Figure 5: Effects of drinking H2-water on neuroprotection via stomach-brain connection. H2 gas dissolved in drinking water induces ghrelin production and release from the stomach via β1- adrenergic receptor stimulation. Released ghrelin in the plasma activates its receptor, growth-hormone secretagogue receptor (GHS-R), which is also expressed in the brain, especially in substantia nigra. The precise mechanism how H2 stimulate β1- adrenergic receptor is not known yet. Whether ghrelin activates GHS-R in substantia nigra directly or indirectly is controversial as well.