Electrophysiological Evaluation of Synaptic Plasticity in Injured CNS - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 117

Change in synaptic effi cacy on a timescale of tens to hundreds
of milliseconds is often referred to as short-term synaptic plasticity,
including synaptic facilitation, augmentation, posttetanic potentia-
tion, and synaptic depression. Short-term synaptic plasticity is
mainly related to changes in the probability of neurotransmitter
release ( 5 ). In epileptogenesis following traumatic brain injury
(TBI), one of the mechanisms may involve change in short-term
plasticity ( 6 ). On the other hand, changes in synaptic effi cacy that
last for hours and days are referred to long-term synaptic plasticity,
such as long-term potentiation (LTP) and long-term depression
(LTD). LTP and LTD are persistent, use dependent increase or
decrease in the effi ciency of synaptic transmission ( 7, 8 ). It is widely
accepted as a synaptic mechanism underlying learning and memory
( 2 ). TBI often causes impaired learning and memory function; the
corresponding LTP has been shown to be reduced ( 9 ).
Field potential recording (FPR) in neocortical or hippocampal
slices is a classical method that allows evaluation of synaptic strength
and synaptic plasticity in vitro. This technique involves cutting
slices of the neocortex, hippocampus, or other interested brain
region, and then using an extracellular electrode to record activi-
ties of slices in a recording chamber. The extracellular fi eld poten-
tials are believed to be originated from synaptic activity of many
simultaneously activated neurons. These activities can either occur
spontaneously or be evoked with a stimulating electrode, which is
placed close to axon bundles afferent to the recorded region. The
FPR technique is a relatively simple electrophysiological technique
in terms of instruments required as well as technical diffi culty. It
has a variety of applications, such as for evaluating synaptic strength,
short-term and long-term synaptic plasticity, and for detecting epi-
leptiform activity. Responses from FPR effi ciently refl ect network
activity from hundreds of neurons simultaneously. However, this
also means that the “spatial resolution” of this technique is not
adequate, which may cause diffi culty in data interpretation and
limit its application.
FPR can also be performed in awake or anesthetized animals
in vivo. Electrodes for stimulating and extracellular recording are
surgically implanted into a target region, and recordings are made
after a period of postsurgical recovery. The major benefi ts of this
approach include the facts that FPR can be done in unanesthe-
tized, free moving animals; interconnections between brain areas
are minimally interrupted; and long-term repeated recording is
possible. These advantages make it possible to relate neuronal
activity to functional behavior.
In addition to extracellular fi eld recording, whole-cell patch
clamp recording in brain slice is also commonly used for evaluating
synaptic plasticity. This technique allows assessment of short-term
and long-term synaptic plasticity at single cell level. It is possible to
target at a specifi c type of neurons in a brain region, dissect out