Magnetoreception in the inner ear of pigeons (Nimpf et al. 2019)
Some animals can sense magnetic fields and use them for orientation. Various mechanisms have been discussed in this regard, yet little is known about whether and if so, where such sensory structures to detect static magnetic fields exist in these animals.
The study by Nimpf et al. (2019) explored such structures in the inner ear of pigeons. The aim was to show that certain structures and cells in the inner ear detect magnetic fields independent of light. They found that magnetic stimuli (150 µT, rotating 360° in steps) activate neurons in the vestibular nucleus of pigeons exposed in Helmholtz coils.
Neuronal activity markers such as the C-FOS protein, which responds very quickly to a variety of stimuli, were used as biomarkers. These stimuli induce a voltage in a semicircular canal, and magnetic fields are thereby detected by electroreceptive sensors through electromagnetic induction.
The authors showed that magnetic field stimulation leads to voltage spikes (1.4 µV) in channel-like structures in cells of the inner ear, facilitating the perception of magnetic fields. A certain orientation of the magnetic field is necessary for detection. This voltage-dependent calcium channel (Cav1.3, long form) has already been described in sharks and skates. The study involved both experimental investigations and theoretical calculations. The detection of the magnetic field could be demonstrated independent of light stimuli.
These new findings are interesting because they corroborate previous studies and support the presence of structures in the inner ear, which can detect electrical activity independently of light
Subsequent experiments that could provide further evidence include:
1. pharmacological intervention in the calcium channels, 2. ablation (targeted destruction) of the hair cells with antibiotics and/or 3. genetic manipulation of the calcium channel.
Nimpf S, Nordmann GC, Kagerbauer D, Malkemper EP, Landler L, Papadaki-Anastasopoulou A, Ushakova L, Wenninger-Weinzierl A, Novatchkova M, Vincent P, Lendl T, Colombini M, Mason MJ, Keays DA (2019): A Putative Mechanism for Magnetoreception by Electromagnetic Induction in the Pigeon Inner Ear. Curr Biol. 2019 Dec 2;29(23):4052-4059.e4. Epub 2019 Nov 14.