The effects of 7-OH-DPAT, quinpirole and raclopride on licking for sucrose solutions in the non-deprived rat

Pharmacological manipulations that alter dopamine (DA) at DA receptor subtypes produce reductions in feeding behaviour. What remains uncertain is the exact way in which these reductions in feeding are achieved as a consequence of differing drug actions at separate receptor subtypes. In this study our aim was to compare the anorectic effects of the preferential D3/D2 agonists 7-hydroxy-2-(di-n-propylamino)tetralin (7-OH-DPAT) and quinpirole and the non-selective D2/D3 antagonist raclopride on the microstructure of licking responses in non-deprived rats. In a 20-min test, trained adult, male hooded rats had access to one of three solutions: 1%, 3% or 10% sucrose. 7-OH-DPAT (0.1-1.0 mg/kg, i.p.), quinpirole (0.03-0.3 mg/kg, s.c.), raclopride (0.03-0.3 mg/kg, i.p.) or vehicle were injected 20 min prior to the start of the licking test. A lickometer recorded the timing of each lick, from which the microstructural parameters of bout frequency and bout duration were also computed. All compounds reduced the mean bout duration, while 7-OH-DPAT and raclopride also brought about a compensatory increase in bout number. Analysis of the licking rates over the test session showed that 7-OH-DPAT, quinpirole and raclopride decreased the initial rate, without affecting the rate of decline of licking. Changes in licking microstructure (i.e. initial rate of licking and mean bout duration) after the administration of 7-OH-DPAT, quinpirole and raclopride, are consistent with an action of these dopaminergic compounds to reduce palatability.