Neuroprotectant effects of iso-osmolar D-mannitol to prevent Pacific ciguatoxin-1 induced alterations in neuronal excitability: a comparison with other osmotic agents and free radical scavengers

The basis for the neuroprotectant effect of D-mannitol in reducing the sensory neurological disturbances seen in ciguatera poisoning, is unclear. Pacific ciguatoxin-1 (P-CTX-1), at a concentration 10 nM, caused a statistically significant swelling of rat sensory dorsal root ganglia (DRG) neurons that was reversed by hyperosmolar 50 mM D-mannitol. However, using electron paramagnetic resonance (EPR) spectroscopy, it was found that P-CTX-1 failed to generate hydroxyl free radicals at concentrations of toxin that caused profound effects on neuronal excitability. Whole-cell patch-clamp recordings from DRG neurons revealed that both hyper- and iso-osmolar 50 mM D-mannitol prevented the membrane depolarisation and repetitive firing of action potentials induced by P-CTX-1. In addition, both hyper- and iso-osmolar 50 mM D-mannitol prevented the hyperpolarising shift in steady-state inactivation and the rise in leakage current through tetrodotoxin (TTX)-sensitive Na(v) channels, as well as the increased rate of recovery from inactivation of TTX-resistant Na(v) channels induced by P-CTX-1. D-Mannitol also reduced, but did not prevent, the inhibition of peak TTX-sensitive and TTX-resistant I(Na) amplitude by P-CTX-1. Additional experiments using hyper- and iso-osmolar D-sorbitol, hyperosmolar sucrose and the free radical scavenging agents Trolox and L-ascorbic acid showed that these agents, unlike D-mannitol, failed to prevent the effects of P-CTX-1 on spike electrogenesis and Na(v) channel gating. These selective actions of D-mannitol indicate that it does not act purely as an osmotic agent to reduce swelling of nerves, but involves a more complex action dependent on the Na(v) channel subtype, possibly to alter or reduce toxin association.     

l-Cysteine reduces oral ethanol self-administration and reinstatement of ethanol-drinking behavior in rats

Our previous findings have shown that l-cysteine, a non essential amino acid, prevented ethanol (EtOH) induced conditioned place preference. The aim of the present study was to examine the effect of l-cysteine on the acquisition and maintenance of oral EtOH self-administration and on the reinstatement of EtOH-drinking behavior in Wistar rats. Rats were pretreated intraperitoneally with saline or l-cysteine (20 and 40 mg/kg) 30 min before each acquisition trial, in an operant nose-poking paradigm where they were given the opportunity to orally self-administer tap water or EtOH (5-10% v/v). Further, to evaluate if l-cysteine reduces the acquired oral EtOH self-administration, we carried out an independent experiment in which rats were trained to self-administer EtOH (10%); after all groups of rats developed similarly stable oral EtOH self-administration, the effect of l-cysteine (0, 40, 60, 80 and 100 mg/kg) was tested. An additional group of rats was pretreated with saline or l-cysteine (80 mg/kg) and tested on reinstatement after EtOH extinction and, at the end of last reinstatement session, were utilized to measure blood and brain EtOH levels. The animals that had access to EtOH solution discriminated between the active and inactive nose-pokes and showed rates of active nose-pokes significantly higher than the tap water group. Furthermore, rats self-administering EtOH (10%) also demonstrated extinction behavior and gradually reinstated active nose-poke responding when EtOH was reintroduced. l-cysteine reduced both the acquisition and maintenance of oral EtOH self-administration. The reduced reinstatement of EtOH-drinking behavior was paralleled by a significant reduction of EtOH intake and correlated with blood and brain EtOH levels. The efficacy of l-cysteine on the various phases of alcohol drinking in rats, could represent an interesting pharmacological approach and could open a new line of research for the development of therapies to reduce EtOH intake in alcoholic patients.     

