Volume 52 (5): 617-628, 2004 Copyright ©The Histochemical Society, Inc. Immunogold Detection of Co-localized Neuropeptides : Methodological Aspects
INSERM E 0358, Université Victor Segalen Bordeaux, Institut François Magendie, Bordeaux, France (ML), and Laboratoire de Neurobiologie des Signaux Intercellulaires, UMR CNRS 7101, Université Pierre et Marie Curie Paris 6, Paris, France (EVP,AC) Correspondence to: Marc Landry, INSERM E 0358, Institut François Magendie, 1, rue Camille Saint-Saëns, 33 077 Bordeaux Cedex, France. E-mail: marc.landry{at}u-bordeaux2.fr Whatever the protocol used, electron microscopic immunogold detection still suffers from a lack of sensitivity. In rat supraopticoposthypophyseal neurons, unlabeled secretory granules are always detectable after electron microscopic immunocytochemistry, and their real status remains questionable. To improve the sensitivity of this approach, we assessed a protocol to visualize either one or the other of co-localized neuropeptides, i.e., vasopressin or galanin, after two successive rounds of immunogold with the same primary antibody performed on both faces of the grid. The use of different-sized gold particles enabled us to visualize the respective contribution of each face of the section to the final labeling. Our results showed a moderate but significant increase in both the proportion of labeled granules and the labeling intensity. Although limited, this improvement of immunogold detection strengthens the relevance of quantitative studies at the electron microscopic level, likely to reveal fine variations of the neuron peptidergic content. However, this enhancement depended on the peptide studied. The present data confirmed a progressive decrease of vasopressin immunoreactivity, already suggested by the single-staining procedure, all along the hypothalamoposthypophyseal tract. In contrast, labeling intensity for galanin remained steady. Finally, our double-face labeling supported a preferential routing of galanin-containing secretory granules towards dendrites. (J Histochem Cytochem 52:617627, 2004)
Key Words: hypothalamus vasopressin galanin electron microscopy immunogold post-embedding quantification rat
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