Galanin mediates features of neural and behavioral stress resilience afforded by exercise.

Exercise promotes resilience to stress and increases galanin in the locus coeruleus (LC), but the question of whether changes in galanin signaling mediate the stress-buffering effects of exercise has never been addressed. To test the contributions of galanin to stress resilience, male Sprague Dawley rats received intracerebroventricular (ICV) cannulation for drug delivery and frontocortical cannulation for microdialysis, and were housed with or without a running wheel for 21d. Rats were acutely injected with vehicle or the galanin receptor antagonist M40 and exposed to a single session of either footshock or no stress. Other groups received galanin, the galanin receptor antagonist M40, or vehicle chronically for 21d prior to the stress session. Microdialysis sampling occurred during stress exposure and anxiety-related behavior was measured on the following day in the elevated plus maze. Dendritic spines were visualized by Golgi impregnation in medial prefrontal cortex (mPFC) pyramidal neurons and quantified. Exercise increased galanin levels in the LC. Under non-stressed conditions, anxiety-related behavior and dopamine levels were comparable between exercised and sedentary rats. In contrast, exposure to stress reduced open arm exploration in sedentary rats but not in exercise rats or those treated chronically with ICV galanin, indicating improved resilience. Both exercise and chronic, ICV galanin prevented the increased dopamine overflow and loss of dendritic spines observed after stress in sedentary rats. Chronic, but not acute M40 administration blocked the resilience-promoting effects of exercise. The results indicate that increased galanin levels promote features of resilience at both behavioral and neural levels.

Galanin: a novel therapeutic target for depression, anxiety disorders and drug addiction?

Galanin is a neuropeptide synthesized in many neuronal types including brainstem norepinephrine-producing cells of the locus coeruleus and the serotonin-producing neurons of the dorsal raphe nucleus. Galanin inhibits the firing of rodent norepinephrine, serotonin and dopamine neurons and reduces release of these neurotransmitters in forebrain target regions. The distribution of galanin and its receptors and its actions on monoamine signaling has fostered interest in this neuropeptide in the field of behavioral pharmacology and the potential role of galanin in the pathophysiology of neurological diseases such as Alzheimer's disease, epilepsy, stroke, and in psychiatric disorders such as anxiety, depression, and drug addiction, particularly withdrawal. In rodent models, expression of galanin in brain is altered by various stressors, while administration of galanin can modulate anxiety-like responses to stress. Emerging evidence further supports a role for galanin in the mediation of depression-related behaviors in rodents. Recently, galanin agonists have been shown to decrease behavioral signs of opiate withdrawal, which are thought to result from hyperactivation of brain stress pathways. Studies using genetically modified mice suggest that galanin normally plays a protective role against opiate reinforcement and withdrawal. The present article reviews current evidence on a potential role for galanin in modulating stress-related neural pathways and behaviors, and speculates on the therapeutic potential of targeting this galanin system for emotional disorders and opiate addiction.

Galanin inhibits the proliferation of glial olfactory ensheathing cells.

The effect of galanin (GAL) on neural proliferation was studied in this article using olfactory ensheathing cells (OECs). OECs were isolated from newborn rat olfactory bulb and cultured in vitro. RT-PCR was used to determine the expression of GAL and its receptors in these cells. MTT analysis and LDH assay were used to detect the effects of GAL and the agonist, antagonist of GAL receptors on the proliferation of OECs. Results show that OECs express mRNAs for GAL and GAL receptor2 (GalR2) but not for the two other GAL receptors, GalR1 and GalR3. In addition, GAL and two receptor agonists, GAL1-11 and GAL2-11, can inhibit the proliferation of OECs significantly, but cause no cytotoxicity in the OECs population. Moreover, the influence can be blocked by M35, a nonspecific antagonist of GAL receptors. It is suggested that GAL is an inhibitory factor in regulating OECs proliferation.

Galanin increases membrane excitability and enhances Ca(2+) currents in adult, acutely dissociated dorsal root ganglion neurons.

