Physiology and Pharmacology
Year:2013 | Volume:17 | Issue:1|Papers Count:18

Introduction: Alzheimer’s disease is a progressive neurodegenerative disorder, characterized by impairment of memory and changes in behavior and personality. Recent evidence suggests that mitochondrial channels play important roles in memory disorders. Accordingly, the biophysical properties of a single potassium channel were investigated in the brain mitochondrial inner membrane of rat with Alzheimer’s disease.Methods: In the male Wistar rats (220-250 g), Alzheimer’s disease was induced by intracerebroventricular injection of amyloid beta 1-42 (4mg/mL). After two weeks, the brain mitochondrial inner membranes were extracted. Vesicles were incorporated into lipid bilayer membranes, and single potassium channel properties were investigated. Also, purity of the cell fraction was tested by Western blotting. Protein samples were probed with specific antibodies.Results: Based on our previous data, mitochondrial inner membrane has a potassium channel with a main conductance 93 pS which was 4-AP sensitive and voltage-insensitive at -50 to+40 mV. In the present study, it was demonstrated that the channel conductance was increased to 114 pS in Alzheimer’s disease. In addition, the currentvoltage relationship showed an inward rectification. Western blotting and antibodies directed against various cellular proteins revealed that the extracted material contains only mitochondria.Conclusion: Our data showed that the biophysical properties (gating, conductance and activities) of potassium channel were significantly altered in Alzheimer’s disease. Based on these findings, we propose that the brain mitochondrial potassium channels are involved in Alzheimer’s disease, and it can be considered as a target for therapeutic plans.

Introduction: Beat-to-beat variation in heart rate shows a complex dynamics, and this complexity is changed during systemic inflammatory response syndrome (e.g. sepsis). It is not known whether or not cardiac pacemaker dynamical rhythm is affected by sepsis. The aim of this study was to investigate heart rate dynamics of isolated heart as well as expression of pacemaker channels (HCN) in a rat model of sepsis (endotoxemia) compared with normal rats.Methods: Male rats weighing 250-300 g were used in this study. Bacterial lipopolysaccharide was injected intraperitoneally (1mg/kg) in the endotoxemia group, and sterile saline in the control group. Three hours after injection, cardiac tissues were isolated and studied using Langendorff apparatus. Heart rate dynamics was assessed by calculating the standard deviation of inter-beat intervals as well as detrended fluctuation analysis (DFA). Quantitative RT-PCR was used to assess HCN expression in atria.Results: Hypoxia had a significantly different effect on heart rate variability in endotoxemic rats compared with controls (P<0.05). DFA analysis showed a linear relationship between logarithm of variance and the logarithm of scale in both endotoxemic and control rats. Atrial expression of HCN1 and HCN2 at mRNA level were significantly higher in endotoxemic rats in comparison with controls (P<0.05).Conclusion: Spontaneous beatings of isolated hearts exhibit a fractal-like dynamics which did not change after global hypoxia and/or endotoxemia. Endotoxemia was associated with altered heart rate variability and increased expression of pacemaker channels that might play a role in pathophysiology of cardiac complications of sepsis.

Introduction: Endorphins are produced by cardiomyocytes, and exert different effects on the heart. The aim of the present study is to assess morphine effects on extracellular atrioventricular (AV) node field potential pattern and ventricular rhythm of isolated rabbit heart during experimental atrial fibrillation (AF).Methods: Effects of different concentrations of morphine (10, 20, 50 and 100 mM) were assessed by applying basic stimuli protocols involving Wenckebach, recovery, zone of concealment and concealed conduction parameters during experimental atrial fibrillation in isolated rabbit heart. Two-way ANOVA was used to compare the groups.Results: Morphine significantly suppressed basic parameters of AV node. Morphine (100 mM) significantly increased wenckebach index (153.6±3.9 to 169.8±2.9 ms) and functional refractory period (156.9±3.0 to 176.4±3.5 ms) (P<0.05). During experimental atrial fibrillation, morphine nonsignificantly increased mean His-His interval, concealed conduction and zone of concealment (P>0.05).Conclusion: The present results showed that morphine has concentration-dependent effects on AV node electrophysiological properties. Morphine at low concentrations can decrease nodal conduction and refractoriness of AV node, but in high concentrations causes increased nodal conduction without concealed conduction changes. Dual effects of morphine can explain the unpredictable behavior of heart in cardiac tachyarrhythmias.

