Autoradiographic distribution of 125I-galanin binding sites in the rat central nervous system

Localization of preprogalanin messenger RNA in rat brain: identification of transcripts in a subpopulation of cerebellar Purkinje cells

Galanin, a 29 amino acid peptide, is widely distributed throughout both the peripheral and central nervous systems and is thought to be involved in multiple physiological functions including smooth muscle relaxation, stimulation of feeding, blood pressure regulation, control of hormone secretion and modulation of nociception. Galanin has been shown to co-exist with several neurotransmitters throughout the neuroaxis and in some cases to modify their presynaptic and postsynaptic actions. In the present study, the anatomical distribution of preprogalanin messenger RNA in rat brain was examined by in situ hybridization histochemistry using specific 35S-labelled oligonucleotide probes. Neurons expressing preprogalanin messenger RNA were found throughout the brain and were particularly abundant in the hypothalamus. High densities of preprogalanin messenger RNA-positive neurons were found in the anteroventral preoptic, supraoptic, paraventricular and dorsomedial nuclei of the hypothalamus, in the locus coeruleus and in the nucleus of the solitary tract. Moderate densities of preprogalanin messenger RNA-positive cells were apparent in the periventricular and arcuate nuclei of the hypothalamus, in the dorsal raphe and dorsal cochlear nuclei. Low densities of preprogalanin messenger RNA-expressing neurons were observed in the piriform cortex, medial septum and the retrochiasmatic area. These findings are consistent with results of previous in situ localization studies of preprogalanin messenger RNA and also with studies reporting the distribution of galanin-like immunoreactivity in rat brain. A novel finding, however, was the detection of preprogalanin messenger RNA in Purkinje cells in the caudal cerebellar vermis (lobules 6 to 10) and the flocculus and paraflocculus of the lateral hemispheres of the cerebellum. Galanin is presumably co-localized in these cells with GABA, which is normally present in Purkinje cells and possibly with tyrosine hydroxylase, which has recently been detected in a similar subpopulation of cerebellar Purkinje cells in both rat and mouse. Thus, the present study reveals a previously unreported site of galanin gene expression in the cerebellum which represents a novel, putative site of action for galanin to add to its already varied physiological roles.

Galanin--a neuropeptide with inhibitory actions

1. Galanin is a 29 (in humans 30) amino acids long neuropeptide with mostly inhibitory, hyperpolarizing actions. 2. Differential structural requirements of truncated forms of galanin and differential agonist/antagonist behaviour of chimeric peptides, high affinity galanin receptor ligands suggest the presence of pharmacologically distinct galanin receptor subtypes. 3. The galanin receptor from human Bowes melanoma cell line--a member of G-protein coupled receptor superfamily--has been cloned. 4. Galanin acts via Gi/G(o) proteins inhibiting cAMP production, inositol phosphate turnover, opening K+ channels or closing Ca2+ channels.

Effect of galanin on growth hormone (GH) response to thyrotropin releasing hormone of rat pituitary GH-secreting adenomatous cells (GH1) in culture

The growth hormone (GH) releasing effect of thyrotropin-releasing hormone (TRH) and galanin, a 29-amino acid peptide widely distributed in mammalian CNS, alone or in combination was investigated in cultured rat pituitary tumor cells (GH1). TRH stimulated GH secretion in GH1 cells (maximal stimulation at the dose of 0.1 microM). Galanin alone had a significant GH inhibitory effect in GH1 cells at all the doses used. When the two peptides were administered in combination, no significant changes as compared to baseline levels were observed. The results of this study indicate that galanin has potent direct inhibitory effects on baseline and TRH-stimulated GH release from rat tumor cells.

Neuropeptide receptors in developing and adult rat spinal cord: an in vitro quantitative autoradiography study of calcitonin gene-related peptide, neurokinins, mu-opioid, galanin, somatostatin, neurotensin and vasoactive intestinal polypeptide receptors

A number of neuroactive peptides including calcitonin gene-related peptide (CGRP), substance P, neurokinin B, opioids, somatostatin (SRIF), galanin, neurotensin and vasoactive intestinal polypeptide (VIP) have been localized in adult rat spinal cord and are considered to participate either directly and/or indirectly in the processing of sensory, motor and autonomic functions. Most of these peptides appear early during development, leading to the suggestion that peptides, in addition to their neurotransmitter/neuromodulator roles, may possibly be involved in the normal growth and maturation of the spinal cord. To provide an anatomical substrate for a better understanding of the possible roles of peptides in the ontogenic development of the cord, we investigated the topographical profile as well as variation in densities of [125I]hCGRP alpha, [125I]substance P/neurokinin-1 (NK-1), [125I]eledoisin/neurokinin-3 (NK-3), [125I]FK 33-824 ([D-Ala2, Me-Phe4, Met(O)ol5]enkephalin)/mu-opioid, [125I]galanin, [125I]T0D8-SRIF14 (an analog of somatostatin); [125I]neurotensin and [125I]VIP binding sites in postnatal and adult rat spinal cord using in vitro quantitative receptor autoradiography. Receptor binding sites recognized by each radioligand are found to be distributed widely during early stages of postnatal development and then to undergo selective modification to attain their adult profile of distribution during the third week of postnatal development. The apparent density of various receptor sites, however, are differently regulated depending on the lamina and the stage of development studied. For example, the density of mu-opioid binding sites, following a peak at postnatal day 4 (P4), declines gradually in almost all regions of the spinal cord with the increasing age of the animal. [125I]substance P/NK-1 binding sites, on the other hand, show very little variation until P14 and then subsequently decrease as the development proceeds. In the adult rat, most of these peptide receptor binding sites are localized in relatively high amounts in the superficial laminae of the dorsal horn. To varying extents, moderate to low density of various peptide receptor binding sites are also found to be present in the ventral horn, intermediolateral cell column and around the central canal. Taken together, these results suggest that each receptor-ligand system is regulated differently during development and may each uniquely be involved in cellular growth, differentiation and in maturation of the normal neural circuits of the spinal cord. Furthermore, the selective localization of various receptor binding sites in adult rat spinal cord over a wide variety of functionally distinct regions reinforces the neurotransmitter/modulator roles of these peptides in sensory, motor and autonomic functions associated with the spinal cord.

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.

Cloning, pharmacological characterization, and anatomical distribution of a rat cDNA encoding for a galanin receptor

We have cloned and expressed a rat cDNA, designated GALR1-rat, that encodes a galanin receptor based on homology, pharmacology, and anatomical criteria. This cDNA was isolated from a rat brain cDNA library. The nucleotide sequence of the cloned receptor revealed an open reading frame encoding a 346-amino-acid protein, showing 90.8% identity with the previously cloned human galanin receptor. Membranes prepared from COS cells transiently expressing GALR1-rat specifically bind 125I-galanin with high affinity (Kd = 0.12 +/- 0.01 nM). Rat, porcine, and human galanin were able to displace 125I-galanin with nanomolar Ki (0.08 +/- 0.03, 0.10 +/- 0.01, and 0.14 +/- 0.03 nM, respectively), whereas the Ki values for the porcine galanin fragments galanin-(1-16), galanin-(2-29), and galanin-(3-29) were 0.95 +/- 0.21 nM, 7.14 +/- 0.51 nM, and > 1 microM, respectively. The rank order potency of these ligands is consistent with that reported for the native galanin receptor. The distribution of the mRNA corresponding to the galanin receptor encoded by GALR1-rat was determined by in situ hybridization to rat brain sections. High levels of galanin receptor mRNA were detected in the ventral hippocampal formation, thalamic, amygdala, and medulla oblongata nuclei, and in the dorsal horn of the spinal cord.

