Objective To investigate the effect of normal saline (NS) of different temperature on morphological changes and nitric oxide synthase (NOS) expression of spinal cord.   Methods  The spinal canal of 96 SD adult rats was opened at T

9

. which of 24 rats was flushed with 37 ℃ NS

24 with 20 ℃ NS

24 with 4 ℃ NS respectively

and which of 24 rats in control group received no flushing. The spinal canal was closed one hour later

and the spinal

cord was taken out 24 hours later. Then the water content in spinal cord was determined by dry-wet method. The morphological changes of spinal cord were observed under light microscope and the electronic microscope. The amount of NOS-positive neuron was measured by β-NADPH histochemical methods.   Results   The water content in spinal cord was (66.53±0.61)% in control group

(66.75±1.00)% in 37 ℃ group

(70.55±0.77)% in 20 ℃ group

(71.92±2.50)% in 4 ℃ group. The spinal cord of control group and 37 ℃ group contained less water than that of 20 ℃ group and 4 ℃ group. There were no obvious morphological changes in the control group and 37 ℃ group. In 20 ℃ and 4 ℃ groups

the demyelination of axon

swelling of cell body and the disappearance of tigroid body were observed under light microscope

the partial disaggregation of medullary sheath

swelling of mitochondria and disappearance of mitochondria crista could be observed under electron microscope. The amount of NOS-positive neuron in spinal cord was (18.75±2.12)

(18.63±1.41)

(14.75±1.67)

(8.13±1.25) in control

37 ℃

20 ℃ and 4 ℃ groups

respectively. The control group and 37 ℃ group showed more NOS-positive neuron than those of 20 ℃ group and 4 ℃ group.   Conclusion  NS below 20 ℃ can injury spinal cord. It is suitable to choose 37 ℃ NS to flush brain and spinal card during operation.