Biomedical subjects

T Bartfai

Publications and source records attributed to T Bartfai.

At least 109 records · Page 6Linked to original sources

PubMed1995

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.

Amino Acid Sequence↗

PubMed1995

Metabolism of galanin and galanin (1-16) in isolated cerebrospinal fluid and spinal cord membranes from rat.

The occurrence of galanin (GAL) in the spinal cord and reports suggesting that it acts as an endogenous inhibitory spinal modulator in sensory/noxious transmission, have focused interest on its metabolism in the spinal cord. The metabolic half-lives and degradation patterns of GAL(1-29) and the high affinity N-terminal fragment GAL(1-16), were determined in isolated cerebrospinal fluid (CSF) from rats, and analysed by reverse phase HPLC. The half-lives for GAL(1-29) and GAL(1-16) in isolated rat CSF at 37 degrees C were 120 min and 60 min, respectively. The first degradation products which we could isolate and identify of GAL(1-16) were: GAL(3-16) and GAL(3-12) and for GAL(1-29): GAL(1-5) and GAL(1-4), all without affinity to spinal galanin receptors. Degradation studies of GAL(1-29) and GAL(1-16) in a spinal cord membrane preparation, in absence or presence of different protease inhibitors: E-64, pepstatin A, 3,4-DCI, bestatin, phosphoramidon, kelatorphan and thiorphan, or metal chelators: EDTA, EGTA and o-phenanthrolin, suggest that a phosphoramidon sensitive zinc-metalloprotease is mainly responsible for the degradation of GAL(1-29) and GAL(1-16), since both o-phenanthrolin (0.3 mM) and phosphoramidon (920 microM) substantially prolong their half-lives.

Amino Acid Sequence↗

PubMed1995

Peripheral axotomy increases the expression of galanin message-associated peptide (GMAP) in dorsal root ganglion cells and alters the effects of intrathecal GMAP on the flexor reflex in the rat.

We have previously reported that galanin message-associated peptide (GMAP), a fragment of galanin precursor protein, occurs in a limited number of dorsal root ganglion (DRG) cells in rats with intact sciatic nerves. In the present study, the localization of GMAP in dorsal root ganglia, dorsal roots and dorsal horn was analyzed immunohistochemically and compared between rats with intact and sectioned sciatic nerves. Furthermore, the effects of intrathecal (i.t.) GMAP on the flexor reflex in rats with intact and sectioned nerves were examined. In rats with intact sciatic nerves, i.t. GMAP elicited a moderate facilitation of the flexor reflex. The facilitation of the flexor reflex induced by conditioning stimulation (CS) of cutaneous C-fibers was strongly blocked by GMAP. GMAP also selectively antagonized the reflex facilitatory effect of i.t. substance P (SP), but not i.t. vasoactive intestinal peptide (VIP). Unilateral sciatic nerve section induced an upregulation of GMAP in the ipsilateral dorsal root ganglia 2 weeks after axotomy. The effect of GMAP on the baseline reflex was similar in normal and axotomized rats, but the blocking effect of GMAP on C-fiber CS-induced facilitation was significantly reduced after axotomy. GMAP did not antagonize the reflex facilitatory effect of SP after axotomy, whereas an antagonism on VIP-induced facilitation was observed. The possible role of GMAP in spinal transmission and comparison with the effects of galanin are discussed.

Animals↗

PubMed1995

Galanin induces a hyperpolarization of norepinephrine-containing locus coeruleus neurons in the brainstem slice.

