Imaging mass spectrometry of diversified cardiolipin molecular species in the brain.

MALDI imaging mass spectrometry (MALDI-IMS) has been used successfully in mapping different lipids in tissue sections, yet existing protocols fail to detect the diverse species of mitochondria-unique cardiolipins (CLs) in the brain which are essential for cellular and mitochondrial physiology. We have developed methods enabling the imaging of individual CLs in brain tissue. This was achieved by eliminating ion suppressive effects by (i) cross-linking carboxyl/amino containing molecules on tissue with 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide hydrochloride and (ii) removing highly abundant phosphatidylcholine head groups via phospholipase C treatment. These treatments allowed the detection of CL species at 100 µm resolution and did not affect the amount or molecular species distribution of brain tissue CLs. When combined with augmented matrix application, these modifications allowed the visualization and mapping of multiple CL species in various regions of the brain including the thalamus, hippocampus, and cortex. Areas such as the dentate and stratum radiatum exhibited higher CL signals than other areas within the hippocampal formation. The habenular nuclear (Hb)/dorsal third ventricle (D3 V) and lateral ventricle (LV) areas were identified as CL "hot spots". Our method also allowed structural MS/MS fragmentation and mapping of CLs with identified fatty acid residues and demonstrated a nonrandom distribution of individual oxidizable (polyunsaturated fatty acid containing) and nonoxidizable (nonpolyunsaturated containing) CLs in different anatomical areas of the brain. To our knowledge, this method is the first label-free approach for molecular mapping of diversified CLs in brain tissue.

Improved spatial resolution of matrix-assisted laser desorption/ionization imaging of lipids in the brain by alkylated derivatives of 2,5-dihydroxybenzoic acid.

RATIONALE: Matrix-assisted laser desorption/ionization (MALDI) is one of the major techniques for mass spectrometry imaging (MSI) of biological systems along with secondary-ion mass spectrometry (SIMS) and desorption electrospray mass spectrometry (DESI). The inherent variability of MALDI-MSI signals within intact tissues is related to the heterogeneity of both the sample surface and the matrix crystallization. To circumvent some of these limitations of MALDI-MSI, we have developed improved matrices for lipid analysis based on structural modification of the commonly used matrix 2,5-dihydroxybenzoic acid (DHB). METHODS: We have synthesized DHB containing -C6H13 and -C12H25 alkyl chains and applied these matrices to rat brain using a capillary sprayer. We utilized a Bruker Ultraflex II MALDI-TOF/TOF mass spectrometer to analyze lipid extracts and tissue sections, and examined these sections with polarized light microscopy and differential interference contrast microscopy. RESULTS: O-alkylation of DHB yields matrices, which, when applied to brain sections, follow a trend of phase transition from crystals to an oily layer in the sequence DHB → DHB-C6H13 → DHB-C12H25 . MALDI-MSI images acquired with DHB-C12H25 exhibited a considerably higher density of lipids than DHB. CONCLUSIONS: Comparative experiments with DHB and DHB-C12H25 are presented, which indicate that the latter matrix affords higher lateral resolution than the former.

High index contrast semiconductor ARROW and hybrid ARROW fibers.

We investigate the guidance properties of two photonic crystal fibers that have been fabricated by filling the holes of a silica template with hydrogenated amorphous silicon inclusions. The first is an all-solid fiber that guides light via an antiresonant reflecting optical waveguiding mechanism and the second is only partially filled so that it guides light by a hybrid of modified total internal reflection and antiresonant reflecting optical waveguiding. It will be shown that, by selectively filling the silica template to leave an unfilled internal ring of holes, the fiber's confinement loss can be reduced significantly. This novel fiber design in which the light guided in the silica core can be modified by the semiconductor cladding provides a route to integrating functional semiconductor fibers with existing silica fiber infrastructures.

Redox phospholipidomics of enzymatically generated oxygenated phospholipids as specific signals of programmed cell death.

