Loss of ganglioglomerular nerve input to the carotid body impacts the hypoxic ventilatory response in freely-moving rats

The carotid bodies are the primary sensors of blood pH, pO2 and pCO2. The ganglioglomerular nerve (GGN) provides post-ganglionic sympathetic nerve input to the carotid bodies, however the physiological relevance of this innervation is still unclear. The main objective of this study was to determine how the absence of the GGN influences the hypoxic ventilatory response in juvenile rats. As such, we determined the ventilatory responses that occur during and following five successive episodes of hypoxic gas challenge (HXC, 10% O2, 90% N2), each separated by 15 min of room-air, in juvenile (P25) sham-operated (SHAM) male Sprague Dawley rats and in those with bilateral transection of the ganglioglomerular nerves (GGNX). The key findings were that 1) resting ventilatory parameters were similar in SHAM and GGNX rats, 2) the initial changes in frequency of breathing, tidal volume, minute ventilation, inspiratory time, peak inspiratory and expiratory flows, and inspiratory and expiratory drives were markedly different in GGNX rats, 3) the initial changes in expiratory time, relaxation time, end inspiratory or expiratory pauses, apneic pause and non-eupneic breathing index (NEBI) were similar in SHAM and GGNX rats, 4) the plateau phases obtained during each HXC were similar in SHAM and GGNX rats, and 5) the ventilatory responses that occurred upon return to room-air were similar in SHAM and GGNX rats. Overall, these changes in ventilation during and following HXC in GGNX rats raises the possibility the loss of GGN input to the carotid bodies effects how primary glomus cells respond to hypoxia and the return to room-air.

Central Kisspeptin Does Not Affect ERK1/2 or p38 Phosphorylation in Oxytocin Neurons of Late-Pregnant Rats

Oxytocin is secreted by hypothalamic supraoptic nucleus (SON) and paraventricular nucleus (PVN) oxytocin neurons to induce uterine contractions during parturition. Increased activation of oxytocin neurons at parturition involves a network of afferent inputs that increase oxytocin neuron excitability. Kisspeptin fibre density increases around oxytocin neurons during pregnancy, and central kisspeptin administration excites oxytocin neurons only in late pregnancy. Kisspeptin signals via extracellular regulated kinase 1/2 (ERK1/2) and p38. Therefore, to determine whether kisspeptin excites oxytocin neurons via ERK1/2-p38 signalling in late-pregnant rats, we performed immunohistochemistry for phosphorylated ERK1/2 (pERK1/2) and phosphorylated p38 (p-p38) in oxytocin neurons of non-pregnant and late-pregnant rats. Intracerebroventricular (ICV) kisspeptin administration (2 µg) did not affect pERK1/2 or p-p38 expression in SON and PVN oxytocin neurons of non-pregnant or late-pregnant rats. Furthermore, ICV kisspeptin did not affect pERK1/2 or p-p38 expression in brain areas with major projections to the SON and PVN: the nucleus tractus solitarius, rostral ventrolateral medulla, locus coeruleus, dorsal raphe nucleus, organum vasculosum of the lamina terminalis, median preoptic nucleus, subfornical organ, anteroventral periventricular nucleus, periventricular nucleus and arcuate nucleus. Hence, kisspeptin-induced excitation of oxytocin neurons in late pregnancy does not appear to involve ERK1/2 or p38 activation in oxytocin neurons or their afferent inputs.

The superior cervical ganglia modulate ventilatory responses to hypoxia independently of preganglionic drive from the cervical sympathetic chain

Superior cervical ganglia (SCG) postganglionic neurons receive preganglionic drive via the cervical sympathetic chains (CSC). The SCG projects to structures like the carotid bodies (e.g., vasculature, chemosensitive glomus cells), upper airway (e.g., tongue, nasopharynx), and to the parenchyma and cerebral arteries throughout the brain. We previously reported that a hypoxic gas challenge elicited an array of ventilatory responses in sham-operated (SHAM) freely moving adult male C57BL6 mice and that responses were altered in mice with bilateral transection of the cervical sympathetic chain (CSCX). Since the CSC provides preganglionic innervation to the SCG, we presumed that mice with superior cervical ganglionectomy (SCGX) would respond similarly to hypoxic gas challenge as CSCX mice. However, while SCGX mice had altered responses during hypoxic gas challenge that occurred in CSCX mice (e.g., more rapid occurrence of changes in frequency of breathing and minute ventilation), SCGX mice displayed numerous responses to hypoxic gas challenge that CSCX mice did not, including reduced total increases in frequency of breathing, minute ventilation, inspiratory and expiratory drives, peak inspiratory and expiratory flows, and appearance of noneupneic breaths. In conclusion, hypoxic gas challenge may directly activate subpopulations of SCG cells, including subpopulations of postganglionic neurons and small intensely fluorescent (SIF) cells, independently of CSC drive, and that SCG drive to these structures dampens the initial occurrence of the hypoxic ventilatory response, while promoting the overall magnitude of the response. The multiple effects of SCGX may be due to loss of innervation to peripheral and central structures with differential roles in breathing control.NEW & NOTEWORTHY We present data showing that the ventilatory responses elicited by a hypoxic gas challenge in male C57BL6 mice with bilateral superior cervical ganglionectomy are not equivalent to those reported for mice with bilateral transection of the cervical sympathetic chain. These data suggest that hypoxic gas challenge may directly activate subpopulations of superior cervical ganglia (SCG) cells, including small intensely fluorescent (SIF) cells and/or principal SCG neurons, independently of preganglionic cervical sympathetic chain drive.

Loss of Cervical Sympathetic Chain Input to the Superior Cervical Ganglia Affects the Ventilatory Responses to Hypoxic Challenge in Freely-Moving C57BL6 Mice

The cervical sympathetic chain (CSC) innervates post-ganglionic sympathetic neurons within the ipsilateral superior cervical ganglion (SCG) of all mammalian species studied to date. The post-ganglionic neurons within the SCG project to a wide variety of structures, including the brain (parenchyma and cerebral arteries), upper airway (e.g., nasopharynx and tongue) and submandibular glands. The SCG also sends post-ganglionic fibers to the carotid body (e.g., chemosensitive glomus cells and microcirculation), however, the function of these connections are not established in the mouse. In addition, nothing is known about the functional importance of the CSC-SCG complex (including input to the carotid body) in the mouse. The objective of this study was to determine the effects of bilateral transection of the CSC on the ventilatory responses [e.g., increases in frequency of breathing (Freq), tidal volume (TV) and minute ventilation (MV)] that occur during and following exposure to a hypoxic gas challenge (10% O₂ and 90% N₂) in freely-moving sham-operated (SHAM) adult male C57BL6 mice, and in mice in which both CSC were transected (CSCX). Resting ventilatory parameters (19 directly recorded or calculated parameters) were similar in the SHAM and CSCX mice. There were numerous important differences in the responses of CSCX and SHAM mice to the hypoxic challenge. For example, the increases in Freq (and associated decreases in inspiratory and expiratory times, end expiratory pause, and relaxation time), and the increases in MV, expiratory drive, and expiratory flow at 50% exhaled TV (EF₅₀) occurred more quickly in the CSCX mice than in the SHAM mice, although the overall responses were similar in both groups. Moreover, the initial and total increases in peak inspiratory flow were higher in the CSCX mice. Additionally, the overall increases in TV during the latter half of the hypoxic challenge were greater in the CSCX mice. The ventilatory responses that occurred upon return to room-air were essentially similar in the SHAM and CSCX mice. Overall, this novel data suggest that the CSC may normally provide inhibitory input to peripheral (e.g., carotid bodies) and central (e.g., brainstem) structures that are involved in the ventilatory responses to hypoxic gas challenge in C57BL6 mice.

The median preoptic nucleus: A major regulator of fluid, temperature, sleep, and cardiovascular homeostasis

Located in the midline lamina terminalis of the anterior wall of the third ventricle, the median preoptic nucleus is a thin elongated nucleus stretching around the rostral border of the anterior commissure. Its neuronal elements, composed of various types of excitatory glutamatergic and inhibitory GABAergic neurons, receive afferent neural signals from (1) neighboring subfornical organ and organum vasculosum of the lamina terminalis related to plasma osmolality and hormone concentrations, e.g., angiotensin II; (2) from peripheral sensors such as arterial baroreceptors and cutaneous thermosensors. Different sets of these MnPO glutamatergic and GABAergic neurons relay output signals to hypothalamic, midbrain, and medullary regions that drive homeostatic effector responses. Included in the effector responses are (1) thirst, antidiuretic hormone secretion and renal sodium excretion that subserve osmoregulation and body fluid homeostasis; (2) vasoconstriction or dilatation of skin blood vessels, and shivering and brown adipose tissue thermogenesis for core temperature homeostasis; (3) inhibition of hypothalamic and midbrain nuclei that stimulate wakefulness and arousal, thereby promoting both REM and non-REM sleep; and (4) activation of sympathetic pathways that drive vasoconstriction and heart rate to maintain arterial pressure and the perfusion of vital organs. The small size of MnPO belies its massive homeostatic significance.

