发信人: yanan (花自飘零水自流), 信区: Biology
标 题: eric kandel_sea slug model &synaptic plasticity
发信站: The unknown SPACE (Mon Oct 9 15:11:47 2000), 站内信件

ERIC KANDEL

Sea slug, a model system for learning
A phosphorylation of proteins has great importance also for the
discoveries for which Eric Kandel is rewarded, that is for
revealing molecular mechanisms, important for the formation of
memories. Eric Kandel started to study learning and memory in
mammals, but realized that the conditions were too complex to
provide an understanding of basic memory processes. He therefore
decided to investigate a simpler experimental model, the nervous
system of a sea slug, Aplysia. It has comparatively few nerve
cells (around 20.000), many of which are rather large. It has
a simple protective reflex that protects the gills, which can
be utilized to study basic learning mechanisms.
Eric Kandel found that certain types of stimuli resulted in
an amplification of the protective reflex of the sea slug. This
strengthening of the reflex could remain for days and weeks and
was thus a form of learning. He could then show that learning was
due to an amplification of the synapse that connects the sensory
nerve cells to the nerve cells that activate the muscle groups
that give rise to the protective reflex.

Short and long term memory
Eric Kandel showed initially that weaker stimuli give rise to a
form of short term memory, which lasts from minutes to hours.
The mechanism for this "short term memory" is that particular
ion channels are affected in such a manner that more calcium ions
will enter the nerve terminal. This leads to an increased amount
of transmitter release at the synapse, and thereby to an
amplification of the reflex. This change is due to a phosphorylation
of certain ion channel proteins, that is utilizing the molecular
mechanism described by Paul Greengard.
A more powerful and long lasting stimulus will result in a form
of long term memory that can remain for weeks. The stronger stimulus
will give rise to increased levels of the messenger molecule cAMP
and thereby protein kinase A. These signals will reach the cell
nucleus and cause a change in a number of proteins in the synapse.
The formation of certain proteins will increase, while others will
decrease. The final result is that the shape of the synapse can
increase and thereby create a long lasting increase of synaptic
function. In contrast to short term memory, long term memory
requires that new proteins are formed. If this synthesis of new
proteins is prevented, the long term memory will be blocked but
not the short term memory.

Synaptic plasticity, a precondition for memory
Eric Kandel thus demonstrated that short term memory, as well as
long term memory in the sea slug is located at the synapse. During
the 1990's he has also carried out studies in mice. He has been able
to show that the same type of long term changes of synaptic function
that can be seen during learning in the sea slug also applies to
mammals.
The fundamental mechanisms that Eric Kandel has revealed are also
applicable to humans. Our memory can be said to be "located in the
synapses" and changes in synaptic function are central, when
different types of memories are formed. Even if the road towards
an understanding of complex memory functions still is long, the
results of Eric Kandel has provided a critical building stone.
It is now possible to continue and for instance study how complex
memory images are stored in our nervous system, and how it is
possible to recreate the memory of earlier events. Since we now
understand important aspects of the cellular and molecular
mechanisms which make us remember, the possibilities to develop
new types of medication to improve memory function in patients
with different types of dementia may be increased.



--
紫霞问：“是不是一到夏天，满山就会开满紫色的木逍花？”

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