Alpha 7 nicotinic receptor agonist and positive allosteric modulators improved social and molecular deficits of MK-801 model of schizophrenia in rats.

Schizophrenia is a common psychiatric disease that cannot be fully treated with current antipsychotic drugs. It has shown that glutamatergic NMDA receptor antagonists such as MK-801 cause schizophrenia-like phenotype in rodents. Recent studies indicated that α7 nicotinic acetylcholine receptor (nAChR) deficits contribute to schizophrenia. Enhancing its activity with agonist or positive allosteric modulators (PAMs) may be a valuable approach for treatment. The certain intracellular pathways such as Akt/Glycogen synthase kinase 3 beta (GSK-3ß) and phosphodiesterase-4 (PDE-4)/cAMP are associated with the pathogenesis of schizophrenia. In this study, we examined the effect of α7 nAChR agonists and PAMs on the behavioral and molecular phenotype of schizophrenia in the subchronic MK-801 administered rats. Social interaction, the levels of α7 nAChR, and related intracellular pathways (cAMP, PDE4A, PDE4D, p-Akt/Akt, p-GSK-3ß/GSK-3ß) were measured by behavioral or ELISA and western blot tests. Subchronic MK-801 administration decreased the following behaviors and increased the avoiding behaviors. However, only α7 nAChR agonist (A-582941) increased the following behavior while α7 nAChR agonist, PAMs (CCMI and PNU-120596), and clozapine decreased the avoiding behavior compared to MK-801. For molecular parameters, MK-801 administration decreased the α7 nAChR, p-Akt/Akt, p-GSK-3ß/GSK-3ß expressions, and cAMP levels while it increased PDE4A, PDE4D expressions in the prefrontal cortex. Besides, MK-801 decreased the α7 nAChR, p-GSK-3ß/GSK-3ß expressions in the hippocampus. We found clozapine, α7 nAChR agonists, and PAMs reversed the molecular deficits induced by MK-801. Herein, we showed that prefrontal cortex is more sensitive to the devastating effects of subchronic MK-801 administration, especially for PDE4, in rats. In addition to clozapine, α7 nAChR agonists and PAMs found to be beneficial on both social and molecular deficits induced by MK-801 in rats. We suggested that α7 nAChR agonists and PAMs might be valuable approaches to treat negative symptoms of schizophrenia when unmet needs and current limitations considered in this pathology.

An experimental study on the relationship of intra-abdominal pressure and renal ischemia.

This study was undertaken in order to determine whether or not the increased intra-abdominal pressure during laparoscopic procedures causes renal ischaemia and parenchymal pathology. Fifteen adult New Zealand rabbits were used in the study. Anaesthesia was maintained by 2% isoflurane, 50% O2 in air. Heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), end-tidal carbon dioxide (PETCO2), airway pressure (Paw) and blood gases were monitored. Rabbits in control group (group C, n = 7) and study group (group S, n = 8) had a Veress needle placed supraumbilically. Group S was insufflated with CO2 sequentially at 5, 10 and 15 mmHg of intra-abdominal pressures (IAP); each pressure level was maintained for 20 minutes. At the end of the study, laparotomy was performed and blood was withdrawn from renal vein for measurements of renin and angiotensin I levels, and the other kidney was removed simultaneously for pathological evaluation. Haemodynamic and respiratory measurements were stable in group C and were variable in group S. The renin level was 7.27 +/- 0.34 ng.mL-1 and angiotensin I was 5.01 +/- 0.32 ng.mL-1 in group C. In group S, levels of renin and angiotensin I were 26.2 +/- 5.9 ng.mL-1 and 39.4 +/- 12.1 ng.mL-1 respectively, being significantly higher than group C (p < 0.05). Pathological scores were 0.02 +/- 0.008 in group C and 0.82 +/- 0.124 in group S (p < 0.05). There were significant histological changes in group S compared with group C. During prolonged laparoscopic operations high intra-abdominal pressures may result in intra-abdominal organ ischaemia.

Prenatal exposure to morphine or naloxone intensifies morphine dependence at maturity.

