Immunocytochemical labelling and controls. Positive labelling (A) with antibodies to protein gene-product 9.5 (PGP 9.5, green), the high-affinity nerve growth factor receptor TrkA (Tropomyosin-related kinase A, blue) and the neuropeptide Calcitonin gene-related peptide (CGRP, red). Arrowheads indicate intra-epidermal nerve fibres. Pre-absorbing the primary antibodies with an excess of their immunogenic proteins abolished all nerve fibre labelling (B), but the stratum corneum labelling persisted unless the CGRP antibody was omitted (C), presumably due to cross-reactivity of the CGRP antibody with keratin. Dermal sebaceous glands were labelled in pre-absorption (B) and negative controls (C), probably due to endogenous biotin. Hairs autofluoresced and were either FITC or coumarin-blue labelled. Scale bar = 100 μm.