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An investigation into the physical basis of the pirouette mutation in the house mouse (Mus musculus) Walden, Adelene Mary

Abstract

The object of this investigation was to study the abnormal behavior produced by the pirouette mutation in the house mouse (Mus musculus) and to determine its physical basis. The pirouette mutation first appeared in 1943 and was described by Wolley and Dickie (1945) who gave it the genetic symbol pi. This recessive mutation is located on the third chromosome of the house mouse. Mice homozygous for this mutation show mixed circling, head shaking and deafness. The abnormal movements commence fourteen days after birth and these mice are evidently deaf throughout their entire lives. Similar abnormal movements and deafness have been produced not only by other mutations in mice but also in other animals including man. A survey of the literature revealed many possible sources of abnormalities which could produce the atypical behavior of the pirouette mouse and these reported sources of abnormalities were investigated with the following results: 1. Muscles of the head, neck and thorax were normal. 2. Liver gross and histological anatomy was normal. 3. Brain gross anatomy was normal. 4. Skull - gross anatomy was normal. 5. Eighth nerve - gross and histological study revealed no tumors. 6. Ear - gross anatomy and blood supply normal. - histological studies showed degenerative changes within the spiral ganglion, stria vascularis and organ of Corti within the cochlea. The degenerative changes within the cochlea of pirouette mice are similar to those reported in waltzing and shaker-1 mice but their time of onset and sequence of degenerative changes are different. In the pirouette mouse the extensive loss of nerve cells within the spiral ganglion later followed by degenerative changes in the stria vascularis and in the organ of Corti suggests that the cause of these changes lies outside the cochlea. The fact that the degenerative changes of all structures are found first and most extensively in the basal whirl and later in the middle and upper whirls of the cochlea also supports the contention that the change is external to the cochlea and gradually involves the whole organ. Similar changes are known to be produced by tumors, osseous compression or severing of the eighth nerve or lesions within the brain. Since in the pirouette mouse no tumors were present and since the nerve was intact, there remains only the possibility, of osseous compression or lesions within the central nervous system causing this abnormality.

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