A 14-day repeat dose oral gavage range-finding study of a first-in-class CDI investigational antibiotic, in rats.

Drug resistant bacteria are winning the fight over antibiotics with some bacteria not responding to any antibiotics, threatening modern medicine as we know it. The development of new, effective and safe antibiotics is critical for addressing this issue. Ramizol, a first-in-class styrylbenzene based antibiotic, is an investigational drug indicated for Clostridium difficile infections (CDI). The objective of this range-finding study was to evaluate the potential general toxicity (based on toxicological endpoints selected) and toxicokinetics of Ramizol in male and female rats that may arise from repeated exposure via oral gavage over a test period of at least 14 days at doses of 50 mg/kg, 500 mg/kg and 1500 mg/kg. There were no mortalities in this study and no Ramizol-related clinical observations. Additionally, there were no changes in mean body weight, body weight gain, food consumption or food efficiency for male and female rats attributable to Ramizol administration. The observed pharmacokinetic behavior showed the presence of Ramizol in plasma at 24 hours post-dosing combined with increasing AUC(0-24) values during the course of this study in groups administered 1500 mg/kg/day, which suggests that at least some dosing groups will show accumulation of compound during repeated dose studies. These toxicology results have shown Ramizol is well-tolerated at very high concentrations in rats and support the further drug development of Ramizol as a first-in-class antibiotic for the treatment of CDI.

Absence of adverse effects following the gavage administration of methyl propyl trisulfide to Sprague-Dawley rats for 90 days.

Methyl propyl trisulfide is a flavoring substance found in foods such as garlic and onions. At the request of the European Food Safety Authority (EFSA) for additional toxicological data on methyl propyl trisulfide, groups of Sprague-Dawley rats (10/sex/group) were gavaged with 0 (corn oil vehicle control), 0.5, 2, or 6 mg methyl propyl trisulfide/kg bw/day in a 90-day GLP-compliant study. No effects on clinical observations, hematology and clinical chemistry parameters, organ weights, or macroscopic and histopathological examinations were found attributable to ingestion of methyl propyl trisulfide. The oral no-observed-adverse-effect level (NOAEL) for rats of both sexes was the highest dose tested of 6 mg/kg bw/day.

In vitro and in vivo safety evaluation of Nephure™.

Nephure™ is a proprietary oxalate decarboxylase (OxDC) enzyme being developed as a food ingredient. In this study, the safety of Nephure™ was evaluated in a bacterial mutagenicity assay and in a sub-chronic (13-week) oral toxicity study in rats. Nephure™ did not show any mutagenic properties in the mutagenicity assay. In the 13-week sub-chronic oral toxicity study in which 10 Sprague Dawley rats per sex were administered 0, 118, 235 and 475 mg/kg bw/day (8260, 16450 and 33,250 Units/kg bw/day, respectively) of Nephure™ by gavage, male and female rats did not show any test article-related clinical observations or effects on body weight, body weight gain, food consumption, food efficiency, ophthalmology, functional observational battery parameters or motor activity. Furthermore, there were no changes in coagulation, clinical chemistry, urinalysis or hematology parameters, macroscopic/microscopic findings or organ weights that could be attributed to the test article. Based on these results, Nephure™ was not mutagenic and the no-adverse-effect level (NOAEL) in the 13-week study was determined to be 475 mg/kg bw/day (33,250 Units/kg bw/day). Evaluation of the estimated consumption of Nephure™, generation of the metabolite formate, and the current safety studies resulted in a conclusion of a tolerable upper limit of 3450 Units of OxDC activity/day (57.5 Units activity/kg bw/day), when Nephure™ is added to food to decrease dietary oxalate.

Robustness of arterial blood gas analysis for assessment of respiratory safety pharmacology in rats.

Whole body plethysmography using unrestrained animals is a common technique for assessing the respiratory risk of new drugs in safety pharmacology studies in rats. However, wide variations in experimental technique make cross laboratory comparison of data difficult and raise concerns that non-appropriate conditions may mask the deleterious effects of test compounds - in particular with suspected respiratory depressants. Therefore, the objective of this study was to evaluate the robustness of arterial blood gas analysis as an alternative to plethysmography in rats. We sought to do this by assessing the effect of different vehicles and times post-surgical catheterization on blood gas measurements, in addition to determining sensitivity to multiple opioids. Furthermore, we determined intra-lab variability from multiple datasets utilizing morphine and generated within a single lab and lastly, inter-lab variability was measured by comparing datasets generated in two separate labs. Overall, our data show that arterial blood gas analysis is a measure that is both flexible in terms of experimental conditions and highly sensitive to respiratory depressants, two key limitations when using plethysmography. As such, our data strongly advocate the adoption of arterial blood gas analysis as an investigative approach to reliably examine the respiratory depressant effects of opioids.

