Physiology and Pharmacology
Year:2008 | Volume:12 | Issue:1|Papers Count:14

Introduction: The aim of this study was to evaluate the ability of the notochord to induce differentiation of mouse embryonic stem cells to neurons and/or motor neurons.Methods: In order to produce embryoid bodies (EBs), mouse embryonic stem cells (ES cells) line Royan Bl were grown in suspension in the absence of LIF for 4 days. Then EBs were divided into 4 groups. EBs in groups 1 and 2 were further cultured in suspension for 4 days in the presence of retinoic acid (RA) while EBs in groups 3 and 4 were cultured in the absence of RA. EBs in groups 1 and 3 were also co-cultured with notochord for 4 more days. Numbers and type of neurons were assessed by immunostaining, flow cytometry and RT-PCR techniques.Results: EBs in groups 3 and 4 lead to 5 to 6 % neuron production while EBs in the groups 1 and 2 lead to 42 and 55% neuron production, respectively. There was a significant difference (P <0.05) between groups 3 and 4 with groups 1 and 2. Percentage of motor neurons (Hb9 positive) were significantly higher in group 1 (20.4%) compared with other groups (2-3%).Conclusion: Co-culture of mouse embryonic stem cells in the presence of notochord did not induce neural differentiation of mouse embryonic stem cells, while notochord may direct neural differentiation of mouse embryonic stem cells toward motor neurons.

Introduction: Stress inhibits the development of tolerance to morphine analgesia via activating Hypothalamic- Pituitary-Adrenal (HPA) axis. Modified catecholamine systems have been reported following morphine tolerance development. In the current study we tried to evaluate changes in the gene expression levels for MAO-A, MAO-B, COMT and thyrosine hydroxylase (TyH) enzymes following chronic pain, development of morphine tolerance and their combined administration.Methods: Analgesic tolerance was induced by intrapritoneal injections of morphine 20 mg/kg twice a day for 4 days. To study the effect of pain on morphine tolerance, 50 ml of formalin 5% was injected into the animal paws prior to morphine injections. Semi-quantitative RT-PCR was used to evaluate the gene expression level in lumbar spinal cord on day 5. Three separate control groups received saline or morphine injections or pain induction.Results: Chronic administration of morphine increased the expression level of MAO-B, decreased the expression of TyH and did not change the expression of COMT and MAO-A. Pain increased the expression of MAO-A, but did not change the expression of MAO-B, COMT and TyH. The combination of morphine treatment and pain induction for 4 days partially reversed the reduced expression of TyH and did not change the expression of MAO-A, MAO-B and COMT.Conclusion: Our results showed that in the context of morphine tolerance, gene expression was changed toward decreased biosynthesis and increased elimination of catecholamine’s. It seems that chronic administration of morphine caused lower level of catecholamine’s in spinal neurons and help development of morphine tolerance. Also, chronic pain partially produced compensational changes in gene expression. This may explain for its anti-tolerance effect.

Introduction: Adenosine as a potent vasodilator has a physiological role in regulation of regional cerebral blood flow (rCBF).Method: Laser-Doppler flow merry technique was used to study pial vessels blood flow responses to adenosine receptors agonists and antagonist. Male Sprague Dawley rats (250-350 g) that were housed in standard conditions were anesthetized with Urethane (1.5 g/kg). Adenosine (general agonist), NECA (A2A and A2B receptor agonist) and CGS- 21380 (A2A selective agonist), were used in absence and presence of A2A receptors selective antagonist, ZM-243185, in naive and morphine-dependent rats.Results: Adenosine, NECA and CGS-21680 increased pial vessels blood flow in naive and dependent rats dose dependently. These responses were blocked significantly by ZM-243185. Responses of pial vessels to adenosine (10-4, 10-5 and 10-6M) and NECA (10-4, 10-5 and 10-6M) were increased significantly in morphine- dependent rats in comparison to naive rats. Pial vessels responses to CGS-21680 did not show any significant differences between morphine dependent and naive rats.Conclusion: Based on these results it could be concluded that the role of A2B receptors in regulation of rCBF in morphine dependent rats is more effective than A2 Areceptors.

