Hi Horsegoer
Many PWP take some kind of MAO-I as one of their medications. I suffered with depression most of my adult life and 15 years ago started taking 10 mg of Selegeline- partially to avoid starting Sinemet, which I succeeded in doing for 13 years. Once I started the Selegeline, my mood improved to a place better than I had felt since childhood. It mostly continues to today.
If your father hasn't tried an MAO inhibitor as one of the categories of anti-depressants he has tried, you may want to have him try one out.
Also, this may seem obvious, but he may be experiencing depression as a result of adjusting to his diagnosis (especially since he did so much to take good care of himself and was so active) and may need help to integrate this new paradigm into his life.
Good luck,
Victoria

Deprenyl medication side effects and benefits, also known as Selegiline by Ray Sahelian, M.D.

Deprenyl (selegiline), a selective MAO-B inhibitor, is known to improve motor functions in Parkinson's disease and delay the need for levodopa therapy in patients with early Parkinson's disease. It is not clear at this time whether it has longevity enhancing potential, but my educated guess would be that high doses would actually be harmful due to potential heart rhythm abnormalities. Deprenyl raises levels of dopamine. The nutrient NADH is also able to raise dopamine levels.

Dr. Sahelian's experience
I have noticed that deprenyl (selegiline) provides a sense of wellbeing with slightly brighter vision and libido. High doses may induce heart palpitations or irregularities. Periods of alertness and sleepiness are possible.

Availability
Deprenyl is a prescription medicine but can be obtained from overseas.

Side effects
Adverse effects include heart rhythm disturbances, sleepiness at times during the day and insomnia at night.

Deprenyl Research study
Pharmacological aspects of deprenyl. Curr Med Chem. 2004.
Deprenyl, the selective irreversible inhibitor of monoamine oxidase-B (MAO-B), has been synthesised as a potential antidepressant, however, due to its dopamine potentiating capacity, became a registered drug in the treatment of Parkinson's disease. Deprenyl possesses a wide range of pharmacological activities; some of them are not related to its MAO-B inhibitory potency. Beside its dopamine potentiating effect, it renders protection against a number of dopaminergic, cholinergic and noradrenergic neurotoxins with a complex mechanism of action. By inducing antioxidant enzymes and decreasing the formation of reactive oxygen species, deprenyl is able to combat an oxidative challenge implicated as a common causative factor in neurodegenerative diseases. In a dose substantially lower than required for MAO-B inhibition, deprenyl interferes with early apoptotic signalling events induced by various kinds of insults in cell cultures of neuroectodermal origin, thus protecting cells from apoptotic death. Deprenyl requires metabolic conversion to a hitherto unidentified metabolite to exert its antiapoptotic effect, which serves to protect the integrity of the mitochondrion by inducing transcriptional and translational changes. Pharmacokinetic and metabolism studies have revealed that deprenyl undergoes intensive first pass metabolism, and its major metabolites also possess pharmacological activities. The ratio of the parent compound and its metabolites reaching the systemic circulation and the brain are highly dependent on the routes of administration. Therefore, in the treatment of neurodegenerative diseases, reconsideration of the dosing schedule, by lowering the dose of deprenyl and choosing the most appropriate route of administration, would diminish undesired adverse effects, with unaltered neuroprotective potency.

and more info on selegeline

http://www.selegiline.com/