Combining sitagliptin/metformin with a functional fiber delays diabetes progression in Zucker rats.

Our primary objective was to determine whether administering the viscous and fermentable polysaccharide PolyGlycopleX (PGX) with metformin (MET) or sitagliptin/metformin (S/MET) reduces hyperglycemia in Zucker diabetic fatty (ZDF) rats more so than monotherapy of each. Glucose tolerance, adiposity, satiety hormones and mechanisms related to dipeptidyl peptidase 4 activity, gut microbiota and, hepatic and pancreatic histology were examined. Male ZDF rats (9-10 weeks of age) were randomized to: i) cellulose/vehicle (control, C); ii) PGX (5% wt/wt)/vehicle (PGX); iii) cellulose/metformin (200  mg/kg) (MET); iv) cellulose/S/MET (10  mg/kg+200  mg/kg) (S/MET); v) PGX (5%)+MET (200  mg/kg) (PGX+MET); vi) cellulose/sitagliptin/MET (5%)+(10  mg/kg+200  mg/kg) (PGX+S/MET) for 6 weeks. PGX+MET and PGX+S/MET reduced glycemia compared with C and singular treatments (P=0.001). Weekly fasted and fed blood glucose levels were lower in PGX+MET and PGX+S/MET compared with all other groups at weeks 4, 5, and 6 (P=0.001). HbA1c was lower in PGX+S/MET than C, MET, S/MET, and PGX at week 6 (P=0.001). Fat mass was lower and GLP1 was higher in PGX+S/MET compared with all other groups (P=0.001). ß-cell mass was highest and islet degeneration lowest in PGX+S/MET. Hepatic lipidosis was significantly lower in PGX+S/MET compared with PGX or S/MET alone. When combined with PGX, both MET and S/MET markedly reduce glycemia; however, PGX+S/MET appears advantageous over PGX+MET in terms of increased ß-cell mass and reduced adiposity. Both combination treatments attenuated diabetes in the obese Zucker rat.

A primer for best practices in tissue preparation for bioanalysis.

Analysis of drugs, biomarkers and their metabolites in tissue samples has always been an important aspect of the drug-development process. In the last decade, significant improvements in equipment and processes have made handling such samples far more efficient, with higher precision, accuracy and ruggedness. The purpose of this paper is to provide a primer for best practices of tissue analysis, including brief but specific tutorials on basic principles and laboratory operation. Included will be a discussion of what to consider when designing a study, tools available to make appropriate pre-study decisions, approaches for tissue acquisition and extraction, sample processing methods, and tips on creation of standards and QCs. We will offer some practical advice to help scientists who have good analytical skills, but are not experienced in tissue analysis to quickly start their own analyses with the minimum amount of time, labor and cost.

Sitagliptin reduces hyperglycemia and increases satiety hormone secretion more effectively when used with a novel polysaccharide in obese Zucker rats.

The novel polysaccharide (NPS) PolyGlycopleX (PGX) has been shown to reduce glycemia. Pharmacological treatment with sitagliptin, a dipeptidyl peptidase 4 (DPP4) inhibitor, also reduces glycemia by increasing glucagon-like peptide-1 (GLP-1). Our objective was to determine if using NPS in combination with sitagliptin reduces hyperglycemia in Zucker diabetic fatty (ZDF) rats more so than either treatment alone. Male ZDF rats were randomized to: 1) cellulose/vehicle [control (C)]; 2) NPS (5% wt:wt)/vehicle (NPS); 3) cellulose/sitagliptin [10 mg/(kg · d) (S)]; or 4) NPS (5%) + S [10 mg/(kg · d) (NPS+S)]. Glucose tolerance, adiposity, satiety hormones, and mechanisms related to DPP4 activity and hepatic and pancreatic histology were examined. A clinically relevant reduction in hyperglycemia occurred in the rats treated with NPS+S (P = 0.001) compared with NPS and S alone. Blood glucose, measured weekly in fed and feed-deprived rats and during an oral glucose tolerance test, was lower in the NPS+S group compared with all other groups (all P = 0.001). At wk 6, glycated hemoglobin was lower in the NPS+S group than in the C and S (P = 0.001) and NPS (P = 0.06) groups. PGX (P = 0.001) and S (P = 0.014) contributed to increased lean mass. Active GLP-1 was increased by S (P = 0.001) and GIP was increased by NPS (P = 0.001). Plasma DPP4 activity was lower in the NPS+S and S groups than in the NPS and C groups (P = 0.007). Insulin secretion and ß-cell mass was increased with NPS (P < 0.05). NPS alone reduced LDL cholesterol and hepatic steatosis (P < 0.01). Independently, NPS and S improve several metabolic outcomes in ZDF rats, but combined, their ability to markedly reduce glycemia suggests they may be a promising dietary/pharmacological co-therapy for type 2 diabetes management.

