Coexistence of neuropeptides and their possible relation to neuritic regeneration in primary cultures of magnocellular neurons isolated from adult rat supraoptic nuclei

The coexistence of vasopressin (VP), oxytocin (OXY), galanin (GAL) and cholecystokinin (CCK) and the synthesis of GAL and CCK during neuritic regeneration was investigated in cultured magnocellular neurons, isolated from adult rat supraoptic nuclei. Double-labelling immunofluorescence was performed after 7 days of culture using primary antibodies for VP, OXY, GAL and CCK (paired in all possible combinations) and secondary antibodies labelled with either fluorescein or rhodamine. Confocal laser scanning microscopy revealed the coexistence of the mentioned peptides in all possible combinations, an unexpected result considering that the only combinations observed in tissue sections are VP-GAL and OXY-CCK. Freshly dispersed cells were devoid of any neuritic processes and showed a very poor immunocytochemical staining reaction for GAL and CCK. In contrast, neurons cultured for 7, 12 and 21 days showed many neurites and a strong immunoreactivity for GAL and CCK indicative of an increased synthesis of both peptides in the regenerating neurons. This increased synthetic activity is consistent with transient upregulation of these peptides observed in situ after hypophysectomy by other authors. The results suggest that the upregulation of GAL and CCK is functionally related to the neuronal regeneration processes observed during culture and that the 'uncommon' coexistences as well as the prolonged sythesis of GAL and CCK may be due to the lack of environmental inputs, which normally regulate the expression and up- and downregulation of these peptides in vivo.