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The objective of this study was to elucidate the effect of chronic stress (CS) on dopamine (DA) level and synaptic efficiency in the hippocampal dentate gyrus (DG) during spatial learning and memory. Sprague Dawley (SD) male rats were randomly divided into control group and CS group (n = 10). CS group was treated with chronic mild unpredictable stress, and control group did not receive any treatments. The levels of epinephrine and corticosterone (CORT) in serum were measured by using enzyme-linked immunosorbent assay (ELISA); the spatial learning and memory abilities of rats were measured by Morris water maze (MWM) test. Meanwhile, the amplitude of field excitatory postsynaptic potential (fEPSP) and concentration of DA in the DG region were determined by in vivo electrophysiology, microdialysis and HPLC techniques during MWM test in rats. After that, the DA D1 receptor (D1R) and its key downstream members in DG were examined by immunohistochemistry or Western blot assay. The results showed that the levels of epinephrine and CORT in the serum of the rats in CS group were significantly increased compared with those in the control group (P0.05). In CS group rats, the escape latency was significantly prolonged and the number of platform crossing was markedly decreased during MWM test, compared with those in control group (P0.05). Furthermore, the amplitude of fEPSP in the DG was not changed during MWM test in CS rats, while it was significantly increased on the 3rd day of MWM test in control group (P0.05). Compared with baseline or control group, CS group showed significantly increased DA level from the 1st to 3rd days of MWM test in the DG (P0.05). In addition, the protein expression of D1R was markedly up-regulated in the DG in CS group, while the protein expression levels of p-PKA, p-CREB and BDNF were significantly reduced, compared with those in control group. These results suggest that CS may impair spatial learning and memory abilities in rats through the enhancement of the DA levels in the hippocampal DG.

The role of norepinephrine of the hippocampal dentate gyrus in spatial learning and memory alteration induced by chronic restraint stress (CRS, 3 h/day, 6 weeks) was investigated in aged rats. Spatial learning and memory were assessed by the Morris water maze (MWM), and the extracellular concentration of norepinephrine and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the dentate gyrus during MWM test in freely-moving rats. Next, the involvement of β-adrenoceptors in spatial learning and memory of CRS rats was examined by microinjection of its antagonist (propranolol) into the dentate gyrus. In addition, we observed the expression of brain-derived neurotrophic factor (BDNF) protein and activation of cAMP-response element binding protein (CREB) in the dentate gyrus. Compared with the control group, the basal level of norepinephrine, BDNF expression and CREB activation in the dentate gyrus were increased, and the spatial learning and memory abilities were enhanced in CRS rats. In the control group, the norepinephrine concentration and fEPSP amplitude in the dentate gyrus were increased on the second to fourth days of MWM test, and these responses were significantly enhanced in CRS rats. Furthermore, in CRS rats, propranolol significantly decreased the spatial learning and memory abilities, and attenuated the fEPSP response during MWM test, and the BDNF expression and CREB activation in the dentate gyrus. Our results suggest that norepinephrine activation of β-adrenoceptors in the hippocampal dentate gyrus is involved in spatial learning and memory enhancement induced by CRS in aged rats, in part via modulations of synaptic efficiency and CREB-BDNF signaling pathway.

Increasing evidence supports that dopamine (DA) plays an important role in the hippocampal function via activation of D1-like receptors (D1Rs). As the entry structure of the hippocampal formation, the hippocampal dentate gyrus (DG) is critically involved in spatial learning and memory. Despite a number of studies investigated how DA influences CA1 plasticity and learning, there are fewer studies examining the influence of DA signaling to the DG. To investigate the roles of DA and D1Rs of the DG in modulation of spatial learning and memory, the spatial learning and memory abilities of rats were measured by Morris water maze (MWM), and then the concentration of DA in the DG region was determined by in vivo brain microdialysis and HPLC. Next, the effects of local microinjection of SCH23390 (an antagonist of D1Rs) on extracellular levels of excitatory amino acids (EAAs), including glutamate (Glu) and aspartate (Asp), were measured in the DG region during MWM test in freely-moving conscious rats. During the place navigation trial of MWM test, the escape latency was decreased with the increase in training days, and DA concentration in the DG was significantly increased. In SCH23390 group rats, the escape latency was increased in place navigation trial and the percentage of time spent in target quadrant and the number of platform crossings were decreased in spatial probe trial during MWM test, compared with vehicle group. Furthermore, in vehicle group rats, the extracellular levels of Glu and Asp in the DG were significantly increased during place navigation trial of MWM test, and these responses were partly inhibited by microinjection of SCH23390. Our results suggest that DA activation of D1Rs in the hippocampal DG promotes spatial learning and memory, in part by modulating the responses of EAAs during spatial learning.

