Objective To observe the effect of regional thermal(moxibustion-like) stimulation on discharges of neurons in the medullary subnucleus reticularis dorsalis(SRD) and to study the best thermal stimulation parameters in the rat.Methods Experiments were performed on 15 male Sprague-Dawley rats under anesthesia(10% urethane

1.0-1.5 g/kg).Unit discharges of single neurons in the medullary SRD were recorded extracellularly with glass micropipettes.Thermal stimulation(warm water filled in a glass bottle) with different temperature(40 ℃

42 ℃

44 ℃

46 ℃

48 ℃

50 ℃

52 ℃) and covering different area(diameter: 1.0 cm

1.5 cm

2.0 cm

2.5 cm

3.0 cm

3.5 cm

4.0 cm) was applied to "Zhongwan"(CV 12) region for 30 s.Firing rates of SRD neurons were analyzed by using Power-Lab Chart 5.0.Results When thermal stimulation with temperature of 40 ℃ and 42 ℃ and the stimulated area of 1.0-4.0 cm in diameter was applied to CV 12 region

discharges of the medullary SRD neurons had no obvious changes.When the temperature was increased to 44 ℃and 46 ℃

the electrical activities of SRD neurons were increased linearly along with the increase of the stimulated area of 1.0-4.0 cm in diameter.When the temperature was increased further from 48 ℃ to 52 ℃

the increased electrical activities of SRD neurons peaked at the stimulated area of 3.5 cm in diameter.In addition

thermal stimulation at a temperature of 50 ℃ and an area of 4.0 cm in diameter induced a larger increase of discharges of SRD neurons in comparison with that of 46 ℃ plus an area of 3.5 cm/4.0 cm in diameter(P<0.05).No significant differences were found between 50 ℃ and 52 ℃ at any stimulated areas mentioned above(P>0.05).Conclusion Noxious thermal(44-52 ℃) stimulation of CV 12 region can activate SRD neuron

which reaches a plateau when the stimulated area is increased to a certain range.