Galanin applied in the bath or by micropipette directly on to locus coeruleus neurons in an in vitro slice preparation caused a hyperpolarization accompanied by a small decrease in membrane resistance. Immunohistochemical staining of intracellularly filled neurons indicated that the effect of galanin was exerted on norepinephrine neurons of the locus coeruleus. The galanin effect was variable in amplitude and duration and often showed desensitization, with subsequent applications producing a smaller response. When cells were exposed to tetrodotoxin or tetrodotoxin/low calcium media, the galanin response was still present. Under voltage clamp galanin application caused a net outward current that did not reverse in normal potassium concentrations; however, by increasing extracellular potassium concentrations the net outward current was reversed and the reversal potential shifted to a less negative potential. The response to galanin was identical when either KCl or KAc was used as the intracellular electrode solution. Tetraethylammonium chloride significantly reduced or abolished the response to galanin in most cells, although in a few cells the galanin response was not affected. Glibenclamide, a blocker of ATP-sensitive potassium channels, did not affect the galanin hyperpolarization. In addition, diazoxide had no effect on the membrane properties of locus coeruleus neurons. These results demonstrate that galanin exerts its inhibitory effect in the locus coeruleus via an increase in K+ conductance; however, not via the pancreatic type of ATP-sensitive K+ channels. Cryostat sections of the locus coeruleus incubated in 125I-labeled galanin revealed binding sites in the locus coeruleus at all levels. Sections of the locus coeruleus processed for ultrastructural immunocytochemistry showed galanin immunoreactivity in many neuronal somata and dendritic processes within the nucleus, confirming earlier evidence for the coexistence of galanin and noradrenaline in locus coeruleus neurons. Galanin-immunoreactive soma and dendrites in the locus coeruleus less frequently received galanin-immunoreactive synapses of axonal origin. These findings suggest that endogenous galanin in the locus coeruleus is mainly released from noradrenaline galanin somata and/or dendrites to act on autoreceptors or on receptors on adjacent neurons.

Animals↗

PubMed1995

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.

Amino Acid Sequence↗

PubMed1995

Interleukin-1 receptor antagonist protein and mRNA in the rat adrenal gland.

The occurrence of the endogenous receptor antagonist for the cytokine interleukin-1 in the rat adrenal gland was analyzed y polymerase chain reaction and by immunohistochemistry using a rabbit polyclonal antiserum. Expression of interleukin-1 receptor antagonist mRNA was demonstrated in both adrenal medulla and cortex, and a marked increase in the transcription was observed after systemic administration of lipopolysaccharides. Interleukin-1 receptor antagonist immunoreactivity was seen in the adrenal medulla, and the immunofluorescence intensity was stronger in the adrenergic, phenylethanolamine N-methyltransferase-positive cells than in the noradrenergic chromaffin cells. The distribution of interleukin-1 receptor antagonist protein is complementary to that of interleukin-1 alpha-like immunoreactivity found in phenylethanolamine N-methyltransferase-negative cells and overlaps with and resembles the distribution of interleukin-1 beta-immunoreactive material. The expression of the interleukin-1 receptor antagonist in the adrenal gland complements previous findings of large constitutive pools of interleukin-1 alpha and interleukin-1 beta in this neuroendocrine organ and also suggests participation of adrenal interleukin-1 receptor antagonist in neuroimmune modulation.

Adrenal Medulla↗

PubMed1995

New high affinity peptide antagonists to the spinal galanin receptor.

1. The role of endogenous galanin in somatosensory processing has been studied with galanin receptor antagonists. The new galanin receptor ligands C7, M32, M38 and M40 bind with high affinity (Kd in nanomolar range) to spinal cord galanin receptors and possess oxidative stability as compared to earlier generations of peptide ligands. These peptides have been examined in the spinal flexor reflex model where exogenous galanin exhibited biphasic excitatory and inhibitory effects. 2. Intrathecal administration of C7 [galanin(1-13)-spantide] and M32 [galanin (1-13)-neuropeptide Y(25-36) amide] blocked facilitation of the nociceptive flexor reflex induced by 30 pmol intrathecal galanin in decerebrate, spinalized rats in a dose-dependent manner, thus behaving as antagonists of the galanin receptor. In contrast, M38[galanin(1-13)-(Ala-Leu)3-Ala amide] and M40 [galanin(1-13)-Pro-Pro-(Ala-Leu)2-Ala amide], exhibited only weak antagonism at high doses in this model. Moreover, lower doses of M40 potentiated galanin-induced reflex facilitation. C7 was neurotoxic at high doses in the rat spinal cord. 3. M32 and C7 were potent antagonists of galanin receptors in rat spinal cord, in correlation with their in vitro binding characteristics. In contrast, M38 and M40, despite their high in vitro affinity, exhibited only very weak antagonism. Moreover, M40 may also behave as a partial agonist. 4. Previous studies have shown that the galanin receptor may be heterogeneous. The discrepancy between in vitro binding and in vivo antagonistic potency of M38 and M40 may also suggest the presence of different galanin receptor subtypes within the rat spinal cord. However, other explanations for the discrepancy, such as differences in metabolic stability, diffusion rates and penetration to the site of action are also possible.

