Galanin is a neuropeptide encoded by the GAL gene, that is widely expressed in the brain, spinal cord, and gut of humans as well as other mammals. Galanin signaling occurs through three G protein-coupled receptors.

The functional role of galanin remains largely unknown; however, galanin is predominately involved in the modulation and inhibition of action potentials in neurons. Galanin has been implicated in many biologically diverse functions, including: nociception, waking and sleep regulation, cognition, feeding, regulation of mood, regulation of blood pressure, it also has roles in development as well as acting as a trophic factor. Galanin is linked to a number of diseases including Alzheimer’s disease, epilepsy as well as depression, eating disorders and cancer. Galanin appears to have neuroprotective activity as its biosynthesis is increased 2-10 fold upon axotomy in the peripheral nervous system as well as when seizure activity occurs in the brain. It may also promote neurogenesis. Galanin is predominantly an inhibitory, hyperpolarizing neuropeptide and as such inhibits neurotransmitter release. Galanin is often co-localized with classical neurotransmitters such as acetylcholine, serotonin, and norepinephrine, and also with other neuromodulators such as Neuropeptide Y, Substance P, and Vasoactive intestinal peptide.

	Obesity Related Peptide
	Peptide Name Function Tracer Tissue or cell    References galantide (M15), galanin-(1-12) -Pro-SP-(5-11) amide antagonist   rat hypothalamus KD(1) less than 0.1 nM and KD(2) approximately 6 nM Langel U, et al. Int J Pept Protein Res. 1992 ; 39(6) :516-22 galanin  agonist [125I] Galanin rat pancreatic beta-cell line Rin m 5F KD: 1 nM Kask K, et al. Regul Pept. 1995 , 59(3):341-8 galanin-(1-16) agonist [125I] galanin rat forebrain and spinal cord IC50: 3 nM Fisone G, et al. Proc Natl Acad Sci U S A. 1989; 86(23) :9588-91 M35 [galanin(1-13)- bradykinin (2-9) amide] antagonist agonist ? [125I] M35 rat pancreatic beta-cell line Rin m 5F KD = 0.9 +/- 0.1 nM; Bmax=72 +/- 3 fmol/mg protein Kask K, et al. Regul Pept. 1995, 59(3) :341-8 M15 (galantide) antagonist     Hill coefficient:0.4-0.5 Ogren SO, et al. Eur J Pharmacol. 1993;242(1):59-64 Galnon non-peptide agonist   spinal cord membranes KD:6+/-0.6 microM Wu WP, et al. Eur J Pharmacol. 2003 ;482(1-3):133-7  M242   Bowes cells& Chinese hamster ovary cells at hGalR1<1 nM and at hGalR2<10 nM Saar K, et al. Regul Pept. 2001; 102(1) :15-9 M38, [galanin(1-13)- (Ala-Leu)3-Ala amide] antagonist       Xu XJ, et al. Br J Pharmacol. 1995 Oct;116(3):2076-80 M40, [galanin(1-13) -Pro-Pro-(Ala-Leu)2-Ala amide] antagonist in vivo       Xu XJ, et al. Br J Pharmacol. 1995 Oct;116(3):2076-80 C7 [galanin (1-13)-spantide] 11 antagonist       Xu XJ, et al. Br J Pharmacol. 1995 Oct;116(3):2076-80 Galanin (Porcine) agonist [125I]galanin (porcine) Bowes melanoma cell line KD = 0.05 +/- 0.01 nM; Bmax = 135 +/- 7 fmol/mg protein Heuillet E, et al. Eur J Pharmacol. 1994 ; 269 (2):139-47 Galanin (Human) agonist [125I]galanin (porcine) Bowes melanoma cell line IC50 = 0.35 +/- 0.13 nM Heuillet E, et al. Eur J Pharmacol. 1994 ; 269 (2):139-47

Pharmacological characterization of GALP Mean values ± S.E. of 6-9 determinations from 2-3 different experiments (receptor binding) or those of 4 determinations from 2 different experiments (GTPγS binding) are shown.
	Receptor binding (IC50)		[35S]GTPγS binding (EC50)
	GALR1	GALR2	GALR1	GALR2
	nM		nM
Rat galanin	0.097  ± 0.004	0.48  ± 0.02	0.16  ± 0.02	5.2  ± 0.5
Porcine GALP	4.3  ± 0.09	0.24  ± 0.01	30  ± 4	2.4  ± 0.4