High fidelity and effective adaptive changes of the cell and tissue metabolism to changing environments require strict coordination of numerous biological processes. Multicellular organisms developed sophisticated signaling systems of monitoring and responding to these different contexts. Among these systems, oxygenated lipids play a significant role realized via a variety of re-programming mechanisms. Some of them are enacted as a part of pro-survival pathways that eliminate harmful or unnecessary molecules or organelles by a variety of degradation/hydrolytic reactions or specialized autophageal processes. When these "partial" intracellular measures are insufficient, the programs of cells death are triggered with the aim to remove irreparably damaged members of the multicellular community. These regulated cell death mechanisms are believed to heavily rely on signaling by a highly diversified group of molecules, oxygenated phospholipids (PLox). Out of thousands of detectable individual PLox species, redox phospholipidomics deciphered several specific molecules that seem to be diagnostic of specialized death programs. Oxygenated cardiolipins (CLs) and phosphatidylethanolamines (PEs) have been identified as predictive biomarkers of apoptosis and ferroptosis, respectively. This has led to decoding of the enzymatic mechanisms of their formation involving mitochondrial oxidation of CLs by cytochrome c and endoplasmic reticulum-associated oxidation of PE by lipoxygenases. Understanding of the specific biochemical radical-mediated mechanisms of these oxidative reactions opens new avenues for the design and search of highly specific regulators of cell death programs. This review emphasizes the usefulness of such selective lipid peroxidation mechanisms in contrast to the concept of random poorly controlled free radical reactions as instruments of non-specific damage of cells and their membranes. Detailed analysis of two specific examples of phospholipid oxidative signaling in apoptosis and ferroptosis along with their molecular mechanisms and roles in reprogramming has been presented.

Electrophysiological effects of agmatine on human atrial fibers.

The objective of the present study was to study the electrophysiological effects of agmatine on human atrial fibers obtained at cardiac surgery using standard microelectrode techniques. Agmatine (1 to approximately 10 mM) decreased the action potential amplitude (APA), maximum upstroke velocity of phase 0 depolarization (Vmax), velocity of diastolic (phase 4) depolarization (VDD), rate of pacemaker firing (RPF), and action potential duration at 50 and 90% of repolarization (APD(50-90)) in a concentration-dependent manner. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 0.5 mM), a NOS inhibitor, did not affect the electrophysiological effects of agmatine (5 mM) on human atrial fibers. The effects of agmatine (5 mM) could be blocked completely by pretreatment with idazoxan (0.1 mM), an alpha-2 adrenergic receptor (alpha2-AR) and imidazoline receptor (IR) antagonist. All these results indicate that the effects of agmatine on human atrial fibers are likely due to a decrease of intracellular calcium mediated by IR and/or alpha2-AR.

[Role of KATP channels in the cardioprotection provided by ischemic preconditioning in anesthetized rabbits].

The effects of KATP channel opener cromaklim (Cro) and ischemic preconditioning (IP) on hemodynamics and myocardial infarct size were examined in both urethane and sodium pentobarbital anesthetized rabbit models of myocardial ischemia-reperfusion to determine whether the KATP channel was involved in the cardioprotection provided by IP. The results were as follows: (1) All hemodynamic parameters and myocardial oxygen consumption were decreased progressively during the course of ischemia (30 min)-reperfusion (180 min). (2) In the urethane anesthetized model, the myocardial infarct size of the left ventricle induced by ischemia-reperfusion was (32.3 +/- 0.8)%. Pretreatment with Cro reduced the myocardial infarct size to (23.3 +/- 2.2)%, while IP significantly reduced the infarct size to (21.6 +/- 1.8)%, which was abolished by a potent KATP channel blocker glibenclamide. (3) In the sodium pentobarbital anesthetized model, myocardial infarct size was (32.7 +/- 1.0)%. IP also reduced the myocardial infarct size to (19.7 +/- 1.5)%, which could not be blocked by cardioprotection of IP by glibenclamide. Cro failed to decrease infarct size. Such results indicated that activation of KATP channels exerted a beneficial action on ischemia-reperfused myocardium only in the urethane anesthetized rabbit.

