In this compilation, the authors begin with a review of the mechanisms of synthesis and secretion, cellular effects and the involvement of serotonin (5-HT) in physiological and behavioral functions horses. In addition, the pathological conditions in which 5-HT is involved at the level of equine clinics are studied. Following this, the capabilities and limitations of PET imaging research on non-human primates are discussed for translation to brain DA research on humans, as well as therapeutic drug development for neurodegenerative diseases. This book also examines the etiology of autism spectrum disorder (ASD). The authors present available data contributing to the appreciation of a serotonergic dysfunction in ASD, as well as discuss new avenues to reveal the pathophysiology of this multifactorial disorder. Next, they review the historical and current evidence that links neurotransmitters with hemopoeitic stem cell mobilization, trafficking, and specially emphasize the role of serotonin in erythropoiesis. Potential actionable myelodysplastic and leukemic pathways are described and investigated.