NITRIC-OXIDE SYNTHASE ACTIVITY IN BRAIN-REGIONS AND SPINAL-CORD OF MICE AND RATS - KINETIC-ANALYSIS

Nitric oxide synthase (NOS) activity was determined by the rate of con version of[H-3]arginine to [H-3]citrulline in brain regions (midbrain, hypothalamus, cerebellum, hippocampus, corpus striatum, cortex, pons- medulla and amygdala) and spinal cord of male Swiss Webster mice and m ale Sprague-Dawley rats. In mice, high activity of NOS was found in ce rebellum, hypothalamus and midbrain; intermediate activity in pons-med ulla, hippocampus, amygdala, corpus striatum and cortex; and low activ ity in the spinal cord. In rat, highest activity of NOS was observed i n cerebellum followed in decreasing order by midbrain, hypothalamus, c ortex, striatum, pons-medulla, hippocampus and spinal cord. In all tis sues, NOS activity was higher in rat than in mouse. Analysis of the Ea die-Hofstee plot indicated that the V-max and K-m values of the enzyme in cortex and cerebellum of rats were higher than in mouse tissues. T hese studies show differential distribution of NOS activity in mouse a nd rat brain regions and spinal cord and higher activity of NOS in rat brain regions and spinal cord compared to mouse tissues.