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)

Galanin receptor binding sites in adult rat spinal cord respond differentially to neonatal capsaicin, dorsal rhizotomy and peripheral axotomy

The discrete distribution and possible changes in specific [125I]galanin binding sites were evaluated in the rat spinal cord following neonatal capsaicin treatment, dorsal rhizotomy and sciatic nerve section. The highest density of [125I]galanin binding sites in the normal rat spinal cord was particularly evident in the superficial layers of the dorsal horn whereas moderate to low amounts of labelling were associated with the deeper dorsal horn, areas around the central canal and the ventral horn. Capsaicin-treated rats, compared to littermate controls, showed a significant bilateral increase in [125]galanin binding in the superficial laminae of the dorsal horn. Similarly, unilateral dorsal rhizotomy evoked a significant increase in the density of [125l]galanin binding sites in the superficial dorsal horn ipsilateral to surgery. Section of the sciatic nerve, on the other hand, induced a significant depletion in [125l]galanin binding in laminae I and II of the ipsilateral dorsal horn. These results, in parallel to those reported for galanin immunoreactivity under similar conditions, suggest that [125I]galanin binding sites are preferentially located postsynaptically to the primary afferent fibre terminals in the dorsal horn of the spinal cord. Thus it seems that galanin, at the level of the dorsal spinal cord, regulates the processing of nociceptive information by acting on its own class of specific receptors located postsynaptically to primary sensory terminals.

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.

Effects of angiotensin II on visual neurons in the superficial laminae of the hamster's superior colliculus

Superficial layer superior colliculus (SC) neurons were recorded extracellularly with multibarreled recording/ejecting micropipettes. Angiotensin II was delivered via micropressure ejection during visual stimulation (n = 215 cells), or during electrical stimulation of either the optic chiasm (OX; n = 150 cells) or visual cortex (CTX; n = 42 cells). Application of angiotensin II decreased visual responses of SC cells to 43.8% +/- 30.7% (mean +/- S.D.) and reduced responses to electrical stimulation of the OX and CTX to 58.6% +/- 34.1% and 43.8% +/- 30.7% of control values, respectively. Angiotensin II enhanced responses by at least 30% in only 6 cells (1.5%). Of the 35 neurons tested with both OX and CTX stimulation, the correlation of evoked response suppression by angiotensin II was highly significant (r = 0.69; P < 0.001). This suggests that the suppressive effects of angiotensin II were common to both pathways. To test whether the inhibitory effects of angiotensin II were presynaptic or postsynaptic, Mg2+ ions were ejected iontophoretically to abolish synaptic responses, and the neurons were activated by iontophoresis of glutamate and then tested with angiotensin II. Angiotensin II reduced the glutamate-evoked responses to an average 29.1% +/- 21.1% of control values (n = 9 cells). This suggest that the site of action of angiotensin II is most likely postsynaptic. To identify which receptors were involved in these effects, angiotensin II was ejected concurrently with the AT1 antagonist Losartan (DUP753) or with either of two AT2 antagonists, CGP42112A or PD123177. Losartan antagonized the action of angiotensin II in 65.6% of the cells tested (n = 99) and CGP42112A and PD123177 had antagonistic effects in 58% (n = 65) and 60% (n = 5), respectively. Both classes of antagonists were tested in 29 cells; and there was no significant correlation between their effectiveness. These results suggest that both AT1 and AT2 receptors may independently mediate the suppressive effects of angiotensin II, and that collicular neurons may have either or both receptor subtypes.

Characterization of galanin and 5-HT1A receptor coupling to adenylyl cyclase in discrete regions of the rat brain

We have studied the coupling of galanin and 5-HT1A receptors with adenylyl cyclase in the hypothalamus, the entorhinal cortex and the hippocampus of the rat brain. Furthermore, we have evaluated the effects of simultaneous activation of galanin and 5-HT1A receptors on adenylyl cyclase activity. Galanin-(1-29) and galanin-(1-15) showed a dose-dependent inhibitory effect on forskolin-stimulated adenylyl cyclase activity in the hypothalamus and entorhinal cortex. No clear effects were observed in the hippocampus. Neither galanin-(1-29) nor galanin-(1-15) had any effect on the basal activity of adenylyl cyclase in these regions. The selective 5-HT1A receptor agonist 8-OH-2-(di-n-propylamino)-tetralin (8-OH-DPAT) induced a dose-dependent inhibition of forskolin stimulated adenylyl cyclase activity in the hippocampus and the entorhinal cortex. 5-HT induced an inhibition in the hypothalamus. In all regions the effects could be fully counteracted by methiothepin. 5-HT was shown to stimulate the basal activity of adenylyl cyclase in the hippocampus and the entorhinal cortex. The effects could be counteracted by methiothepin. When galanin-(1-29) and 5-HT/8-OH-DPAT were incubated simultaneously additive inhibitory effects, but no synergistic interactions, could be observed on the stimulated adenylyl cyclase activity. In conclusion, galanin and 5-HT1A receptors seem to be linked to different independent pools of G proteins, indicating that the previously demonstrated intramembrane interactions between galanin and 5-HT1A receptors involve a mechanism not directly related to adenylyl cyclase.

LY226936 administered orally and centrally to obese Zucker rats suppresses food intake and body weight gain

LY226936, methylcarbamothoic acid-S-(4,5-dihydro-2-thiazolyl) ester, is a new compound that, when administered to obese Zucker rats, caused reduced food intake. LY226936 reduced the food consumption after a single oral dose of 50 and 100 mg/kg. On chronic oral administration to meal-fed obese (5 to 35 mg/kg. once daily) and to fed obese and lean (15 mg/kg. twice daily) Zucker rats, LY226936 reduced food intake and body weight gain for periods ranging from 40 to 48 days. The effect on both parameters was statistically significant. There is no evidence in our studies that tolerance to the actions of LY226936 developed. LY226936 decreased the consumption of both high carbohydrate and high fat diets. Food consumption of meal-fed obese Zucker rats was reduced significantly each time a single dose of 10 ugm LY226936 per rat was infused intracerebroventricularly. None of the receptors studied (mu and kappa opioid, CCK, serotonin, neuropeptide Y, galinin, N-methyl-D-aspartic acid) appeared to bind LY226936 and therefore, appear not to be involved in the depression of food intake by the obese Zucker rat.

Biological activities of two endogenously occurring N-terminally extended forms of galanin in the rat spinal cord

The occurrence of two N-terminally extended forms of galanin in the porcine adrenal medulla was reported earlier by Bersani et al. (1991). We have synthesized and examined the ability of these two extended forms of galanin, galanin-(-7-29) and galanin-(-9-29), to bind to galanin receptors in the rat dorsal spinal cord. The effect of intrathecal (i.t.) injection of these peptides on spinal flexor reflex excitability in decerebrate, spinalized, unanesthetized rats was also studied. Both galanin-(-7-29) and galanin-(-9-29) fully displaced specific 125I-monoido-[Tyr26]porcine galanin (125I-galanin) binding to membranes prepared from rat dorsal spinal cord, with IC50 values 0.13 and 0.14 microM, respectively. The metabolic half-lives in spinal cord membranes for galanin-(1-29), galanin-(-7-29) and galanin-(-9-29) were 117 +/- 17, 271 +/- 23 and 185 +/- 19 min, respectively. I.t. injection of galanin-(-7-29) and galanin-(-9-29) mimicked the biphasic facilitatory and inhibitory effect of i.t. galanin-(1-29) on flexor reflex excitability and antagonized C-fiber conditioning stimulus-induced spinal cord hyperexcitability, but with reduced potencies compared to galanin-(1-29). We suggest that the N-terminally extended forms of galanin act as endogenous ligands with low agonist activity.

