Modulation of feeding behaviour by blocking purinergic receptors in the rat nucleus accumbens: a combined microdialysis, electroencephalographic and behavioural study.

The nonspecific P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), the nonspecific P1 receptor antagonist 8-(p-sulphophenyl)-theophylline (8-SPT) and the combination of both were applied by retrograde microdialysis into the nucleus accumbens (NAc) before and during feeding of 18-h food-deprived rats. In addition to the registration of behavioural parameters, such as the amount and duration of food intake, the feeding-induced changes in dopamine (DA) concentration and the concomitant changes of neuronal activity in the NAc and the ventral tegmental area (VTA) were simultaneously determined. The perfusion with PPADS (20 microm) diminished the amount of food intake and the duration of feeding. Furthermore, the P2 receptor antagonist blocked the feeding-induced DA release and prevented the feeding-elicited changes of the electroencephalography (EEG) power distribution which was characterised by an increase in the power of the 8.0-13.0-Hz frequency band in the NAc and the VTA. The effects of PPADS could be completely prevented by the concomitantly perfused adenosine receptor antagonist 8-SPT (100 microm). When given alone, 8-SPT increased the amount of food ingested, the duration of feeding and the EEG power of the higher frequency range, particularly between 19.0 and 30.0 Hz, in both the NAc and the VTA. The feeding-elicited DA release was supplemented to the enhanced DA level caused by the perfusion with 8-SPT in an additive manner. The P2 and P1 receptor antagonists interact antagonistically in the modulation of feeding behaviour and the feeding-induced changes of EEG activity suggesting that both endogenous extracellular ATP and adenosine are involved in the regulation of the feeding-associated mesolimbic neuronal activity in a functionally antagonistic manner.