I have an indoor vine, it's healthy, but a lot of its leaves turn brown (perhaps more in the winter due to the heating and decreased humidity) and drop on the floor.

I've been throwing them away, but now it just occurred to me they may contain alkaloids and perhaps I should keep them?

I save mine and use them as changa admixture.

Dunno how much gold is inside, but they smoke pretty nice.

Do you have a UV light?

Should be easy enough to soak/brew some of those leaves and see if they fluoresce under UV light. If so, yes to alkaloids

That is an answer but I guess not the one OP is looking for. Perhaps the question should be: does the color brown say anything about the amount of alkaloids ?

I would smoke some of them and feel if there are effects or not .

Yes, my question should have been: Are there usable amounts of alkaloids in brown leaves, and in particular how do they compare to green leaves?

UV light can show that there are alkaloids, but even trace amounts (such as the wash water you discard after the final basing) glow green.

Anyway I'm going to save them from now on and may do a simple extraction and side-by-side comparison one day.