Objective:To explore the distribution and clearance of 99mTc labeled diethylenetriamine pentaacetic acid(99mTc-DTPA)in different brain regions of adult rats after administration through brain extracellular space(ECS)pathway.Methods:After the injection of a volume of 2 μL and radioactive activity of about 3.7 MBq(100 μCi)of 99mTc-DTPA into the caudate nucleus and thalamus of SD rats through stereotactic positioning of rat brain,the single photon emission computed tomography/computed tomography(SPECT/CT)for small animals was used for imaging at different time points,and the dyna-mic distribution and clearance of the tracer in the whole body were observed continuously.The SD rats were injected with 99mTc-DTPA into thalamus and caudate nucleus respectively for biological distribution in vivo.They were put to death 4 h later.Their blood and urine were collected.The brain,cerebellum,heart,liver,spleen,lung,and kidney were taken and weighed by γ counter to measure its radioactivity.Results:SPECT/CT imaging results showed that after 99mTc-DTPA was administered through brain ECS,the radioactivity was concentrated in the brain,kidney and bladder.The tracer administered to the left caudate nucleus was preferentially drained to the right cerebellum,while the tracer administered to the right caudate nucleus was preferentially drained to the left cerebellum.There was a phenomenon of"con-tralateral cerebellar dominant drainage"in the caudate nucleus.The thalamic area preferentially drained to the ipsilateral cerebellum after administration.Four hours after administration via ECS,high radioac-tive uptake appeared in urine,cerebellum and brain,followed by blood and kidney.The radioactive up-take values of heart,liver,spleen and lung were low,which were mainly excreted through urinary sys-tem.Conclusion:Intracerebral ECS administration is a promising method of administration,but there are significant differences in distribution and clearance in different brain regions.This study further ex-pands the content and significance of"ECS regions",and also provides an important theoretical founda-tion for the treatment of encephalopathy and the research of new drugs through brain ECS in the future.

Objective:To explore the distribution and clearance of 99mTc labeled diethylenetriamine pentaacetic acid(99mTc-DTPA)in different brain regions of adult rats after administration through brain extracellular space(ECS)pathway.Methods:After the injection of a volume of 2 μL and radioactive activity of about 3.7 MBq(100 μCi)of 99mTc-DTPA into the caudate nucleus and thalamus of SD rats through stereotactic positioning of rat brain,the single photon emission computed tomography/computed tomography(SPECT/CT)for small animals was used for imaging at different time points,and the dyna-mic distribution and clearance of the tracer in the whole body were observed continuously.The SD rats were injected with 99mTc-DTPA into thalamus and caudate nucleus respectively for biological distribution in vivo.They were put to death 4 h later.Their blood and urine were collected.The brain,cerebellum,heart,liver,spleen,lung,and kidney were taken and weighed by γ counter to measure its radioactivity.Results:SPECT/CT imaging results showed that after 99mTc-DTPA was administered through brain ECS,the radioactivity was concentrated in the brain,kidney and bladder.The tracer administered to the left caudate nucleus was preferentially drained to the right cerebellum,while the tracer administered to the right caudate nucleus was preferentially drained to the left cerebellum.There was a phenomenon of"con-tralateral cerebellar dominant drainage"in the caudate nucleus.The thalamic area preferentially drained to the ipsilateral cerebellum after administration.Four hours after administration via ECS,high radioac-tive uptake appeared in urine,cerebellum and brain,followed by blood and kidney.The radioactive up-take values of heart,liver,spleen and lung were low,which were mainly excreted through urinary sys-tem.Conclusion:Intracerebral ECS administration is a promising method of administration,but there are significant differences in distribution and clearance in different brain regions.This study further ex-pands the content and significance of"ECS regions",and also provides an important theoretical founda-tion for the treatment of encephalopathy and the research of new drugs through brain ECS in the future.

Objective To observe the drainage pathways of interstitial fluid(ISF)and substance clearance pattern in rat brain with fluorescence tracing imaging and treacer-based MRI.Methods Thirty-three male SD rats were randomly divided into fluorescence tracing group(F group,n=18)and treacer-based MRI group(MRI group,n=15),then further divided into thalamic,hippocampal and caudate nucleus subgroups,respectively.Evans blue was injected to rats in F group,and cardiac perfusion was performed after injection,then brain tissue was harvested,and frozen sections were made to observe the drainage pathways of IFS in different subgroups.MRI was performed on rats in MRI group before and after injection of gadolinium-diethylenetriamine pentaacetic acid(Gd-DTPA)to observe signal intensity in ROI of brain regions in different subgroups,the signal unit ratio was calculated,and the changing trend was explored.Results ISF in thalamus,hippocampus and caudate nucleus had different dominant drainage pathways,and the time of tracer reached to adjacent brain regions and whole brain in F group were different.In MRI group,within 4 h after injection of Gd-DTPA,there were differences in direction and clearance rate among tracer in thalamus,hippocampus and caudate nucleus,mainly manifesting as the tracer in thalamus and hippocampus drained to the ipsilateral cortex and lateral ventricle,while the tracer in the caudate nucleus diffused to the cortex and midbrain,and there were differences of the peak time of tracer signal among adjacent drainage brain regions.Conclusion Fluorescence and MR dual-mode imaging showed that there were differences in the dominant drainage pathways of IFS and clearance rates of small molecule substances among hypothalamus,hippocampus and caudate nucleus of rats.