Strychnine-enhanced transsynaptic destruction of medullary dorsal horn neurones following transection of the trigeminal nerve in adult rats including evidence of involvement of the bony environment of the transection neuroma in the peripheral mechanism.

Following transection of a nerve, strychnine (1 mg/kg per day) was intraperitoneally injected for 3-23 days at various post-transectional intervals and the medullary and spinal dorsal horns were histologically examined. Strychnine-enhanced transsynaptic destruction was seen when the inferior alveolar nerve was transected and the proximal stump was left in situ in the mandibular canal. Pyknotic neuronal cell bodies were observed in the dorsal half of the medullary dorsal horn ipsilateral to the nerve transection, an area which is known to receive dense innervation from the ipsilateral inferior alveolar nerve. Three days of strychnine treatment revealed pyknotic cells when the experiment was terminated between 18 and 30 days postoperatively. A longer period of strychnine treatment had a tendency to produce more pyknotic cells. Transection of neither mental, lingual, auriculotemporal nor infraorbital nerve induced strychnine-enhanced transsynaptic destruction in the medullary and spinal dorsal horns which are known to receive primary input from the severed nerves. Strychnine-enhanced transsynaptic destruction following transection of the inferior alveolar nerve was effectively prevented by placing the proximal stump outside the mandibular canal.