Ethanol-induced conditioned place preference, but not aversion, is blocked by treatment with d-penicillamine, an inactivation agent for acetaldehyde

Rationale There is evidence to suggest that acetaldehyde is involved in the control of ethanol-seeking behavior and reward. d-penicillamine, a thiol amino acid, is a highly selective agent for the inactivation of acetaldehyde. Previous studies from our laboratory have demonstrated that d-penicillamine prevents both behavioral stimulation induced by ethanol and acetaldehyde-produced locomotor depression in mice. Objectives The contribution of ethanol-derived acetaldehyde to the affective effects of ethanol (preference and aversion) was assessed using an unbiased place conditioning design. Methods Male mice received four pairings of a distinctive floor stimulus (CS+: GRID+ or HOLE+) with injections of saline and ethanol (2 g/kg) given before (preference) or after (aversion) the 5-min exposure to the place conditioning apparatus. A different floor stimulus (CS−: GRID− or HOLE−), associated with saline-saline injections on alternate days, was presented. For a different group of animals, the pairings with the CS+ were associated with saline and ethanol injections, but on alternate days, they received d-penicillamine (50 or 75 mg/kg) and ethanol injections paired with the CS−floor stimulus. A 60-min preference test was carried out 24 h after the last conditioning trial. A similar procedure was followed to test the effect of d-penicillamine on morphine (16 mg/kg) and cocaine-induced (20 mg/kg) conditioned place preference (CPP). Results CPP and conditioned place aversion (CPA) were observed for ethanol, but d-penicillamine only blocked CPP. d-penicillamine, by itself, did not produce either rewarding or aversive effects. CPP observed for morphine and cocaine was unaffected by d-penicillamine pretreatment. Conclusions The results of the present study suggest that the selective inactivation of acetaldehyde blocked the rewarding, but not aversive, effects of ethanol and support the role of this ethanol metabolite in the affective properties of ethanol.     

D-cycloserine selectively decreases nicotine self-administration in rats with low baseline levels of response

Expanding the variety of treatments available to aid smoking cessation will allow the treatments to be customized to particular types of smokers. The key is to understand which subpopulations of smokers respond best to which treatment. This study used adult female Sprague-Dawley rats to evaluate the efficacy of d-cycloserine, a partial NMDA glutamate receptor agonist, in reducing nicotine self-administration. Rats were trained to self-administer nicotine (0.03 mg/kg/infusion, IV) via operant lever response (FR1) with a secondary visual reinforcer. Two studies of d-cycloserine effects on nicotine self-administration were conducted: an acute dose-effect study (0, 10, 20 and 40 mg/kg, sc) and a chronic study with 40 mg/kg given before each test session for two weeks. Effects on rats with low or high pretreatment baseline levels of nicotine self-administration were assessed. In the acute study there was a significant interaction of d-cycloserine × baseline level of nicotine self-administration. In the low baseline group, 10 mg/kg d-cycloserine significantly decreased nicotine self-administration. In the high baseline group, 40 mg/kg significantly increased nicotine self-administration. In the repeated injection study, there was also a significant interaction of d-cycloserine × baseline level of nicotine self-administration. Chronic d-cycloserine significantly reduced nicotine self-administration selectively in rats with low baseline nicotine use, but was ineffective with the rats with higher levels of baseline nicotine self-administration. NMDA glutamate treatments may be particularly useful in helping lighter smokers successfully quit smoking, highlighting the need for diverse treatments for different types of smokers.     

l-Arginine and l-glutamine as immunonutrients and modulating agents for oxidative stress and toxicity induced by sodium nitrite in rats

Sodium nitrite (NaNO₂) is a flavoring, coloring and preservative agent in meat and fish products. The study aimed to evaluate the efficacy of l-arginine and l-glutamine supplementation as a potentially novel and useful strategy for the modulation of oxidative stress and toxicity induced by NaNO₂ in male rats. Rats were divided into six groups each of 10 rats and treated for 6 weeks: group 1 as normal control; group 2 fed standard diet containing 0.2% NaNO₂; group 3 and 4 fed the previous diet supplemented with 1% and 2% arginine, respectively; group 5 and 6 fed NaNO₂ diet supplemented with 1% and 2% glutamine, respectively. NaNO₂ treatment induced a significant increase in serum malondialdehyde, nitric oxide, arginase, glutathione-S-transferase activities, urea and creatinine as well as differential leucocytes%. However, a significant decrease was recorded in reduced glutathione, catalase activity, total protein, albumin and some hematological parameters as well as immunoglobulin G. On the other hand, arginine or glutamine showed a remarkable modulation of these abnormalities as indicated by reduction of malondialdehyde and improvement of the investigated antioxidant and hematological parameters. It can be concluded that arginine or glutamine supplementation may reduce oxidative stress and improve the hazard effects of NaNO₂.     

