Physiology and Pharmacology
Volume:12 Issue: 4, 2009

Neurohormones like testosterone and estradiol have an important role in learning and memory. The hippocampus is essentially involved in learning and memory, and is known to be a target for estradiol actions. Estrogen receptors (ERs) are highly expressed in CA1 of rat hippocampus, and mediate the effects of estrogen on learning and memory. Estradiol receptor belong to a family of transcription factors, the nuclear receptor superfamily, and has two subtypes ER
and ER. The current research has been conducted to assess the effect of ER selective agonist, diarylpropionitrile (DPN), on passive avoidance of adult male rats, by using passive avoidance task. Male adult rats were bilaterally cannulated into the CA1 area of hippocampus, and then received vehicle (dimethyl sulfoxide, DMSO) or DPN (0.2, 0.5, 1 μg/0.5μl/side), 30 min before training on passive avoidance task. The results showed that pre-training intra-CA1 injections of DPN (0.5, 1 μg/0.5μl/side), significantly decreased step-through latencies and increased time spent in dark on passive avoidance learning (P<0.01). Our data suggest that intra-CA1 administration of DPN could impair learning and memory acquisition on passive avoidance task.

Many of the diseases of adulthood are originated from the intrauterine conditions during fetal life. Because of the importance of thyroid hormones in growth and development of the fetus, the effects of maternal hypothyroidism on carbohydrate metabolism in adulthood was investigated. Pregnant rats were divided into the fetal hypothyroidism (FH) and the control (C) groups. During the gestational period, propylthiouracil (PTU) dissolved in drinking water (100 ppm) was administered to the FH group, while the C group drank tap water. After delivery and maturation of male neonates, intravenous glucose tolerance test (IVGTT) was performed. For IVGTT tests, catheters were inserted into the femoral vein and artery after anesthesia. The first arterial sample was taken before injections, then the glucose solution was injected and other samples were obtained after 5, 10, 15, 20, 30 and 60 minutes. Plasma glucose and insulin concentrations were measured using the glucose oxidase and an ELISA method, respectively. Plasma glucose concentration 5 min after glucose injection in the FH group (239.2 ± 15.6 mg/dL) was significantly higher than the C group (190.1 ± 4.5 mg/dL, P<0.05). There was no significant difference in plasma insulin concentrations of the 2 groups. Daily water consumption during the gestation in PTU administered mothers was significantly lower compared to the C group (P<0.05). The body weight of animals was significantly (P<0.05) lower in the FH group compared with the C group. Maternal hypothyroidism can alter carbohydrate metabolism during adulthood, which may contribute to the development of diabetes.

The bed nucleus of the stria terminalis (BST) is a limbic structure which is involved in cardiovascular regulation and baroreflex modulation. The presence of cholinergic synaptic terminalis with high level of muscarinic receptors in the BST has been demonstrated. This study was performed to find the role of the cholinergic muscarinic receptor in cardiovascular response and baroreflex activity in urethane anesthetized rat. Acetylcholine (Ach, 3, 6 nmol in 50 nl) was microinjected unilaterally into the BST of 53 urethane anesthetized male rats. Femoral artery and vein were cannulated to record the blood pressure (AP) and heart rate (HR), respectively. The maximum average changes in the mean arterial pressure (MAP) and (HR), were compared with control group and before injection using t-test and paired t-test, respectively. To evaluate baroreflex activity, bradycardia values corresponding to progressive 20 mmHg increases in MAP were determined. The slope of the linear regression curves was calculated and compared to before injection using ANOVA repeated measure. Microinjection of Ach into the dorsal, lateral and ventral portion of the BST resulted in an increase of AP (20.69 ± 1.8 mmHg, p<0.01) with no significant changes of the HR. The pressor response evoked by Ach was blocked by microinjection of atropine into the BST. However, atropine did not affect the bradycardia reflex evoked by increased blood pressure caused by intravenous phenylephrine injection. Microinjection of cobalt chloride into the BST did not affect the baseline AP and HR but significantly increased bradycardic response to lower pressure changes (less than 40 mm Hg) and decreased bradycardic response to higher pressure changes (more than 40 mm Hg) (p>0.05) indicating that neuronal circuitry of BST is an essential part of the baroreflex.. The present study indicated that the BST muscarinic receptors are involved in the cardiovascular regulation but are not involved in the modulation of baroreflex activity, although synapses within the BST have influence on the bradycardia baroreflex component.

