Neurobiological profile of Bergamot Essential Oil

Bergamot (classified as Citrus bergamia, Risso) belongs to the Rutacee, genus Citrus, growing almost exclusively in Calabria (Italy), along the southern east coast, in the area of Reggio Calabria. This fruit is most knowledgeable for its essential oil (BEO) that according to the Farmacopea Ufficiale Italiana (1991) is obtained by cold pressing of the epicarp and, partly, the mesocarp of the fresh fruit. This citrus is cultivated for its essential oil, a product in great demand by perfumery and cosmetic industries but also employed by pharmaceutical, food and confectionery industries.

BEO comprises a volatile (93–96% of total) and a non-volatile (4–7% of total) fraction containing coumarins and psoralens [such as bergapten (5-methoxypsoralen) and bergamottine (5-geranyloxypsoralen)]. The most abundant compounds found in the volatile fraction are the monoterpene hydrocarbons limonene, γ-terpinene, and β-pinene, the monoterpene alcohol, linalool, and the monoterpene ester, linalyl acetate which, altogether, constitute more than 90% of the whole oil. Oxygenated compounds, namely linalool and linalyl acetate, mark the flavor notes of BEO, whereas the hydrocarbon fraction does not have a fundamental role in determining the olfactory character of BEO. The nonvolatile residue contains waxes and polymethoxylated flavones and it is a natural odor fixative which influences the olfactory properties of the oil. However, it also contains about 0.2% bergapten which is responsible for the phototoxicity of BEO; therefore, a bergapten-free extract of the essence (BEO-BF) together with a natural essence deprived of the hydrocarbon fraction and of bergapten (BEO-HF/BF) are prepared by extractive industries for perfumery and cosmetic uses.

            Likewise other essential oils, BEO is widely used in aromatherapy, a complementary medicine highly diffused in the industrialized countries to improve mood and mild symptoms of stress-induced disorders such as anxiety, depression, behavioural disturbances in dementia and chronic pain (e.g. cancer pain) though the rational basis for such applications awaits to be discovered. Individual components of essential oils reach the blood, cross the blood-brain barrier and enter the central nervous system (CNS) following inhalation, dermal application, intraperitoneal (i.p.) or subcutaneous (s.c.) injection and oral administration.

A systematic assessment of the neurobiological properties of BEO has recently been completed widening our understanding of the mode of action of this phytocomplex on nerve tissue under normal and pathological experimental conditions. In fact, it is proven that behavioural and EEG spectrum power effects of BEO correlate well with its exocytotic and carrier-mediated release of glutamate, an amino acid endowed with excitatory neurotransmitter function in the mammalian brain (including the hippocampus) supporting the deduction that BEO is able to interfere with normal and pathological synaptic plasticity. The observed in vitro neuroprotection and in the course of experimental brain ischemia and neuropathic pain does support this view and provide a rational basis for the practical use of BEO in complementary medicine.

In conclusion, the data gathered so far provide the rational basis for translation of the essential oil of bergamot into clinic use as neurotherapeutic opening of a broad venue for future research and translation into clinical settings.