Physiology and Pharmacology
Year:2008 | Volume:12 | Issue:2|Papers Count:15

Introduction: (S)- 3,5-Dihydroxyphenylglycine (DHPG) is an agonist for group I metabotropic glutamate receptors. DHPG-induced synaptic depression of excitatory synapses of the hippocampal pyramidal neurons is a well known model for synaptic plasticity studies. The aim of the present study was to examine the effects of DHPG superfusion on the excitatory synapses of the pyramidal and fast-spiking GABAergic cells (FS-GABA) of layer IIIIII of mice visual cortex.Methods: Effects of DHPG was examined in visual cortical slices ofGAD67-GFP knock-in mice using whole-cell recordings of excitatory postsynaptic potentials (EPSPs) in layer IIIIII cells evoked by layer IV stimulation. Experiments also included long term potentiation (LTP) induction by theta burst stimulation (TBS) paired with postsynaptic depolarization.Results: DHPG induced potentiation of EPSPs of the FS-GABA neurons in dose- and use-dependent manners but it had no effect on the pyramidal cell excitatory synapses. An antagonist for type 5 metabotropic glutamate receptors (mGluR5) blocked DHPG-induced LTP, while an antagonist for mGluR1 was not effective. This potentiation and TBS induced LTP blocked each other.Conclusion: Since FS-GABA cells have an important role in the cortical neuronal circuits, mGlur5-dependent LTP may play a role in the enhancement or maintenance of synchronized activity of cortical pyramidal neurons.

Introduction: Recent studies have shown beneficial effects of hyperoxia pretreatment (HOP) against ischemia reperfusion injury in different organs. The aim of the present study was to investigate the effect of early and late phases of preconditioning induced by normobaric hyperoxia ( ³ 95% O2) on ischemia-reperfusion injury in isolated rat heart. Methods: Following 60 and 180 minutes of hyperoxia, rat hearts were isolated immediately (HOP60 and HOP180) or after 24 hours (HOP60/24 and HOPI 80/24), and were subjected to 30 minutes of regional ischemia followed by 120 minutes of reperfusion. Incidence and severity of ventricular arrhythmias, mechanical function of the heart and coronary flow were assessed during 120 min of reperfusion. LDH and CK release into the coronary effluent were measured. Infarct size also was calculated by triphenyl tetrazolium choride staining at the end of reperfusion. Results: Incidence and severity of reperfusion arrhythmias were significantly reduced after hyperoxia pretreatment, especially in the early phase of treatment. Hyperoxia improves mycardial contractile function and decreases coronary flow reduction during reperfusion. Infarct size and enzymes release were also significantly decreased in the early and late phases of hyperoxia pretreatment.Conclusion: These results indicate that hyperoxia pretreatment before induction of regional heart ischemia reduces cardiac infarct size and attenuates reperfusion induced arrhythmias in isolated rat heart.

Introduction: Although formalin-induced activity in primary afferent fibers and spinal dorsal horn is well described, the midbrain neural basis underlying each phase of behavior in the formalin test has not been yet clarified. The present study was designed to investigate the nucleus cuneiforms (CnF) neuronal responses during two phases after subcutaneous injection of formalin into the hind paw of rat.Methods: In this study, 76 male NMRI adult rats, weighing 230-320 g were used. Control group (n = 24) was merely tested for determining spontaneous firing rate of CnF neurons. In the formalin group, formalin-induced neural activity of 37 cells were simultaneously recorded from the CnF during first phase (0-5 min) and second phase (15-60 min) of formalin test at 5-min intervals, using an extracellular single unit recording technique. Saline group (n = 15) received 50~saline s.c. instead offonnalin into the plantar surface of hind paw 15min after baseline recording. Results: The baseline firing rate of neurons in the CnF varied between 1.2 and 39.2 spikes/see and the average frequency of spontaneous activity over 1 h was 11.8±1.1 spikes/sec. There were three neural clusters after formalin injection. Neurons in cluster I (46%) exhibited severe, transient excitatory response in the first (acute) phase, while neurons in cluster 2 (35%) exhibited tonic but long-lasting excitatory response in the second (chronic) phase. Cluster 3, a small portion of neurons (about one fifth), failed to show any evident responses to formalin test. Conclusion: Our findings suggest that alteration of neural activity and pattern in the spontaneous background of CnF neurons can mediate a role in the transmission of nociceptive information induced by the peripheral injection of formalin and can be discussed in light of the role of these neurons in nociceptive information processing following peripheral stimuli.

