Subfornical organ disconnection and Fos-like immunoreactivity in hypothalamic nuclei after intragastric hypertonic saline

• Published in: Brain research 2002-10, Vol.951 (2), p.202-208
• Main Authors: Starbuck, Elizabeth M, Fitts, Douglas A
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; Drinking; Drinking - drug effects; Fundamental and applied biological sciences. Psychology; Hypernatremia; Hypernatremia - metabolism; Hypothalamus - drug effects; Hypothalamus - metabolism; Immediate early gene; Immunohistochemistry; Intubation, Gastrointestinal; Male; Organum vasculosum laminae terminalis; Paraventricular Hypothalamic Nucleus - drug effects; Paraventricular Hypothalamic Nucleus - physiology; Paraventricular nucleus; Proto-Oncogene Proteins c-fos - metabolism; Rats; Rats, Long-Evans; Saline Solution, Hypertonic - administration & dosage; Saline Solution, Hypertonic - pharmacology; Subfornical organ; Subfornical Organ - physiology; Supraoptic nucleus; Supraoptic Nucleus - drug effects; Supraoptic Nucleus - physiology; Vertebrates: nervous system and sense organs
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(02)03162-1

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.