Cellulose membrane coated Mo-doped TiO2nanotube sheets for sustained oxidation of biomolecules.

Titanium dioxide nanotubes (TNT) are widely researched materials for the photocatalytic generation of free radicals, which are useful in wastewater treatment. We aimed to prepare Mo-doped TNT sheets, covered with a cellulose membrane to avoid TNT surface inactivation by protein adsorption. We studied the susceptibility of serum albumin (SA) bound to different molar ratios of palmitic acid (PA) to denaturation and fibrillation by this system, which is meant to mimic oxidative stress conditions such as non-alcoholic fatty liver disease. The results demonstrated that cellulose membrane-covered TNT successfully oxidized the SA, identified by structural changes to the protein. Increasing the molar ratio of PA to protein-enhanced thiol group oxidation while protecting the protein against structural changes. Finally, we propose that in this photocatalyzed oxidation system, the protein is oxidized by a non-adsorptive mechanism mediated by H2O2. Therefore, we suggest that this system could be used as a sustained oxidation system to oxidize biomolecules as well as potentially in wastewater treatment.

Silver nanoparticles (Ag-NPs) in the central amygdala protect the rat conditioned by morphine from withdrawal attack due to naloxone via high-level nitric oxide.

Repeated injection of morphine during conditioned place preference (CPP) leads to spatial craving due to high-level nitric oxide (NO) in the central nucleus of amygdala (CeA). Silver nanoparticles (Ag-NPs) can produce oxygen-free radicals that lead to NO formation. We aimed to show the Ag-NPs protective effect on naloxone (NLX)-induced morphine withdrawal in the conditioned rats. Wistar rats (300-350 g) were implanted with cannulae in the CeA. After recovery, they were randomly divided into experimental and saline groups. CPP was conducted by three-phase unbiased program. Morphine (0.5-7.5 mg/kg) was injected subcutaneously (s.c.) once/per day during the conditioning phase. Naloxone (NLX) (0.05-0.4 µg/rat) was given, intra-CeA, 10 min before the CPP test. Ag-NPs (0.0001-0.01 µg/rat) were administered alone or prior to the NLX effective dose (0.4 µg/rat), intra-CeA. Conditioning score and withdrawal signs (wet dog shaking and scratching) were obtained and compared with saline group data. All rats' brains were collected in formalin 10% and after 48-72 h stained with NADPH-diaphorase, the NO marker. All data were analyzed by one-way or two-way ANOVA. Morphine (2.5-7.5 mg/kg, s.c.) induced a significant CPP vs. saline (1 mL/kg, s.c.). The single Ag-NPs had no significant effect, whereas the NLX caused meaningful WDS and scratching. However, the NLX pre-treatment in combination with Ag-NPs eliminated these signs. Furthermore, the NO level increased in the CeA. The Ag-NPs may protect the morphine-conditioned rats against the NLX-induced withdrawal symptoms due to high-level NO in the CeA.

The Involvement of D1 and D2 Dopamine Receptors in the Restoration Effect of Left Frontal Anodal, but not Cathodal, tDCS on Streptozocin-Induced Amnesia.

BACKGROUND: Transcranial direct current stimulation (tDCS) is a non-invasive method that improves learning and memory. In this study, the effect of tDCS on streptozotocin (STZ) induced amnesia in the presence or absence of SCH23390 (D1 dopamine receptor antagonist) and sulpiride (dopamine D2 receptor antagonist) has been investigated in male Wistar rats. METHODS: Passive avoidance memory, locomotor activity and pain perception have been assessed by step-through, open-field and hot-plate instruments, respectively. Anodal and cathodal tDCS were exerted on the left frontal cortex with an intensity of 0.2 milliamps for 20 minutes twice a day in 2 successive days. RESULTS: Our study showed that STZ at doses of 30 and 60 mg/ml/kg caused amnesia, while they did not alter locomotor activity and a higher dose of STZ induced analgesia 14 days after injection. SCH23390 (0.001 mg/mL/kg) and sulpiride (0.1 mg/mL/kg) did not alter memory formation by themselves and amnesia induced by STZ (30 and 60 mg/mL/kg), while SCH23390 restored the analgesia induced by STZ (60 mg/mL/kg). Moreover, left frontal anodal and cathodal tDCS restored memory impairment induced by STZ (30 and 60 mg/mL/kg). Also, SCH23390 and sulpiride could prohibit the anodic stimulating effect on memory impairment induced by a dose of 60 mg/ml/kg, but they did not hinder the effect of the cathodal stimulation on this phenomenon. CONCLUSION: The study showed that D1 and D2 dopamine receptors are involved in the restoration effect of left frontal anodal- but not cathodal-tDCS in STZ-induced amnesia.

