The Relationship Between Primary Afferent And Firing Patterns And Research Of Hyperpolarizaton Rebound In Spinal Dorsal Horn

Neurons are able to generate action potentials when the stimulation occurred. This is one of the most important functional responses for neurons. In the past study of basic electrophysiological properties of neurons it is found that action potentials have many types of timing pattern, which is also termed as firing pattern. Moreover, it is confirmed that the timing series of action potentials composed can be transmitted to other neurons via synapses. That is, firing pattern in neurons may contain information which needed to be conveyed. However, it is not confirmed whether firing pattern is coding mode of information transmission in nervous system. In addition, it is not known that whether firing pattern have biological significance. Synapse transmission is basic mode of information transmission in central nervous system. Chemical synapse and electrical synapse have two different structure and function. In chemical synapse, transmitter release from presynaptic terminal is a course that electrical signal is transformed to chemical molecular signal in essence. Presynaptic neurons generate action potentials with certain timing series when stimulated. These action potentials form firing pattern, which are delivered to fiber terminal via axon, thus cause transmitter release. In the end, transformation from electrical signal to chemical signal is completed and information transmission is fulfilled. However, it is known that firing pattern have many multiple types and there is no definite classification about it. Moreover, there are many types of neurotransmitter and many types of receptors in the same transmitter. The combination of transmitter and receptor will cause different effects, which result in trouble in study of the relationship between firing pattern and transmitter release. Thus, it is not known that how electrical signal transform to chemical signal and what is the relationship between them. The propose of this study is to explore the relationship between firing pattern and transmitter release in nerve fiber terminal and to study whether the physiological significance of firing pattern is different transmitter release. The efficiency of synapse transmission is the capability of neural information transmission between synapses. The assessed indexes of synapse transmission are as follows: the magnitude and slope rate of PSPs evoked by signal pulse stimulus; the magnitude and area of PSCs. We think it is not adequate to reflect the efficiency of synapse transmission only by analysis of the unitary index of PSPs or PSCs induced by single pulse stimulus. So it is in great need of developing the further study how we establish a set of reasonable indexes of evaluation the efficiency of synapse transmission.Dorsal root ganglion is the first-order neuron of afferent sensory. The spinal dorsal horn play an important role in the processing and relay of primary afferent information。To investigate the synaptic transmission between the primary afferent fiber and the spinal dorsal horn is very important. So we select it to the object of research."Rebound depolarization"is defined as transient depolarization evoked by a prior hyperpolarizing stimulus. The RD can be triggered by the opening of T-type Ca2+ channels. RD duration is regulated by small-conductance Ca2+-gated K+ channels. Previously, RD is shown to contribute to locomotor rhythms and synaptic plasticity in neurons. RD is observed in different brain regions, e.g. the thalamus, cerebellum, and hippocampus. We want to research whether dorsal horn neurons have the property of RD.Methods:Record the EPSC of substantia gelatinosa neurons in spinal cord slice of two weeks old rat using the whole-cell patch clamp technique.Main results:1. We have improved the method that not employing gelatin half-embedding to acquire the slice of spinal cord but conglutinating the spinal cord in the agar cake directly. This method protects the activity of healthy cell.2. Record the single synapse reaction induced by Aβ, Aδand C fiber in 42 Lamina II neurons of the spinal dorsal horn. There are 11neurons that have connection with C fiber.3. Recording the excitatory postsynaptic currents evoked by two types of primary afferent fiber. The amplitude of EPSC evoked by continuous single stimulation is exceed the amplitude of EPSC evoked by burst stimulation.4. AP-5(50μM)can decrease the amplitude of EPSC evoked by burst stimulation obviously.5. Different burst interval can affect the generation of EPSC of the postsynaptic neuron. The shorter interval induces less EPSC. At the same frequency, continuous single stimulations evoke more EPSC than burst stimulations.6. A novel membrane response to hyperpolarization stimulus has been found in spinal substantia gelatinosa neurons of rats. 1 mM extracellular NiCl2 could abolish RH completely. 5 mM extracellular potassium could block RH too. The firing pattern of the tonically firing SG neurons changed after Ni2+ (1 mM) was added to the bath solution to abolish the RH.Main conclusions:1. The continuous single stimulation and the burst stimulation can induce EPSC of different amplitude.2. Different firing patterns of primary afferent fiber can induce different quantity Glutamate to release. It suggests that firing pattern of the primary afferent fiber can affect releasing of neurotransmitter in presynaptic membrane the information transfers from electricity to chemistry by this.3. At the same firing pattern, the firing frequency of the presynaptic neurons is reverse to the stability of the EPSC generation of postsynaptic neurons. At the same frequency, the EPSC evoked by continuous stimulation is comparatively more stable than that evoked by burst stimulation. These suggest that the firing frequency and pattern affect the efficiency of synaptic transmission cooperatively.4. The hyperpolarization stimulus can induce rebound hyperpolarization in a few substantia gelatinosa neurons. RH is dependent on the membrane potential of the cells and independent on the duration of the injected current pulse. K+ currents and T-type Ca2+ channels participate in RH and the corresponding outward currents. RH can adjust the firing pattern of the tonically firing SG neurons.