Coronaviruses have been shown to spread back along the nerve from the peripheral nerve endings, across the synapses, and thus enter the brain, in several small animal studies. This is facilitated by the presence of a pathway for endocytosis or exocytosis between neurons of the motor cortex, and another secretory vesicular pathway between neurons and satellite cells.
Fast axonal transport occurs by employing axonal microtubules, allowing the virus to reach the neuronal cell body by a retrograde version of this mechanism.
Possible olfactory route spread is signaled by the occurrence of isolated anosmia and ageusia. In such a case, the virus could cross the cribriform plate to enter the central nervous system (CNS) from the nose. However, newer unpublished research suggests that olfactory neurons lack ACE2, while cells in the olfactory epithelium do. This could mean that viral injury to the olfactory epithelium, and not to the olfactory neurons, is responsible for anosmia, but further studies will be required to confirm this.