Study of the Role of Dopamine Receptors in Streptozotocin-Induced Depressive-Like Behavior Using the Forced Swim Test Model.

BACKGROUND: Diabetes is one of the most common endocrine diseases characterized by hyperglycemia. It is caused by an absolute or relative insulin deficiency or an insulin function deficiency. It is one of the major risk factors of depression, with the rate of depression in diabetic patients amounting to as high as 30%. This study examined the role of dopamine receptors in streptozotocin (STZ)-induced depressive-like behavior using the forced swim test (FST). MATERIALS AND METHODS: This study was performed on 56 Wistar male rats. STZ at doses of 30 and 60 mg/kg body weight was administered via intraperitoneal (IP) route to induce diabetes and depression in rats. Thereafter, by using halobenzazepine (SCH23390) (D1 dopamine receptor antagonist) and sulpiride (D2 receptor dopamine receptor antagonist), the role of dopamine receptors in STZ-induced depression was studied. The one-way analysis of variance technique, Tukey's range test, and t-test were used to analyze the data. The P-value less than 0.05 was regarded as statistically significant. RESULTS: Our study showed that STZ at doses of 30 and 60 mg/kg, two weeks after injection, caused prolonged immobility in FST, indicating depressive-like behavior (P<0.05 and P<0.01, respectively). SCH23390 (0.001 mg/mL/kg) and sulpiride (0.1 mg/mL/kg) did not change the variables of depression in animals that received STZ (at doses of 30 and 60 mg/mL/kg) two weeks before (P>0.05). CONCLUSION: According to our study, STZ has a depressive-like behavior two weeks after injection, and dopamine receptors do not play a role in depression associated with STZ use.

Aromatase inhibition exacerbates pain and reactive gliosis in the dorsal horn of the spinal cord of female rats caused by spinothalamic tract injury.

Central pain syndrome is characterized by severe and excruciating pain resulting from a lesion in the central nervous system. Previous studies have shown that estradiol decreases pain and that inhibitors of the enzyme aromatase, which synthesizes estradiol from aromatizable androgens, increases pain sensitivity. In this study we have assessed whether aromatase expression in the dorsal horns of the spinal cord is altered in a rat model of central pain syndrome, induced by the unilateral electrolytic lesion of the spinothalamic tract. Protein and mRNA levels of aromatase, as well as the protein and mRNA levels of estrogen receptors α and ß, were increased in the dorsal horn of female rats after spinothalamic tract injury, suggesting that the injury increased estradiol synthesis and signaling in the dorsal horn. To determine whether the increased aromatase expression in this pain model may participate in the control of pain, mechanical allodynia thresholds were determined in both hind paws after the intrathecal administration of letrozole, an aromatase inhibitor. Aromatase inhibition enhanced mechanical allodynia in both hind paws. Because estradiol is known to regulate gliosis we assessed whether the spinothalamic tract injury and aromatase inhibition regulated gliosis in the dorsal horn. The proportion of microglia with a reactive phenotype and the number of glial fibrillary acidic protein-immunoreactive astrocytes were increased by the injury in the dorsal horn. Aromatase inhibition enhanced the effect of the injury on gliosis. Furthermore, a significant a positive correlation of mechanical allodynia and gliosis in the dorsal horn was detected. These findings suggest that aromatase is up-regulated in the dorsal horn in a model of central pain syndrome and that aromatase activity in the spinal cord reduces mechanical allodynia by controlling reactive gliosis in the dorsal horn.

