus, respectively, in rats that became overweight (Ov) or not (NOv) when fed a cafeteria diet. After 2 months of diet, NOv rats showed a significant increase in NPY IR, whereas Ov rats showed a significant increase in GAL mRNA levels. None of these changes was present in rats overfed for 6.5 months. These differential changes in hypothalamic GAL and NPY transmissions may contribute to the different susceptibility of the two rat subpopulations to the weight-promoting effects of the hypercaloric diet.

Regulation of anterior pituitary galanin gene expression by thyroid hormone

Thyroid hormone is required for basal and estrogen-induced expression of anterior pituitary galanin. Steady-state anterior pituitary galanin mRNA levels decreased 6-fold in hypothyroid rats after 3 weeks of treatment. Similarly, hypothyroidism resulted in a 2.6-fold decrease in estrogen induction of galanin gene expression. The effect of thyroid hormone on anterior pituitary galanin gene expression appears to be exerted, at least in part, at the pituitary itself. Transient expression assays in GH 3 cells suggest the involvement of transcriptional mechanisms in the regulation of galanin gene expression by thyroid hormone. A region between −41 and −132 bp upstream of the transcriptional start site confers thyroid hormone responsiveness to the galanin gene. Gel-mobility shift assays show specific binding of `SPI-like' proteins in GH 3 nuclear extracts to this region of the galanin gene. This binding was greatly enhanced by thyroid hormone.

Estrogen regulates galanin but not tyrosine hydroxylase gene expression in the rat locus ceruleus

The neuropeptide galanin (GAL) is coexpressed by the majority of noradrenergic neurons in the rat locus ceruleus (LC) and may function as an inhibitory modulator of noradrenergic transmission. Because estrogen has been shown to induce GAL expression in other brain regions and modulate noradrenergic transmission, we used in situ hybridization histochemistry to assess the effects of chronic estrogen treatment on GAL and tyrosine hydroxylase (TH) gene expression in the LC of ovariectomized female rats. We found that GAL mRNA levels were significantly elevated in rats implanted with a Silastic capsule containing estradiol compared to sham-implanted controls. Both the average optical density ( P ≤ 0.05) and the labelling area ( P ≤ 0.007) differed significantly between the groups. In contrast, TH gene expression measured in alternate brain sections did not differ between the groups. If GAL functions as an inhibitory modulator of noradrenergic transmission as postulated, these findings suggest that chronic estrogen treatment could reduce the noradrenergic tone of the brain in the absence of significant alterations in TH expression by enhancing the level of cosecreted GAL.