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and hormonal alterations (Hatton and Ellisman, 1982). It has also been suggested that a
preserved complement of hippocampal perforated synapses is required for the maintenance of
good spatial memory during aging (Geinisman, 2000).
Calverley and Jones (1987) classified the perforated synapses as follows:
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The site of the perforation projects into the presynaptic terminal.
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The active zone has one or more negatively curved components that are separated by
a central region of the active zone that projects into the presynaptic terminal.
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The presynaptic density is in close association to the spine apparatus or an extension
of it (see figure 4).
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The striatum, a large subcortical nucleus, is an integral part of the basal ganglia, a group
of interconnected structures involved in various aspects of the control of movement
(Calabresi et al., 1997a; Chesselet and Delfs 1996; Marsden and Obeso 1994).
The basal ganglia are a group of nuclei involved in a variety of processes including
motor, associative, cognitive and mnemonic functions. The dorsal division of the basal
ganglia consists of the striatum (or caudate-putamen), the globus pallidus (GP, external
segment of the globus pallidus in primates), entopeduncular nucleus (EP, internal segment of
globus pallidus in primates, GPi), the subthalamic nucleus (STN) and the substantia nigra
(SN), which is divided into two main parts, the dorsal pars compacta (SNc) in which the
dopaminergic nigrostriatal neurons are located and the more ventral pars reticulata (SNr).
The most widely accepted views of basal ganglia function are based on observations of
human afflicted with degenerative diseases that attack these structures. In all cases these
diseases produce severe deficits of movement. In some, such as Parkinson's disease (PD),
movements are more difficult to make, as if the body were somehow made rigid and resistive
to changes in position. In others, such as Huntington´s disease, useless and unintended
movements interfere with the execution of useful and intended ones. In general, these
symptoms affect only voluntary movements, purposive movements, with reflexive
movements being relatively unaffected. These clinical observations have led most
investigators to view basal ganglia as components of a widespread system that is somehow
involved in the generation of goal-directed voluntary movements, but in complex and subtle
aspects of that process (Wilson, 1996).
The major input to the basal ganglia is derived from the cortex; virtually the whole cortex
projects onto the basal ganglia in a highly topographical manner. The main point of entry of
this cortical information to the basal ganglia is the striatum. The corticostriatal projection
imparts functionality on to the striatum and consequently other divisions of the basal ganglia.
In what is now considered the classic view of basal ganglia circuitry (Albin et al., 1989;
DeLong, 1990; Smith et al., 1998), the functional organization is such that cortical
information carried by the corticostriatal projection is processed within the striatum,
integrated with the many other inputs to the basal ganglia (e.g. intralaminar thalamic nuclei,
amygdala, hippocampus, dorsal raphe) which primarily innervate the striatum, and then the
information is transmitted to the output nuclei of the basal ganglia, the EP and the SNr. The
