Basics of Animal Research

Scale of use: Annually, around 29 million animals are used in experiments across the US and European Union.
Common species: Rats and mice constitute 80% of the animals used in research.
Reduction in use: Over the last 30 years, the number of animals used in scientific research has decreased by 50%, indicating progress toward more ethical practices and alternative methods.

Ethical concerns with human experimentation:
- Procedures such as isolation or invasive surgeries are unethical to perform on humans, making animal subjects an alternative when studying similar processes in behavior and physiology.
Lifespan differences:
- Animals have significantly shorter lifespans than humans, which allows researchers to observe the effects of variables, like stress, over a complete life cycle. This also allows researchers to examine these effects across multiple generations in a relatively short time span, something that would be impossible with humans.
Controlled environments:
- Animal behavior can be studied under highly controlled conditions that would be difficult or impossible to replicate with humans. For instance, environmental variables and genetic backgrounds can be controlled to an extent that is not feasible in human research.

Manipulating acetylcholine: Researchers used animal models to manipulate levels of acetylcholine in rats to study its effects on learning and memory.
- Temporary manipulation: The changes to acetylcholine levels were temporary, causing no long-term harm to the animals.
- Controlled learning environment: The study was able to control learning variables strictly, which would be challenging to achieve with human subjects.
- Human implications: The findings from the study helped form hypotheses about acetylcholine’s role in human memory. Later studies connected low levels of acetylcholine to Alzheimer’s disease in humans.
- Practical outcomes: As a result of this line of research, drugs like Aricept and Exelon were developed to help stabilize acetylcholine levels in patients with Alzheimer’s, highlighting how animal research can lead to advances in human medicine.

Animal model: Animals are often used to model human behaviors or diseases when the behaviors or diseases exhibit similar characteristics in both species. For example, research on animal models can provide insights into brain function, hormones, and genetic factors that may be involved in human conditions like depression.
Challenges in modeling mental disorders:
- When using animal models to study complex human conditions like depression, researchers face limitations. For example, animals cannot experience or exhibit human symptoms like pessimism, loss of self-esteem, or suicidal thoughts.
- However, psychologists can study animals with specific endophenotypes (genetic markers associated with certain behaviors) related to disorders like depression, offering insights into the biological and genetic mechanisms behind such conditions.

An endophenotype refers to measurable biological, behavioral, or cognitive markers that are more frequently found in individuals with a particular disorder compared to the general population. These markers can help researchers understand the genetic predispositions that may lead to certain behaviors or mental health conditions.

In 2002, researchers successfully completed the rat genome mapping, revealing that rats and humans both have approximately 30,000 genes.
- Only 300 genes are unique to either species, meaning humans and rats share 99% of their genetic makeup.
- The key differences lie in gene expression. For instance, while both species carry a gene responsible for tail development, it is only expressed in rats, not humans. This highlights how genetic similarities between animals and humans make rats a valuable model for studying human diseases.

Study on fear response: LeDoux used lesioning (surgically damaging specific brain areas) in rats to study the brain’s role in the fear response.
- Amygdala’s role: His research identified the amygdala as playing a key role in processing fear.
- Two-path model of fear response:
  1. Low path: When a fear-inducing stimulus is detected, the visual thalamus sends a signal directly to the amygdala, triggering a rapid fear response. This pathway is faster but less accurate, serving as an immediate survival mechanism. For example, if you see a snake, this quick path triggers the fear response and increases blood pressure.
  2. High path: The visual thalamus sends the signal through the visual cortex and hippocampus for further processing, allowing for a more accurate evaluation of the stimulus. If the brain determines the stimulus is not a threat, the amygdala reduces the fear response, lowering blood pressure. This pathway is slower but more accurate, allowing for better evaluation of the potential threat.