Effects of Kamikihito, a Traditional Chinese Medicine, on Neurotransmitter Receptor Binding in the Aged Rat Brain Determined by In Vitro Autoradiography (2): Changes in GABA_A 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]fhmitrazepam 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.