Intracisternally injected galanin-(1-15) modulates the cardiovascular responses of galanin-(1-29) and the 5-HT1A receptor agonist 8-OH-DPAT

In view of the demonstration of specific binding sites for [125I]galanin-(1-15) in several brain areas including the nucleus of the solitary tract, possibly indicating the existence of multiple galanin receptor subtypes, the effects of intracisternal injections of galanin-(1-15) on cardiovascular parameters were studied. The effects of co-injections of galanin-(1-15) and galanin-(1-29) and co-injections of galanin-(1-15) and the 5-HT1A receptor agonist 8-OH-2-(di-n-propylamino)tetralin (8-OH-DPAT) were also evaluated. Galanin-(1-15) produced a significant increase in mean arterial blood pressure (maximum effect 10% at 3 nmol of galanin-(1-15)) and in heart rate (maximum effect 12% at 1 nmol). When threshold doses of galanin-(1-15) (0.1 nmol) and galanin-(1-29) (3 nmol) were injected simultaneously they elicited an increase in mean arterial blood pressure. The vasodepressor response induced by an ED50 dose of 8-OH-DPAT (6 nmol) was not modulated by a threshold dose of galanin-(1-15), but the increase in heart rate area induced by galanin-(1-15) alone was no longer observed. When threshold doses of both galanin-(1-15) and 8-OH-DPAT (0.3 nmol) were co-injected a vasodepressor response developed and on heart rate a tachycardic response was seen in the peak effects and the overall tachycardic response induced by galanin-(1-15) was sustained. The results show a different role for galanin-(1-15) as compared with galanin-(1-29) in central cardiovascular control.(ABSTRACT TRUNCATED AT 250 WORDS)

The age-related increase in galanin binding sites in the rat brain correlates with behavioral impairment

The regional distribution of [125I]galanin specific binding sites was determined in young (three- to four-month-old), 14-15-month-old and aged (26-27-month-old) male Sprague-Dawley rats, previously tested for their performances in the Morris water-maze task, using the radioautographic method on brain sections. A significant increase in specific binding was observed in piriform and entorhinal cortex, ventral subiculum, and dorsal dentate gyrus in the aged rats, whereas no significant changes were observed in dorsal subiculum, amygdala, septal area and various subcortical structures. The area-specific regional increase in specific binding density in aged rats was significantly correlated with the impairment of the behavioral performance in the Morris water-maze task. The change in [125I]galanin specific binding was a result of an increase in the number of galanin binding sites, but not of an increase in affinity.

Hypothermia induced by cholinomimetic drugs is blocked by galanin: possible involvement of ATP-sensitive K+ channels

Central administration of galanin in the mouse dose-dependently blocked the hypothermia induced by the muscarinic receptor agonist, 2-ethyl 8-methyl-2,8-diazospiro[4,5]decan-1,3-dion hydrobromide, RS86 (minimum effective dose, MED = 3 nmol) and the acetylcholinesterase inhibitor tetrahydroaminoacridine, (MED = 3 nmol). This inhibitory effect was reversed over the dose range (0.1, 0.3, 1, 3 nmol) by the galanin receptor antagonist galantide (MED = 0.3 nmol). Furthermore, the ATP-sensitive K+ channel blockers glibenclamide (MED = 1 nmol) and gliquidone (10 nmol) both prevented the inhibitory effects of galanin on RS86 induced hypothermia. Glibenclamide (10 nmol) also reversed the inhibitory effects of galanin on tetrahydroaminoacridine induced hypothermia. Preincubation of rat cortical membranes with galanin (10 nM, 1000 nM) in vitro had no effect on binding affinity, receptor number or pharmacology of the rat cortical muscarinic receptor. In contrast to the high affinity of glibenclamide, galanin only weakly displaced [3H]glibenclamide binding in mouse whole brain homogenates (36% at 10 microM). These studies suggest that the inhibitory effect of galanin on cholinergically mediated hypothermia induced by RS86 and tetrahydroaminoacridine may be exerted via an action at ATP-sensitive K+ channels but is unlikely to be acting directly at the site labelled by [3H]glibenclamide.

Galanin-(1-15), but not galanin-(1-29), modulates 5-HT1A receptors in the dorsal hippocampus of the rat brain: possible existence of galanin receptor subtypes

The aim of the present study was to evaluate whether galanin-(1-29) and galanin-(1-15) can modulate the 5-hydroxytryptamine1A (5-HT1A) receptors using [3H]8-OH-2-(di-n-propylamino)-tetralin ([3H]8-OH-DPAT) as a radioligand. Membrane preparations of the dorsal hippocampus, an area having the recently described [125I]galanin-(1-15) fragment binding sites, but having very few porcine [125I]galanin-(1-29) binding sites, were used. Galanin-(1-15) produced a concentration-dependent increase in the Kd value of [3H]8-OH-DPAT with a maximum effect of approximately 65% at 3 nM of galanin-(1-15), whereas galanin-(1-29) had no effect. This increase of the Kd value of [3H]8-OH-DPAT could be completely counteracted by the putative galanin antagonist M35 (1 nM). The Bmax values of [3H]8-OH-DPAT were not affected in any experiment. In conclusion, the present results give further evidence for the existence of a galanin receptor subtype mainly recognizing N-terminal galanin fragments, also having the ability to reduce the affinity of 5-HT1A receptors.

Physiological role of galanin in the regulation of anterior pituitary function in humans

The aim of our study was to elucidate the physiological role of the neuropeptide galanin in the regulation of anterior pituitary function in human subjects. Six healthy men (age range 26-35 yr, body mass index range 20-24 kg/m2) underwent in random order 1) an intravenous bolus injection of growth hormone-releasing hormone (GHRH)-(1-29)-NH2 (100 micrograms) + thyrotropin-releasing hormone (TRH, 200 micrograms) + luteinizing hormone-releasing hormone (LHRH, 100 micrograms) + corticotropin-releasing hormone (CRH, 100 micrograms), and 2) intravenous saline (100 ml) at time 0 plus either human galanin (500 micrograms) in saline (100 ml) or saline (100 ml) from -15 to +30 min. Human galanin determined a significant increase in serum GH (GH peak: 11.3 +/- 2.2 micrograms/l) from both baseline and placebo levels. No significant differences were observed between GH values after galanin and those after GHRH alone (24.3 +/- 5.2 micrograms/l). Human galanin significantly enhanced the GH response to GHRH (peak 49.5 +/- 10 micrograms/l) with respect to either GHRH or galanin alone. Human galanin caused a slight decrease in baseline serum adrenocorticotropic hormone (ACTH; 16.3 +/- 2.4 pg/ml) and cortisol levels (8 +/- 1.5 micrograms/dl). Galanin also determined a slight reduction in both the ACTH (peak 27 +/- 8 pg/ml) and cortisol (peak 13.8 +/- 1.3 micrograms/dl) responses to CRH. Baseline and releasing hormone-stimulated secretions of prolactin, thyroid-stimulating hormone, LH, and follicle-stimulating hormone were not altered by galanin. Our data suggest a physiological role for the neuropeptide galanin in the regulation of GH secretion in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of metoclopramide on the paradoxical growth hormone response to galanin in acromegaly

