Behavioral assessment of visual deficits in the taiep mutant.

Taiep (tremor, ataxia, immobility, epilepsy, paralysis) mutants show a significant increase in myelin thickness from 10 to 30 days of age but then demonstrate a decrease in myelin thickness from 1 to 6 months. The severity of the demyelination in the optic nerve suggests that visual deficits may exist in the taiep mutants. Animals were trained on a discrimination task, in which responses to a light stimulus (the SD period) were reinforced on a fixed ratio (FR)-1 schedule, and responses in the absence of the light stimulus (the SΔ period) were not reinforced. Following training, the light intensity presented during the SD period was gradually reduced between sessions until -6.0 candela/m2 was reached. Both groups of animals - taiep mutants and control Sprague Dawley rats - successfully recognized and responded in the presence of the stimulus near perfectly by the final day of training, suggesting that taiep mutants demonstrated normal learning, at least under this paradigm. Despite the severe demyelination of the taiep optic nerve, no visual deficits were detected as both groups of animals performed similarly as the light intensity decreased. Though the myelin loss of the optic nerve may have negatively affected signal transduction, this did not result in an increase in visual threshold.

Non-contingent positive and negative reinforcement schedules of superstitious behaviors.

The role of schedules of reinforcement on the development of superstitious conditioning was investigated in a college age population. Participants were randomly assigned to one of eight operant schedules and instructed to remove (escape), prevent and/or remove (avoidance and escape) or produce (positive) the appearance of a computer generated stimulus using a response pad. Results from the experiment indicate that concomitant (escape and avoidance) schedules of reinforcement are most effective in facilitating acquisition of superstitious behavior as measured by self-reports of participants.

Behavioral effects of chronic melatonin and pregnenolone injections in a myelin mutant rat (taiep).

The taiep (tremor, ataxia, immobility, epilepsy, and paralysis) myelin mutant displays a number of locomotor deficits. Taiep rat gait is characterized by shorter stride and step lengths as well as by larger stride widths. Thirty-day-old taiep mutants were placed under a regimen of daily hormone injections for 60 days. Animals in Condition 1 received melatonin, those in Condition 2 received pregnenolone sulfate, and those in a third control condition received injections of saline. Following the injections, each taiep mutant's gait was analyzed. The animals that received melatonin and pregnenolone displayed significantly larger stride and step lengths than did the controls. In addition, the animals that received hormones displayed shorter stride widths than did the controls. These experimental effects are consistent with a normalization of gait. Possible cellular mechanisms of this behavioral effect are discussed.

Role of US in the detection, characterization, and staging of cholangiocarcinoma.

Cholangiocarcinoma is a rare tumor with a broad range of pathologic and clinical manifestations that demonstrates a myriad of imaging findings. Recent experience indicates that a more definitive role is possible for ultrasonography (US) in the evaluation of cholangiocarcinoma. Dilatation of the intrahepatic bile ducts is the most frequently seen US abnormality in patients with ductal cholangiocarcinoma. Klatskin tumors classically manifest as segmental dilatation and nonunion of the right and left ducts at the porta hepatis. Papillary and nodular ductal cholangiocarcinoma are relatively easy to see at US: Papillary tumors resemble polypoid intraluminal masses, whereas nodular cholangiocarcinoma manifests as a discrete smooth mass with associated mural thickening. Infiltrating ductal cholangiocarcinoma at the porta hepatis is the most common subtype but is the most difficult to appreciate at US. Peripheral cholangiocarcinoma may be either nodular or infiltrating at US: The nodular form predominates and appears as a solitary mass with a distinct right lobe predilection, whereas the infiltrative form is rare and manifests as a diffusely abnormal liver echotexture. In capable hands, modern high-resolution US equipment with color Doppler imaging capability is highly sensitive in the detection, characterization, and determination of the potential for resectability of cholangiocarcinoma. Thus, use of US may obviate more invasive procedures in some patients and help identify those patients for whom further investigation would be contributory.