Biphasic activation of renal afferent by intrarenal artery injection of bradykinin in anesthetized rabbits.

The effect of intrarenal artery injection of bradykinin (BK, 5.0 micrograms/kg) on multi- and single-unit recordings of afferent renal nerve activity (ARNA) was examined in anesthetized 48 rabbits. The results obtained are as follows. (1) There were two phases of increase in ARNA following intrarenal BK. The early phase occurred immediately while the delayed phase made its appearance about 7 min later. The degree of increase in ARNA of the delayed phase induced by intrarenal BK was more prominent than that in the early phase. BP was actually unaltered following intrarenal BK. (2) By pretreatment with indomethacin (Indo, 5.0 mg/kg), the delayed phase of increase in ARNA induced by intrarenal BK was attenuated, while the early phase was not affected. (3) Pretreatment with L-NAME (30 mg/kg) led the delayed phase to be blocked completely while the early phase was partially decreased. From the above-mentioned observations, it is concluded that intrarenal BK induces a significant increase in ARNA in two phases. The early phase may be due to the direct action of BK and partially due to the NO action, while the delayed phase may be attributed to the action of released prostaglandin and NO as a result of intrarenal BK.

Effect of intracarotid administration of adenosine on the activity of area postrema neurons in barodenervated rats.

To observe the effect of intracarotid administration of adenosine on the electrical activity of area postrema (AP) neurons, 76 spontaneous active units were recorded from 45 sino-aortic denervated Sprague-Dawley rats using extracellular recording technique. The results obtained are as follows. (1) Following intracarotid administration of adenosine (Ado, 25 micrograms/kg), the discharge rate of 29 out of 42 units decreased markedly from 6.26 +/- 0.75 to 4.74 +/- 0.76 spikes/s (P < 0.01), whereas that of 6 units increased from 4.13 +/- 0.77 to 4.72 +/- 0.83 spikes/s (P < 0.05), and the other 7 showed no response. Blood pressure (BP) and heart rate (HR) were unaltered throughout the experiment. (2) 8-phenyltheophylline (8-PT, 15 micrograms/kg), a nonselective adenosine receptor antagonist, completely blocked the inhibitory effect of Ado in 10 units. (3) Selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 50 micrograms/kg), blocked the effect of Ado in 12 units to a remarkable extent. (4) Glibenclamide (500 micrograms/kg), a blocker of ATP-sensitive potassium channel, abolished the effect of Ado in 12 units. The above results indicate that Ado can inhibit spontaneous electrical activity of AP neurons, which is mediated by adenosine A1-receptor with the involvement of ATP-sensitive potassium channels.

[Effects of intracarotid injection of capsaicin on electrical activity of rostral ventrolateral medullary neurons in rats].

The effects of intracarotid injection of capsaicin on spontaneous electrical activity of nucleus paragigantocellularis lateralis (PGL) neurons in rostral ventrolateral medulla (RVLM) were examined in 35 anesthetized rats with sino-aortic denervation by using extracellular recording technique. The results obtained were as follows: (1) In response to intracarotid injection of capsaicin (10 mumol, 0.1 ml), MAP was increased from 10.74 +/- 0.13 to 12.56 +/- 0.21 kPa (P < 0.001), and HR from 374 +/- 4 to 395 +/- 5 bpm (P < 0.001). All of 30 PGL neurons recorded responded to intracarotid injection of capsaicin with an increase in spontaneous discharge rate from 12.6 +/- 0.7 to 20.9 +/- 1.1 spikes/s (P < 0.001); (2) In 10 units, the excitatory response of PGL neurons to intracarotid injection of capsaicin was significantly inhibited by pretreatment with the vanilloid receptor (capsaicin receptor) antagonist ruthenium red (200 mmol, 0.1 ml). These results suggest that capsaicin may stimulate the vanilloid receptor of neurons in RVLM, thereby resulting in activation of PGL neurons.

