The inferior olivary nucleus (ION) is a structure found in the medulla oblongata underneath the superior olivary nucleus. In vertebrates, the ION is known to coordinate signals from the spinal cord to the cerebellum to regulate motor coordination and learning. These connections have been shown to be tightly associated, as degeneration of either the cerebellum or the ION results in degeneration of the other.
Neurons of the ION are glutamatergic and receive inhibitory input via GABA receptors. The reason for this spatial distribution is unknown. It has been proposed that the distinct populations of GABAα receptors allows for fine-tuned regulation within the ION.
- Primary olivary nucleus (PO) – This is the major laminar structure, and its distinct folds can be seen clearly. Further investigation of the neuroanatomy confirmed the intimate connection between the IO and the cerebellum in motor coordination and learning. The ION sends signals through different cell clusters. These signals vary in location and in frequency bundles and appear inconsistent. However, the temporal pattern of these signals is consistent. The most crucial of these enzymes is aromatase, which is the enzyme that is necessary for the conversion of testosterone into estradiol. Without aromatase, the ION is unable to make estradiol, and cannot recover from injury properly.
Although the ION is not often investigated on its own, degeneration in the ION has been identified in disorders that are typically associated with the cerebellum. These disorders include supranuclear palsy, Leigh disease, and SCA6, and there are several more. These disorders all involve motor coordination.