The Role of nitric oxide in convulsions induced by lindane in rats

Lindane is an organochloride pesticide and scabicide. It evokes convulsions mainly trough the blockage of GABA_A receptors. Nitric oxide (NO), gaseous neurotransmitter, has contradictor role in epileptogenesis due to opposite effects of l-arginine, precursor of NO syntheses (NOS), and L-NAME (NOS inhibitor) observed in different epilepsy models. The aim of the current study was to determine the effects of NO on the behavioral and EEG characteristics of lindane-induced epilepsy in male Wistar albino rats.The administration of l-arginine (600, 800 and 1000 mg/kg, i.p.) in dose-dependent manner significantly increased convulsion incidence and severity and shortened latency time to first convulsion elicited by lower lindane dose (4 mg/kg, i.p.). On the contrary, pretreatment with L-NAME (500, 700 and 900 mg/kg, i.p.) decreased convulsion incidence and severity and prolonged latency time to convulsion following injection with a convulsive dose of lindane (8 mg/kg, i.p.). EEG analyses showed increase of number and duration of ictal periods in EEG of rats receiving l-arginine prior to lindane and decrease of this number in rats pretreated with L-NAME.These results support the conclusion that NO plays a role of endogenous convulsant in rat model of lindane seizures.     

Icariin isolated from Epimedium brevicornum Maxim attenuates learning and memory deficits induced by d-galactose in rats

The effects of icariin (ICA), a major constituent of flavonoids from the Chinese medical herb Epimedium brevicornum Maxim, on spatial memory performances and expressions of hippocampus brain-derived neurotrophic factor (BDNF) and tyrosine kinase TrkB (tropomyosin receptor kinase B) were investigated in d-galactose (d-gal)-treated rats. Subcutaneous injection of d-gal (500 mg/kg/d) for four months caused memory loss as detected by the Morris water maze, morphologic abnormalities of neurons in hippocampus region and the reduced expression of BDNF and TrkB were observed. ICA (60 mg/kg/d) given orally 1 h after subcutaneous injection of d-gal daily for 4 months markedly attenuated d-gal-induced rats behavioral dysfunction and neurodegeneration, as evidenced by shortened escape latency and searching distance and rescued morphologic abnormalities, and also elevated the mRNA levels and the protein expressions of BDNF and TrkB in hippocampus, as evidenced by quantitative real-time RT-PCR and Western blotting analysis. But ICA had no significant influence on normal rats which were not injected d-gal. These results clearly demonstrated that d-gal produced learning and memory deficits after chronic administration, and ICA can protect neuron from d-gal insults and improve the memory loss.     

Reinforcing behavioral variability: an analysis of dopamine-receptor subtypes and intermittent reinforcement

Variability is a functional and modifiable component of behavior that is necessary for learning or behavior change to occur. An appreciation of drug effects on reinforced variability could contribute to a fuller understanding of potential drug effects on behavior change. Dopamine agonists were examined under conditions that produced low and high levels of variability. In Experiment 1, d-amphetamine and dopamine-receptor-specific agonists (quinpirole and SKF 38393) were examined with rats that lever-pressed under a Multiple VARY 8:4 Fixed Ratio 4 (FR 4) schedule. In the VARY 8:4 condition, reinforcement followed every four-response sequence that differed from the previous eight sequences. Any four-response sequence was reinforced in the FR 4 component. Experiment 2 was an attempt to hold overall reinforcement rate constant by reinforcing criterion sequences under a Variable Interval 60″ schedule of reinforcement. In Experiment 1, d-amphetamine and quinpirole (D₂ agonist) increased variability in the FR 4 component while having no effect on variability in the VARY 8:4 component. SKF 38393 (D₁ agonist) had little effect on variability, even at doses that lowered total responding. In Experiment 2, intermittent reinforcement elevated variability in the FR 4 component and attenuated differential effects of d-amphetamine. Thus, d-amphetamine and quinpirole increased variability when it was low under the FR 4 component in Experiment 1. The high variability under the VARY 8:4 schedule was unaffected by d-amphetamine, except for modest effects at high doses. These observations suggest that dopamine and specifically D₂-type receptors are involved in the production of behavioral variability, and that the drug effects depend upon the baseline level of variability.     

