Abstract
Microdialysis was employed to examine whether osmotic stimulation causes alterations in the release of noradrenaline (NA) in the median preoptic nucleus (MnPO), and whether γ-aminobutyric acid (GABA) receptor mechanisms are involved in the modulation of the stimulus-induced alteration in the NA release in the MnPO. In urethane-anesthetized male rats, intraperitoneal injection of hypertonic saline (0.3 M NaCl, 1 ml) significantly decreased dialysate NA concentration in the MnPO area. The decrease in the NA level elicited by the osmotic stimulation was significantly attenuated by perfusion with phaclofen (10 μM), a GABAB receptor antagonist, but not by perfusion with bicuculline (10 μM), a GABAA receptor antagonist, through a microdialysis probe. Microinjection of the local anesthetic lidocaine (2%, 0.2 µl) into the organum vasclosum of the lamina terminalis (OVLT) significantly attenuated the decrease in the NA release in the MnPO area. We conclude, in conjunction with the previous findings that the OVLT exerts inhibitory influences on the NA release in the MnPO area through GABAB receptor mechanisms, that the decrease in the NA release in the MnPO area elicited by the osmotic stimulation may be mediated in part by GABAergic inputs from the OVLT. [J Physiol Sci. 2008;58 Suppl:S157]