Pregnant rats were SC injected with physiological saline (control) or 10 mg/kg morphine (morphine group) or 2 mg/kg naloxone (naloxone group) three times daily during the last 5 days of gestation. Three weeks after birth, male young rats of each group were taken and placed in separate cages. When their body weight reached 130-150 g, 10 rats from control, morphine, and naloxone groups were SC implanted with two pellets containing 75 mg morphine base (total 150 mg). Three days following implantation, rats were IP given 2 mg/kg naloxone for precipitated abstinence syndrome. Immediately after naloxone injection, rats were strictly observed for 15 min and jumping, wet-dog shakes, teeth-chattering, diarrhoea, defecation, and ptosis counted or rated. All abstinence syndrome signs were significantly higher in the morphine or naloxone group than in control. On the basis of the previous experimental findings supporting the idea that opiate physical dependence is related to the binding of opiate, possibly other than their own, to NMDA receptors and the upregulation and/or supersensitivity associated with the binding, the intensification of morphine dependence has been attributed to the long-lasting NMDA receptor upregulation and/or supersensitivity.

Noradrenergic and serotoninergic depression?

The aim of this study was to test the hypothesis of noradrenergic and serotoninergic depressive subtypes. For this purpose, the correlation between three variables was investigated: urinary 3-methoxy-4-hydroxyphenylglycol (MHPG), dexamethasone suppression test (DST), and clinical response profiles to clomipramine and maprotiline, the effects of which are relatively selective on the uptake of noradrenaline (NA) and 5-hydroxytryptamine (5HT). Our results showed no correlation between these measures. Therefore, the hypothesis of two subtypes of depression was not supported. The only significant finding in this study was the obvious decrease in MHPG excretion during the antidepressant treatment in the group with high pretreatment MHPG.

Effects of neonatal monosodium glutamate and aging on morphine dependence development.

Administration of monosodium glutamate (MSG) to neonatal rats has been reported to destroy aspartatergic (ASPergic) and glutamatergic (GLUergic) neurons. Ageing has been shown to induce cell loss, a rather general CNS atrophy, and slowness in the CNS functions. On the other hand, it has been hypothesized that two of the main reasons for opiate dependence development are the blockade by opiates of the NMDA receptors and their associated upregulation and supersensitivity. Accordingly, the abstinence syndrome precipitating effect of naloxone (NL) has been assumed to be the consequences of the removal by NL of opiate from NMDA receptors without being able to prevent upregulated and supersensitive NMDA receptors from being stimulated stronger than normal. To investigate the role of the decrease in the number of NMDA receptors in the development of morphine (M) physical dependence, 4 g/kg MSG was SC injected into neonatal rats on days 2, 4, 6, 8 and 10 after birth. Their littermate controls SC received equimolar NaCl solution. Three or 14 months later, three pellets containing 75 mg base M were SC implanted into male rats treated neonatally with MSG or equimolar NaCl solution. Seventy-two hours after pellet implantation, all rats were injected with 2 mg/kg NL intraperitoneally. Some abstinence syndrome signs were counted or rated for 15 min immediately after NL injection and then statistically evaluated. The NL-precipitated abstinence syndrome was less intense in 3-month-old MSG-treated rats than in controls, most probably due to the decrease in the number of NMDA receptors in MSG-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of MK 801 on morphine physical dependence: attenuation and intensification.

It has previously been reported that the noncompetitive NMDA receptor antagonists ketamine and dextromethorphan suppressed the naloxone-induced morphine abstinence syndrome. In addition, the previous blockade by ketamine and dextromethorphan of NMDA receptors has been shown to intensify the naloxone-elicited morphine abstinence syndrome. On the basis of this information, another noncompetitive NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo-a,d-cyclohepten-5,10-imine maleate (MK 801), was administered to rats in which two morphine-containing (75 x 2 morphine base) pellets had been implanted. The naloxone-precipitated abstinence syndrome in rats injected with 0.3 mg/kg MK 801 36 h after pellet implantation was found significantly more intense than controls whereas the abstinence syndrome in rats that received 0.1 mg/kg MK 801 before naloxone injection was less intense. The intensification by MK 801 given 36 h following pellet implantation was attributed to the further increase in upregulation and supersensitivity of NMDA receptors caused by morphine. The attenuation was explained by the blockade by MK 801 of NMDA receptors as occurred in the case of ketamine and dextromethorphan.

