The Amazing Spider-Man? More like The Amazing Brain

Do you guys remember this movie??                

                  And do you remember Dr. Curt Connors? The scientist who tried to regrow his arm by combining lizard and human genes, "surprisingly" turning into an evil lizard villain?                                      
                                                         

                                      
Well what I want to talk to you guys about today is not that you should watch the movie, but about one of the many amazing things our brain can do, pathfinding by axons. You may be thinking oh come on this is just a movie, but the concept that leads Dr. Connors to try this "serum" is the regenerative ability of axons to find specific pathways to their original connections. Now I am not saying that it is possible in humans (yet??), but that this is true in some amphibians, (salamanders, newts...) and lizards (tails).

How does regeneration work?

Well in a salamander if you cut off a limb the wound will eventually close and regenerate new cells, bone, and muscle. The first thing is new cells being regenerated, join to form what can be referred to as the wound epidermis  relaying messages for nerves to regenerate. After the amputation, many groups of stem cells join at the wound creating what is called a blastema.


<-------  A=mass of cells 

         B=epidermis 

         C=nerve cells

This leads the cells to essentially start dividing and multiplying again to reform the tissue, bones, muscles, and nerves previously found. However, what I found to be the most interesting is that cells can differentiate between whether they need to regenerate an arm, a leg, or a finger. In other words, they know what is missing and regenerate just that.

The reason that salamanders are able to regenerate limbs are because they can generate new axon branches at the new limb and are able find the correct muscle to respond to. The axons are therefore able to find their way to the correct target.

This video below shows a great summary of how regeneration of limbs in salamanders occurs and how they differ from us.

What about in humans?

Obviously this works in some animals, but what about us? When we get a cut our body quickly adds on new cells patching up the wound creating scar tissue which helps stop blood loss and prevents infections however, it is the scar tissue that prevents us from regenerating. Scar tissue is dead tissue which unlike the blastema will not divide and multiply to reform the limb. It is not easy, but scientists are working to find new and innovative ways, one of which is using the patient's own cells to grow new tissue in a scaffold stimulating natural healing rather than scar tissue.
I turns out Dr. Connors wasn't so crazy after all, if you can get over him turning into a lizard mad-scientist guy.

 

References:

Kalat, J. (2012). Biological psychology. Cengage Learning.
http://www.blastr.com/2012/07/researchers_say_the_scien.php

Addicted to _________? It's because of your nucleus accumbens. Wait, what????

You may be thinking, did I read the title right or is she just making up words? No, you’re right; the nucleus accumbens is an actual area in the brain (proof below). 

As you (may) know, last week I talked about how heroin can pass through the blood brain barrier, but what I did not mention is how we can easily become addicted to drugs. You're probably thinking everyone knows that, but today I want to talk about the role the nucleus accumbens and dopamine plays in addiction.

So to begin with, what is addiction? I know when most people hear addiction they think junkies, rehab, habit, druggies, homeless, unstable, etc,. However, addiction is simply the repetition of a behavior despite the potentially harmful consequences. It has to do with intense cravings and even loss of control in the user. It can "rewire" the brain by changing our motivations  and reinforcing drug experiences and decreasing or inhibiting the pleasure of other experiences. Basically it makes the experiences caused by the drug more alluring, leaving other actions unable to compete for the attention. 

Back to the nucleus accumbens

It is an area rich in dopamine, which is one neurotransmitter responsible for stimulating pleasure centers in the brain and transmitting impulses from neurons to the brain. The nucleus accumbens is also responsible for reinforcing all kinds of experiences we find rewarding as well as in learning new behaviors. It is why it is so“addicting” or rewarding to get high. All drugs  of abuse stimulate the nucleus accumbens by releasing dopamine in the nucleus accumbens. Therefore, when the brain releases this neurotransmitter the "high" felt becomes associated with the drug, reinforcing the usage.  Once the user experiences this high, this memory becomes imprinted as a memory in the hippocampus and is brought back to "memory" every time someone craves, thinks, or takes the drug. Whether the drug usage will lead to addiction depends on many factors such as:

Dopamine

• speed of release
• amount released  
• intensity of release

Drug

• route of administration (injection, inhalation, intranasal, ingestion...)
• dosage
• genetic susceptibility
• frequency of usage

Here is a video explaining the pathology of addiction (it is a little lengthy so I recommend starting at 2:43). I think this video does a good job in explaining how the nucleus accumbens, dopamine, and serotonin play a role in addiction. 

