Convergence And Interaction Between The Inputs Of Visceral Nociception And Acupuncture

AIM Classical description on central pathways holds that there are segregated routes in the centralnervous system (CNS) for visceral and somatic inputs, for pain and tactile processing. Ampleevidence in recent studies however calls for a revision of this traditional view. It has beendemonstrated that visceral nociceptive inputs may travel in the dorsal column-medial lemnicussystem along with the conventionally recognized skin tactile inputs, and convergence andinteractions between the two distinct modalities have been demonstrated at the different levels tothe superspinal centers. As such, the interactions in this shared pathway may interfere each other. The purpose of this experiment was to observe how acupuncture stimulation influences thevisceral nociception in rat and to clarify the interactions between somatic and visceral nociceptiveinputs in the spinal dorsal horn, DCN and ventroposterior lateral (VPL) nucleus in thalamus.METHODS Experiments were performed on 177 Sprague-Dawley rats weighing between 250 and 350 g.The rats were initially anesthetized with an intraperitoneal injection of pentobarbital sodium(50-60mg.kg-1) or urethane (1.0-1.2g.kg-1). The trachea was intubated and a catheter was insertedinto one of the jugular veins to allow a continuous infusion of the anesthetic (maintained with i.v.infusion at ~5mg .kg-1.h-1). Body temperature was monitored and kept around 37℃ by afeedback-controlled heating blanket. The head of the rat was fixed in a stereotaxic apparatus.Incisions were made in the skin alone the midline over the head, cervical and lumbar vertebralcolumn. In the spinalization experiments, thorax vertebral was incised, and the underlying muscleswere retracted. For the thalamic recording, a craniotomy was performed to expose the area ofcortex above the thalamus. For DCN operation, a piece of the occipital bone above the cerebellumwas removed and a small laminectom was made to expose the medullar and C1 cervical spinal cord.The dura mater was cut and brain and spinal cord tissues were exposed and then covered withwarm paraffin oil.摘 要 ·7·STIMULATION Visceral nociceptive stimulus was generated by colorectal distension (CRD). CRD wasapplied by means of an inflatable balloon inserted rectally into descending colon for 4 cm from theanus. The balloon in the colon was consecutively inflated with air to produce pressure rangingbetween 20-100mmHg with increasing steps of 20 mmHg for 20 s. The time interval between thetwo dilations was at least 4 min to avoid overstimulation and sensitization. CRD stimuli with anintensity >40 mmHg are recognized as noxious based on previous studies and experience. Excitatory somatic receptive fields were mapped. Neurons were classified by their responsesto the innocuous (brush and tap) and noxious (pinch) stimuli. The skin receptive field wasidentified initially by gentle tapping and brushing, and then defined with von Frey hairs. Widedynamic range (WDR) neurons were excited by innocuous stimuli but were excited maximallyduring noxious pinch of skin or skin and underling muscles; High-threshold (HT) neurons wereexcited only by noxious pinch; high-threshold inhibitory (HTi) neurons were excited by pinch butinhibited by brushing the receptive field (RF). Manual acupuncture and electroacupuncture wereapplied (EA, 2mA, 5 min, 2Hz, sparse-dense waves) at (Zusanli, ST36), (Quchi, Li11)RF andnon-receptive field (NRF). For the purpose of studying interactions, the maximal tactile response was elicited by an air-jetstimulator with a 10Hz frequency applied to the most sensitive part of the skin receptive field.RECORDING Discharges from individual single neurons were recorded extracellularly with the use oftungsten or glass microelectrodes. The isolated action potentials were fed into a windowdiscriminator and displayed on an oscilloscope screen. The output of the windo...