Galanin is able to enhance growth hormone (GH)-releasing hormone stimulated GH secretion in normal man. In acromegaly circulating GH levels are elevated and the GH response to GHRH may be exaggerated. Galanin has been recently shown to decrease circulating GH levels in acromegaly. Dopaminergic drugs were the only previously known agents able to cause a paradoxical GH fall in acromegaly. Aim of our study was to investigate the effects of a potent central dopaminergic receptor blocker, metoclopramide (MCP), on the galanin-induced paradoxical GH secretion in acromegalic subjects. Two male and three female patients with active acromegaly (age range 44-66 years, body mass index range 24.6-28 Kg/m2) were studied after 45 min i.v. infusion of porcine galanin (0.5 mg in 100 ml of saline) from 0 to 45 min combined with a 60 min i.v. infusion of a) saline (100 ml) or b) MCP (10 mg in 100 ml of saline) from -15 to 45 min. After galanin, GH values fell from baseline (27.5 +/- 10 micrograms/L) to a mean nadir of 16.4 +/- 6.1 micrograms/L; after galanin + MCP, circulating GH levels were also decreased (mean nadir 17.3 +/- 8.1 micrograms/L) in all the patients with respect to baseline (23.6 +/- 9.7 micrograms/L). No significant differences were found in absolute or percent of baseline GH levels after galanin+saline vs galanin + MCP. Our results suggest that the paradoxical GH fall after galanin in acromegalic patients is not mediated through dopaminergic receptor. It can be hypothesized that galanin may interact at the pituitary level with its own receptors expressed by GH-secreting adenomatous cells.

Galanin-receptor ligand M40 peptide distinguishes between putative galanin-receptor subtypes

The galanin-receptor ligand M40 [galanin-(1-12)-Pro3-(Ala-Leu)2-Ala amide] binds with high affinity to [mono[125I]iodo-Tyr26]galanin-binding sites in hippocampal, hypothalamic, and spinal cord membranes and in membranes from Rin m5F rat insulinoma cells (IC50 = 3-15 nM). Receptor autoradiographic studies show that M40 (1 microM) displaces [mono[125I]iodo-Tyr26]galanin from binding sites in the hippocampus, hypothalamus, and spinal cord. In the brain, M40 acts as a potent galanin-receptor antagonist: M40, in doses comparable to that of galanin, antagonizes the stimulatory effects of galanin on feeding, and it blocks the galaninergic inhibition of the scopolamine-induced acetylcholine release in the ventral hippocampus in vivo. In contrast, M40 completely fails to antagonize both the galanin-mediated inhibition of the glucose-induced insulin release in isolated mouse pancreatic islets and the inhibitory effects of galanin on the forskolin-stimulated accumulation of 3',5'-cAMP in Rin m5F cells; instead M40 is a weak agonist at the galanin receptors in these two systems. M40 acts as a weak antagonist of galanin in the spinal flexor reflex model. These results suggest that at least two subtypes of the galanin receptor may exist. Hypothalamic and hippocampal galanin receptors represent a putative central galanin-receptor subtype (GL-1-receptor) that is blocked by M40. The pancreatic galanin receptor may represent another subtype (GL-2-receptor) that recognizes M40, but as a weak agonist. The galanin receptors in the spinal cord occupy an intermediate position between these two putative subtypes.

Functional interactions of galanin and acetylcholine: relevance to memory and Alzheimer's disease

Galanin, a 29-amino acid neuropeptide, is the only peptide known to coexist with acetylcholine in the basal forebrain neurons which degenerate early in the progression of Alzheimer's disease. Biochemical and neurophysiological studies demonstrated inhibitory actions of galanin on cholinergic functions. Behavioral investigations found that intracerebrally administered galanin produces deficits on spatial learning and memory tasks in rats. Taken together, the current literature suggests that galanin acts as an inhibitory modulator of acetylcholine in this coexistence. Particularly in the case of Alzheimer's disease, where cholinergic activity is severely compromised, the negative actions of galanin may be particularly deleterious. Recently developed galanin antagonists may provide a novel therapeutic approach toward enhancing memory processes in Alzheimer's disease, by removing the putative inhibitory actions of endogenous galanin on the remaining basal forebrain cholinergic neurons.

Galanin antagonists block galanin-induced feeding in the hypothalamus and amygdala of the rat

Galanin significantly increased food intake when microinjected into the region of the central nucleus of the amygdala as well as into the paraventricular nucleus of the hypothalamus. In the amygdala this effect was specific to feeding; no change in grooming, resting, or other behaviour was observed after galanin treatment. These results provide evidence that the amygdala may be an important site in the mediation of galanin-induced feeding. The galanin receptor antagonists, C7 and M40, antagonized galanin-induced feeding, while having no effect alone on food consumption in free-feeding rats. These new galanin receptor antagonists provide useful tools for further investigating the role of endogenous galanin in the regulation of feeding.

Microinjection of galanin into the medial preoptic nucleus facilitates copulatory behavior in the male rat

The medial preoptic area (MPOA) is an important region for masculine sexual behavior. Because galanin (GAL) immunoreactive cells within the MPOA are affected by the gonadal steroid environment and GAL binding is apparent, GAL was microinjected site specifically in 0, 10, 50, 100, and 500 ng doses in order to determine effects on copulatory behavior. Unilateral microinjection of GAL within the medial preoptic nucleus facilitated copulatory behavior in a dose-responsive fashion, evidenced by an increase in the percentage of males that displayed sexual behaviors and a decrease in mount and intromission latencies. These effects required the presence of gonadal steroids, and were not due to general arousal as measured in open field testing. The techniques of survival analysis were used to display data and for statistical analysis of intromission and mount latencies; these approaches revealed significant effects that were not evident with more commonly used procedures. The results support the suggestion that sexually dimorphic galaninergic cell groups within the MPOA are involved in gonadal steroid-induced masculine sexual behavior.

Galanin fails to alter both acquisition of a two trial per day water maze task and neurochemical markers of cholinergic or serotonergic neurones in adult rats

The co-existence of galanin with acetylcholine in ventral forebrain neurones combined with evidence that galanin attenuates cholinergic function and is present in senile plaques in Alzheimer's disease all implicate this neuropeptide in the regulation of cognition. This study simultaneously examines the effect of galanin on acquisition in a Morris water maze and post-training markers of cholinergic and serotonergic forebrain neurones thought to be involved in cognition. Synthetic porcine galanin (10(-9) to 10(-6) M) produced dose-related inhibition of atropine sensitive indirectly-evoked contractions of an isolated guinea-pig ileum which was unaffected by naloxone (10(-7) M). This confirmed the bioactivity of synthetic galanin, which reduces acetylcholine, but not opiate, release from the ileal myenteric plexus. Galanin pretreatment (1 or 10 micrograms i.c.v., -15 min) failed to alter acquisition of a Morris water maze task (2 trials per day) in Hooded Lister rats. Following behavioural acquisition, five days of galanin administration did not alter choline acetyltransferase activity, thyrotrophin-releasing hormone-like immunoreactivity or 5-hydroxytryptamine levels or turnover in the frontal cortex, hippocampus or septum, although dopamine levels were significantly elevated in the frontal cortex. These findings suggest that galanin does not affect acquisition in a simple visual-spatial task which taxes reference more than working memory and questions the assumption that a cholinergic mechanism is the major contributor to previously reported cognitive effects of galanin.