Involvement of D1/D2 dopamine antagonists upon open-arms exploratory behaviours induced by intra-nucleus accumbens shell administration of N-methyl-D-aspartate.

Glutamatergic system stimulation in some parts of the brain may affect anxiety-related behaviours, aversive learning and memory. This system retains many interactions with dopaminergic neurotransmission. We have studied the effect of nucleus accumbens (NAc) shell glutamatergic system activation on anxiety-related behaviours as well as aversive learning and memory in adult male Wistar rats using the N-methyl-D-aspartate (NMDA) receptor agonist, NMDA. Furthermore, the possible involvement of the NAc shell dopamine D1 and D2 receptors upon NMDA-induced effects was evaluated. The elevated plus-maze task was used to assess the drugs' concomitant effects on anxiety, learning and memory in rats. All drugs were delivered into the NAc shell via bilaterally implanted indwelling cannulae. The NMDA-induced anxiolytic-like behaviours upon retest could possibly be attributed to the further avoidance acquisition impairments. Moreover, the inhibition of dopaminergic system using SCH 23390 and sulpiride induced an anxiolytic-like response and impaired the aversive memory acquisition during retest. However, the concurrent intra-NAc shell microinjection of the subthreshold dose of SCH 23390 and sulpiride (0.125 µg/rat) reversed the anxiolytic-like effect and blocked the aversive memory impairment induced by intra-NAc shell NMDA. Our results suggest a modulatory role of the NAc shell dopaminergic system on NMDA-induced effects in the aversive memory.

The effect of carvacrol on serum cytokines and endothelin levels of ovalbumin sensitized Guinea-pigs.

OBJECTIVE(S): Different pharmacological effects of carvacrol including relaxant effect, its inhibitory effect on muscarinic and histamine (H1) and stimulatory effect on ß-adrenoceptors have been demonstrated on guinea pig tracheal chains in previous studies. In the present study, the effect of carvacrol on blood IL-4, IFN- γ and endothelin levels of sensitized guinea pigs is examined. MATERIALS AND METHODS: Five groups of guinea pigs sensitized to ovalbumin (OA) were given pure drinking water (group S), drinking water containing three concentrations of carvacrol (40, 80 and 160 µg/ml)) and dexamethasone. The blood IL-4, IFN- γ and endothelin levels of sensitized and control guinea pigs were evaluated (n=6, for all groups). RESULTS: Blood IL-4 and IFN-γ levels (P<0.001 for both cases) as well as endothelin (P<0.01) were increased but IFN-γ/IL-4 ratio decreased (P<0.05) in sensitized animals compared to controls. The treatment of S animals by dexamethasone (P<0.01) and two higher concentrations of carvacrol (P<0.001 for both cases) significantly decreased IL-4 level. The treatment of S animals with dexamethasone did not changed IFN-γ levels but treatment with high concentration of carvacrol significantly increased its level (P<0.001). In addition, IFN-γ/IL-4 ratio was significantly increased in S groups, who were treated with dexamethasone (P<0.05) and two higher concentrations of carvacrol (P<0.001 for both cases). Treatment of S animals by dexamethasone (P<0.01) and all concentrations of carvacrol also significantly decreased endothelin level (P<0.01 to P<0.001). CONCLUSION: The results show that carvacrol causes the reduction of IL-4 and endothelin, but it increases IFN-γ and IFN-γ/IL-4 ratio in the blood of sensitized guinea pigs. The results also suggest more specific effect of carvacrol compared to dexamethasone due to the absence of the effect of later on IFN-γ.

Septo-hippocampo-septal loop and memory formation.

