Paradoxical kinesia refers to a sudden transient ability of akinetic patients to perform motor tasks they are otherwise unable to perform. The mechanisms underlying this phenomenon are unknown due a paucity of valid animal models that faithfully reproduce paradoxical kinesia. Here, in a first experiment, we present a new method to study paradoxical kinesia by "awakening" cataleptic rats through presenting appetitive 50-kHz ultrasonic vocalizations (USV), which are typical for social situations with positive valence, like juvenile play or sexual encounters ("rat laughter"). Rats received systemic haloperidol to induce catalepsy, which was assessed by means of the bar test. During that test, 50-kHz USV, time- and amplitude-matched white noise (NOISE), or background noise (BACKGROUND) were played back and compared to SILENCE. Every animal was exposed to all four acoustic stimuli in random order, with four independent groups of rats being tested. Only when exposed to playback of appetitive 50-kHz USV, the otherwise akinetic rats rapidly started to move efficiently. The acoustic control stimuli, in contrast, did not release rats from catalepsy, despite eliciting the auditory pinna reflex and head movements towards the sound source. Moreover, in a second experiment, playback of aversive 22-kHz USV and relevant acoustic control stimuli did also not significantly affect catalepsy time. Together, our animal model provides a completely new approach to study mechanisms of paradoxical kinesia, which might help to improve behavioral therapies for Parkinson's disease and other disorders, where akinetic or cataleptic states occur.
The long-term effects of comfort food in an anxiogenic model of stress have yet to be analyzed. Here, we evaluated behavioral, endocrine and metabolic parameters in rats submitted or not to chronic unpredictable mild stress (CUMS), with access to commercial chow alone or to commercial chow and comfort food. Stress did not alter the preference for comfort food but decreased food intake. In the elevated plus-maze (EPM) test, stressed rats were less likely to enter/remain in the open arms, as well as being more likely to enter/remain in the closed arms, than were control rats, both conditions being more pronounced in the rats given access to comfort food. In the open field test, stress decreased the time spent in the centre, independent of diet; neither stress nor diet affected the number of crossing, rearing or grooming episodes. The stress-induced increase in serum corticosterone was attenuated in rats given access to comfort food. Serum concentration of triglycerides were unaffected by stress or diet, although access to comfort food increased total cholesterol and glucose. It is concluded that CUMS has an anorexigenic effect. Chronic stress and comfort food ingestion induced an anxiogenic profile although comfort food attenuated the endocrine stress response. The present data indicate that the combination of stress and access to comfort food, common aspects of modern life, may constitute a link among stress, feeding behavior and anxiety.
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