Physiology and Pharmacology
Year:2006 | Volume:10 | Issue:1|Papers Count:13

Introduction: Sex differences are observed in the development of tolerance to antinociceptive effect of opioid drugs such as morphine, but the underlying mechanisms remain unclear. Critical role of glutamate in the development and maintenance of opioid tolerance has been reported by many investigators. There are also evidences about interaction between gonadal hormones and neuromodulatory systems including opioidergic and glutamatergic systems. The present study examined the sex differences and role of gonadal hormones on the glutamate level in the nucleus accumbens in morphine tolerant rats using in vivo microdialysis.Methods: Intact, gonadectoized and sham-operated male and female rats were used. Morphine (7 mg/kg/day, SC) was administered for 8 days. Response to thermal noxious stimuli were measured by tail-flick test. Tolerance was defined as the response which was not significantly different from baseline.Results: The results showed that after chronic morphine administration, antinociceptive tolerance in male rats was significantly greater than females (P<0.05). Sex differences in morphine tolerance disappeared with gonadectomy of animals. There was also significant sex difference in glutamate level in nucleus accumbens of morphine tolerant rats (P<0.05), Glutamate level was decreased after ovariectomy of female rats (P<0.05), but gonadectomy had not significantly effect on glutamate level in males.Conclusion: Results of this study provide evidence of sex differences in development of tolerance to morphine in rats and mediatory roles of gonadal hormones and glutamate levels in these differences.

Introduction: To evaluate the cAMP -mediated IBMX (3-IsoButyle -1-Methyl Xanthin) and db-cAMP (dibutyryl cAMP) effects on differentiation of human Embryonic Stem Cells (hESCs) into nerve cells were the objectives of this study.Methods: We have used Royan H1 hESC- derived embryoid bodies with four treatment groups: six days treatment with IBMX (5×10 -4M) and db-cAMP (10 -9M) (referred to as cAMP), retinoic acid (RA, 10-6 M), IBMX + db-cAMP + RA, and control (no treatment). Immunocytochemistry was carried out for neural specific antibodies including b-Tubulin III, Microtubule Associated Protein 2 (MAP-2), Neurofilament Protein-Heavy chain (NF-H), Glial Fibrilary Acidic Protein (GFAP) and Synaptophysin as well as morphological studies. Semi quantitative RT-PCR was also used to evaluate gene expression involved in neurogenesis.Results: In the 4+6+4 days the neuronal process were apparently observed. Immunocytochemical studies using nerve specific antibodies for proteins such as b- Tubulin III, MAP-2, NF-H, GFAP and Synaptophysin showed the presence of these neuronal and astrocyte markers in differentiated cells by cAMP. Evaluation of expression of genes involved in neurogenesis showed that Hash1, Synaptophysin, β-Adrenergic Receptor and Acetylcholine Receptor- which were silent in embryoid bodies - switched on after treatment with cAMP and/or RA. Relative expression of nerve specific genes showed a significant enhancement in expression of Synaptophysin, NFM and b-Adrenergic Receptor during differentiation, which, with the enhancement in cAMP treated groups were more than those treated with RA and control (p<0.05).Conclusion: In conclusion, this study showed that cAMP could be a neurogenic agent for human embryonic stem cells differentiation.

Introduction: Verapamil, a phenylalkylamin –type Ca2+ channel blocker, is widely used in the treatment of cardiovascular disorders especially as an antiaryhthmic and antiangina agent. Theoretically, calcium can influence thyroid function and there are evidences that Ca2+ channel blockers are able to interfere with thyroid function. In this study, the effects of chronic oral administration of verapamil on thyroid function of male Wistar rats were investigated.Methods: Study was performed on 5 groups of animals; groups 1 to 3 were treated with verapamil at doses of 10, 20 and 50 mg /kg respectively for two months via oral tube. Sham group received only distilled water, while control group received neither verapamil nor distilled water. At the end of this period animals were anaesthetized, abdomen was opened and blood samples were obtained from abdominal aorta. The samples were centrifuged; sera were separated and stored at – 20°C until the time of the assays. Total triiodothyronine (TT3), total thyroxin (TT4), free triiodothyronine (FT3) and free thyroxin (FT4), T3 uptake levels were assayed by ELISA (DRG). Thyroid stimulating hormone (TSH) was determined by radioimmunoassay using DRG kits.Results: Total T4 level was significantly lower in sham (3.49±0.1mg/dl) and verapamil dose 10 mg /kg (3.6±0.14) groups than in control group (4.5±0.34), while it was significantly higher in verapamil 50 mg /kg (4.24±0.2) group as compared to the sham group. Total T3 concentration in verapamil 20 mg /kg group (62±8.9ng/ dl) was decreased significantly compared to the control group (103.3±14). Free T3 and free T4 were significantly lower in sham group (p<0.005) compared to control group, while it was increased in verapamil groups of 20 and 50 mg /kg compared to sham group. Level of T3 up-take was decreased significantly (p<0.005) in sham (20.97±1.49%) and verapamil 20 (20.7±1.4) mg /kg compared to control group (27.6±1), while it was higher in verapamil 10 and 50 mg /kg groups than sham group. Thyroid stimulating hormone levels were similar in all groups. There were no significant differences in the T3/T4 ratio and body weights on first and last day of the groups compared to control group.Conclusion: It can be concluded that long term oral administration of verapamil doesn’t have inhibitory effect on thyroid function, however it can block adverse effect of handling stress on thyroid function. Therefore, from thyroid function point of view, the drug can be used safely for the duration of this study.

