VASOPRESSIN-INDUCTION OF THE IMMEDIATE-EARLY GENE, NGFI-A, IN CULTURED HIPPOCAMPAL GLIAL-CELLS

Our earlier autoradiographic work had documented a wide distribution o f vasopressin receptors in the hippocampus [R.E. Brinton, K.W. Gee, J. K. Wamsley, T.P. Davis, H.I. Yamamura, Regional distribution of putati ve vasopressin receptors in rat brain and pituitary by quantitative au toradiography, in: Proc. Natl. Acad. Sci. USA, 81 (1984) pp. 7248-7252 ; C. Chen, R.D. Brinton, T.J. Shors, R.F. Thompson, [Arg 8]-Vasopressi n-induction of long lasting potentiation of synaptic transmission in t he dentate gyrus, Hippocampus 3 (1993) 193-203.] which suggested the p ossibility that receptors for vasopressin were present in both neurons and glia. In the periphery, vasopressin is a potent mitogen in select proliferative cell types [E. Rozengurt, A. Legg, P. Pettican, Vasopre ssin stimulation of mouse 3T3 cell growth, Proc. Natl. Acad. Sci. USA, 76 (1979) pp. 1284-1287.] which also suggested a possible association between vasopressin receptor activation and the proliferative capacit y of astrocytes. We therefore investigated whether vasopressin would i nduce the expression of the immediate early response gene, NGFI-A (als o known as zif/268, ZENK, egr-1, krox 24), which is associated with in itiation of mitogenesis [M. Sheng, M.E. Greenberg, The regulation and function of c-fos and other immediate early genes in the nervous syste m, Neuron, 4 (1990) pp. 477-485.]. Cultured hippocampal glial cells we re exposed to vasopressin or a selective V-1 vasopressin receptor agon ist and in situ hybridization for NGFI-A mRNA was conducted. Results o f these experiments demonstrated that vasopressin induced a highly sig nificant dose-dependent increase in the number of cells expressing NGF I-A. Studies to determine the receptor subtype mediating vasopressin i nduction of NGFI-A were conducted utilizing the specific V-1 agonist, [Phe(2), Ile(3), Orn(8)]-vasopressin. The V-1 receptor agonist induced a highly significant dose dependent increase in the number of grains per NGFI-A positive cell. Time course exhibited a gradual decline with in 30 min of exposure which continued to decline over the 60 min time course. Glial cell responsivity was selective in that vasopressin and V-1 agonist induction of NGFI-A occurred in a subpopulation of glial c ells. Within a sea of glial cells, vasopressin and V-1 agonist would i nduce islands of NGFI-A positive cells. Results of combined immunocyto chemical labeling for the astrocyte specific marker, GFAP, and in situ hybridization for NGFI-A demonstrated that V-1 agonist-induced NGFI-A expression occurred in GFAP positive cells. We observed no evidence f or V-1 agonist induction of NGFI-A in neurons. Collectively, these dat a document that vasopressin, acting via V-1 vasopressin receptors, ind uces a highly significant increase in NGFI-A expression in select GFAP positive hippocampal astrocytes. To our knowledge, these data are the first report of a vasopressin mediated response in hippocampal glial cells. The potential functional significance of these findings is disc ussed. (C) 1998 Elsevier Science B.V. All rights reserved.