Distribution of dorsal root fibers in the medulla oblongata of the cat

TLDR

The authors examined afferent fibers to the cat medulla oblongata in 25 animals after dorsal root section, using Nauta‑Laidlaw staining to map fiber distribution to dorsal column nuclei and to other bulbar nuclei such as nucleus cuneatus lateralis, lateral reticular nucleus, the descending root of CN 5, and the nucleus tractus solitarii. They found a somatotopic arrangement in the intermediate nucleus gracilis and caudal two‑thirds of nucleus cuneatus, with dorso‑ventral and medio‑lateral shifts from caudal to cranial segments; a bilateral projection in nucleus gracilis after extensive root section, limited contralateral degeneration to its rostral pole, no bilateral degeneration in nucleus cuneatus, and persistent degeneration in nucleus cuneatus lateralis and lateral reticular nucleus from T6–T7, with only a single case of degeneration in the descending root of CN 5 after third sacral root section.

Abstract

Abstract Afferent fibers to the medulla oblongata of the cat were studied in 25 animals following section of one or more dorsal roots. Using the Nauta‐Laidlaw stain a map was constructed of the distribution of the fibers to the dorsal column nuclei and a survey made of the afferents to other bulbar nuclei: nucleus cuneatus lateralis, lateral reticular nucleus, descending root of the fifth cranial nerve and the nucleus tractus solitarii. In the intermediate segment of the nucleus gracilis and the caudal two thirds of the nucleus cuneatus, there is a somatotopical arrangement with a dorso‐ventral and medio‐lateral shifting of the fibers from the dorsal roots as one goes from caudal segments to more cranial ones. A bilateral projection is demonstrated in the nucleus gracilis after section of nearly all the coccygeal‐sacro‐lumbar‐thoracic roots; the contralateral degeneration is confined to the rostral pole of the nucleus gracilis. No bilateral degeneration is found in the nucleus cuneatus after section of the roots projecting to it. Degenerated axons in the nucleus cuneatus lateralis and in the lateral reticular nucleus are always present beginning from T6–T7 while in the descending root of the fifth cranial nerve they are recognizable in only one case with a section of the third sacral root.