Galanin Receptor Antagonist M35 Research Articles

Galanin/alpha2-receptor interactions in central cardiovascular control

The modulation of the central cardiovascular effects of α 2-adrenoceptor activation by galanin and its N-terminal fragment galanin-(1-15) has been evaluated by quantitative receptor autoradiography and cardiovascular analysis. Intracisternal coinjections of threshold doses of galanin and the selective and hypotensive α 2-receptor agonist clonidine induced rapid and maintained vasopressor and tachycardic responses ( p<0.001) instead of a hypotensive response, whereas the coinjections of threshold doses of the N-terminal galanin fragment (1–15) and clonidine did not elicit significant cardiovascular changes. Receptor autoradiographical experiments showed that galanin (1 nM) significantly increased the K d ( p<0.01) and B max values ( p<0.01) of [ 3H] p-Aminoclonidine binding sites in the nucleus tractus solitarii (NTS) compatible with a possible antagonistic interaction with the α 2-adrenoceptors, and this effect was blocked by the presence of the specific galanin receptor antagonist M35. In addition, clonidine (30 nM) induced a 50% increase in the B 0 values of galanin based on competition experiments with [ 125I]-galanin binding in the NTS. These findings suggest the existence of an antagonistic effect of galanin, but not of galanin fragment (1–15), on the cardiovascular responses mediated by α 2-receptors as well as a reciprocal facilitatory effect of α 2-receptors on galanin binding. These mechanisms could be mediated by a reciprocal galanin-α 2 receptor interaction within the NTS.

Galanin attenuates the effects of scopolamine but not exposure to a novel environment on acetylcholine release in the rat ventral hippocampus

In vivo microdialysis was used to measure the effects of galanin on extracellular acetylcholine concentrations in the ventral hippocampus of rats produced by exposure to a novel environment or scopolamine. The novel environment produced a significant increase in acetylcholine release, to 58% above baseline. This effect was insensitive to pretreatment with galanin (5 µg, i.c.v.) or the peptidergic galanin receptor antagonist M40 (16 µg, i.c.v.). In contrast, galanin strongly attenuated the increase in acetylcholine release produced by scopolamine (0.3 mg/kg, s.c.). These results indicate that galanin differentially affects the increases in acetylcholine neurotransmission produced by a pharmacological and an environmental stimulus.

Intracerebroventricular infusion of the galanin antagonist M40 attenuates heterosexual partner preference in ferrets.

Gonadectomized, estradiol-treated male and female ferrets (Mustela furo) received intracerebroventricular (i.c.v.) infusions of 4 doses of the galanin receptor antagonist M40 or galanin and were allowed to approach breeding male or female ferrets that were placed behind wire mesh barriers in the goal boxes of a T maze. After i.c.v. infusion of saline, subjects strongly preferred to approach stimulus ferrets of the opposite sex. Male and female subjects approached these preferred stimulus animals on significantly fewer trials after i.c.v. infusion of the 2 highest doses of M40, whereas this drug failed to affect males' coital behavior in separate tests with an estrous female. Endogenous galanin may facilitate neural reward mechanisms that control heterosexual partner preference in both sexes.

Galanin inhibits performance on rodent memory tasks.

Central administration of galanin produces performance deficits on a variety of rodent learning and memory tasks. Galanin impairs acquisition and/or retention of the Morris water task, delayed nonmatching to position, T-maze delayed alternation, starburst radial maze, and passive avoidance in normal rats. A primary site of action is the ventral hippocampus, with an additional modulatory site in the medial septum-diagonal band. The behavioral actions of galanin at rat septohippocampal sites mediating cognitive processes are consistent with previous reports of inhibitory actions of galanin on acetylcholine release and cholinergically activated transduction at the M1 muscarinic receptor in rat hippocampus. The peptidergic galanin receptor antagonist M40 blocks the inhibitory actions of galanin on memory tasks. Treatment combinations of M40 with an M1 agonist, TZTP, improves performance on delayed nonmatching to position, in rats with 192IgG-saporin-induced cholinergic lesions of basal forebrain neurons. Nonpeptide, bioavailable, subtype-selective galanin receptor antagonists may provide tools to test the hypothesis that antagonism of endogenous galanin, which is overexpressed in the basal forebrain in Alzheimer's patients, can contribute to the alleviation of the cognitive deficits associated with Alzheimer's disease.

Differential effects of the neuropeptide galanin on striatal acetylcholine release in anaesthetized and awake rats.

