Whole body sodium depletion modifies AT1 mRNA expression and serotonin content in the dorsal raphe nucleus.

Angiotensin II (Ang II) acts on Ang II type 1 (AT1) receptors located in the organum vasculosum and subfornical organ (SFO) of the lamina terminalis as a main facilitatory mechanism of sodium appetite. The brain serotonin (5-HT) system with soma located in the dorsal raphe nucleus (DRN) provides a main inhibitory mechanism. In the present study, we first investigated the existence of Ang II AT1 receptors in serotonergic DRN neurones. Then, we examined whether whole body sodium depletion affects the gene expression of the AT1a receptor subtype and the presumed functional significance of AT1 receptors. Using confocal microscopy, we found that tryptophan hydroxylase-2 and serotonin neurones express AT1 receptors in the DRN. Immunofluorescence quantification showed a significant reduction in 5-HT content but no change in AT1 receptor expression or AT1/5-HT colocalisation in the DRN after sodium depletion. Whole body sodium depletion also significantly increased Agtr1a mRNA expression in the SFO and DRN. Oral treatment with the AT1 receptor antagonist losartan reversed the changes in Agtr1a expression in the SFO but not the DRN. Losartan injection into either the DRN or the mesencephalic aqueduct had no influence on sodium depletion-induced 0.3 mol L-1 NaCl intake. The results indicate the expression of Agtr1a mRNA in the DRN and SFO as a marker of sodium depletion. They also suggest that serotonergic DRN neurones are targets for Ang II. However, the function of their AT1 receptors remains elusive.

Transportin 1 in the mouse brain: appearance in regions of neurogenesis, cerebrospinal fluid production/sensing, and circadian clock.

Transportin1 (Tnpo1) is a carrier protein belonging to the importin-ß family, which transports substrates between the cytoplasm and the nucleus. To gain insight into the role of Tnpo1 gene in the brain, we investigated the localization of Tnpo1-, Tnpo2-, and Tnpo3-expressing cells by in situ hybridization histochemistry. Tnpo1 mRNA-positive cells were distributed throughout the brain from the olfactory bulb to the medulla oblongata. The cells in the subventricular zone of the lateral ventricle, where neurogenesis occurs even in the adult, and its progeny neurons in the granular cells of the olfactory bulb and the islands of Calleja were strongly labeled. It is also noteworthy that cerebrospinal fluid (CSF)-generating epithelial cells in the choroid plexus and CSF-contacting and -sensing circumventricular organs, including organum vasculosum lamina terminalis, subfornical organ, and subcommissural organ, expressed high amounts of Tnpo1. The strongest signals were found in the suprachiasmatic nucleus (SCN), where the biological clock resides, which prompted us to examine the circadian characteristics of Tnpo1. Under constant-dark conditions, the circadian expression profiles of Tnpo1 mRNA in the SCN showed a peak in the subjective night and a trough in the subjective day. Tnpo2 and Tnpo3 showed similar patterns of expression, except in the choroids plexus, the subventricular zone, and the SCN, where the expression was notably weaker. These findings suggest that Tnpo1 is involved in a variety of functions in the adult brain, including neurogenesis, CSF production and sensing, and circadian rhythms.

Microarray analysis of the transcriptome of the subfornical organ in the rat: regulation by fluid and food deprivation.

We have employed microarray technology using Affymetrix 230 2.0 genome chips to initially catalog the transcriptome of the subfornical organ (SFO) under control conditions and to also evaluate the changes (common and differential) in gene expression induced by the challenges of fluid and food deprivation. We have identified a total of 17,293 genes tagged as present in one of our three experimental conditions, transcripts, which were then used as the basis for further filtering and statistical analysis. In total, the expression of 46 genes was changed in the SFO following dehydration compared with control animals (22 upregulated and 24 downregulated), with the largest change being the greater than fivefold increase in brain-derived neurotrophic factor (BDNF) expression, while significant changes in the expression of the calcium-sensing (upregulated) and apelin (downregulated) receptors were also reported. In contrast, food deprivation caused greater than twofold changes in a total of 687 transcripts (222 upregulated and 465 downregulated), including significant reductions in vasopressin, oxytocin, promelanin concentrating hormone, cocaine amphetamine-related transcript (CART), and the endothelin type B receptor, as well as increases in the expression of the GABA(B) receptor. Of these regulated transcripts, we identified 37 that are commonly regulated by fasting and dehydration, nine that were uniquely regulated by dehydration, and 650 that are uniquely regulated by fasting. We also found five transcripts that were differentially regulated by fasting and dehydration including BDNF and CART. In these studies we have for the first time described the transcriptome of the rat SFO and have in addition identified genes, the expression of which is significantly modified by either water or food deprivation.