Nitric oxide (NO)-dependent pathways may play a significant role in the decline of synaptic and cognitive functions in Alzheimer's disease (AD). However, whether NO in the hippocampal dentate gyrus (DG) is involved in the spatial learning and memory impairments of AD by affecting the glutamate (Glu) response during these processes is not well-understood. Here, we prepared an AD rat model by long-term i.p. of D-galactose into ovariectomized rats, and then the effects of L-NMMA (a NO synthase inhibitor) on Glu concentration and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the DG region during the Morris water maze (MWM) test in freely-moving rats. During the MWM test, compared with the sham group, the escape latency was increased in the place navigation trial, and the percentage of time spent in target quadrant and the number of platform crossings were decreased in the spatial probe trial, in addition, the increase of fEPSP amplitude in the DG was significantly attenuated in AD group rats. L-NMMA significantly attenuated the spatial learning and memory impairment in AD rats, and reversed the inhibitory effect of AD on increase of fEPSP amplitude in the DG during the MWM test. In sham group rats, the Glu level in the DG increased significantly during the MWM test, and this response was markedly enhanced in AD rats. Furthermore, the response of Glu in the DG during spatial learning was recovered by microinjection of L-NMMA into the DG. Our results suggest that NO in the DG impairs spatial learning and memory and related synaptic plasticity in AD rats, by disturbing the Glu response during spatial learning.

Long-term potentiation (LTP) is widely accepted as the best studied model for neurophysiological mechanisms that could underlie learning and memory formation. Despite a number of studies indicating that β-adrenoceptors in the hippocampal dentate gyrus (DG) is involved in the modulation of learning and memory as well as LTP, few studies have used glutamate release as a visual indicator in awake animals to explore the role of β-adrenoceptors in learning-dependent LTP. Therefore, in the present study, the effects of propranolol (an antagonist of β-adrenoceptor) and isoproterenol (an agonist of β-adrenoceptor) on extracellular concentrations of glutamate and amplitudes of field excitatory postsynaptic potential were measured in the DG region during active avoidance learning in freely moving conscious rats. In the control group, the glutamate level in the DG was significantly increased during the acquisition of active avoidance behavior and returned to basal level following extinction training. In propranolol group, antagonism of β-adrenoceptors in the DG significantly reduced the change in glutamate level, and the acquisition of the active avoidance behavior was significantly inhibited. In contrast, the change in glutamate level was significantly enhanced by isoproterenol, and the acquisition of the active avoidance behavior was significantly accelerated. Furthermore, in all groups, the changes in glutamate level were accompanied by corresponding changes in field excitatory postsynaptic potential amplitude and active avoidance behavior. Our results suggest that activation of β-adrenoceptors in the hippocampal DG facilitates active avoidance learning by modulations of glutamate level and synaptic efficiency in rats.

Propofol is an intravenous sedative-hypnotic agen, which causes rapid and reliable loss of consciousness. Under in vitro conditions, propofol activates GABAA and glycine receptors in spinal cord, hippocampus and hypothalamus neurons. However, the effects of propofol on the cerebellar neuronal activity under in vivo conditions are currently unclear. In the present study, we examined the effects of propofol on the spontaneous activity of Purkinje cells (PCs) in urethane-anesthetized mice by cell-attached recording and pharmacological methods. Our results showed that cerebellar surface perfusion of propofol (10-1000 μM) induced depression of the PC simple spike (SS) firing rate in a dose-dependent manner, but without significantly changing the properties of complex spikes (CS). The IC50 of propofol for inhibiting SS firing of PCs was 144.5 μM. Application of GABAA receptor antagonist, SR95531 (40 μM) or GABAB receptor antagonist, saclofen (20 μM), as well as glycine receptor antagonist, strychnine (10 μM) alone failed to prevent the propofol-induced inhibition of PCs spontaneous activity. However, application the mixture of SR95531 (40 μM) and strychnine (10 μM) completely blocked the propofol-induced inhibition of PC SS firing. These data indicated that cerebellar surface application of propofol depressed PC SS firing rate via facilitation of GABAA and functional glycine receptors activity in adult cerebellar PCs under in vivo conditions. Our present results provide a new insight of the anesthetic action of propofol in cerebellar cortex, suggesting that propofol depresses the SS outputs of cerebellar PCs which is involved in both GABAA and glycine receptors activity.

The hippocampus is a key structure for learning and memory in mammals, and long-term potentiation (LTP) is an important cellular mechanism responsible for learning and memory. Despite a number of studies indicating that nitric oxide (NO) is involved in the formation and maintenance of LTP as a retrograde messenger, few studies have used neurotransmitter release as a visual indicator in awake animals to explore the role of NO in learning-dependent long-term enhancement of synaptic efficiency. Therefore, in the present study, the effects of l-NMMA (a NO synthase inhibitor) and SNP (a NO donor) on extracellular glutamate (Glu) concentrations and amplitudes of field excitatory postsynaptic potential (fEPSP) were measured in the hippocampal dentate gyrus (DG) region during the acquisition and extinction of active-avoidance behavior in freely-moving conscious rats. In the control group, the extracellular concentration of Glu in the DG was significantly increased during the acquisition of active-avoidance behavior and gradually returned to baseline levels following extinction training. In the experimental group, the change in Glu concentration was significantly reduced by local microinjection of l-NMMA, as was the acquisition of the active-avoidance behavior. In contrast, the change in Glu concentration was significantly enhanced by SNP, and the acquisition of the active-avoidance behavior was significantly accelerated. Furthermore, in all groups, the changes in extracellular Glu were accompanied by corresponding changes in fEPSP amplitude and active-avoidance behavior. Our results suggest that NO in the hippocampal DG facilitates active avoidance learning via enhancements of glutamate levels and synaptic efficiency in rats.

