Phase-locking between respiration and whisker motion in rats
Martin Deschênes1, Maxime Demers1, Jeffrey Moore2, David Kleinfeld2
1Department of Psychiatry and Neuroscience, Université Laval, Canada, 2Department of Physics, UCSD, USA
When they explore the environment rats and mice repeatedly sweep their facial vibrissae back and forth to locate and palpate objects. It is generally believed that exploratory whisking is controlled by a central pattern generator CPG) located in the brainstem. Yet, beyond the obvious participation of facial motoneurons as downstream command neurons, to date the premotor whisking circuitry has remained elusive. It was proposed that facial motoneurons themselves generate whisking in response to tonic input from serotonergic pre-motoneurons. Yet, this hypothesis does not explain the synchrony of motoneuron discharges, nor how different pools of facial motoneurons are activated in an antiphasic manner to generate the protraction/retraction cycle. In the present study carried out in behaving rats, we obtained direct evidence that whisking is driven by a respiratory CPG that controls sniffing. Transient blockade of breathing by injection of glycine into the preBotzinger nucleus or by provoking an apneic reflex (ammonia) abolished the whisking behavior. These results suggest that no separate CPG generates whisking, but that whisking is coupled to sniffing, which is a modulation of the respiratory pacemaker.