GAP-43 and its relation to autonomic and sensory neurons in sciatic nerve and gastrocnemius muscle in the rat

Abstract

The presence of the growth-associated protein, GAP-43, in rat sciatic nerve and gastrocnemius muscle was studied, using indirect immunofluorescence, in lumbar sympathectomized and sham-sympathectomized rats. To study fast axonal transport and accumulation of immunogenic GAP-43, the sciatic nerves were crush operated, 6 h before perfusion fixation. In sections of normal, crushed sciatic nerve GAP-43 like immunoreactivity (LI) rapidly accumulated, on both sides of the crushes, in medium and thin sized axons. In double immunostaining experiments, GAP-43-LI was mainly colocalized with tyrosine hydroxylase (TH)-LI, or neuropeptide Y (NPY)-LI, markers of sympathetic nerves. In some axons, GAP-43-LI was colocalized with Substance P (SP)-LI. In perivascular nerve terminals in the gastrocnemic muscle, strong GAP-43-immunofluorescence was observed, in most cases colocalized with TH-LI, but in some terminals with SP-LI. Three days after lumbar sympathectomy (removal of the L1–L4 sympathetic ganglia bilaterally), TH-LI and NPY-LI positive axons in the sciatic nerve were reduced in number by more than 90%. GAP-43-LI positive axons were reduced by about 50%. In the gastrocnemic muscle, some GAP-43-LI positive terminals, but very few TH-LI positive nerve fibres, were found around blood vessels. No further changes were seen 8 days after sympathectomy. SP-LI in axons in the sciatic nerve and in perivascular nerve terminals of the gastrocnemic muscle, did not change after sympathectomy; most of these axons also contained GAP-43-LI. S-100-LI was present periaxonally in the sciatic nerves, but it did not colocalize with GAP-43, indicating that Schwann cells contained no GAP-43-LI in these experiments. The results show that, in normal adult rats, GAP-43-LI is mainly present in sympathetic and sensory nerve fibers in sciatic nerve and in perivascular nerve terminals. The peptide is axonally transported, mainly in sensory and adrenergic axons.