Synaptic plasticity Definition Alteration of synapse response to

Synaptic plasticity

Definition • Alteration of synapse response to input

Synaptic plasticity • Relevance – Adapting to environment – Neurodevelopment – Learning & memory

Examples • PTP versus fatigue • LTP vs LTD

LTP • NMDA hypothesis

LTP • Presynaptic modification – AA → G-protein – NO → GC Glutamate release • Postsynaptic modification – Ca. M Kinase II – c. AMP, c. GMP-dependent – Tyrosine kinase (fyn) • Synaptic structure – widening of neck of spine TF Activation Receptor Upregulation

Spike timing • Variant of Hebbian learning – Donald Hebb (1949) • NMDA Dependent • Reversible • strengthening is function of EPSP-spike delay

Integration • Convergence of much information – Input: – Output: up to 10, 000 synapses + sensory input one axon • Time dependent – Long term state of cell – State of receptors + membrane in short term • Each synapse different – distance from soma, other synapses – neurotransmitter combination – receptor types, number and sensitivity

Neuronal mechanisms of integration • Dendritic tree – diameter – voltage gated ion channels • EPSP and IPSP – temporal + spatial summation – decay with distance and time – shunting inhibition • Axon hillock – threshold behaviour

Calcium mediated integratory effects Fast (ionic) • • • Repetitive firing Adaptation Accommodation Delay firing Subthreshold oscillation Slow (second messenger) • • LTP / LTD (De-)sensitisation Down- / Upregulation Synaptic growth

Membrane properties • RM (per unit length) = s p d • RI (per unit length) = 4 r / p d 2 • CM (per unit length) = c p d