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Alternating and Synchronous Rhythms in Reciprocally Inhibitory Model Neurons

Alternating and Synchronous Rhythms in Reciprocally Inhibitory Model Neurons. Xiao-Jing Wang, John Rinzel Neural computation (1992). 4: 84-97. Ubong Ime Udoekwere and Vanessa Boyce December 16th 2004. Introduction. What is a pacemaker?

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Alternating and Synchronous Rhythms in Reciprocally Inhibitory Model Neurons

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  1. Alternating and Synchronous Rhythms in Reciprocally Inhibitory Model Neurons Xiao-Jing Wang, John Rinzel Neural computation (1992). 4: 84-97 Ubong Ime Udoekwere and Vanessa Boyce December 16th 2004

  2. Introduction • What is a pacemaker? • Network capable of generating oscillatory behavior without peripheral input • i.e. spontaneous activity • Pacemaker cell qualities: • Cellular properties: threshold, bursting pattern • Synaptic properties: time course, release mechanism • Patterns of Connection: inhibitory, excitatory

  3. Cell i - - Cell j Circuitry • Reciprocal inhibition or inhibitory feedback loop • Fire out of phase • Exhibit Post Inhibitory Rebound (PIR) • Transient increase in excitability of neuron after end of inhibitory input. • E.g. Thalamic neurons: • Low threshold T-type ICa • Hyperpolarization --> de-inactivation--> excitation

  4. Asynchronous oscillation Post synaptic conductance (sji) is instantaneous and depends on presynaptic potential Synchronous oscillation Post synaptic conductance (sji) is not instantaneous, but decays slowly. Two scenarios

  5. Release: Due to presynaptic termination of inhibition Active Cell i exerts an inhibitory synaptic effect on Cell j. As the voltage of active Cell i drops below a certain threshold (synaptic threshold [Qsyn]) then Cell j is released from Cell i synaptic influence and exhibits PIR Cell j becomes active and inhibits Cell i Escape: Due to intrinsic membrane properties Slowly developing Ipir during inhibition of Cell j >> the hyperpolarizing effect caused by active Cell i Hence the inhibited Cell j spontaneously depolarizes and inhibits Cell i Both process repeat periodically Cell i - - Cell j Asynchronous oscillation

  6. Aim of paper • Examine and generate a model of rhythmic activity in non-oscillatory neurons, i.e. where pace-making input is absent.

  7. = postsynaptic conductance in cell i due to j = sigmoid function Their Model • Based on rapidly activating, slowly inactivating T-type Ca current (thalamic neurons) • Constant conductance IL and voltage dependant inward Ipir. Where:

  8. Reversal potentials Vpir= 120 mV Vsyn= -80 mV VL= -60 mV Where… Variable values Voltage dependant gating functions ksyn= 2 m∞(V) = 1/{1+ exp[-(V + 65)/7.8]} gsyn= 0.4 mS/cm2 gL= 0.1 mS/cm2 h∞(V) = 1/{1+ exp[(V + 81)/11]} t0 = 10 msec th(V) = h∞(V) exp[(V + 162.3)/17.8]} f = 3 gpir= 0.3 mS/cm2 qsyn = - 44mV gL = Conductance of Leak current gpir = Conductance of PIR current qsyn = synaptic threshold

  9. Alternating Oscillation by the release mechanism • Period of oscillation linked to synaptic input

  10. Alternating Oscillation by the escape mechanism • Period of oscillation DOES NOT depend on presynaptic cell. • Can occur with non-phasic input

  11. Pacemaker Period Release Mechanism

  12. Pacemaker Period Escape Mechanism

  13. Synchronization by a Slowly Decaying synaptic system • First order kinetics for sji synaptic variable • Slow decay rate such that inhibition outlast the PIR event

  14. Application: Central Pattern Generators • Network of spinal interneurons that generate rhythmic output

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