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The nigrostriatal dopaminergic pathway has generally been used as an experimental model for basic investigations into the release of dopamine (DA) from central dopaminergic neurons. The release of DA from striatal nerve endings is not only dependent on nerve impulse flow but also on regulation processes mediated by D2 autoreceptors (Starke 1981; L’hirondel et al. 1998). These autoreceptors are not only involved in the inhibitory control of DA release but also in its synthesis, and the efficacy of these presynaptic regulatory mechanisms depends on the state of depolarisation of the plasma membrane. While the DA autoreceptors involved in the regulation of the release process of DA are mainly coupled to potassium channels (Bowyer et al. 1989; Cass and Zahniser 1991), those which control the rate of the transmitter synthesis are negatively coupled to adenylyl cyclase (El Mestikawy et al. 1985, 1986; Onali et al. 1988). In addition, these D2 autoreceptors regulate the state of excitability of nerve terminal arborisations (Romo and Schultz 1985; Tepper et al. 1986). |
