Studies of the axoplasmic transport of somatostatin in the vagus nerve of the rat

Abstract

These studies were performed to examine the axoplasmic transport of somatostatin (SS) in the cervical vagus nerve of the rat. As a preliminary step, the immunoreactive SS (IR-SS) obtained from extracts of the vagal nodose ganglion and the vagus nerve was subjected to chromatographic analysis. On a Bio-Gel P-10 column, 92% of the nodose ganglion IR-SS and 98% of the vagal IR-SS coeluted with synthetic SS-14. The remaining immunoreactivity in both areas coeluted with synthetic SS-28. Vagal IR-SS demonstrated migratory characteristics identical to those of synthetic SS-14 on high performance liquid chromatography. A larger molecular weight form of IR-SS, which may correspond to prosomatostatin, was not identified in either site. When the vagus nerve was ligated distal to the nodose ganglion, the content of IR-SS increased in a time-dependent manner in the 3-mm segment of nerve proximal to the ligature. No increase in IR-SS was observed in an equal segment of nerve distal to the ligation or in the unligated contralateral nerve. Twenty-four hours after the ligation, the content of IR-SS (picograms per 3 mm; mean +/- SD) was: proximal segment, 33.9 +/- 9.6; distal segment, 3.4 +/- 3.0; and contralateral nerve, 1.7 +/- 0.7. The apparent transport velocity of IR-SS was estimated to be 2.1 +/- 1.5 mm/h. A variety of experimental approaches were used to characterize the mechanisms underlying the transport process and to define the anatomical sites of origin of the transported peptide. The application of colchicine to the vagus nerve resulted in an accumulation of IR-SS above the area which was not significantly different from that obtained after nerve ligation. When the vagus nerve was crushed above the nodose ganglion, the accumulation of IR-SS in the proximal segment was reduced by 50%, although the IR-SS content in the nodose ganglion and in the intervening nerve segments was unchanged by this procedure. The induction of a chemical sympathectomy with guanethidine had no effect on the accumulation of IR-SS. The administration of capsaicin during the neonatal period or in adult life had no effect on the transport of IR-SS, but greatly decreased the transport of substance P.(ABSTRACT TRUNCATED AT 400 WORDS)