Preparation and in vitro evaluation of thienorphine-loaded PLGA nanoparticles

Poly (d,l-lactic-co-glycolide) nanoparticles (PLGA-NPs) have attracted considerable interest as new delivery vehicles for small molecules, with the potential to overcome issue such as poor drug solubility and cell permeability. However, their negative surface charge decreases bioavailability under oral administration. Recently, cationically modified PLGA-NPs has been introduced as novel carriers for oral delivery. In this study, our aim was to introduce and evaluate the physiochemical characteristics and bioadhesion of positively charged chitosan-coated PLGA-NPs (CS-PLGA-NPs), using thienorphine as a model drug. These results indicated that both CS-PLGA-NPs and PLGA-NPs had a narrow size distribution, averaging less than 130?nm. CS-PLGA-NPs was positively charged (+42.1?±?0.4?mV), exhibiting the cationic nature of chitosan, whereas PLGA-NPs showed a negative surface charge (?2.01?±?0.3?mV). CS-PLGA-NPs exhibited stronger bioadhesive potency than PLGA-NPs. Furthermore, the transport of thienorphine-CS-PLGA-NPs by Caco-2 cells was higher than thienorphine-PLGA-NPs or thienorphine solution. CS-PLGA-NPs were also found to significantly enhance cellular uptake compared with PLGA-NPs on Caco-2 cells. An evaluation of cytotoxicity showed no increase in toxicity in either kind of nanoparticles during the formulation process. The study proves that CS-PLGA-NPs can be used as a vector in oral drug delivery systems for thienorphine due to its positive surface charge and bioadhesive properties.     

Chlorogenic acid protects d-galactose-induced liver and kidney injury via antioxidation and anti-inflammation effects in mice

Context Oxidative stress and inflammation are implicated in the aging process and its related hepatic and renal function decline. Chlorogenic acid (CGA) is one of the most abundant polyphenol compounds in the human diet. Recently, CGA has shown in vivo and in vitro antioxidant properties.

Objective The current study investigates the effects of protective effects of chlorogenic acid (CGA) on d-galactose-induced liver and kidney injury.

Materials and methods Hepatic and renal injuries were induced in a mouse model by subcutaneously injection of d-galactose (d-gal; 100?mg/kg) once a day for 8 consecutive weeks and orally administered simultaneously with CGA included in the food (200?mg/kg of diet). The liver and renal functions were examined. Histological analyses of liver and kidney were done by haematoxylin and eosin staining. The oxidative stress markers and pro-inflammatory cytokines in the liver and the kidney were measured.

Results CGA significantly reduced the serum aminotransferase, serum creatinine (SCr) and blood urea nitrogen (BUN) levels in d-gal mice (p?<0.05). CGA also restored superoxide dismutase, catalase, and malondialdehyde levels and decreased glutathione content in the liver and kidney in d-gal mice (p?<0.05). Improvements in liver and kidney were also noted in histopathological studies. CGA reduced tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) protein levels in the liver and kidney in d-gal mice (p?<0.05).

Discussion and conclusion These findings suggest that CGA attenuates d-gal-induced chronic liver and kidney injury and that this protection may be due to its antioxidative and anti-inflammatory activities.     

Structures of the glycine-rich diastereomeric peptides bombinin H2 and H4

Skin secretions of the European frog Bombina variegata contain a family of hydrophobic peptides, called bombinins H, which probably play a role in the defense against microbes. These peptides are rich in glycine (25%), which may allow structural polymorphism. Indeed, there is increasing evidence that bombinin H can, dependent on the environment, adopt different conformations. Moreover, some of these peptides contain a d-amino acid; the bombinins H2 and H4 differ from each other in that they contain either L-Ile or D-allo-Ile at position 2.In this paper we report the solution structure obtained by using NMR techniques of the mainly helical conformation, which these peptides adopt upon binding to the bilayer mimetics SDS and DPC. A glycine ridge is exposed at one side of the helix and may provide a helix-helix interaction site. In this respect, the structure of bombinin H resembles the influenza hemagglutinin fusion peptide and the helical conformer of Alzheimer peptide Aβ(25-40). Neither structure nor orientation of bombinin H are affected by the chiral inversion.Environmental conditions can trigger self-aggregation of bombinin H in solution due to hydrophobic interaction. Under these conditions the stereochemistry of the randomly ordered N-terminal segment modulates the preference to fold into a particular conformation.     

