Origin of acoustic–vestibular ganglionic neuroblasts in chick embryos and their sensory connections

Origin of Neuroblasts in the Avian Otic Placode and Their Distributions in the Acoustic and Vestibular Ganglia

“…Quail–chick grafts were performed by replacing a specific portion of the chicken otic placode at the stage HH10 (10-somate stage [ 60 ]), long after the extensive cell movements that occur during the earlier stages of otic placode formation had finished [ 1 ], as confirmed in our previous fate map [ 5 ]. Unilateral homotopic and isochronic transplants were carried out based on our previous fate mapping study [ 5 , 48 ]. Six types of grafting experiment were performed, containing the expanded sensory area of the macula utriculi (type-1 graft; n = 9), of the macula sacculi (type-2 graft; n = 9), of the basilar papilla (type-3 graft; n = 8), of the macula lagena plus the macula neglecta (type-4 graft; n = 8), of the anterior crista plus the lateral crista (type-5 graft; n = 7), and of the posterior crista (type-6 graft; n = 6).…”

“…Interestingly, several studies have shown that otic neurogenesis could also occur within the auditory organ [ 44 , 45 , 46 , 47 ]. As a final consequence, the axonal innervation of the developing sensory patches is carried out by these placodal-derived ganglionic neurons [ 48 ].…”

“…To better examine whether the origin-relative topological dissimilarities among different subpopulations of otic neuroblasts in the otic placode could be essential for early fate assignment and future differentiation and segregation in the mature vestibular and acoustic ganglia (VG and AG), an experimental study using the chick/quail chimeric graft method was performed. Considering our previous fate map of the avian otic placode [ 5 ] and earlier otic connection studies [ 48 ], we grafted small portions of the otic placode containing the presumptive territory of specific sensory patches, together with small portions of the nearby prospective non-sensory epithelium. Such mixed grafts were designated as “expanded sensory areas” [ 48 ].…”

“…Considering our previous fate map of the avian otic placode [ 5 ] and earlier otic connection studies [ 48 ], we grafted small portions of the otic placode containing the presumptive territory of specific sensory patches, together with small portions of the nearby prospective non-sensory epithelium. Such mixed grafts were designated as “expanded sensory areas” [ 48 ]. It is worth noting that the set of transplants contained the neurogenic zone of the otic placode [ 24 , 33 ], except the grafts containing the presumptive territory of the posterior crista, located in the most posterior-ventral portion of the chick otic placode [ 48 ].…”

“…Such mixed grafts were designated as “expanded sensory areas” [ 48 ]. It is worth noting that the set of transplants contained the neurogenic zone of the otic placode [ 24 , 33 ], except the grafts containing the presumptive territory of the posterior crista, located in the most posterior-ventral portion of the chick otic placode [ 48 ]. It is also interesting to highlight that each type of otic placode graft contained otic neuroblast precursors that generated otic neurons throughout the entire otic neurogenic period.…”