Intracarotid injection of endothelin-1 facilitates the activity of rostral ventrolateral medullary neurons via area postrema in rats.

To observe the effect of intracarotid administration of endothelin (ET-1) on electrical activity of neurons within rostral ventrolateral medulla (RVLM) region, 87 spontaneous active units were extracellularly recorded in 35 Sprague-Dawley rats with sino-aortic denervation. The results obtained are as follows. (1) Intracarotid administration of ET-1 (0.3 nmol/kg) increased the discharge firing rate from 17.8 +/- 1.5 to 20.9 +/- 1.4 spikes/s (P < 0.01) in 30 out of 36 RVLM neurons, while blood pressure and heart rate had no significant change. (2) BQ-123 (0.67 nmol/kg), a selective ETA blocker, completely blocked the facilitatory effects of ET-1 in 11 out of 14 units. (3) In 10 out of 11 units, glibenclamide (3.3 nmol/kg), a blocker of ATP-sensitive potassium channel, had no effect on the action of ET-1. (4) After ablation of area postrema (AP), the facilitatory action of intracarotid administration of ET-1 on 19 units of RVLM was abolished, while in 7 units of sham ablation animals the response of neurons to ET-1 remained unchanged. Taken together, intracarotid-administered ET-1 may act on the ETA receptors in neurons of AP, thereby resulting in the facilitating effect on RVLM neurons through the efferent projection of AP.

[Bradykinin inhibits carotid sinus baroreflex in anesthetized rats].

The effects of bradykinin (BK) on the carotid baroreflex were examined in 36 anesthetized rats with isolated carotid sinus perfusion. The results obtained are as follows. (1) By perfusing the isolated carotid sinus with BK (1.0 mumol/L), the functional curve of baroreflex was shifted to the right and upward, its peak slope (PS) decreasing from 0.44 +/- 0.14 to 0.31 +/- 0.01 kPa (P < 0.01) and the reflex decrease in mean arterial pressure (RD) was lowered from 6.85 +/- 0.18 to 4.46 +/- 0.16 kPa (P < 0.05), while the threshold pressure (TP), equilibrium pressure (EP) and saturation pressure (SP) were significantly enhanced from 7.76 +/- 0.20 to 10.04 +/- 0.09 kPa (P < 0.001), 12.72 +/- 0.29 to 13.74 +/- 0.31 kPa (P < 0.05) and 23.28 +/- 0.24 to 25.31 +/- 0.20 kPa (P < 0.01), respectively. Among the functional parameters of carotid baroreflex, the changes in RD, PS and TP induced by BK were dose-dependent. (2) By pretreatment with indomethacin (10 mumol/L), an inhibitor of prostaglandin synthesis, the above-mentioned effects of BK on carotid baroreflex were not affected. (3) Preperfusion with an inhibitor of NO synthase L-NAME (100 mumol/L) could completely eliminate the effects of BK. (4) Pretreatment with angiotensin-converting enzyme inhibitor captopril (20 mumol/L) could potentiate the effects of BK. Taken together, it is indicated that BK may cause vascular endothelium to release NO, thereby inhibiting the carotid baroreflex.

[Electrophysiological effects of agmatine on guinea pig papillary muscles in vitro].

The cardiac electrophysiological effects of agmatine (AGM) were examined in guinea pig papillary muscle using intracellular microelectrode technique. The results obtained are as follows. (1) Duration of action potential (APD) in normal papillary muscles were decreased by AGM in a concentration-dependent manner. (2) In partially depolarized papillary muscles, amplitute of action potential, overshoot, maximal velocity of phase 0 depolarization and APD were depressed by AGM. (3) Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 0.5 mmol/L) did not affect the above effects of AGM (1 mmol/L) on papillary muscles. (4) The effects of AGM (1 mmol/L) could be blocked completely by pretreatment with idazoxan (0.1 mmol/L), an alpha 2-adrenoceptor (alpha 2-AR) and imidazoline receptor (IR) antagonist. All these results indicate that the effects of AGM on papillary muscles are likely due to a decrease of intracellular calcium mediated by alpha 2-AR and IR.

