Effects of the deafferentation of the trigeminal area on the motility of the chick embryo

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Abstract
The neural crest and placodal primordia of the trigeminal ganglion were extirpated bilaterally at stages 11–12. Tests of the tactile sensitivity of different head regions showed the absence of responses to stimulation in 31 of 35 deafferented embryos. In a histological study of eight randomly selected experimental embryos small residual ganglia and trigeminal nerves were found; however, they were apparently functionally ineffective. Midbrain and cerebellar defects were found in 60% of the embryos.Periodic motility was recorded mechanically, as in previous studies, in embryos between 9 and 17 days. Random motility up to 15 days was not different in normal and deafferented embryos. This implies that self‐stimulation of the head, for instance, by brushing of legs or wings against the head, or proprioceptive self‐stimulation, play no role in the random motility at least up to 15 days. A decline of spontaneous motility which occurs in normal embryos after 17 days, begins in experimental embryos already at 15 days. This may be due to the absence of sensory input or, at least in the majority of cases, to the above‐metioned brain damage.The operated embryos did not hatch but remained in a position characteristic of the 17‐day stage. The failure to perform the integrated prehatching and hatching behavior may be due to either one of the following causes: (1) Absence of specific sensory information; (2) Absence of non‐specific excitatory stimulation reducing muscle tonus; (3) Transneuronal degeneration in trigeminal medullary or in higher centers; (4) Damage in the midbrain and/or cerebellum.
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