Sensory innervation of the brain (primary interoceptor neurons of the brain and their asynaptic dendrites)

Published data and our own studies on the sensory innervation of the brain are summarized. Primary interoceptive sensory neurons were analyzed: brain neurons bearing cilia; supraependymal plexuses and intraependymal neurons in contact with the cerebrospinal fluid; Cajal-Retzius neurons in the boundary layer of the cerebral cortex; Dolgo-Saburov paravasal neurons in the brain and spinal cord; Lugaro cells in the cerebellum; and various synaptically NO-positive neurons in the cerebral cortex, whose asynaptic dendrites innervate the precapillary space. Consideration of the lack of pain sensitivity of the brain and the parenchymatous tissues of the internal organs, which contain local primary sensory neurons similar to intramural metasympathetic sensory neurons of Dogel type II, led to the hypothesis that brain and other intraorgan tissue receptors are involved in short "autonomic" reflex arcs controlling only local metabolism but not pain reactions.