Interaction of substituted hexose analogues with the Trypanosoma brucei hexose transporter

Glucose metabolism is essential for survival of bloodstream form Trypanosoma brucei subspecies which cause human African trypanosomiasis (sleeping sickness). Hexose analogues may represent good compounds to inhibit glucose metabolism in these cells. Delivery of such compounds to the parasite is a major consideration in drug development. A series of D-glucose and D-fructose analogues were developed to explore the limits of the structure-activity relationship of the THT1 hexose transporter of bloodstream form African trypanosomes, a portal that might be exploited for drug uptake. D-glucose analogues with substituents at the C2 and C6 position continued to interact with the exofacial hexose binding site of the transporter. There was a limit to the size at C6 which still permitted recognition, although compounds carrying large groups at position C2 were still recognised. However, radiolabelled N-acetyl-D-[1-14C] glucosamine was not internalised by trypanosomes, in spite of the ability of this compound to inhibit glucose uptake, indicating that there is a limit to the size of C2 substituent that allows translocation. Addition of an alkylating group (bromoacetyl) at position C2 in the D-glucose series and at position 6 in the D-fructose set, created two analogues which interact with the transporter and kill trypanosomes in vitro. This indicates that inhibition of the transporter may be a good means of killing trypanosomes.     

High molecular weight persimmon tannin ameliorates cognition deficits and attenuates oxidative damage in senescent mice induced by d-galactose

Mice were subcutaneously injected with d-galactose (d-gal, 150mg/kg per day) for 6 weeks and were administered high molecular weight persimmon condensed tannin (HMWPT) simultaneously. After 6 weeks of treatment, the animal behavior was observed in the open field test and water maze test, and the morphology of hippocampus and skin were checked. Meanwhile, the activities of antioxidant enzymes, the levels of non-enzymatic antioxidants, as well as malondialdehyde (MDA) were evaluated. The results indicated that HMWPT markedly inhibited the d-gal induced learning and memory impairment in both open field test and Morris water maze. Biochemical examination revealed that HMWPT significantly increased the decreased activities of superoxide dismutase (SOD), catalase (CAT), elevated the lowered total anti-oxidation capability (T-AOC), glutathione (GSH) and hydroxyproline (Hyp) contents (p < 0.01 or p < 0.05), and decreased the raised monoamine oxidase (MAO), total cholinesterase (TChE) activities and MDA level (p < 0.01) in serum, liver or brain of aging mice induced by d-gal in a dose-dependent fashion. Furthermore, HMWPT significantly and (p < 0.01) attenuated the d-gal induced number decrease, neuronal degeneration and karyopycnosis in cells in the hippocampus and decrease of thickness of skin epidermis and dermis.     

Validation of fumonisin biomarkers in F344 rats

Fumonisins (FNs) are ubiquitous contaminants of cereal grains. Fumonisin B(1) (FB(1)) was linked to several animal and human diseases. To validate FB(1) biomarkers for studying human disease risks, F344 rats were administered by gavage with either a single dose of 0, 10 or 25 mg FB(1)/kg body weight (BW) or repeated doses of 0, 1.0, or 2.5 mg FB(1)/kg BW/day for 5 weeks. FB(1) excretion and FB(1)-induced metabolic alterations of sphingolipids in rat urine, feces and serum were assessed. Dose-dependent urinary and fecal excretion of free FB(1) were found in both single-dose- and repeat-dose-treated rats. In the single-dose study, urinary sphinganine (Sa) to sphingosine (So) ratio (Sa/So) reached a maximum at day 7 for the high-dose group and at day 5 for the low-dose group, whereas serum Sa/So showed only marginal changes. In the repeat-dose study, urinary Sa/So was persistently elevated at 2 weeks, while serum Sa/So was unchanged. Time course changes of sphinganine 1-phosphate (SaP) and sphingosine 1-phosphate (SoP) were also examined. Although serum Sa/So and SaP/SoP ratios showed no signs of time- or dose-dependent changes, a 10-fold increase in urinary SaP/SoP was observed, suggesting that urinary SaP/SoP is a more sensitive biomarker for FB(1) exposure. The accumulation of SaP and SoP was evident in the time course of SaP/Sa and SoP/So, which may reflect activity changes of enzymes closely related to the metabolism and catabolism of SaP and SoP. These results provide concrete evidence towards the practical use of excreted FB(1), Sa/So and SaP/SoP as biomarkers of exposure to FNs.     