1. In the present study the mechanisms were examined by which the neuropeptide galanin modulates the extracellular concentrations of striatal acetylcholine (ACh) in enflurane anaesthetized and in freely moving male rats by use of in vivo microdialysis and high performance liquid chromatography. 2. The perfusion of galanin through the microdialysis probe (0.3 nmol microl(-1), flow rate: 2 microl min(-1)) caused a statistically significant increase in the basal striatal ACh levels in anaesthetized but a decrease in awake animals. No significant effect was revealed after a low dose (0.1 nmol microl(-1), flow rate: 2 microl min(-1)) of galanin perfusion. Both the stimulating and inhibitory effects of galanin on basal ACh release were reversible. 3. The muscarinic antagonist scopolamine (0.1 mg kg(-1), subcutaneously (s.c.)) caused a significant increase in ACh release in both anaesthetized and awake animals. 4. The combination of galanin plus scopolamine attenuated the stimulant effect on ACh release caused by scopolamine alone in awake animals. 5. The putative galanin receptor antagonist M35 at 0.3 nmol microl(-1) but not at 0.1 nmol microl(-1) caused a significant reduction (20%) in ACh release, supporting the view that M35 at higher concentrations behaves as a partial agonist at the galanin receptor. When M35 (0.1 nmol microl(-1)) was co-infused with galanin (0.3 nmol microl(-1)) the galanin-evoked decrease in ACh release was completely blocked. 6. Taken together, these results indicate that galanin affects basal ACh release via stimulation of galanin receptors within the striatum. The mechanism involved is dependent on the anaesthesia procedure which may act via enhancement of gamma-aminobutyric acidA (GABA(A)) mediated transmission within striatal and/or output neurones. In addition, anaesthesia may also decrease the activity of glutamatergic striatal afferents. The results with M35 indicate that the role of galanin perfused in striatum is permissive in the normal rat. Furthermore, galanin is a potent inhibitory modulator of basal ACh release also in the striatum, as recently was shown in the ventral hippocampus in awake animals.

Effects of the capsaicin analogue resiniferatoxin on spinal nociceptive mechanisms in the rat: behavioral, electrophysiological and in situ hybridization studies

The effect of a single subcutaneous (s.c.) injection of the ultrapotent capsaicin analogue resiniferatoxin (RTX) on responses of adult rats to noxious thermal and mechanical stimulation was examined. The effects of RTX treatment on the nociceptive flexor reflex and activity-dependent increase in spinal excitability after conditioning C-fiber stimulation (CS) were also assessed. Finally, the expression of galanin message associated peptide (GMAP) mRNA in dorsal root ganglion (DRG) cells and the effects of the high affinity galanin receptor antagonist M35 on the flexor reflex in RTX-treated rats were evaluated. RTX, but not vehicle, produced marked thermal hypoalgesia on the hot plate test with partial recovery in about 50% of animals after about 2 weeks and no recovery in the remaining rats after 4 weeks. In all animals there was only a transient and moderate increase in paw withdrawal threshold to mechanical pressure. The flexor reflex in response to a C-fiber CS train was recorded 15–35 days after RTX or vehicle treatment. There was no difference between RTX and vehicle treated rats on baseline response, but RTX treatment lead to less wind-up during the CS and reduced hyperexcitability. This was particularly the case for rats which did not recover from RTX-induced hypoalgesia. The C-fiber mediated hyperexcitability was potentiated by the galanin receptor antagonist M35, more so in the non-recovered rats than in the partially recovered rats. The number of DRG cells expressing GMAP mRNA was significantly higher in non-recovered than in partially recovered rats. Thus, RTX produced marked and prolonged impairment of capsaicin-sensitive afferents and upregulation of the inhibitory neuropeptides GMAP and galanin in DRG neurons, which may underlie the prolonged effect of RTX.

Galanin receptor antagonist M40 blocks galanin-induced choice accuracy deficits on a delayed-nonmatching-to-position task.

Galanin is a 29-amino acid neuropeptide that coexists with acetylcholine in the medial septum/diagonal band in the rat and impairs choice accuracy on an operant delayed-nonmatching-to-position (DNMTP) working-memory task. M40, a peptidergic galanin antagonist, has previously been shown to block several physiological actions of galanin. The present experiments tested the ability of M40 to block the effects of galanin on DNMTP performance. M40 completely blocked choice-accuracy deficits induced by galanin administration in both the lateral ventricle and ventral hippocampus, at doses of M40 approximately 5-fold the molar dose of galanin. M40 appears to be an effective galanin antagonist in a rodent memory paradigm, indicating that this compound may prove useful in investigating the role of endogenous galanin in learning and memory.

Galanin receptor antagonist M40 blocks galanin-induced choice accuracy deficits on a delayed-nonmatching-to-position task.

Galanin receptor antagonist M40 blocks galanin-induced choice accuracy deficits on a delayed-nonmatching-to-position task.

Galanin and the galanin antagonist M40 do not change fat intake in a fat-chow choice paradigm in rats

The neuropeptide galanin has been proposed to play a role in the regulation of fat intake. The purpose of the present investigation was to determine if galanin and the galanin receptor antagonist M40 would have selective effects on fat intake in a fat-chow choice paradigm in rats. Rats were adapted to 22-h access to chow alone and 2-h daily access to separate sources of fat and chow in the early dark cycle. Galanin (300 pmol, 1 nmol) or M40 (2-500 pmol) was microinjected bilaterally into the paraventricular nucleus of the hypothalamus (PVN) before the 2-h choice period, and chow and fat intake were measured. M40 had no effect on chow or fat intake. Galanin stimulated chow intake and increased the ratio of chow to fat consumed but had no significant effect on fat intake alone. These results suggest that endogenous galanin in the PVN may not play a primary role in the regulation of fat intake when fat is available in addition to a nutritionally balanced diet.

Radiolabeling and characterization of binding sites for the galanin receptor antagonist M35

Radiolabeling and characterization of binding sites for the galanin receptor antagonist M35