Neural tuning characteristics of auditory primary afferents in the chicken embryo

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Abstract

Primary afferent activity was recorded from the cochlear ganglion in chicken embryos (Gallus domesticus) at 19 days of incubation (E19). The ganglion was accessed via the recessus scala tympani and impaled with glass micropipettes. Frequency tuning curves were obtained using a computerized threshold tracking procedure. Tuning curves were evaluated to determine characteristic frequencies (CFs), CF thresholds, slopes of low and high frequency flanks, and tip sharpness (Q10dB). The majority of tuning curves exhibited the typical 'V' shape described for older birds and, on average, appeared relatively mature based on mean values for CF thresholds (59.6 ± 20.3 dBSPL) and tin sharpness (Q10dB = 5.2 ± 3). The mean slopes of low (61.9 ± 37 dB/octave) and high (64.6 ± 33 dB/octave) frequency flanks although comparable were somewhat less than those reported for 21-day-old chickens. Approximately 14% of the tuning curves displayed an unusual 'saw-tooth' pattern. CFs ranged from 188 to 1623 Hz. The highest CF was well below those reported for post-hatch birds. In addition, a broader range of Q10dB values (1.2 to 16.9) may relate to a greater variability in embryonic tuning curves. Overall, these data suggest that an impressive functional maturity exists in the embryo at E19. The most significant sign of immaturity was the limited expression of high frequencies. It is argued that the limited high CF in part may be due to the developing middle ear transfer function and/or to a functionally immature cochlear base.

Original languageEnglish (US)
Pages (from-to)139-148
Number of pages10
JournalHearing Research
Volume82
Issue number2
DOIs
Publication statusPublished - Feb 1995

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Keywords

  • Aves
  • Basilar papilla
  • Cochlea
  • Development
  • Frequency tuning
  • Ontogeny

ASJC Scopus subject areas

  • Sensory Systems

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