PET examination of three potent cocaine derivatives as specific radioligands for the serotonin transporter.

Several positron emission tomography (PET) radioligands based on the aryl tropane structure have been used for studies on monoamine reuptake sites. RTI-364, RTI-330, and RTI-357 (3-beta-(4'-n-propyl-,4'-iso-propyl-, and 4'-iso-propenyl-phenyl)nortropane-2-beta-carboxylic acid methyl ester) are three recently synthesized cocaine analogues with higher affinity for the serotonin (5-HTT) than the dopamine transporter (DAT). Unlabelled RTI-364 and RTI-330 were prepared in a two-step synthesis. The key step was the addition of the appropriate propyl Grignard reagent to anhydroecgonine methyl ester. RTI-357 was prepared in a three-step synthesis with a palladium-catalyzed coupling reaction of beta-CIT and isopropenylzinc bromide as key step. Hydrolysis of the ester functions gave the carboxylic acid analogues of RTI-364, RTI-330, and RTI-357, which were labelled with 11C using [11C]methyl iodide in dimethyl formamide (DMF) and tetrabutylammonium hydroxide (TBAH) as base. All three compounds entered the monkey brain in a high degree (approximately 5-10%). There was a low uptake of [11C]RTI-364 in serotonin-rich brain areas, whereas [11C]RTI-330 and [11C]RTI-357 showed a marked uptake of radioactivity in the thalamus and the brainstem, regions known to contain serotonin transporters. Transient equilibrium was reached at 15 and 40 min for [11C]RTI-330 and [11C]RTI-357, respectively. After pretreatment with citalopram, the ratio of radioactivity in the thalamus and the brainstem to the cerebellum were markedly reduced for [11C]RTI-357 but not for [11C]RTI-330. The results indicate that [11C]RTI-357 is a potential PET radioligand for quantitation of the serotonin reuptake site.

Airborne manganese particulates and methylcyclopentadienyl manganese tricarbonyl (MMT) at selected outdoor sites in Montreal.

This study aims to assess the atmospheric concentrations of methylcyclopentadienyl manganese tricarbonyl (MMT), respirable manganese (MNR) and total manganese (MnT) in certain specific microenvironments and to provide an estimation of human exposure to MnR. Sampling was carried out in five microenvironments: a gas station, an underground car park, downtown Montreal, near an expressway and near an oil refinery. The samples were collected using Gil-Air portable pumps during three days and were analyzed by instrumental neutron activation analysis (INAA). The mean concentrations of MnR, MnT and MMT were 0.036 microgram m-3, 0.103 microgram m-3 and 0.005 microgram m-3 respectively. The MnR/MnT ratios vary from 25% to 43% (mean 35%) while the MMT/MnT ratios averaged about 5%. Furthermore, the mean concentration of the MnR measured near the expressway (0.053 microgram m-3) is similar to the United States Environmental Protection Agency (U.S. EPA) reference concentration (RfC = 0.05 microgram m-3). The average daily environmental exposure dose to MNR is estimated at 0.010 microgram kg-1 d-1 and its contribution to the multimedia exposure (air, food and water) is low. The overall results show a lack of potential exposure to MMT and substantial concentrations of MnR near an expressway.

A perspective on forage production in Canada.

Over the past decade, the cattle industry has experienced practically a full circle. With the promising beef prices in the early 1970s, with the glut of grain and a generous assist from government incentive programs, the forage acreage and cattle population have increased at a record rate. By 1974, the tide began to turn - grain prices went up sharply and beef prices became sluggish - and by 1976 a major crisis faced the producers. The cattle industry which had been developing on a cheap grain economy was now obliged to rely more on forage for its survival. Unfortunately, the forage was not existent and the only salvation of the industry was the gift of Providence - weather patterns that provided ample moisture conditions and above normal forage crops, the utilization of cereals and the intervention of government cow-calf support programs. Over the past year, the cycle was completed and record beef prices again prevail. The barley bins are full again and the cattlemen are gearing up for a few fat years. Demands for forage seed are brisk and the seeding down of forage acreage is bound to increase substantially over the next few years. And with this increase, cattle population expansion is bound to follow: how much expansion can the economy support? The production cost factors will determine the extent, but one can almost be certain that any expansion will either be modest or of short duration. At least, it should be. If the cattle industry is to establish solid foundations, it cannot be dependent upon the instability of a grain surplus-shortage position. With the present resources and the potential for developing it in direct competition with other crops, one can only expect a small and steady expansion over a long time span. One must agree with the range researchers and specialists of the Canada Research Stations at Lethbridge and Swift Current that pasture and range will continue to be the limiting factors of cattle expansion as they have been for the past 50 years. It is interesting to note that in the Prairie Provinces at least, the number of livestock raised each year has not changed since 1930 although cattle have largely replaced the horses. It is easy to speculate on paper that Canada can double in the next 20 years its forage and cattle production on its large expanses of land on the fringes of the agriculturally settled areas. It is true that these lands, while marginal for cash crops, could produce excellent forage. But at what cost? And what kind of pasture could we grow on them?It is easy to speculate that our livestock geneticists can breed a ruminant-type animal that will feed on poplar saplings and poplar leaves, or develop a new breed of cattle with buffalo vigor that will thrive in the extreme north. But looking at the musk-ox experience in the Northwest Territories and the history of the Wood Buffalo National Park leaves little room for optimism. The present generation is not likely to see in its lifetime the cattle population go beyond the 20 million mark. We can look, however, with good assurance on the present cattle numbers remaining stable and can look forward to gradual increase brought about by normal improvement in both forage and cattle management.Hopefully, both the cattle producer and the veterinarian will be able to reap the benefits of this most important segment of Canada's agricultural industry.