You'll have to go with an indirect method such as immunoreactivity, but it should work as long as the brain was fixed properly. There are antibodies against fixed-forms of neurotransmitters, so you can use those. Why dopamine/monoamine and not a dopamine/monoamine transporter or receptor? There's also a good fair amount of great antibodies for neurotransmitter receptors and transporters.

Dear Tracy,

We have used anti-DAT (dopamine transporter) antibody as a dopamine neurone marker previously, albeit in postmortem human brain tissue. From what I remember (it's a few years ago now), it did work quite well in labelling DA neurones.

Hope this helps.

Ahmad