The ablation technique is one of the important therapeutic interventions for treatment of AV Nodal tachyarrhythmia. Different animal models have been developed to study the effects of ablation on the functional interanodal structure. The aim of the present study was to develop a new model of computer analysis to produce lesions by using direct voltage in isolated perfused rabbit AV-Node. The model of Superfused-perfused isolated AV-Node of rabbit was used in our study. Posterior nodal extension (slow pathway) and anterior nodal approaches (fast pathway) were ablated by using direct voltage (100-110 V) in 30 sec. All stimulation protocols and computer analysis were performed by the custom made software that has been developed in the Electrophysiology laboratory of Golestan Cardiovascular Research Center. All protocols were applied to 2 groups (5 rabbits in each group). His deflection was detected by software (AV-Node pack) and nodal recovery curved was constructed on line. By using specific electrophysiological criteria, we could precisely predict the place of nodal ablation. Slow pathway ablation caused significant ERP and AHmax prolongation and fast pathway ablation caused significant AHmin prolongation. Histology examination confirmed the ablation results. Computer analysis of nodal ablation is a new method to induce specific lesions in AV-nodal pathways. Changing dynamic electrophysiological behavior of AV-node after ablation is an important index for predication of outcome of ablations.

The cholinergic system plays an important role in learning and memory. Administration of either extracts of Crocus Sativus (Saffron) or its constituent, crocin, reduced ethanol-induced memory impairment. Based on the above findings, we investigated the effect of crocin in antagonizing spatial learning and memory impairment induced by scopolamine, a cholinergic receptor antagonist, in rats by using Morris water maze (MWM). Male rats received crocin (1, 5 or 10 mg/kg, i.p.) 30 min after injection of scopolamine (0.5 mg/kg, i.p.) or saline for 6 consecutive days. Control animals received only scopolamine or saline. Spatial learning and memory parameters in the same days were tested using MWM. For this purpose, escape latency and swim distance to hidden platform were tested for four consecutive days. In probe trials, percentages of time that animals spent in target quadrant were recorded. 24 h later, visible version of MWM was performed in which escape latency to visible platform and swim speed were tested. The results indicated that administration of scopolamine impaired the formation of spatial learning and memory processes. Application of crocin in a dose-dependent manner ameliorated the effects of scopolamine. In the visible version of MWM, there was not any significant difference in spatial performance among animals in studied groups.

Nicotine is the psychoactive substance responsible for establishing and maintaining smoking dependence. CYP2A6 is the primary enzyme that inactivates nicotine to cotinine. Genetic variation in CYP2A6 accounts for some of the inter-individual variability in nicotine metabolism and has been indicated to influence smoking behavior and dependence. Therefore, the aim of this study was to examine whether there is a relationship between CYP2A6 genetic polymorphism and smoking dependence in an Iranian population. We assessed 118 male non-smokers (1-99 cigarette/ lifetime) and 133 dependent current smokers for demographic, cigarette use history and DSM-IV dependence. CYP2A6 alleles associated with decreased nicotine metabolism (* 2, *4, or *9 allele) were determined using allele-specific nested PCR. Genotypes were grouped into slow metabolizers (one or two copies of *2 or *4, or two *9 alleles), intermediate (one *9 allele), and normal (have no copies of *2, *4, or *9 alleles). Intermediate nicotine metabolizers were at higher risk for becoming a dependent smoker odd ratio (OR = 3.71; p=0.009). Slow metabolizers had a significantly lower age of first smoking compared to normal and intermediate metabolizers (p = 0.037). Cigarette consumption and the degree of smoking dependence were not significantly different among smokers with different CYP2A6 genotypes. In Iranian population, the risk for becoming a dependent smokers increases with genotypes for intermediate metabolism of nicotine and slow nicotine metabolizers experience smoking in lower ages. These findings increase our understanding of the effect of CYP2A6 genotypes on smoking dependence in Iranian population and may help us to develop new strategies for quitting smoking.

