The anomalies oe the labyrinth of the mutants varitint-waddler, shaker-2 and jerker in the mouse

Summary

• 1. The genesVa, sh-2 anclje have fundamentally the same effect on behaviour, growth rate and the labyrinth in the mouse.

• 2. They all produce deafness, shaking movements of the head and a tendency to run in circles in the affected animal.

• 3. They have no significant effect on birth weight, but retard growth somewhat in the first 4 weeks of life.

• 4. In the cochlea of affected mice the first organ to show abnormality is the tectorial membrane. It does not thin out to normal dimensions till about the end of the 2nd week.

• 5. It is followed by degeneration of the spiral ganglion and the hair cells and dedifferentiation of the organ of Corti during the 2nd week. This degeneration is progressive.

• 6. The stria vascularis degenerates in the 3rd week.

• 7. The development of the anomaly in the pars superior is not quite the same in all the three mutants. InVa/+ mice the cristae ampullares are severely affected and the maculae only slightly; inVa/Va mice all the five sense organs are severely affected; in shakers-2 and jerkers the maculae are affected even at the time of birth, while the cristae are apparently normal throughout. The anomaly, however, always consists in a progressive degeneration of the neuro-epithelial cells.

• 8. The average cell size in the vestibular ganglion is considerably reduced inVa/+ andVa/Va mice and only slightly in shakers-2, while in jerkers it is unaffected.

• 9. As in waltzer and skaker-1 the degeneration sets in in an organ which is fully differentiated. However, various minor anomalies, present before the degenerative changes set in, suggest that the labyrinthine sense organs may not be quite sound from the very beginning. The group differs fundamentally from the mutants shaker-short, kreisler, dreher and fidget, in which gross defects of morphogenesis become apparent early in development.

• 10. The deafness of these mice is fully explained by the cochlear degeneration; but nothing so certain can be said of their behaviour. The shaking of the head may be due to loss of tone in the neck muscles resulting from the defects of the utricular macula and the ampullary cristae or it may be central in origin.

• 11. The interpretation suggested by Griineberget al. (1940) in the case of shaker-1 cannot be valid for the mutants dealt with here for a variety of reasons. It is suggested that these mutants represent cases of ‘abiotrophy’, i.e. a breakdown of tissue due to unidentified biochemical causes.