Hi Nigel, What an innovative question!
1-There is some info in recent literature about this topic but they mostly discuss use in hypothermia and circulatory issues. The language in this abstract is a bit challenging but below is a small part of an article published by PubMed.
2- Below is a brief statement similar to what you said Nigel about the 250% improvement in mood/dopamine. I'll keep looking and let you know if I learn more.
3- This short statement indicates that even short bouts of cold exposure can cause a lasting increase in dopamine and sustained elevation of mood, energy, and focus.

Hope you find it interesting and informative.
PS: I might be able to handle a 1 min cold shower for a days worth of 'happy' but I know cold emersion is not in my future.

1- Abstract
The basal skin microcirculatory blood flow and its change in response to a cold caloric stimulus (cold water, 5 degrees C, exposure of one foot for 30 s) were investigated in nine patients with Parkinson's disease (PD) and nine normal subjects (controls). The results revealed a significant (p < 0.001) difference between the groups. In the controls there was a strong decrease in the red cell flux (RCF) on cold water exposure, while eight of the nine PD patients revealed no detectable change in RCF; in one patient only there was a less pronounced reaction. It was concluded that the regulation of the microcirculatory blood flow was affected in PD patients; the cold caloric reflex was attenuated or absent but there was no difference in the basal microcirculatory blood flow compared to normal subjects.
PubMed Disclaimer

2-Cold water emersion and effect on dopamine
Czech researchers found that cold water plunging can increase blood concentrations of dopamine — another so-called happy hormone made in the brain — by 250%.Feb 10, 2023

3- Even short bouts of cold exposure can cause a lasting increase in dopamine and sustained elevation of mood, energy, and focus.

I've never intentionally submerged myself in cold water as a therapy. There have been several times that I had to jump into cold water and I don't know anything about the chemical responses, dopamine, or otherwise, but I absolutely know it caused an immediate response.
I was severely pissed off about it. Yep, it was unmistakable. LOL

Well...and I'm really reaching now...there's a known effect called MDS or Mammalian diving syndrome. Its been known that humans, particularly babies/children go into a special state when immersed in very cold water. It allows them to survive without oxygen for far longer than normally expected.

It would be nice to think the same or a similar trigger might "reset" or at least boost our poor, broken dopamine manufacturing sites. But I've no proof for it at all. And I hate the cold. So...I could probably give it a go if someone else did the research first!

Hi Nigel, I found lot's of info about alternative, non-medication treatments options for PD and additional confirmation that cold effects dopamine levels but no literature putting the 2 processes together. I love the Cleveland Clinic PD site but I didn't find anything there connecting cold water treatment to improve PD symptoms. The well being consultant might be on to something. It looks like there are some member of our community who are willing to try it so maybe the consultant is ahead of our time. I'll let you know if I find more info.
Om a colder but lighter side, I don't think my muscles, brain or heart could survive this level of cold. Not sure my body would reward me with more happy hormone 🙂.
Please keep the ideas and questions coming.
Maria

I’m willing to try anything.