Ohtaki T, et al. J Biol Chem. 1999 Dec 24;274(52):37041-5

Comparison of galanin and galnon in inhibition of adenylate cyclase activity (basal and forskolin stimulated) in membranes from rat ventral hippocampi and displacement of 125I-galanin from its specific binding sites
	EC50, M of inhibition of adenylate cyclase activity in rat hippocampal membranes		KD, M
	Basal	Forskolin stimulated	Rat hippocampus	Bowes cells (GalR1)
Galanin	1.1  × 10-9	1.1  × 10-9	0.8  × 10-9	0.4  × 10-9
Galnon	8  × 10-6	10  × 10-6	4.8  × 10-6	2.9  × 10-6

Saar K, et al. Proc Natl Acad Sci U S A. 2002 May 14;99(10):7136-41

Saturation isotherms of ¹²⁵I-human galanin to human GALR1 receptors in HEK293E membranes and whole cells. Saturation experiments were performed with the addition of ¹²⁵I-human galanin up to 5 nM, whereas from 5.0 to 60 nM, unlabeled cold human galanin was added along with a fixed concentration of 1.5 to 3.0 nM ¹²⁵I-human galanin as indicated in "Methods." A, Depicted is a saturation isotherm (and Scatchard transformation inset) using GALR1 membranes that is representative of four experiments. Nonlinear regression analysis (LIGAND) significantly fit (P < .05) a two site/state model better than a one site/state model. B, A representative saturation isotherm (and Scatchard transformation inset) using GALR1 whole cells. Depicted are data that are representative of three independent experiments (K_DH = 419 pM, K_DL = 5.8 nM; P = .07, LIGAND). As reported in "Results" and shown in table 1, a composite analysis (LIGAND) using data from three experiments (64 individual data points) was performed to adequately defined the low-affinity site. This analysis gave sufficient statistical power to yield a significant two-site/two state model (P < .001) with binding parameters (see table 1) that closely matched this individual experiment. 

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Binding parameters of 125I-human galanin at GALR1 receptors in HEK 293E membranes and whole cells
Membranes
KDH (pM)	48.9  ± 7.3
BmaxH (fmol/mg protein)	554.3  ± 24.9
% Total	21.0
KDL (nM)	14.7  ± 4.3
BmaxL (pmol/mg protein)	2.07  ± 0.13
% Total	79.0
Whole cells
KDH (pM)	288.0
BmaxH	3,493 receptors/cell, (94 fmol/mg proteina)
% Total	18.8
KDL (nM)	12.8
BmaxL	15,057 receptors/cell, (425 fmol/mg proteina)
% Total	81.2

 

Binding parameters were determined as described in "Methods." All values for the membrane-based assay represent the mean ± S.E.M. of three to four experiments all carried out in duplicate or triplicate. For the whole cell saturation isotherm, a composite, nonlinear regression analysis of data from three independent experiments was required to adequately determine the low affinity component. Data from both membranes and whole cells were best fit by a two-state/two-site model (P < .05).

B_max values from the whole cell saturation isotherm were expressed conventionally as receptors/cell, but also as fmol/mg protein assuming a membrane protein yield of 60 ×g/10⁶ GALR1 HEK293E cells 

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Comparison of ¹²⁵I-human galanin competition experiments in membranes using filtration vs. the scintillation proximity assay. 

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Inhibition of forskolin-stimulated cAMP production by galanin-related peptides. HEK293E cells expressing human GALR1 receptors were exposed to forskolin and galanin-related peptides. 

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Potencies of galanin-related peptides in stimulating [³⁵S]GTPS binding to cell membranes containing the human GALR1 receptor. 

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Radioligand binding and forskolin-stimulated cAMP production by human galanin or M40 in GALR1 whole cells subject to irreversible receptor alkylation by phenoxybenzamine (PBZ).

Fitzgerald LW, et al. J Pharmacol Exp Ther. 1998 Nov;287(2):448-56

Galanin Sequence Comprison among Species

Human Rat Porcine Bovine

Links to publications that use Galanin:

Santic et al. Alarin is a vasoactive peptide.

Proc Natl Acad Sci U S A. 2007 Jun 12;104(24):10217-22.

Janovick et al. Rescue of hypogonadotropic hypogonadism-causing and manufactured GnRH receptor mutants by a specific protein-folding template: misrouted proteins as a novel disease etiology and therapeutic target.

J Clin Endocrinol Metab. 2002 Jul;87(7):3255-62.