[Hemodynamic effects of agmatine and its cellular mechanism in anesthetized rats].

The hemodynamic effects of intravenous injection of agmatine and their cellular mechanism were investigated in anesthetized rats. The results obtained are as follows. (1) Following intravenous injection of agmatine (10 mg/kg), HR, MAP, LVP, +/- LV dp/dtmax, CI and TPRI were significantly decreased. (2) Pretreatment with N-nitro-L-arginine (15 mg/kg) or methylene blue (50 mg/kg), did not affect the hypotensive effect of agmatine. (3) The hemodynamic effects induced by agmatine could be inhibited by prior intravenous injection of idazoxan (2 mg/kg), an alpha 2-adrenoceptor (alpha 2-AR) and imidazoline receptor antagonist. The results indicate that the hypotensive effect induced by i.v. agmatine may be attributed to the decrease in cardiac output resulting from depression of myocardial contractility, as well as to the reduction in total peripheral resistance resulting from vasodilatation. These effects of agmatine may be mediated by imidazoline receptor and/or alpha 2-AR.

Effect of intracarotid injection of adenosine on the activity of RVLM neurons in barodenervated rats.

To observe the effect of intracarotid administration of adenosine on neurons in the rostral ventrolateral medulla (RVLM) region, 72 spontaneous active units were extracellularly recorded from 28 Sprague-Dawley rats with sino-aortic denervation. The results obtained are as follows: (1) intracarotid administration of Ado (25 micrograms/kg) reduced the discharge rate from (23.5 +/- 3.0) to (16.5 +/- 2.6) spikes/s (P < 0.001) in 31 out of 36 RVLM neurons, while the blood pressure and heart rate had no significant change (P > 0.05); (2) 8-phenyltheophylline (8-PT, 15 micrograms/kg), a nonselective adenosine receptor antagonist, and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 50 micrograms/kg), a selective A1 adenosine receptor antagonist, completely blocked the inhibitory effects of Ado in 24 units; and (3) in 12 units, glibenclamide (500 micrograms/kg), a blocker of ATP-sensitive potassium channel, abolished the effect of Ado. These results indicate that Ado can induce an inhibition of spontaneous electrical activity of RVLM neurons, an effect which is mediated by adenosine A1-receptor with the involvement of ATP-sensitive potassium channels.

Changes in heart rate, blood pressure and renal sympathetic nerve activity induced by microinjection of capsaicin into area postrema in rats.

The effects of capsaicin microinjection into area postrema (AP) on mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were investigated in 36 anesthetized Sprague-Dawley rats. The results obtained are as follows. (1) Following microinjection of capsaicin (10 micromol/L, 50 nl) into the AP, MAP, HR and RSNA were significantly increased from 12.34+/-0.53 kPa, 328.52+/-7.54 bpm and 100+/-0% to 15.17+/-0.25 kPa (P<0.001), 354.81+/-8.54 bpm (P<0.001) and 156.95+/-7.57% (P<0.001), respectively. (2) Ruthenium red (RR, 100 mmol/L, 0.2 ml, iv), a capsaicin receptor antagonist, significantly inhibited these effects of capsaicin. (3) Pretreatment with a NMDA receptor antagonist MK-801 (500 microgram/kg, 0.2 ml, iv) also reduced these effects of capsaicin. The above results indicate that microinjection of capsaicin into AP induces excitatory effects on MAP, HR and RSNA, which are mediated by capsaicin receptors with glutamate involvement.

[Role of calcium in the mechanism underlying the inhibitory effect of streptomycin on carotid sinus baroreflex in rats].