Edible salt (ES) is also thought to exacerbate the symptoms of Alzheimer, however, the in vivo function of ES remains poorly understand. In this work, we investigated the phenomenon using the model of Alzheimer induced by D-gal. The behavious examination results exhibited that D-gal plus ES can weaken spatial memory function in the Morris water maze; the activities of T-SOD, GSH-Px and the CAT level in both hippocampus and cortex showed that D-gal plus ES decreased the expression of T-SOD and GSH-Px, but the expression of CAT increased, the protein expression determined in both of the hippocampus and cortex demonstrated that COX-2, iNOS, NFκ-B-p65-N proteins were significantly increased. It is possible that ES acts through several mechanisms, mediating a potential role in memory damage in mice. These results suggest that further study is necessary to evaluate the effect of salt on damage of memory and to determine the molecular mechanisms.

Stresscopin-related peptide (SRP), which is a member of the corticotropin-releasing factor (CRF) family, is a high-affinity ligand for the type 2 corticotropin-releasing factor receptor (CRF-R2) and is involved in stress-coping responses. Central treatment with SRP suppresses food intake, delays gastric emptying and decreases heat-induced edema, but the effects of central administration of SRP on the cardiovascular system are unclear. Here we examined the effects of intracerebroventricular (i.c.v.) administration of SRP on cardiovascular function, and compared the cardiovascular effects of SRP and stresscopin (SCP). Our results showed that i.c.v. administration of SRP (0.5nmol) increased mean arterial blood pressure (MABP) and heart rate (HR), but failed to increase plasma norepinephrine and epinephrine levels. Compared with an equivalent dose of SCP, the area under the curve (AUC) values for the changes in MABP and HR were significantly smaller with SRP, indicating that the cardiovascular effects of SRP were weaker than those mediated by SCP. Pre-treatment with a selective CRF-R2 antagonist, antisauvagine-30 (4nmol, i.c.v.) abolished the SRP and SCP induced changes in MABP and HR. These results indicate that central administration of SRP induces a weaker enhancement of cardiovascular function through CRF-R2 than that induced by SCP and that these effects are mediated without increasing plasma norepinephrine and epinephrine levels.

The hippocampus is the key structure for learning and memory in mammals and long-term potentiation (LTP) is an important cellular mechanism responsible for learning and memory. The influences of norepinephrine (NE) on the modulation of learning and memory, as well as LTP, through β-adrenoceptors are well documented, whereas the role of α1-adrenoceptors in learning-dependent LTP is not yet clear. In the present study, we measured extracellular concentrations of NE in the hippocampal dentate gyrus (DG) region using an in-vivo brain microdialysis and high-performance liquid chromatography techniques during the acquisition and extinction of active-avoidance behavior in freely moving conscious rats. Next, the effects of prazosin (an antagonist of α1-adrenoceptor) and phenylephrine (an agonist of the α1-adrenoceptor) on amplitudes of field excitatory postsynaptic potential were measured in the DG region during the active-avoidance behavior. Our results showed that the extracellular concentration of NE in the DG was significantly increased during the acquisition of active-avoidance behavior and gradually returned to the baseline level following extinction training. A local microinjection of prazosin into the DG significantly accelerated the acquisition of the active-avoidance behavior, whereas a local microinjection of phenylephrine retarded the acquisition of the active-avoidance behavior. Furthermore, in all groups, the changes in field excitatory postsynaptic potential amplitude were accompanied by corresponding changes in active-avoidance behavior. Our results suggest that NE activation of α1-adrenoceptors in the hippocampal DG inhibits active-avoidance learning by modulation of synaptic efficiency in rats.

Surface reconstruction by alpha geometric shape based on triangulation is a new idea and method in computer graphics and reverse engineering. In the process of Topology reconstruction, the points are reduced and projected to a middle slice plane. The adjacency among slices is established by section line subdivision, and triangle mesh is stored and called by the form of STL. The simplexes are classified and computed in order to obtain α interval by the external-ball radius and center of every simplex, and the data structure is designed to save them. Through the man-machine interactive selection modes, α-shape can be reconstructed by different α parameters. The surface reconstruction is completed.

First principles calculations of the total energy of Mg2Si as a function of unit cell volume have been carried out for the cubic anti-fluorite (Fm3m) structure, the orthorhombic phase with anti-cotunnite (Pnma) structure and the hexagonal phase with Ni2In-type (P63/mmc) structure on the basis of density functional theory (DFT). All these calculations are performed with the CRYSTAL06 program package. In agreement with experiment, we also obtained the sequence of high-pressure phases for Mg2Si as: anti-fluorite → anti-cotunnite → Ni2In-type. Several structural properties (equilibrium lattice constant, bulk modulus, etc.) of the anti-fluorite structure have been calculated, which are also in agreement with the previous experimental results.