Direct projections from caudal ventrolateral medullary depressor sites to the subfornical organ.

Experiments were performed in the male Wistar rat to investigate the projections from cardiovascular responsive sites in the ventrolateral medulla (VLM) to the subfornical organ (SFO). Unilateral iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHA-L) were made into either caudal VLM (CVLM) sites at which microinjection of l-glutamate (10 nl; 0.25 M) elicited decreases in mean arterial pressure or into rostral VLM (RVLM) sites at which l-glutamate microinjection elicited increases in arterial pressure. After a survival period of 7-10 days, transverse sections of the forebrain and brainstem were processed for PHA-L immunoreactivity. After injections of PHA-L into the CVLM, axonal and presumptive terminal labeling was found bilaterally throughout the rostrocaudal extent of the SFO, although most of the projections were observed within the rostral half of the nucleus. Within the SFO, labeling was found primarily in the lateral aspects of the nucleus, often in close proximity to blood vessels. In addition, CVLM injections resulted in labeling within the organum vasculosum of the laminae terminalis (OVLT) and within the ventral and dorsal components of the median preoptic nucleus (MnPO) bilaterally, but with an ipsilateral predominance. In contrast, PHA-L injections into the RVLM did not result in axonal labeling in the SFO or OVLT, although a few labeled axons were found to course through the region of the ventral component of MnPO. These data have demonstrated that neurons within the cardiovascular responsive region of the CVLM send direct axonal projections to the SFO and other structures of the laminae terminalis, and suggest that the CVLM may function in the modulation of the activity of neurons of circumventricular organs to intra- and extracellular signals of body fluid balance.

Evidence for the presence of nicotinic receptors on rat subfornical organ neurons.

The sensitivity of subfornical organ (SFO) neurons in rat slice preparations to nicotine was studied using whole-cell patch-clamp recordings and immunohistochemistry. In the current-clamp mode, nicotine at 10 microM depolarized the membrane and increased the firing rate. In the voltage-clamp mode, nicotine elicited inward currents in a dose-dependent manner. The net current-voltage relationships of the nicotine-induced currents displayed inward rectification above -40 mV. The relatively alpha4beta2-selective nicotinic acetylcholine (ACh) receptor antagonist, dihydro-beta-erythroidine, reduced the peak amplitudes of the nicotine-induced inward currents. Immunohistochemical experiments with alpha4 antibody showed the existence of immunopositive cells in the subfornical organ. These results suggest that neurons in the subfornical organ are excited via alpha4beta2 nicotinic acetylcholine receptors.

Water deprivation-induced sodium appetite: humoral and cardiovascular mediators and immediate early genes.

Adult rats deprived of water for 24-30 h were allowed to rehydrate by ingesting only water for 1-2 h. Rats were then given access to both water and 1.8% NaCl. This procedure induced a sodium appetite defined by the operational criteria of a significant increase in 1.8% NaCl intake (3.8 +/- 0.8 ml/2 h; n = 6). Expression of Fos (as assessed by immunohistochemistry) was increased in the organum vasculosum of the lamina terminalis (OVLT), median preoptic nucleus (MnPO), subfornical organ (SFO), and supraoptic nucleus (SON) after water deprivation. After rehydration with water but before consumption of 1.8% NaCl, Fos expression in the SON disappeared and was partially reduced in the OVLT and MnPO. However, Fos expression did not change in the SFO. Water deprivation also 1) increased plasma renin activity (PRA), osmolality, and plasma Na+; 2) decreased blood volume; and 3) reduced total body Na+; but 4) did not alter arterial blood pressure. Rehydration with water alone caused only plasma osmolality and plasma Na+ concentration to revert to euhydrated levels. The changes in Fos expression and PRA are consistent with a proposed role for ANG II in the control of the sodium appetite produced by water deprivation followed by rehydration with only water.

Anatomical distribution of NPY-like immunoreactivity in the domestic chick brain (Gallus domesticus).