The effect of streptomycin (SM) on carotid baroreflex was examined in 23 anesthetized rats with isolated carotid sinus perfusion. The results obtained are as follows. (1) In response to perfusion with SM (200 micromol/L), the functional curve of carotid baroreflex was shifted to the right and upward with a decrease of peak slope (PS) and a reflex decrease in mean arterial pressure (RD)(P<0.01), indicating an inhibitory effect of SM on carotid sinus baroreflex. (2) By perfusing the isolated carotid sinus with high Ca(2+) solution (4 mmol/L), the inhibitory effect of SM on carotid baroreflex was partially eliminated. The functional curve of SM was shifted to the left and downward with PS increasing from 0.27+/-0.04 kPa to 0.37+/-0.02 kPa (P<0.01) and RD was enhanced from 4.32+/-0.14 kPa to 6.18+/-0.17 kPa (P<0.01). On the other hand, the threshold pressure (TP) and saturation pressure (SP) were significantly decreased from 10.29+/-0.29 kPa to 9.98+/-0.33 kPa (P<0.05) and from 27.26+/-0.42 kPa to 25.22+/-0.38 kPa (P<0.05), respectively. (3) By pretreatment with Bay K 8644 (500 nmol/L), an agonist of calcium channels, the effect of SM on carotid baroreflex was completely abolished. (4) Exposure of the carotid sinus to SM following pretreatment with charybdotoxin (ChTX,100 nmol/L), a blocker of the Ca(2+)-activated K(+) channel (KCa), still inhibited the baroreflex. These results suggest that the inhibitory action of SM on carotid baroreflex may be mediated by suppressing Ca(2+) influx.

Hemodynamic effects of agmatine in Dahl salt-sensitive hypertensive and Dahl salt-resistant rats.

The hemodynamic effects of agmatine were investigated in anaesthetized Dahl salt-sensitive (DS) hypertensive and Dahl salt-resistant (DR) rats. The results are as follows. (1) Agmatine (1, 10, 20 mg/kg i.v.) decreased heart rate (HR), mean arterial pressure (MAP), left ventricular blood pressure (LVP), the first derivative of LVP (LV dp/dt), cardiac index (CI) and total peripheral resistance index (TPRI) in a dose-dependent manner in both DS and DR rats, and the decreases in MAP, LVP, +/- LV dp/dtmax and TPRI at the same dose of agmatine in DR rats were less than those in DS hypertensive rats. Specifically, agmatine at high dose (20 mg/kg) induced a delayed increment of hemodynamic parameters in DS hypertensive rats, but not in DR rats. (2) Idazoxan (2.5 mg/kg), an antagonist for I2 over I1-imidazoline receptors and alpha 2-adrenoceptor receptors (alpha 2-AR), only partially blocked the effects of agmatine (10 mg/kg). (3) Yohimbine (4 mg/kg), a selective alpha 2-AR antagonist, also partially attenuated the effects of agmatine. (4) Efaroxan (2.5 mg/kg), a selective antagonist for I1 over I2-imidazoline receptors and alpha 2-AR, could completely block the effects of agmatine. Taken together, the results indicate that agmatine can dose-dependently decrease HR, MAP, LVP, +/- LV dp/dtmax, CI and TPRI in DS hypertensive and DR normotensive rats. The hemodynamic effects of agmatine are mediated mainly by I1-IR with the participation of I2-IR and alpha 2-AR.

[Action of agmatine on tension of isolated aortic artery and its receptor mechanism in rats].