Hormone-dependent medial preoptic/lumbar spinal cord/autonomic coordination supporting male sexual behaviors

Testosterone (T) can act directly through neural androgen receptors (AR) to facilitate male sexual behavior; however, T's metabolites also can play complicated and interesting roles in the control of mating. One metabolite, dihydrotestosterone (DHT) binds to AR with significantly greater affinity than that of T. Is that important behaviorally? Another metabolite, estradiol (E), offers a potential alternative route of facilitating male mating behavior by acting through estradiol receptors (ER). In this review we explore the roles and relative importance of T as well as E and DHT at various levels of the neuroaxis for the activation of male sex behavior in common laboratory animals and, when relevant research findings are available, in man.

Role of angiotensin-converting enzyme 1 within the median preoptic nucleus following chronic intermittent hypoxia

Sustained hypertension is an important consequence of obstructive sleep apnea. An animal model of the hypoxemia associated with sleep apnea, chronic intermittent hypoxia (CIH), produces increased sympathetic nerve activity (SNA) and sustained increases in blood pressure. Many mechanisms have been implicated in the hypertension associated with CIH, including the role of ΔFosB within the median preoptic nucleus (MnPO). Also, the renin-angiotensin system (RAS) has been associated with CIH hypertension. We conducted experiments to determine the possible association of FosB/ΔFosB with a RAS component, angiotensin-converting enzyme 1 (ACE1), within the MnPO following 7 days of CIH. Retrograde tract tracing from the paraventricular nucleus (PVN), a downstream region of the MnPO, was used to establish a potential pathway for FosB/ΔFosB activation of MnPO ACE1 neurons. After CIH, ACE1 cells with FosB/ΔFosB expression increased colocalization with a retrograde tracer that was injected unilaterally within the PVN. Also, Western blot examination showed ACE1 protein expression increasing within the MnPO following CIH. Chromatin immunoprecipitation (ChIP) assays demonstrated an increase in FosB/ΔFosB association with the ACE1 gene within the MnPO following CIH. FosB/ΔFosB may transcriptionally target ACE1 within the MnPO following CIH to affect the downstream PVN region, which may influence SNA and blood pressure.

Adrenaline: insights into its metabolic roles in hypoglycaemia and diabetes

Adrenaline is a hormone that has profound actions on the cardiovascular system and is also a mediator of the fight-or-flight response. Adrenaline is now increasingly recognized as an important metabolic hormone that helps mobilize energy stores in the form of glucose and free fatty acids in preparation for physical activity or for recovery from hypoglycaemia. Recovery from hypoglycaemia is termed counter-regulation and involves the suppression of endogenous insulin secretion, activation of glucagon secretion from pancreatic α-cells and activation of adrenaline secretion. Secretion of adrenaline is controlled by presympathetic neurons in the rostroventrolateral medulla, which are, in turn, under the control of central and/or peripheral glucose-sensing neurons. Adrenaline is particularly important for counter-regulation in individuals with type 1 (insulin-dependent) diabetes because these patients do not produce endogenous insulin and also lose their ability to secrete glucagon soon after diagnosis. Type 1 diabetic patients are therefore critically dependent on adrenaline for restoration of normoglycaemia and attenuation or loss of this response in the hypoglycaemia unawareness condition can have serious, sometimes fatal, consequences. Understanding the neural control of hypoglycaemia-induced adrenaline secretion is likely to identify new therapeutic targets for treating this potentially life-threatening condition.

The OVLT initiates the fall in arterial pressure evoked by high dose lipopolysaccharide: evidence that dichotomous, dose-related mechanisms mediate endotoxic hypotension

This study tested the hypothesis that lipopolysaccharide (LPS) lowers arterial pressure through two different mechanisms depending on the dose. Previously, we found that a low hypotensive dose of LPS (1mg/kg) lowers arterial pressure by activating vagus nerve afferents. Here we report that hypotension evoked by high dose LPS (15mg/kg) can be prevented by injecting lidocaine into the OVLT but not by vagotomy or inactivation of the NTS. The hypotension produced by both LPS doses was correlated with elevated extracellular norepinephrine concentrations in the POA and prevented by blocking alpha-adrenergic receptors. Thus, initiation of endotoxic hypotension is dose-related, mechanistically.

The median preoptic nucleus: front and centre for the regulation of body fluid, sodium, temperature, sleep and cardiovascular homeostasis

Located in the midline anterior wall of the third cerebral ventricle (i.e. the lamina terminalis), the median preoptic nucleus (MnPO) receives a unique set of afferent neural inputs from fore-, mid- and hindbrain. These afferent connections enable it to receive neural signals related to several important aspects of homeostasis. Included in these afferent projections are (i) neural inputs from two adjacent circumventricular organs, the subfornical organ and organum vasculosum laminae terminalis, that respond to hypertonicity, circulating angiotensin II or other humoural factors, (ii) signals from cutaneous warm and cold receptors that are relayed to MnPO, respectively, via different subnuclei in the lateral parabrachial nucleus and (iii) input from the medulla associated with baroreceptor and vagal afferents. These afferent signals reach appropriate neurones within the MnPO that enable relevant neural outputs, both excitatory and inhibitory, to be activated or inhibited. The efferent neural pathways that proceed from the MnPO terminate on (i) neuroendocrine cells in the hypothalamic supraoptic and paraventricular nuclei to regulate vasopressin release, while polysynaptic pathways from MnPO to cortical sites may drive thirst and water intake, (ii) thermoregulatory pathways to the dorsomedial hypothalamic nucleus and medullary raphé to regulate shivering, brown adipose tissue and skin vasoconstriction, (iii) parvocellular neurones in the hypothalamic paraventricular nucleus that drive autonomic pathways influencing cardiovascular function. As well, (iv) other efferent pathways from the MnPO to sites in the ventrolateral pre-optic nucleus, perifornical region of the lateral hypothalamic area and midbrain influence sleep mechanisms.

5-HT neurons of the area postrema become c-Fos-activated after increases in plasma sodium levels and transmit interoceptive information to the nucleus accumbens

Serotonergic (5-hydroxytryptamine, 5-HT) neurons of the area postrema (AP) represent one neuronal phenotype implicated in the regulation of salt appetite. Tryptophan hydroxylase (Tryp-OH, synthetic enzyme-producing 5-HT) immunoreactive neurons in the AP of rats become c-Fos-activated following conditions in which plasma sodium levels are elevated; these include intraperitoneal injections of hypertonic saline and sodium repletion. Non-Tryp-OH neurons also became c-Fos-activated. Sodium depletion, which induced an increase in plasma osmolality but caused no significant change in the plasma sodium concentration, had no effect on the c-Fos activity in the AP. Epithelial sodium channels are expressed in the Tryp-OH-immunoreactive AP neurons, possibly functioning in the detection of changes in plasma sodium levels. Since little is known about the neural circuitry of these neurons, we tested whether the AP contributes to a central pathway that innervates the reward center of the brain. Stereotaxic injections of pseudorabies virus were made in the nucleus accumbens (NAc), and after 4 days, this viral tracer produced retrograde transneuronal labeling in the Tryp-OH and non-Tryp-OH AP neurons. Both sets of neurons innervate the NAc via a multisynaptic pathway. Besides sensory information regarding plasma sodium levels, the AP→NAc pathway may also transmit other types of chemosensory information, such as those related to metabolic functions, food intake, and immune system to the subcortical structures of the reward system. Because these subcortical regions ultimately project to the medial prefrontal cortex, different types of chemical signals from visceral systems may influence affective functions.

Effects of exercise training on SFO-mediated sympathoexcitation during chronic heart failure

Exercise training (ExT) has been shown to reduce sympathetic drive during heart failure (HF). The subfornical organ (SFO) is involved in the neural control of sympathetic drive. We hypothesized that an activated SFO contributes to enhanced sympathetic activity in HF. We also postulated that ExT would reduce the activation of the SFO and its contribution to the sympathetic drive during HF. Sprague-Dawley rats were subjected to coronary artery ligation to induce HF. Rats were assigned to ExT for 3-4 wk. Rats with HF had a 2.5-fold increase in FosB-positive cells in the SFO compared with sham-operated rats, and this was normalized by ExT. Microinjection of ANG II (100 pmol) into the SFO resulted in a greater increase in renal sympathetic nerve activity (RSNA), blood pressure, and heart rate in the HF group than in the sham-operated group. These responses were normalized after ExT (change in RSNA: 23 ± 3% vs. 8 ± 2%). ExT also abolished the decrease in RSNA in HF rats after the microinjection of losartan (200 pmol) into the SFO (-21 ± 4% vs. -2 ± 3%). Finally, there was elevated mRNA (5-fold) and protein expression (43%) of ANG II type 1 receptors in the SFO of rats with HF, which were reversed after ExT. These data suggest that the enhanced activity of the SFO by elevated tonic ANG II contributes to the enhanced sympathoexcitation exhibited in HF. The decrease in ANG II type 1 receptor expression in the SFO by ExT may be responsible for reversing the neuronal activation in the SFO and SFO-mediated sympathoexcitation in rats with HF.