Amino Acid Sequence↗

PubMed1995

Synthesis of an N-methyldehydroalanine-containing fragment of microcystin by combination of solid phase peptide synthesis and beta-elimination in solution.

A new method for the synthesis of dehydroalanine (delta Ala)-containing peptides has been developed by combining solid phase peptide synthesis (tert-butyloxycarbonyl/HF-chemistry) with solution synthesis. A sequence from cyanobacterial hepatotoxin microcystin, Ac-D-gamma-Glu-[N-Me-delta Ala]-D-Ala-Leu amide was chosen as a model peptide. The precursor for the synthesis of the dehydroalanine-containing peptide, Ac-D-gamma-Glu-[N,S-diMeCys]-D-Ala-Leu, was synthesized on a solid phase followed by sulfonium salt formation on the resin. The resulting S,S-dimethylated peptide was cleaved from the resin with liquid HF. The HPLC-purified S,S-dimethylated cysteine-containing precursor peptide was subjected to beta-elimination in solution catalysed by DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) in methanol. The final product, Ac-D-gamma-Glu-[N-Me-delta Ala]-D-Ala-Leu amide, was purified by HPLC, and analysed by mass spectrometry and 1H NMR spectroscopy. The stability of the model peptide under acidic, neutral and basic conditions has been studied.

Alanine↗

PubMed1994

Galanin antisense oligonucleotides reduce galanin levels in dorsal root ganglia and induce autotomy in rats after axotomy.

Antisense (AS) oligonucleotides (ONs) to galanin (GAL) were applied to the proximal end of a transected sciatic nerve, allowing their cellular uptake and transport into injured axons. GAL expression in dorsal root ganglia and self-mutilation behavior (autotomy) were then studied. AS-ONs with phosphorothioate or allyl modifications significantly suppressed the axotomy-induced increase in GAL levels, as demonstrated by immunohistochemistry and exaggerated autotomy behavior, whereas no significant effect on GAL mRNA levels could be demonstrated with in situ hybridization. Allyl-ONs were more effective than phosphorothioate-ONs. An AS-ON with three base mismatches did not induce any of the above effects. These results support the view that the inhibition of axotomy-induced GAL up-regulation is related to autotomy.

Animals↗

PubMed1994

Immunohistochemical demonstration of galanin-, and galanin message-associated peptide-like immunoreactivities in sympathetic ganglia and adrenal gland of the guinea pig.

