PLASTICITY IN EXPRESSION OF IMMUNOREACTIVITY FOR NEUROPEPTIDE-Y, ENKEPHALINS AND NEUROTENSIN IN THE HYPOTHALAMIC TUBEROINFUNDIBULAR DOPAMINERGIC SYSTEM DURING LACTATION IN MICE

In lactating nursing vs lactating pup-deprived mice, single or multipl e immunolabeling was performed to compare immunoreactivities (ir) for neuropeptide Y (NPY), enkephalins (ENK) and neurotensin (NT) in the ty rosine hydroxylase (TH)-ir hypothalamic tubero-infundibular dopaminerg ic (TIDA) system. NPY-, ENK- and NT-irs were intensely expressed and c o-existed in virtually all TH-ir endings in the median eminence (ME) o f nursing mice. Removal of the pups induced a marked depletion of the peptide-irs from the ME TH-ir endings. In the arcuate nucleus (ARC) of colchicine-treated nursing mice which received peripheral injections of Fluoro-Gold (FG) to retrogradely label neuroendocrine cells, virtua lly all dorsal A12 TH-ir perikarya simultaneously expressed, with indi vidual variations, NPY-, ENK- and NT-irs, and all contained FG. These results suggest that the synthesis of NPY, ENK and NT is enhanced in T IDA neurons during lactation and that these neuromessengers may be co- released together with DA from the ME to regulate the suckling-induced prolactin secretion at the hypothalamic and/or pituitary levels.