The development of the neurons of the glossopharyngeal (1x1 and vagal (X) sensory ganglia in chick embryos

Abstract

The timetable of cell generation, neuronal death and neuron numbers in the fused proximal glossopharyngeal (IX) and vagal (X) ganglion and distal IX and X ganglia were studied in normal and nerve growth factor (NGF) treated chick embryos. 3H-thymidine was injected between the 3rd and 7th days of incubation and embryos sacrificed on the 1 lth day. Neurons in the distal IX and X ganglia were generated between the 2nd and 5th days of incubation, the peak mitotic activity occurring on the 4th and 3rd days, I respectively. Neurons of the proximal IX and X ganglion were generated between the 4th and 7th days, with maximum neuron generation on the 5th day of incubation. I Counts of neurons in the 3 ganglia between the 5th and Key words: Sensory neurons - Cell generation - Neuron death - Autoradiography - NGF - Chick embryo 1 Introduction 18th days of incubation showed a maximum of 22,000 on the 8th day in the proximal IX and X ganglion and this decreased to 12,000 by the 13th day. In the distal IX ganglion, the neuron number decreased by 44% from 4,500 on the 6th day to 2,500 by the l lth day. A similar decrease of 43% was found in the distal X ganglion, the neuron number falling from 11,500 on the 7th day to 6,500 by the llth day of incubation. Neuronal cell death in these ganglia extended from the 5th to the 12th day of incubation, maximum cell death occurring at or after the cessation of mitotic activity. NGF administration from the 5th to the llth day of incubation did not have a measurable effect on the neurons of proximal IX and X and distal IX ganglia, but increased neuronal survival by 30% in the distal X ganglion. The temporal patterns of cell generation and neuron death are discussed in relation to embryonic origin of neurons and factors controlling the survival of cranial sensory neurons.