The Cholinergic and GABAergic fibers of the medial septal/diagonal band of Broca (MS/ DB) area project to the hippocampus and constitute the septo-hippocampal pathway, which has been proven to play a role in learning and memory. In addition, the hippocampus has bidirectional connections with the septum so that to self-regulate of cholinergic input. The activity of septal and hippocampal neurons is modulated by several neurotransmitter systems including glutamatergic neurons from the entorhinal cortex, serotonergic fibers from the raphe nucleus, dopaminergic neurons from the ventral tegmental area (VTA), histaminergic cells from the tuberomammillary nucleus and adrenergic fibers from the locus coeruleus (LC). Thus, changes in the glutamatergic, serotonergic and other systems-mediated transmission in the MS/DB may influence cholinergic or GABAergic transmission in the hippocampus.

The role of glutamatergic pathway between septum and hippocampus in the memory formation.

The N-methyl-D-aspartate (NMDA) receptor is a subtype of glutamate receptor that is presented in highest density in the hippocampus and septum. NMDA receptors of the septum and the hippocampus are involved in cognitive performance, especially in learning and memory processes. The septum nucleus and hippocampal formation are two regions of the limbic system. The septum and the hippocampus are anatomically and functionally connected to each other. These areas made the septo-hippocampal and hippocampo-septal pathways, which are implicated in the cognitive processes. The activity of septal and hippocampal neurons is modulated by several neurotransmitters such as glutamate. Thus, changes in the glutamatergic transmission in the septum and hippocampus may influence learning and memory processes in these pathways.

Indole and trans-chalcone attenuate amyloid ß plaque accumulation in male Wistar rat: in vivo effectiveness of two anti-amyloid scaffolds.

Alzheimer's disease (AD) is an irreversible neurodegenerative condition in which abnormal accumulation of amyloid plaques is observed, and for which no effective treatment still exist. In recent years, many aromatic small molecules have been observed to have anti-amyloid effect, and may have the potential to attenuate AD symptoms. The indole core and the flavonoid precursor trans-chalcone have been studied here as representative of these group of molecules. Formation of amyloid plaques has been induced in a rat model of AD, after what the two compounds were given to experimental groups. Shuttle box experiment and histological examination of brain amyloid plaques was then performed in order to test the effect of 28 days treatment on rats memory and brain tissue integrity. In conclusion, it was found that both compounds were effective in ameliorating the rats condition, and could be considered as interesting potential drug candidates.

Scopolamine induced memory impairment; possible involvement of NMDA receptor mechanisms of dorsal hippocampus and/or septum.

BACKGROUND AND AIM: The anatomical connections of septum and hippocampus and the influence of cholinergic and glutamatergic projections in these sites have been reported. In the present study, the effect of pre-training intra-dorsal hippocampal (CA1) and intra-medial septal (MS) administration of scopolamine, a nonselective muscarinic acetylcholine antagonist, and NMDA receptor agents and their interactions, on acquisition of memory have been investigated. METHODS: The animals were bilaterally implanted with chronic cannulae in the CA1 regions and in the medial septum. Animals were trained in a step-through type inhibitory avoidance task, and tested 24h after training to measure step-through latency as memory retrieval. RESULTS: Intra-CA1 or intra-MS injections of scopolamine (0.5, 1 and 2 µg/rat) and D-AP7 (a competitive NMDA receptor antagonist; 0.025, 0.05 and 0.1 µg/rat) reduced, while NMDA (0.125 and 0.25 µg/rat) increased memory. Intra-MS injection of a subthreshold dose of NMDA reduced scopolamine induced amnesia in the MS. However, similar injection of NMDA into CA1 did not alter scopolamine response when injected into CA1. Moreover, intra-MS or -CA1 injection of a subthreshold dose of NMDA did not alter scopolamine response in the CA1 or MS respectively. On the other hand, co-administration subthreshold doses of D-AP7 and scopolamine into CA1 and/or MS induced amnesia. CONCLUSIONS: The cholinergic system between septum and CA1 are modulating memory acquisition processes induced by glutamatergic system in the CA1 or septum and co-activation of these systems in these sites can influence learning and memory.

