What many seem to be missing is that PD is a degeneration of neurons: the
projection of the A9 region of the VTA to the SN degenerates, so that
whether cocaine, or any other substance prolonging the effect of DA
in the synapse is given, it won't matter if there are NOT terminals with
DA to release in the area. L-dopa is given until the degeneration is so
bad that there is essentially NO response, so something like bromocriptine
is then instituted to activate the D2 receptors in the striatum.
Cocaine's rewarding properties, mediated mostly thru the NAc, causes inc.
locomotor activity due to the regulatory balance between DA and ACh in the
striatum. Lack of DA leaves a relative 'lack of control' of ACh, and, hence
motor impairment.
Jeff