We examined the effect of galanin (10(-15) - 10(-7) M) on dispersed, mainly small-sized dorsal root ganglion (DRG) neurons in adult rats using whole-cell patch-clamp. Galanin and AR-M1896, a selective galanin type 2 receptor (GalR2) agonist, both significantly increased the number of action potentials in response to current pulses in 77% of the neurons, indicating an increase in excitability. Galanin also caused a rise in input resistance, decreased the holding current for -60 mV and depolarized the resting potential. In addition, Ca(2+) currents elicited by voltage steps were significantly increased by both galanin and AR-M1896 in nearly 70% of the cells. This enhancement was observed in 30% of the neurons in the presence of nimodipine or omega-conotoxin, but in each case approximately 60% less than without blocking either N- or L-type Ca(2+) channels, indicating modulation of both types of Ca(2+) channels. The percentage of small- and medium-sized neurons expressing GalR2 mRNA in DRGs in situ was similar to that showing increased excitability and Ca(2+) current after galanin application, i.e. approximately 70-80% of the neurons. The findings suggest that GalR2 has a role in controlling both the excitability, probably by inhibition of GIRK or leak K(+) channels, and Ca(2+) entry in a large population of presumably nociceptive neurons. The combination of the two effects, which possibly arise from separate biochemical pathways, would increase excitability and enhance intracellular Ca(2+) signalling which would enhance sensory transmission. These mechanisms involving GalR2 receptors may underlie the pronociceptive effects of galanin described in the literature.

The neuropeptide galanin modulates behavioral and neurochemical signs of opiate withdrawal.

Much research has focused on pathways leading to opiate addiction. Pathways opposing addiction are more difficult to study but may be critical in developing interventions to combat drug dependence and withdrawal. Galanin decreases firing of locus coeruleus neurons, an effect hypothesized to decrease signs of opiate withdrawal. The current study addresses whether galanin affects morphine withdrawal signs by using a galanin agonist, galnon, that crosses the blood-brain barrier, and mice genetically engineered to under- or overexpress galanin peptide. Galnon significantly decreased morphine withdrawal signs in C57BL/6 mice. Further, knockout mice lacking galanin showed exacerbated morphine withdrawal signs, suggesting that endogenous galanin normally counteracts opiate withdrawal. Transgenic mice overexpressing galanin in noradrenergic neurons also showed decreased morphine withdrawal signs, suggesting a possible neuroanatomical locus for these effects of galanin. Both c-fos immunoreactivity, a marker of neuronal activity, and phosphorylation of tyrosine hydroxylase at Ser-40, a marker of cAMP levels, are decreased in the locus coeruleus by galnon treatment after morphine withdrawal, suggesting a possible molecular mechanism for the behavioral effects of galanin. These studies suggest that galanin normally acts to counteract opiate withdrawal and that small molecule galanin agonists could be effective in diminishing the physical signs of withdrawal.

Actions of galanin on neurotransmission in the submucous plexus of guinea pig small intestine.

Electrophysiologic recording methods were used to study the actions of galanin on synaptic transmission in the submucous plexus of guinea pig ileum. Exposure to galanin resulted in concentration-dependent suppression of slow noradrenergic inhibitory postsynaptic potentials and fast nicotinic excitatory postsynaptic potentials in the majority of neurons. Failure of galanin to suppress nicotinic depolarizing responses to micropressure pulses of acetylcholine and failure to suppress hyperpolarizing responses to micropressure pulses of norepinephrine suggested that galanin acted at presynaptic inhibitory receptors to suppress release of acetylcholine and norepinephrine. Galanin suppressed slow excitatory postsynaptic potentials in eight of eight neurons with AH (after-hyperpolarization) type electrical behavior and in none of 26 neurons with S (synaptic) type electrical behavior. Suppression of excitatory neurotransmission in AH neurons was always associated with membrane hyperpolarization. Excitatory responses caused by experimentally applied substance P were also inhibited by galanin. Galanin-(1-16) and galanin-like peptide mimicked the inhibitory actions of galanin on neurotransmission. The selective galanin GAL2 receptor agonist [D-Trp(2)]galanin was inactive. The chimeric peptides, galanin-(1-13)-spantide I, galantide, galanin-(1-13)-neuropeptide Y(25-36) amide, galanin-(1-13)-bradykinin-(2-9)amide and galanin-(1-13)-Pro-Pro-Ala-Leu-Ala-Leu-Ala amide all produced varying degrees of suppression of the synaptic potentials. The evidence suggests that the galanin GAL1 receptor, but not the galanin GAL2 receptor, mediated the presynaptic and postsynaptic inhibitory actions of galanin.