The roles of γ-aminobutyric acid (GABA) and GABAB receptors of the hippocampal dentate gyrus (DG) in spatial learning and memory impairment were investigated in a rat model of vascular dementia (VaD) established by permanent bilateral carotid occlusion. The extracellular concentration of GABA in the DG was determined by in vivo microdialysis and HPLC, and spatial learning and memory were assessed by the Morris water maze (MWM) test. Next, the possible involvement of GABAB receptors in spatial learning and memory impairments of VaD rats was examined by microinjection of its antagonist into the DG region. In VaD group rats, the extracellular concentration of GABA in the DG was significantly increased, and during MWM test, the escape latency was increased in place navigation trial and the percentage of time spent in target quadrant and the number of platform crossings were decreased in spatial probe trial, compared with the sham group. In sham-operated rats, the extracellular concentrations of glutamate (Glu) and glycine (Gly) in the DG were significantly increased during place navigation trial of MWM test, and these responses were inhibited in VaD rats. Saclofen (an antagonist of GABAB receptor) significantly attenuated the spatial learning and memory impairment in VaD rats, and partly reversed the inhibitory effects of VaD in responses of Glu and Gly in the DG during MWM test. Our results suggest that GABA and GABAB receptors in the hippocampal DG are involved in spatial learning and memory impairment in VaD rats, in part by attenuating the responses of Glu and Gly during spatial learning.

To investigate the effects of serotonin (5-HTIA) receptors in the hippocampal dentate gyrus (DG) on active avoidance learning in rats.Totally 36 SD rats were randomly divided into control group, antagonist group and agonist group(n = 12). Active avoidance learning ability of rats was assessed by the shuttle box. The extracellular concentrations of 5-HT in the DG during active avoidance conditioned reflex were measured by microdialysis and high performance liquid chromatography (HPLC) techniques. Then the antagonist (WAY-100635) or agonist (8-OH-DPAT) of the 5-HT1A receptors were microinjected into the DG region, and the active avoidance learning was measured.(1) During the active avoidance learning, the concentration of 5-HT in the hippocampal DG was significantly increased in the extinction but not establishment in the conditioned reflex, which reached 164.90% ± 26.07% (P0.05) of basal level. (2) The microinjection of WAY-100635 (an antagonist of 5-HT1A receptor) into the DG did not significantly affect the active avoidance learning. (3) The microinjection of 8-OH-DPAT(an agonist of 5-HT1A receptor) into the DG significantly facilitated the establishment process and inhibited the extinction process during active avoidance conditioned reflex.The data suggest that activation of 5-HT1A receptors in hipocampal DG may facilitate active avoidance learning and memory in rats.

Micrometer-sized MoO2 hollow spheres were synthesized hydrothermally with ammonium heptamolybdate tetrahydrate as molybdenum source, Cetyltrimethylammonium bromide as structure-directing agent and C2H5OH as reducing agent, respectively. The products were investigated by X-ray diffraction, thermogravimetry and differential thermal analysis, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A morphology transition of "blocks-solid spheres-hollow spheres" during the growth process was observed and the possible mechanism for the formation of MoO2 samples was proposed to be through a microscale Kirkendall effect.

Chronically instrumented, conscious rats were used to examine whether mild exteroceptive stress produces differential neurochemical changes in the hypothalamic paraventricular nucleus (PVN) region. We constructed systems for stress experiment of air jet and swing rotation that were conducted on freely moving conscious rats in a computer-controlled home cage. Concentration of extracellular norepinephrine (NE) and nitric oxide metabolites (NO X − ), nitrite (NO 2 − ) and nitrate (NO 3 − ), in the PVN region was then measured by high-performance liquid chromatography with the respective detector; blood pressure (BP) and heart rate (HR) were also measured. Both stressors increased NE concentration in the PVN region as well as BP and HR. Neither stressor altered NO X − in the PVN region. Cardiovascular and NE changes showed reproducibility in intensity-dependent manner in response to repeated stressors. This finding demonstrated that exteroceptive stress produced different effects on the neurochemical mediators, NE and NO, in the PVN region.

The purpose of this study was to determine whether the application of mild intermittent footshock stress can cause changes in the nitric oxide (NO) and norepinephrine (NE) releases in the hypothalamic paraventricular nucleus (PVN) region and medial prefrontal cortex (mPFC). Extracellular levels of NO metabolites and NE in the PVN region and mPFC were determined using an in vivo brain microdialysis technique in conscious rats. In the PVN region, we demonstrated that perfusion of N-methyl-D-aspartate through a microdialysis probe resulted in a dose-dependent increase in NO metabolite levels, whereas intraperitoneal administration of N(G)-nitro-L-arginine methyl ester produced a dose-dependent reduction in the levels of NO metabolites. The levels of NO metabolites in the PVN region increased after intraperitoneal administration of interleukin-1beta in a dose-dependent manner, as we previously reported. This increase in NO metabolite levels was abolished 60 min after systemic administration of N(G)-nitro-L-arginine methyl ester compared to the vehicle-treated control group. Twenty minutes of intermittent footshock induced NE release but did not induce NO release in the PVN region. On the contrary, in the mPFC, 20 min of intermittent footshock induced both NO and NE releases. The present results reveal different patterns and time courses in NO and NE releases between the PVN region and the mPFC in response to mild intermittent footshock stress. These findings are likely to have helpful suggestions for our understanding of the hypothalamic-pituitary-adrenal axis and the limbic forebrain system response to different kinds of stress.

