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1.
Behav Brain Res ; 136(2): 449-53, 2002 Nov 15.
Article in English | MEDLINE | ID: mdl-12429407

ABSTRACT

Circumventricular organs such as the subfornical organ (SFO) may mediate the effects of circulating angiotensin (ANG) II on salt appetite under conditions of sodium depletion in the rat. We studied the effects of an electrolytic lesion of SFO on salt appetite after adrenalectomy (ADX) in Long-Evans rats. The SFO lesion had no effect on saline intake, but it did abolish water intake after acute peripheral treatments with 2 mg/kg of captopril or a 10 mg/kg of furosemide. These findings contrast with other recent data from this laboratory demonstrating large reductions in salt appetite in adrenal-intact rats with lesions of either SFO or the organum vasculosum laminae terminalis during acute iv infusions of ANG II. Thus, the SFO may contribute to the salt appetite response to circulating ANG II, but it is not essential for the response to adrenalectomy.


Subject(s)
Adrenalectomy , Appetite/physiology , Sodium Chloride, Dietary , Subfornical Organ/physiology , Angiotensin II/pharmacology , Animals , Body Weight/physiology , Diuretics/pharmacology , Drinking/drug effects , Furosemide/pharmacology , Male , Rats , Rats, Long-Evans , Subfornical Organ/anatomy & histology
2.
Brain Res ; 949(1-2): 42-50, 2002 Sep 13.
Article in English | MEDLINE | ID: mdl-12213298

ABSTRACT

Two circumventricular organs, the subfornical organ (SFO) and organum vasculosum laminae terminalis (OVLT), may mediate salt appetite in response to acute intravenous infusions of angiotensin (ANG) II. Fluid intakes and mean arterial pressures were measured in rats with sham lesions or electrolytic lesions of the SFO or OVLT during an intravenous infusion of 30 ng/min ANG II. Beginning 21 h before the 90-min infusion, the rats were depleted of sodium with furosemide and given a total of 300 mg/kg captopril in 75 ml/kg water in three spaced gavages to block the usual salt appetite and to hydrate the rats. No other food or fluids were available for ingestion. Sham-lesioned rats drank 9.3+/-1.2 ml if 0.3 M NaCl alone was available and drank 8.9+/-1.6 ml of saline and 3.7+/-1.6 ml of water if both were available. Either SFO or OVLT lesions reduced the intakes of saline to <5 ml in both conditions and of water to <1 ml. Mean arterial pressure did not differ among the groups and was maintained above 100 mmHg after the depletion and captopril treatments because of the large doses of water. Thus, a full expression of salt appetite in response to an acute intravenous infusion of ANG II requires the integrity of both the SFO and OVLT.


Subject(s)
Angiotensin II/pharmacology , Appetite/drug effects , Hypothalamus/physiology , Prosencephalon/physiology , Sodium Chloride, Dietary , Subfornical Organ/physiology , Angiotensin II/physiology , Angiotensin-Converting Enzyme Inhibitors/pharmacology , Animals , Blood Pressure/drug effects , Captopril/pharmacology , Drinking/drug effects , Heart Rate/drug effects , Hypothalamus/injuries , Injections, Intravenous , Male , Rats , Rats, Long-Evans , Sodium Chloride , Subfornical Organ/injuries , Time Factors , Water
3.
Brain Res ; 951(2): 202-8, 2002 Oct 04.
Article in English | MEDLINE | ID: mdl-12270498

ABSTRACT

The subfornical organ (SFO) may act as a sodium- or osmoreceptor that drives hypothalamic and other nuclei to secrete vasopressin and to elicit drinking. However, in response to mild doses of hypertonic saline, Fos-like immunoreactivity (Fos-ir) is absent in the SFO whereas it is well expressed in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. This suggests that the hypothalamus may be activated in advance of the SFO. In this study, the fibers connecting the SFO and hypothalamus were disconnected by a wire knife cut so that Fos-ir could be examined in both the SFO and hypothalamus after an intragastric (ig) load of 0.5% of body weight of 0.6 M NaCl. Compared with Fos-ir in isotonic-loaded rats, Fos-ir after the hypertonic load was not significantly elevated in the SFO or median preoptic nucleus in sham-cut or knife-cut rats and was only slightly elevated in the OVLT in sham-cut rats. However, the hypertonic load in sham-cut rats greatly elevated Fos-ir in the SON and in the entire PVN, but this expression was reduced significantly by 30-50% in knife-cut rats. Thus, the connectivity between SFO and the hypothalamus is critical for the full expression of Fos-ir in the hypothalamus during moderate ig hypertonic saline loading even when the SFO itself does not yet express Fos-ir.


Subject(s)
Hypothalamus/metabolism , Proto-Oncogene Proteins c-fos/metabolism , Saline Solution, Hypertonic/pharmacology , Subfornical Organ/physiology , Animals , Drinking/drug effects , Hypernatremia/metabolism , Hypothalamus/drug effects , Immunohistochemistry , Intubation, Gastrointestinal , Male , Paraventricular Hypothalamic Nucleus/drug effects , Paraventricular Hypothalamic Nucleus/physiology , Rats , Rats, Long-Evans , Saline Solution, Hypertonic/administration & dosage , Supraoptic Nucleus/drug effects , Supraoptic Nucleus/physiology
4.
Brain Res ; 931(2): 159-67, 2002 Mar 29.
Article in English | MEDLINE | ID: mdl-11897101

ABSTRACT

If receptors in the gut relay information about increases in local osmolality to the brain via the vagus nerve, then vagotomy should diminish this signaling and reduce both thirst and brain Fos-like immunoreactivity (Fos-ir). Water intake in response to hypertonic saline (i.p. or i.g., 1 M NaCl, 1% BW; i.g., 0.6 M NaCl, 0.5% BW) was reduced during 120 min in rats with subdiaphragmatic vagotomy (VGX) compared to sham-VGX rats. Brain Fos-ir was examined in response to both i.g. loads. After the smaller load, VGX greatly reduced Fos-ir in the supraoptic nucleus (SON) and the magnocellular and parvocellular areas of the paraventricular nucleus (PVN). Fos-ir in the subfornical organ (SFO) and nucleus of the solitary tract (NTS) was not affected. After the larger load, VGX significantly reduced Fos-ir in the parvocellular PVN and in the NTS, but not in the other regions. Thus, decreased water intake by VGX rats was accompanied by decreased Fos-ir in the parvocellular PVN after the same treatments, indicating a role for the abdominal vagus in thirst in response to signaling from gut osmoreceptors. The decreased water intake in the VGX group was not reflected as a decrease in Fos-ir in the SFO. Absorption of the larger i.g. load may have activated Fos-ir through more rapidly increasing systemic osmolality, thereby obscuring a role for the vagus at this dose in the SON and magnocellular PVN.


Subject(s)
Drinking/drug effects , Proto-Oncogene Proteins c-fos/metabolism , Saline Solution, Hypertonic/pharmacology , Thirst/physiology , Vagotomy , Animals , Behavior, Animal/drug effects , Behavior, Animal/physiology , Body Weight , Brain/anatomy & histology , Brain/drug effects , Brain/metabolism , Diaphragm/innervation , Drinking/physiology , Drinking Behavior/drug effects , Drinking Behavior/physiology , Feeding Behavior/drug effects , Feeding Behavior/physiology , Injections, Intraperitoneal , Intubation, Gastrointestinal , Male , Osmolar Concentration , Rats , Rats, Long-Evans , Reaction Time/drug effects , Thirst/drug effects , Vagotomy/methods
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