Introduction: Nucleus accumbens (NAc) plays a critical role in neuronal reward circuits that are responsible for motivated and goal-directed behaviors. Some data suggest that morphine induces apoptosis in neurons, while other evidences show that morphine could have beneficial effects against neuronal cell death. This study was designed to evaluate the effect of morphine on apoptosis in the NAc in rat brain by assessing the changes in apoptotic factors.Methods: To investigate the effects of 3 different doses (0.5, 5 and 10 mg/kg) of morphine on induction of apoptotic factors in the NAc after its sub-chronic consumption, conditioned place preference paradigm was used in three groups of rats compared with the control group that received saline, and then the changes in apoptotic factors caspase-3, PARP and Bax/Bcl-2 ratio were assessed by western blot technique.Results: Our results showed that apoptotic factors increase in all three groups treated with morphine. In the nucleus accumbens, morphine induced significant increase (p<0.01) in caspase-3, PARP and Bax/Bcl-2 ratio, in the lowest dose (0.5 mg/kg) compared with the control group that received saline instead of morphine.Conclusion: Increase in apoptotic factors by low dose morphine in the nucleus accumbens of morphine-treated rats shows that morphine can affect the molecular mechanisms which interfere with apoptosis through one kind of its receptors with high affinity. However, with increase in dose of morphine, it seems that other kinds of opioid receptors have been involved which exert some neuroprotective effects of morphine against apoptosis.

Introduction: Under pathological conditions, abnormal increase in intracellular calcium concentrations is believed to induce cell death. In the present study, a voltage-sensitive calcium channel blocker (loperamide hydrochloride) was used to investigate its role in inhibition of apoptosis in sensory neurons of cultured spinal dorsal root ganglia (DRG).Methods: L5 DRG from adult rats were dissected and divided into three groups: 1. Freshly prepared DRG; 2.Control DRG; and 3. DRG treated with voltage-sensitive calcium channel blocker (loperamide hydrochloride, 200 mM).The control and the treated DRG were incubated in a culture medium for 72 hours. The DRG were then fixed and sectioned by a cryostat. Morphological and biochemical features of apoptosis in sensory neurons were studied by fluorescent staining (Propidium iodide and Hoechst) and TUNEL methods, respectively.Results: After 72 hours in culture, sensory neurons displayed morphological features of apoptosis. Most of these neurons also appeared as TUNEL positive. At this time period, the application of loperamide hydrochloride not only inhibited both morphological and biochemical features of apoptosis in the sensory neurons but also significantly increased the mean diameter of nucleus in these neurons compared to the control.Conclusion: This study showed that elevated intracellular calcium concentration might be one of reasons for apoptosis of sensory neurons in the cultured DRG.

Introduction: The present study is aimed to evaluate electrophysiological remodeling of atrioventricular (AV) node and ventricular conduction during experimental atrial fibrillation (AF) model in isolated heart of cirrhotic rats.Methods: Cirrhosis-induced electrophysiological remodeling was evaluated in 24 isolated retrogradely perfused rat hearts in 2 groups (control and cirrhotic). Cirrhosis was induced after 6 weeks of common bile duct ligation in rats.Extracellular filed potential was recorded from upper atrium and right ventricle. The conduction time, refractoriness and frequency-dependent properties of AV node were characterized by specific stimulation protocols. Experimental AF was simulated by high-rate atrial pacing with random coupling intervals (range 75-125 ms).Results: Nodal conduction time and ventricular responsiveness were significantly increased in the cirrhotic rats compared to the control (95.8±4.2 ms vs.78.8±3.3 ms) (P<0.05). Nodal protective function during AF was potentiated with increased R-R interval, concealed beats, ventricular refractoriness and zone of concealment in the cirrhotic group. Cirrhosis evoked rate-dependent ventricular conduction time shortening with different patterns during arrhythmia.Conclusion: Cirrhosis-induced electrophysiological remodeling was shown by increased AV nodal conduction and shortened ventricular conduction. This electrophysiological remodeling may be considered as a new manifestation of cirrhotic cardiomyopathy in the heart, which can change ventricular rhythm during arrhythmia.

