Abstract
The present study aims to evaluate in rats the activity changes associated to treatments with D2-like receptor agonists using a simple behavioral procedure. Rats receiving a single dose of 1 mg/kg quinpirole or vehicle were scored for 6 spontaneous behaviors at different post-injection times. In each time point, the animals were placed in testing cages for 12 min and video-recorded during the last 2 min. The number of forelimb steps and the time spent sniffing were significantly increased by 15 min post-injection in the quinpirole group. Forelimb steps remained increased for at least 24 h. Scores of time spent sniffing, as well as time inactive and number of hindlimb steps appeared greatly altered at 90 and 180 min, but not at later time points. By 48 h, no differences between control and quinpirole-treated rats were observed. In conclusion, the simple behavioral procedure here proposed—or adaptations of it—provides a sensitive test to evaluate the time course of the effects of D2-like receptor agonists on rat spontaneous activity. Additionally, this test takes into account context-dependent sensitization. It can be adapted to different treatment conditions. This methodology would be useful for the preclinical screening of D2-like receptor drugs, using reduced numbers of animals to test those doses and treatment schedules producing less side-effects.
Highlights
Dopaminergic drugs produce complex patterns of behavioral effects as a result of the diversity of nervous structures receiving dopamine input, the duality of dopamine receptors with opposed action and the existence of bothHow to cite this paper: Paíno, C.L. (2014) Evaluation of Activity Patterns in Quinpirole-Treated Rats
Based on previous observations of quinpirole-treated rats, six behaviors that appeared altered after drug administration were quantified as follows: Sniffing: Time spent by the animal in active smelling, as evidenced by periods of rapid movements of nose and whiskers; Grooming: Time spent by the animal in self-care activities, which include rubbing, licking, scratching or biting parts of its own body for cleaning; Inactive: Total time during which the animal is not involved in any salient activity or movement but only in resting or basal activity
Its eyes may be open or closed but the rat does not move the head or the ears in orienting responses nor is sniffing; Rearing: N umber of t imes t hat t he a nimal r aises both f orelimbs f rom the f loor, keeping t hem i n t he a ir o r standing against a wall, but not using them for other activity like grooming; Forelimb stepping: Number of times that the animal r aises the r ight hand from the f loor, whether for body displacement or not, except when done for grooming; Hindlimb stepping: Number of times that the animal raises the right foot from the floor, whether for body displacement or not, except when done for grooming
Summary
Dopaminergic drugs produce complex patterns of behavioral effects as a result of the diversity of nervous structures receiving dopamine input, the duality of dopamine receptors with opposed action and the existence of bothHow to cite this paper: Paíno, C.L. (2014) Evaluation of Activity Patterns in Quinpirole-Treated Rats. Paíno presynaptic (which regulate dopamine synthesis and release [1]) and postsynaptic receptors with different affinity [2]. Phenomena such as desensitization [3] or sensitization [4] [5] of dopamine receptors add additional uncertainty on the outcome of a given treatment. Even in controlled experimental conditions, a given dose of a dopaminergic drug may elicit biphasic patterns of behavioral activity [6] [7], different doses may produce opposite responses, and the effect of chronic treatments may differ from the effect of acute drug administration [8] [9]
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