Toll-like receptors (TLRs) in the brain significantly contribute to various central nervous system (CNS) disorders, including addiction. Morphine’s interaction with TLR4 contributes to dependence and withdrawal. Alpha-pinene, a monoterpene with anti-inflammatory properties, has not been studied for its effects on TLR signaling in morphine dependence and withdrawal. This study investigated alpha-pinene’s impact on hippocampal TLR pathways in morphine-dependent and withdrawing rats. Male Wistar rats were divided into two categories: dependence and withdrawal. The three dependence groups received saline + dimethyl sulfoxide 5% (DMSO), morphine (10 mg/kg) + DMSO, or morphine + alpha-pinene (20 mg/kg) for 10 days. The three withdrawal groups received the same saline or morphine treatments as the dependent groups for ten days. Following this, they went through a 30-day morphine washout phase with daily DMSO (the first and second groups) or alpha-pinene (the third group) administration. Rats in all groups were sacrificed either on day 10 (after repeated injections) or 30 days post-withdrawal. Hippocampal tissues were then dissected and analyzed via Western blot and ELISA to assess protein level changes. Results showed increased hippocampal expression of TLR2, TLR4, TLR10, and MyD88 following morphine dependence and withdrawal, while levels of PI3K, p-AKT1B, and IL-1Ra decreased. Alpha-pinene treatment, whether administered during the 10-day dependence induction period or the 30-day withdrawal period, partially restored these alterations in the TLR pathway. These findings suggest alpha-pinene modulates central immune responses by regulating TLR signaling. This highlights therapeutic potential of alpha-pinene for controlling neuroinflammation and subsequent morphine-related complications like tolerance, addiction, and withdrawal.