Introduction: RFamide-related peptide (RFRP) is believed to act as an inhibitor of gonadotropin releasing hormone (GnRH) secretion. The aim of the present study was to compare the expression pattern of RFRP neurons in the dorsomedial nucleus of hypothalamus (DMH) at different phases of the rat estrous cycle.Methods: The phases of the estrous cycle were determined in 16 adult female Sprague-Dawley rats using vaginal smears. The rats were divided into five groups: proestrus phase (n=4), early estrus phase (n=3), estrus phase (n=3), metestrus phase (n=3) and diestrus phase (n=3). After transcardial perfusion, their brains were removed and fixed.Diencephalon of each rat brain was sectioned, and DMH-containing sections were stained using an immunohistochemical method. The number of RFRP positive neurons in DMH was counted microscopically.Results: Almost all of the neurons expressing RFRP in the DMH were bipolar. Mean and standard error of the number of RFRP neurons during diestrus (45.8±12.6) and estrus phases (44.7±3.6) were greater (P<0.05) than early estrus (18.8±0.8) and proestrus phases (16.2±2.0).Conclusion: Results confirm a regulatory role for RFRP in DMH in the control of rat estrous cycle.

Introduction: Previous studies and our works have indicated several cation channels in the rat brain mitochondrial inner membrane. In this work, we report the single-channel characterization of a cation channel from the rat brain mitochondrial inner membrane incorporated into a planar lipid bilayer.Methods: After removing and homogenizing the adult rat brain, its supernatant was centrifuged in MSE-digitonin, H2O and Na2CO3, separately. Then, mitochondrial inner membrane vesicles were prepared in MSE solution. L-a- Phosphatidylcholine (for preparing membrane lipid bilayer) was extracted from fresh egg yolk. Bilayer lipid membranes were formed in a 150 mm diameter hole. All single channel recordings were filtered at 1 kHz and stored at a sampling rate of 10 kHz for offline analysis by PClamp10. Statistical analysis was performed based on Markov noise free single channel analysis.Results: The channel conductance was 93 pS in 200 mM KCl cis /50 mM KCl trans. The channel open probability appeared voltage-independent at -50 to+40 mV. The main characteristic of channel gating was its marked bursting behavior. Adding 10 mM 4-aminopyridine (4-AP) at positive and negative potentials inhibited the channel activities.Conclusion: These results demonstrate that a new cation channel, present in the brain mitochondrial inner membrane, displays different kinetics and biophysical properties than those classically described for brain mitochondria.

Introduction: Pulicaria gnaphalodes contains terpenoids and flavonoids. Referring to the role of benzodiazepine (BZD) receptor ligands as drug candidates in the treatment of epilepsy, anxiety and sleep disturbances, and since natural flavonoids are among these candidates and hold promise as BZD receptor ligands, this research was done to assess the effects of aqueous extract and essential oil of Pulicaria gnaphalodes on seizures induced by pentylenetetrazol (PTZ).Methods: In this research, male Wistar rats (200±20 g) were injected intracerebroventrically by vehicle, aqueous extract (125, 250 and 500 mg) or essential oil (0.125%, 0.25% and 0.5%) (1 mL volume in each), before intraperitoneal administration of PTZ (80 mg/kg) for induction of seizure. Then, onset times of myoclonic (stages 1, 2 and 3) and tonicclonic (stages 4 and 5) seizures were recorded during 20 minutes after PTZ administration. Data were analyzed by oneway analysis of variance.Results: The results of this study showed that aqueous extract and essential oil of Pulicaria gnaphalodes increase initiation time of PTZ-induced myoclonic and tonic-clonic seizures.Conclusion: Aqueous extract and essential oil of Pulicaria gnaphalodes probably have dose-dependent anticonvulsant property.

