Retrograde and orthograde axon transport by brief-exposure to nickel chloride: Methodology and parameters for success in the brain-retrocerebral complex of the cockroach Diploptera punctata

Abstract

Exposure of the intact brain-retrocerebral complex of the cockroach Diploptera punctata to 500 mM NiCl 2 in 0.1% bovine serum albumen for 10 min resulted in the filling of neurones connecting the components of the brain-retrocerebral complex. Following severance of one corpus cardiacum from the brain prior to exposure to NiCl 2, a larger number of neurones filled in the contralateral side of the pars intercerebralis. Reducing exposure time to NiCl 2 to 30s did not result in backfilling of intact preparations. However, if the nervi corporis allati I (NCA 1) were sectioned, then exposed to NiCl 2 for 30s and incubated in culture medium at 4°C for 24 h, neurones of the severed NCA I backfilled to somata originating in the pars intercerebralis and pars lateralis. In addition, the axons distal to the cut also filled with the tracer in the orthograde direction, revealing a complex network of axon terminals investing the corpora allata. Sectioned nervi corporis allati I exposed to the tracer solution, then incubated in culture medium for 0.5 h, rapidly backfilled at a rate of 30–100 mm/day. Rapid backfilling did not occur in the absence of BSA. One per cent fluorescein isothiocyanide-labelled BSA backfilled as rapidly as the NiCl 2 BSA solution. 2,4-Dinitrophenol and cytochalasin B inhibited brief-exposure backfilling whereas colchicine had no effect in short term incubations but partially inhibited backfilling in long term incubations. Backfilling is thus a metabolically mediated event and the rate of transport of the tracer is similar to that of retrograde fast axonal transport of proteins.