The answer is sort of both.

The cell has its perikaryon (body) in the hypothalamus (supraoptic nucleus) and axonal extensions in the posterior pituitary. So its inside of a cell of the supraoptic nucleus but its in the region called the posterior pituitary

Neurons are often quite long and synthesize neurotransmitters (or neurotransmitter precursors) in one area but then transport them intracellularly to a target area.