The effects of stresscopin (SCP) on rat paraventricular nucleus (PVN) neurons were examined using whole-cell patch-clamp recordings and single-cell reverse-transcription multiplex polymerase chain reaction (SC-RT-mPCR) techniques. Under current-clamp conditions, bath application of SCP (100 nM) induced inhibition in 35.2% (37/105) of putative magnocellular neurons and 24.7% (20/81) of putative parvocellular neurons, and excitation in 5.7% (6/105) of putative magnocellular neurons and 18.5% (15/81) of putative parvocellular neurons. SCP-induced inhibition persisted in the presence of a mixture of TTX, a voltage-gated Na+ channel blocker, CNQX, an AMPA/kainate receptor antagonist and bicuculline, a GABA(A) receptor antagonist, whereas SCP-induced excitation of PVN neurons was reversed by the mixture. The SCP-induced inhibition of PVN neurons was abolished by bath application of antisauvagine-30, a selective CRF receptor 2 (CRF-R2) antagonist. Under voltage-clamp conditions, SCP evoked outward currents at the holding potential (-60 mV), which reversed near the potassium equilibrium potential. The SCP-evoked membrane currents were completely blocked by bath application of tertiapin-Q, a selective blocker of G protein-activated inwardly rectifying potassium (GIRK) channels. SC-RT-mPCR analysis indicated that all the SCP-sensitive PVN neurons (57 SCP-inhibited neurons, 21 SCP-excited neurons) expressed CRF-R1 and CRF-R2 mRNAs. Among SCP-hyperpolarized PVN neurons, oxytocin (OT) mRNA was detected in 91.8% of putative magnocellular neurons and 45.0% of putative parvocellular neurons. OT mRNA was also detected in 26.6% of SCP-depolarized parvocellular neurons, but not in SCP-depolarized magnocellular neurons. These results indicate that SCP inhibits a subpopulation of PVN neurons, especially OTergic magnocellular neurons, by enhancing the activity of GIRK channels via CRF-R2.

To investigate the possible involvement of glutamate(Glu) in the paraventricular nucleus (PVN) in the central regulation of baroreflex.The baroreflex was induced by intravenous injection of phenylephrine in conscious rats, and the extracellular concentration of Glu in the PVN region was measured by microdialysis and high performance liquid chromatography (HPLC) techniques. To determine whether the observed Glu release was involved in the baroreflex, NMDA and non-NMDA receptor antagonists, MK-801 and CNQX, were perfused in the PVN region during baroreflex.During baroreflex, the Glu concentration in the PVN region immediately increased to 384.82% +/- 91.77% of basal level (P0.01). (2) During baroreflex, direct perfusion of MK-801 and CNQX in the PVN were attenuated the increase of blood pressure and enhanced the decrease of HR (P0.01),resulting a significant increase in baroreflex sensitivity (P0.01).Glutamate in PVN is involved in central regulation of baroreflex, which may inhibit baroreflex via ionothopic glutamate receptors.

To investigate the possible involvement of gamma-aminobutyric acid (GABA) in the paraventricular nucleus (PVN) in cardiovascular responses induced by central salt loading.Direct perfusion into PVN region with hypertonic saline (0.6 mol/L) was performed in conscious rats by using an in vivo brain microdialysis technique. Then, the extracellular concentration of GABA in the PVN region was measured by microdialysis and high performance liquid chromatography (HPLC) techniques, and the blood pressure (BP) and heart rate (HR) were with recorded simultaneously. Bicuculline (an antagonist of GABAA receptor) or saclofen (an antagonist of GABAB receptor) were coperfused hypertonic saline into PVN region, then the cardiovascular responses were examined.(1) The local perfusion of 0.6 mol/L saline elicited significant increases on BP and HR (P0.01). In addition, perfusion of 0.6 mol/L saline increased the extracellular GABA levels in the PVN region, which reached 561.96% +/- 173.96% (P0.05) of the basal level. (2) Bicuculline or salcofen significantly attenuated the in-response of BP (P0.01, respectively), whereas the antagonists did not influence the response of HR induced by hypertonic saline.Local perfusion of hypertonic saline in the PVN region elicits a local release of GABA, which may act via GABA(A) and GABA(B) receptors to produce pressor response.

To understand whether some amino acids in the medial vestibular nucleus (MVN) of conscious rats are involved in the regulation of blood pressure, microdialysis technique and high performance liquid chromatography (HPLC) were used to measure the changes of gamma-aminobutyric acid (GABA) and glycine (Gly) in this central area. Wistar rats (250-350 g) were randomly divided into three experimental groups: the control group with intact labyrinths; the ipsilateral MVN of unilateral labyrinthectomy (UL); contralateral MVN of the UL. Acute hypotension was induced by intravenous infusion of sodium nitroprusside (SNP). Unilateral chemical labyrinthectomy was performed 14 days before the start of the experiment to eliminate afferent signals from the peripheral vestibular receptors in the inner ear. Blood pressure decreased by 30% after SNP injection. In the control group, GABA and Gly release reduced to 43.53%+/-6.58% (P0.01) and 62.24%+/-7.51% (P0.01) respectively in the MVN following SNP-induced acute hypotension in conscious rats. In the contralateral MVN of UL, GABA and Gly release also reduced to 45.85%+/-17.27% (P0.01) and 73.30%+/-3.00% (P0.01) respectively following SNP-induced acute hypotension in conscious rats. In contrast, in the ipsilateral MVN of UL, GABA and Gly releases were not changed following SNP-induced acute hypotension in conscious rats. These results suggest that the SNP-induced acute hypotension may influence the activity of the neurons in the MVN by the afferent impulses from the peripheral vestibular organ, and that GABA and Gly may be involved in this process.

