Depression In Female Rats example essay topic

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 neuro trophic 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 colleagues (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 stressor's 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 stressor's 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 na " ive 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. The restraint stress were given for 6 hours each day at random times during the light and dark cycles.

They were placed in a Plexiglass restraint tube. The tubes were small enough to limit the head and limb movements of the rats. In order to control for the handling of the rats the rats in the handling groups were quickly picked up and put back into the home cage. The behavioral testing consisted of an open field and resistance to capture tests. These were done in the light cycle of the light / dark cycles. The injections and restraint manipulations still occurred during the behavior testing.

The open field test was done in a black wooden box with no top and a clear Plexiglass bottom with the floor divided into 36 identical squares with tape. This test is frequently used in anxiety testing. After the open field testing the rats were tested in their resistance to capture. An unfamiliar experimenter wore a leather glove and tried to pick the rat up from the top and the resistance was measured on a seven point scale. 0 being the easiest to pick up, 1 vocalizes or shies away from glove, 2, shies sway from hand and vocalizes, 3 runs away from hand, 4 runs away and vocalizes, 5 bites or attempts to bite, 6 begins a jump attack. A forced swim test was also measured for the behavioral testing.

The first day of swim testing the rats were place in the swim tank for 15 minutes, and 10 minutes on the second day which was the measured trial for depressive symptoms. The last behavioral testing was a social interaction test. This test was conducted in an unfamiliar white wooden box with not top. The room was brightly lit and box was placed on the floor.

Rat from the same experimental groups were place in opposing corners of the box. The behaviors recorded were the amount of time the rats spent in non aggressive interaction, amount of time the rats spent in aggressive interaction and amount of time spent with no reaction at all. A decrease in the interaction was noted as an increase in anxiety. The rats in the CORT groups and restraint groups had effects on body weight gain. The rats with vehicle injections gained more than the CORT injection group. The restraint rats gained less than the handled rats.

It was also found that the rats with the CORT injections showed more depressive behaviors than the restraint rats. Memory and Learning Animal models have greatly contributed to the knowledge base of depression. Animal models are ideal in studying depression because of the limitations on human research. The next set of studies looked at in this section will look at depression and it's impact on memory and learning.

A study by Sun and Alkon (2004) looked at how induced depression influences learning and memory in 144 male Wistar rats. The two antidepressants used were and. The vehicle control used was these drugs solubilize d in saline. The rats were put in an open space swim test and observed through a video monitor so the observer would not be seen.

The rats were free to swim or not for 15 minutes and then placed back into their home cage. Overall, the rats that were given the vehicle drug showed a decrease in the distance moved over the trials in the swim tests. To see how the induced depression affected the memory and learning in the rats the antidepressants were not given in the memory and learning tasks. The first task was the spatial water maze learning and memory task. The water maze was divided into four quadrants. The control rats were allowed to swim around for 2 minutes without a hidden platform while the treatment rats were on their third day of induced depression.

The next day all the rats were given this task and the platform was hidden and the rats were to find it. The rats were allowed to swim around until they found the platform and were left there for 20 seconds. The rats that did not find the platform in 2 minutes were guided there. After the training trials the platform was removed and the rats were tested for memory of the location of the platform. All the rats showed a impairment of learning in this task, however the rats that were given the vehicle drug had a more significant impairment. The next task was the visible platform test.

This was the same except the platform was visible with a pole that stuck out of the water 9 inches and was in a different location. The behavior recorded here was the latency of the rats finding the platform. This task did not provide any significant differences between the groups. Next task was the passive avoidance learning and memory task. The rats were placed in an avoidance chamber. The rats would be placed in the initial side and allowed to explore for 60 seconds then the door to the dark chamber would be opened simultaneously with a light and tone.

If the rat went into the dark chamber the door would shut and an inescapable foot shock was given through the grid floor. Then a retention trial was given after the acquisition trial to see if the rat would remember the avoidance behavior conditioned the previous trials. The shock was not administered in the retention trials. The rats that were given the had higher mobility than the vehicle or groups. The last task was a response to US shock as a motivator.

The rats were place in the avoidance chamber on the dark side with the door open to the light side. The tone and light were administered simultaneous with the foot shock this time the foot shock was es capable. If no escape was attempted the shock was discontinued after 20 seconds. All the rats tested in this task escaped the shock before the 20 second cutoff.

