Peripheral administration of GLP-1 or EX4 reduces voluntary alcohol intake. In an intermittent-access 20% ethanol drinking paradigm, Wistar rats peripherally injected with GLP-1 (0.1 mg/kg) drank less alcohol than those injected with vehicle at 1 h (n = 12 per treatment group (A)).

<p>The reduced alcohol drinking response was primarily exhibited by high alcohol consuming rats (HIGH C, top 30% consumers) and was not detected in low alcohol consuming rats (LOW C; bottom 30%) (B). Rats that received an IP injection of EX4 at a dose of either 0.3 µg (C) or 1.0 µg/kg (D) reduced their 20% ethanol intake at 1 h after alcohol exposure n = 13−25. All values represent mean ± SEM. VEH, vehicle for GLP-1 (glucagon-like-peptide-1); EtOH, ethanol. *p<0.05, **p<0.01.</p

Peripheral administration of GLP-1 reduces alcohol reward.

<p>Mice treated with vehicle on the testing day spent significantly more time in the compartment previously (during the conditioning sessions) paired with alcohol as compared to the compartment paired with saline. In contrast, mice treated with 0.02 mg of GLP-1 spent an equal amount of time in both the saline- and alcohol-paired compartments (A). Alcohol induced a significant preference for the compartment it was paired with over the compartment paired with saline during the conditioning sessions in NMRI mice injected with vehicle (n = 48) but not those treated with GLP-1 (n = 31) (B). %CPP was determined with the following formula ((test-pretest)/(total time- pretest))×100 to indicate the % preference above a neutral response (i.e. equal preference for each compartment). All values represent mean ± SEM. *p<0.05, **p<0.01.</p

Identification of the mesolimbic VTA as the neuroanatomical substrate for GLP-1R-linked effects on alcohol consumption.

<p>VTA-selective unilateral microinjections of GLP-1 (vehicle n = 11; GLP-1 1 µg n = 7, A−B) and EX4 (vehicle n = 9; EX4 0.1 µg n = 9, C−D) reduced 20% ethanol consumption during a 16 h drinking session. A diagram based on Paxinos and Watson at the level of bregma −5.40 mm shows a representative VTA injection site (E). Additionally, schematics illustrate the injection site for each rat from the GLP-1 (F) and the EX4 (G) study. Black circles represent vehicle-injected rats, grey drug-injected and white missed placement. All values represent mean ± SEM. Aq; aqueduct, SNR; <i>substantia nigra pars reticulata</i>. ^#p<0.1,*p<0.05, ***p<0.005.</p

Role of ghrelin in novelty place preference.

<p>A. Ghrelin-treated rats tend to have slightly higher preference for exploring a novel environment. In contrast those that received GHSR antagonist display much lower preference for a novel environment as compared to the more familiar one. B. Ghrelin markedly increases and the GHSR antagonist strikingly decreases exploration of a novel environment in high NILA rats (HLA). C. When only the low NILA (LLA) rats are considered ghrelin does not significantly alter the place preference, however GHSR antagonist is still effective at reducing the preference. ***P<0.0005. Ghrelin alters the relationship between preference for novelty and NILA. D. Novelty place preference (NPP, here time spent exploring the novel environment) is not correlated with locomotor activity during NILA at baseline. E. The two traits become significantly correlated after ghrelin treatment. F. GHSR antagonist does not influence the correlation.</p

Plasma ghrelin levels in high and low NILA rats.

<p>A. Total ghrelin levels and B. active ghrelin levels are not different in animals with low (n = 12) vs. high (n = 12) NILA. C. The same rats display a markedly different activity level in the novel environment. Data on the bar graphs represent mean ± SEM. ***P<0.0005.</p

The <i>GHSR</i> SNPs rs2948694 and rs495225 are significantly associated with novelty seeking (p = 0.002 and p = 0.026, respectively).

<p>For both rs2948694 and rs495225, the less common G/G genotype is associated with lower scores on the personality trait novelty seeking.</p

Ghrelin induces a significant preference for exploration of a novel object in rats that do not show a preference for a novel object at baseline.

<p>GHSR blockade does not alter this behavior. ***P<0.0005.</p

The analyzed tag SNPs, the genotype frequencies and the p-values for the association tests using linear regression.

<p><i>GHRL, pro-ghrelin gene; GHSR, growth hormone secretagogue receptor gene</i>; β, β-value describing the slope of the curve in the linear regression model; p, p-value using linear regression; p_corrected, p-value corrected for multiple testing using permutation test.</p

Role of the VTA ghrelin and GHSR in the NILA response.

<p>A. Rats that received the VTA directed ghrelin microinjection had an elevated NILA response after 45 min of the NILA test. B. Conversely rats that received a VTA microinjection of the GHSR antagonist JMV2959 displayed a reduced NILA response. C. Rat brain section (right) and equivalent panel from the rat brain atlas (left) showing an example of the VTA microinjection used. *P<0.05. SNR, substantia nigra, reticular part; ml, medial longitudinal fasciculus; fr, fasciculus retroflexus; VTA, ventral tegmental area.</p