Lysine14galanin(1-15)-NH2: a partial agonist at galanin receptors in rat isolated gastric fundus.

The study was undertaken to characterize the effects of the porcine galanin [pGal(1-29)-NH2] analogue [Lys14]pGal(1-15)-NH2 on rat gastric fundus. [Lys14]pGal(1-15)-NH2 is a less potent contractile agent than pGal(1-29)-NH2 (EC50 74.1 vs. 43.7 nmol/l, respectively) and shows a significantly lower maximal response than pGal(1-29)-NH2. Concentration-contraction curves were constructed for pGal(1-29)-NH2 alone (control) and pGal(1-29)-NH2 in the presence of 10, 100, and 1,000 nmol/l of [Lys14]pGal(1-15)-NH2. [Lys14]pGal(1-15)-NH2 shifted the concentration-contraction curves of pGal(1-29)-NH2 significantly to the right, whereas their linear portions remained parallel to that for the pGal(1-29)-NH2 control. [Lys14]pGal(1-15)-NH2 markedly increased the EC50 of the respective pGal(1-29)-NH2 concentration-contraction curves. It did not substantially change the maximal response of the muscles to pGal(1-29)-NH2 and the form of the respective concentration-contraction curves. Schild's plot gave a straight line with a slope of 0.84. The pA2 value for [Lys14]pGal(1-15)-NH2 was 8.23. [Lys14]pGal(1-15)-NH2 seems to be a partial Gal receptor agonist. Since the lack of specific Gal receptor antagonists in the gastrointestinal tract makes a precise characterization of its role as a motility modulator difficult, the position 14 in the pGal(1-29)-NH2 molecule looks as an attractive target in the search of a pure Gal receptor antagonist in the smooth muscles of the gut.

Binding and agonist/antagonist actions of M35, galanin(1-13)-bradykinin(2-9)amide chimeric peptide, in Rin m 5F insulinoma cells.

The chimeric peptide M35 [galanin(1-13)-bradykinin(2-9) amide] is a high-affinity galanin receptor ligand acting as a galanin receptor antagonist in the rat spinal cord, rat hippocampus and isolated mouse pancreatic islets. We have radiolabelled M35 and performed equilibrium binding studies with [125I]M35 on the rat pancreatic beta-cell line Rin m 5F, whereby we show the existence of high-affinity binding site (KD = 0.9 +/- 0.1 nM) with a Bmax of 72 +/- 3 fmol/mg protein. Galanin displaces [125I]M35 with the same affinity (KD = 1 nM) as it displaces [125I]galanin. Displacement of [125I]galanin by M35 from Rin m 5F cell membranes shows the presence of two binding sites for M35 with KD-values of 0.3 +/- 0.1 nM and 0.52 +/- 0.03 microM, respectively. The GTP- and pertussis toxin-sensitivity of M35 binding to Rin m 5F membranes shows that binding of [125I]M35 is almost completely abolished by the presence of GTP or after pertussis toxin treatment of the cells, indicating an agonist-like binding of M35 to the galanin receptors. M35 has a dual effect on the galanin mediated inhibition of forskolin stimulated cyclic AMP production in Rin m 5F cells: at low concentrations M35 antagonises the effect of galanin, whereas at concentrations above 10 nM M35 acts as a galanin receptor agonist. These agonist-like effects of galanin and M35 are not additive, thus the mixed agonist/antagonist properties arise from the chimeric nature of M35[galanin(1-13)-bradykinin(2-9)amide] acting solely at galanin receptors.