Microdialysis and high performance liquid chromatography (HPLC) were used to measure the changes of certain amino acids in the medial vestibular nucleus (MVN) of conscious rats in order to understand whether those amino acids are involved in the regulation of blood pressure. Acute hypotension was induced by infusing sodium nitroprusside (SNP) into the femoral vein. In the control group, glutamate (Glu) release increased, though gamma-aminobutyric acid (GABA) and taurine (Tau) release decreased in the MVN following acute hypotension. In the unilateral labyrinthectomy group, the levels of Glu, GABA, and Tau were unchanged in the ipsilateral MVN to the lesion following acute hypotension. Furthermore, in the contralateral MVN to the lesion, Glu release increased, and GABA and Tau release decreased following acute hypotension. These results suggest that SNP-induced acute hypotension can influence the activity of neurons in the MVN through afferent signals from peripheral vestibular receptors, and that certain amino acid transmitters in the MVN are involved in this process.

The hypothalamic paraventricular nucleus (PVN) is a central site for integration of the endocrine system and the autonomic nervous system. Despite a number of studies have pointed out the importance of the PVN in the central regulation of cardiovascular functions, the chemical mediators in the PVN responsible for mediating baroreflex are not well understood. In the present study, we used the conscious rats to investigate the possible involvement of glycine (Gly) in PVN in the central regulation of baroreflex induced by intravenous injection of phenylephrine (0.8 mug/0.04 mL, in 3 min). Then, the microdialysis sampling was performed in the PVN and the concentration of Gly in the microdialysate was measured by high performance liquid chromatography (HPLC) combined with electrochemical techniques, and mean arterial pressure (MAP) and heart rate (HR) were recorded simultaneously. Injection of phenylephrine elicited a significant increase (P0.01) in MAP from the baseline of (99.5+/-14.2) mmHg to the maximum of (149.8+/-19.5) mmHg and a decrease (P0.01) in HR from the baseline of (400.8+/-33.1) beats/min to the minimum of (273.4+/-40.8) beats/min, respectively. Synchronously, the injection of phenylephrine increased the level of Gly in the microdialysate from the PVN to (162.9+/-27.3)% of the basal level (P0.05). Perfusion of strychnine (100 mumol/L), an antagonist of Gly receptor, into the PVN enhanced the pressor response and attenuated the bradycardic response during the baroreflex, resulting in a decrease in baroreflex sensitivity (P0.001). Whereas, the perfusion of Gly (1 mmol/L) into the PVN did not affect the pressor response but enhanced the bradycardic response during the baroreflex, resulting in an increase in baroreflex sensitivity (P0.001). These results suggest that endogenous Gly in the PVN may act via strychnine-sensitive Gly receptor to produce a facilitative effect on baroreflex.

To understand the neurochemical mechanisms underlying the vestibular compensation, we determined the levels of amino acids such as aspartate, glutamate, glutamine, glycine, taurine, alanine in the medial vestibular nucleus (MVN) following unilateral labyrinthectomy (UL), by using in vivo brain microdialysis and high-performance liquid chromatography technique. Rats were pretreated by infusing 2% lidocaine 1.2 mL or 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ, and then the levels of amino acids were determined in MVN of normal control and ipsilateral or contralateral lesional (ipsi-/contra-lesional) rats. In the control experiment, the levels of aspartate, glutamate, glutamine, glycine, taurine, and alanine were (6.15 +/- 0.59), (18.13 +/- 1.21), (33.73 +/- 1.67), (9.26 +/- 0.65), (9.56 +/- 0.77) and (10.07 +/- 0.83) pmol/8 muL sample, respectively. The concentrations of aspartate and glutamate decreased, while the concentration of taurine increased in the ipsi-lesional MVN of rats 10 min after infusing 2% lidocaine into middle ear to obstruct uni-periphery vestibular organ. Whereas the concentration of glutamate increased, the concentrations of glycine and alanine decreased in the contra-lesional MVN, accompanied by imbalances of glutamate, glycine and alanine in the bilateral nuclei. In contrast, the levels of glutamate and alanine decreased, the level of glutamine increased in the ipsi-lesional MVN, and the level of glutamate decreased in the contra-lesional MVN of rats 2 weeks after infusing 10 mg arsanilic acid into the tympanic cavity to obstruct uni-periphery vestibular organ. Furthermore, the level of glutamine in the ipsi-lesional MVN was obviously higher than that in the contra-lesional MVN. These results demonstrate that an imbalance of different amino acids appeared in bilateral MVN after UL, and this imbalance decreased after the development of vestibular compensation. Whereas the imbalance of glutamine release in bilateral nuclei appeared after vestibular compensation.

In order to understand whether some special amino acids in the medial vestibular nucleus (MVN) of rats are involved in the regulation of blood pressure, we used microdialysis technique and high performance liquid chromatography (HPLC) to measure the changes of glutamate and taurine in this central area. Acute hypotension was induced by hemorrhage from the femoral artery. It was observed that the basal release of glutamate and taurine in the MVN was stable about 90 min after the beginning of microdialysis. The basal release of glutamate was (18.96 +/- 0.27) pmol/sample (8 mul), and that of taurine was (7.73 +/- 0.05) pmol/sample (8 mul). Glutamate release increased (P0.05) and taurine release reduced (P0.05) in the MVN in the hemorrhage-induced acute hypotensive rats. Nevertheless, these changes were not observed in the hemorrhage-induced acute hypotensive rats which were pretreated by infusing 2% lidocaine into the middle ear or 100 mg arsanilic acid into the tympanic cavity. These results suggest that the hemorrhage-induced acute hypotention can influence the activity of the neurons in the MVN by the afferent impulses from vestibular organ, and that some special amino acid transmitters in the MVN are involved in this process.

