Spontaneous Activity In The Statoacoustic Ganglion Of The Chicken Embryo. Timothy A. Jones,1,2 and Sherri M. Jones,1. 1Department of Surgery/Otolaryngology and 2Department of Physiology, School of Medicine, University of Missouri-Columbia, Columbia, MO 65212.
APStracts 6:0551N, 1999.
Statoacoustic ganglion cells in the mature bird include neurons that are responsive to sound (auditory) and those that are not (non-auditory). Those that are non-auditory have been shown to innervate an otolith organ, the macula lagena, whereas auditory neurons innervate the basilar papilla. In the present study, single unit recordings of statoacoustic ganglion cells were made in embryonic (E19, mean = 19.2 days of incubation) and hatchling (P6 to P14, mean = 8.6 days post-hatch) chickens. Spontaneous activity from the two age groups was compared to determine developmental changes. Activity was evaluated for 47 auditory, 11 non-auditory and 6 undefined eighth nerve neurons in embryos and 29 auditory, 26 non-auditory and 1 undefined neurons in hatchlings. For auditory neurons, spontaneous activity displayed an irregular pattern (discharge interval coefficient of variation [CV] was greater than 0.5, mean CV for embryos was 1.46 ± 0.58 and mean CV for hatchlings was 1.02 ± 0.25). Embryonic discharge rates ranged from 0.05 to 97.6 spikes per second (Sp/s) for all neurons (mean 18.6 ±16.9 Sp/s). Hatchling spontaneous rates ranged from 1.2 to 185.2 Sp/s (mean 66.5 ± 39.6 Sp/s). Discharge rates were significantly higher for hatchlings (p <0.001). Many embryonic auditory neurons displayed long silent periods between irregular bursts of neural activity, a feature not seen post-hatch. All regular bursting discharge patterns were correlated with heart rate in both embryos and hatchlings. Preferred intervals were visible in the time interval histograms (TIHs) of only one embryonic neuron in contrast to 55% of the neurons in post-hatch animals. Generally, the embryonic auditory TIH displayed a modified quasi-Poisson distribution. Non-auditory units generally displayed regular (CV <0.5) or irregular (CV >0.5 ) activity and Gaussian and modified-Gaussian TIHs. Long silent periods or bursting patterns were not a characteristic of embryonic non-auditory neurons. CV varied systematically as a function of discharge rate in non-auditory but not auditory primary afferents. Minimum spike intervals (dead time) and interval modes for auditory neurons were longer in embryos (dead time: embryos 2.88 ± 6.85 ms; hatchlings 1.50 ± 1.76 ms; modal intervals: embryo 10.09 ± 22.50 ms, hatchling 3.54 ± 3.29 ms). The results show that significant developmental changes occur in spontaneous activity between embryonic day 19 (E19) and post-hatch. It is likely that both presynaptic and postsynaptic changes in the neuroepithelium contribute to maturational refinements during this period of development.
Received 10 June 1999; accepted in final form 28 October 1999.
APS Manuscript Number J468-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999