Effects of acute verjuice consumption with a high-cholesterol diet on some biochemical risk factors of atherosclerosis in rabbits.

BACKGROUND: Metabolic changes in postprandial state particularly after fatty meals lead to atherosclerosis progression. Verjuice is an acidic juice made from unripe grape, commonly used as a popular ingredient in Iran. In this study the acute effects of verjuice intake on postprandial values of some biochemical atherosclerosis risk factors in rabbits fed high-cholesterol diets were investigated to see if it has is a possible protective role. MATERIAL/METHODS: Rabbits were allowed free access to diets containing: no cholesterol, 1% cholesterol, 1% cholesterol with 5 ml of verjuice, and 1% cholesterol with 10 ml of verjuice. C-reactive protein (CRP), malondialdehyde (MDA), nitrite, nitrate, glucose, LDL-cholesterol (LDL-C), oxidized-LDL (ox-LDL), total cholesterol (TC), apolipoprotein B (ApoB), triglyceride (TG), HDL-cholesterol (HDL-C), apolipoprotein A(ApoA), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetate transaminase (SGOT), and fibrinogen levels were measured before and three hours after feeding these diets. RESULTS: Significant differences were observed in fibrinogen and glucose levels between the high-cholesterol diet with 5 and 10 ml verjuice and the high-cholesterol diet alone. Using 10 ml verjuice with the the high-cholesterol diet caused a significant reduction in ox-LDL, MDA, and nitrite compared with the high-cholesterol diet alone. No significant difference was found between the groups receiving verjuice and the high-cholesterol diet group in TC, HDL-C, TG, LDL-C, ApoA, ApoB, SGPT, SGOT, nitrate, or CRP. CONCLUSIONS: These results suggest that there might be an acute protective effect in the postprandial use of verjuice on some of the risk factors of atherosclerosis, particularly as an antioxidant.

Effects of cannabinoids infused into the dorsal hippocampus upon memory formation in 3-days apomorphine-treated rats.

In the present study, the effects of intra-dorsal hippocampus (intra-CA1) injection of cannabinoid receptor agents on memory formation have been investigated in 3-days apomorphine-treated rats. Step-through inhibitory avoidance task of memory has been used to examine retrieval of memory formation, 24h after training. Apomorphine was injected subcutaneously (S.C.), once daily for 3-days followed by 5 days free of the apomorphine before training. Bilateral post-training intra-CA1 infusions of the non selective CB1-CB2 receptor agonist, WIN55,212-2 (0.1, 0.25 and 0.5 microg/rat), dose-dependently shortened the step-through latency, suggesting amnesia by the drug, whereas bilateral post-training intra-CA1 micro-injections of the selective CB1 receptor antagonist, AM251 (25, 50 and 100 ng/rat), did not affect memory formation. Intra-CA1 infusions of AM251 and WIN55,212-2, two min apart, modify the WIN55,212-2-induced reduction of step-through latency. Furthermore, the deleterious effect of WIN55,212-2 (0.25 microg/rat) was completely abolished in rats previously given apomorphine (0.5 and 1 mg/kg/day, S.C.) for 3 days. This prevention of WIN55,212-2-induced amnestic-like effect was counteracted by the dopamine D2 receptor antagonist, sulpiride (0.25, 0.5 and 1 mg/kg/day x 3-days, S.C.), administered 30 min before each injection of apomorphine (0.5 mg/kg/day x 3-days, S.C.). The D1 receptor antagonist, SCH 23390 (0.01, 0.02, 0.07 and 0.1 mg/kg/day x 3-days, S.C.), was ineffective in this respect. The results suggest that subchronic apomorphine treatment may induce dopamine D2 receptor sensitization, which in turn prevented amnesia induced by WIN55,212-2.

Intra-dorsal hippocampal microinjections of lithium and scopolamine induce a cross state-dependent learning in mice.

