Biology Reference
In-Depth Information
Chapter 4
T
HE
P
RESENCE OF
P
ERFORATED
S
YNAPSES IN
THE
S
TRIATUM
A
FTER
D
OPAMINE
D
EPLETION
:
I
S
T
HIS A
S
IGN OF
N
EGATIVE
B
RAIN
P
ASTICITY
?
Maria Rosa Avila-Costa
1
, Ana Luisa Gutierrez-Valdez,
Jose Luis Ordoñez-Librado, Verónica Anaya-Martínez,
Laura Colin-Barenque, César Sánchez Vázquez del Mercado
and Leonardo Reynoso-Erazo
Universidad Nacional Autonoma de Mexico, FES Iztacala, Dept. Neurociencias, Mexico
A
BSTRACT
Synaptic plasticity is the process by which long-lasting changes take place at
synaptic connections. The concept of plasticity can be applied to molecular as well as to
environmental events. The phenomenon itself is complex and can involve many levels of
organization. Some authors separate forms into adaptations that have positive or negative
consequences for the animal. For example, if an organism, after a stroke, can recover to
normal levels of performance, that adaptiveness could be considered an example of
"positive plasticity". An excessive level of neuronal growth leading to spasticity or tonic
paralysis, or an excessive release of neurotransmitters in response to injury, which could
kill nerve cells, would have to be considered perhaps as a "negative or maladaptive"
plasticity.
The striatum is the point of entry of information into the basal ganglia, and it has
important roles in motor control and habit learning. The neocortex provides the major
excitatory inputs to striatal medium spiny projection neurons. Morphological studies have
demonstrated that the majority of these afferent terminals impinge on the head of the
spines on the dendrites of these striatal neurons, whereas most dopaminergic afferent
fibers coming from the substantia nigra make synapses on the necks of the same dendritic