The role of atrial natriuretic peptide (ANP) in the central regulation of the circulation is known to be a neurotransmitter or a neuromodulator, but its actions on baroreceptor reflex function are not fully resolved. The present study examined the role of ANP (6, 60 ng/0.2 microl) by direct microinjection into the hypothalamic paraventricular nucleus (PVN) in conscious rats. OPC-21268 (0.45 microg/3 microl), an antagonist of the V(1) receptor, was microinjected into the lateral ventricle to examine whether the effect of ANP on baroreflex sensitivity is mediated by vasopressin (VP). ANP significantly increased the baroreflex sensitivity, and OPC-21268 attenuated the increase of baroreflex sensitivity induced by ANP. Intravenous injections of ANP (60 ng/0.04 ml) did not affect baroreflex sensitivity. These results suggest that ANP in the PVN may produce a facilitative effect on baroreflex, and the effect may be via, at least in part, the central vasopressin.

The present study is an investigation of the responses of the cardiovascular system and Fos expression to intracerebroventricular (i.c.v.) administration of hypertonic saline (HS) in conscious arginine vasopressin (AVP)-overexpressing transgenic (Tg) and control rats. Central HS (0.3, 0.67, or 1.0 M NaCl, 1 μl/min for 20 min) significantly increased the mean arterial blood pressure (MABP) and Fos-like immunoreactivity (FLI) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus, the area postrema (AP), the median preoptic nucleus (MnPO), and the organum vasculosum laminae terminalis (OVLT) in both Tg and control rats. The changes in MABP and FLI were significantly larger in Tg rats than in control rats. i.c.v. pretreatment with the AVP V 1 receptor antagonist, OPC-21268, blocked the increase in MABP and significantly decreased the Fos expression in the PVN (posterior magnocellular (pm) component) induced by 0.3 M HS in the Tg rats. The present study demonstrates an increased responsiveness to i.c.v. administration of HS in AVP Tg rats, suggesting the relationship between the vasopressinergic drive and central cardiovascular response via, at least in part, the V 1 receptor in the PVN magnocellular neurons.

The objective of this study was to elucidate the possible involvement of nitric oxide (NO) in the cardiovascular responses induced by central salt loading. Direct perfusion of the hypothalamic paraventricular nucleus (PVN) region with hypertonic saline (0.3 or 0.45 M) was performed in conscious rats by using an in vivo brain microdialysis technique. The extracellular concentration of NO metabolites in the PVN region was measured, as were the blood pressure (BP) and heart rate (HR). Perfusion of 0.45 M saline increased the BP, HR, and NO metabolite levels in the PVN region; however, perfusion of 0.3 M saline enhanced only the level of NO metabolites but did not induce changes in the BP and HR. Next, we determined whether the NO was involved in the cardiovascular responses induced by hypertonic saline. Pretreatment with N(G)-methyl-L-arginine (L-NMMA), an inhibitor of NO synthase, attenuated the increases in the BP and HR induced by direct perfusion of 0.45 M saline, while direct infusion of 3-morpholinosyndnonimine (SIN-1, a NO donor) in the PVN region induced increases in the BP and HR. These results suggest that local perfusion of the PVN region with hypertonic saline elicits a local release of NO, which may be carried out by activating nitric oxide synthase to produce cardiovascular responses.

Neuromedin U (NMU) is a brain-gut peptide, which peripherally stimulates smooth muscle, increases of blood pressure, alters ion transport in the gut, controls local blood flow, and regulates adrenocortical function. Although intracerebroventricular (i.c.v.) administration of NMU is known to decrease food intake and body weight, little is known about its effect on other physiological functions. We examined the effects of i.c.v. administration of NMU on mean arterial pressure (MAP), heart rate (HR), and plasma norepinephrine in conscious rats. Neuromedin U (0.05 and 0.5 nmol) provoked an increase in MAP (93.8 +/- 0.5 to 123.5 +/- 1.7 and 94.7 +/- 0.8 to 132.7 +/- 3.0 mm Hg, respectively) and HR (334.9 +/- 6.0 to 494.1 +/- 6.9 and 346.3 +/- 3.3 to 475.1 +/- 8.9 beats/min, respectively). In contrast, plasma norepinephrine increased only with a high dose of neuromedin U. Intravenously administered NMU (0.5 nmol) elicited a small and short lasting increase in MAP, compared to that by i.c.v. NMU. These results indicate that central neuromedin U regulates sympathetic nervous system activity and affects cardiovascular function.

