Pharmacokinetics of natural borneol after oral administration in mice brain and its effect on excitation ratio

Previous studies have indicated that borneol has double side effects on the central nervous system (CNS), but the mechanism is unknown. The aim of this study was to clarify the relationship between excitation ratio [contents of excitatory amino acids (AAs) versus that of inhibitory] and the content of natural borneol after a single oral dose. Mice were administered a 1.2 g/kg dose of natural borneol (containing 98% d-borneol) by oral ingestion. Brain samples were collected before administration and at 0.083, 0.167, 0.25, 0.333, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 4 and 5 h after administration. The brain concentration of natural borneol and contents of AA neurotransmitters in mice brain were determined by GC-MS and HPLC-FLU, respectively. After per oral application, natural borneol was absorbed rapidly into the brain and could be determined 5 min after dosing. The maximal brain concentration (86.52 mu g/g) was reached after 1 h post-dosing. Natural borneol could affect the contents of AA neurotransmitters in mice brain: l-aspartic acid increased significantly from 0.083 to 1 h after administration, l-glutamic acid increased significantly at 0.333 h and decreased from 1.5 to 5 h, gamma-amino-N-butyric acid increased significantly from 0.167 to 5 h, whereas glycine was not affected. The excitation ratio is the contents of excitatory AAs versus that of inhibitory AAs, which reflects the excitatory or inhibitory state of the body. The excitation ratio elevated transitorily and then declined 0.5 h post-dosing; there were significant differences between 1.5-5 h post-dose compared with pre-dose. The present study indicated that natural borneol could affect the contents of AA neurotransmitters, and the change in excitatory ratio led to borneol's double side effects on the CNS.