Animal model of post-traumatic stress disorder (PTSD): Effects of propranolol on exploration in an elevated plus maze in ratsG.H. Gotthard, J. Marini, S. Mangel, J. Block, D. Tate, C. Hackmyer, and C. Burgdorf

Muhlenberg CollegeAllentown, PA 18104

Introduction

PTSD is an anxiety disorder that is caused by exposure to a traumatic, often life-threatening, event. One relatively new line of research is employing β-blockers (drugs that lower adrenaline) to weaken traumatic memories. In a limited number of studies, β-blockers were given to human participants shortly after a traumatic event to prevent PTSD from forming (Pitman et al., 2001; Vaiva et al., 2003). In these studies, when β-blockers were given shortly after trauma, the development of PTSD was significantly less than with a placebo.

While preliminary research into the use of β-blockers for PTSD prevention is encouraging, there is still a considerable amount of work that needs to be done before these treatments can be safely used with PTSD patients. And because many of the manipulations that need to be carried out cannot ethically be done with human participants, an animal model of PTSD would be a valuable tool.

A limited number of animal models of PTSD exist in the literature, and none use a full sensory experience (Cohen et al., 2006; Do Monte et al., 2008). Both use predator threat as the traumatic event, but with limited sensory modalities. The proposed study aimed to more carefully quantify the feared stimulus as a full sensory experience, so that it could be consistent from one exposure to the next. In the present study, rats were exposed to a dog followed by a test for anxiety reactions on an elevated plus maze. After the plus maze test, rats received an injection of propranolol (β-blocker) or vehicle (distilled water). One week later, rats were tested again on the elevated plus maze to examine long-term effects of predator exposure and to examine the effects of propranolol on attenuating that anxiety reaction. One month after predator exposure, rats were trained on the sand maze (an appetitive spatial task) to examine the long-term fear-attenuating effects of propranolol.

Method

SubjectsNinety-day old, naïve, male Long-Evans rats (N=20) were used in the present study. Water and food was available ad libitum. Animals were kept on a 12 hour light/dark cycle, with the lights coming on at 7:00 a.m. All procedures employed in the present study were approved by the IACUC at Muhlenberg College prior to experimentation.

ApparatusPredator and room exposures were carried out in a Plexiglas cage identical to the rats’ home cages (that was thoroughly cleaned following each rat’s trial). An elevated plus maze (EPM) (Harvard Apparatus) was used to collect dependent measures of exploration. A sand maze apparatus (Gotthard, 2006) was used to collect dependent measures of ability to learn a spatial task.

Discussion

• The animal model of PTSD presented in this study served as an effective means to produce a fear reaction in rats (as evidenced by less exploration on an EPM test following exposure).

• Propranolol presented after predator exposure effectively attenuated fear, which resulted in increased levels of exploration on an EPM test one week following exposure.

• The same fear attenuating effects seen on the EPM test did not carry over to later learning in an appetitive spatial task. This can be seen by shorter latencies to find the buried reward by non-exposed rats, as compared to exposed rats (both propranolol and vehicle).

• Future studies in our lab will further refine this animal model of PTSD. For example, critical control groups, like non-exposed propranolol-injected or vehicle-injected rats, need to be included in future studies using this model to rule out effects of injection and/or propranolol on behavior in general.

References

Cohen, H., Kaplan, Z., Matar, M. A., Loewenthal, U., Kozlovsky, N. & Zohar, J. (2006). Anisomycin, a protein synthesis inhibitor, disrupts traumatic memory consolidation and attenuates posttraumatic stress response in rats. Biological Psychiatry, 60, 767-776.Do Monte, F. H. M., Canteras, N. S., Fernandes, D., Assreuy, J. & Carobrez, A. P. (2008). New perspectives on β-adrenergic mediation of innate and learned fear responses to predator odor. Journal of Neuroscience, 28, 13296 –13302.Gotthard, G.H. (2006). The sand maze. In M.J. Anderson (Ed.), Tasks and techniques: A sampling of the methodologies for the investigation of animal learning, behavior, and cognition (pp. 87-95). New York: Nova Science Publishers.Pitman, R. K., Sanders, K. M., Zusman, R. M., Healy, A. R., Cheema, F., Lasko, N. B., Cahill, L. & Orr, S. P. (2002). Pilot study of secondary prevention of posttraumatic stress disorder with propranolol. Biological Psychiatry, 51, 189-192.Vaiva, G., Ducrocq, F., Jezequel, K., Averland, B., Lestavel, P. Brunet, A. & Marmar, C. R. (2003). Immediate treatment with propranolol decreases posttraumatic stress disorder two months after trauma. Biological Psychiatry, 54, 947-949.Yehuda, R. & LeDoux, J. (2007). Response variation following trauma: A translational neuroscience approach to understanding PTSD. Neuron, 56, 19-32.Zoladz, P. A., Conrad, C. D., Fleshner, M. & Diamond, D. M. (2008). Acute episodes of predator exposure in conjunction with chronic social instability as an animal model of post-traumatic stress disorder. Stress, 11, 259-281. 

Figure 3. Sand Maze Acquisition: The fear attenuating effects of propranolol did not transfer to learning a new task one month after predator exposure. A one-way ANOVA revealed statistically significant differences in latency for location acquisition in the sand maze [Day 1: F(2, 21)=6.325 , p< .01; Day 2: F(2, 21)=9.373 , p< .001; Day 3: F(2,21)=14.477 , p< .001; Day 4: F(2, 21)=16.491 , p< .001]. LSD post hoc analyses showed that propranolol rats did not differ significantly from vehicle rats on latency to find the reward (p>.05), while unexposed controls differed significantly from propranolol and vehicle groups (p< 0.01).

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Figure 2. Plus Maze Exploration: Exposure to a predator resulted in increased fear (as evidenced by decreased exploration in the elevated plus maze, EPM) that was alleviated by post-exposure injections of propranolol . Post-Exposure EPM Test (Test 1): A one-way ANOVA revealed statistically significant differences in exploration between groups [F(2,17)=21.712, p<.0001]. Tukey post hoc analyses indicated that rats exposed to the predator explored less than non-exposed control rats (p<.0001), with no differences between exposed rats that would later receive propranolol or vehicle (p>.05). One-Week EPM Test (Test 2): A one-way ANOVA revealed statistically significant differences in exploration between groups [F(2,17)=8.291, p<.01]. Tukey post hoc analyses showed that exposed propranolol rats explored significantly more than exposed vehicle rats (p<.01), and did not differ significantly from non-exposed control rats (p>.05).

Figure 1. Procedure of exposure, drug injections, and testing

Acknowledgments•Dr. Jeremy Teissere•Muhlenberg College Dean’s Office•Dana Associates•Sentience Foundation•R.J. Fellows

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