Evidence for a Neural Source of Acute Accumulation of Serotonin in Platelets in the Injured Spinal Cord of Rats. An Experimental Study Using 5,6-Dihydroxytryptamine Treatment

It was found previously that large numbers of platelets showing high serotonin (5-hydroxytryptamine; 5-HT) immunoreactivity appeared in hemostatic plugs at the traumatized cord segment in the acute phase of a trauma. In order to determine the origin of 5-HT in the platelets, we investigated the 5-HT immunoreactivity of platelets accumulating in hemostatic plugs at the traumatized spinal cord segment at 5 minutes after injury. This investigation was carried out by light and electron microscopic immunohistochemistry in rat spinal cord pretreated with 5,6-dihydroxytryptamine (5,6-DHT). The hemorrhagic lesion formed at the neural 5-HT-depleted spinal cord segment was completely 5-HT immunonegative, while platelets in lesions in cord segments of control animals or rostral to the injection site of 5,6,-DHT in experimental animals where neural 5-HT was not depleted were 5-HT immunoreactive. The results strongly suggest that a significant amount of 5-HT is released from neural elements at the injury site and is transiently incorporated into the platelets in situ.