Severing the corpus callosum in rats using ultrasound: Theoretical and experimental correlations

Abstract

A single, focused, ultrasound beam of 3.5 W total acoustic output for 2 s at 3.3 MHz was used to create a series of overlapping lesions to sever the corpus callosum of the rat on the midline. A theoretical and experimental determination of the ultrasound field is described and histological evidence of the lesions is provided. Good correlation occurred between the theoretical and experimental results only for the intensity contour lines examined. The experimentally derived focal intensity of 162 W cm−2 (at 25 °C) was 24% of the intensity predicted from theoretical calculations. A difference of 2 mm was found for the axial position of maximal intensity, thermocouple plotting showing the focal region to be nearer the transducer than expected from the theory. Histological results indicated that, under certain conditions, from a single dose of ultrasound two lesions could be obtained corresponding to both the theoretically and experimentally derived locations. At lower intensities it was possible to ulitize the upper location to sever the corpus callosum, the lower intensity site then being subthreshold for the rat brain. The trackless localized damage caused by ultrasound makes this method of obtaining split-brain rats suitable for behavioral and biochemical studies, where any nonspecific damage may have undesirable effects.