GABAergic projection neurons

This is the case when the excitatory Dx receptors on these striatal GABAergic projection neurons are no longer activated since the transmitter dopamine is reduced (green broken arrows at 2). The indirect pathway is... 

Marino, M. J., Wittmann, M., Bradley, S. R., Hubert, G. W., Smith, Y., and Conn, P. J. (2001). Activation of group I metabotropic glutamate receptors produces a direct excitation and disinhi-bition of GABAergic projection neurons in the substantia nigra pars reticulata. J. Neurosci. 15,... 

Treatment with NMDA receptor antagonists leads to a marked, dose-dependent increase of amphetamine-induced dopamine release (Miller and Abercrombie, 1996). In schizophrenics, this amphetamine-induced dopamine release is much higher compared to healthy controls (LarueUe et al., 1996). This observation is in accordance with the view that activation of the nigrostriatal dopamine system can take place by opposing activation of inhibitory striatonigral GABAergic projection neurons (Carlsson et al., 2001). 

As mentioned in the preceding text, striatal GABAergic projection neurons do contain CB, receptors (Herkenham, Lyrm, de Costa, et al., 1991) and their activation stimulates GABA transmission (Maneuf et al., 1996 Romero, de Miguel, et al., 1998), which would result in a greater inhibition of nigral dopamine neurons. 

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