Introduction: Repetitive transcranial magnetic stimulation (rTMS) modulates the excitability of cortical neural networks. The effect of rTMS on excitability of cortical networks depends on its frequency. According to the previous reports, a distinction is made between low «1 Hz) and high frequencies of rTMS. Low frequencies of rTMS inhibit seizure but high frequencies increase it. In the current study, we tried to investigate the effect of different frequencies of rTMS on chemical kindling induced seizure in rats.Methods: Chemical kindling was induced by i.p. injections of penthylentetrazol (PTZ) 45 mg/kg, 3 times per week. Effects of different frequencies of rTMS (0.25, 1 and 5 Hz) on kindling acquisition were investigated. rTMS was applied 30 minutes after PTZ injections. Stimulation was delivered at motor threshold intensity (4s, 4 stimulus interval of 10 s).Results: Maximum stage of behavioral seizure decreased by 0.25 Hz rTMS and increased by 5 Hz rTMS. Stages 4 and 5 latencies were increased by 0.25 Hz rTMS and decreased by 5 Hz rTMS. Stage 5 duration was decreased by 0.25 Hz rTMS and increased by 5 Hz rTMS.Discussion: Our results showed that application of rTMS had significant effect on seizure parameters in the acquisition period. Lower frequencies of rTMS seem to be more effective.

Introduction: Previous studies have shown that exercise affects cognitive function. Considering that exercise in anima] studies can be either voluntary or forced, effects of exercise (specially forced exercise) on learning and memory remains a matter of controversy. The present study aimed to investigate the effects of treadmill exercise on LTP in the dentate gyrus of rats.Methods: A moderate exercise program was used consisting of treadmill running at 17 m/min and O-degree inclination for 40 min/day, 7 days/week, for duration of 12 weeks. Field excitatory postsynaptic potentials (fEPSP) were recorded in dentate gyrus (DG) after stimulation of Perforant pathway by 400 Hz titanization.Results: The indices of responses including the amplitude of population spike and the slope of excitatory postsynaptic potential were significantly smaller in the exercise group with respect to the control group. But the stimulus-response curves in DG area measured before induction of LTP, showed no significant difference between the groups.Conclusion: The present results suggest that alternative stress due to electrical shock in order to motivate the animal to run in treadmill exercise affects synaptic transmission and impairs LTP induction in DG. Therefore, these experiments indicate that chronic treadmill exercise can decline learning and memory.

Introduction: Pain as a complex process in central nervous system (CNS) has been studied by many researchers. Pain is controlled by several CNS pathways, one of the most important of which is the descending noradrenergic system. This system begins from locus coeruleus (Le) nucleus in pons and ends in the spinal cord in this research, the effect of pain induced by formalin was studied.Methods: Male Sprague-Dawley rats weighing 280-320 g were categorized into two groups of control (injection of 50 ml normal saline) and test (injection of 50 ml 2.5% formalin). Rats were anesthetized by pentobarbital sodium (50 mg/kg i.p.). Microdialysis probes were inserted 24 hrs before the test was done. Rats were anesthetized by urethane and formalin test for induction of chemical and tonic pain was performed on the hind paw of the animals. Micro dialysis samples were taken in 15 minutes intervals and noradrenaline (NA) and its metabolite, 3-methoxy 4-hydroxy phenylglycol (MHPG), were measured by HPLC-ECD.Results: The NA and MHPG concentration in the first and second phases of formalin test did not change significantly in neither test nor control groups.Conclusion: LC has no role in perception of pain induced by formalin test during anesthesia.

Instruction: Measurement of brachial artery diameter variation by ultrasound methods has commonly been used to test the endothelial function. It is known that the artery diameter is increased by flow stimulation. Therefore in the present study, the effect of external obstruction, as flow stimulation, on the radial strain of the brachial artery was assessed. Also the biomechanical behavior of the artery due to the changes in obstruction cuff position was evaluated.Methods: Firstly, for evaluating the effect of flow stimulation on healthy men's brachial artery, 200 mmHg pressure and 5 minutes of obstruction was applied. Then, without flow stimulation, it was evaluated by ultrasonic method. In order to evaluate the optimum cuff position with maximum biomechanical variation of the brachial artery, arteries of two regions including the proximal brachial (upper arm) and middle forearm of 10 healthy men were obstructed by 200 mmHg of stress. By acquiring artery diameter variation and estimation of radial strain, multiple frames of the B-mode ultrasonic images were saved on personal computer and maximum artery diameter in the systolic phase, artery diameter in the end of the diastolic phase and the shape of offline were measured. According to relative diameter variations, radial strain percentages were estimated. The effects of external obstruction and the position of this obstruction on the radial strain of the brachial artery were analyzed by t-test.Results: In the first stage, the results of ultrasonic evaluation of the left brachial artery showed that the radial strain induced by stress (200 mmHg) was significantly increased 3.5 times compared to the normal condition without stress. Evaluation of the obstruction's location and its effect on the relative brachial artery diameter showed that with the application of 200 mmHg obstruction in 1/3 of the superior ann and the middle forearm, the radial strain of the artery were 10.44±2.63 % and 4.97±3.61 %, respectively. The statistical analysis of the brachial artery radial strain showed a significant difference between the two obstruction's locations and 33% increase of the obstructed brachial artery's diameter variation in 1/3 of the superior ann. Conclusion: The brachial artery's radial strain is increased by the external obstruction of the artery. This increase seems to be larger in the upper arm region of the artery compared to the middle forearm region.

