An Animal Model of a BehavioralIntervention for Depression Daniela D. Pollak, Francisco J. Monje,1 Lee Zuckerman, Christine A. Denny, Michael R. Drew,1 and Eric R. Kandel Neuron,2008 Speaker: Kuo Chung-Hsun(郭忠訓) Advisor: Dr. Hong Chen-Jee (洪成志)
Outline Introduction Materials Methods & Results Conclusion Comment
Fear And Depression • Instinctive and learned fear are essential for survival. • In humans, pathological forms of learned fear are hallmarks of severe psychopathologies such as anxiety disorders, posttraumatic stress disorders, and depression
Learned Fear And Learned Safety • Learned fear- a positive correlation (pairing). • Learned safety - a negatively correlated (unpaired). • Learned safety as the learning and memory resulting from a conditioned inhibition of fear training procedure (Rogan et al.,2005). • The ability to identify events that afford relief from ongoing strain is thought to be crucial for the prevention of chronic stress, a precipitating factor for the development of anxiety disorders and depression (Chan et al., 2001; Davis and Shi, 1999; LeDoux,1993; Rogan et al., 2001).
Hypothesis • Learned safety, as a predictor of a break from continuously imminent, stress-producing danger, may have antidepressant effects
Aim • Antidepressant effects in animal model. • The molecular mechanisms of learned safety.
Materials • Male C57BL6/N mice (10–12 weeks old) • Charles River Laboratories, Willington,MA • Mice were kept in clear plastic cages with ad libitum food and water.
Freezing • Freezing, defined as complete immobility except for breathing, is a common response to sudden fearful situations in many species • CS (cue) – Tone, 350Hz, 72dB, 20s • US (shock) – 0.6mA, 2S
Behavior protocol preCS
Learned Safety Retards Subsequent Fear Conditioning to the Same Stimulus Learned safety + Learned fear 1day naive + Learned fear 1day naive + Learned fear 2day Learned safety + Learned fear 2day
Learned Safety Acts to Induce Antidepressant-like Behaviors No training Learned safety Learned safety No training
Unpredictable Chronic Mild Stress (UCMS) • Brain interleukin-1 mediates chronic stress-induced depression in mice via adrenocortical activation and hippocampal neurogenesis suppression. Mol. Psychiatry, 2007 • The following stimuli were administered each week in a random order for four weeks • 3hrs of 45°cage tilt, two times a week • Shocked cage for 12hrs, once a week • Water deprivation for 14hrs, once a week • Lights on for 9hrs during the dark phase, once a week • Noise in the room for 3hrs, three times a week • Flashing light for 30mins, three times a week
Sucrose Preference Test • Twelve hours after exposure to the last stressor of the UCMS regime • Animals were deprived of food and water and tested for sucrose preference 23 hr later. • Testing was carried out in the home cage in the form of a two bottle choice paradigm (2% sucrose versus water) in the presence of the CS for 1 hr. • Sucrose preference rate was calculated according to the formula: % preference = [(sucrose intake/total intake) × 100%]
Brain-Derived Neurotrophic Factor • Brain-derived neurotrophic factor – BDNF • BDNF is known to be induced by antidepressant treatment in the hippocampus, particularly in the dentate gyrus.(Nibuya et al., 1995; Russo-Neustadt et al., 2004) • BDNF could be responsible for the increase in and survival of hippocampal neurons following antidepressant drug treatment (Duman, 2004a, 2004b)
Learned Safety Leads to IncreasedExpression of BDNF in the DentateGyrus of the Hippocampus • Dentate gyrus BDNF immunohistochemistry in mice sacrificed 4 hr after the last day of behavioral training
BrdU • Bromodeoxyuridine (5-bromo-2-deoxyuridine, BrdU) • BrdU is commonly used in the detection of proliferating cells in living tissues • BrdU can be incorporated into the newly synthesized DNA of replicating cells.
Learned Safety AndNewborn Cellsin the Hippocampal Dentate Gyrus Survival Learned Fear How many cells remain after different behavior protocol? Learned Safety Tone Control BrdU labeled How many cells born after different behavior protocol? Proliferation Learned Fear Learned Safety Tone Control BrdU labeled
Learned Safety Promotes the Survival ofNewborn Cellsin the Hippocampal Dentate Gyrus No data
Genes Differentially Expressed in the BasolateralAmygdala of Learned-Safetyand Learned-Fear Mice • Dopamine 2 receptor • Substance P • Prodynorphin • Preproenkephalin 1
mRNA Expressed in the BasolateralAmygdala Dopamine 2 receptor Substance P
Dopamine 2 Receptor Is Critically Involved in Learned Safety Agonist before the memory recall test Blockade before the memory recall test Blockade Prior to the FST
Substance P IsCritically Involved in Learned Safety Agonist During training on the response to the CS in the memory recall test Blockade During training on the response to the CS in the memory recall test
5-HT1A Receptors Are Not Critically Involved in Learned Safety Blockade before the memory recall test Blockade During training on the response to the CS in the memory recall test
Learned Safety • Behavioral outcomes similar to pharmacological interventions. • Inducecell-biological changes known to result from antidepressant pharmacotherapy but is mediated through different molecular pathways.
Comment • Learned safety is like the protection in clinical • In author’s data, the learned fear is hard to be changed. • Learned fear is like the depression
Ablation of Hippocampal Neurogenesis Inactivates the Antidepressant Effect of the Safety Signal
X-Ray Irraditation • Siemens Stabilopan X-ray • A cumulative 15Gy dose was the minimum necessary to produce a reduction of cell proliferation greater than 85% in thedentate gyrus, which lasted for at leasted two month. • Used x-irradiation of the dentate gyrus to ablate hippocampal neurogenesis in mice. • Verified the absence of newly generated cells by doublecortin immunohistochemistry (a marker for neurons younger than 1 month of age) 6 weeks later.