[125I]galanin binding sites in the rat frontal lobe are guanine nucleotide-sensitive and display a low regional index of occupancy

As the neuropeptide galanin is possibly involved in spatial learning, we investigated both the precise location and the binding features of the receptors within the rat frontal cortex using quantitative autoradiography. Galanin receptors predominated in layers I and V of medial and lateral frontal cortex with a low regional index of occupancy by endogenous galanin. These receptors might be of functional relevance since the guanylnucleotide Gpp(NH)p inhibited [125I]galanin specific binding in each labeled region in the frontal lobe. Nevertheless, the striking areal difference of expression of this effect within the medial frontal cortex suggests that [125I]galanin binding sites might be coupled to one or more types of G-proteins related to the functionally distinct cortical subareas.

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

The regulation of galanin (GAL) gene expression in the bed nucleus of the stria terminalis (BNST) by testosterone (T) was investigated using in situ hybridization histochemistry. Castration of adult male rats significantly reduced both the number of cells which expressed GAL mRNA and the average number of grains per cell. These effects were reversed by testosterone treatment. Testosterone stimulates GAL gene expression in the same neurons that have previously been shown to exhibit steroid regulation of vasopressin gene expression.

Extra-hypothalamic vasopressin neurons coexpress galanin messenger RNA as shown by double in situ hybridization histochemistry

Vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BNST) and medial amygdala (AMe) exhibit sexual dimorphism and steroid dependency. VP neurons in the supraoptic nucleus and paraventricular nucleus have been shown to coexpress other transmitters including galanin (GAL). However, little is known about what other neurotransmitters may be colocalized with VP in the BNST and AMe. Here, we have used radio-labeled and digoxigenin-labeled cRNA probes to perform double in situ hybridization histochemistry for VP and GAL in the BNST and AMe of intact, adult male rats. We provide evidence that in the basal state, the majority of VP-synthesizing cells in the BNST and AMe of the adult male rat also express galanin mRNA. Likewise, the majority of GAL-expressing neurons in these regions also contain VP mRNA. These findings give further evidence for the similarity of the BNST and AMe and provide a rationale for studies investigating the role of GAL in functions involving extrahypothalamic VP pathways.

Galanin reduces release of endogenous excitatory amino acids in the rat hippocampus

Galanin is a 29-amino acid peptide widely distributed in the central nervous system where it modulates the release of several neurotransmitters and neurohormones. Because previous data had postulated that galanin could inhibit the release of excitatory amino acids and protect hippocampal neurons against anoxia, we have investigated the effect of galanin on the release of endogenous glutamate and aspartate evoked by potassium depolarization in rat hippocampal slices. Galanin, added to a concentration of 0.3 microM, produced a 50-60% reduction in the release of endogenous glutamate and aspartate as evoked by 40 mM K+. This effect was concentration-dependent with half-maximal effective galanin concentrations (EC50) of 1.7 and 5.9 nM for glutamate and aspartate, respectively. Such an effect was found to occur preferentially in the ventral rather than in the dorsal region of the hippocampus. The inhibitory effect of galanin on the K(+)-evoked release of excitatory amino acids was reversed by the specific galanin antagonist M-15 (0.3 microM), and by the ATP-sensitive potassium channel blocker glibenclamide (10 microM). Furthermore, M-15 alone increased the basal and the K(+)-evoked release of glutamate and aspartate from hippocampal slices. It is concluded that galanin exerts a tonic inhibition of excitatory glutamate/aspartate neurotransmission in the rat ventral hippocampus. The efficacy of glibenclamide in antagonizing the effect of galanin suggests the involvement of ATP-sensitive or -insensitive potassium channels in such a regulation.

Localisation of mRNA encoding the protein precursor of galanin in the monkey hypothalamus and basal forebrain

The hypothalamic and basal forebrain sites of synthesis of preprogalanin mRNA were identified in three adult monkeys (Macaca fascicularis) by in situ hybridisation performed with a radiolabelled cRNA probe transcribed from human preprogalanin cDNA. With stringent hybridisation conditions, the cRNA probe was hybridised to free-floating sections containing structures contiguous with the rostral hypothalamus through to the caudal limit of the hypothalamus as defined by the mammillary bodies. Specific hybridisation of the preprogalanin cRNA probe occurred throughout the hypothalamus but was particularly intense in the arcuate, paraventricular (parvicellular and magnocellular portions), and dorsomedial nuclei. Moderate hybridisation was found in the periventricular nucleus and scattered hybridisation in the medial preoptic nucleus. The medial preoptic area and the anterior and lateral hypothalamic areas showed moderate to intense hybridisation in scattered cells. A few cells in the tuberal portion and dorsal cap of the anterior portion of the supraoptic nucleus were labelled. Isolated cells were also labelled in the zona incerta. There was little labelling in the dorsal hypothalamic area but moderate labelling in the posterior hypothalamic area. Structures contiguous with the rostral hypothalamus including the diagonal band of Broca, bed nucleus of stria terminalis, substantia innominata, and basal nucleus of Meynert showed intense hybridisation. These data indicate a widespread distribution of preprogalanin mRNA in the monkey hypothalamus. A comparison with the previously reported distribution of preprogalanin mRNA in the rat, as well as with the distribution of galanin-like immunoreactivity in the rat and human, suggests some important species differences. Of particular interest were differences in the supraoptic, suprachiasmatic, and dorsomedial nuclei. The intense hybridisation throughout the paraventricular nucleus and in the rostral arcuate nucleus suggests that galanin may play a role in the regulation of both posterior and anterior pituitary function.

Galanin receptor antagonists M40 and C7 block galanin-induced feeding

Two peptide antagonists of the galanin receptor, M40 (galanin[1-13]-Pro-Pro-[Ala-Leu]2-Ala amide) and C7 (galanin[1-13]-spantide amide), significantly inhibited galanin-induced consumption of a palatable wet cookie mash, when microinjected intraventricularly to satiated rats. Antagonists were effective at doses equimolar to or less than the active doses of galanin. Feeding induced by an overnight fast was not significantly different in rats microinjected with saline as compared to M40 or C7, at doses which inhibited galanin-induced feeding. The activity of the chimeric compound, C7, did not appear to be linked to the properties of its C-terminal spantide-like sequence, as C7 did not induce barrel rolling at doses which inhibited galanin-induced feeding. The IC50 for displacement of 125I-[Tyr26]-porcine galanin 1-29 binding in rat hypothalamic membranes was 15 nM for M40, and 0.2 nM for C7, as compared to 0.8 nM for unlabelled porcine galanin(1-29). These two structurally different galanin antagonists, both demonstrating antagonist activity in vivo in awake, behaving rats, provide promising tools for further analyses of the functional activity of galanin in the mammalian brain.

The role of galanin in cholinergically-mediated memory processes

1. Galanin, a 29 amino-acid neuroactive peptide, has been shown to affect diverse processes throughout the nervous system and to coexist with several "classical" neurotransmitters, including norepinephrine, serotonin, and acetylcholine. 2. Galanin coexists with acetylcholine in neurons of the medial septum, diagonal band, and nucleus basalis of Meynert, cells which degenerate during the course of Alzheimer's disease. 3. In the ventral hippocampus, galanin inhibits the release of acetylcholine and inhibits carbachol stimulated phosphatidyl inositol hydrolysis. 4. Galanin impairs choice accuracy in learning and memory paradigms in rats, and is therefore hypothesized to be a contributory factor in the memory and cognitive disabilities found in Alzheimer's patients. 5. Newly developed galanin antagonists, by eliminating putative inhibitory effects of endogenous galanin on cholinergic function, may serve as useful therapies for memory disorders.

