Short-term swimming exercise attenuates the sensitization of dorsal horn neurons in rats with NGF-induced low back pain

BackgroundPhysical exercise has been shown to be an effective therapy for non-specific low back pain. The study investigated if swimming exercise is a means to reduce the spinal sensitization in an animal model of non-specific low back pain. MethodsIn deeply anesthetized rats, dorsal horn neurons were recorded in spinal segment L2. To induce sensitization of dorsal horn neurons, two injections of nerve growth factor were made into the lumbar multifidus muscle at an interval of 5days. Swimming exercise for 30min was performed on the 5days between both NGF injections. A control group received the NGF injections without exercise treatment. ResultsSwimming exercise caused a significant decrease in the NGF-induced hyperexcitability of dorsal horn neurons. Compared to control, the proportion of neurons with input from deep somatic tissues and of convergent neurons with input from at least two types of different tissues decreased significantly (50% vs. 25% and 37% vs. 15%; both p<0.05). Swimming exercise also reduced the NGF-induced increase in neuronal resting activity. Both the proportion of active neurons and the mean discharge frequency of all neurons decreased significantly (60%, 76.323.1imp/min; vs. 25%, 51.735.1imp/min; both p<0.01). ConclusionsIn our animal model of low back pain, short-term swimming exercise effectively reduced the latent sensitization of spinal dorsal horn neurons. Swimming exercise decreased the hyperexcitability of the neurons to low back input and lowered the resting activity of sensitized neurons. SignificancePhysical exercise is a common treatment for low back pain. The possible mechanisms underlying the effects of exercise are probably multifold. This work shows that swimming exercise prevents sensitization of dorsal horn neurons, which may be one mechanism for the positive effects of exercise.