Dopamine, Libido, and Testosterone - a Question

[johndoesmith]

I have seen them improve libido several times. Interestingly, from my own experience I've seen generic modafinil work better than brand name provigil...though I'm sure it's likely coincidental and/or circumstantial specific to the cases I've seen. The guys who experience better libido with those meds may be due to dopamine enhancement (blocks re-uptake) or perhaps simply due to better energy from the stimulant effect. Libido is so multifactorial that it's a difficult nut to crack for some. Having a partner with a healthy libido goes a long way too.

From my understanding that dopamine plays a huge role in libido, for example any D2/D3 agonists like parkinson's drugs are known to possibly cause hypersexuality.

Amphetamines especially AFAIK, is it possible that long term medical use of amphetamines can cause enough downregulation to permanently stunt libido? My understanding is that the dopamine system is fairly robust, and recovers easily?

Random pharmacologic question: wikipedia lists dopamine receptors as functioning through gene transcription, as does the androgen receptor, yet dopamine ligands will elicit a noticable effect nearly immediately while testosterone does not. So I'm probably massively misunderstanding this complex process of gene regulation, but why does testosterone not?