Expression of the IgLON cell adhesion molecules Kilon and OBCAM in hypothalamic magnocellular neurons

The vasopressin (AVP) and oxytocin (OXT) magnocellular neurons in the hypot halamic supraoptic (SON) and paraventricular nuclei (PVN) display reversibl e structural plasticity of neurons and glial cells under different conditio ns of neuropeptide secretion. In the present study, we investigated the exp ression of two immunoglobulin superfamily (IgSF) proteins, Kilon and OBCAM, in the magnocellular neurons by using monoclonal antibodies. Anti-Kilon an tibody reacted specifically with the bacterially expressed recombinant Kilo n but not with the recombinant OBCAM, and similarly anti-OBCAM antibody spe cifically recognized the recombinant OBCAM. Western blotting analysis revea led the specific expression of Kilon and OBCAM in the SON homogenates. Alth ough Kilon and OBCAM of the SON homogenates were present as the insoluble f orm, most Kilon was present in the Triton-insoluble fraction, and OBCAM was localized mainly in the Triton-soluble fraction. Immunocytochemistry revea led Kilon and OBCAM immunoreactivity in the magnocellular neurons of the SO N and PVN of the rat hypothalamus compared with outside of the SON and PVN in the hypothalamus. The double-labeling study with confocal microscopy fur ther demonstrated that Kilon immunoreactivity was observed mainly in the de ndrites of AVP-secreting neurons and also occasionally OXT-secreting neuron s. However, OBCAM immunoreactivity was exclusively seen in the dendrites of AVP-secreting magnocellular neurons. Chronic physiological stimulation by 2% NaCl had no effect on the expression levels of either IgLON protein in t he SON. Our study thus demonstrated specific expression of Kilon and OBCAM in the hypothalamic magnocellular neurons, particularly in dendrites, sugge sting that they confer on magnocellular neurons the ability to rearrange de ndritic connectivity. J. Comp. Neurol. 424:74-85, 2000. (C) 2000 Wiley-Liss , Inc.