Re: Does the human brain contain melanin?

The answer to the question is: yes. Scientists gave this substance the name neuromelanin to distinguish it from melanin in the skin.
Neuromelanin has been identified (in 1965) as a polymer made up of units of 5,6-dihydroxy indole (see figure), an oxidative product of dopamine metabolism. The only feature actually making it different from skin melanin is the metabolic pathway leading to its formation. This 'auto-oxidative pathway' has only recently been elucidated (more detailed description in ref. 1).

Neuromelanin's role is rather obscure (as of yet). It gives specific populations of (dopaminergic) neurons in the substantia nigra ('black substance'), an assembly of cells in the midbrain, their characteristic color. Scientists assume a role for it in neurodegenerative diseases such as Alzheimer's Disease and most notably Parkinson's Disease (which is characterized by destruction of dopamine/neuromelanin containing cells). Whether this is pure conincidence or whether neuromelanin actively contributes to cell death is subject of intensive research. Neuromelanin chelates metal ions such as aluminum and iron and binds some neurotoxic substances (MPTP - note though that this is a substance used in experimental research), all of them implicated in the etiology of Parkinson's.
In addition, one of the intermediates in the pathway (adrenochrome) is itself cytotoxic and polymorphonuclear leucocytes (immune cell which kills bacteria) use it as a weapon in the body's defense against pathogens. Yet, in other cells it should probably be sequestered or eliminated in other ways (antioxidants, radical scavengers, cytochrome P450 system, etc., see also p. 161 in ref. 1) for else it would harm these cells.
Smythies and Galzigna also hypothesize that some toxic intermediates in the auto-oxidative pathway (dopamine quinones, highly reactive molecules) might contribute to PD if not kept at bay by specific mechanisms.

That's the more interesting information I retrieved after browsing the literature on the subject. Actually, I only read one article completely (ref. 1), the abstracts of others for lack of availability of the journals (refs. 2 - 6) and checked on some on-line references.
You see, there are still a lot of questions waiting to be answered.

I hope this helps a little bit. For further questions you are welcome to email me.

1-6: Medline search for 'neuromelanin AND review' (URL: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&te rm=neurom elanin+AND+review)

7-8: Google Search for 'neuromelanin' (http://www.google.com/). You may check some of the other links if you want to.

1. Smythies J and Galzigna L (1998): The oxidative metabolism of catecholamines in the brain: a review. Biochimica et Biophysica Acta 1380: 159-162.
   
2. D'Ischia and Prota (1997). Biosynthesis, structure, and function of neuromelanin and its relation to Parkinson's disease: a critical update. Pigment Cell Research 10: 370-76.
   
3. Smythies J (1996). On the functional of neuromelanin. Proceedings of
4. Youdim MB, Ben-Shachar D, Riederer P. The enigma of neuromelanin in
5. Langston JW. Neuromelanin-containing neurons are selectively vulnerable in parkinsonism. Trends Pharmacol Sci. 1988 Oct;9(10):347-8
6. Breathnach AS. Extra-cutaneous melanin. Pigment Cell Res.
7. Googl e 1
8. Google 2