Projections from the subfornical organ to the supraoptic nucleus in the rat: ultrastructural identification of an interposed synapse in the median preoptic nucleus using a combination of neuronal tracers

The functional projections from pressor sites in the subfornical organ (SFO) were identified using the 2-deoxyglucose (2-DG) autoradiographic method in urethane-anesthetized, sinoaortic-denervated rats. Autoradiographs of brain and spinal cord sections taken from rats whose SFO was continuously stimulated electrically for 45 min with stereotaxically placed monopolar electrodes (150 μA, 1.5-ms pulse duration, 15 Hz) following injection of tritiated 2-DG were compared with control rats that received intravenous infusions of pressor doses of phenylephrine to mimic the increase in arterial pressure observed during SFO stimulation. Comparisons were also made to autoradiographs from rats in which the ventral fornical commissure (CFV), just dorsal to the SFO, was electrically stimulated. The pressor responses during either electrical stimulation of the SFO or intravenous infusion of phenylephrine were similar in magnitude. On the other hand, stimulation of the CFV did not elicit a significant pressor response. Electrical stimulation of the SFO increased 2-DG uptake, in comparison to the phenylephrine-infused rats, in the nucleus triangularis, septofimbrial nucleus, lateral septal nucleus, nucleus accumbens, bed nucleus of the stria terminalis, dorsal and ventral nucleus medianus (median preoptic nucleus), paraventricular nucleus of the thalamus, hippocampus, supraoptic nucleus, suprachiasmatic nucleus, paraventricular nucleus of the hypothalamus, and the intermediolateral nucleus of and central autonomic area of the thoracic spinal cord. In contrast, in rats whose CFV was stimulated, these nuclei did not demonstrate changes in 2-DG uptake compared with control animals that received pressor doses of phenylephrine. These data have demonstrated some of the components of the neural circuitry likely involved in mediating the pressor responses to stimulation of the SFO and the corrective responses to activation of the SFO by disturbances to circulatory and fluid balance homeostasis.Key words: cardiovascular reflex pathways, drinking, median preoptic nucleus, osmoreceptors, paraventricular nucleus of the hypothalamus, supraoptic nucleus.

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Subfornical organ disconnection alters Fos expression in the lamina terminalis, supraoptic nucleus, and area postrema after intragastric hypertonic NaCl

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00570.2004 ◽

2005 ◽

Vol 288 (4) ◽

pp. R947-R955 ◽

Cited By ~ 6

Author(s):

Julia A. Freece ◽

Julie E. Van Bebber ◽

Dannielle K. Zierath ◽

Douglas A. Fitts

Keyword(s):

Supraoptic Nucleus ◽

Area Postrema ◽

Anterior Commissure ◽

Subfornical Organ ◽

Main Body ◽

Lamina Terminalis ◽

Preoptic Nucleus ◽

Median Preoptic Nucleus ◽

Organum Vasculosum Laminae Terminalis ◽

Initial Load

The lamina terminalis was severed by a horizontal knife cut through the anterior commissure to determine the effects of a disconnection of the subfornical organ (SFO) on drinking and Fos-like immunoreactivity (Fos-ir) in the rat brain in response to an intragastric load of hypertonic saline (5 ml/kg of 1.5 M NaCl by gavage). After an initial load, knife-cut rats drank significantly less water than sham-cut rats, thus confirming a role for the SFO in osmotic drinking. After a second load at least 1 wk later, the rats were not allowed to drink after the gavage and were perfused for analysis of Fos-ir at 90 min. Compared with sham-cut rats, the knife-cut rats displayed significantly elevated Fos-ir in the main body of the SFO, in the dorsal cap of the organum vasculosum laminae terminalis, and in the ventral median preoptic nucleus after the hypertonic load. The knife cut significantly decreased Fos-ir in the supraoptic nucleus. Fos-ir was expressed mainly in the midcoronal and caudal parts of the area postrema of sham-cut rats, and this expression was greatly reduced in knife-cut rats. These findings strengthen the case for the presence of independently functioning osmoreceptors within the SFO and suggest that the structures of the lamina terminalis provide mutual inhibition during hypernatremia. They also demonstrate that the Fos-ir in the area postrema after intragastric osmotic loading is heavily dependent on the intact connectivity of the SFO.

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Neurons in the median preoptic nucleus of the rat with collateral branches to the subfornical organ and supraoptic nucleus

Brain Research ◽

10.1016/0006-8993(92)91375-o ◽

1992 ◽

Vol 586 (1) ◽

pp. 86-90 ◽

Cited By ~ 28

Author(s):

B.J. Oldfield ◽

D.K. Hards ◽

M.J. McKinley

Keyword(s):

Supraoptic Nucleus ◽

Subfornical Organ ◽

Preoptic Nucleus ◽

Median Preoptic Nucleus

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Central noradrenergic activity in intact and sinoaortic denervated Dahl rats

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y89-072 ◽

1989 ◽

Vol 67 (5) ◽

pp. 450-455 ◽

Cited By ~ 2

Author(s):

K. P. Patel ◽

J. D. Peuler ◽

D. A. Morgan ◽

B. J. Pardini ◽

D. D. Lund ◽

...

Keyword(s):

Paraventricular Nucleus ◽

Genetic Predisposition ◽

Supraoptic Nucleus ◽

Locus Ceruleus ◽

Preoptic Nucleus ◽

Brain Areas ◽

Brain Nuclei ◽

Salt Diet ◽

Median Preoptic Nucleus ◽

Norepinephrine Turnover

Lesions in forebrain areas richly innervated by noradrenergic terminals and involved in cardiovascular function reduce or prevent hypertension in the Dahl salt-sensitive (S) rats fed a high (H) salt diet. This led us to examine two questions. (1) Is the noradrenergic activity altered in discrete forebrain and brainstem areas of SH rats? (2) Are these changes in noradrenergic activity eliminated by sinoaortic denervation (SAD)? Studies were done in 10-week-old female SH and Dahl salt-resistant (RH) rats. Half of the rats in each group had SAD surgery 1 week prior to study. An index of norepinephrine (NE) turnover was determined by measuring the decline in tissue NE concentration 8 h after administering α-methyl-p-tyrosine, a NE synthesis blocker, to animals from each of four groups: sham-RH, SAD-RH, sham-SH, and SAD-SH (n = 18–20 per group). Various discrete brain areas were obtained using the "punch technique." In SH rats the index of NE turnover was increased in the median preoptic nucleus and decreased in the paraventricular nucleus compared with RH rats regardless of SAD. In contrast, in SH rats the index of NE turnover was increased in the supraoptic nucleus and locus ceruleus compared with RH rats; however, SAD-RH had greater turnover of NE at these sites than SAD-SH. In summary, changes in noradrenergic activity in the median preoptic nucleus and the paraventricular nucleus may be related to genetic predisposition to hypertension in SH rats. In contrast, changes in the locus ceruleus and the supraoptic nucleus of SH rats may be related to impaired baroreflexes and thereby contribute to hypertension.Key words: hypertension, brain nuclei, norepinephrine, turnover.

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