Using the indirect immunofluorescence method, the distribution of galanin (GAL)- and galanin message-associated peptide (GMAP)-like immunoreactivities (LI) were studied in sympathetic ganglia and the adrenal gland of the guinea pig. A rather dense network of GAL-immunoreactive nerve fibers was found in the inferior mesenteric ganglion (IMG) and in the superior mesenteric pole of the celiac-superior mesenteric ganglion complex (C-SMG). The celiac pole of the C-SMG, the stellate ganglion, and the superior cervical ganglion contained fewer, mostly scattered fibers. SIF-cells in prevertebral and paravertebral ganglia contained GAL-LI, as did the adrenal medullary cells. The GAL fibers in the IMG surrounded mainly principal ganglion cells containing somatostatin-immunoreactivity (SOM-IR), whereas fewer fibers were seen around neuropeptide Y (NPY) cells and cells in which SOM and NPY coexisted. Application of colchicine or vinblastine onto the IMG did not result in the appearance of GAL-IR in the principal ganglion cells. In denervation experiments it was revealed that most of the GAL fibers reach the IMG via the lumbar splanchnic nerves. GAL-IR appears to be colocalized with substance P (SP) in fibers of the IMG, indicating an origin of the GAL-containing fibers in dorsal root ganglia (DRG). This conclusion was supported by the finding in lumbar DRGs of GAL-positive cell bodies that contained SP. The role of GAL in prevertebral ganglia is unclear. It may be suggested that GAL modulates the slow, long-lasting membrane depolarization of the principal ganglion cells caused by SP in the primary afferents related to the IMG. GMAP-LI was detected in SIF cells and adrenal medullary cells in which GMAP-LI parallels the immunoreactivity of GAL. GMAP-LI was not observed in neuronal cell bodies or nerve fibers of the ganglia.

Adrenal Glands↗

PubMed1994

N-terminally elongated fragments of galanin(1-16) inhibit insulin secretion from isolated mouse islets.

The neuropeptide galanin inhibits insulin secretion and has been suggested to be an adrenergic co-transmitter in the endocrine pancreas. Recently, N-terminally elongated forms of galanin have been identified in both porcine brain and adrenals. Whether these elongated peptides show galanin-like biological effects is not known. We therefore synthesized two N-terminally elongated fragments of galanin(1-16), which contains the active site of galanin. The synthesized peptides were galanin(-9-16) and galanin(-7-16), which correspond to amino acids 24-61 and 26-61 in the galanin precursor molecule. Both these peptides were found to potently inhibit glucose-(11.1 mM)-stimulated insulin secretion from isolated mouse islets of Langerhans in all concentrations studied (1-1000 nM) (P < 0.0001). The potency of the peptides was not different from that of synthetic rat galanin. Thus, at 100 nM, insulin secretion was inhibited by galanin(-7-16) by 83 +/- 7% and by galanin(-9-16) by 71 +/- 17% and by rat galanin by 93 +/- 4% (not statistically different). Furthermore, the galanin receptor antagonist, M35 (10 nM), prevented the inhibitory action of the two N-terminally galanin fragments. This study thus shows that N-terminally elongated galanin-fragments as entire galanin inhibits insulin and thus indicates that the effect of galanin on insulin secretion is not dependent on a free amino-terminus.

Animals↗

PubMed1994

Impulse flow dependency of galanin release in vivo in the rat ventral hippocampus.

Using microdialysis and a sensitive RIA, we have studied the in vivo release of the neuropeptide galanin (GAL) from the ventral hippocampus of freely moving rats. The spontaneous outflow of GAL-like immunoreactivity (GAL-LI) (1.8 +/- 0.3 fmol per ml per 20 min) was dependent on the presence of extracellular Ca2+ and was inhibited by tetrodotoxin. Evoked release induced by infusion of KCl (60 mM) or veratridine (148 microM) was also Ca(2+)-dependent and sensitive to tetrodotoxin. Electrical stimulation of the ventral limb of the diagonal band nuclei induced a frequency-dependent (50-200 Hz) and tetrodotoxin-sensitive overflow of GAL-LI in the hippocampus. In vitro GAL-LI release (1.0 +/- 0.02 fmol per ml per 5 min), studied in slices of rat ventral hippocampus, was also Ca(2+)-dependent and was increased in a concentration-dependent manner by KCl depolarization. This study demonstrates the release of the neuropeptide GAL in the rat central nervous system. The in vivo release is related to the activity of the cholinergic GAL-LI-containing cells in the septal diagonal band nuclei. The results are discussed in relation to the coexistence of GAL and acetylcholine within the septal/diagonal band complex.

Animals↗

PubMed1994

Upregulation of nitric oxide synthase and galanin message-associated peptide in hypothalamic magnocellular neurons after hypophysectomy. Immunohistochemical and in situ hybridization studies.