A within-subject analysis of d-amphetamine exposure on delay discounting in rats

Studies concerning the relation between stimulant drug exposure and subsequent delay discounting (impulsive choice) have resulted in mixed findings that could be related to the type of stimulant drug exposure or the use of between-subject comparisons. The purpose of the present study was to examine effects of prior d-amphetamine exposure on subsequent delay discounting using a within-subject assessment. Two groups of rats were trained under a discrete-trials choice procedure until delay discounting was stable. One group of rats then received repeated administration of 3.0 mg/kg d-amphetamine in their home cage for 14 consecutive days, while the other group received saline. After a three-week drug-free period, delay discounting was reassessed. No significant differences in area under the curve within (before or after drug exposure) or between (saline or d-amphetamine) groups were found. Thus, delay discounting was not systematically affected following termination of repeated 3.0 mg/kg d-amphetamine exposure in the present experimental arrangement. The current results, coupled with past research, indicate that there may be a distinction between cocaine exposure and d-amphetamine exposure on subsequent delay discounting; however, within-subject comparisons of cocaine exposure on delay discounting are warranted.     

Measurement of Protein Diffusion Through Poly(d,l-Lactide-Co-Glycolide)

A novel method was developed for studying the diffusion of proteins through poly(d,l-lactide-co-glycolide) (PLG), using a diffusion cell. To develop improved formulations for the controlled release of encapsulated drugs it is important to understand the underlying release mechanisms. When using low-molecular-weight PLG as the release-controlling polymer, diffusion through the pores is often proposed as the main release mechanism. The experimental set-up and method of determining the diffusion coefficient were thoroughly evaluated with regard to the reliability and the influence of the stirring rate. A procedure for spraying thin films of PLG onto a filter, which could be placed in the diffusion cell, was optimized. The method was then applied to the determination of the diffusion coefficient of human growth hormone (hGH) through a PLG film. The results show that the method enables measurements of the diffusion coefficient through the polymer film. Neither the stirring rate nor the concentration of hGH influenced the diffusion coefficient. The diffusion coefficient of hGH through degraded PLG films was 5.0 · 10^{? 13} m²/s, which is in the range that could be expected, i.e., several orders of magnitude smaller than its the diffusivity in pure water. The reproducibility was good, considering the dynamic properties of PLG, i.e., the difference in diffusion coefficients, at, for example, different stages of degradation and for different compositions of PLG, is expected to be much higher. The variation is probably also present in PLG films used for controlled-release formulations. Although the PLG film contains a large amount of water, a considerable time elapsed before pores of sufficient size formed and diffusion through the film started. In two-component diffusion experiments, the difference in diffusion rate did not correspond to the difference in molecular weight of the solutes, indicating a size exclusion effect. This method can be used to study the effect of changes in the formulation specification. By studying the change in the diffusion coefficient through the degradation process of PLG, or similar polymers, a better understanding of diffusion and, thus, also release mechanisms can be obtained.     

The GABA-B antagonist 2-hydroxysaclofen reverses the effects of baclofen on the discriminative stimulus effects of d-amphetamine in the conditioned taste aversion procedure

