Intergeniculate leaflet c‐Fos induction is attenuated in mice lacking normal vestibular input

Abstract

The circadian pacemaker can be phase shifted by appropriately timed locomotor activity, however the mechanism(s) involved remain poorly understood. Investigations suggest the intergeniculate leaflet of the thalamus is an integral part of the pathway utilized by locomotor stimuli in modulation of the circadian timing system (CTS). We have demonstrated a role for the neurovestibular system in phase shifts of the pacemaker in mice exposed to the gravitoinertial input associated with locomotion. This study tested the hypothesis that timed access to a running wheel would induce IGL c‐Fos in only those animals with functional input from the vestibular macular organs. This study used head tilt (het) mice lacking vestibular otoconia, chemically labyrinthectomized (Labx) mice and wildtype (WT) littermates. After 10 days in constant darkness, animals were assigned to either a running‐wheel pulse (WP) or cage control (CC) group. At circadian time (CT) 4, WP mice were moved to a running wheel and CC mice to a wheel‐free cage. At CT 8, animals were sacrificed and brain tissue processed for histology. We found significantly more IGL c‐fos in WP WT mice than in CC WT or het or Labx mice in either condition. The increase in IGL c‐fos induction among only WT mice supports the role of macular gravity receptive cells in modulation of the CTS while also providing a functional mechanism by which locomotor activity may affect the pacemaker.