EXPRESSION OF INSULIN-LIKE-GROWTH-FACTOR BINDING PROTEIN-2 DURING POSTNATAL-DEVELOPMENT OF THE RAT NEUROINTERMEDIATE PITUITARY

The expression of insulin-like growth factor binding protein-2 (IGFBP- 2) during postnatal development of the rat neurointermediate pituitary was characterized using immunocytochemistry and in situ hybridization . Glial cells in the neural lobe (NL) showed robust expression of IGFB P-2 throughout the postnatal period and continuing into adulthood. The se were identified as pituicytes by the presence of S-100 protein; IGF BP-2 was not present in microglia in the NL. IGFBP-2 immunoreactivity was more punctate in mature pituicytes, suggesting a possible associat ion with the cell membrane. No expression of IGFBP-2 by brain astrocyt es was observed at any age examined, even in regions such as the media n eminence and subfornical organ that lack a blood-brain barrier. IGFB P-2 was also localized immunocytochemically in melanotropes and glial- like cells of the intermediate lobe (IL). Positive cells were most num erous in neonates and declined thereafter, with immunoreactivity undet ectable by 65 days of age. IGFBP-2 mRNA was detected in the IL only at 1 day of age. These findings are consistent with a potential role for IGFBP-2 in modulating effects of the insulin-like growth factors duri ng development of the neurointermediate lobe. The constitutive express ion of high levels of IGFBP-2 by mature pituicytes also suggests that this protein could be secreted and/or influence a variety of processes in the mature NL, such as glial proliferation, axonal growth, or morp hological plasticity of pituicytes.