Role of the Median Preoptic Nucleus in Arterial Pressure Regulation and Sodium and Water Homeostasis during High Dietary Salt Intake

Changes in the osmolality and level of angiotensin II (ANG II) are important peripheral signals modulating appropriate central sympathetic output and maintaining a normal arterial pressure during high salt intake. The median preoptic nucleus (MnPO) receives reciprocal inputs from the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), the circumventricular organs that have been shown to be necessary in multiple central effects of changes in the osmolality and circulating ANG II directed toward the maintenance of sodium and water homeostasis. We, therefore, hypothesized that the MnPO is a crucial part of the central neuronal mechanisms mediating the blood pressure control by altered osmolality and/or ANG II signaling during chronic high dietary salt intake. Male Sprague-Dawley rats were randomly assigned to either sham (operation), or electrolytic lesion of the MnPO. After a 7-day recovery, rats were instrumented with radiotelemetric transducers and aortic flow probes for the measurement of the mean arterial pressure + heart rate (HR) and cardiac output (CO), respectively. Femoral venous catheters were also implanted to collect blood for the measurements of plasma osmolality and sodium concentration, as well as plasma renin activity. Rats were given another 10 days to recover and then were subjected to a 28-day-long study protocol that included a 7-day control period (1.0% NaCl diet), followed by 14 days of high salt (4.0% NaCl), and a 7-day recovery period (1.0% NaCl). The data showed, that despite a slight increase in the MAP observed in both MnPO- (n = 12) and sham-lesioned (n = 8) rats during the high-salt period, there were no significant differences between the MAP, HR, and CO in the two groups throughout the study protocol. These findings do not support the hypothesis that the MnPO is necessary to maintain normal blood pressure during high dietary salt intake. However, MnPO-lesioned rats showed less sodium balance than sham-lesioned rats during the first 4 days of high salt intake. Although, these results may be explained partly by the plasma hyperosmolarity and hypernatremia observed in MnPO-lesioned rats; they also shed light on the role of the MnPO in central neuronal control of renal sodium handling during chronic high dietary salt intake.

Central neuromodulatory pathways regulating sympathetic activity in hypertension

The classical neurotransmitters, glutamate and GABA, mediate fast (milliseconds) synaptic transmission and modulate its effectiveness through slow (seconds to minutes) signaling processes. Angiotensinergic pathways, from the lamina terminalis to the paraventricular nucleus (PVN)/supraoptic nucleus and rostral ventrolateral medulla (RVLM), are activated by stimuli such as circulating angiotensin type II (Ang II), cerebrospinal fluid (CSF) sodium ion concentration ([Na(+)]), and possibly plasma aldosterone, leading to sympathoexcitation, largely by decreasing GABA and increasing glutamate release. The aldosterone-endogenous ouabain (EO) pathway is a much slower neuromodulatory pathway. Aldosterone enhances EO release, and the latter increases chronic activity in angiotensinergic pathways by, e.g., increasing expression for Ang I receptor (AT(1)R) and NADPH oxidase subunits in the PVN. Blockade of this pathway does not affect the initial sympathoexcitatory and pressor responses but to a large extent, prevents chronic responses to CSF [Na(+)] or Ang II. Recruitment of these two neuromodulatory pathways allows the central nervous system (CNS) to shift gears to rapidly cause and sustain sympathetic hyperactivity in an efficient manner. Decreased GABA release, increased glutamate release, and enhanced AT(1)R activation in, e.g., the PVN and RVLM contribute to the elevated blood pressure in a number of hypertension models. In Dahl S rats and spontaneous hypertensive rats, high salt activates the CNS aldosterone-EO pathway, and the salt-induced hypertension can be prevented/reversed by specific CNS blockade of any of the steps in the cascade from aldosterone synthase to AT(1)R. Further studies are needed to advance our understanding of how and where in the brain these rapid, slow, and very slow CNS pathways are activated and interact in models of hypertension and other disease states associated with chronic sympathetic hyperactivity.

Central mechanisms involved in pilocarpine-induced pressor response

Pilocarpine (cholinergic muscarinic agonist) injected peripherally may act centrally to produce pressor responses; in the present study, using c-fos immunoreactive expression, we investigated the forebrain and brainstem areas activated by pressor doses of intravenous (i.v.) pilocarpine. In addition, the importance of vasopressin secretion and/or sympathetic activation and the effects of lesions in the anteroventral third ventricle (AV3V) region in awake rats were also investigated. In male Holtzman rats, pilocarpine (0.04 to 4μmol/kg b.w.) i.v. induced transitory hypotension followed by long lasting hypertension. Sympathetic blockade with prazosin (1mg/kg b.w.) i.v. or AV3V lesions (1 day) almost abolished the pressor response to i.v. pilocarpine (2μmol/kg b.w.), whereas the vasopressin antagonist (10μg/kg b.w.) i.v. reduced the response to pilocarpine. Pilocarpine (2 and 4μmol/kg b.w.) i.v. increased the number of c-fos immunoreactive cells in the subfornical organ, paraventricular and supraoptic nuclei of the hypothalamus, organ vasculosum of the lamina terminalis, median preoptic nucleus, nucleus of the solitary tract and caudal and rostral ventrolateral medulla. These data suggest that i.v. pilocarpine activates specific forebrain and brainstem mechanisms increasing sympathetic activity and vasopressin secretion to induce pressor response.

Median preoptic nucleus and subfornical organ drive renal sympathetic nerve activity via a glutamatergic mechanism within the paraventricular nucleus

The paraventricular nucleus (PVN) of the hypothalamus is involved in the neural control of sympathetic drive, but the precise mechanism(s) that influences the PVN is not known. The activation of the PVN may be influenced by input from higher forebrain areas, such as the median preoptic nucleus (MnPO) and the subfornical organ (SFO). We hypothesized that activation of the MnPO or SFO would drive the PVN through a glutamatergic pathway. Neuroanatomical connections were confirmed by the recovery of a retrograde tracer in the MnPO and SFO that was injected bilaterally into the PVN in rats. Microinjection of 200 pmol of N-methyl-d-aspartate (NMDA) or bicuculline-induced activation of the MnPO and increased renal sympathetic activity (RSNA), mean arterial pressure, and heart rate in anesthetized rats. These responses were attenuated by prior microinjection of a glutamate receptor blocker AP5 (4 nmol) into the PVN (NMDA - ΔRSNA 72 ± 8% vs. 5 ± 1%; P < 0.05). Using single-unit extracellular recording, we examined the effect of NMDA microinjection (200 pmol) into the MnPO on the firing activity of PVN neurons. Of the 11 active neurons in the PVN, 6 neurons were excited by 95 ± 17% (P < 0.05), 1 was inhibited by 57%, and 4 did not respond. The increased RSNA after activation of the SFO by ANG II (1 nmol) or bicuculline (200 pmol) was also reduced by AP5 in the PVN (for ANG II - ΔRSNA 46 ± 7% vs. 17 ± 4%; P < 0.05). Prior microinjection of ANG II type 1 receptor blocker losartan (4 nmol) into the PVN did not change the response to ANG II or bicuculline microinjection into the SFO. The results from this study demonstrate that the sympathoexcitation mediated by a glutamatergic mechanism in the PVN is partially driven by the activation of the MnPO or SFO.

FoxP2 brainstem neurons project to sodium appetite regulatory sites

The transcription factor Forkhead box protein 2 (FoxP2) is expressed in two cell groups of the brainstem that have been implicated in sodium appetite regulation: the pre-locus coeruleus (pre-LC) and parabrachial nucleus--external lateral-inner subdivision (PBel-inner). Because the connections of these two groups are unknown, neuroanatomical tracing methods were used to define their central projections. The pre-LC outputs were first analyzed using an anterograde axonal tracer--Phaseolus vulgaris leucoagglutinin (PHAL) to construct a brain map. Next, we examined whether the FoxP2 immunoreactive (FoxP2+) neurons of the pre-LC contribute to these projections using a retrograde neuronal tracer--cholera toxin β-subunit (CTb). CTb was injected into selected brain regions identified in the anterograde tracing study. One week later the rats were killed, and brainstem sections were processed by a double immunohistochemical procedure to determine whether the FoxP2+ neurons in the pre-LC and/or PBel-inner contained CTb. FoxP2+ pre-LC neurons project to: (1) ventral pallidum; (2) substantia innominata and bed nucleus of the stria terminalis; (3) paraventricular, central medial, parafascicular, and subparafascicular parvicellular thalamic nuclei; (4) paraventricular (PVH), lateral, perifornical, dorsomedial (DMH), and parasubthalamic hypothalamic nuclei; and (5) ventral tegmental area (VTA), periaqueductal gray matter (PAG), dorsal and central linear raphe nuclei. FoxP2+ PBel-inner neurons project to the PVH and DMH, with weaker connections to the LHA, VTA, and PAG. Both the pre-LC and PBel-inner project to central sites implicated in sodium appetite, and related issues, including foraging behavior, hedonic responses to salt intake, sodium balance, and cardiovascular regulation, are discussed.

