Rick,

You obviously say things much better than I do in your own language so never hesitate and give corrections to my writings if uncorrect because of language.
Great from you to have accepted to "play" with Karine and myself, and many others if involved as much as we are , and discover other way(s) to look at "the big puzzle with no pattern" PD seems to be
(but is not...just we don't know it yet!).

Let's go back to sensitive-motor loops and, more generally speaking, to anykind of loops or coupled actions (co-actions, retrofeedback and so on) in human or animal body.

In french, we call it the " egg and hen dilemna".
Who makes the egg? The hen. But who made the hen, the egg...

Here, it is the same: no motor command without sensory data, no sensory data without movement.

How is it possible to neglect half of this circle?

"E pur si muove" ("And yet it moves") Galileo Galilei (around 1623-1630)

Yes, "it" moves and when something goes wrong on one side (let say on the sensory one), well "it" does not turn the same, eventually, "it" may stop turning!

One may hypothetize that in PD, the absence or abnormalities in modulation of motor neuronal signals in supraspinal areas and in spinal neuronal network regulation may be the cause of high disturbances in motor signals, all this leading to a final signal of hypertonia (stiffness) and slowness/absence of movement (bradykinesia / akinesia).

But where is substantia nigra in all this?
Well, substantia nigra is a part of the whole supraspinal system, but only a part of it.....only the dopaminergic part of it, other parts depending on NE (norepinephrine, called noradrenaline (NA) in Europe) and on 5-HT (serotonine) and .......on Glutamatergic synapses too.

But dopamine is the only or major neurotransmitter involved in PD as far as we all know?
No, not as far as we we all know but as far as we have all been TOLD....

If no more has been told to you, then more knowledge is required for a better understanding.
Please, read further and more particularly what has been described by neuropathologists from Ohama in 1976 , then Takeda, Wakabayashi and Takahashi in the 1980's to Braak and his staging (first publication in 1996).

See on pubmed :

Ohama E, Ikuta F.
Parkinson's disease: distribution of Lewy bodies and monoamine neuron system.
Acta Neuropathol (Berl). 1976 Apr 26;34(4):311-9.

Wakabayashi K, Takahashi H, Takeda S, Ohama E, Ikuta F.
Lewy bodies in the enteric nervous system in Parkinson's disease.
Arch Histol Cytol. 1989;52 Suppl:191-4.

Braak H, Braak E, Yilmazer D, de Vos RA, Jansen EN, Bohl J.
Pattern of brain destruction in Parkinson's and Alzheimer's diseases.
J Neural Transm. 1996;103(4):455-90.


and all related articles.


Anne
;-)