Stimulation and inhibition of food intake by the selective dopamine D2 agonist, N-0437: a meal pattern analysis

Feeding and drinking responses were recorded in home-caged rats over 24-hour periods, and the data were analysed in terms of meal patterns. The highly selective dopamine D2 receptor agonist, N-0437, was injected IP at the start of the night phase. At the smallest dose (0.3 mg/kg), N-0437 increased food intake as a result of increases in meal size and duration. The rate of feeding during meals was not increased. This effect lasted 1-2 hours in the night phase. At higher doses (1.0 and 3.0 mg/kg), N-0437 inhibited food intake for 3-6 hours. The inhibition was due to a substantial reduction in meal size, with no change in meal frequency. Rate of feeding during meals tended to be reduced. A biphasic dose-effect relationship was not apparent in the drinking data, and there was not a significant effect of N-0437 on drinking responses. The meal pattern analysis results indicate the stimulation of D2 receptors produces increases and decreases in food intake and meal size. These results are discussed in terms of dose-dependent stimulation of presynaptic (autoreceptor) and postsynaptic D2 receptors, and the relationship to satiety within meals.