Day 1– Stress Exposure

1. Ultrasonic Vocalizations during Intermittent Swim Stress predict proficiency in Spatial Learning. Andrew Van Hoogenstyn, John Christianson and Robert Drugan Psychology Department, University of New Hampshire, Durham, NH 03820, USA Laura Castracane, Nate Stafford, Timothy Warner, and Rob Drugan Psychology Department, University of New Hampshire, Durham, NH 03820, USA Laura Castracane, Nathaniel Stafford, Timothy Warner, and Robert Drugan Psychology Department, University of New Hampshire, Durham, NH 03820, USA Hypothesis Results Introduction Conclusions • 80 trials of ISS did not alter spatial learning in the MWM. However, there are individual differences in USVs. • Of the 10 rats exposed to stress (ISS), 6 rats vocalized, the remaining four did not. • Stressed animals that did not vocalize performed poorly in spatial learning, requiring a longer time to find the hidden platform. • However, high vocalizers had exceptional scores, showing their resilience to stress. • This verifies the high caller’s brain needs to be looked at more closely to find better pharmalogical treatments. Depression is among the top five leading cause of disability and disease burden throughout the world 1. Untreated depression is the leading cause of suicide, which validates ongoing research to better understand the disorder2. Of the 121 million suffering world wide from depression2, 30% have a treatment-resistant form of the illness6. New preclinical research needs to discover alternative pharmacotherapy to help those people. The historical focus is on the depression-vulnerable group, but focusing on the more resilient population of depression is a better approach.. Understanding the neurochemical correlates of resilience may lead to novel insight into the development of new pharmalogical treatments. Human depressed patients suffer from spatial learning and memory deficits, which are associated with the hippocampus7. In previous studies, high stress levels translated to enhanced hippocampal cell loss and spatial memory deficits2. Consequently, those who are vulnerable to depression may undergo hippocampal change greater than a resilient subject. There are many animal models of depression. The exteroceptive model is more representative of the human condition, in not assuming pathology. Increasing evidence has shown that fundamental mechanisms of neuronal change are disrupted in animal models of stress, supporting the symptomology of stress3. The Intermittent swim stress model of depression has been shown to be a ecologically relevant stressor3. The stress has been observed to cause depression-like deficits in behavior. During the ISS, some rats have been observed to emit ultrasonic vocalizations 4. In a preliminary report using ISS-induced USV’s of rats predicted whether they would be resilient or vulnerable, based on their learning in a subsequent swim escape task 4. This study extended previous research that concluded ISS-induced USV’s forecast resilience in instrumental learning. The aim of the current study wass to investigate if ISS induced USV’s predict good performance in a subsequent spatial learning and memory task. If High USV’s during the ISS procedure predict or forecasts resilience, then we would expect high USV calling rats to perform better in the Morris Water maze than the rats who do not call. Procedure Day 1– Stress Exposure • Rats were randomly assigned to one of three groups: ISS (n=10) or confined control (n=10) • ISS rats were exposed to 80 trials. Confined controls were placed in the stress apparatus for the same 80 trials, but without water. • USV’s were recorded during the ISS with a ultrasonic microphone and the Labview data collecting program, which allowed frequency and duration of calls to be recorded. • Day 2—Spatial Learning • Twenty-four hours after ISS, all rats were trained in the Morris water maze in pairs by the experimenter blind to group membership. • Rats underwent 18 learning trials presented in 9 blocks of two trials each. • Rats were placed in different cardinal directions (N, S, E, W) for each trial and latency to find a hidden platform was recorded. If the rat failed to find the platform in 60 seconds the animal was guided to the platform. Every rat was left on the platform for 10 seconds at the conclusion of each trial. Figure 1: A line graph showing no significant difference between the spatial learning scores the Control (non stressed) and ISS group (stressed). 