BACKGROUND: Lithium, a mood stabilizer, may exert adverse effects on memory. We have previously shown that lithium induces state-dependent learning. Cholinergic systems of the brain may play an important role in memory function and mood regulation. In the present study, the effects of intra-dorsal hippocampal (intra-CA1) injections of lithium and scopolamine on memory and cross state-dependent learning between the two drugs were investigated. METHODS: For memory assessment, a one-trial step-down inhibitory avoidance task was used in adult male NMRI mice. RESULTS: Intra-CA1 administration of lithium (0.5 and 1 microg/mouse) after training or injection of the drug (0.5microg/mouse) before testing impaired memory when retrieval was tested 24 hours later. The memory impairment by post-training lithium was reversed by pretest administration of the drug (0.5 microg/mouse, intra-CA1) suggesting lithium state-dependent learning. On the other hand, intra-CA1 administration of scopolamine (0.5, 1, and 2 microg/mouse) after training or injection of the drug (2 microg/mouse) before testing impaired memory when retrieval was tested 24 hours later. The impairment of memory by post-training injection of scopolamine (2 microg/mouse) was restored by the pretest injection of the drug (1 and 2 microg/mouse). Furthermore, memory impairment induced by post-training injection of lithium (0.5 microg/mouse) and scopolamine (2 microg/mouse) was reversed by pretest administration of scopolamine (0.5, 1, and 2 microg/mouse) and lithium (0.5 and 1 microg/mouse), respectively. The impairment by lithium was also reversed by physostigmine. CONCLUSION: The results suggest that microinjections of both lithium and scopolamine induce state-dependent memory and there may be a cross state-dependency between the two drugs.

N-Methyl-D-aspartate receptors in the ventral tegmental area are involved in retrieval of inhibitory avoidance memory by nicotine.

The interaction of opiate, cholinergic, glutamatergic and (possibly) dopaminergic inputs in the ventral tegmental area (VTA) influencing a learned behavior is certainly a topic of great interest. In the present study, the effect of intra-VTA administration of N-methyl-d-aspartate (NMDA) receptor agents on nicotine's effect in morphine state-dependent learning was investigated. An inhibitory avoidance (IA) task was used for memory assessment in male Wistar rats. Subcutaneous (s.c.) administration of morphine (5 and 7.5mg/kg) immediately after training decreased IA response on the test day, which was reinstated by pre-test administration of the same doses of the opioid; this is known as state-dependency. Moreover, pre-test administration of nicotine (0.2, 0.4 and 0.6 mg/kg, s.c.) also reversed the decrease in IA response because of post-training morphine (5mg/kg). Here, we also show that when infused into the VTA before testing, NMDA (0.01 and 0.1 microg/rat) reverse the post-training morphine effect on memory. In addition, the sub-effective doses of NMDA (0.0001 and 0.001 microg/rat) in combination with a low dose of nicotine (0.1mg/kg) which had no effects by themselves, synergistically improved retrieval of IA memory on the test day. In contrast, pre-test administration of a competitive NMDA receptor antagonist D-AP5 (0.5, 1 and 2 microg/rat) which had no effect alone prevented the nicotine reversal of morphine effect on memory. Our data indicate that NMDA receptors in the VTA are involved in the reversing effect of nicotine on morphine induced state-dependency.

Nicotine improves morphine-induced impairment of memory: possible involvement of N-methyl-D-aspartate receptors in the nucleus accumbens.

