Chandelier
Cells
An interneuron is basically an
association neuron, and is used in the central nervous system
for small and local connections. There are a large variety of
different types of interneurons which exist in the cerebral
cortex and in the subcortical structures around it. Because of
having to distinguish one type from another, researchers have
created a complex hierarchy of sets and subsets. One set of
cortical interneurons are known as GABA-ergic because they all
respond to the neurotransmitter y-aminobutyric acid which is
another name for GABA.
GABA is the main type of inhibitory neurotransmitter that
exists in the central nervous system. There are a set of
receptors known as GABA receptors which respond to the
y-aminobutyric acid neurotransmitter, in turn they produce
strong local inhibitory effects which help to regulate the
nervous system. This GABA-ergic interneuron type is further
divided into smaller sub sets of which one type is known as
chandelier (Kronleuchter) neurons or chandelier
cells. These cells can be distinguished because of their
striking axonal endings which look a lot like old style
chandeliers.
An alternate name for chandelier cells is axoaxonic cells,
named because of the amazing ability of these neurons to act
exclusively on the axon initial segment of certain types of
cells known as pyramidal. In fact each chandelier cell is known
to innervate several hundred pyramidal neurons.
They are also set apart from the other types of GABA-ergic
neurons because they are fast-spiking, which is another way of
saying that they are quick nerve impulse action. The axon
endings which when connected up look just like chandeliers are
known individually as cartridges and look like a group of
swellings that are connected together with a thin piece to
create the chandelier (Lüster) type effect.
One incredibly interesting avenue of study is in the linking of
schizophrenic type conditions with disturbances in the GABA
neurotransmitter class. Chandelier cells may be very important
in helping to understand this condition. There are three basic
types of components within cortical circuitry, excitory
pyramidal neurons, inhibitory GABA neurons which include the
chandelier sub set and excitory and modulatory inputs that come
in from external regions. All of these factors are equally
important for normally functioning cortical activity. In
schizophrenia there is evidence of disturbance in each of these
brain components, and a lot of study is going in to this to try
and find some answers to this most complex of conditions.
Within this area of study, chandelier cells are very important.
As they are the only source of synaptic input to the site on
pyramidal cells where the action potential is generated,
understanding chandelier neurons could be the crucial link in
the study of schizophrenia. Chandelier cells are considered to
be the most powerful of the GABA-ergic neurons, and because of
this their disturbance can probably be associated with many
other conditions as well. They act as a basic and yet
specialised part of our nervous system and it is crucial that
they functioning correctly for normal brain activity to take
place.
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