Yes the basophils release serotonin in your body.
Your basophils mature and arise in the bone marrow.
When your basophils activate the basophils degranulate and also release histamine, proteoglycans (e.g. heparin and chondroitin), and proteolytic enzymes (e.g. elastase and lysophospholipase).
The basophils also secrete lipid mediators like leukotrienes (LTD-4), and several cytokines.
They are also very important to your immune system to keep you healthy and your basophils also help to boost your immune system to fight off viruses and other infections.
When your basophil counts are low or at 0 it can be caused by some condition that is causing too many white blood cells to be produced in your bone marrow.