Imaging Diagnosis: Thoracic radiographic features of toxoplasmosis in a 14-month-old Red Kangaroo (Macropus rufus).

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.

INTRAOCULAR PRESSURE IN CLINICALLY NORMAL BROOK TROUt (SALVELINUS FONTINALIS) BY MEANS OF REBOUND TONOMETRY.

The purpose of this study was to establish physiologic reference values for intraocular pressure (IOP) in clinically healthy trout (Salvelinus fontinalis). The study population consisted of 15 adult brook trout (14 male, 1 female); body weight ranged from 0.47 to 1.15 kg; length from 33.5 to 45.2 cm; and eye diameter from 11 to 14 mm. Animals were anesthetized, and a preliminary ophthalmic exam was performed. IOP was then measured by rebound tonometer. Three values were obtained for each eye. The animals were subsequently euthanized, and postmortem IOP was measured by the same method. A standard necropsy was performed on each fish to determine sex and to examine it for gross lesions. Premortem results (mm Hg) of measurements in the right eyes (n = 15) were 8.82 ± 2.45 mm Hg (minimum-maximum [min/max], 5-14 mm Hg; median, 8.33 mm Hg), and postmortem results were 6.31 ± 2.31 mm Hg (min/max, 3-11 mm Hg; median, 6 mmHg). Premortem results (mm Hg) of measurements in the left eyes (n = 15) were 9.20 ± 1.91 mm Hg (min/max, 5.33-12.33 mm Hg; median, 10 mm Hg), and postmortem results were and 9.81 ± 2.19mm Hg (min/max, 5-13 mmHg; median, 10.17mm Hg). A Mann-Whitney U-test was performed and revealed no significant difference within an eye under both pre- and postmortem conditions, and no significant difference between eyes between pre- and postmortem conditions. Rebound tonometry is a practical and efficient means of determining IOP in freshly euthanized fish or in anesthetized fish, where it requires minimal anesthetic and restraint time; it could potentially serve as a useful diagnostic tool when evaluating ophthalmic health.

Blocking in autoshaped lever-pressing procedures with rats.

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 (Exps. 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 (Exp. 3) or lever-insertion (Exp. 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 discuss 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.