Role of the organum vasculosum of the lamina terminalis for the chronic cardiovascular effects produced by endogenous and exogenous ANG II in conscious rats

Endogenous and exogenous circulating ANG II acts at one of the central circumventricular organs (CVOs), the subfornical organ (SFO), to modulate chronic blood pressure regulation. However, at the forebrain, another important CVO is the organum vasculosum of the lamina terminalis (OVLT). In the present study, we tested the hypothesis that the OVLT mediates the hypertension or the hypotension produced by chronic infusion of ANG II or losartan (AT1 antagonist), respectively. Six days after sham or OVLT electrolytic lesion, male Sprague-Dawley rats (280–320 g, n = 6 per group) were instrumented with intravenous catheters and radiotelemetric blood pressure transducers. Following another week of recovery, rats were given 3 days of saline control infusion (7 ml/day) and were then infused with ANG II (10 ng·kg−1·min−1) or losartan (10 mg·kg−1·day−1) for 10 days, followed by 3 recovery days. Twenty-four hour average measurements of mean arterial pressure (MAP) and heart rate (HR) were made during this protocol. Hydromineral balance (HB) responses were measured during the experimental protocol. By day 9 of ANG II treatment, MAP had increased 16 ± 4 mmHg in sham rats but only 4 ± 1 mmHg in OVLT lesioned rats without changes in HR or HB. However, the hypotension produced by 10 days of losartan infusion was not modified in OVLT lesioned rats. These results suggest that the OVLT might play an important role during elevation of plasma ANG II, facilitating increases of blood pressure but is not involved with baseline effects of endogenous ANG II.

Hypothalamic control of energy metabolism via the autonomic nervous system

The hypothalamic control of hepatic glucose production is an evident aspect of energy homeostasis. In addition to the control of glucose metabolism by the circadian timing system, the hypothalamus also serves as a key relay center for (humoral) feedback information from the periphery, with the important role for hypothalamic leptin receptors as a striking example. The hypothalamic biological clock uses its projections to the preautonomic hypothalamic neurons to control the daily rhythms in plasma glucose concentration, glucose uptake, and insulin sensitivity. Euglycemic, hyperinsulinemic clamp experiments combined with either sympathetic-, parasympathetic-, or sham-denervations of the autonomic input to the liver have further delineated the hypothalamic pathways that mediate the control of the circadian timing system over glucose metabolism. In addition, these experiments clearly showed both that next to the biological clock peripheral hormones may "use" the preautonomic neurons in the hypothalamus to affect hepatic glucose metabolism, and that similar pathways may be involved in the control of lipid metabolism in liver and white adipose tissue.

Role of the median preoptic nucleus in the chronic hypotensive effect of losartan in sodium-replete normal rats

1. We have shown previously that the chronic hypotensive effect of the angiotensin II AT1 receptor antagonist losartan is mediated, in part, by the subfornical organ (SFO). However, the neural pathway(s) mediating this central effect of losartan downstream from the SFO has not been completely elucidated. 2. The present study was designed to test the hypothesis that the median preoptic nucleus (MnPO) is a crucial part of the neural pathway necessary for the chronic hypotensive effect of losartan. To test this hypothesis, male Sprague-Dawley rats were subjected to either Sham or electrolytic lesion of the MnPO (MnPOx). Rats were instrumented with radiotelemetric transducers and aortic flow probes for the continuous measurement of mean arterial pressure (MAP) and heart rate and cardiac output (CO), respectively. Total peripheral resistance (TPR) was calculated as MAP/CO. After 3 days of baseline measurements, rats were infused intraperitoneally with losartan (10 mg/kg per day) via an osmotic minipump at a rate of 5 microL/min. 3. The data revealed that, by Day 9 of losartan treatment, MAP had decreased 34 +/- 2 mmHg in MnPOx rats (n = 9), whereas the MAP of Sham-lesioned rats (n = 8) had only decreased 24 +/- 3 mmHg. These findings were accompanied by a greater decrease in TPR in MnPOx compared with Sham rats (-0.464 vs-0.237 mmHg/mL per min, respectively), whereas CO remained unchanged throughout the study protocol. 4. These results do not support the hypothesis that an intact MnPO is necessary to mediate the full chronic hypotensive effect of losartan in normal rats. Instead, they appear to suggest that the MnPO may play an important role in buffering the profound hypotension induced by losartan.

Enhanced pressor response to increased CSF sodium concentration and to central ANG I in heterozygous alpha2 Na+ -K+ -ATPase knockout mice

Intracerebroventricular (ICV) infusion of NaCl mimics the effects of a high-salt diet in salt-sensitive hypertension, raising the sodium concentration in the cerebrospinal fluid (CSF [Na]) and subsequently increasing the concentration of an endogenous ouabain-like substance (OLS) in the brain. The OLS, in turn, inhibits the brain Na(+)-K(+)-ATPase, causing increases in the activity of the brain renin-angiotensin system (RAS) and blood pressure. The Na(+)-K(+)-ATPase alpha (catalytic)-isoform(s) that mediates the pressor response to increased CSF [Na] is unknown, but it is likely that one or more isoforms that bind ouabain with high affinity are involved (e.g., the Na(+)-K(+)-ATPase alpha(2)- and/or alpha(3)-subunits). We hypothesize that OLS-induced inhibition of the alpha(2)-subunit mediates this response. Therefore, a chronic reduction in alpha(2) expression via a heterozygous gene knockout (alpha(2) +/-) should enhance the pressor response to increased CSF [Na]. Intracerebroventricular (ICV) infusion of artificial CSF containing 0.225 M NaCl increased mean arterial pressure (MAP) in both wild-type (+/+) and alpha(2) +/- mice, but to a greater extent in alpha(2) +/-. Likewise, the pressor response to ICV ouabain was enhanced in alpha(2) +/- mice, demonstrating enhanced sensitivity to brain Na(+)-K(+)-ATPase inhibition per se. The pressor response to ICV ANG I but not ANG II was also enhanced in alpha(2) +/- vs. alpha(2)+/+ mice, suggesting an enhanced brain RAS activity that may be mediated by increased brain angiotensin converting enzyme (ACE). The latter hypothesis is supported by enhanced ACE ligand binding in the organum vasculosum laminae terminalis. These studies demonstrate that chronic downregulation of Na(+)-K(+)-ATPase alpha(2)-isoform expression by heterozygous knockout increases the pressor response to increased CSF [Na] and activates the brain RAS. Since these changes mimic those produced by the endogenous brain OLS, the brain alpha(2)-isoform may be a target for the brain OLS during increases in CSF [Na], such as in salt-dependent hypertension.

Inputs to the ventrolateral bed nucleus of the stria terminalis

The ventrolateral bed nucleus of the stria terminalis (BSTvl) receives direct input from two specific subpopulations of neurons in the nucleus tractus solitarius (NTS). It is heavily innervated by aldosterone-sensitive NTS neurons, which are selectively activated by sodium depletion, and by the A2 noradrenergic neurons, which are activated by visceral and immune- and stress-related stimuli. Here, we used a retrograde neuronal tracer to identify other brain sites that innervate the BSTvl. Five general brain regions contained retrogradely labeled neurons: cerebral cortex (infralimbic and insular regions), rostral forebrain structures (subfornical organ, organum vasculosum of the lamina terminalis, taenia tecta, nucleus accumbens, lateral septum, endopiriform nucleus, dorsal BST, substantia innominata, and, most prominently the amygdala--primarily its basomedial and central subnuclei), thalamus (central medial, intermediodorsal, reuniens, and, most prominently the paraventricular thalamic nucleus), hypothalamus (medial preoptic area, perifornical, arcuate, dorsomedial, parasubthalamic, and posterior hypothalamic nuclei), and brainstem (periaqueductal gray matter, dorsal and central superior raphe nuclei, parabrachial nucleus, pre-locus coeruleus region, NTS, and A1 noradrenergic neurons in the caudal ventrolateral medulla). In the arcuate hypothalamic nucleus, some retrogradely labeled neurons contained either agouti-related peptide or cocaine/amphetamine-regulated transcript. Of the numerous retrogradely labeled neurons in the perifornical hypothalamic area, few contained melanin-concentrating hormone or orexin. In the brainstem, many retrogradely labeled neurons were either serotoninergic or catecholaminergic. In summary, the BSTvl receives inputs from a variety of brain sites implicated in hunger, salt and water intake, stress, arousal, and reward.