This was very important in understanding the lack of memory as a symptom of depression and can have great impact on the way that depression is treated to insure the long term effects on memory be reduced. Ovarian Hormone The female hormones in the ovaries may play a role in depression in females. This is important in understanding postpartum depression. To better understand this a study was done by Stoffel and Craft (2004).

This study consisted of female Sprague-Dawley rats. The rats underwent surgery to remove the ovary on each side of the body. The rats were allowed to recover for one week before trials started. Daily injections were given to the rats to produce a hormone induced pregnancy, and the vehicle rats were given safflower oil on the same schedule. The rats were given paper towels to use for nesting following the injections. Nesting behavior was scored as positive if the paper towel was shredded and placed in a circular nest in a corner of the cage, and was scored negative in the absence of this criteria.

Once the daily injections were stopped the rats were given a forced swim test after withdrawal began. Each rat was only tested once. Testing was videotaped and two observers blind to treatment group assignment scored the behavior from the videotape. The elevated plus-maze was used in the behavior testing, and scored according to entering of the open and closed arms of the apparatus. The rats were also tested on withdrawal days for the locomotor activities.

Fifteen photo beams were used in this apparatus and the number of photo beams broken every 5 minutes for a total of 45 minutes was scored. The results in this study showed that the withdrawal from the ovarian hormones increased the depressive symptoms in the forced swim test, and decreased mobility in the locomotor activity testing. This may suggest that after a woman gives birth to the infant then the sudden change in the levels of hormones may affect the depressive symptoms in her. This gives rise to future studies in treating this illness in postnatal women and better help them cope with the changes in hormones and the demanding job of a new mother. Neuroplasticity According to Fossati, Radtchenko and Boyer (2004) the brain's structure and function is a result of genetics and environmental factors. Important results have come from tissue studies.

These studies suggest that depression is caused from the improper development of the structure and function in the prefrontal cortex, hippocampus and amygdala. This is supported by studies done with imaging. Brain imaging was preformed on the changes in the function and structure of the hippocampus, prefrontal cortex and the amygdala. The reduced hippocampus volume was recorded, the correlation between duration of depressed patients and volume loss and recovery of volume after the antidepressant was administered.

This is all important to know because these can provide for better medical treatment of depression, and can contribute to the scarce understanding of the causes of depression. Limitations and Future Research It is important for continued research on depression for the further advancement of the models that are in existence. Research on the causes is important to the treatment of depression, because without a cause the treatment will not be as effective as it could be. With a cause known there could be a cure developed to eliminate it completely. This may be years or decades down the road but it may be possible once depression is better understood.

The research on postpartum depression could be advanced with more researchers looking at this phenomenon. This would contribute greatly to the aid of the mothers that suffer from this illness. Some of the limitations to the rats being used in the experiments are the Fawn Hooded rat have a high immobility to the forced swim test naturally and the Wistar Kyoto rat becomes hyperactive to stress (Angelucci, Brene, Mathe, 2005). Conclusion Animal studies contribute great data to the research of human behavior.

The animal models are important in the research that is not ethical in humans. The animal models have given the research community great ideas to expand on, and have given more knowledge to the understanding of human behavior and illnesses. Depression has benefited from the animal studies because depression is not very well understood. With continued research using animals the depression mystery may be solved. Angelucci, F., Brene, S., Mathe, A.A. (2005). BDNF in schizophrenia, depression and corresponding animal models.

Molecular Psychiatry, 1-8. Fossati, P., Radtchenko, A. and Boyer, P. (2004). Neuroplasticity: from MRI to depressive symptoms. European Neuro psychopharmacology, 14, S 503-S 510.

Gregus, A., Wintink, A.J., David, A.C., Kalynchik, L.E. (2005). Effect of repeated corticosterone injections and restraint stress on anxiety and depression-like behavior in male rats. Behavioral Brain Research, 156,105-114. Grippo, A.J., Sullivan, N.R., Damjanoska, K.J., Crane, J.W., Carrasco, G.A., Shi, J. et al.

(2004). Chronic mild stress induces behavioral and physiological changes, and may alter serotonin 1 A receptor function, in males and cycling female rats. Psychopharmacology, unknown pages. Stoffel, E.C. and Craft, R.M. (2004). Ovarian hormone withdrawal-induced "depression" in female rats. Physiology & Behavior, 83,505-513.

Sun, M.K., Alkon, D.L. (2004). Induced depressive behavior impairs learning and memory in rats. Neuroscience, 129,129-139.