Involvement of the median preoptic nucleus in the regulation of paraventricular vasopressin neurons by the subfornical organ in the rat.
Extracellular recordings in urethane-anesthetized male rats indicated that electrical stimulation of the subfornical organ (SFO) alters the activity of 54 out of 62 phasically firing neurosecretory neurons in the hypothalamic paraventricular nucleus (PVN); 44 cells demonstrate an increase in excitability; 10 cells display a depression in their activity. In 14 out of 38 PVN cells tested, SFO stimulation-evoked excitations were abolished by pretreatment with the angiotensin II (ANG II) antagonist, saralasin (Sar), in the region of the median preoptic nucleus (MnPO). Inhibitory responses (n = 7) were not affected. Microinjection of ANG II into the region of the SFO produced either a facilitation (n = 28) or no effect (n = 6) on the excitability of phasically active PVN neurosecretory cells and the facilitatory effect of 9 out of 23 cells tested was prevented by pretreatment with Sar in the region of the MnPO. All the PVN cells which had excitatory responses to either electrical (n = 7) or chemical (n = 9) stimulation of the SFO that were blocked following the pretreatment could also be activated by intravenous administration of ANG II. Furthermore, this activation was blocked (n = 10) or attenuated (n = 6) by pretreatment with Sar in the region of the MnPO. These results show an involvement of both the MnPO and the SFO for the regulation of excitability of putative vasopressin (VP)-secreting PVN neurons, and suggest that MnPO neurons sensitive to ANG II may relay activation of SFO neurons by circulating ANG II to putative VP-secreting PVN neurons which result in enhanced excitability.
Tanaka
J
J
Department of Animal Science, College of Agriculture and Veterinary Medicine, Nihon University, Kanagawa, Japan.
D000200:Action Potentials / Q000187:drug effects; D000804:Angiotensin II / Q000037:antagonists & inhibitors / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation; D008297:Male; D009490:Neurosecretory Systems / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism / Q000502:physiology*; D011301:Preoptic Area / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012504:Saralasin / Q000494:pharmacology*; D013356:Subfornical Organ / Q000502:physiology*; D014667:Vasopressins / Q000378:metabolism*
D014667:Vasopressins; D000804:Angiotensin II; D012504:Saralasin