A neurobiological look at Addiction and Rhesus monkeys

Addiction is a complex and widespread problem that afflicts people across the world. This prevalence and the devastating consequences to a person's life feed the current search for a cure to addiction. Rhesus monkeys have often been used to study the effects of addiction on a purely mechanistic level because they are closely related to humans, they have the ability to self-administer drugs, and they have similar metabolic and physiological responses. Rhesus monkeys have been used in the past to study diseases such as AIDS and HIV and create vaccines for small pox, rabies and polio. They have also been used to further the understanding of primate evolution and has enhance medical research in neuroscience, behavioral biology, reproductive physiology, endocrinology, heart and blood vessel disease and immunodeficiency. [2]

Rhesus monkeys are often used as a representative model when researching human addiction. The reason why this is an acccurate assumption is because of the biologicaly similarities above. Neurological similarities between the species should also be noted:

"Researchers point out that the human brain is only 15 times larger than that of a rhesus macaque and, because most of the critical cortical cells are in organised layers near the surface, they argue that the relevant ratio from human to macaque is much smaller. In gross appearance, the human and non-human primate brain is packed into the skull with numerous folds of the thin outer layer of its cortical mantle called sulci, whereas those of rodents have a smooth appearance with few sulci. The brain of a rhesus macaque is also more like the human brain in having the major parts of the visual system folded into the medial walls of each hemisphere."[25]

Most of the work done to observe drug addiction with Rhesus monkeys has been with stimulant drugs, primarily cocaine. In order to maintain a logical continuum, the information here will also focus on cocaine.

Tinbergen's 4 Questions

Tinbergen was a Dutch ethologist in the 20th century that developed a categorical system to adress multiple facets of behavior. A behavior must have both proximate (how) and ultimate (why) causes and those cause can be divided further into dynamic (over time) versus static (immediate/snapshot) views:

(Tinbergen's 4 questions in a simplifying table. Provided by Professor Suzy Renn)

Addiction is often treated as a purely mechanical human problem. However the mechanism that is focus of most modern research, the dopaminergic reward circuit is in many other animal models as well, and this circuit is a facet in many aspects of behavior. This website will address how this mechanism works, how it is conserved across animal species, how a clearly non-adaptive thing like addiction can survive and be induced in many animals, and how the brain changes with addiction. These statements are all necessary in identifying how to best deal with addictive behavior, especially biological addiction (when the body adapts to need a drug and will go through a painful sick period or withdrawal without it).