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Andén NE. 
“Effect of Acute Axotomy (Spinal Cord Transection) on the Turnover of 5-Hydroxytryptamine”. 
Advanc Biochem Psychopharmacol. 1974;10:35-43.
Like most other parts of the central nervous system the spinal cord contains 5-hydroxytryptamine (5-HT). Actually, the whole spinal cord has a higher concentration of 5-HT than the whole brain in the rat. The highest concentrations are found in the cervical and lumbar enlarge-ments and in the sacral segments (Andén, 1965). All the 5-HT in the spinal cord is present in nerve terminals of neurons whose cell - bodies are localized in the raphe region of the lower brainstem (Carlsson, Falck, Fuxe, and Vimcgs, 1964; Dahlström and Fuxe, 1965). After a complete transection of the spinal cord, the 5-HT nerve terminals caudal tň the lesion are separated from the 5-HT cell bodies of the same neurons, whereas the 5-HT nerve terminals cranial to the lesion are still connected with their 5-HT cell bodies. Since the nerve impulses are generated in the cell - bodies, the nerve impulse flow to the caudal, but not to the cranial, part of the spinal cord ceases immediately after a midthoracic transection. The importance of the nerve'impulses for the turnover of 5-HT can thus be studied by a comparison of the changes in the innervated cranial part and in the denervated caudal part. Such investigations can be performed during the first day after the operation, before the start of the anterograde degeneration of the 5-HT nerve terminals caudal to the axotomy. This degeneration can be revealed as a disappearance of the 5-HT concomitant with the disintegration of the nerve terminals (Carlsson, Magnusson, and Rosengren, 1963; Andéll, Häggendal, Magnusson, and Rosengren, 1964). The most careful study of the time course of the changes in 5-HT in the rat spinal cord after a mid'horacic transection has recently been performed by Magnusson (1973). After a very small increase initially, the 5-HT in the caudal part starts to disappear after 1 day (Fig. 1). The 5-HT is reduced to 'insignificant values after 5 days and then remains low,'showing that all the 5-HT nerve terminals caudal to the lesion have degenerated or died. Cranial to the lesion, the 5-HT slowly increases, perhaps due to transport to the cranial part of 5-HT storage granules and synthesizing enzymes meant for the caudal part.
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