Effects of the Soluble Fiber Complex PolyGlycopleX on Glucose Homeostasis and Body Weight in Young Zucker Diabetic Rats.

Dietary fiber can reduce insulin resistance, body weight, and hyperlipidemia depending on fiber type, water solubility, and viscosity. PolyGlycopleX(®) (PGX(®)) is a natural, novel water soluble, non-starch polysaccharide complex that with water forms a highly viscous gel compared to other naturally occurring dietary fiber. We determined the effect of dietary PGX(®) vs. cellulose and inulin on the early development of insulin resistance, body weight, hyperlipidemia, and glycemia-induced tissue damage in young Zucker diabetic rats (ZDFs) in fasted and non-fasted states. ZDFs (5 weeks old) were fed a diet containing 5% (wgt/wgt) cellulose, inulin, or PGX(®) for 8 weeks. Body weight, lipids, insulin, and glucose levels were determined throughout the study and homeostasis model assessment (HOMA) was used to measure insulin sensitivity throughout the study in fasted animals. At study termination, insulin sensitivity (oral glucose tolerance test, OGTT) and kidney, liver, and pancreatic histopathology were determined. Body weight and food intake were significantly reduced by PGX(®) vs. inulin and cellulose. Serum insulin in fasted and non-fasted states was significantly reduced by PGX(®) as was non-fasted blood glucose. Insulin resistance, measured as a HOMA score, was significantly reduced by PGX(®) in weeks 5 through 8 as well as terminal OGTT scores in fed and fasted states. Serum total cholesterol was also significantly reduced by PGX(®). PGX(®) significantly reduced histological kidney and hepatic damage in addition to reduced hepatic steatosis and cholestasis. A greater mass of pancreatic ß-cells was found in the PGX(®) group. PGX(®) therefore may be a useful dietary additive in the control of the development of the early development of the metabolic syndrome.

The soluble fiber complex PolyGlycopleX lowers serum triglycerides and reduces hepatic steatosis in high-sucrose-fed rats.

Viscous soluble fibers have been shown to reduce risk factors associated with type 2 diabetes and cardiovascular disease. The novel functional fiber, PolyGlycopleX (PGX) (InovoBiologic Inc, Calgary, Alberta, Canada) displays greater viscosity than other currently identified soluble fibers. The objective of this study was to determine if PGX lowers serum and hepatic triglycerides (TGs) in a high-sucrose-fed rat model. In this rodent model, feeding a high-sucrose diet consistently increases serum TGs. We hypothesized that consumption of PGX would attenuate hypertriglyceridemia and reduce hepatic steatosis compared with cellulose in rats fed a high-sucrose background diet. Male Sprague-Dawley rats were fed diets containing 65% sucrose and supplemented with either 5% cellulose (control) or 5% PGX (wt/wt) for 43 weeks. At study termination, serum insulin and TGs, hepatic steatosis, and hepatocellular injury were assessed. Body weight increased over time in both groups, but weight gain was attenuated in rats fed PGX vs cellulose in weeks 2 through 22 (P < .05). Serum TGs did not differ from baseline for the first half of the study but consistently increased in the cellulose group thereafter. PolyGlycopleX significantly reduced serum TG to near-baseline levels. At study termination, rats fed PGX had significantly lower hepatic steatosis scores (measured by Sudan black staining) compared with rats fed cellulose. Hepatocellular injury scores did not differ between the groups. In conclusion, PGX reduced serum TG and lipid accumulation in the liver of sucrose-fed rats. Further examination of its potential as a fiber supplement aimed at lessening the burden of hepatic steatosis is warranted.

