Dextromethorphan, an N-methyl-D-aspartate receptor antagonist, inhibits glutamatergic transmission in the regions of the brainstem and cerebellum, which are hypothesized to be involved in pseudobulbar symptoms, and acts as a sigma ligand, binding to the sigma-1 receptors that mediate the emotional motor expression. See also
Corticobulbar tract
Bulbar palsy, a similar syndrome caused by the damage of lower motor neurons. Motor neuron disease

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Orthokeratosis is hyperkeratosis without parakeratosis. No nucleus is seen in the cells. There is also formation of an anuclear keratin layer, as in the normal epidermis. == References ==