Ipsilateral motor control of the forelimb in the congenitally acallosal mouse.

The corticospinal projections of mice with callosal agenesis were investigated using electro-physiological and horseradish peroxidase techniques. In the normal mouse, intracortical stimulation of the motor area with the microelectrode resulted in contralateral contraction of the forelimb, whereas ipsilateral contraction was observed in the acallosal mouse. Hence, mice with congenital absence of the corpus callosum show physiologically ipsilateral motor control. Furthermore, latency of the forelimb contraction elicited by electrical stimulation of the acallosal mouse was slightly shorter than that of the normal mouse. On the other hand, it was confirmed by a horseradish peroxidase technique that the corticospinal tract and peripheral motor neurons in the spinal cord of the acallosal mouse were identical to those of the normal mouse.