Expression of BDNF and TH mRNA in the brain following inhaled administration of α-pinene.

Essential oils are mainly administered by inhalation. Administration by inhalation is considered to occur through two pathways, neurological transfer and pharmacological transfer. However, the relationship between the two routes is not clear. To clarify this relationship, we administered α-pinene, which has an anxiolytic-like effect, to mice. Emotional behavior and accumulation and expression of relevant mRNAs in the brain (brain-derived neurotrophic factor (BDNF); tyrosine hydroxylase (TH)) were examined following inhaled administration of α-pinene (10 μL/L air for 60 or 90min). To evaluate the anxiolytic-like effect, the elevated plus maze (EPM) test was used. Inhalation of α-pinene for 60 min produced a significant increase in the total distance traveled in the EPM test compared with control (water). The concentration of α-pinene in the brain after 60 min of inhalation was significantly increased compared with that after 90 min of inhalation. The expression of BDNF mRNA in the olfactory bulb and in the hippocampus was almost the same after 60 min of inhalation compared to that after 90 min of inhalation. The expression of TH mRNA in the midbrain after 60 min of inhalation was significantly increased compared with that of the control. Thus, an increase in α-pinene in the brain induces an increase in TH mRNA expression and increases locomotor activity. The anxiolytic-like effect may be related to both neurological transfer and pharmacological transfer.