Guanosine (G), also known as 2-amino-inosine, belongs to the class of organic compounds known as purine nucleosides. Purine nucleosides are compounds comprising a purine base attached to a ribosyl or deoxyribosyl sugar moiety. Guanosine consists of a guanine base attached to a ribose (ribofuranose) ring via a beta-N9-glycosidic bond. Guanosine is a white, crystalline powder with no odor and mild saline taste. It is very soluble in acetic acid, and slightly soluble in water, but insoluble in ethanol, diethyl ether, benzene, and chloroform. Guanosine exists in all living species, ranging from bacteria to plants to humans. High levels of guanosine can be found in clovers, coffee plants, and the pollen of pines. It has been detected, but not quantified in, several different foods, such as leeks, garlic, chicory roots, green bell peppers, and black-eyed peas. Guanosine plays an important role in various biochemical processes including the synthesis of nucleic acids such as RNA and intracellular signal transduction (cGMP). The antiviral drug acyclovir, often used in herpes treatment, and the anti-HIV drug abacavir, are both structurally similar to guanosine. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP). In humans, guanosine is involved in intracellular signalling through the adenosine receptors A1R and A2AR (PMID: 31847113). Evidence from rodent and cell models has shown a number of important neurotrophic and neuroprotective effects of guanosine. In particular, it is effective in preventing deleterious consequences of seizures, spinal cord injury, pain, mood disorders and aging-related diseases, such as ischemia, Parkinson‚Äôs and Alzheimer‚Äôs diseases (PMID: 27699087). Studies with rodent models of Parkinson‚Äôs disease have shown that guanosine decreases neuronal apoptotic cell death and increases dopaminergic neurons at substantia nigra pars compacta, accompanied by an improvement of motor symptoms in Parkinson‚Äôs disease (i.e. a reduction of bradykinesia). Guanosine promotes neurite arborization, outgrowth, proliferation and differentiation. Systemic administration of guanosine for eight weeks (8 mg/kg) has been shown to stimulate neuroprogenitors proliferation in the subventricular zone (SVZ) in a mouse model of Parkinsonism (PMID: 27699087). The effect of guanosine treatment is accompanied by an increased number of fibroblast growth factor (FGF-2)-positive cells which is an important regulator of neuroprogenitor/stem cell proliferation, survival and differentiation (PMID: 27699087). Guanosine prevents reactive oxygen species (ROS) generation and cell death in hippocampal slices subjected to the oxygen/glucose deprivation (PMID: 31847113).