How many chromosomes does a brain cell have?

46 just like any other body cell in a human. Gametes ( sex cells ) are the only cells in the human body which don't have 46, they have 23 so that when fusion between sperm and egg occurs a new cell of 46 chromosomes will be formed.

On the other hand a dog has a regular diploid chromosome number of 78 chromosomes and therefore has gametes with a haploid chromosome number of 39 chromosomes.