In the Kindling-induced seizure model, low and repeated electrical or chemical stimulations, can elevate the neural network excitability and induce epileptiform seizures. Opioid receptors are widely distributed in different areas of the brain. On the other hand, morphine has paradoxical effects and induces elevation or alleviation of the pain sensation and excitability, at different doses. The present study is designed to investigate the effect of ultra low dose morphine on seizures induced by pentylentetrazol (PTZ). PTZ (32 mg/kg i.p.) was administered for 12 constitutive days to kindle the male Wistar rats (200-250 g). Animals were treated by saline or morphine (0.1 μg/kg, 1 μ g/kg, 10 μ g/kg and 10 mg/kg), 30 min before PTZ administration (n = 7-9) and seizure severity was recorded during 30 min after PTZ administrations. Morphine at the dose of 10 mg/kg was able to elevate the seizure intensity and accelerate the kindling process (p<0.001), but at the dose of 10 μg/kg, attenuated the seizure intensity and kindling development (p<0.05). The reason for this paradoxical effect of morphine on PTZ-induced seizure could be that morphine, at ultra low doses, can elicit the stimulatory signaling pathway of Gs protein, rather than the inhibitory Gi pathway. It seems that ultra low does of morphine by inducing the activity of Gs signaling can lead to the attenuation of PTZinduced seizures, while activation of Gi signaling using ordinary doses of morphine can cause potentiation of PTZinduced seizures.

Previous studies have shown that morphine administration could inhibit neural tube development in rat embryos and produce behavioral defects in human and animals. In the present study, the effects of maternal morphine consumption on embryonic neural plate development in Wistar rats were investigated. Twenty-four female Wistar rats (250-300 g) were crossed with males. After pregnancy, the treatment group received 0.1 mg/ml of morphine in drinking water daily (14 ml water/100 g of body weight for each rat), while the control group received tap water. Eight days and 12 hours after the onset of pregnancy, the animals were anesthetized by chloroform and the embryos were taken out surgically. Lengths of embryos were determined by a Caliper. Embryos were fixed in formalin 10% and tissue was processed, sectioned and stained with H&E. The sections were examined for neural plate development by a light microscope and the MOTIC software. Embryonic length in the treatment group was significantly decreased compared with the control group. Neural plate was observed in the control group. Development of neural plate and other embryonic layers (ectoderm, mesoderm and endoderm) were delayed in the treatment group. The ectoderm layer group was poorly developed in embryos exposed to morphine. Morphine consumption during pregnancy could cause a delay in the development of the neural plate as well as the embryonic layers and especially the ectoderm.

Pervious studies have shown that pentoxifylline (PTX) has beneficial effects in reduction of stroke and brain trauma injuries in experimental animals. However, there is very little and controversial information about the effect of PTX on brain edema in cerebral ischemia. Therefore, the aim of this study was to determine the effects of different doses of PTX on brain edema and neurological motor dysfunction in a rat model of transient focal cerebral ischemia. Transient focal cerebral ischemia was induced in Wistar rats by 60 min middle cerebral artery occlusion, followed by 23 h reperfusion. PTX was injected at doses of 15, 30 and 60 mg/kg ip at the beginning of ischemia. Twenty-four h after ischemia, neurological motor dysfunction and the percentage of brain water content (edema) were determined. Administration of PTX at the dose of 60 mg/kg significantly reduced brain water content (P<0.001) and neurological motor dysfunction (P<0.01) in comparison with the control group, while 15 and 30 mg/kg of PTX had no significant effect on any of the parameters. The findings of this study indicate that PTX only at the dose of 60 mg/kg exerts anti-edematous effects and improves neurological motor dysfunction in the acute phase of transient focal cerebral ischemia in rat.

