How animal research has advanced the understanding of depression

Animal models have made numerous progresses in the last century. This type of research has made a difference in the way we look at psychological issues such as depression. This paper is a review of the literature on animal models of depression. The issue of what advances have been made will be explored. The effects of serotonin on many issues have been studied. In this paper stress, learning, memory, brain derived neurotrophic factor, ovarian hormone withdrawal, and effects of certain drugs will be looked at. Let’s look at stress and serotonin first.

Stress

A study done by Grippo, Sullivan, Damjanoska and colleages (2004) shows that chronic mild stress provokes behavioral and physiological changes and may change serotonin receptor function in rats. In this study sixty four Sprague-Dawley rats were used. Half were male and the other half were female. The following stimuli were used as stressors which include:

Continuous light for 2 12 hour periods

Forty degree tilt along vertical axis of cage for 6 hour period

Paired housing for a 16 hour period and 4 hour period

Damp bedding with 300 mL water spilled on bedding for 16 hour period

Water deprivation for 16 hour period

Empty water bottle following 16 hour water deprivation for 1 hour

Stroboscopic light with 300 flashes a minute for a 6 hour period and 4 hour period

White noise at approximately 90 dB for 4 hour period of continuous noise and a 3 hour period with random intermittent noise

All the stressors were given over a period of one week, and randomly presented for 3 additional weeks for a total of 4 week trial. All the rats were injected with a receptor agonist and were decapitated 15 minutes after the injection for the trunk blood. The 4 week trial resulted in the rats showing signs of depression, and satisfied adrenocorticotropic hormone (ACTH) responses to the receptor agonist. The trials also sparked a lack of pleasure in both male and female rats.

Another studied related to stress was done by Gregus, Wintink, David and Lalynchik (2005). This study looked at corticosterone injections and stress and how this relates to depression. Sixty naïve Long-Evans male rats were used. The rats were randomly assigned to 4 groups and were given corticosterone injections (CORT), vehicle injections, repeated restraint stress and repeated handling. These treatments were given for 21 days. The CORT group and vehicle group were given injections at random times during the light and dark cycles.