Neuropeptide Y-immunoreactive (NPY-ir) fibers and neurons in the brain of the domestic chick (Gallus domesticus) were described using an immunohistochemical technique. NPY-ir neurons were seen in the lobus parolfactorius; hyperstriatum, neostriatum, paleostriatum, and archistriatum; hippocampal and parahippocampal areas; dorsolateral corticoid area; piriform cortex; two thalamic areas contiguous to the n. rotundus; n. dorsolateralis anterior thalami, pars lateralis, and pars magnocellularis; n. periventricularis hypothalami; n. paraventricularis magnocellularis; regio lateralis hypothalami; n. infundibuli; inner zone of the median eminence; dorsal and lateral portions of the n. opticus basalis; n. raphes; and n. reticularis paramedianus. NPY-ir fibers were seen throughout the entire chick brain, but were more abundant in the hypothalamus where they formed networks and pathways. They were also observed in some circumventricular organs. The anatomical data of the present study regarding the distribution of NPY ir in the chick brain, together with the physiological findings of other studies, suggest that NPY plays a key role in the regulation of the neuroendocrine, vegetative, and sensory systems of birds by acting as a neuromodulator and/or neurotransmitter.

Cardiovascular responses to subseptic doses of endotoxin contribute to differential neuronal activation in rat brain.

The contribution of cardiovascular activity in the early central responses to systemic inflammation was assessed in rats following intravenous administration of subseptic doses of lipopolysaccharide (LPS). LPS at 12.5 microg/kg increased heart rate (HR) but did not alter mean arterial pressure (MAP), and induced interleukin-1 beta (IL-1 beta) gene expression at 1 h in circumventricular organs (CVOs), choroid plexus, meninges, blood vessels, and pituitary gland. IL-1 beta mRNA levels were attenuated at 2 h in most regions studied. LPS at 50 microg/kg caused a biphasic change in MAP, increased HR, increased levels of arginine vasopressin heteronuclear RNA in the hypothalamic paraventricular nucleus (PVN), and induced IL-1 beta gene expression in the nucleus of the solitary tract (NTS) at 1 h. LPS (both doses) induced Fos-like immunoreactivity (FLI) in the area postrema, organum vasculosum of the lamina terminalis, NTS, preoptic area, supraoptic nucleus, and PVN at 1 h. In the PVN, neurons with FLI were found primarily in the dorsal and dorsal medial parvocellular divisions after 12.5 microg/kg of LPS whereas neurons with FLI were found throughout the PVN after 50 microg/kg of LPS. After 2 h, FLI was widespread throughout the brain. Plasma ACTH levels were elevated at 1 and 2 h in response to both doses of LPS, and levels of CRF mRNA were increased after 2 h in the parvocellular PVN. Our results reveal that central responses to increasing doses of LPS show different patterns which are related to activation of distinct immune and viscerosensory pathways, and that cardiovascular responses contribute to early neuronal activation as LPS concentrations are increased.

Glial angiotensinogen regulates brain angiotensin II receptors in transgenic rats TGR(ASrAOGEN).

TGR(ASrAOGEN)680, a newly developed transgenic rat line with specific downregulation of astroglial synthesis of angiotensinogen, exhibits decreased brain angiotensinogen content associated with a mild diabetes insipidus and lower blood pressure. Autoradiographic experiments were performed on TGR(ASrAOGEN) (TG) and Sprague-Dawley (SD) control rats to quantify AT(1) and AT(2) receptor-binding sites in different brain nuclei and circumventricular organs. Dose-response curves for drinking response to intracerebroventricular injections of ANG II were compared between SD and TG rats. In most of the regions inside the blood-brain barrier [paraventricular nucleus (PVN), piriform cortex, lateral olfactory tract (LOT), and lateral preoptic area (LPO)], AT(1) receptor binding (sensitive to CV-11974) was significantly higher in TG compared with SD. In contrast, in the circumventricular organs investigated [subfornical organ (SFO) and area postrema], AT(1) receptor binding was significantly lower in TG. AT(2) receptors (binding sensitive to PD-123319) were detected at similar levels in the inferior olive (IO) of both strains. Angiotensin-binding sites sensitive to both CV-11974 and PD-123319 were detected in the LPO of SD rats and specifically upregulated in LOT, IO, and most notably PVN and SFO of TG. The dose-response curve for water intake after intracerebroventricular injections showed a higher sensitivity to ANG II of TG (EC(50) = 3.1 ng) compared with SD (EC(50) = 11.2 ng), strongly suggesting that the upregulation of AT(1) receptors inside the blood-brain barrier of TG rats is functional. Finally, we showed that downregulation of angiotensinogen synthesized by astroglial cells differentially regulates angiotensin receptor subtypes inside the brain and in circumventricular organs.

