Role of CaMKIIa reticular neurons of caudal medulla in control of posture.

Terrestrial quadrupeds actively stabilize dorsal-side-up orientation of the body in space due to activity of the postural control system. Supraspinal influences, including those from the reticular formation, play a crucial role in the operation of this system. However, the role of specific molecularly identified populations of reticular neurons in control of posture remains unknown. The aim of the present study was to reveal the role of CaMKIIa reticular neurons (CaMKIIa-RNs) located in the caudal medulla in control of posture. For this purpose, the effects of unilateral chemogenetic activation/inactivation of CaMKIIα-RNs on different aspects of postural control were studied in mice. It was found that unilateral activation of CaMKIIa-RNs evoked ipsilateral roll tilt of the head and trunk, caused by flexion/adduction of the ipsilateral limbs and extension/abduction of the contralateral limbs. The body roll tilt was actively stabilized on the tilting platform and maintained during walking. Unilateral inactivation of CaMKIIa-RNs evoked the opposite effects. Histological analyses showed that the population of CaMKIIa-RNs in the caudal medulla contains reticulospinal neurons that project to the spinal cord mainly through ipsilateral lateral funiculus and terminate in the intermediate area of the gray matter. We demonstrated that although the population of CaMKIIa-RNs contains both excitatory and inhibitory neurons, the excitatory ones dominate. Thus, CaMKIIa-RNs located in the caudal medulla play a crucial role for maintenance of the dorsal-side-up body orientation in different environments. Left/right symmetry and asymmetry in activity of CaMKIIa-RNs allows animals to maintain dorsal-side-up body orientation on horizontal and laterally inclined surfaces, respectively.