Elsevier

Behavioural Brain Research

Volume 214, Issue 2, 25 December 2010, Pages 402-408
Behavioural Brain Research

Research report
Brief light as a practical aversive stimulus for the albino rat

https://doi.org/10.1016/j.bbr.2010.06.020Get rights and content

Abstract

Bright light was an effective aversive stimulus for Wistar rats in punishment, escape, and avoidance paradigms. Contingent punishment of lever pressing maintained by concurrent schedules of food delivery shifted presses to an alternate lever, and depressed overall response rates. Periodic non-contingent presentation of the light prompted escape responding (head entry into a hole). Unsignaled avoidance contingencies were not effective, but pre-pulse signaling of light supported avoidance behavior. These results demonstrate a possible alternative to foot-shock, one with greater ecological validity, and one that might avoid some of the physiological effects that accompany electric shock.

Introduction

Electric footshock has served as the prototypical aversive stimulus in experimental preparations using rats [34], [30]. Footshock is popular for its reliability, utility at a wide range of current, and the feasibility of titrating shock levels for individual subjects. But electric shock has its downsides: It often induces secondary effects such as long-term sleep disruption [41], altered social behavior [27], reduction in locomotion, rearing, and grooming behaviors, as well as an increase in immobility and defecation [44]. Footshock has also received criticism when used to model conditions such as depression or anxiety disorder that are produced by stressors that lack a comparable component of pain [28]. Finally, the nature of footshock stimulation precludes its full inclusion in some modern experimental techniques, such as electrophysiology.

As neural, behavioral, and genetic research strives to create better animal models of human disorders, the availability of options other than footshock as aversive stimuli becomes increasingly important. Reed and Yoshino [39] recently noted the utility of a broader range of aversive stimuli, including some that might replace shock and avoid some of the drawbacks that accompany its use. For instance, they demonstrated that response suppression could be effected by a loud, short tone presented with long inter-trial intervals.

The present study aims to systematically test whether bright light is an effective aversive stimulus for rats. Early experiments demonstrated that rats will press a lever to terminate a light stimulus, and that rate of lever pressing increases with light intensity [19]. The rate of escape lever presses is also sensitive to the schedule of negative reinforcement [16], [17], [18]. When allowed to control their own daily exposure to light by lever pressing, albino rats decrease their exposure to light intensities greater than 1.25 lux over days, and maintain their exposure to light below this threshold [22], [23], [24], [25]. Further examination led Campbell and Messing [6] to suggest that light is likely aversive even at the lowest levels of illumination in rats. However, a considerable number of studies have proposed that light – at some levels – may not be aversive [36], and might even act as a reinforcer [2], [14], [40].

The following experiments provide a systematic test of light's efficacy as an aversive stimulus. Experiment 1 examined the aversiveness of bright light in a choice situation by adding a light contingency onto one of two otherwise identical alternatives. Experiments 2 and 3 examined escape from and avoidance of light, respectively. It has long been suggested that defensive responses are more efficiently learned when they are consistent with the natural repertoire of the animal [4]. Burrowing is a commonly observed defensive behavior in Rattus norvegicus [3], [20], [33], [35]. It was thus expected that entering a short tunnel would be an effective escape/avoidance response to light.

Section snippets

Experiment 1: punishment

It has been shown that rats prefer dark or dim areas over those that are brightly lit, in both Pavlovian (e.g. [42]) and operant paradigms (e.g. [22], [23], [24], [25]). However, lights have also been used as effective reinforcers during operant conditioning [2], [27], [14]. Experiment 1 aimed to determine whether a brief bright light serves as a punisher. If it does, making the light contingent on pressing one of two levers for food should reduce preference for that lever.

Experiment 2: escape/avoidance

Experiment 2 examined escape responses of albino rats using the operant burrow apparatus. The rates of head entries into the burrow were examined when a bright light was presented at various rates and durations, with entry terminating the light, and also when burrowing did not terminate the light. Given that each successful escape response produced an extended ITI, the present experiment also has a Sidman avoidance component.

Experiment 3: escape and avoidance

The escape paradigm used in Experiment 2 was replicated, with additional measures taken to eliminate temperature as a factor. The ability of bright light to support an avoidance response was then tested using the burrow apparatus.

General discussion

Our results demonstrate that light may bring behavior under aversive control within three paradigms: punishment, escape, and signaled avoidance. When rats had a choice between food and food plus light (Experiment 1), they displayed an unambiguous preference for food alone. When light was presented non-contingently (Experiments 2 and 3), rats escaped to an artificial burrow; this response was rarely emitted in the dark. Changes in the frequency (Experiment 1) and duration (Experiments 2 and 3)

Acknowledgments

This work was supported by NIDA-R01 DA006886 to Mark West (David J. Barker), Arizona State University-College of Liberal Arts and Sciences (Federico Sanabria), and NIMH-R01MH066860 (Peter Killeen). We thank Natalie Cole, Liliana Oldenburg, and Lara Olson for data collection.

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