Abstract
We know little about mammalian anemotaxis, wind-sensing. Recently, however, Hartmann and colleagues showed whisker-based anemotaxis in rats. This groundbreaking study prompted us to investigate how rat whiskers sense airflow. To this end, we tracked whisker tips in anesthetized or cadaver rats under no (shielded) airflow, low (ambient) airflow and high (fan-blowing) airflow conditions. Whisker tips showed little movement under no airflow conditions and all whisker tips moved during high airflow. Low airflow conditions – most similar to naturally occurring wind stimuli – engaged whisker tips differentially. While most facial whiskers showed little movement, the long supraorbital, α, A1, β, and γ whiskers showed strong movements, with the long supraorbital whisker showing maximal displacement in low airflow. We mapped the cortical representation of the long supraorbital whiskers and found wind-sensitive-whisker barrels cluster in the posterolateral barrel map. Interestingly, the long supraorbital whisker differs from other whiskers in its exposed dorsal position, upward bending, length and thin diameter. Ex vivo extracted long supraorbital whiskers also showed exceptional airflow displacement, suggesting whisker-intrinsic biomechanics endow the supraorbital whisker with unique airflow sensitivity. To study the behavioral significance of whisker airflow responses we developed an airflow-sensing paradigm. We found that rats spontaneously turn towards weak (hand-flap) and strong (cardboard-flap) airflow stimuli in complete darkness. We then found selective trimming of wind-responsive whiskers diminished airflow turning responses more than trimming of non-wind-responsive whiskers. Lidocaine injections targeted to supraorbital whisker follicles also diminished airflow turning responses compared to control injections. We conclude that supraorbital whiskers act as wind antennae.
Significance statement Animals rely on sensory processing of airflow in their environment (anemotaxis) to guide decisions related to navigation and survival. We examined the mechanisms of rat anemotaxis by combining whisker tracking, biomechanical analysis of whisker airflow responses, behavioral analysis of airflow turning and whisker interference by trimming and lidocaine injections. This diversity of methods led to a coherent pattern of results. Whiskers greatly differ in their airflow sensitivity and strongly wind-responsive whiskers – in particular the long supraorbital whiskers – determine behavioral responses to airflow stimuli in rats.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵‡ shared senior authorship