HTR4 and Anxiety: Among others, it is highly expressedin the human CNS, especially in the hippocampus, basal ganglia, andcortex132 but also in peripheral tissuesincluding the gastrointestinal (GI)-tract, bladder, adrenal glands,intestine, and the heart.133 Within thehuman heart, 5-HT4R expression was shown in cardiomyocytes for bothatrium and ventricles (see Figure 1).83 While in the CNS, itsfunctions have been linked to anxiety, cognition, and memory,134 the 5-HT4R can directly influence cardiaccontractility.84