The Medullary Audio-Vocal Network in the Toad Bombina orientalis

Area of Science:

• Neuroscience
• Bioacoustics
• Comparative Physiology

Background:

• Anurans (frogs and toads) utilize lung inflation for vocalization, a mechanism shared with breathing.
• Vocal behavior is highly responsive to auditory stimuli, enabling coordinated calling in anuran choruses.
• The Chinese fire-bellied toad (Bombina orientalis) serves as a model for studying auditory-vocal integration.

Purpose of the Study:

• To investigate the neural pathways involved in audio-vocal integration in anurans.
• To determine if audio-vocal processing occurs in lower brain centers, such as the medulla oblongata.
• To elucidate the role of specific motor nuclei in coordinating vocalization and respiration.

Main Methods:

• Electrophysiological recordings were performed on an isolated whole-brain preparation of Bombina orientalis.
• Neurons were recorded in the motor nuclei of cranial nerves V, X, and XII.
• Auditory stimulation was delivered via the statoacoustic nerve (N. VIII) to elicit vocal and respiratory motor patterns.

Main Results:

• Auditory stimulation of N. VIII rapidly activated hypoglossal motor neurons (latency 9.9 ± 2.3 ms).
• Interneurons in the hypoglossal area exhibited even faster activation (minimum latency 2.9 ms).
• These findings indicate rapid audio-vocal integration within the medulla oblongata, preceding higher brain centers.

Conclusions:

• The medulla oblongata, specifically the area between vagal (N. X) and hypoglossal (N. XII) nerve roots, is crucial for breathing rhythm generation.
• The hypoglossal area plays a significant role in controlling other motor nuclei for vocalization.
• This region acts as a supplementary interface for audio-vocal integration, initiating and coordinating vocal patterns while potentially inhibiting buccal respiration.