A quick word about tolerance

Tolerance is when more of the drug is needed for the user to experience the same effects and happens when the user habitually uses. Habitual use of the drug leads our brain to adapt and make the effects of the drug less pleasurable or stimulating. When our brain adapts, dopamine has less effect on the nucleus accumbens and we need more and more every time. 

Disclosure

Do not think that drugs are the only thing you can become addicted or that stimulate the pleasure centers in the brain!

References:

Kalat, James. Biolgical Psychology: Eleventh Edition

http://www.wisegeek.com/what-is-the-nucleus-accumbens.htm

http://addiction-dirkh.blogspot.com/2010/02/nucleus-accumbens.html

http://www.helpguide.org/harvard/addiction_hijacks_brain.htm

Blame it on the BBB: The blood-brain barrier

As you may or may not know, actor Philip Seymour Hoffman recently passed away from a heroin overdose. Now you may be wondering, what does this have to do with physiological psychology or more importantly  the blood-brain barrier? Well, I am here to tell you, but first let me explain what the BBB is, how it works, and why we definitely need it.

THE BBB...
The blood-brain barrier is a semi-permeable wall, that runs along the sides of the blood vessels in the brain, in the sense that it allows some materials to cross such as oxygen and carbon dioxide and keeps harmful ones away. You can think of it as your personal Border Customs Agent telling you what you can and cannot pass through the "border" (aka brain).

HOW DOES IT DO IT???
The BBB works by tightly joining endothelial cells to one another so almost nothing can get through. There are several molecules and chemicals that can pass through.

• Small uncharged molecules

• These include the essential elements, oxygen and carbon dioxide. Water is able to cross through the walls of the endothelial cells that make up the BBB through protein channels.

• Lipid soluble molecules

• This refers to the molecules that are able to dissolved in fats such as Vitamins A and D as well as psychoactive drugs. Ex., antidepressants, sleeping aids, and even drugs like heroin.

• Some chemicals
• These are transported to the brain by active transport and include chemicals such as glucose (fuel), certain hormones, and amino acids among a few others.

WHY???
The BBB is needed to keep the brain protected from harmful and toxic substances that can cause damage. Since neurons are hardly ever repaired or replaced the brain needs a "gatekeeper" controlling the entrance to viruses, harmful chemicals, and bacteria. 

THE BBB AND HEROIN
Heroin crosses through the blood brain barrier approximately 100 times faster than morphine! The reason is because it is highly soluble in lipids and therefore passes easily as mentioned above.  As it passes through the BBB it is turned into morphine and the user then feels this intense "euphoric" feeling pass through them. A heroin overdose is caused by the chemicals in the drug altering the brain's neurons oppositely. What do I mean by oppositely? Although you may know it is wrong and your brain is "telling" you not to do it, the pleasure centers in your body are telling you "YES!!" With each use tolerance builds and leads the user to need more. Excess use of heroin stops many automatic process including breathing and beating (heart) which eventually may lead to death.

Below is a video describing the death of the actor, Philip Seymour Hoffman as explained by a drug addiction expert.


Hopefully I have enlightened you, dear reader, on the blood-brain barrier and how important it is for our health.


References
Kalat, James. Biological Psychology:Eleventh Edition
http://news.nationalgeographic.com/news/2014/02/140204-philip-seymour-hoffman-actor-heroin-overdose/
http://www.howitworksdaily.com/science/the-blood-brain-barrier-explained/
http://faculty.washington.edu/chudler/hero.html