Norepinephrine microinjections in the hypothalamic paraventricular nucleus increase extracellular dopamine and...

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Neurochemistry

Background:

• The paraventricular nucleus (PVN) is implicated in feeding behavior.
• Norepinephrine (NE) in the PVN can stimulate appetite and carbohydrate preference via alpha 2 receptors.
• The nucleus accumbens (NAc) is a key area for reward and reinforcement.
• A balance of dopamine (DA) and acetylcholine (ACh) in the NAc is thought to regulate motivated behaviors.

Purpose of the Study:

• To investigate the role of norepinephrine (NE) in the paraventricular nucleus (PVN) on dopamine (DA) and acetylcholine (ACh) release in the nucleus accumbens (NAc).
• To test the hypothesis that NE in the PVN modulates the DA/ACh balance in the NAc to influence eating behavior and reinforcement.

Main Methods:

• Microinjection of NE into the PVN of satiated rats.
• Microdialysis to measure extracellular DA and ACh levels in the NAc.
• Behavioral testing in the presence and absence of food.

Main Results:

• NE microinjection into the PVN significantly increased extracellular DA (109%) and decreased ACh (-27%) in the NAc when food was absent.
• When food was available and ingested, NE microinjection into the PVN caused an increase in ACh (51%) in the NAc.
• These neurochemical changes in the NAc correlated with the initiation and cessation of feeding behavior.

Conclusions:

• A functional connection exists between the PVN and NAc in regulating eating behavior.
• Dopamine (DA) in the NAc appears to play a role in initiating appetitive behavior.
• Acetylcholine (ACh) in the NAc seems to be involved in stopping appetitive behavior.
• This study elucidates a neurochemical mechanism underlying the reinforcement of eating.