The possible involvement of N-methyl-D-aspartate (NMDA) receptors in the nucleus accumbens (NAc) in nicotine's effect on impairment of memory by morphine was investigated. A passive avoidance task was used for memory assessment in male Wistar rats. Subcutaneous (s.c.) administration of morphine (5 and 10 mg/kg) after training impaired memory performance in the animals when tested 24 h later. Pretest administration of the same doses of morphine reversed impairment of memory because of post-training administration of the opioid. Moreover, administration of nicotine (0.2 and 0.4 mg/kg, s.c.) before the test prevented impairment of memory by morphine (5 mg/kg) given after training. Impairment of memory performance in the animals because of post-training administration of morphine (5 mg/kg) was also prevented by pretest administration of a noncompetitive NMDA receptor antagonist, MK-801 (0.75 and 1 microg/rat). Interestingly, an ineffective dose of MK-801 (0.5 microg/rat) in combination with low doses (0.075 and 0.1 mg/kg) of nicotine, which had no effects alone, synergistically improved memory performance impaired by morphine given after training. On the other hand, pretest administration of NMDA (0.1 and 0.5 microg/rat), which had no effect alone, in combination with an effective dose (0.4 mg/kg, s.c.) of nicotine prevented the improving effect of nicotine on memory impaired by pretreatment morphine. The results suggest a possible role for NMDA receptors of the NAc in the improving effect of nicotine on the morphine-induced amnesia.

GABA(A) receptors of hippocampal CA1 regions are involved in the acquisition and expression of morphine-induced place preference.

In the present study, the effects of bilateral intra-hippocampal CA1 (intra-CA1) injections of GABA(A) receptor agonist and/or antagonist on the acquisition and expression of morphine-induced place preference in male Wistar rats have been investigated. The conditioning treatments with subcutaneous (s.c.) injections of different doses of morphine (0.5-7.5 mg/kg) induced a conditioned place preference (CPP) for the drug-associated place in a dose-dependent manner. Intra-CA1 administration of the GABA(A) receptor agonist, muscimol (0.25, 0.5 and 1 microg/rat) significantly inhibited the morphine (5 mg/kg, s.c.)-induced CPP. Intra-CA1 injections of different doses of the GABA(A) receptor antagonist, bicuculline (0.25, 0.5 and 1 microg/rat), in combination with an ineffective dose of morphine (0.5 mg/kg, s.c.) elicited a significant CPP. However, muscimol or bicuculline by themselves did not elicit any effect on place conditioning. Furthermore, the muscimol-induced inhibition of morphine response was reversed by bicuculline (1 microg/rat, intra-CA1) administration. On the other hand, the bilateral intra-CA1 injections of muscimol (0.25, 0.5 and 1 microg/rat) or bicuculline (0.5, 1 and 2 microg/rat) significantly decreased the expression of morphine-induced CPP. Intra-CA1 administration of different doses of muscimol or bicuculline had no effect on locomotor activity in the testing phase. Our data indicated that the GABA(A) receptors of the hippocampal CA1 regions may play an important role in the acquisition and expression of morphine-induced place preference.

Morphine-induced place preference: involvement of the central amygdala NMDA receptors.

In the present study, the effects of bilateral injections of N-methyl-d-aspartate (NMDA) receptor agonist and/or antagonist into the central amygdala (CeA) on the acquisition and expression of morphine-induced conditioned place preference (CPP) were investigated in male Wistar rats. Animals that received 3 daily subcutaneous (s.c.) injections of morphine (1-9 mg/kg) or saline (1.0 ml/kg) indicated a significant preference for compartment paired with morphine in a dose dependent manner. Intra-CeA administration of the NMDA (0.01, 0.1 or 1 microg/rat) with an ineffective dose of morphine (1 mg/kg, s.c.) elicited a significant CPP. Administration of the non-competitive NMDA receptor antagonist, MK-801 (0.1, 0.3 or 0.5 microg/rat), into the central amygdala dose-dependently inhibited the morphine (6 mg/kg, s.c.)-induced place preference. Furthermore, intra-CeA administration of MK-801 (0.25, 0.5 or 1 microg/rat) reduced the response induced by NMDA (1 microg/rat, intra-CeA) plus morphine (1 mg/kg, s.c.). Neither NMDA nor MK-801 alone produce a significant place preference or place aversion. Moreover, intra-CeA injection of NMDA but not MK-801 before testing significantly increased the expression of morphine (6 mg/kg, s.c.)-induced place preference. NMDA or MK-801 injections into the CeA had no effects on locomotor activity on the testing sessions. These results suggest that the NMDA receptor mechanisms in the central amygdala may be involved in the acquisition and expression of morphine-induced place preference.

