Nucleus accumbens

nucleus accumbens shellnucleus accumbens coreaccumbalaccumbensnucleus accumbens (NAcc)accumbens nucleusbrain's reward centercoreDopamine D2 receptor expressing medium spiny neurons (D2-MSNs)dorsorostral nucleus accumbens
The nucleus accumbens (NAc or NAcc), also known as the accumbens nucleus, or formerly as the nucleus accumbens septi (Latin for nucleus adjacent to the septum) is a region in the basal forebrain rostral to the preoptic area of the hypothalamus.wikipedia
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Basal forebrain

Forebrain cholinergic nuclei
The nucleus accumbens (NAc or NAcc), also known as the accumbens nucleus, or formerly as the nucleus accumbens septi (Latin for nucleus adjacent to the septum) is a region in the basal forebrain rostral to the preoptic area of the hypothalamus.
They include the nucleus accumbens, nucleus basalis, diagonal band of Broca, substantia innominata, and the medial septal nucleus.

Basal ganglia

basal nucleibasalbasal ganglia (BG)
The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The output neurons of the nucleus accumbens send axonal projections to the basal ganglia and the ventral analog of the globus pallidus, known as the ventral pallidum (VP).
The main components of the basal ganglia – as defined functionally – are the striatum; both dorsal striatum (caudate nucleus and putamen) and ventral striatum (nucleus accumbens and olfactory tubercle), globus pallidus, ventral pallidum, substantia nigra, and subthalamic nucleus.

Striatum

ventral striatumdorsal striatumcorpus striatum
The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum.
The ventral striatum consists of the nucleus accumbens and the olfactory tubercle.

Mesolimbic pathway

mesolimbicreward pathwaymesolimbic reward pathway
The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle.
The ventral striatum includes the nucleus accumbens and the olfactory tubercle.

Olfactory tubercle

tuberculum olfactorium
The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum.
The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle.

Medium spiny neuron

medium spiny neuronsMedium spiny cellsneurons
The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle. Cell types: Neurons in the nucleus accumbens are mostly medium spiny neurons (MSNs) containing mainly D1-type (i.e., DRD1 and DRD5) or D2-type (i.e., DRD2, DRD3, and DRD4) dopamine receptors.
In the nucleus accumbens (NAcc), these mixed-type MSNs that contain both D1-type and D2-type receptors are mostly contained in the NAcc shell.

Motivational salience

incentive salienceaversive saliencetask saliency
As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep.
Incentive salience is regulated by a number of brain structures, but it is assigned to stimuli by a region of the ventral striatum known as the nucleus accumbens shell.

Basolateral amygdala

basolateral complexbasolateralbasolateral nucleus
Major glutamatergic inputs to the nucleus accumbens include the prefrontal cortex (particularly the prelimbic cortex and infralimbic cortex), basolateral amygdala, ventral hippocampus, thalamic nuclei (specifically the midline thalamic nuclei and intralaminar nuclei of the thalamus), and glutamatergic projections from the ventral tegmental area.
The basolateral amygdala and nucleus accumbens shell together mediate specific Pavlovian-instrumental transfer, a phenomenon in which a classically conditioned stimulus modifies operant behavior.

Dopamine receptor D1

D 1 dopamine receptor D 1 D1
Cell types: Neurons in the nucleus accumbens are mostly medium spiny neurons (MSNs) containing mainly D1-type (i.e., DRD1 and DRD5) or D2-type (i.e., DRD2, DRD3, and DRD4) dopamine receptors.
Based upon Northern blot and in situ hybridization, DRD1 mRNA expression in the central nervous system is highest in the dorsal striatum (caudate and putamen) and ventral striatum (nucleus accumbens and olfactory tubercle).

Euphoria

euphoriceuphorianthigh
These neurons are activated directly or indirectly by euphoriant drugs (e.g., amphetamine, opiates, etc.) and by participating in rewarding experiences (e.g., sex, music, exercise, etc.).
Exercise is known to affect dopamine signaling in the nucleus accumbens, producing euphoria as a result, through increased biosynthesis of three particular neurochemicals: anandamide (an endocannabinoid), β-endorphin (an endogenous opioid), and phenethylamine (a trace amine and amphetamine analog).

Subiculum

subicularsubicular layer
Another major source of input comes from the CA1 and ventral subiculum of the hippocampus to the dorsomedial area of the nucleus accumbens.
The pyramidal neurons send projections to the nucleus accumbens, septal nuclei, prefrontal cortex, lateral hypothalamus, nucleus reuniens, mammillary nuclei, entorhinal cortex and amygdala.

Amphetamine

speedbenzedrineamphetamines
These neurons are activated directly or indirectly by euphoriant drugs (e.g., amphetamine, opiates, etc.) and by participating in rewarding experiences (e.g., sex, music, exercise, etc.).
Pathological overactivation of the mesolimbic pathway, a dopamine pathway that connects the ventral tegmental area to the nucleus accumbens, plays a central role in amphetamine addiction.

Slow-wave sleep

slow wave sleepdeep sleepslow-wave
As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep.
the nucleus accumbens core (GABAergic medium spiny neurons; specifically, the subset of these neurons that expresses both D2-type dopamine receptors and adenosine A 2A receptors), located within the striatum

Ventral tegmental area

ventral tegmentumventral tegmental area (VTA)ventral tegmental nuclei
Major glutamatergic inputs to the nucleus accumbens include the prefrontal cortex (particularly the prelimbic cortex and infralimbic cortex), basolateral amygdala, ventral hippocampus, thalamic nuclei (specifically the midline thalamic nuclei and intralaminar nuclei of the thalamus), and glutamatergic projections from the ventral tegmental area.
GABAergic inputs to the VTA include the nucleus accumbens, ventral pallidum, and rostromedial tegmental nucleus (RMTg).

