A modified method of injection into the cerebellomedullary (CM) cistern of mice was developed based on fixation of the mouse with a special mask under inhalation anesthesia, and exposure of the sagittal suture of the cranium and midline of the nape to allow us to visualize injection point directly. The accuracy of the modified method was evaluated using the temporal and spatial intracranial distribution of dye by intracisternal injection of methylene blue aqueous solution. A high concentration of dye was found in the CM cistern, the ventral cisterns, and intracranial proximal portion of the main cranial nerves at 1 hour after injection. The color of the dye in the CM cistern and the ventral cisterns was lighter, and the dye had reached the intracranial distal portion of the main cranial nerves at 6 hours after injection. The dye was completely eliminated by cerebrospinal fluid (CSF) circulation at 24 hours after injection. No severe brain injury was found in any of the 20 mice. Intracisternal injection was successful in all 14 mice sacrificed 1 hour or 6 hours after injection according to the confirmation of dye distribution. The effects of central administration of endothelin-1 (ET1) were evaluated on cerebral blood supply, constriction of cerebral arteries, and change of respiration in mice. Three doses of ET1 were studied: 2 ^g (0.8 nmol), 4 ^g (1.6 nmol), and 6 ^g (2.4 nmol). Cerebral blood flow (CBF) was monitored for 60 minutes following injection using a laser Doppler probe. Intracisternal ET1 injection induced dose-dependent reduction of CBF, constriction of cerebral arteries, and respiratory depression in mice. This modified method of injection into the CM cistern under direct visualization provides accurate and reproducible injection into the CSF, and can be used to investigate the effects of various chemical substances on the central nervous system in mice.
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