Introduction: In the present study, the prophylactic effect of vitamin C, as a potent anti-oxidant, on tracheal responsiveness to methacholine and ovalbumin, bronchoalveolar lavage fluid white blood cell (WBC) count and differential count, and also lung pathology in chronic obstructive pulmonary disease (COPD) -guinea pigs (cigarette exposed guinea pigs) were examined. In addition, the relaxant effects of theophylline on tracheal chains of guinea pigs were studied.Methods: Twenty four male guinea pigs were randomly divided to three groups; control (C group), COPD model of guinea pigs (COPD group) and pretreated group (COPD+Vit C group). The two first groups were given drinking water alone, and the third group used water containing vitamin C. The relaxant effects of four cumulative concentrations of theophylline were examined by their relaxant effects on precontracted tracheal chains of guinea pig by 60 mM KCl (group 1) and 10 μM methacholine (group 2).Results: The tracheal responsiveness to methacholine and ovalbumine, and WBC count of COPD guinea pigs were significantly higher than those of controls (p<0.05 to p<0.001). The lung in COPD group showed significant pathological changes. The tracheal responsiveness to methacholine and avalbumine and WBC count were significantly decreased in pretreated group compared with the COPD guinea pigs (COPD group) (p<0.05 to p<0.001). In both groups, the relaxant effect of theophylline in the COPD group was lower than the control group (group C) (p<0.05 to p<0.001).Conclusion: These results showed prophylactic effect of vitamin C on tracheal responsiveness and pulmonary inflammation of COPD-guinea pigs.

Introduction: Despite significant progress in understanding pain control mechanism, there are numerous questions about central nervous mechanisms underlying stress-induced analgesia. The rostral ventromedial medulla (RVM) in the brainstem integrates a variety of functions, including pain modulation and pain perception. In the present study, we investigated the effect of temporary inactivation of RVM on stress-induced analgesia.Methods: This study was performed using adult male Wistar rats (200-250 gr). Swim stress was induced using a cylinder filled with water (50 cm height, 20±1oC) in which the rats were kept for 3 min. For induction of pain, 50 mL of 2% formalin was injected subcutaneously in the hind paw. For temporary inactivation of RVM, 0.5 mL of 2% lidocaine was injected into RVM.Results: Injection of lidocaine into RVM, before inducing swim stress, potentiated the anti-nociceptive effects of swim stress in phase 1 and phase 2A. In phase 2B swim stresses increased nociceptive scores of formalin test; so administration of lidocaine into RVM inhibited the effect of swim stress.Conclusion: The result of this study demonstrated that temporal inactivation of RVM by lidocaine potentiated stress-induced analgesia.

Introduction: Ascorbic acid (AA) is present as a vitamin and neuromodulator in most part of the mammalian brain, especially in nucleus accumbens shell (Acbsh), which is one of the important areas controlling motor activity and anxiety. This study evaluates the effect of injection of AA and its co-administration with bromocriptin (Br) in Acbsh on motor activity and anxiety of rats by Open Field test.Methods: Forty nine adult male Wistar rats (220-270 g) were allocated into 7 groups: control (intact), sham AA (normal saline injected as AA vehicle), 3 groups of AA (12, 24 and 48 mg/rat/side), AA plus Br (AA 24 mg/rat/side and Br 25 mg/rat/side), sham AA plus Br. Drugs were injected (volume=1 mL) once, and duration of the test was 5 minutes.Results: Intra-accumbance injection of AA increased locomotor activity and decreased anxiety. Co-administration of AA and Br resulted in less motor activity and attenuation of Br-induced anxiety.Conclusion: Our results support the previous findings which introduced AA as an effective factor in regulation of locomotor activity and anxiety in Acbsh, that may be mediated by D2 receptors.