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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 degrees C, 42 degrees C, 44 degrees C, 46 degrees C, 48 degrees C, 50 degrees C, 52 degrees C) and covering different area (diameter: 1.0 cm x 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 degrees C and 42 degrees C 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 degrees C and 46 degrees C, 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 degrees C to 52 degrees C, 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 degrees C and an area of 4.0 cm in diameter induced a larger increase of discharges of SRD neurons in comparison with that of 46 degrees C plus an area of 3.5 cm/4.0 cm in diameter (P < 0.05). No significant differences were found between 50 degrees C and 52 degrees C at any stimulated areas mentioned above (P > 0.05)., Conclusion: Noxious thermal (44-52 degrees C) stimulation of CV 12 region can activate SRD neuron, which reaches a plateau when the stimulated area is increased to a certain range.

The distribution of cell bodies containing serotonin (5-HT)-, substance-P (SP)-, L-enkephalin (L-ENK)- and neuropeptide Y (NPY)-like immunoreactivity (IR) in the nucleus paragigantocellularis lateralis (PGCL) of the rat was studied immunocytochemically. Perikarya containing 5-HT-, SP- or L-ENK-IR were found throughout the rostro-caudal extent of the PGCL. Large, well-staining 5-HT cells densely clustered rather near the ventrolateral surface of the medulla. SP- and L-ENK-IR were distributed more extensively and located more lateraly. A few of perikary on containing NPY-IR were found primarily in the area from the medium to caudal region. The results provided morphological basis for further study of the neurochemical properties of PGCL neurons involved in the regulation of cardiovascular, respiratory and other functions in the rat.