CJH332 FINAL

• plastic changes can vary in length
• short-term synaptic plasticity lasts seconds to minutes
• long-term synaptic plasticity lasts hours or days
• a key feature of synaptic plasticity is that the change in strength of the synapse persists after the activity that induced the plasticity has ended (e.g. train of APs)
• CNS synaptic plasticity is often long-term
• PNS synaptic plasticity is often short-term
• long term changes: LTP (long-term potentiation) and LTD (long-term depression)
• LTP and LTD are the cellular basis of learning and memory among other behavioural effects
• LTP: increase in size of a synaptic potential lasting hours or more
• LTP and LTD are produced by previous synaptic activity
• LTD decrease in size of a synaptic potential lasting hours or more
• DIV (days in vitro) is a reflection of developmental maturity
• autapse is a synapse that occurs when the axon of one neuron forms a synapse onto dendrites of the same neuron
• autapses are stained with 3 different antibodies:

  1. proline-rich synapse-associated protein-1 (ProSap-1)
  2. Vesicular glutamate transporters (VGLUT1)
  3. Microtubule Associated Protein (MAP2)
• ProSap-1 is post-synaptic specific
• VGLUT1 is a pre-synaptic marker
• MAP2 is a neuronal dendrite marker
• Homosynaptic plasticity:

  1. Stimulate Schaffer collateral axons, record PSP or increased responsiveness from neuron B
  2. Stimulate neuron A tetanically
  3. Record PSP from B with test pulses at varying intervals
  4. PSP augmented for several days or months
  5. This increase is known as LTP
• Stimulating neuron A by: burst of stimuli at 100Hz
• only specifically activated synapses become potentiated (strengthened) not all synapses
• neurons have a discrete level to which they can be strengthened
• there must be a pairing of the input presynaptically and postsynaptically (i.g. they have to be active together)
• synaptic plasticity involves modifying a neural circuit
• LTP involves the strengthening of synapses in a time-dependent manner
• LTP is measured for glutamatergic synapses in the hippocampus
• medial temporal lobe has 2 subdivisions:

  1. lateral portion: audition, speech, sensory processing
  2. ventromedial portion: limbic system
• limbic system is composed of: entorhinal cortex, hippocampal formation, and amygdala
• hippocampal circuit:

  1. integrated sensory signals
  2. entorhinal cortex
  3. dentate gyrus
  4. hippocampus
  5. fimbria fornix
• LTP was first described by bliss and lomo at glutamatergic synapses in the CNS
• hippocampal formation lies in the temporal lobe
• temporal lobe consists of 2 regions: hippocampus and dentate gyrus
• hippocampus is desirable for experiments because it has a laminate structure of neurons (e.g. it looks like layers)
• synaptic transmission in the hippocampus occurs through a directional circuit
• trisynaptic hippocampus:

  1. perforant pathway is the major group of fibres that enters the hippocampus
  2. mossy fibres from the dentate gyrus granule cells then synapse on CA3 neurons
  3. CA3 neurons send their axonal projections out to CA1 region via. schaffer collateral
• schaffer collateral is NMDAR dependent
• CA3 neurons are LTP (NOT NMDAR dependent)
• hippocampal models are brain slices and use electrophysiology
• most hippocampal models use tetanic high frequency stimulation of schaffer collaterals (100Hz for a few seconds)
• some hippocampal models use theta burst patterns (most useful in rodents since it mimic behaviour)
• theta burst patterns are short bursts of 100Hz at millisecond intervals