Fos immunoreactivity in the lamina terminalis of adrenalectomized rats and effects of angiotension II type 1 receptor blockade or deoxycorticosterone.

Neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in the lamina terminalis, a thin strip of tissue forming the anterior wall of the third brain ventricle, after adrenalectomy. Several weeks after surgery, the adrenalectomized rats were maintained with access to water and a low sodium diet for five days. In addition, hypertonic (0.5M) NaCl solution was available for the entire five-day period (sodium available) or only during the first four days (sodium unavailable). The number of neurons expressing Fos, determined at the end of the fifth day, was increased in the adrenalectomized rats with or without NaCl solution to drink. Fos activity in the median preoptic nucleus was increased only in adrenalectomized rats without access to NaCl solution. Treatment of adrenalectomized rats with the sodium-retaining mineralocorticoid hormone, deoxycorticosterone, at the end of the fourth day, decreased Fos expression in the subfornical organ and the organum vasculosum of the lamina terminalis when NaCl solution was available but not when the NaCl solution was unavailable. In the adrenalectomized rats with NaCl solution available, mineralocorticoid treatment decreased both urinary sodium excretion and daily sodium intake. Brain nuclei in the lamina terminalis also became activated in intact rats made sodium deplete by treatment with the diuretic, furosemide. Relative to sodium-deplete intact rats, however, sodium-deplete adrenalectomized rats had a greater number of neurons expressing Fos in the organum vasculosum. Treatment of sodium-deplete rats, adrenalectomized or intact, with the angiotensin II-type 1 receptor antagonist, ZD7155, decreased sodium intake and Fos expression in the subfornical organ but not in the organum vasculosum of the lamina terminalis or median preoptic nucleus. In conclusion, the results demonstrated that activation of the brain nuclei located in the lamina terminalis of adrenalectomized rats was primarily related to sodium deficit and not to the absence of the mineralocorticoid hormones, although the adrenal hormones may have a role in limiting the activation of organum vasculosum of the lamina terminalis during sodium depletion. Furthermore, the results obtained with the administration of the angiotensin receptor antagonist are consistent with the proposal that sodium appetite of the sodium-deplete rat, adrenalectomized or intact, is mediated by circulating angiotensin II acting in the subfornical organ.

Induction of pro-inflammatory cytokine mRNAs in the brain after peripheral injection of subseptic doses of lipopolysaccharide in the rat.

Although it is generally accepted that pro-inflammatory cytokines produced by cells of the central nervous system play important roles in the communication between the central nervous system and the immune system during sepsis, it is not clear whether these cytokines are produced in the brain under subseptic conditions. In this study, we used in situ hybridization to examine the mRNA expression of the pro-inflammatory cytokines IL-1beta and TNFalpha in the brains of rats 2 and 12 h after they were challenged by peripheral injections of lipopolysaccharide (LPS) ranging from 0.01 to 1000 microg/kg. Unlike septic doses of LPS (> 500 microg/kg), which induce global expression of pro-inflammatory cytokines in the brain, subseptic doses of LPS (0.01-10 microg/kg) induced IL-1beta and TNFalpha mRNA expression only in the choroid plexus, the circumventricular organs, and meninges. The expression of the cytokine-responsive immediate early gene I kappaB alpha was induced in the brain after doses of LPS as low as 0.1 microg/kg. I kappaB alpha mRNA expression was confined to sites where IL-1beta and TNFalpha were expressed. These results indicate that the induction and action of pro-inflammatory cytokines during subseptic infection occur at the blood-brain barrier and at circumventricular organs, which may be sites for elaboration of signal molecules that communicate peripheral immune status to the brain.

Drinking and Fos-immunoreactivity in rat brain induced by local injection of angiotensin I into the subfornical organ.

Previous studies suggested that angiotensinergic stimulation in the subfornical organ (SFO) has effects on the anterior third ventricle (AV3V) region and the hypothalamus for dipsogenic response and vasopressin release. In this study, Angiotensin I (ANG I) was directly injected into the SFO and this stimulated drinking. Injection of ANG I into the SFO also induced Fos-immunoreactivity (Fos-ir) in the AV3V region and in the vasopressin neurons of the supraoptic and paraventricular nuclei (SON and PVN). Pretreatment of the SFO with either captopril, an ANG converting enzyme inhibitor, or losartan, an AT1 receptor antagonist, abolished both drinking and Fos-ir induced by ANG I. Water intake partially decreased ANG I-induced Fos-ir in the SON and PVN, but not in the other areas. These results indicate that there is an ANG converting system in the SFO and suggest that neurons in the AV3V region and vasopressin cells in the hypothalamus can be regulated by angiotensinergic components in the SFO.

