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Colloid droplets in the magnocellular secretory neurons of the reptilian hypothalamus: An immunocytochemical and lectin-histochemical study

Research paper by P. Fernández-LLebrez, A. M. Lancha Bernal, E. M. Rodríguez, J. Pérez, J. A. Andrades, J. M. Grondona, J. M. Mancera, J. M. Pérez-Fígares

Indexed on: 01 Apr '90Published on: 01 Apr '90Published in: Cell and Tissue Research



Abstract

The immunocytochemical and lectin-binding properties of the magnocellular neurosecretory neurons in the hypothalamus of 2 reptilian species, the snake Natrix maura and the lizard Liolaemus cyanogaster, were investigated. Particular attention was paid to the secretory droplets present in these neurons. Antisera against bovine neurophysins I+II, arginine-vasotocin, and mesotocin were used. The following lectins were applied: concanavalin A (Con A), wheat-germ agglutinin (WGA), and Limax flavus agglutinin (LFA). Adjacent 1-μm-thick methacrylate sections were used to investigate the same secretory neuron and the same colloid droplets with all three antisera and all three lectins. Several sections were treated with trypsin and urea before immunostaining or lectin binding. Con A bound to both vasotocin- and mesotocin-immunoreactive neurons, WGA exclusively to vasotocin neurons; neither of these neurons reacted with LFA. The colloid droplets were present in vasotocin neurons but absent in the mesotocin neurons. These secretory droplets showed an affinity for Con A but not for WGA, and reacted with antisera against neurophysins and vasotocin. In Natrix maura, the colloid droplets became reactive with Con A and the antisera used only after pretreatment of the sections with trypsin and urea. Within the hypothalamo-neurohypophyseal system, antiserum against vasotocin and WGA revealed the same fiber bundles. It is concluded (i) that in reptiles the vasotocin-neurophysin precursor is glycosylated, (ii) that vasotocin neurons have the exclusive capacity to form colloid droplets, and (iii) that these droplets are an intracisternal (RER) storage form of the vasotocin-neurophysin precursor.