An autometallographic technique for myelin staining in formaldehyde-fixed tissue

A new autometallographic (AMG) technique for staining myelin in formaldehyde- or paraformaldehyde- (PFA) fixed tissue is presented. The tissue sections were exposed to AMG development without prior treatment with silver salts. The method was examined on PFA-fixed tissue from mouse, rat, pig, and formaldehyde-fixed human autopsy material. Samples from brain, spinal cord, cranial, and spinal nerves were either cut on a vibratome, frozen and cryostat sectioned, or embedded and microtome sectioned, before AMG development and counterstaining. The AMG-myelin technique results in a specific black/dark-brown staining of myelin in all parts of the CNS and PNS. It works on all species examined, independent of the histological preparation techniques applied. The AMG staining is stable, stays unchanged through decades, allows counterstaining, and has previously been used with immunohistochemical techniques. On perfusion-fixed tissue the technique works without further fixation, but the intensity of the AMG-myelin staining is increased by increased postfixation time. Additionally, immersion fixation has to last for days depending on the size of the tissue block in order to obtain proper myelin staining. The most feasible explanation of the chemical events underlying the AMG-myelin technique is that nano-sized clusters of metallic silver are formed in the myelin as a result of chemical bounds with reducing capacity, exposed or created by the formaldehyde molecule. The AMG method is simple to perform and as specific as the conventional osmium and luxol fast blue stainings. The present technique is thus an effective, simple, inexpensive, and quick myelin staining method of formaldehyde- or PFA-fixed tissue

SorCS2 regulates dopaminergic wiring and is processed into an apoptotic two-chain receptor in peripheral glia

Balancing trophic and apoptotic cues is critical for development and regeneration of neuronal circuits. Here we identify SorCS2 as a proneurotrophin (proNT) receptor, mediating both trophic and apoptotic signals in conjunction with p75(NTR). CNS neurons, but not glia, express SorCS2 as a single-chain protein that is essential for proBDNF-induced growth cone collapse in developing dopaminergic processes. SorCS2- or p75(NTR)-deficient in mice caused reduced dopamine levels and metabolism and dopaminergic hyperinnervation of the frontal cortex. Accordingly, both knockout models displayed a paradoxical behavioral response to amphetamine reminiscent of ADHD. Contrary, in PNS glia, but not in neurons, proteolytic processing produced a two-chain SorCS2 isoform that mediated proNT-dependent Schwann cell apoptosis. Sciatic nerve injury triggered generation of two-chain SorCS2 in p75(NTR)-positive dying Schwann cells, with apoptosis being profoundly attenuated in Sorcs2(-/-) mice. In conclusion, we have demonstrated that two-chain processing of SorCS2 enables neurons and glia to respond differently to proneurotrophins