Complex sentence: Dextromethorphan has been shown to cause vacuolization, also known as Olney's lesions, in rats, however oral administration of dextromethorphan did not cause vacuolization in laboratory tests.
Split into simpler sentences: Dextromethorphan has been shown to cause vacuolization in animals, also known as Olney's lesions. In rats, however oral administration of dextromethorphan did not cause vacuolization in laboratory tests.