Introduction: Since organophosphorus compounds (OP) are toxic and designed to destroy insects and pest species, there are many hazards associated with their use. Although, the main target site of these compounds is acetylcholinesterase (AChE), however it has become increasingly evident that OPs have also other direct effects on cellular processes. In the present study, the effects of low concentrations of paraoxon and its interaction with forskolin, an activator of protein kinase A (PKA), were studied on Ca2+ spike configuration and frequency in neurons of snail Caucasotachea atrolabiata.Methods: Subesophageal ganglia neurons were recorded in current clamp mode in Na+ free Ringer solution that contained voltage dependent potassium channel blockers, 4AP and TEA.Results: Paraoxon (0.3-0.6 mM) decreased the duration of spontaneous Ca2+ spikes. This effect was seen with a suppression of single spike AHPs, leading to an increment in firing rate. Paraoxon induced hyperactivity appeared to be a consequence of decrease in Ca2+ influx during spikes which is the main determinant of AHP duration by activating Ca2+ dependent potassium channels. Forskolin (25 mM), in the absence of a significant change in spike duration, decreased the duration of single spike AHPs and increased the frequency of spikes. After forskolin application, paraoxon decreased the duration of Ca2+ spikes and AHPs, and increased the activity. However, these effects, especially on spike duration, were not as pronounced as in the absence of forskolin.Conclusion: These findings suggest that although forskolin, similar to paraoxon, decreases the AHP and increases the frequency of spikes but it employs mechanism(s) different from paraoxon which also oppose the effects of paraoxon on Ca2+ spikes configuration and frequency.

Introduction: Neurotrophins belong to growth factor family and their function is based on their receptors. They bind two types of receptors: p75 and tyrosine kinase. The motoneuron survival or death depends upon the neurotrophic factors. Recent studies have demonstrated that axotomy in peripheral nerve induces apoptosis of motoneuron. Deprenyl or Selegiline is known as a drug with neuroprotective effect on motoneurons. In this investigation, we evaluated mRNA changes in p75 receptor by anti-apoptic effect of deprenyl in motoneuron death induced by axotomy of rat sciatic nerve.Methods: The left sciatic nerves of Sprague-Dawley newborn 3 days old rats, were axotomized in the middle of thigh. The newborn rats were divided into two groups; one group was treated with intra peritoneal injection of 2.5 mg/kg deprenyl (treated) and the other group with normal saline (untreated). Each group was divided to 3 sub groups as, the first was treated with 2.5 mg/kg deprenyl or normal saline one hour before surgical transection, the second and third were treated at, and one hour after surgery, respectively. Molecular studies for mRNA changes Trk-B and P75NTR receptor were done on two groups of animals which were sacrificed 4 hours after injection and other one, 24 hours after injection.Results: The RT-PCR revealed that deprenyl has reduced the mRNA P75 after 24 hours.Conclusion: Deprenyl can maintain motoneurons by reducing mRNA P75 receptor.