Chronic activation of brain areas by high-sodium diet in Dahl salt-sensitive rats.

To map changes in neuronal activity in the brains of Dahl salt-sensitive (Dahl S) vs. salt-resistant (Dahl R) rats by high-sodium diet, we used immunohistochemical detection of Fra-like proteins as a marker for long-term neuronal activation. Compared with Dahl R rats during regular sodium intake, Dahl S rats showed modestly higher expression of Fra-like immunoreactivity (Fra-LI) in the supraoptic nucleus, anterior hypothalamic area (AHA), central gray, and nucleus of solitary tract (NTS) at 5,6, and 9 wk of age but clearly elevated Fra-LI in the magnocellular part of the paraventricular nucleus (PVN) at 6 wk of age (but not at 5 and 9 wk). In the median preoptic nucleus (MnPO) Fra-LI was lower at 9 wk of age and no differences were observed in the parvocellular PVN and subfornical organ in Dahl S vs. Dahl R rats on regular sodium intake. Compared with Dahl S rats on a regular-sodium diet, Dahl S rats on a high-sodium diet from 4 to 9 wk of age had significantly increased blood pressure and experienced transient activation of magnocellular PVN and MnPO and virtually no changes in the activity of the parvocellular PVN, AHA, and NTS. In contrast, Dahl R rats showed marked activation in the magnocellular PVN after 1 and 2 wk on a high-sodium diet compared with Dahl R rats on a regular-sodium diet. The present study demonstrates that Dahl S rats show differential activation of brain areas participating in regulation of osmotic and cardiovascular homeostasis during development of sodium-sensitive hypertension.

Selective chronic sodium or chloride depletion specifically modulates subfornical organ atrial natriuretic peptide receptor number in young rats.

1. We studied the effects of selective chronic sodium depletion of chloride depletion on atrial natriuretic peptide receptor number in the subfornical organ and paraventricular nucleus of young rats. 2. Sodium or chloride depletion decreased plasma levels of atrial natriuretic peptide, increased plasma renin activity, and induced extracellular fluid volume contraction. Chloride depletion induced more significant changes in extracellular fluid volume contraction than sodium depletion. 3. In the subfornical organ, atrial natriuretic peptide receptor number significantly decreased (30%) after sodium depletion, while chloride depletion induced a smaller, not statistically significant decrease. Conversely, atrial natriuretic peptide receptors located in the paraventricular nucleus of young rats were not significantly affected by sodium or chloride depletion. 4. Water deprivation reversed the decrease in atrial natriuretic peptide receptors produced by sodium depletion. Water-deprived sodium-depleted rats actually had higher numbers of atrial natriuretic peptide receptors in the subfornical organ than control rats. These changes were associated with severe extracellular fluid volume contraction and up regulation of brain vasopressin mRNA steady-state levels. Thus, the direction of change in the number of subfornical organ atrial natriuretic peptide receptors was dependent on the degree of extracellular fluid volume contraction. 5. Our results suggest that atrial natriuretic peptide receptors located in the subfornical organ, and not in the paraventricular nucleus, are selectively regulated by sodium depletion and extracellular fluid volume contraction.

Water deprivation increases the expression of pituitary adenylate cyclase-activating polypeptide gene in the rat subfornical organ.

The effect of water deprivation on the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in the rat subfornical organ (SFO), using a combination of immunohistochemistry and in situ hybridization histochemistry. In the euhydrated condition, PACAP-immunoreactivity (PACAP-IR) and the expression of PACAP gene was observed in the SFO. Water deprivation for 24 h and 48 h caused a significant increase in PACAP gene transcripts in the SFO, compared with euhydrated animals. Additionally, water deprivation for 48 h caused an increase in PACAP-IR. This increase of PACAP-IR was demonstrated in both nerve fibers and cell bodies. High correlation was found between the localization of PACAP-IR cell bodies and PACAP messenger RNA synthesizing cell bodies in the peripheral part of the SFO. These results suggest that PACAP in the SFO may play a role in the humoral and neural changes associated with the regulation of body fluid balance after water deprivation.

Relaxin-induced expression of Fos in the forebrain of the late pregnant rat.