Effects of the soluble fiber complex PolyGlycopleX® (PGX®) on glycemic control, insulin secretion, and GLP-1 levels in Zucker diabetic rats.

AIMS: The effects of the novel water soluble, viscous fiber complex PolyGlycopleX® [(α-D-glucurono-α-D-manno-ß-D-manno-ß-D-gluco), (α-L-gulurono-ß-D mannurono), ß-D-gluco-ß-D-mannan (PGX®)] on body weight, food consumption, glucose, insulin, and glucagon-like peptide (GLP-1) levels were determined in Zucker diabetic rats (ZDFs). Such fibers are thought to improve glycemic control through increased GLP-1 induced insulin secretion. MAIN METHODS: ZDFs were treated 12 weeks with normal rodent chow supplemented with cellulose (control, inert fiber), inulin or PGX® at 5% wt/wt and effects on body weight, glycemic control, and GLP-1 determined. KEY FINDINGS: In the fed state, PGX® reduced blood glucose compared to the other groups from week 5 until study termination while insulin was significantly elevated when measured at week 9, suggesting an insulin secretagogue effect. Fasting blood glucose was similar among groups until 7-8 weeks when levels began to climb with a modest reduction caused by PGX®. An oral glucose tolerance test in fasted animals (week 11) showed no change in insulin sensitivity scores among diets, suggesting an insulinotropic effect for PGX® rather than increased insulin sensitivity. PGX® increased plasma levels of GLP-1, while HbA(1c) was markedly reduced by PGX®. Body weights were not changed despite a significant reduction in food consumption induced by PGX® up to week 8 when the PGX®-treated group showed an increase in body weight despite a continued reduction in food consumption. SIGNIFICANCE: PGX® improved glycemic control and reduced protein glycation, most likely due to the insulin secretagogue effects of increased GLP-1.

Plant-derived polysaccharide supplements inhibit dextran sulfate sodium-induced colitis in the rat.

Several plant-derived polysaccharides have been shown to have anti-inflammatory activity in animal models. Ambrotose complex and Advanced Ambrotose are dietary supplements that include aloe vera gel, arabinogalactan, fucoidan, and rice starch, all of which have shown such activity. This study was designed to evaluate these formulations against dextran sulfate sodium (DSS)-induced colitis in rats and to confirm their short-term safety after 14 days of daily dosing. Rats were dosed daily orally with vehicle, Ambrotose or Advanced Ambrotose. On day six groups of rats received tap water or 5% Dextran Sulfate sodium. Ambrotose and Advanced Ambrotose significantly lowered the disease scores and partially prevented the shortening of colon length. An increase in monocyte count was induced by dextran sulfate sodium and inhibited by Ambrotose and Advanced Ambrotose. There were no observable adverse effects after 14-day daily doses. The mechanism of action of the formulations against DSS-induced colitis may be related to its effect on monocyte count.

Rapid and sensitive determination of acetylsalicylic acid and salicylic acid in plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study.

A simple and sensitive analytical method using liquid chromatography-tandem mass spectrometry (LC/MS/MS) for determination of acetylsalicylic acid (aspirin, ASA) and its major metabolite, salicylic acid (SA), in animal plasma has been developed and validated. Both ASA and SA in plasma samples containing potassium fluoride were extracted using acetonitrile (protein precipitation) with 0.1% formic acid in it. 6-Methoxysalicylic acid was used as the internal standard (IS). The compounds were separated on a reversed-phase column. The multiple reaction monitoring mode was used with ion transitions of m/z 178.9 --> 136.8, 137.0 --> 93.0 and 167.0 --> 123.0 for ASA, SA and IS, respectively. The lower limits of quantification for ASA and SA were 3 and 30 ng/mL, respectively. The developed method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after p.o. and i.v. administration of 1 mg/kg to rats.

Energetic signalling in the control of mitochondrial F1F0 ATP synthase activity in health and disease.