Theophylline inhibits tolerance and sensitization induced by morphine: a conditioned place preference paradigm study in female mice.

The effect of theophylline on reward properties of morphine was examined in the present study. A biased conditioned place preference paradigm was used to study the effects of theophylline on the development of conditioned place preference by morphine in sensitized and tolerant female mice. Subcutaneous injection of morphine (0.5-10 mg/kg) induced conditioned place preference in mice, while intraperitoneal administration of theophylline (2.5-100 mg/kg) did not induce conditioned place preference or conditioned place aversion. Theophylline (2.5-100 mg/kg) in combination with morphine (5 mg/kg), during conditioning sessions, decreased the acquisition of morphine conditioned place preference dose independently. Administration of theophylline (2.5-100 mg/kg) before testing also caused a significant reduction of the expression of morphine-induced conditioned place preference in a dose-independent manner. Administration of morphine (12.5, 25 or 50 mg/kg) daily, for 3 days, produced tolerance to conditioned place preference induced by the drug (5 mg/kg). Administration of theophylline (2.5 and 10 mg/kg) 1 h before morphine (12.5, 25 mg/kg), during development of tolerance, abolished morphine tolerance. A higher dose of theophylline (100 mg/kg), however, did not alter morphine tolerance. In addition, theophylline (2.5, 10 and 100 mg/kg) failed to reduce tolerance to a higher dose of morphine (50 mg/kg). Daily administration of morphine (5 mg/kg) for 3 days followed by a 5-day interval caused sensitization to morphine place conditioning. When theophylline was administered (2.5, 10 and 100 mg/kg) 1 h before morphine (5 mg/kg), during development of sensitization, inhibition of morphine-induced sensitization was demonstrated. The effect of theophylline was dose independent. It is concluded that while theophylline has no effect by itself, it reduced both the acquisition and expression of morphine conditioned place preference. In addition, theophylline reduced the acquisition of morphine conditioned place preference in morphine-sensitized and morphine-tolerant mice.

Effects of ultra-low doses of nicotine on the expression of morphine-induced conditioned place preference in mice.

In the present study, the effects of acute administration of nicotine, as well as nicotinic and muscarinic acetylcholine receptor antagonists, on the expression of morphine-induced conditioned place preference, have been investigated in male Swiss-Webster mice. Animals received different doses of morphine 5 days after surgical cannulation in the lateral ventricle. Subcutaneous injections of morphine (2-5 mg/kg) in mouse produced place preference in a dose-dependent manner. Furthermore, both intraperitoneal (0.0006-0.1 mg/kg) and intracerebroventricular (0.007-25 ng) nicotine administration significantly reduced the expression of morphine-induced place preference, in a dose-dependent manner. Nicotine, however, was effective over narrow ultra-low dose ranges (0.0012, 0.0025, 0.005 and 0.01 mg/kg; intraperitoneal) and (0.03, 0.1, 0.3 and 0.6 ng/mouse; intracerebroventricular). In addition, locomotor activity was reduced when higher doses of nicotine [both intraperitoneal (0.02, 0.03 and 0.1 mg/kg) and intracerebroventricular (10 and 24 ng/mouse)] were used. Nicotine alone, however, did not cause motivational effects. Intracerebroventricular injection of hexamethonium (0.03, 0.1 and 0.3 mug/mouse; 10 min before nicotine) diminished the effects of nicotine on morphine-induced conditioned place preference. This effect could neither be obtained by intraperitoneal administration of hexamethonium (1, 5 and 10 mg/kg; 30 min before nicotine), nor be reproduced after either intracerebroventricular or intraperitoneal injection of atropine (a muscarinic receptor antagonist). The antagonists, themselves, did not show any motivational effects when used alone and were unable to affect the expression of morphine-induced conditioned place preference. It appears that ultra-low doses of nicotine can reduce the expression of morphine-induced place preference, and that central nicotinic acetylcholine receptors play a role in this regard.