Relaxin, administered parenterally, has been shown to increase the release of oxytocin (OT) into the circulation and increase the firing rate of OTergic neurons. The objective of the present study was to determine if relaxin administration can result in the expression of a transcription factor, suggesting that it alters transcriptional activity within OTergic neurons at the level of the hypothalamus. Primigravid rats were ovariectomized and a jugular cannula was inserted on day 11 of gestation (g11). Pregnancy was maintained by implanting 17 beta-estradiol and progesterone caplets subcutaneously at the time of ovariectomy. At gl9, rats were challenged with intravenous relaxin or isotonic saline and the brains were removed for study. Immunohistochemistry was performed on coronal brain sections, utilizing Fos as a marker of cellular activation. In the group receiving relaxin, Fos-like immunoreactivity (Fos-IR) was abundant only in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus as well as in the subfornical organ (SFO). In contrast, Fos-IR in the group given isotonic saline was lacking in these three brain regions. A double label study using antibodies against Fos and OT demonstrated that a majority of the Fos-labeled cells in the hypothalamus were OTergic. Because Fos can act as a transcription factor, we interpret these data to indicate that transcription within OTergic cells is altered following relaxin administration, with abundant Fos-IR being limited to the SON and PVN of the hypothalamus and the SFO during late pregnancy in the rat.

Distribution of Fos immunoreactivity in the lamina terminalis and hypothalamus induced by centrally administered relaxin in conscious rats.

The effect of intracerebroventricular (ICV) injections of synthetic human or rat relaxin (25 or 250 ng) on the distribution of Fos detected immunohistochemically in the rat forebrain was investigated. Following ICV relaxin, many Fos-positive neurons were observed in the periphery of the subfornical organ, dorsal part of the organum vasculosum of the lamina terminalis, throughout the median preoptic nucleus, supraoptic nucleus and hypothalamic paraventricular nucleus. Such effects did not occur following ICV injection of artificial cerebrospinal fluid or the separated A and B chains of relaxin, nor following the intravenous injection of 250 ng of relaxin. Both vasopressin and oxytocin containing neurons identified immunohistochemically in the supraoptic and paraventricular nuclei exhibited Fos following ICV relaxin, and many neurons in the medial parvocellular part of the paraventricular nucleus contained Fos. The results indicate that centrally administered relaxin may increase neuronal activity in regions of the hypothalamus and lamina terminalis which are associated with cardiovascular and body fluid regulation and oxytocin secretion.

Lectin-binding glycoconjugates in the subfornical organ of the rat.

In the rat subfornical organ (SFO), lectin-binding glycoconjugates were histochemically examined by 9 biotinylated lectins using a streptavidin-biotin peroxidase system. The strong or moderate binding of Canavalia ensiformis (Con A), Lens culinaris (LCA) and Phaseolus vulgaris erythroagglutinin (ePHA) indicated overall distributions of high mannose, intermediate, hybrid N-linked, and non-bisected, bi/triantennate N-linked complex oligosaccharides in the rat SFO. Nonsialylated terminal N-acetylglucosamines were detected throughout this organ, as revealed by its stainabilities with Triticum vulgaris (WGA) and Limax flavus (LFA). In this organ, Ricinus communis (RCA-1) specifically bound to vessel-associated structures, whereas Arachis hypogaea (PNA) reacted with selected neurons in the central and rostral regions of this organ. Dolichos biflorus (DBA) and Ulex europaeus (UEA-1) did not stain any histologic structures in the rat SFO. The results obtained in this study provide a basis for comprehensive analyses of glycoconjugates in the rat SFO.

Localization of calcium receptor mRNA in the adult rat central nervous system by in situ hybridization.

The capacity to sense changes in the concentrations of extracellular ions is an important function in several cell types. For example, hormone secretion by parathyroid cells and thyroid C-cells is primarily regulated by the level of extracellular ionized calcium (Ca2+). The G-protein-coupled receptor that mediates the parathyroid cell response to Ca2+ has been cloned and we have used in situ hybridization to map calcium receptor (CaR) mRNA expression in the adult rat brain. Cells expressing CaR mRNA were present in many areas of the brain suggesting that a variety of cell types express the CaR. Particularly high numbers of CaR expressing cells were found in regions associated with the regulation of fluid and mineral homeostasis, most notably the subfornical organ. These data suggest that the capacity to detect changes in extracellular Ca2+ concentrations may have important functional consequences in several neural systems.