Biology Reference
In-Depth Information
S
TRUCTURAL AND
F
UNCTIONAL
O
RGANIZATION OF THE
S
TRIATUM
The striatum is not a unitary structure, but consists of two anatomical and functional
subregions, the dorsal striatum and ventral striatum, which includes the NAc. In turn, the NAc
includes two different structural and functional subregions, the core and the shell (Heimer et
al., 1991; Voorn et al., 1989. The core appears to be a functional extension of the dorsal
striatum and there is evidence that the NAc core is involved in the control of goal-directed
behavior by associative processes (Cardinal et al., 2002), in instrumental (response-
reinforcement) learning (Kelley et al.,1997), and in supporting behavioral responses to
motivationally significant conditioned stimuli (Bassareo and Di Chiara, 1999; Parkinson et
al., 2000). The NAc shell is connected with the network of descending neuronal influences
over reflexive autonomic and motor responses. The shell is a limbic structure included in the
extended amygdala and seems to be involved in the processing of the primary reinforcing
effect of natural rewards (Bassareo and Di Chiara, 1999) and drugs of abuse (Carlezon and
Wise, 1996; Di Chiara et al., 1993), including initial stages of behavioral sensitization to
cocaine (Todtenkopf et al., 2002). The NAc core and shell get excitatory input from the
basolateral nucleus of the amygdala (BLA) (Wright et al.,1996; Cardinal et al., 2002). Two
amygdala nuclei, the BLA and the central nucleus (Ce), are involved in emotional processes
of addiction. Whereas BLA is required for Pavlovian conditioning, Ce acts as a control of
brainstem arousal (see figure 5).
Figure 5. Basic circuitry in cocaine addiction. Includes the primary neurotransmitters, topographic
organization and interconnections between the reward related pathways, learning and memory
pathways, and circuits involved in cocaine seeking. The mesencephalic ventral tegmental area (VTA)
projects its dopaminergic (DA) efferents to the limbic nuclei, nucleus accumbens (NAc) core and shell,
amygdala and hippocampus, as well as dorsolateral prefrontal cortex (DLPF) and ventral prefrontal
cortex (VPF). The hippocampus and amygdala, the latter through its basolateral subnucleus (BLA), as
well as the DLPF and VPF cortex project their glutamatergic (GLU) efferents to the shell and core of
the NAc. The figure also includes the dorsal striatum (DSTM) and its connexions to the substantia nigra
(SN). (Source: Adapted from Corominas-Roso et al. 2007).
