This does not necessarily follow. The neurotransmitter chemicals can remain the same but whole areas of the brain can be rewired such that the area processing the pain can be connected differently to the rest of the brain, including an area which experiences pleasure.
(This is not an endorsement of the grandparent.)
Followup to Stuck in the middle with Bruce:
Bruce is a description of masochistic personality disorder. Bruce's dysfunctional behavior may or may not be related to sexual masochism [safe for work], which is demonized by most people in America. Yet there are ordinary, socially-accepted behaviors that seem partly masochistic to me:
Question 1: Can you list more?
Question 2: Doubtless some of the behaviors I listed have completely different explanations, some of which might not involve masochism at all. Which do you think involve enjoying pain? Can you cluster them by causal mechanism?
Question 3: When we find ourselves acting masochistically, should we try to "correct" it? Or is it part of a healthy human's nature? If so, what's the evolutionary-psych explanation? (I was surprised not to find any evo-psych explanations for masochism on the web; or even any general theory of masochism that tried to unite two different behaviors. All I found were the ideas that sexual masochism is caused by bad childhood models of love, and that masochistic personality is caused by other, unspecified bad experiences. No suggestion that masochism is part of our normal pleasure mechanism.)
Some hypotheses:
My guess is that, if it's a side-effect (e.g., 3) or a non-causal association (4), it's okay to eliminate masochism. Otherwise, that could be risky.
These all lead up to Question 4, which is a fun-theory question: Would purging ourselves of masochism make life less fun?
ADDED: Question 5: Can we train ourselves not to be Bruce without damaging our enjoyment of these other things?