Neurotensin receptor type 1 regulates ethanol intoxication and consumption in mice

Abstract

Neurotensin receptor type 1 (NTS1) is known to mediate a variety of biological functions of neurotensin (NT) in the central nervous system. In this study, we found that NTS1 null mice displayed decreased sensitivity to the ataxic effect of ethanol on the rotarod and increased ethanol consumption when given a free choice between ethanol and tap water containing bottles. Interestingly, the administration of NT69L, a brain-permeable NT analog, increased ethanol sensitivity in wild-type littermates but had no such effect in NTS1 null mice, suggesting that NTS1 contributes to NT-mediated ethanol intoxication. Furthermore, the daily treatment of NT69L, for 4 consecutive days, significantly reduced alcohol preference and consumption in wild-type littermates but had no such effects in NTS1 null mice in a two-bottle drinking experiment. Our study provides evidence for possible pharmacological roles of NT69L in which it increases sensitivity to the ataxic effect, and decreases voluntary consumption, of ethanol. Our study also demonstrates NTS1-mediated behavioral effects of NT69L. Therefore, our findings will be useful for understanding some aspects of alcoholism as well as to develop novel pharmacological therapeutic options for humans.

Figure 1

Effect of ethanol-induced locomotor activity and ataxia in NTS1 null mice. (A) Basal locomotor activity was similar between genotypes (n = 22 for wild-type and n = 16 for NTS1 null mice). (B) 1.0 g/kg (i.p.) ethanol (n = 11 for wild-type and n = 7 for NTS1 null mice) and (C) 1.5 g/kg (i.p.) ethanol did not induce any changes in initial locomotor activation (n = 11 for wild-type and n = 9 for NTS1 null mice). In the rotarod test, (D) 1.0 g/kg ethanol had no effect (n = 19 for wild-type and n = 15 for NTS1 null mice), but (E) at a 1.5 g/kg ethanol dose, NTS1 null mice (n = 18) showed a significant reduction in ethanol-induced ataxia in a rotarod test compared to their wild-type littermates (n = 21). *p < 0.05 compared to the wild-type littermates at same time after ethanol injection (Tukey test). (F) Blood ethanol clearances after acute administration of 3.6 g/kg ethanol were similar between genotypes (n = 11 for wild-type and n = 9 for NTS1 null mice). p > 0.05 by Tukey test. All data are expressed as mean ± s.e.m.

Figure 2

Ethanol consumption, preference and taste preference of NTS1 null mice. (A) Ethanol consumption and (B) preference of NTS1 null mice (n = 18) in a two-bottle choice experiment. *p < 0.05 compared to their wild-type littermates (n = 14) at the same ethanol concentration (Tukey test). (C) No differences (p > 0.05 by Tukey test) in genotype-associated taste (saccharin for sweet and quinine for bitter tastes) preference in NTS1 null mice (n = 9) compared to their wild-type littermates (n = 11). All data are expressed as mean ± s.e.m.

Figure 3

Effect of 1.0 g/kg ethanol on NT69L pretreated mice in open-field locomotor activity and rotarod ataxia experiments. (A) NT69L-treated mice traveled less in the open field activity compared to saline-treated mice in a dose-dependent fashion after ethanol administration (i.p.) to observe the effect of NT69L in ethanol-mediated spontaneous locomotor activity. The Tukey test showed reduced spontaneous locomotor activity from 20 min to 40 min (at 1.0 and 2.0 mg/kg NT69L + 1.0 g/kg ethanol) after NT69L administration in wild-type mice. (B) Dose-dependency of increased alcohol-induced ataxic responses of NT69L-treated wild-type mice. The Tukey test showed that NT69L treatment was effective from 15 min to 1 h after the ethanol treatment at doses of 1.0 mg/kg and 2.0 mg/kg NT69L. Conditions were 1.0 g/kg ethanol and various concentrations of NT69L (saline, 0.5, 1.0, and 2.0 mg/kg NT69L) for both experiments. n = 5–6 for each treatment. *p < 0.05 compared to the saline+ethanol-injected mice at the same time after injection. (C) No significant difference (p > 0.05 by Tukey test) between blood ethanol clearances after acute administration of NT69L. Conditions were 1.0 g/kg ethanol and 1.0 mg/kg NT69L for blood ethanol clearance experiment (n = 6). At 1.5 g/kg ethanol-injected mice showed sedative-like phenotype when pretreated with 1.0 mg/kg NT69L (n = 8) both in (D) locomotor activity and (E) ataxia compared to saline-treated mice (n = 8). *p < 0.05 by Tukey test. All data are expressed as mean ± s.e.m.

Figure 4

Effect of NT69L-induced locomotor activity and ataxia in NTS1 null mice. (A) 1.0 mg/kg NT69L (i.p. in saline) did not induce any significant alteration of initial locomotor activation compared to their saline-treated groups both in NTS1 null mice (n = 6) and wild-type littermates (n = 9; p > 0.05 by t-test). (B) However, NTS1 null mice stayed on the rotarod significantly longer than the wild-type littermates from 30 min after NT69L injection (n = 12 for each genotype). *p < 0.05 compared to their saline-treated groups both in NTS1 null mice and wild-type littermates (Tukey test). All data are expressed as mean ± s.e.m.

Figure 5

Effect of NT69L on ethanol consumption and preference in NTS1 null mice. (A) Experiment design scheme for the modified two-bottle choice experiment to examine pharmacological effect of NT69L. (B) Ethanol consumption and (C) preference for ethanol are significantly reduced in the wild-type littermates (n = 9) but not changed in NTS1 null mice (n = 11). *p < 0.05 compared to the pre- or post-injection period as indicated by Tukey test. All data are expressed as mean ± s.e.m.