Introduction: Neuropathic pain syndromes are changes resulting from damage to neuronal pathways that are characterized by spontaneous burning sensation with accompanying allodynia and hyperalgesia. Since the treatments of neuropathic pain are poorly understood and existing treatments are often ineffective, it is important to increase our understanding of the neuropathic pain states in order to identify strategies for the development of effective therapies. The purpose of this study was to investigate the involvement and pre-emptive treatment of morphine and / or NMDA receptor antagonist MK-801, and co-administration of both drugs on behavioural responses in an experimental model of neuropathic pain (CCI).Methods: Experiments were performed on six groups (n=8) of male Sprague-Dawley rats (230-280g). In the groups that received drugs, two groups were injected with MK-801 (0.3 mg/kg, 20 min before, and 6 h after the operation) or morphine (8 mg/kg, 30 min prior to the operation). Another group received both drugs with the same doses and protocols. Finally, one group received normal saline in same volumes. The animals were tested for allodynia and hyperalgesia reactions at 0, 3, 7, 14, 21 and 28 days after CCI of the sciatic nerve. Results: Our data revealed that the CCI produces mechanical and cold allodynia and a hypersensitivity to noxious stimulations. MK-801 and morphine produced only a slight cold anti-allodynic response. On the other hand, co-injection of morphine and MK-801 markedly reduced cold allodynia at the days 7 (P<0.01), 14 (P<0.05) and 21 (P<0.05) when compared with the saline group. However, there was slight alleviation of the mechano allodynia, and, heat- and mechano-hyperalgesia. Results demonstrate that the CCI model importantly influences the behavioural responses to both the thermal and mechanical stimulations.Conclusion: We conclude that co-administration of both drugs can be more effective than MK-801 and morphine administered alone in the induced neuropathic pain.

Introduction: The influence of ascorbic acid on the nicotine-induced conditioned place preference (CPP) and behavioral sensitization was investigated in the present study.Methods: In a pilot study, place conditioning and locomotor activity were investigated after nicotine (0.25, 0.5, 0.75, 1, 1.5 and 2 mg/kg) or ascorbic acid (1, 10, 100 and 1000 mg/kg) administration. Different doses of ascorbic acid in conditioning days or on the test days were used. Behavioral sensitization was induced in animals by daily intraperitoneal administration of nicotine (0.25 mg/kg) for seven cosecutive days followed by one day interval. On 9th day, locomotor activity was induced by ineffective dose of nicotine (0.1 mg/kg). Ascorbic acid was injected 20 min before each injection of nicotine (acquisition of sensitization) or acutely 20 min before a challenge nicotine injection (expression of sensitization).Results: The results showed that intraperitoneal nicotine (1 mg/kg) administration can induce place preference whereas acute administration of the drug induces catalepsy. Administration of ascorbic acid did not induce place preference nor place aversion and also did not change the locomotor activity. Locomotor sensitization in mice was produced by intraperitoneal injection of nicotine (0.25 mg/kg) for 7 consecutive days. On the 9th day of experiments, activity of the mice was recorded after challenge with nicotine (0.1 mg/kg, i.p.). The senisitization was better achived when the ineffective dose of nicotine (0.1 mg/kg) was applied. Administration with ascorbic acid reduced both the acquisition and expression of nicotine-induced CPP. It was shown that ascorbic acid attenuated the acquisition of nicotine sensitization in a dose-independent manner but the expression of nicotineinduced sensitization was not affected by ascorbic acid.Conclusion: We conclude that ascorbic acid may interfere with nicotine-induced place preference and behavioral sensitization.

Introduction: Several researches have reported that stress is able to inhibit the development of morphine tolerance via activating of Hypothalamic-Pituitary-Adrenal (HPA) axis. In the present study we tried to examine the effect of epinephrine, the product of adrenal medulla, on the development of morphine tolerance. Methods: Analgesic tolerance was induced by intrathecal (i.t.) injection of morphine 15 mg/kg, twice a day for 5 days. To study the effect of epinephrine on morphine tolerance, epinephrine (2, 5, 10 or 20 mg/kg, i.t.) was administrated 20 minutes before morphine injection. Analgesia was assessed using tail flick test. Results: In animals that received combined treatments of morphine and epinephrine in doses 2, 5, 10 or 20 mg/ kg for 5 days, at 6th day, morphine produced a more potent analgesia comparing with animals that received saline and morphine during days 1-5. Following tolerance induction during first 5 days, co-administration of epinephrine and morphine during days 6 – 10 reduced the initial tolerance as it induced potent analgesia on day 11th.Conclusion: Our results showed that i.t. administration of epinephrine is able to inhibit and reverse the analgesic tolerance to morphine. It also suggests the possible role of adrenal medulla and epinephrine in mediating the inhibitory effect of stress and HPA activation of the development of analgesic tolerance to morphine.