Convergence of nociceptive information in the forebrain of female rats: reproductive organ response variations with stage of estrus

Neurons in the preoptic area (POA) of the hypothalamus and the bed nucleus of stria terminalis (BST) play an important role in the neuroendocrine control of the reproductive cycle, mating behaviors and nociception. Single unit extracellular recordings were performed in the POA and BST region of 20 urethane anesthetized female rats during either the proestrus (elevated levels of estrogen/progesterone) or metestrus (low circulating hormones) stage of the estrous cycle. A total of 118 neurons in the POA and 65 neurons in the BST responded to the search stimuli, bilateral electrical stimulation of the viscerocutaneous branch of the pelvic nerve and/or sensory branch of the pudendal nerve (i.e., dorsal nerve of clitoris). Most of the neurons responding to the electrical search stimuli received a high degree of somatovisceral convergence, including inputs from the abdominal branches of the vagus, cervix, vagina, colon and skin territories on the perineum and trunk. Mean neuronal response thresholds for vaginal and cervical stimulation but not colon distention were significantly higher for animals tested during proestrus. Also, there was a shift in POA and BST neuronal responsiveness towards more inhibition and less excitation during proestrus for a variety of somatovisceral inputs. These data demonstrate that the changes in hormonal status affect the properties of POA and BST neurons, which likely relates not only to the functional importance of these inputs for reproductive behaviors but also for nociceptive processing as well.

Identification of central nervous system sites involved in the water diuresis response elicited by central microinjection of nociceptin/ Orphanin FQ in conscious rats via c-Fos and inducible cAMP early repressor immunocytochemistry

Intracerebroventricular (i.c.v.) administration of the opioid-like peptide, nociceptin/Orphanin (nociceptin), in conscious rats produces diuretic and antinatriuretic effects. The present study utilised changes in Fos and inducible cAMP early repressor (ICER) immunocytochemistry expression to examine the central nervous (CNS) sites activated or inhibited, respectively, by central administration of nociceptin. Urine samples were collected during control (15 min) and after i.c.v. vehicle (5 microl, n = 12) or nociceptin (10 microg/5 microl; n = 12). Four additional urine samples (15-min) were collected after the i.c.v. injection. The brain was processed for Fos using a commercially available antibody (Oncogene AB-5) and for ICER using a polyclonal anti-ICER antibody raised in rabbits. In vehicle-injected conscious rats, renal excretion of water or sodium was not altered. However, nociceptin produced a rapid and marked increase in urine flow (V) and a decrease in urinary sodium excretion rate. In addition, i.c.v. nociceptin produced a significant increase in Fos staining in the dorsomedial nucleus of the hypothalamus, the perinuclear zone of the supraoptic nucleus, the organum vasculosum of the lamina terminalis (OVLT), the lateral preoptic area and the lateral hypothalamic area compared to control. By contrast, Fos expression decreased in the area postrema and locus coeruleus compared to controls. Furthermore, ICER staining was significantly increased in the perinuclear zone of the supraoptic nucleus, supraoptic nucleus, median preoptic nucleus, OVLT, medial preoptic area, central nucleus of the amygdala, and medial nucleus of the solitary tract. Together, central opioid receptor-like type 1 activation in these CNS regions may participate in the neural pathways involved in the diuretic and antinatriuretic effects of nociceptin.

A theoretical framework for CNS arousal

Rapid changes of state in central nervous systems (CNS), as required following stimuli that must arouse the CNS from a quiescent state in order to activate a behavioral response, constitute a particularly appropriate application of non-linear dynamics. Chaotic dynamics would provide tremendous amplification of neuronal activity needed for CNS arousal, sensitively dependent on the initial state of the CNS. This theoretical approach is attractive because it supposes dynamics that are deterministic and it links the elegant mathematics of chaos to the conception of a fundamental property of the CNS. However, a living system must be able to exit from chaotic dynamics in order to avoid widely divergent, biologically impossible outcomes. We hypothesize that, analogous to phase transitions in a liquid crystal, CNS arousal systems, having 'woken up the brain' to activate behavior, go through a phase transition and emerge under the control of orderly movement control systems.

Projections from bed nuclei of the stria terminalis, dorsomedial nucleus: implications for cerebral hemisphere integration of neuroendocrine, autonomic, and drinking responses

The overall projection pattern of a tiny bed nuclei of the stria terminalis anteromedial group differentiation, the dorsomedial nucleus (BSTdm), was analyzed with the Phaseolus vulgaris-leucoagglutinin anterograde pathway tracing method in rats. Many brain regions receive a relatively moderate to strong input from the BSTdm. They fall into eight general categories: humeral sensory-related (subfornical organ and median preoptic nucleus, involved in initiating drinking behavior and salt appetite), neuroendocrine system (magnocellular: oxytocin, vasopressin; parvicellular: gonadotropin-releasing hormone, somatostatin, thyrotropin-releasing hormone, corticotropin-releasing hormone), central autonomic control network (central amygdalar nucleus, BST anterolateral group, descending paraventricular hypothalamic nucleus, retrochiasmatic area, ventrolateral periaqueductal gray, Barrington's nucleus), hypothalamic visceromotor pattern-generator network (five of six known components), behavior control column (ingestive: descending paraventricular nucleus; reproductive: lateral medial preoptic nucleus; defensive: anterior hypothalamic nucleus; foraging: ventral tegmental area, along with interconnected nucleus accumbens and substantia innominata), orofacial motor control (retrorubral area), thalamocortical feedback loops (paraventricular, central medial, intermediodorsal, and medial mediodorsal nuclei; nucleus reuniens), and behavioral state control (subparaventricular zone, ventrolateral preoptic nucleus, tuberomammillary nucleus, supramammillary nucleus, lateral habenula, and raphé nuclei). This pattern of axonal projections, and what little is known of its inputs suggest that the BSTdm is part of a striatopallidal differentiation involved in coordinating the homeostatic and behavioral responses associated thirst and salt appetite, although clearly it may relate them to other functions as well. The BSTdm generates the densest known inputs directly to the neuroendocrine system from any part of the cerebral hemispheres.

Effects of losartan and irbesartan administration on brain angiotensinogen mRNA levels

Losartan, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'(1H-tetrazol-5-yl)-biphenil-4-yl)methyl]imidazole, and Irbesartan, 2-n-butyl-3-[(2'-(1H-tetrazol-5-yl)-biphenyl-4-yl)methyl]-1,3-diaza-spiro[4,4]non-1-en-4-one, are two angiotensin AT1 receptor antagonists largely used in human health care as antihypertensive agents. Their ability to cross the blood-brain barrier and to influence the central renin-angiotensin system are widely investigated, but how this brain system responds to the subchronic and chronic block of the angiotensin AT1 receptor is still unknown. Normotensive rats were intragastrically implanted for 7- and 30-day administration, with a dose of 3 and 30 mg/kg body weight. Treatments were shown to influence, in a dose-, time- and brain-area-dependent manner, angiotensinogen mRNA levels in scanned areas. This study showed a general up-regulation of angiotensinogen mRNA expression after 7 days and a widespread down-regulation or basal level of expression after a 30-day administration of two angiotensin AT1 receptor antagonists.

Translation of salt retention to central activation of the sympathetic nervous system in hypertension

1. Increased dietary salt increases blood pressure in many hypertensive individuals, producing salt-sensitive hypertension (SSH). The cause is unknown, but a major component appears to be activation of the sympathetic nervous system. The purpose of this short review is to present one hypothesis to explain how increased dietary salt increases sympathetic activity in SSH. 2. It is proposed that increased salt intake causes salt retention and raises plasma sodium chloride (NaCl) concentrations, which activate sodium/osmoreceptors to trigger sympathoexcitation. Moreover, we suggest that small and often undetectable increases in osmolality can drive significant sympathoexcitation, because the gain of the relationship between osmolality and increased sympathetic activity is enhanced. Multiple factors may contribute to this facilitation, including inappropriately elevated levels of angiotensin II or aldosterone, changes in gene expression or synaptic plasticity and increased sodium concentrations in cerebrospinal fluid. 3. Future studies are required to delineate the brain sites and mechanisms of action and interaction of osmolality and these amplification factors to elicit sustained sympathoexcitation in SSH.

