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, 63 (1), 161-8

Cannabinoid Facilitation of Behavioral and Biochemical Hedonic Taste Responses

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Cannabinoid Facilitation of Behavioral and Biochemical Hedonic Taste Responses

M A De Luca et al. Neuropharmacology.

Abstract

Cannabinoid receptor agonists are known to stimulate feeding in humans and animals and this effect is thought to be related to an increase in food palatability. On the other hand, highly palatable food stimulates dopamine (DA) transmission in the shell of the nucleus accumbens (NAc) and this effect undergoes one trial habituation. In order to investigate the relationship between the affective properties of tastes and the response of NAc shell DA we studied the effect of delta-9-tetrahydrocannabinol (THC) on behavioral taste reactivity to intraoral infusion of appetitive (sucrose solutions) and aversive (quinine and saturated NaCl solutions) tastes and on the response of in vivo DA transmission in the NAc shell to intraoral sucrose. Rats were implanted with intraoral cannulae and the effect of systemic administration of THC on the behavioral reactions to intraoral infusion of sucrose and of quinine or saturated NaCl solutions were scored. THC increased the hedonic reactions to sucrose but did not affect the aversive reactions to quinine and NaCl. The effects of THC were completely blocked by the CB1 receptor inverse agonist/antagonist rimonabant given at doses that do not affect taste reactivity to sucrose. In rats implanted with microdialysis probes and with intraoral cannulae, THC, made sucrose effective in raising dialysate DA in the shell of the NAc. As in the case of highly palatable food (Fonzies, sweet chocolate), the stimulatory effect of sucrose on shell DA under THC underwent one trial habituation. Altogether, these findings demonstrate that stimulation of CB1 receptors specifically increases the palatability of hedonic taste without affecting that of aversive tastes. Consistent with the ability of THC to increase sucrose palatability is the observation that under THC pretreatment sucrose acquires the ability to induce a release of DA in the shell of the NAc and this property undergoes adaptation after repeated exposure to the taste (habituation). This article is part of a Special Issue entitled 'Central Control of Food Intake'.

Figures

Fig. 1
Fig. 1
Effects of THC (0.5 and 1.0 mg/kg i.p.) on behavioral hedonic score after 20% sucrose solution (1 ml, i.o.). Data are expressed as means (±SEM) of hedonic score at 30, 60, 120 and 240 minutes after THC administration (panel A) or means of total hedonic score (panel B). *p<0.05 and ***p<0.001 with respect to vehicle, # p<0.05 with respect to THC 0.5, ### p<0.001 with respect to THC 0.5 total hedonic.
Fig. 2
Fig. 2
Behavioral hedonic scores after intraoral administration of water, 5% sucrose and 20% sucrose solutions in rats pretreated with THC (1.0 mg/kg i.p.) or vehicle. Data are expressed as means (±SEM) of hedonic score at 30, 60, 120 and 240 minutes after treatment (panel A, B, C) or means of total hedonic scores (panel D). *p<0.05 and ***p<0.001 with respect to vehicle, # p<0.0001 with respect to 5% sucrose or water THC rats, § p<0.002 with respect to water vehicle rats.
Fig. 3
Fig. 3
Behavioral aversive scores after quinine HCl (5 × 10−4 M, 1 ml i.o.) or NaCl (saturated, 1 ml i.o.) bitter solutions in rats pretreated with THC (1.0 mg/kg i.p.) or vehicle. Data are expressed as means (±SEM) of hedonic score at 30, 60, 120 and 240 minutes after THC administration (panel A, B) or means of total hedonic scores (panel C).
Fig. 4
Fig. 4
Blockade of the THC effect on hedonic score by rimonabant (1.0 mg/kg i.p.). Data are expressed as means (±SEM) of hedonic score after 20% sucrose administration 30, 60, 120 and 240 minutes after THC treatment (panel A) or means of total hedonic scores (panel B) ***p<0.001 with respect to vehicle, SR-vehicle and SR-THC. Note that total hedonic score of rats pretreated with vehicle or THC (panel B) are the same as in Fig. 1.
Fig. 5
Fig. 5
Effect of THC (1 mg/kg i.p.) and of intraoral sucrose 20% administration (1 ml, i.o.) on NAc shell (panel A), NAc core (panel B) and PFCX (panel C) dialysate DA levels. Data are expressed as means (±SEM) of change in DA extracellular levels expressed as a percentage of basal values. The arrow indicates the start of THC and sucrose administration. Solid symbols: p<0.05 with respect to basal values; * p<0.05 with respect to THC group.
Fig. 6
Fig. 6
Effect of THC (1 mg/kg i.p.), and blockade of THC’s effects by rimonabant (SR, 1 mg/kg i.p., 30 min before THC), on changes in NAc shell dialysate DA produced by 20% sucrose administration (1 ml, i.o.). Data are expressed as means (±SEM) of change in DA extracellular levels expressed as a percentage of basal values. The arrow indicates the start of THC and sucrose administration. Solid symbols: p<0.05 with respect to basal values; * p<0.05 with respect to THC group. Note that DA extracellular levels of rats pretreated with vehicle-THC are the same as in Fig. 6 (panel A).
Fig. 7
Fig. 7
Effects of THC (1 mg/kg i.p.) on changes in NAc shell dialysate DA produced by repeated 20% sucrose administration (1 ml, i.o.). Data are expressed as means (±SEM) of change in DA extracellular levels expressed as percentage of basal values. The arrow indicates the start of Veh (panel A, B) or THC (panel C, D) and water-sucrose (panel A, C) or sucrose-sucrose (panel B, D) administration. Solid symbols: p<0.05 with respect to basal values; * p<0.05 with respect to panel.

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