The mitochondrial F1F0 ATP synthase is a critical enzyme that works by coupling the proton motive force generated by the electron transport chain via proton transfer through the F0 or proton-pore forming domain of this enzyme to release ATP from the catalytic F1 domain. This enzyme is regulated by calcium, ADP, and inorganic phosphate as well as increased transcription through several pathways. This enzyme is also an ATP hydrolase under ischemic conditions. This "inefficient" hydrolysis of ATP consumes 90% of ATP consumed during ischemia as shown with non-selective ATPase inhibitors oligomycin and Aurovertin B. A benzopyran analog, BMS-199264, selectively inhibits F1F0 ATP hydrolase activity with no effect on ATP synthase activity. BMS-199264 had no effect on ATP before ischemia, but reduced the decline in ATP during ischemia. Selective hydrolase inhibition seen with the small molecule BMS-199264 suggests a conformational change in the F1F0 ATPase enzyme when switching from synthase to hydrolase activity.

Pharmacological and pharmacokinetic characterization of the cannabinoid receptor 2 agonist, GW405833, utilizing rodent models of acute and chronic pain, anxiety, ataxia and catalepsy.

To date, two cannabinoid receptors have been identified, CB1 and CB2. Activation of these receptors with non-selective cannabinoid receptor agonists reduces pain sensitivity in animals and humans. However, activation of CB1 receptors is also associated with central side effects, including ataxia and catalepsy. More recently, a role for selective CB2 agonists in pain modification has been demonstrated. GW405833, a selective CB2 agonist, was recently reported to partially reverse the inflammation and hyperalgesia in a rat model of acute inflammation. In the current report, we extend the characterization and therapeutic potential of this compound. For the first time, we show that GW405833 selectively binds both rat and human CB2 receptors with high affinity, where it acts as a partial agonist (approximately 50% reduction of forskolin-mediated cAMP production compared to the full cannabinoid agonist, CP55,940). We also report for the first time that intraperitoneal administration of GW405833 (0.3-100 mg/kg) to rats shows linear, dose-dependent increases in plasma levels and substantial penetration into the central nervous system. In addition, GW405833 (up to 30 mg/kg) elicits potent and efficacious antihyperalgesic effects in rodent models of neuropathic, incisional and chronic inflammatory pain, the first description of this compound in these models. In contrast, analgesia, sedation and catalepsy were not observed in this dose range, but were apparent at 100 mg/kg. Additionally, GW405833 was not antihyperalgesic against chronic inflammatory pain in CB2 knockout mice. These data support the tenet that selective CB2 receptor agonists have the potential to treat pain without eliciting the centrally-mediated side effects associated with non-selective cannabinoid agonists, and highlight the utility of GW405833 for the investigation of CB2 physiology.

Intrathecal protease-activated receptor stimulation produces thermal hyperalgesia through spinal cyclooxygenase activity.

Activation of protease-activated receptors (PARs) in non-neural tissue results in prostaglandin production. Because PARs are found in the spinal cord and increased prostaglandin release in the spinal cord causes thermal hyperalgesia, we hypothesized that activation of these spinal PARs would stimulate prostaglandin production and cause a cyclooxygenase-dependent thermal hyperalgesia. PARs were activated using either thrombin or peptide agonists derived from the four PAR subtypes, delivered to the lumbar spinal cord. Dialysis experiments were conducted in conscious, unrestrained rats using loop microdialysis probes placed in the lumbar intrathecal space. Intrathecal thrombin stimulated release of prostaglandin E (PGE)(2) but not aspartate or glutamate. Intrathecal delivery of the PAR 1-derived peptide SFLLRN-NH(2) and the PAR 2-derived peptide SLIGRL both stimulated PGE(2) release; PAR 3-derived TFRGAP and PAR 4-derived GYPGQV were inactive. Intrathecal thrombin had no effect upon formalin-induced flinching or tactile sensitivity but resulted in a thermal hyperalgesia. Intrathecal SFLLRN-NH(2) and SLIGRL both produced thermal hyperalgesia. Consistent with their effects on spinal PGE(2), hyperalgesia from these peptides was blocked by pretreatment with the cyclooxygenase inhibitor ibuprofen. SLIGRL-induced hyperalgesia was also blocked by the selective inhibitors SC 58,560 [5-(4-fluorophenyl)-1-[4-(methylsulfonyl)phenyl]-3-(trifluoromethyl)-1H-pyrazole; cyclooxygenase (COX) 1] and SC 58,125 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole; COX 2]. These data indicate that activation of spinal PAR 2 and possibly PAR 1 results in the stimulation of the spinal cyclooxygenase cascade and a prostaglandin-dependent thermal hyperalgesia.