Introduction: In this study, gene expression and purification of luciferases from the firefly, Lampyris turkestanicus, and optimization of cellular ATP measurements were performed.Methods: cDNA encoding luciferases from Lampyris turkestanicus was transferred from pQE30 vector into pET28a expression vector and pLtu28 was built. Newly constructed vector was expressed in E. coli XLI Blue and the recombinant luciferase was purified using Ni-NTA Sepharose column. Enzymatic properties (Km and Vmax) for ATP were measured using luminescence assay. Standard curve of ATP was obtained by Promega ATP detection kit and the designed method based on the L. turkestanicus luciferase and ATP serial dilution. Moreover, bacterial ATP was measured by Promega kit and the designed method using L. turkestanicus luciferase.Results: Results showed that ligation of L. turkestanicus luciferase encoding cDNA into pET28a and transformation of competent cells induced by the recombinant vector was performed efficiently. Using luciferin, positive colonies were screened and cultured. SDS-PAGE showed that recombinant luciferase was efficiently purified by Ni-NTA Sepharose column. ATP standard curve and measurement of bacteria, using Promega and the designed method by L. turkestanicus luciferases showed high similarities.Conclusion: A method based on L. turkestanicus luciferases was designed. Comparison of the developed assay with promega kits in identification of bacterial concentration shows its high quality and potent ability in ATP detection.

Introduction: Feverfew (Tanacetumparthenium) (T.p.) is widely used in folk medicine to treat many diseases. We have reported the analgesic effect of T.p. flowers and leaves previously. The present study was designed to find the mechanisms underlying the anti-nociceptive effect of the aqueous extract of T.p. flower. Methods: Based on our previous study, the dose of 50 mg/kg Lp. of the T.p. aqueous extract has a potent analgesic effect on mice (NMRI) (20±2g) in formalin test. The same dose was used in the present study. Here, we studied the roles of opioidergic, serotoninergic and a-adrenergic systems in the anti-nociceptive effect of the T.p. extract. 15 min before the administration of the extract, animals were pretreated with drugs, including opioid antagonist naloxane (5mg/kg, i.p.), serotoninergic antagonist cyproheptadine (4 mg/kg, i.p.) and a-adrenergic antagonist phentolamine (20 mg/kg, i.p.) separately (n³6 in each group). Saline and the T.p. extract were used as controls. Results: Pretreatment with naloxane increased the pain sensation in the neurogenic phase of formalin test compared to the control (p<0.001). Pretreatment with cyproheptadine increased the sensation of pain in both early and late phases (p<0.05). Inhibition of  a-adrenergic system was not able to attenuate the anti-nociceptive effect of the extract. Conclusion: These results propose the involvement of sertoninergic and opioidergic systems in the anti-nociceptive effect of the T.p. extract.

Introduction: Previous studies have shown the effects of water extract of Crocus sativus on the euphoric and behavioral properties of morphine in mice. In the present study, the effects of intra-accumbal administration of alcohol extract of Crocus sativus stigma on the acquisition and expression of morphine-induced conditioned place preference (CPP) in male Wistar rats (250-300 g) were investigated.Methods: This study was conducted on 78 male rats that were divided in 13 groups (n =6 each group). In a pilot study, different doses of morphine (0.5, 1, 2.5, 5, 7.5 and 10 mg/kg) were injected to the animals for evaluation of the drug's ability to induce place preference. In the second phase of the experiments, the extract of the C. sativus (1, 5 and 10 mg/rat), was administered into the nucleus accumbens shell during or after induction of morphine CPP. Then, CPP was tested in the animals. One-way Analysis of Variance (ANOVA) was preformed for statistical procedure. Results: Administration of morphine (0.5, 1,5,7.5 and 10mg/kg), increased the time spent in the compartment paired with morphine (i.e. conditioned place preference-CPP) (P<0.05). This increase reached significance at the dose of 10 mglkg. Injection of the same doses of the extract (1,5 and 10 mg/rat) 5 min before morphine (10 mg/kg) administration, caused a decrease in the time spent in drug-paired side in doses 5 and 10 mg/rat of the extract (P < 0.0001). In addition, injection of the plant extract (1,5 and 10 mg/rat) in to the shell part of nucleus accumbens in the test day to the animals that received morphine (10 mg/kg) in the conditioning days decreased the expression of morphine CPP in the animals. This effect was statistically significant for doses 5 and 10 mg/rat of the extract (P<0.0001). Conclusion: It may be concluded that intra-acumens shell compartment injection of the alcoholic extract of C sativus can inhibit the acquisition and expression of morphine-induced CPP and then shift it to the aversive state in rats.

Introduction: Anesthetic agents, blood pressure, arterial pH and blood gases have been found to influence on the pathophysiology of experimental stroke. However, there are very few studies on the effects of anesthetic agents in the animal models of cerebral ischemia. Therefore, in this study, we compared the effects of chloral hydrate and pentobarbital anesthesia on the infarct size, motor neurological dysfunctions and physiological parameters in a transient model of focal cerebral ischemia.Methods: Twenty-four male Sprague-Dawley rats were divided into 2 groups and received either chloral hydrate (400 mg/kg, n=10) or pentobarbital sodium (60 mg/kg i.p., n=14) by intra-peritoneal injection. Temporary focal cerebral ischemia was induced by 90 min middle cerebral artery occlusion (MCAO), followed by 23 h reperfusion. Physiological parameters were measured before and after ischemia. Cortical and striatal infarct volumes and motor dysfunctions were determined 24 h after MCAO.Results: Cortical and striatal infarct volume in pentobarbital sodium anesthetized rats were 84±8 and 26 ±2 mm3, which were significantly lower than chloral hydrate group (208±10, 62±2 mm3,respectively, P < 0.00 I). Moreover, neurological motor dysfunction was significantly lower in pentobarbital sodium anesthetized in comparison with chloral hydrate group (P < 0.01). Physiological values were similar between 2 groups, except that the mean arterial pressure was significantly higher in the pentobarbital group compared with the chloral hydrate group (P < 0.05). Conclusion: The findings of this study indicate that chloral hydrate anesthesia causes higher brain injury and motor neurological deficits compared with pentobarbital sodium anesthesia in a temporary model of focal cerebral ischemia. Thus, the effects of anesthetic agents must be considered in experimental cerebral ischemia studies.