Autoradiographic localization of 125I-galanin binding sites in the blowfly brain

The localization of porcine galanin (pGAL) binding sites in the brain of the blowfly Phormia terraenovae was investigated by autoradiography using the following radioiodinated ligands: pGAL 1-29 (two isoforms), pGAL 15-29 and rat (r) GAL 1-29. The different porcine radioligands bound specifically with the following intensity: 125I-[Tyr26]-pGAL15-29 > > 125I-[Tyr26]-pGAL1-29 > > 125I-[Tyr9]-pGAL1-29. With rat galanin 125I-[Tyr9]-rGAL1-29 no specific binding could be shown. In addition, displacement of 125I-[Tyr26]-pGAL1-29 was tested with pGAL 1-29, pGAL 1-22 and pGAL 15-29 (at 0.1 nM-1 microM). A gradual displacement was achieved with increasing concentrations of pGAL 1-29 and pGAL15-29, whereas no displacement with pGAL 1-22 was detected. The results indicate that the C-terminal portion of pGAL is important for binding in the blowfly. The pGAL binding sites were localized in synaptic neuropils of the central body, the antennal lobes, the optic lobes, the pars intercerebralis and the subesophageal ganglion, all of which contain GAL-like immunoreactive neural processes.

Evidence for specific N-terminal galanin fragment binding sites in the rat brain

The existence and widespread distribution of specific [125I]galanin-(1-15) fragment binding sites in the rat brain was demonstrated by using [125I]galanin-(1-15) as a radioligand in quantitative receptor autoradiographical studies. These binding sites were also present in several areas lacking or having very few [125I]galanin-(1-29) binding sites, such as the dorsal hippocampal formation, the neocortex and the neostriatum. [125I]Galanin-(1-15) binding sites showed a high selectivity for the fragment, since galanin-(1-15) could displace 80% of the binding whereas porcine galanin-(1-29) could only displace 30%. The binding was saturable with a Kd of 0.63 +/- 0.02 nM and a Bmax of 15.3 +/- 1.7 fmol/mg in sections from the dorsal hippocampal formation. Thus, a new type of galanin receptor selective for N-terminal galanin fragments may exist in the rat brain.

Galanin receptors in the brain of a teleost: autoradiographic distribution of binding sites in the Atlantic salmon

The distribution of galanin (GAL) binding sites in the brain of the Atlantic salmon (Salmo salar) was investigated by means of radioligand binding in conjunction with autoradiography by using high-performance liquid chromatography (HPLC) characterized radio-iodinated porcine galanin ([125I]GAL). On slide-mounted sections of frozen salmon brain homogenate, [125I]GAL (4 nM) bound rapidly and reversibly to a single population of sites with a Kd of 1.0 +/- 0.08 nM (n = 3) and Bmax of 2.38 +/- 0.19 fmol/mg wet tissue. Specific [125I]GAL binding was found in cellular regions, in fiber tracts, and in neuropil areas throughout the brain, except for in the olfactory bulb, pineal organ, and cerebellum. Autoradiographic microdensitometric measurements revealed high total [125I]GAL binding in the ventral hypothalamus (inferior lobes; around 7-12 fmol/mg tissue), the dorsal spinal cord (between 6 and 12 fmol/mg tissue), sublayers of the optic tectum (around 8 fmol/mg), torus semicircularis (around 7 fmol/mg), and glomerular complex (around 6 fmol/mg). Intermediate densities of [125I]GAL binding (3-5 fmol/mg tissue) were found in the pituitary, telencephalon, dorsolateral thalamic nucleus, and raphe nuclei and in association with the forebrain bundles. Except for in the optic tectum, there is a good concordance of [125I]GAL binding sites and GAL-immunoreactive fiber projections in most brain areas of the salmon. The wide distribution of GAL binding sites provides further evidence that a GAL-like substance might be involved in a diversity of brain functions of teleosts. The topographic distribution of target sites in the hypothalamo-hypophyseal axis indicates that GAL-like substances may have both direct and indirect effect on pituitary functions while in extrahypothalamic areas, functional implications by GAL may include involvement in somatosensory, central gustatory, olfactory, and visual functions. This study provides evidence for the presence of a specific GAL receptor in the brain of the Atlantic salmon. Together the distribution of GAL binding and GAL-like molecules provide a covering delineation of the GAL neuronal system in the brain of the Atlantic salmon. Comparisons with mammals suggest that the GAL receptor molecule has been well preserved during evolution and that GAL-like substances may be present, and even possess similar functional properties, throughout the vertebrate phylogeny.

Estrogen-concentrating cells within cell groups of the medial preoptic area: sex differences and co-localization with galanin-immunoreactive cells

Male and female rats have approximately equal numbers of estrogen(E)-concentrating cells within the medial preoptic area (MPOA). Several cell groups within this brain region are sexually dimorphic, however, and these groups may have sexually different numbers of E-containing cells; this, in turn, may reflect sex differences in neural-regulated functions. In order to study this possibility, the distribution of E-concentrating cells was determined using estrogen autoradiography. Except for the lateral portion of the medial preoptic nucleus (MPNl), the density of E-concentrating cells was 3-5-times higher within the most medially situated cell groups of the female than the male, i.e., within the anteroventral periventricular nucleus (AVPv), periventricular preoptic area (PVPO), medial portion of the medial preoptic nucleus (MPNm), and its central portion (MPNc). In addition, we determined whether E-concentrating cells also express the neuropeptide, galanin. An average of 13% of the E-concentrating cells were galanin positive, which represented 15% of the galanin-immunoreactive population. These results demonstrate a frank and dramatic sex difference in the distribution of E-concentrating cells within sexually dimorphic regions of the MPOA, and also suggest that an interaction between galanin and gonadal steroids may be an important means by which cells within the MPOA regulate reproductive function.

Evidence for a role of the neuropeptide galanin in spatial learning

The neuropeptide galanin coexists with acetylcholine (ACh) in the basal forebrain cholinergic neurons and modulates cholinergic activity in the forebrain. The cholinergic forebrain neurons appear to play a significant role in learning and memory, as suggested by a severe loss of these neurons in Alzheimer's disease. The involvement of endogenous galanin in learning is demonstrated here by the use of the recently synthesized high-affinity galanin antagonist M35 [galanin(1-13)-bradykinin(2-9) amide] (Kd = 0.1 nM). Intracerebroventricular (i.c.v.) administration of M35 (6 but not 3 nmol) produced a significant (P < 0.025) facilitation of acquisition in a spatial learning test (Morris swim maze) without any increase in swim speed. Thus, M35 (6 nmol) shortened the escape latency, reduced the number of failures to reach the platform, and shortened the path length to reach the hidden platform. M35 (3 and 6 nmol) tended to enhance retention performance seven days after the last training session. Receptor autoradiographic studies on the distribution of [125I]M35 following i.c.v. administration show that it binds preferentially in the periventricular regions including the hippocampus. These results suggest that galanin may modulate spatial learning and memory and that galanin antagonists may provide a new principle in the treatment of Alzheimer's disease.

