PLASTICITY OF POSTGANGLIONIC SYMPATHETIC NEURONS IN THE RAT SUPERIOR CERVICAL-GANGLION AFTER AXOTOMY

The neuropeptides galanin (GAL) and vasoactive intestinal polypeptide (VIP) are upregulated in spinal and vagal sensory as well as in crania l motor neurons after axonal transection. In this study an increase of both peptides is demonstrated in axotomized principal ganglionic neur ons (PGN) of the rat sympathetic superior cervical ganglion by use of double-labeling immunofluorescence. Compared to control ganglia that d o not contain more than 1% GAL- or VIP-positive cells, about 26% of al l PGN exhibit GAL immunoreactivity by day 1 after transection of the m ajor postganglionic branches. The proportion of immunoreactive neurons reaches its maximum after 30 days (40%) and decreases to about 27% wi thin the second month after axotomy. The percentage of VIP-positive ne urons is much lower than for GAL: 2% of the PGN exhibit VIP immunoreac tivity at day 1 and about 7% are observed 30 and 60 days after axotomy . In order to further characterize newly GAL- and VIP-positive PGN, th eir cell diameters were determined 12 days after axotomy. Compared to the mean overall neuron diameter of 24.8 mu m, GAL-immunoreactive neur ons are predominantly of small and intermediate size (22.2 mu m), wher eas VIP occurs mainly in larger neurons (26.1 mu m), Besides cell bodi es, many intraganglionic nerve fibers stain positive for GAL or VIP, p articularly at day 6. Most likely, these fibers represent axons, as in dicated by the absence of MAP2, a cytoskeletal protein found in neuron al somata and dendrites. They establish direct membrane contacts with postganglionic perikarya, as revealed by pre-embedding immune-electron microscopy. Some cell bodies and fibers contain both peptides. Coloca lization of GAL or VIP with tyrosine hydroxylase (TH), the rate-limiti ng enzyme of catecholamine synthesis, reveals a reduced immunoreactivi ty for TH in intensely GAL- or VIP-positive cells, and vice versa at d ay 6. However, no difference in staining intensity for VIP or GAL, and TH, is observed after 30 and 60 days. Possible implications of GAL an d VIP for peripheral nerve regeneration and their regulation by target -derived factors are discussed. (C) 1994 Wiley-Liss, Inc.