The Mediating Affect of CRF Within the Central Nucleus of the Amygdala in Rats
1.Summarize the background of the article, and how does it relate to the general article.
Alcohol consumption is characterized by excessive consumption which leads to feelings of increased anxiety and other negative emotional states.Consequently, these emotions lead to further consumption.Similar to human alcoholics, ethanol- dependent animals show signs of anxiety like behaviors and self administrate ethanol during periods of withdrawal. CRF, also known as corticotropin releasing factor helps mediate the increased anxiety during withdrawal.Additionally,regions of the amygdala are comprised of the CRF system, although unknown where the specific sites are responsible for the CRF component of excessive drinking. Also, numerous studies have shown that the amygdala is involved in “mediating the behavioral and physiological responses associated with anxiety.”
This relates to the general article which focuses on the consumption of drug and alcohol, triggering feelings of anxiety which can be quieted by consuming more of it.Specifically, the amygdala is the part of the brain where the feelings of anxiety are triggered. Moreover, new research is showing alcohol's involvement in the transformation of the chemical architecture of the brain, allowing the brain's stress response to contribute to its dependency. CRF, also known as the corticotrophin releasing factor, is a chemical that is involved in the brain's stress response. Through substance consumption, CRF is triggered, helping the brain to return to its normal state after experiencing significant amounts of pleasure.However, too much alcohol and drug use causes the brain's stress response to go into overdrive and transitions from feeling moments of pleasure to feelings of pain, known as anxiety. As soon as the person is temporarily relieved from the CRF and takes in more alcohol, the pleasure aspect is lost.
2.State the specific hypotheses to be tested.
Do ethanol-dependent and non-dependent rats react differently after going into withdrawal?
Does the CRF antagonist, which is administered in CeA, lateral BNST and NacSh (regions in the Amygdala) play a role in mediating excessive ethanol consumption in both dependent and non-dependent rats?
3.Identify the dependent variable(s) and how are they measured
1.Density
The relative density of CRF immuno- reactive cell bodies, fibers, and terminals in the CeA and the BNST were recorded with the help of a Zeiss Axiphot.The mean optical density numbers were derived by subtracting the negative background and nonspecific DAB background from the positive CRF-immunoreactive areas.
2.Quantification of CRF positive cell bodies
The total number of CeA CRF-positive cell bodies was estimated by using a Zeiss Axiophot Microscope and only neurons with a focused nucleus within the non forbidden regions were counted
4.Identify the independent variable(s) and how they are manipulated.
1.The administration of ethanol
The rats self-administered ethanol by being trained to press a lever, using the sweetened solution fading process. There was also a lever that produced water which is crucial because the researchers would alter the levers daily to prevent bias from the rats.
2.Time
The chambers were connected to a time that would turn the ethanol vapor on(4:00 pm) and off (6:00 pm) every day, allowing animals to receive ethanol vapor for a total of 14 hours and control air for 10 hours.
3.Concentration of Ethanol vapor and CRF antagonist
To induce dependance, two rat cages were intermittently introduced to ethanol vapor and varied the concentration of ethanol vapor which varied from 22-27 mg/L. Additionally, the concentration of the CRF receptor antagonist varied from 0-.5.
4.Regions of the brain-specifically, the CeA,BNST, and the NAcSh
5.Identify any variables that are controlled (e.g., gender, time of test, one area of brain)
Rats that were not given alcohol
6.Diagram how the study was done.
Rats were first trained to administer 10 percent ethanol.Once they were stable, rats were surgically implanted with bilateral intra-cerebral cannulas aimed at the CeA, lateral BNST, or NacSh. After the rats recover from surgery, they are placed into the ethanol (dependent group) or the control group(nondependent group)vapor for four weeks.At the end of four weeks, they are either retested for ethanol self-administration or killed for immunohisto-chemistry. At this point, dependent rats show a significant increase in level pressing. Then, the CRF density measurements and the total number of CeA CRF positive cell bodies are quantified. Then, the CRF receptor antagonist is administered into the intra-CeA and intra-lateral BNST, and intra-NAcSh in dependent and nondependent rats;the effects of the CRF receptor antagonist are recorded along with the concentrations.After that, the CRF immuno-reactivity within the CeA, BNST, and NacSh are recorded.
To conclude, a CRF antagonist administered in the CeA significantly reduces ethanol self administration in ethanol-dependent rats but not in nondependent rats.However, in the BNST and nucleus accumbens shell has no effect.These results show the “functional organization of CRF systems in mediating critical motivational aspects of alcohol dependence.