Regional stimulatory and inhibitory effects of guanine nucleotides on [125I]galanin binding in rat brain: relationship with the rate of occupancy of galanin receptors by endogenous galanin

Galanin has been shown to stimulate feeding or modulate neuroendocrine secretions when administered centrally. In the present work, using quantitative autoradiography, we documented the existence of [125I]galanin specific binding sites in several hypothalamic nuclei expected to mediate these effects. In standard binding conditions, [125I]galanin specific binding can be visualized in the hypothalamic ventromedial nucleus, stria terminalis, piriform cortex, central amygdaloid nucleus and medial amygdaloid nucleus, while it is almost undetectable in most neuroendocrine or autonomic hypothalamic areas. We hypothesized that high endogenous galanin levels in these regions might mask galanin receptors. We first showed that a high ionic strength/acid wash of brain slices is effective in removing more than 80% of specifically prebound [125I]galanin in all tested regions. After such treatments, specific binding sites could be revealed in the hypothalamus namely in the parvocellular paraventricular nucleus, periventricular nucleus, arcuate nucleus and median eminence. In contrast, regions already labeled in standard conditions exhibited a slight decrease in [125I]galanin binding. Thus, regions were ranked from low to high rate of occupancy of galanin receptors by endogenous galanin, the rate of occupancy of galanin receptors being maximal in median eminence (greater than 90%). We thus studied the regional effect of guanine nucleotides on [125I]galanin specific binding. A high concentration (100 microM) of guanyl 5'-yl imidodiphosphate, a nonhydrolyzable analog of GTP directly added to the incubation medium, inhibited [125I]galanin binding in all telencephalic regions. On the same sections and only in regions of high index of galanin receptor occupancy (arcuate nucleus, median eminence, dorsomedial nucleus, paraventricular nucleus, and periventricular hypothalamic nucleus), guanyl 5'-yl imidodiphosphate paradoxically enhanced [125I]galanin binding. The effects of acid preincubation and guanyl 5'-yl imidodiphosphate incubation on [125I]galanin binding were strongly correlated in these hypothalamic areas (r = 0.97). In all regions, guanyl 5'-yl imidodiphosphate increased the rate of dissociation of [125I]galanin. In competition studies, guanyl 5'-yl imidodiphosphate decreased the IC50 s of unlabeled galanin which were homogenized around 4 nM in most telencephalic and hypothalamic regions. Thus, the guanyl 5'-yl imidodiphosphate-induced stimulation of [125I]galanin specific binding measured in the neuroendocrine and autonomic hypothalamus is linked to an increase in receptor capacity and not to a rise in receptor affinity. Both inhibitory and stimulatory guanyl 5'-yl imidodiphosphate effects observed in [125I]galanin equilibrium binding studies were dose-dependent and guanine nucleotide-specific with guanyl 5'-yl imidodiphosphate more potent than GTP or GDP.(ABSTRACT TRUNCATED AT 400 WORDS)

Galanin-like immunoreactivity in the adult and developing Brazilian opossum brain

The distribution of galanin-like immunoreactivity has been characterized in the brain of the adult and developing Brazilian opossum (Monodelphis domestica). Two commercially available antisera were used to examine the distribution of galanin-like immunoreactive (GAL-IR) cells and fibers. Nuclear groups containing GAL-IR cell bodies and fibers were seen throughout the adult opossum brain. The distribution of GAL-IR elements seen is similar to that reported for other mammals. Based on these findings, we believe that galanin may have similar physiological functions in the adult Brazilian opossum as has been reported for other mammals. In the developing brain, GAL-IR structures were seen as early as 1 day postnatal (PN) in the developing hypothalamus and brainstem. By days 5 and 10 PN, there was a robust expression of galanin-like immunoreactivity in specific regions of the brain. Since neurogenesis and brain morphogenesis are actively occuring postnatally in the opossum, galanin may be playing a role in the differentation of specific regions of the brain.

Galanin immunoreactivity in the primate central nervous system

Galanin-immunoreactive profiles were localized within the monkey and human central nervous system. In the monkey telencephalon, galanin-immunoreactive perikarya were seen within the anterior olfactory nucleus, basal forebrain, endopiriform nucleus, hippocampus, and bed nucleus of the stria terminalis. The caudate nucleus and putamen contained galanin-immunoreactive perikarya whereas the nucleus accumbens displayed only galanin-immunoreactive fibers. In the diencephalon, galanin-immunoreactive profiles were seen within the medial preoptic area, periventricular, suprachiasmatic, paraventricular, and arcuate nuclei as well as the lateral hypothalamic area. Within the thalamus, only galanin-immunoreactive fibers were seen within the midline paraventricular, reuniens, and rhomboid nuclei. In the mesencephalon, scattered galanin-immunoreactive fibers were seen in the periaquaductal gray, ventral tegmental area, and midbrain reticular formation. In the metencephalon, galanin-immunoreactive neurons were observed in the medial vestibular nucleus and nucleus prepositus. In the myelencephalon, galanin-immunoreactive perikarya were seen within the nucleus of the tractus solitarius and hypoglossal nucleus. Dense collections of galanin-immunoreactive fibers were found in the spinal descending tract of V, nucleus of the tractus solitarius, and dorsal motor nucleus of X. Galanin immunoreactivity was also observed within all circumventricular organs. Spinal anterior horn neurons expressed galanin immunoreactivity, and immunopositive fibers were seen within the tract of Lissauer and the substantia gelatinosa. Although the distribution of galanin immunoreactivity was generally similar between monkeys and humans, there were a few striking exceptions. The human supraoptic nucleus contained galanin-immunoreactive neurons, whereas the monkey supraoptic nucleus displayed only immunopositive fibers. Similarly, galanin-immunoreactive perikarya and fibers were seen in the human locus coeruleus and subcoeruleus, whereas in monkeys these regions contained only fibers. These data demonstrate a widespread distribution of galanin-containing profiles in primates, suggesting that galanin may modulate cognitive, sensory, motor, and autonomic processes.

Attempts to make models for Alzheimer's disease

Profound reductions in cortical acetylcholine levels together with degeneration of cholinergic neurons in the basal forebrain have been reported in patients with Alzheimer's disease. A similar loss of the cholinergic neurons of the basal forebrain and impairment of learning and memory occur in animals injected with a nerve growth factor-diphtheria toxin conjugate, suggesting that this animal model is suitable to analyze cholinergic roles on learning and memory processes, and also the pathogenesis of Alzheimer's disease. In addition, animal models constructed by electrolytic or neurotoxic lesioning of the basal magnocellular nucleus, and models made by transgenetic technology were described.

Galanin receptors and their second messengers in the lumbar dorsal spinal cord

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr26 galanin as ligand. The equilibrium binding of [125I]galanin showed the presence of a single population of high-affinity binding sites with KD = 0.6 +/- 0.2 nM in a concentration of 55 +/- 15 fmol mg-1 protein (Bmax). The N-terminal fragments galanin (1-16) and galanin (1-12) fully displaced specific [125I]galanin binding from membranes with IC50 values 6 nM and 4 microM, respectively. The C-terminal fragment galanin (17-29) did not displace [125I]galanin when applied in the concentration range 10(-11)-10(-4) M. GTP inhibited the specific binding of [125I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10 microM) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 microM) did not inhibit the noradrenalin (100 microM) activated cAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on Bmax or KD of the galanin receptor was found.

M-15: high-affinity chimeric peptide that blocks the neuronal actions of galanin in the hippocampus, locus coeruleus, and spinal cord

The 20-amino acid peptide M-15 binds with high affinity (IC50 approximately 0.1 nM) to 125I-labeled galanin (125I-GAL) binding sites in membranes from the ventral hippocampus, midbrain, and rat spinal cord. Receptor autoradiographic studies show that M-15 can displace 125I-GAL from all labeled sites. M-15 acts as a reversible high-affinity antagonist in blocking the inhibitory effects of GAL on the evoked release of acetylcholine in vivo in the hippocampus and on the GAL-induced hyperpolarization of locus coeruleus neurons in slices. M-15 also blocks the facilitatory effects of GAL on the spinal flexor reflex. Thus, the chimeric peptide M-15 [GAL-(1-13)-substance P-(5-11)amide] represents the first antagonist to the neuronal actions of GAL.

