Here are two hormones that are classically thought of as female reproductive hormones—this is what goes up and goes down during the estrous cycle: estrogen and progesterone—and yet, they're playing a very important role in controlling aggression in male mice and presumably in male humans as well.

One way of looking at fetishes from a neurobiological standpoint is that they represent a kind of appetitive conditioning where something that is natively aversive or disgusting, by being repeatedly paired with a rewarding experience, changes its valence, it's sign, so that, now, it somehow produces the anticipation of reward the next time a person sees it.

People don't develop fetishes to mailboxes or to the color red or to random objects and things; they develop fetishes to things that are highly infectious and counter reproductive appetitive states.

The preoptic area has many different subsets of neurons that are specifically active during different behaviors, even different phases of mating behavior. So, there are mounting neurons, there are intromission thrusting neurons, and ejaculation neurons, and sniffing neurons.

Now, the thing that you mentioned about it not hurting when you got beat up during martial arts, there is a well-known phenomenon called fear-induced analgesia where, when an animal is in a high state of fear, like if it's trying to defend itself, there is a suppression of pain responses.

When we finally identified the neurons in VMH (ventromedial nucleus of the hypothalamus) that control aggression with a molecular marker, we found out that that marker was the estrogen receptor.

Social isolation increases aggressiveness. So, putting a violent prisoner in solitary confinement is absolutely the worst, most counterproductive thing you could do to them.

The word aggression, in my mind, refers more to a description of behavior than it does to an internal state.

The state of aggressiveness is multi-faceted. It depends on the type of aggression, and it involves different sorts of circuits.