Morphine and naloxone act similarly on glutamate-caused guinea pig ileum contraction.

Both morphine (M) and naloxone (NL) have been reported to have NMDA receptor blocking effects, regarded as the reason of opiate physical dependence development. On the other hand, glutamate (GLU) has been known to induce the contraction of isolated guinea pig ileum via acetylcholine release. Therefore, different concentrations of M or NL were investigated on the 1 mM GLU-induced contraction of isolated guinea pig ileum fixed at a resting tension of 1 g in isolated organ bath. The mean value (359.3 +/- 20 mg) of the GLU-elicited contraction force was significantly reduced (318.4 +/- 19.4) by 25 nM M concentration in the medium. Consequently, 500 and 750 nM M caused further decreases in a rather dose-dependent manner (270.8 +/- 17.4 and 167.8 +/- 16.5 mg, respectively). One micromolar M contraction nearly abolished (8.0 +/- 8.2 mg) the GLU-induced contraction. A similar effect was obtained with the naloxone concentrations of 10, 20, 40, and 50 microM. In addition, NL has been shown to elicit the contraction of the isolated M-dependent guinea pig ileum. In the present study, 20- and 30-microM NL concentrations in the bathing medium caused the contraction of the ileum made M-dependent by preincubation with M (333.0 +/- 32.4 and 309.5 +/- 17.7 mg, respectively). These contraction forces were significantly reduced when the NL concentration was increased to 40 microM. And, 50 microM NL concentration not only failed to induce contraction but caused a relaxation (-10.6 +/- 2.3) as well. The results were considered supporting evidence for the fact that both M and NL are NMDA receptor blockers.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tizanidine on morphine physical dependence: attenuation and intensification.

It has previously been shown that subchronic and acute administration of L-asparaginase and glutaminase inhibitors D-Aspartic acid (D-ASP) and prolyl-leucyl-glycinamide (PLG) intensifies and attenuates morphine (M) physical dependence, respectively, by the inhibition of ASP and glutamic acid (GLU) production, and subsequently their normal releases. Tizanidine (TIZ) has long been known to be an alpha 2-adrenoceptor agonist and inhibitor of ASP and GLU release. Therefore, in this study TIZ has been administered subchronically during the development of M physical dependence to rats in which M-containing pellets had been implanted or acutely 30 min before naloxone (NL)-induced abstinence syndrome. The subchronic administration of TIZ intensified NL-precipitated abstinence syndrome whereas its acute administration attenuated it, as did D-ASP and PLG. On the other hand, TIZ added into the medium prevented the in vitro M-dependent-made guinea pig ileum from contracting following NL application. Furthermore, TIZ stopped the already started contraction by NL of the M-dependent ileum, which completely relaxed later. These effects of TIZ on M-dependent ileum were antagonized by the alpha 2-adrenoceptor antagonist yohimbine. The intensification by subchronic TIZ administration of abstinence syndrome was attributed to the lesser release of ASP and GLU, which resulted in the larger blockade of M of ASPergic/GLUergic receptors due to the lesser release of their endogenous agonist ASP and GLU and consequently the higher upregulation of the receptors. The attenuation by acute TIZ administration of NL-precipitated abstinence syndrome was explained with lesser release of ASP and GLU and concomitantly the lesser stimulation of the receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous chronic blockade of NMDA receptors intensifies morphine dependence in rats.