Centrally coinjected galanin and a 5-HT1A agonist act synergistically to produce vasodepressor responses in the rat

The present study was undertaken to evaluate the possible functional implications of the previously demonstrated in vitro interactions between galanin and 5-HT1A receptors. To this end we analysed the interactions between galanin and the 5-HT1A receptor agonist 8-OH-2-(di-n-propylamino)-tetralin (8-OH-DPAT) in central cardiovascular regulation. 8-OH-DPAT given intracisternally (i.c.) produced a dose-dependent reduction of blood pressure, the peak action being 32% at 10 nmol of 8-OH-DPAT. Heart rate and respiration rate were not affected. The vasodepressor action of 8-OH-DPAT was counteracted by the 5-HT1A receptor antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN-190). A threshold dose (1 nmol) of galanin given i.c. was shown to enhance the vasodepressor effect of both an ED50 dose and a threshold dose of 8-OH-DPAT. Quantitative receptor autoradiography showed that the IC50 values for [125I]galanin binding sites were reduced in the presence of 8-OH-DPAT (10 nM) by approximately 40% in the dorsal region of the nucleus of the solitary tract, the area postrema, and the raphe pallidus and obscurus nuclei. Galanin (10 nM) also significantly increased the IC50 value for [3H]8-OH-DPAT binding sites within the nucleus of the solitary tract. The results provide evidence for a synergistic interaction between 8-OH-DPAT and galanin in cardiovascular regulation after their central administration, an interaction possibly related to the ability of 8-OH-DPAT to enhance the affinity of the galanin receptor within regions of the medulla oblongata involved in cardiovascular control.

Galanin immunoreactivity in the blowfly nervous system: localization and chromatographic analysis

In this study chromatographic, immunochemical, and immunocytochemical methods provide evidence of a galanin-like peptide(s) in an invertebrate, the blowfly Phormia terraenovae. The major portion of the galanin-like immunoreactivity (GAL-LI) in fly heads was extractable in acetic acid but not in boiling water, which suggests that the peptide(s) may be highly basic in nature. GAL-LI was present both in the head and body portion of the blowfly in roughly the same amounts. Initial gel filtration data, using a G-50 Sephadex column and a weak phosphate-buffer (pH 6.5) as eluent, suggested that a fly GAL-LI peptide(s) from fly heads, eluting as an apparent single peak, was smaller than porcine GAL(1-29) and GAL(1-15). However, concomitant analysis using a G-25 Sephadex column and acetic acid (0.2 M) as eluent, spread the immunoreactive material over a great portion of the chromatogram, although the main portion of the material eluted in the same size range as porcine GAL(1-29). Taken together, the gel filtration data thus suggest that fly GAL-LI peptide(s) may be highly basic but presumably similar in size to vertebrate GAL(1-29). However, the hydrophobic properties of the fly GAL-LI peptide(s) differ from that of porcine GAL as demonstrated by the presence of several immunoreactive components eluting both early as well as late in the chromatogram when using reverse-phase high performance liquid chromatography (HPLC); early peaks may represent highly basic and/or possibly smaller GAL-immunoreactive peptide(s), whereas later peaks may represent less basic and possibly elongated forms. Immunocytochemistry indicated that GAL-LI was present in the nervous system of the blowfly. About 160 GAL-immunoreactive neurons were found in the brain and subesophageal ganglion, 26 in the fused thoracic ganglion and 30 in the fused abdominal ganglion. In the brain, GAL-immunoreactive fibers supply specific subdivisions of the central body, optic lobe, superior protocerebrum, and tritocerebrum as well as neuropil in the subesophageal ganglia. In the thoracico-abdominal ganglia, GAL-immunoreactive neuron processes are found inside synaptic neuropil as well as in the neural sheath of the ganglia and several of the dorsal nerve roots. Many of the GAL-immunoreactive neurons react also with an antiserum against porcine galanin message associated peptide, a peptide present in the preprogalanin protein. Immunocytochemical double-labeling indicated that some GAL-immunoreactive neurons also reacted with antisera against the molluscan peptides FMRFamide and SCPB, whereas no evidence could be found for colabeling with antisera against tyrosine hydroxylase, substance P and physalaemin.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of 5-hydroxytryptamine1A receptors increases the affinity of galanin receptors in di- and telencephalic areas of the rat

Since galanin in vitro selectively increases the KD value of 5-HT1A receptors without altering the binding of 5-HT1B or 5-HT2 receptors, we have studied whether 5-HT1A receptor activation in turn may affect galanin binding in the ventral di- and telencephalon and the substantia nigra of the rat. As analyzed by autoradiography, the binding of 125I-galanin was increased by about 55% in the presence of 3-30 nM of 8-OH-2-(di-n-propylamino)-tetralin (DPAT) in the paraventricular thalamic nucleus, the nucleus reuniens and rhomboideus, the zona incerta, the medial and the lateral hypothalamus, and the medial and the lateral amygdaloid area, but not in the pars compacta of the substantia nigra, which lacks 5-HT1A binding sites. DPAT (10 nM) reduced the IC50 values of galanin at 125I-galanin binding sites by approximately 55% within all the analyzed di- and telencephalic regions. The overall increase in BO values was 50 +/- 11%. Using the filter wipe technique in cryostat sections at Bregma -2.8 mm covering all the brain regions at this level, DPAT (10 nM) decreased the IC50 values of galanin from 21.6 +/- 1.1 nM (control) to 15.5 +/- 0.9 nM, and increased the BO values by 19.4 +/- 4.1%. In membrane preparations from the ventral di- and telencephalon, DPAT decreased the IC50 values of galanin binding sites by 20 +/- 3% at 100 nM of DPAT. This effect could be completely blocked by the specific 5-HT1A receptor antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of histamine release in rat hypothalamus and hippocampus by presynaptic galanin receptors

The effect of galanin, a peptide present in a subpopulation of histaminergic neurons emanating from the rat posterior hypothalamus, was investigated on K(+)-evoked [3H]histamine release in slices and synaptosomes from rat cerebral cortex, striatum, hippocampus and hypothalamus. Porcine galanin (0.3 microM) significantly inhibited histamine release induced by 25 mM K+ in slices from hypothalamus and hippocampus, but not from cerebral cortex and striatum, i.e., only in regions in which a colocalization of histamine and galanin has been described. The inhibitory effect of galanin was concentration dependent, with an EC50 value of 5.8 +/- 1.9 nM. The maximal inhibition was of 30-40% in hypothalamic and hippocampal slices depolarized with 25 mM K+. The galanin-induced inhibition observed in hypothalamic slices was not prevented in the presence of 0.6 microM tetrodotoxin and also occurred in hippocampal and hypothalamic synaptosomes, strongly suggesting the activation by galanin of presynaptic receptors located upon histaminergic nerve endings. The maximal inhibitory effect of galanin in slices or synaptosomes was lower than that previously reported for histamine acting at H3-autoreceptors, possibly suggesting that not all histaminergic axon terminals, even in the hypothalamus and hippocampus, are endowed with galanin receptors. It increased progressively in hypothalamic and hippocampal synaptosomes as the strength of the depolarizing stimulus was reduced. It is concluded that galanin modulates histamine release via presynaptic receptors, presumably autoreceptors located upon nerve terminals of a subpopulation of cerebral histaminergic neurons.