Brain-imaging studies have revealed increased dopaminergic activity in the when heterosexual men look at pictures of attractive women and in individuals who think that they are about to receive money.

Neuron

Explanation:

Dopaminergic activity means "working on dopamine", related to dopamine. It increases the level of dopamine in brain in reaction to a stimulus. The adrenaline rush in the blood excites the pleasure received by the cells.

Various brain imaging studies show that an increased dopamine in the neuron when a heterosexual man looks at a picture of attractive women is due to the signals sent into the brain that increases the level of dopamine. It is a reaction of body to pleasure and a comfort received by the neuro-cells. It is also noted when they receive money as it also excites a stimulus reaction in the body. Thus, increasing the level of dopamine in the brain.  

i think it is the third one.