Orexins, also called hypocretins, are newly discovered hypothalamic peptides that are thought to be involved in various physiological functions. In spite of the fact that orexin receptors, especially orexin receptor 2, are abundant in the hypothalamic paraventricular nucleus (PVN), the effects of orexins on PVN neurons remain unknown. Using a whole cell patch-clamp recording technique, we investigated the effects of orexin-B on PVN neurons of rat brain slices. Bath application of orexin-B (0.01–1.0 μM) depolarized 80.8% of type 1 ( n = 26) and 79.2% of type 2 neurons tested ( n = 24) in the PVN in a concentration-dependent manner. The effects of orexin-B persisted in the presence of TTX (1 μM), indicating that these depolarizing effects were generated postsynaptically. Addition of Cd2+(1 mM) to artificial cerebrospinal fluid containing TTX (1 μM) significantly reduced the depolarizing effect in type 2 neurons. These results suggest that orexin-B has excitatory effects on the PVN neurons mediated via a depolarization of the membrane potential.

To elucidate neurochemical mechanisms responsible for cardiovascular responses induced by central salt loading, we directly perfused the paraventricular nucleus (PVN) of the hypothalamus region with hypertonic saline (0.3 or 0.45 M) by using an in vivo brain microdialysis technique. We then measured the extracellular concentrations of glutamate in the PVN region in conscious rats along with the blood pressure and heart rate. Blood pressure, heart rate, and glutamate levels were increased by perfusion of 0.45 M saline; however, they did not change by perfusion of 0.3 M saline. Next, we examined the possible involvement of glutamate in the cardiovascular responses induced by hypertonic saline. Dizocilpine, a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, attenuated the increases of blood pressure and heart rate, although 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the non-NMDA receptor, did not affect the blood pressure and heart rate. Our results show that local perfusion of the hypothalamic PVN region with hypertonic saline elicits a local release of glutamate, which may act via NMDA-type glutamate receptors to produce cardiovascular responses.

There is growing recognition that the immune system does not act in isolation. It is widely accepted that there are bidirectional interactions between the immune system and the central nervous system (CNS) that allow reciprocal regulation of immune and CNS responses to infection. Interleukin113 (IL-113) is a possible mediator, conveying feedback information from the immune system to the CNS. This chapter is a summary of our recent work concerning the effects of IL-113 on the autonomic, endocrine, and metabolic functions involved in the control of body fluid and electrolyte balance. IL-1s inhibits water intake and urinary sodium and potassium excretion, the latter of which is via renal nerves. Both sympathetic outflow and the hypothalamo-pituitary-adrenal (HPA) axis are concomitantly activated after IL-1s injections, which are sensitive to a cyclo-oxygenase inhibitor, indomethacin. Noradrenergic and nitrexinergic systems in the hypothalamic paraventricular nucleus (PVN) and the abdominal vagal nerves may be involved in the activation of sympathetic outflow and the HPA axis by peripheral IL-ls. These adjustment changes in the autonomic and endocrine systems might contribute to maintenance of the homeostasis of body water balance accompanied by fever during infectious and inflammatory states.

Using an in vivo brain microdialysis technique, we measured extracellular levels of nitric oxide (NO) metabolites (NO x − ) in the medial prefrontal cortex (mPFC) upon perfusion of γ-aminobutyric acid (GABA) receptor antagonists as well as agonists, and also examined the effects of GABA receptor agonists on mild intermittent footshock-induced NO releases in the mPFC in conscious rats. Perfusion of either bicuculline methiodide, a GABA A receptor antagonist, or saclofen, a GABA B receptor antagonist, through a microdialysis probe resulted in dose-dependent increases in NO x − levels. Higher-dose perfusion of either muscimol (50 μM), a GABA A receptor agonist, or baclofen (250 μM), a GABA B receptor agonist resulted in a significant decrease in NO x − levels. The elevated levels of NO x − after mild intermittent footshock were attenuated by perfusion of either muscimol (10 μM) or baclofen (50 μM), either of which alone did not affect basal NO x − levels. These findings are likely to provide helpful clues to our understanding of the inhibitory modulation of basal and footshock-induced NO metabolites releases by GABA A and GABA B receptors in the mPFC.

Nitric oxide (NO) has recently been shown to modulate the hypothalamic-pituitary-adrenal axis response to interleukin-1 beta (IL-1 beta). We measured levels of nitrite (NO2-) and nitrate (NO3-) in the hypothalamic paraventricular nucleus (PVN) region using an in vivo brain microdialysis technique in conscious rats. Intraperitoneally administered IL-1 beta produced a significant increase in both NO2- and NO3- levels in the PVN region. We also examined the possible involvement of the abdominal vagal afferent nerves in this effect. In abdominal-vagotomized rats, the increase was significantly attenuated compared to that in sham-operated rats. Our results suggest that the abdominal vagal afferent nerves are involved in intraperitoneally administered IL-1 beta-induced NO release in the PVN region.

The effects of pentobarbital sodium, chloralose and urethane on norepinephrine (NE) release in the hypothalamic paraventricular nucleus (PVN) region were examined in awake rats. An in vivo microdialysis method was used. Extracellular NE concentrations in the PVN region were measured by high performance liquid chromatography with electrochemical detection. Pentobarbital sodium (30 mg/kg, intravenously [i.v.]) and chloralose (50 mg/kg, i.v.) caused a 30-40% decrease in NE release while urethane (800 mg/kg, i.v.) caused a 50% increase. Plasma NE concentration was not altered after pentobarbital sodium and chloralose administrations, except for its increase in chloralose at 5 h, while the concentration increased significantly (P < 0.01) after urethane. These results suggest that, in the rat, these anesthetic agents have different effects on noradrenergic activity in the PVN region as well as on plasma NE.