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

TL;DR

This study identifies a specific group of brainstem neurons that help mice maintain upright posture on flat and sloped surfaces.

Contribution

The study reveals that CaMKIIa-expressing reticular neurons in the caudal medulla are crucial for postural control in mice.

Findings

Unilateral activation of CaMKIIa-RNs causes ipsilateral roll tilt of the head and trunk.

CaMKIIa-RNs project to spinal cord regions controlling limb movement for posture.

These neurons stabilize posture on flat surfaces and adapt to inclined ones.

Abstract

Terrestrial quadrupeds stabilize dorsal-side-up body orientation (the vertical orientation of its dorso-ventral axis) through the postural control system, with supraspinal inputs, including those from the reticular formation, playing a central role. The contribution of specific molecularly identified reticular neuron populations to posture, however, has remained unclear. We investigated CaMKIIa-expressing reticular neurons (CaMKIIa-RNs) in the caudal medulla and their role in postural regulation. Using chemogenetic activation and inactivation in mice, we found that unilateral activation of CaMKIIa-RNs produced ipsilateral roll tilt of the head and trunk, driven by flexion/adduction of ipsilateral limbs and extension/abduction of contralateral limbs. This tilt was actively stabilized on a tilting platform and maintained during locomotion. In contrast, unilateral inactivation evoked opposite effects. Histological analysis revealed that CaMKIIa-RNs include reticulospinal neurons projecting via the ipsilateral lateral funiculus to the intermediate gray matter of the spinal cord. While both excitatory and inhibitory neurons are present, excitatory neurons predominate. Our results demonstrate that CaMKIIa-RNs in the caudal medulla are essential for maintaining dorsal-side-up orientation in diverse environments. Their left/right symmetry supports stability on horizontal surfaces, whereas asymmetry enables compensation on inclined surfaces, underscoring their key role in supraspinal control of posture.

While CaMKIIα is best known for roles in synaptic plasticity, this study shows that CaMKIIα-expressing brainstem neurons maintain upright posture in mice, stabilizing on flat ground and adapting on slopes.

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