Fig. 1.
Schematic outline of the proposed hypothesis depicting how in coronavirus patients serotonin deficiency state arises, and how it explains anosmia, ageusia, chemesthetic dysfunctions and increased severity of illness in COVID-19 [B0AT1 → Broad neutral (0) Amino acid Transporter 1, ACE2 → Angiotensin-Converting Enzyme 2, TRP → Transient Receptor Potential, 5-HTP → 5-Hydroxytryptophan, 5-HT → 5-Hydroxytryptamine (Serotonin), NAD → Nicotinamide Adenine Dinucleotide, HPV → Hypoxic Pulmonary Vasoconstriction]