Thermoregulatory role of periventricular tissue surrounding the anteroventral third ventricle (AV3V) during acute heat stress in the rat

1. Thermoregulatory effector mechanisms are strongly influenced by hydration status. Dehydration delays the onset of evaporative heat loss and the redistribution of cardiac output in response to elevations in core temperature, yet very little is known about how and where thermal and non-thermal information is integrated. 2. The anteroventral third ventricular (AV3V) region encompasses several distinct neural structures, including the organum vasculosum of the lamina terminalis, the median preoptic nucleus, the preoptic periventricular nucleus and the medial aspects of the medial preoptic nucleus. In addition to its well-documented role in body fluid and cardiovascular homeostasis, recent anatomical and in vitro evidence has indicated the AV3V region may also be pivotal in the integration of thermal and osmotic information. 3. Electrolytic lesions of the AV3V region produce a markedly reduced thermal tolerance in rats. Elevations in mean arterial pressure, heart rate and mesenteric resistance were all attenuated in the AV3V-lesioned animals in response to a heat stress; however, hindquarter resistance was unaffected. Heat-induced salivation was also attenuated, severely reducing the ability of rats to lose heat via evaporation. 4. The AV3V region clearly has a functional role in thermoregulation, as well as cardiovascular and body fluid homeostasis. These data add further support to the hypothesis that thermal and non-thermal information may be integrated within this region.

Forebrain patterns of c-Fos and FosB induction during cancer-associated anorexia-cachexia in rat

Forebrain structures are necessary for the initiation of food intake and its coupling to energy expenditure. The cancer-related anorexia-cachexia syndrome is typified by a prolonged increase in metabolic rate resulting in body weight loss which, paradoxically, is accompanied by reduced food intake. The aim of the present work was to study the forebrain expression of Fos proteins as activation markers and thus to identify potential neurobiological mechanisms favouring catabolic processes or modulating food intake in rats suffering from cancer-related anorexia-cachexia. Neurons in forebrain structures showing most pronounced induction of Fos proteins were further identified neurochemically. To provoke anorexia-cachexia, cultured Morris hepatoma 7777 cells were injected subcutaneously in Buffalo rats. This resulted in a slowly growing tumour inducing approximately 7% body weight loss and a 20% reduction in food intake when the tumour represented 1-2% of body mass. Anorexia-cachexia in these animals was found to be accompanied by Fos induction in several hypothalamic nuclei including the paraventricular and ventromedial hypothalamus, in the parastrial nucleus, the amygdala, the bed nucleus of the stria terminalis, ventral striatal structures and the piriform and somatosensory cortices. Neurochemical identification revealed that the vast majority of FosB-positive neurons in the nucleus accumbens, ventral caudate-putamen and other ventral striatal structures contained prodynorphin or proenkephalin mRNA. These findings indicate that forebrain structures that are part of neuronal networks modulating catabolic pathways and food ingestion are activated during tumour-associated anorexia-cachexia and may contribute to the lack of compensatory eating in response to weight loss characterizing this syndrome.

Median preoptic neurones projecting to the hypothalamic paraventricular nucleus respond to osmotic, circulating Ang II and baroreceptor input in the rat

The present study sought to determine whether individual neurones of the median preoptic nucleus (MnPO) with axonal projections to the hypothalamic paraventricular nucleus (MnPO-PVN) respond to osmotic, circulating angiotensin II (Ang II), and baroreceptor stimulation. Hypertonic NaCl (0.75 or 1.5 osmol l(-1)) or Ang II (150 ng) was injected into the internal carotid artery (ICA). Baroreceptor stimulation was performed by i.v. injection of phenylephrine or sodium nitroprusside to increase or decrease arterial blood pressure, respectively. Of 65 MnPO neurones, 50 units were antidromically activated from the PVN with an average onset latency of 11.3 +/- 0.7 ms. Only 9.5% of MnPO-PVN neurones were antidromically activated from the PVN bilaterally. Type I MnPO-PVN neurones (n = 14) responded to osmotic but not Ang II stimulation. In 79% (11/14) of these type I neurones, the response was an increase in cell discharge. Type II MnPO-PVN neurones (n = 7) displayed a significant increase in cell discharge in response to ICA injection of Ang II but not hypertonic NaCl. Type III MnPO-PVN neurones (n = 16) responded to both ICA injection of hypertonic NaCl and Ang II. In 88% (14/16) of type III neurones, osmotic and Ang II stimulation each increased cell discharge. Type IV MnPO-PVN neurones (n = 13) displayed no change in cell discharge in response to ICA injection of hypertonic NaCl or Ang II. Baroreceptor stimulation altered the discharge in subpopulations of type I, II and III MnPO-PVN neurones (43-63% depending on neuronal type). Only one MnPO-PVN neurone responded solely to baroreceptor stimulation (type IV). In addition, a subset of type I, II and III neurones displayed a significant correlation with sympathetic nerve activity and/or the cardiac cycle. These findings suggest that a significant population of MnPO-PVN neurones respond to osmotic and circulating Ang II stimulation and thereby represents a neural substrate through which neurohumoral inputs are integrated within the forebrain lamina terminalis.

Vivid dreams, hallucinations, psychosis and REM sleep in Guillain–Barré syndrome

We conducted a prospective controlled study of the clinical and biological determinants of the mental status abnormalities in 139 patients with Guillain-Barré syndrome (GBS) and 55 patients without GBS placed in the intensive care unit (ICU controls). There were mental status changes in 31% of GBS patients and in 16% of controls (odds ratio = 2.3; P = 0.04). In GBS patients, they included vivid dreams (19%), illusions (30%, including an illusory body tilt), hallucinations (60%, mainly visual) and delusions (70%, mostly paranoid). They appeared a median 9 days after disease onset (range 1-40 days, during the progression or the plateau of the disease), and lasted a median 8 days. Seven (16%) patients experienced the symptoms before their admission to the ICU. Hallucinations were frequently hypnagogic, occurring as soon as the patients closed their eyes. Autonomic dysfunction, assisted ventilation and high CSF protein levels were significant risk factors for abnormal mental status in GBS patients. CSF hypocretin-1 (a hypothalamic neuropeptide deficient in narcolepsy) levels, measured in 20 patients, were lower in GBS patients with hallucinations (555 +/- 132 pg/ml) than in those without (664 +/- 71 pg/ml, P = 0.03). Since the mental status abnormalities had dream-like aspects, we examined their association with rapid eye movement sleep (REM sleep) using continuous sleep monitoring in 13 GBS patients with (n = 7) and without (n = 6) hallucinations and 6 tetraplegic ICU controls without hallucinations. Although sleep was short and fragmented in all groups, REM sleep latency was shorter in GBS patients with hallucinations (56 +/- 115 min) than in GBS patients without hallucinations (153 +/- 130 min) and in controls (207 +/- 179 min, P < 0.05). In addition, sleep structure was highly abnormal in hallucinators, with sleep onset in REM sleep periods (83%), abnormal eye movements during non-REM sleep (57%), high percentages of REM sleep without atonia (92 +/- 22%), REM sleep behaviour disorders and autonomic dysfunction (100%), reminiscent of a status dissociatus. The sleep abnormalities, that were almost absent in non-hallucinated GBS patients, were not exclusively related to ICU conditions, since they also appeared out of ICU, and were reversible, disappearing when the mental status abnormalities vanished while the patients were still in ICU. In conclusion, the mental status abnormalities experienced by GBS patients are different from the ICU delirium, are strongly associated with autonomic dysfunction, severe forms of the disease and possibly with a transitory hypocretin-1 transmission decrease. Sleep studies suggest that mental status abnormalities are wakeful dreams caused by a sleep and dream-associated disorder (status dissociatus).

GABAergic and glycinergic presympathetic neurons of rat medulla oblongata identified by retrograde transport of pseudorabies virus and in situ hybridization

Electron microscopy suggests that up to half the synaptic input to sympathetic preganglionic neurons (SPGNs) is GABAergic or glycinergic. A proportion of this input is suspected to originate from neurons located within the medulla oblongata. The present study provides definitive evidence for the existence of these supraspinal presympathetic (PS) neurons with inhibitory phenotypes. PS neurons were identified by retrograde trans-synaptic migration of pseudorabies virus (PRV) injected into the adrenal gland. GABAergic or glycinergic cell bodies were identified by the presence of glutamate decarboxylase (GAD)-67 mRNA or glycine transporter (GlyT)-2 mRNA detected with in situ hybridization (ISH). Neither GABAergic nor glycinergic PS neurons were tyrosine hydroxylase (TH)-immunoreactive (ir). GABAergic PS neurons were located within the ventral gigantocellular nucleus, gigantocellular nucleus alpha, and medial reticular formation, mostly medial to the TH-ir PS neurons. About 30% of GABAergic PS neurons were serotonergic cells located in the raphe pallidus (RPa) and parapyramidal region (PPyr). Glycinergic PS neurons had the same general distribution as the GABAergic cells, except that no glycinergic neurons were located in the RPa or PPyr and none were serotonergic. PRV immunohistochemistry combined with ISH for both GlyT2 and GAD-67 mRNAs showed that at least 63% of midline medulla GABAergic PS neurons were also glycinergic and 76% of glycinergic PS neurons were GABAergic. In conclusion, the rostral ventromedial medulla contains large numbers of GABAergic and glycinergic neurons that innervate adrenal gland SPGNs. Over half of these PS neurons may release both transmitters. The physiological role of this medullary inhibitory input remains to be explored.

