In castrated male rats, the medial preoptic area

In the case of castrated or neutered male rats, the medial preoptic area has as much dopamine as normal rats, but the presence of a receptive female does not evoke much release of dopamine. Dopamine helps male sexual behavior in many species and is released just before and/or during copulation in three neural systems. 

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.