Rats will approach and contact a lever whose insertion into the chamber signals response-independent food delivery. This “autoshaping” or “sign-tracking” phenomenon has recently attracted considerable attention as a platform for studying individual differences in impulsivity, drug sensitization, and other traits associated with vulnerability to drug addiction. Here we examined two basic stimulus selection phenomena, blocking and overshadowing, in the autoshaped lever-pressing of rats. Blocking and overshadowing were decidedly asymmetrical. Previously reinforced lever-extension conditioned stimuli (CSs) completely blocked conditioning to auditory cues (Experiments 1 and 2), and previously nonreinforced lever-extension CSs overshadowed conditioning to auditory cues. By contrast, conditioning to lever-extension CSs was not blocked by either auditory (Experiment 3) or lever insertion (Experiment 4) cues, and was not overshadowed by auditory cues. Conditioning to a lever insertion cue was somewhat overshadowed by the presence of another lever, especially in terms of food cup behavior displayed after lever withdrawal. We discussed several frameworks in which the apparent immunity of autoshaped lever-pressing to blocking might be understood. Given evidence that different brain systems are engaged when different kinds of cues are paired with food delivery, it is worth considering the possibility that interactions among them in learning and performance may follow different rules. In particular, it is intriguing to speculate that the roles of simple cue-reinforcer contiguity as well as of individual and aggregate reinforcer prediction errors may differ across stimulus classes.

A privately owned 14‐month‐old intact female red kangaroo (Macropus rufus) was presented for acute onset respiratory distress and lethargy. On presentation, the kangaroo was laterally recumbent, tachypneic, dyspneic, lethargic, and obtunded. Thoracic radiographs revealed a severe diffuse mixed pulmonary pattern (alveolar pattern superimposed on a bronchial pattern) and subjective mild generalized cardiomegaly. Due to the severity of clinical signs and grave prognosis, euthanasia was elected. Postmortem examination was consistent with systemic toxoplasmosis. Histopathology and immunohistochemistry staining on infected tissues confirmed Toxoplasma gondii. This is the first published report of radiographic findings for confirmed toxoplasmosis in a red kangaroo or marsupial.

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There are very few studies describing euthanasia complications in non-domestic species. The goal of this study was to survey veterinarians to determine what complications may commonly occur during the euthanasia of non-domestic species. An online survey was sent to seven professional organization listservs containing veterinarians most likely to practice on non-domestic species. Forty-one cases of euthanasia complications were reported. The most common taxa reported were mammals, (23/41, 56%), followed by avian (8/41, 20%), reptile (7/41, 17%), and fish (3/41, 7%). Most animals were reported to have been anesthetized prior to euthanasia (28/41, 68%). The most common method of euthanasia was pentobarbital (27/41, 66%). The reported euthanasia complications included “took an excessive amount of euthanasia solution” (12/41, 29%), “heart would not stop” (9/41, 22%), “animal awoke at a later time” (4/41, 10%), “a secondary method of euthanasia was required” (4/41, 10%), and “other” (12/41, 29%). This study reports complications that can occur during the euthanasia of non-domestic species. The concept of dysthanasia, a euthanasia with an undesirable outcome, has not been previously discussed in the context of zoo, wildlife, aquarium, and exotic pet practice. Strategies to reduce dysthanasia from both animal and human perspectives are explored, including alternative euthanasia techniques, principal-based euthanasia, and mental health implications.