Increased osmolality of conscious water-deprived rats supports arterial pressure and sympathetic activity via a brain action

To test the hypothesis that high osmolality acts in the brain to chronically support mean arterial pressure (MAP) and lumbar sympathetic nerve activity (LSNA), the osmolality of blood perfusing the brain was reduced in conscious water-deprived and water-replete rats by infusion of hypotonic fluid via bilateral nonoccluding intracarotid catheters. In water-deprived rats, the intracarotid hypotonic infusion, estimated to lower osmolality by approximately 2%, decreased MAP by 9+/-1 mmHg and LSNA to 86+/-7% of control; heart increased by 25+/-8 beats per minute (bpm) (all P<0.05). MAP, LSNA, and heart rate did not change when the hypotonic fluid was infused intravenously. The intracarotid hypotonic fluid infusion was also ineffective in water-replete rats. Prior treatment with a V1 vasopressin antagonist did not alter the subsequent hypotensive and tachycardic effects of intracarotid hypotonic fluid infusion in water-deprived rats. In summary, acute decreases in osmolality of the carotid blood of water-deprived, but not water-replete, rats decreases MAP and LSNA and increases heart rate. These data support the hypothesis that the elevated osmolality induced by water deprivation acts via a region perfused by the carotid arteries, presumably the brain, to tonically increase MAP and LSNA and suppress heart rate.

Lesions of the anteroventral third ventricle region (AV3V) disrupt cardiovascular responses to an elevation in core temperature

Blood flow is redistributed from the viscera to the periphery during periods of heat stress to maximize heat loss. The heat-induced redistribution of blood flow is strongly influenced by nonthermal inputs such as hydration status. At present, little is known about where thermal and nonthermal information is integrated to generate an appropriate effector response. Recently, the periventricular tissue that surrounds the anteroventral third ventricle (AV3V) has been implicated in the integration of thermal and osmotic information. The purpose of the present study was to determine the effects of electrolytic lesions of the AV3V on the cardiovascular response to a passive heat stress in unanesthetized, free-moving male Sprague-Dawley rats. Core temperature was elevated at a constant rate of approximately 0.03 degrees C/min in sham- and AV3V-lesion rats using an infrared heat lamp. Changes in mesenteric and hindquarter vascular resistance were determined using Doppler flow probes, and heat-induced salivation was estimated using the spit-print technique. The rise in mean arterial pressure (MAP), heart rate (HR), and mesenteric resistance in response to elevations in core temperature were all attenuated in AV3V-lesion rats; however, hindquarter resistance was unaffected. Heat-induced salivation was also diminished. In addition, AV3V-lesion rats were more affected by the novelty of the experimental environment, resulting in a higher basal core temperature, HR, and MAP. These results indicate that AV3V lesions disrupt the cardiovascular and salivatory response to a passive heat stress in rats and produce an exaggerated stress-induced fever triggered by a novel environment.

Sequence of forebrain activation induced by intraventricular injection of hypertonic NaCl detected by Mn2+ contrasted T1-weighted MRI

In order to define the sequence of forebrain activation involved in osmoregulation, central activation in response to intracerebroventricular injection of NaCl solution (10 microl of 0.15, 0.5, or 1.5 M) was detected using manganese-contrasted magnetic resonance imaging (MRI) in anesthetized rats. Changes in renal sympathetic nerve activity (RNA) were also measured, and the time courses of forebrain activation and RNA changes compared. NaCl injection resulted in rapid activation of the subfornical organ (SFO), organum vasculosum lamina terminalis (OVLT), and periventricular regions and the lateral hypothalamic area (LHA), then of the paraventricular hypothalamic nucleus (PVN) and supraoptic nucleus (SON). The delay in activation in the PVN and SON showed a wide variation from 0 to 5.78 min, and the average delay in the PVN (2.88+/-0.34 min) and SON (2.90+/-0.39 min) was significantly greater than that in the SFO (0.40+/-0.10 min) and OVLT (0.74+/-0.13 min). NaCl (1.5 M) injection elicited a rapid, large increase in RNA, which consisted of two components, an early rapid increase at 99 s after injection (160+/-27%) and a slower increase at 9 min after injection (209+/-34%). These results suggest that the PVN and SON are activated not only by the afferent input from the SFO and OVLT but also by diffusion of the hypertonic stimulus to these regions and probably by their intrinsic osmosensitivity. The PVN might be responsible for the second slower component of the RNA response, but cannot be responsible for the first component.

Suprachiasmatic nucleus input to autonomic circuits identified by retrograde transsynaptic transport of pseudorabies virus from the eye

Intraocular injection of the Bartha strain of pseudorabies virus (PRV Bartha) results in transsynaptic infection of the hypothalamic suprachiasmatic nucleus (SCN), a retinorecipient circadian oscillator. PRV Bartha infection of a limited number of retinorecipient structures, including the SCN, was initially interpreted as the differential infection of a subpopulation of rat retinal ganglion cells, followed by replication and anterograde transport via the optic nerve. A recent report that used a recombinant strain of PRV Bartha (PRV152) expressing enhanced green fluorescent protein demonstrated that SCN infection actually results from retrograde transneuronal transport of the virus via the autonomic innervation of the eye in the golden hamster. In the present study using the rat, the pattern of infection after intravitreal inoculation with PRV152 was examined to determine if infection of the rat SCN is also restricted to retrograde transsynaptic transport. It was observed that infection in preganglionic autonomic nuclei (i.e., Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus) precedes infection in the SCN. Sympathetic superior cervical ganglionectomy did not abolish label in the SCN after intraocular infection, nor did lesions of parasympathetic preganglionic neurons in the Edinger-Westphal nucleus. However, combined Edinger-Westphal nucleus ablation and superior cervical ganglionectomy eliminated infection of the SCN. This observation allowed a detailed examination of the SCN contribution to descending autonomic circuits afferent to the eye. The results indicate that in the rat, as in the hamster, SCN infection after intraocular PRV152 inoculation is by retrograde transsynaptic transport via autonomic pathways to the eye.

Inhibitory effect of atriopeptinergic neurons in AV3V region on angiotensinII pressor system in rat brain

In the central nervous system and the periphery, atrial natriuretic peptide (ANP) and angiotensinII(AngII) play important and opposite roles in regulating blood pressure and fluid electrolyte balance. Their central mechanisms are unclear. In the brain the anteroventral third ventricle region (AV3V) contains the most prominent collection of atriopeptin-like immunoreactive perikarya. Our previous studies show that: (1) AV3V stimulation by glutamate produces a fall in blood pressure; (2) there is an AngII pressor system composed of the lateral hypothalamus/perifornical region (LH/PF), subfornical organ (SFO), nucleus paraventricularis (NPV) and rostral ventrolateral medulla (RVL). The present study was to examine whether ANPergic projections from the AV3V could act on nuclei involved in the above-mentioned AngII pressor system. Here we demonstrate that: (1) Injection of atriopeptinIII into the LH/PF, SFO, NPV, or RVL induces a depressor response; whereas injection of normal saline has no effect. (2) Pre-injection of A 71915 (an atriopeptinIII antagonist) into the LH/PF, SFO, NPV, or RVL reverses the depressor response of the AV3V to glutamate (Glu). The results suggest that excitation of atriopeptinergic neurons in the AV3V by Glu produces an inhibitory effect on each nucleus in the LH/PF-SFO-NPV-RVL AngII pressor system.

Orexin neurons project to diverse sympathetic outflow systems

The viral transneuronal labeling method was used to demonstrate that orexin-containing neurons of the lateral hypothalamic area (LHA) are linked via multisynaptic connections to different sympathetic outflow systems. Two different types of transneuronal tracing experiments were performed: single- and double-virus studies. In the first series of experiments, Bartha pseudorabies virus (PRV), a retrograde transneuronal tracer, was injected into single sympathetic targets, viz., stellate ganglion, adrenal gland, celiac ganglion, and kidney. Six to 7 days post-injection, orexin (hypocretin) neurons were transneuronally labeled. In a second set of experiments, the double-virus tracing method was used to determine whether single orexin LHA neurons are linked to two different sympathetic outflow systems. Two isogenic forms of Bartha PRV were used that differed by a single gene. beta-Galactosidase Bartha PRV was injected into the stellate ganglion and green fluorescent protein Bartha PRV into the adrenal gland of the same rat. The reverse placement of viral injections was made in another set of rats. In both paradigms, some orexin LHA neurons were transneuronally labeled with both viruses, indicating that they are capable of modulating multiple sympathetic outflow systems. These findings raise the possibility that orexin LHA neurons regulate general sympathetic functions, such as those that occur during arousal or the fight-or-flight response.

