Inhibition of phosphodiesterase-4 decreases ethanol intake in mice

Abstract

Rationale: Cyclic AMP (cAMP)-protein kinase A signaling has been implicated in the regulation of ethanol consumption. Phosphodiesterase-4 (PDE4) specifically hydrolyzes cAMP and plays a critical role in controlling intracellular cAMP levels in the brain. However, the role of PDE4 in ethanol consumption remains unknown.

Objective: The objective of this study is to examine whether PDE4 was involved in regulating ethanol intake.

Methods: The two-bottle choice paradigm was used to assess intake of ethanol, sucrose, and quinine in C57BL/6J mice treated with the selective PDE4 inhibitor rolipram or Ro 20-1724; locomotor activity was also monitored using the open-field test in mice treated with rolipram.

Results: Administration (i.p.) of either rolipram (0.25 and 0.5 mg/kg) or Ro 20-1724 (10 mg/kg) reduced ethanol intake and preference by 60-80%, but did not alter total fluid intake. In contrast, rolipram even at the higher dose of 0.5 mg/kg was not able to affect intake of sucrose or quinine, alcohol-induced sedation, or blood ethanol elimination. At 0.5 mg/kg, rolipram did decrease locomotor activity, but the effect only lasted for approximately 40 min, which did not likely affect behavior of ethanol drinking.

Conclusions: These results suggest that PDE4 is a novel target for drugs that reduce ethanol intake; PDE4 inhibitors may be used for treatment of alcohol dependence.

Fig. 1

Rolipram reduced ethanol intake in the two-bottle choice paradigm in C57BL/6J mice. Animals were provided with one bottle containing the ethanol solution at the concentration of 7%, 9%, or 12%, each for 3-4 d and another bottle containing water. Rolipram (0.1, 0.25, or 0.5 mg/kg) or vehicle was injected twice daily. Ethanol intake (g) was adjusted by body weight (kg). Data were analyzed with two-way repeated measures ANOVA, followed by Dunnett's post hoc analysis. Rolipram at either 0.25 or 0.5 mg/kg profoundly reduced ethanol intake, while at 0.1 mg/kg it did not have a significant effect. Data shown are means ± SEM; n = 8 – 10 except for the vehicle control group (n = 26); * P < 0.05, *** P < 0.001 vs. corresponding vehicle.

Fig. 2

Rolipram reduced ethanol preference in the two-bottle choice paradigm in C57BL/6J mice. Animals were provided with one bottle containing the ethanol solution at the concentration of 7%, 9%, or 12%, each for 3-4 d, and another bottle containing water. Rolipram (0.1, 0.25, or 0.5 mg/kg) or vehicle was injected twice daily. Ethanol preference = ethanol intake/(ethanol intake + water intake). Data were analyzed with two-way repeated measures ANOVA, followed by Dunnett's post hoc analysis. Rolipram at either 0.25 or 0.5 mg/kg profoundly reduced ethanol preference, while at 0.1 mg/kg it did not have a significant effect. Data shown are means ± SEM; n = 8 - 10 except for the vehicle control group (n = 26); ** P < 0.01, *** P < 0.001 vs. corresponding vehicle.

Fig. 3

The PDE4 inhibitor Ro 20-1724 reduced ethanol intake (A) and preference (B) in the two-bottle choice paradigm in C57BL/6J mice. Mice were provided with an ethanol (9%) bottle and a water bottle for 3 d. Ro 20-1724 (10 mg/kg) was administered (i.p.) twice a day. Data shown are means ± SEM; n = 7; *** P < 0.001 vs. corresponding vehicle.

Fig. 4

Rolipram did not change intake of sucrose, quinine, or water. (A) Intake of sucrose at the concentrations of 2% and 4%; (B) water intake while the sucrose solution was provided; (C) intake of quinine at the concentrations of 0.03 or 0.1 mM; (D) water intake while the quinine solution was provided. The sweet (sucrose) or bitter (quinine) taste was tested for 3 d for each concentration also using the two-bottle choice paradigm in C57BL/6J mice. Rolipram (0.5 mg/kg) or vehicle was injected twice daily. Both vehicle- and rolipram-treated mice preferred 2% and 4% sucrose, while they avoided 0.1 mM quinine; however, there was no difference between the two treatment groups (P > 0.05). Data shown are means ± SEM; n = 8 - 10.

Fig. 5

Effect of rolipram on locomotor activity in the open-field test in C57BL/6J mice. Animals were injected with vehicle or rolipram (0.5 mg/kg) immediately before the test; locomotor activity expressed as beam breaks was recorded every 10 min for 4 h using the PAS-Open Field (see text). Rolipram reduced locomotor activity only within 40 min of treatment. Data shown are means ± SEM; n = 6. * P < 0.05 vs. corresponding vehicle.

Fig. 6

Rolipram did not affect ethanol elimination. Rolipram (0.5 mg/kg) or vehicle was injected 30 min prior to the ethanol (2 g/kg) injection. Blood ethanol concentrations (mM) from the retro-orbital sinus were examined 15, 30, 60, and 120 min after the ethanol injection using an enzymatic assay (see the text). Data shown are means ± SEM; n = 4.