The expression of several bioactive molecules in magnocellular hypothalamic neurons is modified when the axons of these cells are transected. In this study we have evaluated by means of immunocytochemistry and in situ hybridization the effect of hypophysectomy on the expression of nitric oxide synthase (NOS)- and of galanin message-associated peptide (GMAP)-like immunoreactivities (-LIs) as well as on their respective mRNAs in hypothalamic magnocellular neurosecretory neurons. The results show a transient increase in NOS- and GMAP-LIs in magnocellular neurons of both the paraventricular and supraoptic nuclei when compared to normal animals. The maximal increase in staining was observed between 5 and 7 days, and by 14 days NOS-LI was back to normal levels, whereas strong GMAP-LI could still be detected in a few cells. A similar picture was observed for the NOS and GMAP mRNAs. The functional significance of the present findings is unclear, but they indicate a possible role of nitric oxide and GMAP in neurosecretory neurons after injury.

Amino Acid Oxidoreductases↗

PubMed1994

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.

Action Potentials↗

PubMed1994

Galanin message-associated polypeptide (GMAP) does not affect insulin secretion from isolated islets.

Galanin message-associated polypeptide (GMAP) is processed from preprogalanin. Recently, GMAP-like immunoreactivity was demonstrated in insulin cells in the endocrine pancreas. We therefore examined whether synthetic rat GMAP, like galanin, inhibits glucose-stimulated insulin secretion from isolated rat and mouse islets. We found, however, that over a wide dose range (0.1 nM to 1 microM) GMAP did not affect insulin secretion stimulated by 8.3 or 11.1 mM glucose during a 60-min incubation of single rat or mouse islets. In contrast, rat galanin, as expected, completely abolished glucose-stimulated insulin secretion at 100 nM. Thus, in contrast to galanin, GMAP does not affect insulin secretion in isolated rodent islets.

Amino Acid Sequence↗

PubMed1994

Deletion mutants of human interleukin 1 beta with significantly reduced agonist properties: search for the agonist/antagonist switch in ligands to the interleukin 1 receptors.

The existence of an endogenous high affinity interleukin 1 receptor antagonist (IL-1ra) suggests that this molecule lacks some structural motif(s) which are present in the closely homologous agonist interleukin 1 beta (IL-1 beta) and which serve as the 'agonist switch' causing signal transduction by the agonist-receptor complex. The primary sequence alignment of IL-1 beta and IL-1ra sequences from different species reveals a six amino acid long motif that is quasi conserved among IL-1 beta sequences, but is missing from the IL-1ra sequences. The three-dimensional structure of human IL-1 beta was used as a template for building structural models of deletion mutants (delta SND 52-54 and delta EESNDK 50-55) using molecular graphics. These models indicated that the middle three residues SND 52-54 from the EESNDK 50-55 loop may be deleted without causing major changes in the tertiary structure of the mutant as compared to that of IL-1 beta. Residues SND 52-54 from the above loop were deleted. When compared with IL-1 beta the IL-1 beta-delta SND analog (delta SND 52-54) binds with the same affinity to type 2 IL-1 receptor but with a more than 10-fold lower affinity to type 1 IL-1 receptor. Despite of this small decrease in affinity at the type 1 receptor the delta SND 52-54 has a 1000-fold lower biological activity than IL-1 beta when tested in a thymocyte activating factor assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Functional effects and ligand binding of chimeric galanin-neuropeptide Y (NPY) peptides on NPY and galanin receptor types.