Circulating angiotensin II activates neurones in circumventricular organs of the lamina terminalis that project to the bed nucleus of the stria terminalis

The aim of this study was to determine, in conscious rats, whether elevated concentrations of circulating angiotensin II activate neurones in both the subfornical organ and organum vasculosum of the lamina terminalis (OVLT) that project to the bed nucleus of the stria terminalis (BNST). The strategy employed was to colocalize retrogradely transported cholera toxin B subunit (CTB) from the BNST, with elevated levels of Fos protein in response to angiotensin II. Circulating angiotensin II concentrations were increased by either intravenous infusion of angiotensin II or subcutaneous injection of isoproterenol. Neurones exhibiting Fos in response to angiotensin II were present in the subfornical organ, predominantly in its central core but with some also seen in its peripheral aspect, the dorsal and lateral margins of the OVLT, the supraoptic nucleus and the parvo- and magnocellular divisions of the paraventricular nucleus. Fos-labelling was not apparent in control rats infused with isotonic saline intravenously or injected with either CTB or CTB conjugated to gold particles (CTB-gold) only. Of the neurones in the subfornical organ that were shown by retrograde labelling to project to BNST, approximately 50% expressed Fos in response to isoproterenol. This stimulus also increased Fos in 33% of neurones in the OVLT that project to BNST. Double-labelled neurones were concentrated in the central core of the subfornical organ and lateral margins of the OVLT in response to increased circulating angiotensin II resulting from isoproterenol treatment. These data support a role for circulating angiotensin II acting either directly or indirectly on neurones in subfornical organ and OVLT that project to the BNST and provide further evidence of functional regionalization within the subfornical organ and the OVLT. The function of these pathways is yet to be determined; however, a role in body fluid homeostasis is possible.

Neuroglobin, a novel member of the globin family, is expressed in focal regions of the brain

Hemoproteins are widely distributed among unicellular eukaryotes, plants, and animals. In addition to myoglobin and hemoglobin, a third hemoprotein, neuroglobin, has recently been isolated from vertebrate brain. Although the functional role of this novel member of the globin family remains unclear, neuroglobin contains a heme-binding domain and may participate in diverse processes such as oxygen transport, oxygen storage, nitric oxide detoxification, or modulation of terminal oxidase activity. In this study we utilized in situ hybridization (ISH) and RT-PCR analyses to examine the expression of neuroglobin in the normoxic and hypoxic murine brain. In the normoxic adult mouse, neuroglobin expression was observed in focal regions of the brain, including the lateral tegmental nuclei, the preoptic nucleus, amygdala, locus coeruleus, and nucleus of the solitary tract. Using ISH and RT-PCR techniques, no significant changes in neuroglobin expression in the adult murine brain was observed in response to chronic 10% oxygen. These results support the hypothesis that neuroglobin is a hemoprotein that is expressed in the brain and may have diverse functional roles.

Neurochemistry of nerve fibers apposing sympathetic preganglionic neurons activated by sustained hypotension

Sympathetic preganglionic neurons (SPN) in rat spinal cord were activated by the reflex stimulation of bulbospinal sympathetic neuronal pathways after a nitroprusside-induced hypotension. Hypotension-sensitive SPN, identified by immunoreactivity (IR) to the product of the immediate early gene c-fos and to choline acetyltransferase, were localized in the intermediolateral cell column of thoracic and upper lumbar cord, particularly middle to lower thoracic cord. Putative neurotransmitters, or their markers, in varicose fiber networks around SPN were identified. Nearly all hypotension-sensitive (Fos-IR) SPN were apposed by varicose fibers immunoreactive for tyrosine hydroxylase, serotonin, substance P, or enkephalin. Neuropeptide Y (NPY)- or phenylethanolamine-N-methyl transferase (PNMT)-IR varicose fibers apposed Fos-IR SPN in the upper and middle thoracic spinal cord, but in lower thoracic segments some Fos-IR SPN lacked these appositions. In thoracic segment 12, 51% +/- 5% of Fos-IR SPN (n = 9 rats) lacked PNMT contacts and 25% +/- 3% of Fos-IR SPN (n = 8 rats) lacked NPY contacts. In contrast to other chemically defined afferents, galanin-IR varicose fibers apposed fewer than half of the Fos-IR SPN in the middle to lower thoracic cord. Neurotransmitters/neuromodulators that might influence the activity of SPN acting in the baroreflex-mediated control of blood pressure have been identified. Uniformity in the neurochemistry of some fibers making connections with Fos-IR SPN, regardless of their segmental origin, suggests that common sets of neurons provide convergent inputs to all hypotension-sensitive SPN. Other fibers show topographic differences in their contacts with Fos-IR SPN, suggesting that subgroups of hypotension-sensitive SPN are targeted by particular neuron groups.

CNS inputs to the suprachiasmatic nucleus of the rat

The neural circuits that modulate the suprachiasmatic nucleus (SCN) of the rat were studied with the retrograde transneuronal tracer--pseudorabies virus. First-order afferents were also identified using cholera toxin beta subunit. Olfactory processing regions (viz., main olfactory bulb, anterior olfactory nucleus, taenia tecta, endopiriform nucleus, medial amygdaloid nucleus, piriform cortex, and posteriomedial cortical amygdaloid nucleus) were virally labeled. The subfornical organ directly innervates SCN; two other circumventricular organs: organum vasculosum of the lamina terminalis and area postrema provide multisynaptic inputs. Direct limbic afferents arise from lateral septum, bed nucleus of the stria terminalis, amygdalohippocampal zone, and ventral subiculum; multineuronal connections come from the basolateral and basomedial amygdaloid nuclei, ventral hippocampus, amygdalopiriform area, as well as lateral entorhinal, perirhinal, and ectorhinal cortices. Most preoptic regions project directly to SCN. Multisynaptic inputs come from the lateral preoptic region. Hypothalamic inputs originate from the anterior, arcuate, dorsal, dorsomedial, lateral, paraventricular, posterior, periventricular posterior, retrochiasmatic, subparaventricular, ventromedial and tuberomammillary nuclei. Paraventricular thalamic nucleus, intergeniculate leaflet and zona incerta directly innervate SCN. Polyneuronal inputs arise from the subparafascicular parvicellular thalamic nucleus. Brainstem afferents originate from the pretectum, superior colliculus, periaqueductal gray matter, parabrachial nucleus, pedunculopontine nucleus, raphe system, locus coeruleus, nucleus incertus and reticular formation. Nucleus tractus solitarius, C3 catecholamine region, rostral ventrolateral medulla and spinal trigeminal nucleus provide indirect inputs. We propose that the SCN receives feedback primarily from interoceptive systems such as the circumventricular, autonomic, and neuroendocrine systems that are important in the central regulation of glucose metabolism (e.g., insulin and glucocorticoids).

Neural pathways from the lamina terminalis influencing cardiovascular and body fluid homeostasis

1. The lamina terminalis, a region of the brain with a high concentration of angiotensin AT1 receptors, consists of three distinct nuclei, the median preoptic nucleus, the subfornical organ and organum vasculosum of the lamina terminalis (OVLT). These latter two regions lack a blood-brain and detect changes in plasma angiotensin (Ang) II concentration and osmolality. 2. Efferent neural pathways from the lamina terminalis to the hypothalamic paraventricular and supraoptic nuclei mediate vasopressin secretion in response to plasma hypertonicity and increased circulating levels of AngII. 3. Studies using the neurotropic virus pseudorabies, which undergoes retrograde transynaptic neuronal transport following injection into peripheral sites, show that neurons in the lamina terminalis have efferent polysynaptic neural connections to the peripheral sympathetic nervous system. Some of these neurons have been shown to have polysynaptic connections to the kidney and to express AT1 receptor mRNA. We propose that circulating AngII acts at AT1 receptors in the subfornical organ and OVLT to influence the sympathetic nervous system. It is likely that the neural pathway subserving this influence involves a synapse in the hypothalamic paraventricular nucleus. 4. The lamina terminalis may exert an inhibitory osmoregulatory influence on renin secretion by the kidney. This osmoregulatory influence may be mediated by inhibition of renal sympathetic nerve activity and appears to involve a central angiotensinergic synapse. 5. The lamina terminalis exerts an osmoregulatory influence on renal sodium excretion that is independent of the renal nerves and is probably hormonally mediated.