Introduction: Ischemia/reperfusion (IR) injury involves a complex interrelated sequence of events. High levels of nitric oxide (NO) are generated with inducible form of nitric oxide synthase (iNOS) leading to the renal IR injury and glutathione (GSH) depletion. The present study was designed to investigate the effect of L-Nil (N6- (1-Iminoethyl)-L- lysine hydrochloride), a selective inhibitor of iNOS, in prevention of renal GSH depletion and IR injury.Methods: Ischemia was induced by 40-min clamping of the renal arteries followed by 6 h reperfusion. Rats were randomly assigned to four groups: Sham operated, Sham- L-Nil, IR and IR- L-Nil. In the IR groups, rats were administered saline or L-Nil (3 mg/kg iv bolus followed by infusion of 1 mg/kg/h) 15 min prior ischemia. Other groups underwent surgery protocol but did not undergo renal arteries occlusion and were maintained under anesthesia for the duration of the experiment (40 min + 6 h). Renal function was assessed by plasma creatinine (Cr), Blood Urea Nitrogen (BUN), and aspartate aminotransferase (AST) measurements. Fractional excretion of Na+(FENa+), urinary N-acetyl-b-D-glucosaminidase(NAG) activity and renal GSH level were also measured.Results: We found that L-Nil significantly reduced the IR mediated increases in Cr BUN, AST, FENa+, NOx and urine NAG activity.Conclusion: These results emphasize the multifactorial nature of renal IR injury and the need for a multidrug therapy in the future.

Introduction: Our previous studies showed that hydroalcoholic extract of leaf of Vitis vinifera relaxes the phenylephrine-induced contraction in rat thoracic aorta. This effect was dependent on endothelial integrity and NO-cGMP system. The vasorelaxant effect of extract was much lesser on KCl-induced contraction. We, therefore, postulated that K+ channels are involved. The main aim of the present study was to determine the type of K+ channels involved in this vasorelaxant effect.Methods: Thoracic aorta with intact endothelium was removed from adult male Wistar rats (170-220g). The aorta was mounted in an organ bath containing Krebs-Henseleit (37 °C, pH 7.4) bubbled with O2. Aortic contractions were recorded isometrically under 1 g resting tension. The aorta endothelium was considered intact if acetylcholine (1 mM) could induce more than 70% aorta relaxation on 1μM phenylephrine-induced contraction. Extract was prepared by maceration method using 70% alcohol and the solvent was then evaporated.Results: The results showed that in the presence of tetraethyl ammonium (10 mM), the vasorelaxant effect of extract (0.25, 0.5, 1 and 2 mg/ml) was reduced (P<0.001, n=7). In contrast, glibenclamide (1 mM) had no effect. In calcium-free (plus 0.1 mM of EDTA) Krebs-Henseleit solution, the vasorelaxant effect of extract (0.25, 0.5 and 1 mg/ml) was reduced (P<0.0001, n=8). Furthermore, the vasorelaxant effect of extract was unaffected by indomethacin (1 mM).Conclusion: These results suggest that Vitis vinifera leaf hydroalcoholic extract induces relaxation in rat aorta possibly by opening the Ca2+ -operated K+ channels but, not ATP- sensitive K+ channels and extracellular calcium was essential for inducing vasorelaxation by extract. Furthermore, cyclooxigenase was not involved in this vasorelaxant effect.

Introduction: Effects of exercise on different body systems, especially cardiovascular and musculoskeletal systems are evidenced. There is a dynamic homeostatic balance between coagulation and fibrinolysis in normal circulation. Effect of exercise and training on this homeostatic balance has been studied extensively but there are a few studies with regards to analysis of the effects of training programs on coagulation factors. Therefore, we studied the effect of 8 weeks aerobic training program on coagulation factors in healthy young men.Methods: Subjects were 16 young sedentary men without any history of cardiac, coagulation or respiratory problems in their first-degree family and their cardiovascular health was confirmed by a cardiac specialist. We randomly selected 10 of them as test group who participated in a submaximal training program on cycle ergometer 3 times a week for 8 weeks. Each training session consisted of 1 minute warm up, 15 minute aerobic exercise, 8 minute active recovery and 45 minute passive recovery. The remaining individuals were controls and restrained from exercise in this period. Before and after training period, response of coagulation system to a submaximal exercise on cycle ergometer was studied by a standardized Ergometery test.Results: Basic value of coagulation variables were the same in both groups before and after training period. After 8 weeks, there was no significant change in anthropometric variables in both groups and so the change in blood variables was independent to physical characteristics of individuals. After 8 weeks of aerobic training, FVIII:c, FIX:c, Fbg and vwF:ac increased in response to exercise that was statistically significant only in Tr group. There was a significant decrease in vwF:ag, aPTT, FVII in this group. We conclude that 8 weeks aerobic training enhances the response of FVIII:c, FIX:c, FVII:c, vwF:ac, Fbg and aPTT to exercise but has no effect on the response of vwF:ag and PT.Conclusion: It seems that the recommended aerobic exercise training protocol will enhance the response of coagulation factors to one session of Ergometric exercise in healthy young men. Due to the importance of blood homeostasis and the effects of coagulation and fibrinolysis imbalance, any type of physical activity especially any exercise program should be analyzed carefully for its effect on haemostatic balance.