1. The effects and binding characteristics of a series of chimeric galanin-neuropeptide Y (NPY) peptides were examined in various preparations known to contain a predominant population of either Y1 or Y2 receptors for NPY or galanin receptors. 2. NPY suppressed the electrically stimulated twitches of the rat vas deferens (Y2 receptors), while galanin enhanced the electrically stimulated twitches. The galanin-NPY peptides M 32 (galanin(1-13)-NPY(25-36)), M69A (galanin(1-13)-Lys-[epsilon NH-Gly-NPY(4-1)]NPY(25-36)) and M88 (galanin(1-12)-Ala-NPY(25-36)) evoked a concentration-dependent suppression of the electrically stimulated twitches. These chimeric peptides were about equipotent with NPY, while NPY (13-36) was about five times less potent than NPY itself. Also a stochiometric combination of the N- and C-terminal fragments NPY (1-24)NH2 and NPY (25-36) (each at 1 microM) was inactive in vas deferens. M120 (galanin (1-13)-NPY(14-36) (1 microM) did not affect the NPY-mediated suppression of the stimulated twitches. 3. NPY evoked a concentration-dependent contraction in the guinea-pig isolated caval vein (Y1 receptors), while galanin (< or = 1 microM) was inactive. M32, M69A and M88 induced a slight contraction at very high concentrations only (> or = 0.3 M), while M120 was inactive at 1 microM. None of the four chimeric peptides affected the contraction evoked by NPY. 4. Since the number of NPY receptors in the rat vas deferens and guinea-pig caval vein were too low,the affinities of the galanin-NPY peptides for [3H]-NPY binding sites were examined in membranes from rat brain areas known to contain predominant populations of Y1 receptors (cerebral cortex) and Y2 receptors (hippocampus), respectively. The chimeric peptides M32, M69A, M88, M120 and NPY (13-36)all had higher affinities for hippocampal binding sites than for cerebral cortical binding sites. These peptides were 90-440 times less potent than NPY at cerebral cortical binding sites and 15-125 times less potent than NPY at hippocampal binding sites. The most selective chimeric peptide was M32, which had a 20 fold higher affinity for hippocampal than for cerebral cortical binding sites.5. At hypothalamic [125I]-galanin binding sites M32, M88 and M69A were equipotent with galanin,while M120 was about 10 times less potent than galanin. M32, M88 and M69A, like galanin contracted the rat isolated jejunum.6. The N-terminal portion (1-12) of galanin seems to permit a steric conformation of the attached NPY (25-36) part of the chimeric galanin-NPY peptides, which results in a facilitated Y2 but not Y1.receptor recognition and activation. None of the galanin-NPY peptides appeared to act as antagonists at either type of NPY receptor, probably due to their low affinity. Instead, they displayed a very high affinity for hypothalamic galanin receptors and probably act as galanin agonists in the rat jejunum.

Amino Acid Sequence↗

PubMed1994

Analogs of galanin (1-16) modified in positions 1-3 as ligands to rat hypothalamic galanin receptors.

Structure-activity relationship (SAR) studies have revealed that the first three residues of galanin (Gly1-Trp2-Thr3) are of critical importance for high-affinity binding to the galanin receptor. Furthermore degradation studies have shown that galanin is easily cleaved to yield inactive fragments in rat hypothalamus (t1/2 = 100 min). To obtain galanin receptor ligands with long-lasting biological activity the amino-terminus of galanin must be protected. We have therefore synthesized analogs of rat galanin(1-16) carrying modifications at the three amino-termini of galanin. All modifications of the peptide backbone flanking Trp2 as in the analogs [N-Me-Trp2]-galanin(1-16), [Tcc2]-galanin-(1-16), (Trp2-psi[CH2NH]-Thr3)-galanin-(1-16) produced a dramatic loss of affinity toward the galanin receptor. [N-Me-Thr3]-galanin(1-16) was the most active of the peptide backbone modified analogs (KD = 997 +/- 1 nM). Modifications of the indole ring in Trp2 ([For-Trp2]-galanin-(1-16), [Tcc2]-galanin-(1-16)) yielded analogs which, at concentrations up to 10 microM, did not displace [125I]galanin binding. N-Methylation of Gly1 by the introduction of sarcosine ([Sar1]-galanin(1-16)) did not significantly affect the ligand-binding properties of galanin(1-16) (KD = 8.7 +/- 0.1 nM).

Amino Acid Sequence↗