Introduction: Tamoxifen is a nonstroidal antiestrogen prescribed for treatment of breast cancer. The aim of this study was to investigate the effect of tamoxifen on testosterone level in the serum and sperm count in the epididymis of adult male Wistar rats.Methods: Three groups of rats received 200, 400 and 600 mg/kg body weight tamoxifen dissolved in solvent (60% ethanol in physiological solution) for 30 consecutive days. The sham group received the solvent and controls did not receive any drug or solvent. 1, 12 and 36 days after treatment, serum testosterone was measured by radioimmunoassay and sperm numbers in the epididymis were counted.Results: Results showed that testosterone concentration in the serum and sperm count in the epididymis significantly decreased in groups which received tamoxifen compared with the control group. The most profound effects were observed in the first samplings of the group which received 600 mg/kg tamoxifen.Conclusion: These findings indicate that tamoxifen decreases the fertilization ability in adult male rats in a dose dependent manner and this effect disappears after a period of time.

Introduction: Previous studies have shown that ghrelin inhibits the activity of Hypothalamus -Pituitary – Thyroid (H-P-T) axis. It is also proved that ghrelin increases the appetite via Agouti Related Protein and neuropeptide Y pathway, decreases T3 and T4 secretion and inhibits serotonin release from hypothalamic synaptosomes. Serotonin may interact with ghrelin over the control of thyroid hormones secretion. Thus, the goal of this study was to determine the influence of the interaction between ghrelin and serotonin agonist on thyroid hormones concentration. Methods: Twenty four male Wistar rats weighing 230-250 g were randomly divided into 3 groups. The groups received 5 nmol ghrelin, 20 nmol serotonin agonist (R)-8-0H-DPAT or 5 nmol ghrelin together with 20 nmol (R)-8- OH-DPAT in lateral cerebral ventricle in volumes of 5 ml for 3 days. The blood samples were collected every day, starting one day before and up to one day after injections. Brain slices were taken to ensure that the place of the canulae was right. The plasma was analysed by Radioimmunoassay technique to determine T3 and T4 concentrations. Results: The results showed that the i.c.v injection of ghrelin significantly decreased and (R)-8-0H-DPAT significantly increased the mean plasma concentrations of thyroid hormones (p < 0.05). Co-dministration of these two substances showed that (R)-8-0H-DPAT can decrease the inhibitory effect of ghrelin on thyroid hormones concentration, but this effect was not statistically significant (p<0.05).Conclusion: This study showed that ghrelin significantly decreased mean plasma concentration of T3 and T4. Coadministration of a serotonin agonist partially blocked the inhibitory effect of ghrelin on thyroid hormones, but this effect did not reach significance. (p<0.05).

Introduction: Using brief episodes of ischemia and reperfusion (IR) prior to a more sustained IR insult, i.e., ischemic preconditioning (IPe), can reduce IR injury of the heart, brain and many other tissues. The purpose of the present study was to investigate the effect of 2 min ischemic periods on subsequent rat renal IR injury.Methods: Renal IR injury was investigated in a right nephrectomized model in male rats. For this purpose, plasma creatinine (Cr) and urea, creatinine clearance, fractional excretion of sodium and histological injury score (Jablonski score; 0-4) were compared among the following groups; IR group (40min of renal ischemia followed by 24 h reperfusion), sham group (no IR) and IPC group (3 times of "2 min ischemia-5min reperfusion" before 40 min of renal ischemia followed by 24h reperfusion).Results: Necrosis score was significantly lower in the IPC compared with the IR group. Furthermore, rats with a Jablonski score of 4 were significantly less frequent in the IPC group compared to the IR group (11.1% vs. 75%). Plasma Cr and urea, creatinine clearance and fractional excretion of sodium were not significantly different between the IPC and IR groups. Rats with plasma urea levels higher than 190 mg/dl and also rats with fractional excretion of sodium beyond 2% were significantly less frequent in the IPC group compared to the IR group. Also Fractional excretion of sodium was not significantly different between IPC and sham groups.Conclusion: Using 3 times of "2 min ischemia-5 min reperfusion" before the injurious ischemic insult can reduce rat renal histological injury and partially attenuate functional renal injury.