effects of the DNA-binding proteins on transcription of other genes; and the 
downstream effects of such changes (for example, insertion of new receptor 
proteins into the cell membrane or regulation of neurotransmitter expression). 
Some progress has been made in identifying the signaling pathways likely to be 
involved in the induction of lEGs by acute exposure to psychomotor stimulants, 
but there is little firm information about the effects of this induction. It is known 
that neurotransmitters and neuropeptides as well as receptors and messenger 
molecules undergo altered expression with prolonged exposure to dopamine 
agonists and antagonists (see Graybiel 1990; Grimes et al. 1990; Gerfen et al. 
1991). Several neuropeptide genes have recently been shown to contain AP-1- 
like DNA binding motifs in the upstream regions of their promoters. Thus, the 
signaling pathways may be in place for direct effects of Fos-like transcription 
factors on neuropeptide expression. With transgenic mice it may be possible to 
test this possibility directly and also to test whether regulatory control is exerted 
through particular combinations of lEGs on expression of neurotransmitters, 
receptors, and messenger molecules that could bring about long-term changes 
in neural function. 
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