2 trial blocks were plotted on the x-axis and time to find platform in seconds was plotted on the y-axis. References 1.Caspi, A., Sugden ,K., Moffitt T., Taylor A., et al (2003) Influence of life Stress on Depression: Moderation by Polymorphism in the 5-HTT Gene. Science 301, 386-392 2.Castro J. E., Diessler, J., Varea E., Márquez, C., Larson, M.H., (2011).Personality traits in rats predict vulnerability and resilience to developing stress-induced depression-like behaviors, HPA axis hyper-reactivity and brain changes in pERK1/2 activity. Psychoneuroendocrinology, vol. 37, num. 8, p. 1209-23, 2012. 3.Christianson, J.P., Drugan, R.C. (2005). Intermittent cold water swim stress increases immobility and interferes with escape performance in rat. Behavioural Brain Research, 165,58-62 4.Drugan, R.C., Christianson, J.P., Stine,W.W., Soucy,D,P.(2009) Swim stress induced ultrasonic vocalizations forecast resilience in rats, Behavioural Brain Research, 202, 142-145 5. Drugan,R.C., Skolnick, P, Paul.S., Crawley,J.N. (1989) A pretest procedure reliably predicts performance in two animal models of inescapable stress. Pharmacology Biochemistry and Behavior 33(3) 649-654 6. Krishnan, V. and Nestler, E.J., (2010)Linking Molecules to Mood: New Insight Into the Biology of Depression. American Journal of Psychiatry;167:1305-1320 Materials Apparatuses Figure 2: A scatter plot characterizing the USVs of the rats in the ISS. Plotted are the number of USVs on the x-aixs and average duration of vocalizations on the y-axis, in ms, for each individual. Animals 20 male Sprague-Dawley rats (CD Derived, Charles River Labs, NY), each weighing 180-200 grams on arrival. Animals were housed for at least 6 days before experimentation four to a cage with free access to food and water. Following day 1 of procedures animals were individually housed with food and water ad lib. ISS Apparatus ISS treatments were administered in Plexiglas cylinders (21 X 42 cm – DIA. X H.) with 0.64cm wire mesh on the bottom, suspended over a tank of 15°Cwater. On a swim trial, the cylinders were lowered into the water to a depth of 20 cm. Space heaters blew warm air ( 36°C) into the cylinders during inter-trial-intervals. The swim stress apparatus was controlled by a computer with Med-PC hardware and software (Med-Associates, VT). The ultrasonic vocalizations were recorded with a microphone and data was collected with the program Labview. Morris Water Maze (MWM) Apparatus Spatial learning tests were conducted in a circular pool (122 cm in diameter) filled with water to a depth of approximately 51 cm. Water was made opaque with approximately 200 ml of white nontoxic liquid tempera paint. The water temperature was maintained at 24°C (+/- 1°C). The hidden platform was painted white and constructed out of PVC pipe and clear Plexiglas, with a diameter of 10 cm and a height of approximately 50 cm. On each wall of the room different distinct symbols were placed for orientation during procedures on day 2. Some learning trials and all memory probes were recoded using video camera from above, an HVS image tracking system and computer analyzed the data. ~Thank you Robert Drugan, Nate Stafford, and Tim Warner for all of your patience and guidance in the lab. ~Funding was provided from Mr. Dana Hamel through the Hamel Center’s URA. ~ All behavioral procedures were reviewed and approved by the UNH institutional Animal Care and Use committee (IACUC). Acknowledgements ISS apparatus (Above Left) Stress animals are lowered into water by the cylinders, confined are lowered without water. All other conditions remain identical. Morris Water Maze (MWM) (Top Right) Picture of rat on hidden platform. Diagram of MWM During A Hypothetical Learning Trial (Lower Right) Animals are placed at the outside of the pool at different cardinal directions (N, S, E, W). Animal search for a hidden platform during learning trials or are left to swim freely for 60 seconds during the memory probe test. Figure 3: A line graph showing rats who vocalized during the ISS had significantly better scores than the rats who did not emit vocalizations. Plotted are the 2 trial intervals on the x-axis and mean time to locate platform on the y-axis.