Anemotoxis is a term that refers to the ability of animals to react to air stimuli. Insects exhibit these traits in some well-studied cases. The animotactic abilities of mammals were not well understood until recently, but a new study shows that mice can sense airflow in a conditioning paradigm.
Mystacial whiskers and rat trigeminal ganglion cells were examined for mechanical responses to ventilatory stimulation. The scientists examined the function of all facial hair in anemotaxis, rather than the five rows of mystical whiskers depicted in the well-known posteromedial-barrel-subfield.
The scientists chose to study multiple whisker subfields because the functional properties of these subfields differ. These whiskers appear to have biomechanical adaptations for ground sensing and can provide the animal with information such as its movement, speed and heading.
Because of their exposed anatomical location, the supra-orbital whiskers above the eye have obvious relevance in wind sensing. The DeepLabCut toolkit, which has recently shown advances in automated animal tracking, was used for this research on whisker type in wind sensing.
Scientists asked questions like:
- Which whiskers are maximally reactive to ventilatory stimuli?
- Are whisker ventilatory responses dependent on whisker biomechanics and substructure?
- How do mechanical whisker ventilation responses relate to cortical barrel mapping?
- How do whiskers differentially contribute to airflow sensitivity?
The scientists discovered that the responses of different whiskers to airflow varied significantly. Supra-orbital whiskers respond differently to low airflow stimuli, and these responses to airflow reflect the specific biomechanics of supra-orbital whiskers. Micro-computed tomography (micro-CT) has revealed distinct follicular structures in supra-orbital and pad whiskers.
In recordings made with neuropixel studies, supra-orbital vs. Pad barrel field shows a great wind response. Rats can detect and recognize low-level ventilatory stimuli. These abilities are weakened by blocking supra-orbital whiskers or focusing on air-sensitive hairs.
In mice, scientists observed whisker-based anemotaxis. To better understand how the whiskers detect airflow, the scientists observed the hair tips of anesthetized mice in low and high airflow conditions. Low-ventilation conditions are very similar to commonly occurring wind stimuli, with distinctly involved whisker tips. In contrast, high wind conditions caused all whisker tips to move.
Most of the whiskers barely moved, but the long supra-orbital (LSO) whisker, followed by the A1 whiskers, showed the most displacement. The LSO whisker differs from other whiskers in that it is narrower in diameter, longer, and more dorsally exposed. Ex vivo removed lSO whiskers also showed significant airflow displacement, indicating that whisker-intrinsic biomechanics may be the mechanism behind the abnormal airflow sensitivity.
Micro-computed tomography (micro-CT) revealed that the loop is more complete/closed in LSO and other air-sensitive whiskers than in non-air-sensitive whiskers, suggesting specialization of the super-orbital for omni-directional sensing. .
The scientists noted, „We localized and targeted the cortical supra-orbital whisker representation in simultaneous neuropixel recordings with D/E-Row whisker barrels. The supra-orbital whisker representation responded better to wind stimulation than the D/E-Row barrel cortex. We evaluated the behavioral significance of whiskers in the airflow sensing paradigm. We observed that rats spontaneously turned toward the ventilatory stimuli in complete darkness.
„We observed that rats spontaneously turned toward ventilatory stimuli in total darkness. Selective trimming of wind-tolerant whiskers reduced ventilatory-turn responses more than trimming of wind-intolerant whiskers. Compared with control injections, lidocaine injections targeting supra-orbital whisker follicles reduced ventilatory-turn responses. Supra-orbital We conclude that the whiskers act as wind antennae.
Journal Note:
- Mathias Mugnaini, Dhruv Mehrotra and others. Supra-orbital whiskers function as wind-sensing antennae in mice. PLoS Biology. DOI: 10.1371/journal.pbio.3002168