Nonopioid actions of intrathecal dynorphin evoke spinal excitatory amino acid and prostaglandin E2 release mediated by cyclooxygenase-1 and -2.

Spinal dynorphin is hypothesized to contribute to the hyperalgesia that follows tissue and nerve injury or sustained morphine exposure. We considered that these dynorphin actions are mediated by a cascade involving the spinal release of excitatory amino acids and prostaglandins. Unanesthetized rats with lumbar intrathecal injection and loop dialysis probes received intrathecal NMDA, dynorphin A(1-17), or dynorphin A(2-17). These agents elicited an acute release of glutamate, aspartate, and taurine but not serine. The dynorphin peptides and NMDA also elicited a long-lasting spinal release of prostaglandin E2. Prostaglandin release evoked by dynorphin A(2-17) or NMDA was blocked by the NMDA antagonist amino-5-phosphonovalerate as well the cyclooxygenase (COX) inhibitor ibuprofen. To identify the COX isozyme contributing to this release, SC 58236, a COX-2 inhibitor, was given and found to reduce prostaglandin E2 release evoked by either agent. Unexpectedly, the COX-1 inhibitor SC 58560 also reduced dynorphin A(2-17)-induced, but not NMDA-induced, release of prostaglandin E2. These findings reveal a novel mechanism by which elevated levels of spinal dynorphin seen in pathological conditions may produce hyperalgesia through the release of excitatory amino acids and in part by the activation of a constitutive spinal COX-1 and -2 cascade.

Characterization of butyrylcholinesterase antagonism of cocaine-induced hyperactivity.

Although there are several published demonstrations that exogenous butyrylcholinesterase (EC 3.1.1.8) works to antagonize cocaine in vivo, a systematic characterization of the enzyme-drug interaction is lacking as is confirmation of the mechanism of effect. This has been addressed using cocaine-induced locomotor activity in mice as a behavioral endpoint. The enzyme was effective, but the enzyme dose-antagonist effect relationship revealed an asymptotic partial maximum effect. This effect was not due to dose-dependent enzyme pharmacokinetics or to a stimulant effect of the cocaine metabolites but rather to partial metabolism of cocaine. Since neither metabolite of cocaine inhibited enzyme activity as potently as cocaine, partial metabolism is not likely due to end-product inhibition. The enzyme reduced the maximum effect of cocaine on locomotor activity. The mechanistic data are generally consistent: the enzyme was inactive against the nonester dopamine/norepinephrine uptake inhibitor, nomifensine, and a paraoxon-inactivated sample of enzyme was ineffective. However, the enzyme was effective against bupropion, a nonester dopamine uptake inhibitor.

Characterization of equine butyrylcholinesterase disposition in the mouse.

Butyrylcholinesterase administration has been shown to block the effects of cocaine. However, even in model systems, the pharmacokinetics of the enzyme are only partly understood. Measurements of plasma enzyme concentration, antibody titer determinations, and measurement of cocaine-induced locomotor activity in mice were used to describe the disposition of butyrylcholinesterase. Clearance of the enzyme showed biexponential kinetics; the first component was sensitive to asialofetuin, suggesting a role for the asialoglycoprotein receptor. Cocaine did not influence enzyme disposition. An antibody response to enzyme injection was seen; the role of this response is not clear. The antagonist effect of the enzyme was eliminated faster than the enzyme was eliminated from plasma; this may be due to a contribution of tissue esterases to cocaine metabolism. Intraperitoneal enzyme administration was not effective against cocaine, suggesting that the utility of the enzyme is route-dependent.

Tetrabenazine fails to antagonize a behavioral effect of cocaine in rhesus monkeys.

For research and therapeutic purposes, a cocaine antagonist is an important drug development goal. The vesicular monoamine transport inhibitor tetrabenazine was tested for interaction with cocaine using food-reinforced responding in rhesus monkeys as an assay. Both tetrabenazine and cocaine suppressed food-maintained behavior individually. However, a low-dose tetrabenazine pretreatment did not alter the rate-suppressing effects of cocaine and cocaine did not alter the rate-suppressing effects of a high dose tetrabenazine pretreatment. Because tetrabenazine interacts with the monoamine oxidase inhibitor deprenyl in this assay, we conclude that cocaine does not produce an effect through vesicular catecholamines in this assay.