Learned helplessness: Validity and reliability of depressive-like states in mice
Section snippets
Type of research
- (1)
The protocol described here allows murine studies of molecular, neurochemical, stress-physiological, and behavioral consequences of the learned helplessness paradigm, a behavioral model of depression.
- (2)
A detailed characterization of this model, defining a time course of coping deficits (helplessness) and employing clearly structured definitions of helpless behavior, also evaluated by pharmacological treatment, supplies good validity and reliability of this model.
- (3)
As a result, this protocol can be
Time required
The course of the learned helplessness paradigm starts with an inescapable shock procedure on two consecutive days, each of these shock sessions lasting approximately 52 min. Learned helplessness is assessed 24 h after the second shock procedure and lasts up to 24 min, depending on the animals' performance in the shuttle box. More then 80% of helpless animals remain helpless for at least 1 week (Fig. 1).
Special equipment
The shock procedure was applied in a transparent plexiglas shock chamber (18 × 18 × 30 cm3), equipped with a stainless steel grid floor (diameter of each grid: 0.5 cm, spacing: 0.6 cm) (Coulborn precision regulated animal shocker, Coulborn Instruments, Düsseldorf, Germany).
The two-way avoidance test was conducted in a two-compartment shuttle box (Coulborn Instruments, Düsseldorf, Germany), equipped with infrared-light beams at the bottom of each of the two compartments to monitor spontaneous
Animals
10-week-old male C57BL/6N mice were purchased from Charles River, Sulzfeld, Germany, and acclimatized to single housing in macrolon cages (type II) at constant conditions with a 12 h dark–light cycle and an average room temperature of 22 °C for 2 weeks prior to the experiments, with food and water ad libitum. All experiments were approved by German animal welfare authorities (Regierungspräsidium Karlsruhe).
Inescapable shock procedure
- (1)
Mice were exposed to inescapable shocks during their active (dark) phase. Animals had to
Definition of helplessness
Cluster analysis (Fig. 2) is a group of exploratory data analysis tools, which aim at sorting different objects into groups in a way that the degree of association between two objects is maximal if they belong to the same group and minimal otherwise. Thus, cluster analysis can be used to discover structures in data without providing an explanation or interpretation. Among the different clustering algorithms available, we used the k-means procedure, because it allows the a priori specification
Setup of the protocol
In order to establish a valid and reliable mouse model of depression as it has been described in rats [25], we designed a learned helplessness procedure, in which two series of unpredictable and uncontrollable footshocks applied over 2 days under dark conditions evoke helpless performance in a shuttle box, while controllable shock “immunizes” against helplessness. This is in line with most rodent depression models that use stress as a tool to induce depression-like symptoms.
Time course
Supporting the face
Quick procedure
- (a)
Expose the mice to 360 scrambled footshocks (intensity: 0.150 mA) on two consecutive days.
- (b)
24 h later, perform a two-way avoidance paradigm (30 shuttle escape trials) in a shuttle box.
- (c)
Analyze the data by considering “failures” and “escape latency” as the most relevant parameters for the identification of helpless animals.
Alternative protocols
Training procedures reported previously, based on the paradigm by Shanks and Anisman (1988) and Caldarone et al. (2000) may represent alternative protocols [2], [21]. In these protocols, learned helplessness is induced by administering 120 inescapable 4 s footshocks (0.30 mA) with a random interval (range 3–50 s) over a 1 h session. Training is given in two sessions that are spaced approximately 24 h apart. Mice are placed on either side of the shock chamber, so that the shock is administered
Essential literature references
[2], [4], [5], [6], [10], [12], [13], [16], [20], [22], [25], [27]
Acknowledgments
This work was supported by grants from the Deutsche Forschungsgemeinschaft to P.G. (GA427/4-2, SFB636/B3). S.C. had a scholarship from the GK 791, University of Heidelberg.
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