Effects of Kamikihito, a traditional Chinese medicine, on neurotransmitter receptor binding in the aged rat brain determined by in vitro autoradiography (2): changes in GABAA and benzodiazepine receptor binding.

We investigated the effects of the long-term administration of Kamikihito (KKT) on the specific binding of [3H]muscimol and [3H]flunitrazepam in the brains of young and aged rats using in vitro quantitative autoradiography. Specific [3H]muscimol binding in aged rats was decreased in all brain regions examined compared with that in young rats, whereas [3H]flunitrazepam binding did not change in any of the brain regions. Scatchard analysis revealed that the maximal number of [3H]muscimol binding sites in the cortex and thalamus was significantly decreased in aged rats compared with young rats, while its affinity remained unchanged. Long-term administration of KKT in young rats had no effect on either [3H]muscimol or [3H]flunitrazepam binding. In contrast, the same treatment in aged rats produced a significant increase in [3H]flunitrazepam binding to the cortex, caudate/putamen and accumbens, and it tended to decrease the [3H]muscimol binding. These results suggest that the selective reduction of specific [3H]muscimol binding in the brain may be responsible, at least in part, for anxiety-related behavior in aged rats. Furthermore, it appears that the significant increase in specific [3H]flunitrazepam binding produced in the brains of aged rats by the long-term administration of KKT may be responsible for the anxiolytic effects of this agent.