Discussion of the sensory innervation of the brain.

In response to a commentary from another author, the present investigator provides new data obtained in his laboratory on the similarity of a number of brain neurons bearing asynaptic dendrites and innervating the perivascular space, the pia mater (from within), and making direct contact with the cerebrospinal fluid in the ventricles on the one hand with local intramural autonomic Dogiel type II neurons in the internal organs on the other. Our own electron microscopy data on the terminals of asynaptic dendrites in the brain are presented, these showing no difference in terms of ultrastructure from the terminals of receptors in the internal organs. Factual data are presented which, in the author's opinion, refute the other author's views that cilia in general and ciliated neurons in particular cannot have a variety of receptor functions, that sensory neurons arise exclusively from the neural crest, and that it is fundamentally impossible for brain tissues to have sensory innervation.