The effect of agmatine (Agm) on vascular tension and the underlying receptor mechanism were investigated in the isolated aortic artery of rats. The results are as follows. (1) Agm (10(-7)-10(-2) mol/L) relaxed aortic rings in a concentration-dependent manner under the condition of precontraction induced by phenylephrine (PE) at a concentration of 10(-6) mol/L. (2) Either in the intact or the endothelium-denuded rings, pretreatment with NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 0.5 mmol/L) did not affect the vascular relaxant action of Agm, implying that the concentration-dependent vasorelaxation caused by Agm is not endothelium-dependent and NO is not involved. (3) Agm also relaxed aortic rings in a concentration-dependent manner under the condition of precontraction induced by CaCl2 at a concentration of 3 mmol/L. (4) Idazoxan (10(-4) mol/L), an alpha 2-adrenergic receptor (alpha 2-AR) and imidazoline receptor (IR) antagonist, abolished the Agm-induced vasorelaxation completely under the condition of CaCl2-induced precontraction. (5) Yohimbine (10(-4) mol/L), a selective alpha 2-AR antagonist, could partially block the vascular relaxant action of Agm. It is suggested that the vascular relaxant effect of Agm on the rat aortic artery may be mediated by alpha 2-AR and IR.

[Adenosine inhibits spontaneous and glutamate induced discharges of hippocampal CA1 neurons].

Effects of adenosine (Ado) on spontaneous and glutamate induced discharges of neurons in CA1 area of hippocampal slices were examined using extracelluar recording technique. The results are as follows. (1) In response to the application of Ado (0.01 0.1 micromol/L, n=20) into the superfusate, spontaneous discharge rates (SDR) of 20 neurons decreased significantly in a dose dependent manner. (2) Both Ado non selective receptor antagonist 8 phenyltheophylline (8-PT, 0.5 mmol/L) and Ado selective A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 50 nmol/L), completely blocked the inhibitory effects of Ado in 22 CA1 units. (3) In 10 units, ATP sensitive K(+) channel blocker glibenclamide (Gli, 15 mmol/L) also abolished the effect of Ado. (4) Application of glutamate (Glu, 0.2 mmol/L) into the superfusate for 2 min led to a marked increase in the discharge rate of 15 neurons in an epileptiform pattern; the epileptiform discharges induced by glutamate (Glu, 0.2 mmol/L) in 15 neurons were suppressed significantly by application of Ado (10 micromol/L) into the superfusate. (5) 8-PT (2 mmol/L), DPCPX (200 nmol/L) and Gli (7 mmol/L) were all capable of abolishing the inhibiting effect of Ado on the action of glutamate. Taken together, it is suggested that Ado can bind with adenosine A1-receptors on CA1 neurons, resulting in an activation of K(ATP) channels and inhibition of neuronal activity. The inhibitory effect of Ado on glutamate induced epileptiform activities in rat hippocampal neurons is also mediated by adenosine A1-receptor with involvement of ATP-sensitive potassium channels.

Effects of microinjection of adenosine into area postrema on heart rate, blood pressure and renal sympathetic nerve activity in rats.

The effects of microinjection of adenosine (Ado) into area postrema (AP) on mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were examined in 53 anesthetized Sprague Dawley rats. The results obtained are as follows. (1) Following microinjection of Ado (1 ng/60 nl) into AP, MAP, HR and RSNA were decreased from 13.76+/-0.46 kPa, 356.28+/-4.25 bpm and 100+/-0% to 11.23+/-0.49 kPa (P<0.001), 336.91+/-5.23 bpm (P<0.01) and 70.95+/-5.19% (P<0.001), respectively; (2) 8-phenyltheophylline (150 microgram/kg, 0.2 ml,iv), a nonselective adenosine receptor antagonist, and 8-cyclopentyl-1,3-dipropylxanthine (500 microgram/kg, 0.2 ml, iv), a selective A(1) adenosine receptor antagonist, blocked the inhibitory effect of Ado completely; and (3) glibenclamide (5 mg/kg, 0.2 ml, iv), a blocker of ATP-sensitive potassium channel, also abolished the effect of Ado. The above results indicate that microinjection of Ado into AP induces inhibitory effects on MAP, HR and RSNA, which may be related to activation of ATP-sensitive potassium channels mediated by A(1) receptors.