Impulsivity

impulsiveimpulsivenessimpulsive behavior
The nucleus accumbens plays a lesser role in processing fear (a form of aversion), impulsivity, and the placebo effect.
Lesions of the nucleus accumbens core subregion or basolateral amygdala produce shifts towards choosing the smaller-sooner reward, suggesting the involvement of these brain regions in the preference for delayed reinforcers.

Dopamine receptor

dopaminedopamine receptorsdopaminergic
Cell types: Neurons in the nucleus accumbens are mostly medium spiny neurons (MSNs) containing mainly D1-type (i.e., DRD1 and DRD5) or D2-type (i.e., DRD2, DRD3, and DRD4) dopamine receptors.
D 3 is encoded by the Dopamine receptor D 3 gene . Maximum expression of dopamine D 3 receptors is noted in the islands of Calleja and nucleus accumbens.

Pavlovian-instrumental transfer

transfer to the primary reinforcerspecific Pavlovian-instrumental transfer
As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep.
Based upon studies on rats that involved PIT with rewards, specific PIT is mediated by the nucleus accumbens shell and basolateral amygdala, while general PIT is mediated by the nucleus accumbens core and central amygdala.

Reward system

rewardrewardingrewards
As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep. Dopamine: Dopamine is released into the nucleus accumbens following exposure to rewarding stimuli, including recreational drugs like substituted amphetamines, cocaine, and morphine.
The reward system includes the ventral tegmental area, ventral striatum (i.e., the nucleus accumbens and olfactory tubercle), dorsal striatum (i.e., the caudate nucleus and putamen), substantia nigra (i.e., the pars compacta and pars reticulata), prefrontal cortex, anterior cingulate cortex, insular cortex, hippocampus, hypothalamus (particularly, the orexinergic nucleus in the lateral hypothalamus), thalamus (multiple nuclei), subthalamic nucleus, globus pallidus (both external and internal), ventral pallidum, parabrachial nucleus, amygdala, and the remainder of the extended amygdala.

Rostromedial tegmental nucleus

tail of the ventral tegmental area
Other efferents from the nucleus accumbens include connections with the tail of the ventral tegmental area, substantia nigra, and the reticular formation of the pons.
Nucleus accumbens

Cocaine

cokecocaine traffickingcrack
Dopamine: Dopamine is released into the nucleus accumbens following exposure to rewarding stimuli, including recreational drugs like substituted amphetamines, cocaine, and morphine.
Cocaine addiction occurs through ΔFosB overexpression in the nucleus accumbens, which results in altered transcriptional regulation in neurons within the nucleus accumbens.

Globus pallidus

pallidumpallidalglobal pallidus
The output neurons of the nucleus accumbens send axonal projections to the basal ganglia and the ventral analog of the globus pallidus, known as the ventral pallidum (VP).
The ventral pallidum lies within the substantia innominata (Latin for unnamed substance) and receives efferent connections from the ventral striatum (the nucleus accumbens and the olfactory tubercle).

Dopamine

DAdopaminergic systemdopaminergic
Dopamine: Dopamine is released into the nucleus accumbens following exposure to rewarding stimuli, including recreational drugs like substituted amphetamines, cocaine, and morphine.
The most prominent group of VTA dopaminergic neurons projects to the prefrontal cortex via the mesocortical pathway and another smaller group projects to the nucleus accumbens via the mesolimbic pathway.

Κ-opioid receptor

κ-opioidKORkappa opioid receptor
Microinjections of μ-opioid agonists, δ-opioid agonists or κ-opioid agonists in the rostrodorsal quadrant of the medial shell enhance "liking", while more caudal injections can inhibit disgust reactions, liking reactions, or both.
High levels of the receptor have been detected in the prefrontal cortex, periaqueductal gray, raphe nuclei (dorsal), ventral tegmental area, substantia nigra, dorsal striatum (putamen, caudate), ventral striatum (nucleus accumbens, olfactory tubercle), amygdala, bed nucleus stria terminalis, claustrum, hippocampus, hypothalamus, midline thalamic nuclei, locus coeruleus, spinal trigeminal nucleus, parabrachial nucleus, and solitary nucleus.

TAAR1

trace amine-associated receptor 1hTAAR1trace amine associated receptor 1
Both compounds function as dopaminergic neuromodulators which regulate the reuptake and release of dopamine into the Nacc via interactions with VMAT2 and TAAR1 in the axon terminal of mesolimbic dopamine neurons.
These regions include the dorsal and ventral caudate nucleus, putamen, substantia nigra, nucleus accumbens, ventral tegmental area, locus coeruleus, amygdala, and raphe nucleus.

Addiction

drug addictiondrug addictdrug addicts
As a whole, the nucleus accumbens has a significant role in the cognitive processing of motivation, aversion, reward (i.e., incentive salience, pleasure, and positive reinforcement), and reinforcement learning (e.g., Pavlovian-instrumental transfer); hence, it has a significant role in addiction. In addition, part of the nucleus accumbens core is centrally involved in the induction of slow-wave sleep.
Two decades of research into ΔFosB's role in addiction have demonstrated that addiction arises, and the associated compulsive behavior intensifies or attenuates, along with the overexpression of ΔFosB in the D1-type medium spiny neurons of the nucleus accumbens.