Chronic exposure of receptors to antagonists generally results in upregulation and/or supersensitivity. On the other hand, the noncompetitive NMDA receptor antagonists ketamine (K) and dextromethorphan (DM) suppress opiate abstinence syndrome by blocking NMDA receptors. Therefore, 40 mg/kg ketamine (K), 5 mg/kg dextromethorphan (DM), 5 mg/kg morphine (M) and 2 mg/kg naloxone (NL) alone or in combination with NL were IP administered to the rats five times during the daytime only for five days to see whether they would intensify abstinence syndrome through upregulation and/or supersensitivity of NMDA receptors. Three days following the implantation of three M-containing pellets, abstinence syndrome was brought about by 2 mg/kg NL injection. Jumping, wet dog shake, writhing, teeth chattering, diarrhoea, defecation and ptosis were observed for ten min. All drugs used alone or in combination with NL increased the intensity of abstinence syndrome. Since K and DM are noncompetitive NMDA receptor antagonists, the intensifying effect of NL or M was considered to be related to their interactions with NMDA receptors. Furthermore, on the basis of the results of the previous and present study, NL was claimed to act on NMDA receptors, like other opioids, but with higher affinity for and weaker blocking effect on NMDA receptors.

The effect of parenteral iron administration on the development of Staphylococcus aureus-induced experimental pyelonephritis in rats.

The first of the three groups of rats was taken as a control and the other two groups were injected with high (15 mg/kg) and low (5 mg/kg) doses of ferric ammonium citrate given intramuscularly twice daily for 5 days. Pyelonephritis was produced in all groups by intravenous inoculation with Staphylococcus aureus. Serum and urine of each rat was collected periodically and their iron content was determined. The severity of pyelonephritis was evaluated by determination of bacterial growth and pathological lesions in kidneys after 10 days of bacterial inoculation. The results showed that parenteral iron administration markedly aggravated pyelonephritis development in rats. But there was no significant difference in the severity of pyelonephritis between rats treated with high or low iron doses.

Suppression by ketamine and dextromethorphan of precipitated abstinence syndrome in rats.

The development of physical dependence on opiates appears to involve an inhibition by opiates of L-asparaginase and glutaminase, and the blockade by opiates of aspartatergic (ASPergic)/glutamatergic (GLUergic) receptors. Ketamine (K) (0.5 or 1 mg/kg) or dextromethorphan (DM) (1 or 2 mg/kg), both of which are known to decrease the responsiveness of ASPergic/GLUergic receptors, were administered to the three morphine (M)-containing pellets implanted rats prior to 2 mg/kg naloxone (NL) injection. Whereas 0.5 mg/kg K showed no significant effect on abstinence syndrome signs, 1 mg/kg K and 1 mg/kg DM significantly attenuated some of the signs. The attenuation or prevention of all the signs were observed after 2 mg/kg DM administration. Almost complete prevention was seen from the second minute on during the ten-minute observation period. As ASP and GLU antagonists K and DM have this antagonizing effect on the precipitated abstinence syndrome signs, the manifestation of abstinence syndrome may mainly result from the normalization of ASP and GLU production because of the disinhibition by NL of the enzymes and the stronger stimulation of ASPergic/GLUergic receptors which have no opiate blockade after NL injection.

Intensification and attenuation of morphine dependence by D-aspartic acid and PLG.

The inhibition by opiates and the sudden normalization by opioid antagonists of the brain L-asparaginase activity (BAA) have previously been reported to be the main factors in the development of physical dependence and the manifestation of precipitated abstinence syndrome, respectively. As a result, L-asparaginase inhibitors D-aspartic acid and prolyl-leucyl-glycinamide (PLG) were separately given to mice and rats either just after morphine (M)-containing pellet implantation or 15 min before naloxone (NL)-precipitated abstinence syndrome. The animals treated in this manner were used to assess the intensity of the physical dependence and to determine the BAA. D-ASP or PLG administration following pellet implantation significantly increased all of the observed signs such as flying, jumping, wet dog shake and writhing. When D-ASP or PLG were given 15 min before precipitated abstinence they significantly decreased the number of the signs. The determination of the BAA showed significant decreases or increases more or less parallel to the severity of the physical dependence on M. The intensification of physical dependence by D-ASP or PLG given just after the pellet implantation was attributed to their additional inhibitory effect to that of M on the BAA at the beginning of the physical dependence development. The attenuating effect of BAA inhibitors D-ASP or PLG administered before precipitated abstinence was explained with the prevention of the increase in the BAA.