Brian, you wrote on the list in reply to Ron Reiner: <<Hello Ron, This is the Dopamine story as I understand it: The Dopamine production system is one which is dedicated to providing Dopamine where it is needed, when it is needed, and in the right quantities. It is a constantly flowing system because when the Dopamine has done its work as a neuro transmitter, it decomposes and is transported out of the way by the brain's clean-up system. So it is a self-regulating system with apparently quite a fast reaction time. The best proof that I know is to consider what happens to a person with a normal healthy brain if you give them a large dose of Sinemet - one that would drive a PWP into wild Dyskinesias. The answer is that virtually nothing happens! The reason is that a healthy brain can sense the invasion of the tablet, and immediately cut-back productionto compensate. The brain of a PWP simply doesn't have enough Dopamine -producing cells to shut down to compensate for the large intruder, and so an overdose condition exists, causing what we know as dyskinesias. This model (because that is all it is) has worked pretty well for me: it explains: Why it gets progressively more difficult to achieve the ideal dosage of levodopa. Why a newly-diagnosed PWP can tolerate a large input of Sinemet, although he doesn't need it. Why a long-term PWP has to take small doses of levodopa, when ideally he needs large doses.>> I must argue differently about a normal person's response to levodopa. (actually I have not seen such an experiment or read about such.) My argument is to dispute the assignment of cause for "virtually nothing happens". Per my understanding, the healthy brain has no shortage of levodopa or dopamine. The dopamine is in containers (storage) at the synapses - available to be released to cross the nerve-to-nerve gap (synapse) when the signal to transmit gets to that locus. There is some concentration of dopamine in the fluids in equilibrium with levodopa et cetera in the fluids of the brain (as well as all other fluids in cells, brain, blood, eural networks, ... The added levodopa into the stomach->intestines of a normal person may not enter the blood at the same rate as in you or I - because the concentration gradient there at the intestine-blood membrane. Then, what happens at the brain membrane will also be dependent upon the membrane transport inhibition mechanisms - may be concentration difference primarily?) - and reslt in little or none getting into the brain fluids. then, if the normal storage is full and the normal backup storage is full, the new levodopa may drift about as increased concentration until usage or metabolic equilibrating factors use it or destroy it. Do you know of a report describing the experiment of normal persons taking Sinemet? Normal persons eating lots of fava beans would not have the carbidopa or benzarazide. Do we know the causation of dyskinesia? chorea? Since the carbidopa and benzaride are both similar in not preventing chorea, we can assume it comes from large amounts of levodopa when the brain gets too much. However, the too much may be due to lack of any significant active synapses number remaining functional in the advanced Parkinsonian. It may be that high concentration acts to drive the CNS random walk dance (chorea)? Maybe, the mechanical analogy of the clutch is pertinent to chorea: the CNS controller is not functioning smoothly when there is too much dopamine and no storage capacity of significance, such that the dopamine that is free reaches concentrations that cause signals by absorption from fluid to the receiving synapse sites ( not from the sending neuron); id est, there is random application of the clutch or random releases of the clutch for various muscle controller neurons. The blood pressure and blood flow to the brain are also involved in how much of all things supplied by the blood and removed from the brain fluids into the blood. The hypotension chemistry, mechanics, physics, pharmacokinetics may be involved in the transporting and crossing of barriers - there are pressure and flow rate effects as well as concentration, thermal and mass transport mechanics as well as electrochemical effects, hydrophobic, hydrophilic, et cetera complications as the pipes clog and lack of exercising all the parts is hard to accomplish when the brady- prefixes more of our functions. (G) this will clear it all up for you, I imagine (G g ...gad!) tafn, ron v -- ron 1936, dz PD 1984 Ridgecrest, California Ronald F. Vetter <[log in to unmask]> http://www.ridgecrest.ca.us/~rfvetter