Nucleus accumbens

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The nucleus accumbens is a collection of neurons in the basal forebrain region of reptiles and higher organisms which play an important role in reward, pleasure and addiction. It is part of the ventral continuation of the dorsal striatum and shares general principles of connectivity with the striatum. The nucleus accumbens is also called ventral striatum.

The principal neuronal cell type found in the nucleus accumbens is the medium spiny neuron. The neurotransmitter produced by these neurons is gamma amino butyric acid, more commonly known as GABA. GABA is the main inhibitory neurotransmitter of the central nervous system. These neurons are also the main projection or output neurons of the nucleus accumbens.

While 95% of the neurons in the nucleus accumbens are medium spiny GABAergic projection neurons, other neuronal types are also found such as large aspiny cholinergic interneurons.

The output neurons of the nucleus accumbens send axon projections to the ventral analog of the globus pallidus known as the ventral pallidum (VP). The VP, in turn, projects to the mediodorsal (MD) nucleus of the thalamus which projects to the prefrontal cortex. Major inputs to the nucleus accumbens include the prefrontal cortex and dopaminergic neurons located in the ventral tegmental area (VTA) which connect via the mesolimbic pathway. Thus the nucleus accumbens is often described as one part of a cortico-striato-thalamo-cortical loop.

Dopaminergic input from the VTA is thought to modulate the activity of neurons within the nucleus accumbens. These terminals are also the site of action of highly addictive drugs such as cocaine and amphetamine which cause a several-fold increase in dopamine levels in the nucleus accumbens. In addition to cocaine and amphetamine, almost every drug abused by humans has been shown to increase dopamine levels in the nucleus accumbens.

Although the nucleus accumbens has traditionally been studied for its role in addiction, there is a growing body of evidence that it plays a major role in mediating natural rewards.

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