Introduction: Previous studies have shown that vitamin A and its derivatives such as retinoid and all-trans retinoic acid has a crucial role in memory, learning and synaptic plasticity. The receptors of vitamin A are seen in different parts of the brain such as hippocampus, where vitamin A has an important role in learning. In this study, the effect of intrahippocampal (CA1) injection of all-trans retinoic acid on spatial learning was investigated in adult male rats.Methods: 49 adult male rats divided in 7 groups were used. Test groups (1 -4) received 1 m of all-trans retinoic acid dissolved in DMSO at concentrations of 1, 2, 4 and 8 g/m for 4 consecutive days, 90 minutes before training. Group 5 received DMSO and 6th and 7th groups were designated as sham operation and control (intact) group, respectively. After each injection, Morris Water Maze (MWM) was used as a method to measure learning task. Results: This study showed that all -trans retinoic acid at the concentration of 1 g/m improved spatial learning in Morris Water Maze (p< 0.05).Conclusion: Our findings show that all -trans retinoic acid improves spatial learning in rats via enhancing the expression of learning related proteins.

Introduction: In this study the role of PGE2 as an important inflammatory mediator in indomethacin and theophylline effects on joint diameter and vascular response to saphenous nerve stimulation in chronically inflamed rat knee joint was investigated.Methods: Inflammation was induced by intraarticular injection of 0.2 ml Freunds Complete Adjuvant (FCA). 3,7, 14 and 21 days post injection, knee joint diameter, blood flow changes induced by saphenous nerve stimulation and PGE2 content of the joint were assessed using micrometer, laser Doppler flow meter and an enzyme immunoassay kit, respectively. These variables were also determined in another three groups, control, inflamed receiving indomethacin or inflamed receiving theophylline also.Results: After induction of inflammation in the knee joint, constrictory response of the joint vessels to saphenous nerve stimulation was reduced but joint diameter was enhanced significantly. Theophylline administration decreased both vascular response of the knee joint to nerve stimulation and joint diameter. Daily administration of indomethacin had no effect on joint edema but increased the constrictory response of the joint vessels to nerve stimulation.Furthermore PGE2 content increased in inflamed knee joint in comparison with control (un-inflamed) during two weeks but in rats receiving indomethacin it was reduced significantly on days 3, 14. Also in inflammation induced rats treated by theophylline, PGE2 content was significantly decreased only on day 14.Conclusion: In chronic inflammation, PGE2 as an inflammatory mediator play an important role in edema and modulation of constrictory response of the joint vessels to nerve stimulation. Furthermore antiedema effect of theophylline also may be mediated by PGE2 through reduction of vascular permeability.

Introduction: Stress has many effects on the development of systems and organs in the fetal period, and these effects appear after birth. Since hemopoietic system is susceptible to stress, effects of restraint stress were studied in offspring of pregnant rats.Methods: Pregnant rats were divided into one control and three stress groups. The control group did not receive any stress during the gestational period. Stress groups 1, 2 and 3 were subjected to restraint stress from 8 to 21, 8 to 17, and 17 to 21 days of gestation, respectively. At the age of 60 days, the blood samples were taken from the male offspring rats. Results: The results in the off springs were as follows: a) Restraint stress markedly decreased the total number of white blood cells in off springs of groups 1 and 3 The percentage of granulocytes decreased and lymphocytes increased significantly in these groups. b) The number of red blood cells increased significantly in groups 1 and 2 compared with the control group. c) The number of platelets increased in group 1, although their hemoglobin decreased significantly. d) As for the index of RBC, the prenatal stress had an effect on MCV, MCH and MCHC in all groups.Conclusion: Our results showed that prenatal restraint stress causes long lasting changes in the blood parameters after birth. These data prove that restraint stress alters the function of immune and hemopoietic systems.