User:Denisej 2/Dopaminergic pathways

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Dopaminergic pathways (dopamine pathways, dopaminergic projections) in the human brain are involved in both physiological and behavioral processes including movement, cognition, executive functions, reward, motivation, and neuroendocrine control. Each pathway is a set of projection neurons, consisting of individual dopaminergic neurons or dopamine neurons.

' The four major dopaminergic pathways are the mesolimbic pathway, the mesocortical pathway, the nigrostriatal pathway, and the tuberoinfundibular pathway.  Other dopaminergic pathways include the hypothalamospinal tract and the incertohypothalamic pathway  .The mesolimbic pathway and the mesocortical pathway form the mesocorticolimbic system. Two other pathways to be considered are the hypothalamospinal and incertohypothalamic pathways. '

The dopamine neurons of the dopaminergic pathways synthesize and release the neurotransmitter dopamine.[2][3] Enzymes tyrosine hydroxylase and dopa decarboxylase are required for dopamine synthesis.[4] These enzymes are both produced in the cell bodies of dopamine neurons. Dopamine is stored in the cytoplasm and vesicles in axon terminals. Dopamine release from vesicles is triggered by action potential propagation-induced membrane depolarization.[4] The axons of dopamine neurons extend the entire length of their designated pathway.

Four Major pathways (same as above)

 *  Mesolimbic 
 *  VTA → Prefrontal cortex 
 *  Mesocortical 
 *  VTA → Ventral striatum (nucleus accumbens and olfactory tubercle) 
 * Nigrostriatal
 *  Zona compacta →  Dorsal striatum (caudate nucleus and putamen)
 * Tuberoinfundibular
 * Tuberal hypothalamus (Infundibular nucleus) →  pituitary gland  Median eminence (dopamine released at the median eminence reaches the pituitary gland via the hypophyseal portal system)

Hypothalamospinal

 * Hypothalamus → Spinal cord

Incertohypothalamic


 * Zona incerta → Hypothalamus
 * Zona incerta → Brainstem

Mesocorticolimbic projection[edit]
The mesocortical pathway  mesocorticolimbic system (mesocorticolimbic circuit)  refers to both the mesocortical and mesolimbic pathways. Both pathways originate at the ventral tegmental area (VTA). Through separate connections to the prefrontal cortex (mesocortical) and ventral striatum (mesolimbic), the mesocorticolimbic projection has a significant role in learning, motivation, reward, memory and movement. Dopamine receptor subtypes, D1 and D2 have been shown to have complementary functions in the mesocorticolimbic projection, facilitating learning in response to both positive and negative feedback. Both pathways of the  mesocorticolimbic   system  are associated with ADHD, schizophrenia and addiction.

Mesocortical pathway[edit]


 * The mesocortical pathway projects from the ventral tegmental area to the prefrontal cortex (VTA → Prefrontal cortex). This pathway is involved in cognition and the regulation of executive functions (e.g., attention, working memory, inhibitory control, planning, etc.) Dysregulation of the neurons in this pathway has been connected to ADHD.

Mesolimbic pathway[edit]


 * Referred to as the reward pathway, mesolimbic pathway projects from the ventral tegmental area to the ventral striatum ( VTA → Ventral striatum (nucleus accumbens and olfactory tubercle). When a reward is anticipated, the firing rate of dopamine neurons in the mesolimbic pathway increases. The mesolimbic pathway is involved with incentive salience, motivation, reinforcement learning, fear and other cognitive processes. In animal studies, depletion of dopamine in this pathway, or lesions at its site of origin, decrease the extent to which an animal is willing to go to obtain a reward (e.g., the number of lever presses for nicotine or time searching for food). Research is ongoing to determine the role of the mesolimbic pathway in the perception of pleasure.

Nigrostriatal pathway

 *  The nigrostriatal pathway is involved in behaviors relating to movement and motivation. The transmission of dopaminergic neurons to the dorsal striatum particularly plays a role in reward and motivation while movement is influenced by the transmission of dopaminergic neurons to the substantia nigra.  The  nigrostriatal pathway is associated with conditions such as Huntington's disease, Parkinson's disease, ADHD, Schizophrenia, and Tourette's Syndrome. Huntington's disease, Parkinson's disease, and Tourette's Syndrome are conditions affected by motor functioning while schizophrenia and ADHD are affected by reward and motivation functioning. This pathway also regulates associated learning such as classical conditioning and operant conditioning.



Tuberoinfundibular pathway

 *  The tuberoinfundibular pathway transmits dopamine   the hypothalamus to the pituitary gland.  This pathway also regulates the secretion of prolactin from the pituitary gland, which is responsible for breast milk production in females. Hyperprolactinemia is an associated condition caused by an excessive amount of prolactin production that is common in pregnant women.