title: Quantitive studies of the reactions to horizontal angular accelerations in axolotls. II. head-turning reflexes in animals with a supernumerary pair of labyrinths.
abstract: In axolotls (Ambystoma mexicanun) the labyrinths and the associated parts of the medulla were doubled artificially. In these so-called tandem-heads the vestibular afferent fibres from both labyrinths on one side united within the medulla to form common bundles. The head-turning reflexes following impulse acceleration and during long-lasting acceleration were measured quantitatively and compared with those for normal animals. The form and the time-course of the reactions were almost identical in both groups. Tandem-heads showed a linear relationship between stimulus intensity and reaction strength, parallel to that in normal animals but with a greater reaction for a given stimulus. Consequent to this shift in the relationship, there was a significant decrease in the reaction threshold. The removal of one horizontal semicircular canal in tandem-heads proved that both pairs of labyrinths were functionally connected with the brain. It was suggested that during ontogenesis there exists a kind of specificity in the connexion of vestibular fibres. From the parallel shift of the intensity functions it was concluded that the input from both pairs of labyrinths in tandem-heads is not simply accumulate but compared with a reference parameter, which is also double in tandem-heads.
mesh_terms: D000557:Ambystoma / Q000196:embryology / Q000502:physiology*; D000818:Animals; D007758:Ear, Inner / Q000033:anatomy & histology / Q000294:innervation* / Q000502:physiology; D006257:Head / Q000502:physiology; D008526:Medulla Oblongata / Q000166:cytology; D009038:Motion; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology; D010507:Periodicity; D012018:Reflex; D012399:Rotation; D012621:Seasons; D012665:Semicircular Canals / Q000502:physiology*; D014722:Vestibule, Labyrinth / Q000294:innervation