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

Abstract

The glanin-receptor Hlgand M40 [galanin-(1-12)-Pro3-(Ala-Leu)2-AIa amide] binds with high affinity to galanin-binding sites in hippocampal, hypothalamic, and spinal cord membranes and in membranes from Rin m5F rat insulinoma cells . Receptor autoradlographic studies show that M40 (1 "M) displaces 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 glanin on feeding, and it blocks the galaninergic inhibition of the scopolamine-induced acetylcholne release in the ventral hippocampus in vivo. In contrast, M40 completely fails to antagonize both the galanin-mediated inhibition of the glucoseinduced insulin release in isolated mouse pancreatic islets and the inhibitory effects of galanin on the forskolin-stimulated accumulation of 3',5'-cAMP in Rin mSF 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 glanin receptor may exist. Hypothalamic and hippocampal galanin receptors represent a putative central galaninreceptor subtpe (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.Galanin is an important neuroendocrine peptide with multiple biological and pharmacological actions (1). It is a potent inhibitor of glucose-induced insulin release (2), it inhibits hippocampal acetylcholine release (3) induced by systemic administration of scopolamine (4), it impairs cognitive performance (5, 6), it stimulates feeding behavior upon hypothalamic or intracerebroventricular injection (7,8), it stimulates growth hormone secretion (9), and it has a biphasic effect on the spinal flexor reflex (10). Galanin hyperpolarizes noradrenergic cell bodies in the locus coeruleus (11) Accordingly, a galanin-receptor subtype has been suggested, which is composed of nervous tissue and pancreatic galanin receptors that recognize the N-terminal 1-to 15-aa or 1-to 16-aa fragment of galanin as high-affinity agonists, whereas another putative galanin-receptor subtype in smooth muscle requires both the N and C terminus of galanin for binding and biological action (25). On the basis of the differential affinity ofgalanin (3-29) and ofa galanin-receptor antagonist M15 (17), existence of an additional galaninreceptor subtype has been suggested in the rat anterior pituitary (26), which differs from other CNS galanin receptors. Finally, galanin-(1-15)-binding sites have been demonstrated in the dorsal hippocampus, neocortex, and neostriatum, areas that seem to lack galanin-(1-29)-binding sites (27).

Modulatory Effects of Galanin in the Lateral Bed Nucleus of the Stria Terminalis on Behavioral and Neuroendocrine Responses to Acute Stress

“…Bilateral microinjections of vehicle, or the galanin antagonist M40 (0.2 or 1.0 nmole per side) were made into the BSTL. These doses of M40 were shown to be effective in previous studies by us (Khoshbouei et al 2001) and by others (Crawley et al 1993;McDonald and Crawley 1996). All drugs were injected in a volume of 0.2 l at a rate of 0.2 l/min.…”

“…The galanin antagonist M40 (Bartfai et al 1993) has been shown in vivo to block the effects of exogenous galanin administration on memory tasks (McDonald and Crawley 1996) and food intake (reviewed in Crawley 1999). Thus, in this experiment, we administered M40 directly into BSTL to address the potential role of endogenous galanin in modulating behavioral and neuroendocrine responses to acute stress.…”

“…Recent studies have suggested a mutually antagonistic interaction between galanin and norepinephrine acting at ␣ 2 adrenergic receptors (DiazCabiale et al 2000a,b). Thus, whether galanin release from local neurons is affected by noradrenergic afferent activity, or is co-released directly from a subset of noradrenergic terminals innervating BST, both possibilities suggest that galanin might play a role in modulating stress-induced behavioral reactivity and stress-induced HPA activation in the BSTL.The galanin antagonist M40 (Bartfai et al 1993) has been shown in vivo to block the effects of exogenous galanin administration on memory tasks (McDonald and Crawley 1996) and food intake (reviewed in Crawley 1999). Thus, in this experiment, we administered M40 directly into BSTL to address the potential role of endogenous galanin in modulating behavioral and neuroendocrine responses to acute stress.…”

“…Furthermore, it has been hypothesized that galanin may also be involved in disease states such as depression (Seutin et al 1989), feeding disorders (Crawley et al 1990(Crawley et al , 1993, and Alzheimer's disease (Bartfai et al 1992;Mufson et al 1993Mufson et al , 1998Mufson et al , 2000.…”

Expression Cloning of a Rat Hypothalamic Galanin Receptor Coupled to Phosphoinositide Turnover

“…To clone additional members of the galanin receptor family, we used an expression cloning strategy based on the hypothesis that there were multiple galanin receptors present in hypothalamus (17,29). A randomly primed cDNA expression library was constructed from rat hypothalamus and screened in pools by radioligand binding/photoemulsion detection using 125 IpGAL.…”