Some of the behavioral effects of d-amphetamine (d-AMPH) are mediated by an increase in dopamine neurotransmission in the nucleus accumbens. However, there is evidence that gamma-amino-butyric-acid-B (GABA-B) receptors are involved in some behavioral effects of d-AMPH and cocaine. Here, we examined the effects of baclofen on the discriminative stimulus properties of d-AMPH, using conditioned taste aversion (CTA) as the drug discrimination procedure. Male Wistar rats were deprived of water and trained in the CTA procedure. They received d-AMPH (1 mg/kg, i.p.) before gaining access to saccharin, which was followed by an injection of LiCl. On alternate days, the subjects received saline before and after the access to saccharin. After the rats learned the d-AMPH-saline discrimination, the standard dose of d-AMPH was replaced by different doses of d-AMPH, baclofen (a GABA-B receptor agonist), 2-hydroxysaclofen (a GABA-B receptor antagonist), a combination of baclofen + d-AMPH, or a combination of 2-hydroxysaclofen + baclofen + d-AMPH. Baclofen did not substitute for d-AMPH, but, when combined with d-AMPH, it produced a small but significant decrease in the discriminative stimulus effects of d-AMPH. This effect was reversed by administration of 2-hydroxysaclofen. These data suggest that GABA-B receptors play a regulatory role in the discriminative stimulus effects of d-AMPH.     

Effects of altering motivation for food in rats trained with food reinforcement to discriminate between d-amphetamine and saline injections

Previous studies have shown that altering motivation typically affects stimulus generalization in animals trained to discriminate exteroceptive stimuli, but few studies have evaluated the effects of manipulating motivation on drug stimuli. In the few published studies, motivation levels were manipulated by arranging different feeding conditions prior to stimulus generalization tests with rats trained to discriminate morphine from vehicle and in pigeons trained to discriminate phencyclidine or pentobarbital from vehicle. In the present study, rats maintained at 80% of free-feeding weights were trained to discriminate between injections of 1.0 mg/kg d-amphetamine and saline in a two-lever food-reinforced operant procedure. Generalization tests were then conducted with a range of d-amphetamine doses (0, 0.03, 0.1, and 0.3, 1.0 mg/kg) when the rats were not fed before experimental sessions (high motivation) and when they were pre-fed 1 g of food (moderate motivation) or their daily ration of food (low motivation) 1 h before test sessions. Changing the motivation level significantly affected response rate and latency to the first response in generalizations tests, but did not significantly affect mean percentage of drug-appropriate responding (a continuous measure) or percentage of animals that selected the drug-appropriate lever (a quantal measure). The present findings indicate that manipulating motivation for food minimally impacts d-amphetamine discrimination, however, the range of conditions used to examine the effects of motivating operations on stimulus control by d-amphetamine drugs and other drugs is limited and the topic may warrant further investigation.     

Preparation and characterization of D,L-PLA loaded 17-β-Estradiol valerate by emulsion/evaporation methods

PLA microparticles containing 17-β-estradiol valerate were prepared by an emulsion/evaporation method in order to sustain drug release. This system was characterized concerning particle size, particle morphology and the influence of formulation and processing parameters on drug encapsulation and in vitro drug release. The biodegradation of the microparticles was observed by tissue histological analysis. Scanning electron microscopy and particle size analysis showed that the microparticles were spherical, presenting non-aggregated homogeneous surface and had diameters in the range of 718–880 nm (inert micro-particles) and 3–4 µm (drug loaded microparticles). The encapsulation efficiency was ～80%. Hormone released from microparticles was sustained. An in vivo degradation experiment confirmed that microparticles are biodegradable. The preparation method was shown to be suitable, since the morphological characteristics and efficiency yield were satisfactory. Thus, the method of developed microparticles seems to be a promising system for sustained release of 17-β-estradiol.     

Prolonged analgesic effect of PLGA-encapsulated bee venom on formalin-induced pain in rats

To enhance the medicinal activity of bee venom (BV) acupuncture, bee venom was loaded into biodegradable poly(d,l-lactide-co-glycolide) nanoparticles (BV-PLGA-NPs) by a water-in-oil-in-water-emulsion/solvent-evaporation technique. Rat formalin tests were performed after subcutaneous injection of BV-PLGA-NPs to the Zusanli acupuncture point (ST36) at 0.5, 1, 2, 6, 12, 24, and 48 h before plantar injection of 2% formalin. BV-PLGA-NPs treatment showed comparable analgesic activity to typical BV acupuncture during the late phase, compared with saline-treated controls, and the analgesic effect lasted for 12 h. PLGA-encapsulation was also effective in alleviating the edema induced by allergens in bee venom. These results indicate that PLGA-encapsulation provided a more prolonged effect of BV acupuncture treatment, while maintaining a comparable therapeutic effect.