| Neurons in dorsal root ganglion are primary sensory neurons, whose axon has two branches: one projecting to the periphery and one prejecting to the central nervous system. The terminal of the peripheral branch of the axon is the only portion of the dorsal root ganlion neuron that is sensitive to natural stimuli. The properties of the nerve terminal determine the sensory function of each dorsal root ganglion neuron. The remainder of the peripheral branch, together with the central branch, is called the primary afferent fiber; it transmits the encoded stimulus information to the spinal cord or brain stem. Spinal dorsal horn is the region where the primary afferent fibers terminate and form synaptic contacts with the central neurons. In somatosensory system, spinal dorsal horn plays an important role in relaying and processing the sensory information. So it is of great biological significance to comprehensively study the syanptic transmission bentween primary afferent fiber and spinal dorsal horn neuron.Through early research, the anatomy, physiology and pharmacology of primary afferent syanpse are rather clear now. In previous research, intracellular recording and blind patch-clamp methods were used to study the synaptic transmission at primary afferent synapse. Both methods have shortcomings in certain aspects. In addition, early research mainly focused onthe long-term plasticity of primary afferent synapse, and there is no systemic study on short-term synaptic plasticity between primary afferent fiber and dorsal horn neuron. Moreover, in previous studies our group recorded spike trains coming from the periphery on primary afferent fibers. Analyses showed that these spike trains contain various temporal structures, and many of them are composed of bursts. With nonlinear analytic methods, the behaviors of deterministic dynamics have been detected in the time series of irregular burst firing coming from the periphery. These results indicate that spike trains with various temporal structures will be synaptically transmitted between primary afferent fiber and spinal dorsal horn neuron. How spike trains that comtain various temporal structures are transmitted across primary afferent synapse has not been clearly studied.The present research includes three objectives: (1) To modifying the method of obtaining the spinal cord slice with attached dorsal root, and establish our lab's visual patch-clamp method to study the synaptic transmission at primary afferent synapse in spinal dorsal horn; (2) To study the short-term plasticity at primary afferent syanpse and its mechanism, fit the experimental results with a mathematic modal, and analyze the influence of different conditions on short-term synaptic plasiticy; (3) To explore how spike trains with different temporal structures are synaptically transmitted between primary afferent fiber and spinal dorsal horn neuron, with nonlinear dynamics and information theory methods.Main results:1. Visually guided patch-clamp recording of spinal dorsal horn neuron's postsynaptic current evoked by primary afferent fiber a. By employing gelatin half-embedding method, spinal cord slices 250-300 um thick with attached dorsal root were obtained and used to makepatch-clamp recording.b. With the help of infrared visualization, neurons residing in both superficial and deep dorsal horn could be observed and clamped. Healthy neurons that have a smooth surface and show a good perception of relief were chosen to be clamped.c. Under the different holding voltages, spontaneous and dorsal root-stimulation evoked postsynaptic currents, including excitatory or inhibitory ones, could be recorded on spinal dorsal horn neurons.d. Excitatory postsynaptic currents evoked by different types of primary afferent fiber were distinguished with two measurements: the conduction velocity of afferent fibers and stimulus threshold. Using strychnine or bicuculline, GABAergic or glycinergic inhibitory postsynaptic currents could be isolated, respectively.2. Short-term plasticit...
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