Goldschmidt staining of auditory cortical fields - the new method of Thallium autometallography applied around onset of hearing in juvenile Mongolian gerbils (Meriones unguiculatus)

Abstract

Investigations on the development of functional activity in the auditory cortex (AC) of non-human mammals give insights into the principles of map formation. The plasticity of cortical maps suffered from auditory deprivation was already described with Fluoro-2-deoxyglucose (FDG) in domesticated Gerbils (Meriones unguiculatus forma domestica ). A new method to map functional activity, named Thallium (TL) autometallography, was recently developed by Goldschmidt . Here, we apply this technique in juvenile gerbils to visualize map formation around hearing onset.TL autometallography is based on the tight coupling of neuronal activity and potassium K+ uptake. Neurons have to compensate for the loss of potassium, TL as its analogue accumulates in active cells. TL distribution in cortical layers could be mapped with staining based on silver intensification of heavy metal sulphides . Onset of hearing in gerbils takes place around postnatal day 14. Specimen between P11 and P17 were injected with 50-200 µl of the K+ analogue TL i.p. and kept without further sensory stimulation. Brains were removed, frozen and sectioned (25 µm). Neuronal activity marked by TL was compared with activity patterns obtained by the FDG method. TL applied to juveniles gave sufficient visualisation of cortical activity, including the spatial resolution of cortical columns. Prominent activity in the primary auditory field (A1) and the anterior auditory field (AAF) were evident in TL as well as in FDG images. Methodological restrictions arose neither from small hearts perfused (<100 mg) nor from histology in premature brains. Ongoing research should allow the visualization of neuronal activity with cellular resolution