The N-methyl-D-aspartate (NMDA) receptors, which have been implicated in memory formation, could be noncompetitively blocked by ketamine. The present study examines the short term effect of ketamine on induction of anterograde and retrograde amnesia in male rats using Morris water maze (MWM). Male N-MRI rats were randomly divided into nine experimental groups. MWM studies were performed to evaluate spatial learning and memory parameters. In order to examine the effect of ketamine on the induction of anterograde amnesia, 4 groups of animals received daily injections of ketamine (1, 3, 6 or 12 mg/kg, i.p.) 10 min before testing on training days. To examine the effect of drug on the induction of retrograde amnesia four other groups of rats received daily injection of normal saline (on training days) and ketamine (1, 3, 6, or 12 mg/kg, i.p.) (in probe trial) 10 min before testing. Rats of the control group received normal saline on all days of experiments. Spatial learning and memory parameters were recorded and subjected to the analysis of variance (ANOVA). Difference was considered significant if p<0.05. Data showed that injection of ketamine at the dose of 3 mg/kg and higher inhibits spatial learning and memory parameters and induces both anterograde and retrograde amnesia in rats. It seems that ketamine induces inhibitory effects on spatial learning and memory via blocking the NMDA receptors. On the other hand, ketamine induced dose dependent decrease in swim speed which was significant at the dose of 12 mg/kg.

Cigarette smoking affects nitric oxide production. The aim of this study was to determine associations between tobacco smoke and serum nitric oxide metabolites (NOx) concentration. Serum NOx concentration was measured by the Griess method in 230 nonsmokers, 238 active, 196 passive and 29 waterpipe smokers. Subjects were selected from participants of Tehran Lipid and Glucose Study and blood samples were taken 12-14 h after overnight fasting. Mean NOx values were compared between groups by analysis of variance and p values less than 0.05 were considered significant. Serum NOx concentration was significantly higher in smokers (28.2±1.0 μmol/l) compared to passive (25.8±1.0 μmol/l) and nonsmokers (25.3±1.0 μmol/l) (p<0.05), while no significant difference was found in the level of NOx between passive and waterpipe smokers (29.0 ±1.1 μmol/l) compared to nonsmokers. Serum NOx concentration is increased in active smokers, which may be involved in the development of vascular diseases.

N-methyl-D-aspartate (NMDA) receptors play a pivotal role in the development of tolerance and physical dependence to opiates. Activation of NMDA receptors involves the induction of long term potentiation (LTP) in hippocampus. Our previous study suggested that chronic oral administration of morphine enhanced NMDA dependent LTP in the CA1 area of hippocampal slices of rats. The present study examines the expression levels of individual NMDA receptor subunits, NR1, NR2A and NR2B, in the hippocampus of morphine-dependent rats by using western blotting. Total proteins of hippocampus were extracted by Tris-HCl buffer containing anti proteases and sodium dodecyl sulfate (SDS). The extracted proteins were resolved by SDS-PAGE and transferred to polyvinylidenefloride (PVDF) membrane by tank blotting and the subunits of NMDA receptor were analyzed by immunoblotting by using specific antibodies. Obtained results provide both biochemical and statistical evidence to suggest that NMDA receptor function in the hippocampus, at least in terms of expression of NR1, NR2A and NR2B protein subunits, increases in morphinedependent rats. Taken together, these data support several studies in the literature indicating that NMDA receptors in the hippocampus are involved in the process of opiate dependence.