Understanding the physiology of glutamate receptors by use of a protocol for neuronal staining

Teaching students about the physiology of neurotransmitter receptors usually requires practical lessons with the use of sophisticated equipment and complex analysis of data. Here, we report our experience in teaching medical students with a simple, practical protocol that transforms the physiology of glutamate receptors into neuronal staining, observable under bright-field microscopy. Essentially, the students were challenged to selectively stain a subpopulation of cultured neurons expressing Ca(2+)-permeable alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors (a subgroup of ionotropic glutamate receptors). Neurons expressing this type of receptors were loaded with Co(2+) (in substitution for Ca(2+)) after nondesensitizing activation of AMPA receptors. After precipitation, the Co(2+) was revealed after treatment with silver. At the end of the procedure, the neurons expressing Ca(2+)-permeable AMPA receptors were visually identified under bright-field microscopy. The procedure allowed the visualization of the complete dendritic network of the stained neurons and allowed the students to learn very efficiently about the physiology of glutamate receptors.