CROSSTALK IN THE MAGNOCELLULAR SYSTEM DURING OSMOTIC STIMULATION OF ONE SUPRAOPTIC NUCLEUS

Neural connections linking the four magnocellular nuclei, i.e.,. the p aired supraoptic (SON) and paraventricular (PVN) nuclei, may contribut e to the simultaneous and parallel changes in firing patterns of oxyto cinergic neurons during reflex milk ejection. To investigate these neu ral connections in the absence of suckling, intranuclear release of ox ytocin (OT) was stimulated by microdialysis of hypertonic CSF containi ng 1 M NaCl (HS-CSF) into the right SON area and glucose metabolism of both SONs and PVNs and the neural lobe of virgin and lactating (10-12 day) rats was mapped by the autoradiographic [C-14]deoxyglucose (DG) method. OT in the microdialysates and in plasma, obtained before and a fter 80-90 min of dialysis with CSF or HS-CSF, was quantified by RIA. In both virgin and lactating rats, microdialysis of HS-CSF unilaterall y into the SON area significantly (p < 0.05) increased release of OT i n the nucleus and into plasma, which was associated with enhanced (p < 0.05) metabolic activity in the ipsilateral and contralateral SON and the neural lobe but not in either PVN. Compared with virgins, lactati ng rats were less active, had lower (p < 0.05) glucose utilization in the hypothalamo-neurohypophysial system, and less (p < 0.05) OT in pla sma during microdialysis of HS-CSF into the SON area. The osmotic stim ulus did not activate neural structures (suprachiasmatic and medial am ygdaloid nuclei) near the SON in either hemisphere. Thus, neural conne ctions or, less likely, transport of OT via the subarachnoid space, ma y function to recruit activation of cells in the contralateral SON fol lowing hypertonic stimulation of cells in the other SON.