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  • 1
    ISSN: 1432-2072
    Keywords: Key words Opioid antagonists ; Oral self-administration ; Intravenous self-administration ; Alcohol ; Operant behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  These experiments evaluated the ability of naltrexone (NTX) to reduce selectively oral and IV ethanol-reinforced responding, and examined the ethanol-NTX interaction in terms of the competitive opioid antagonist property of NTX. Five rhesus monkeys self-administered ethanol or sucrose and concurrently available water. Ethanol concentration was varied from 0.25% to 8% (w/v). Naltrexone (0.032–0.32 mg/kg) or saline was given IM 30 min prior to some drinking sessions. NTX (0.32 mg/kg) reduced ethanol-reinforced responding at the concentration that maintained the most responding (1% or 2%). NTX (0.1 mg/kg) reduced ethanol-reinforced responding, both at a low ethanol concentration (0.25%) that produced little ethanol intake (g/kg), and at a higher concentration (4%) with an appreciable intake. Thus, NTX (0.1 mg/kg) shifted the ethanol concentration-consumption curve down, in an insurmountable manner. NTX (0.1 and 0.32 mg/kg) also reduced reinforced responding for sucrose 100 g/l. In another experiment, three rhesus monkeys were given opportunities to self-administer ethanol IV. NTX (0.1 mg/kg) reduced the number of ethanol injections obtained by the monkeys at all ethanol doses tested (0.01, 0.032, and 0.1 g/kg per injection).The dose-effect curve was also shifted down. These results showed that NTX reduced behavior maintained by either ethanol or sucrose non-selectively. Furthermore, the ability of NTX to suppress ethanol-reinforced responding did not depend on the route of ethanol administration and was not overcome by increasing the concentration or dose per injection of ethanol.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 105 (1996), S. 428-434 
    ISSN: 1432-1939
    Keywords: Sabal palmetto ; Cabbage palm ; Sea level rise ; Salt tolerance ; Tidal flooding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sabal palmetto (Walt.) Lodd. ex Schultes (cabbage palm) dominates the coastal limit of many forests in North Florida and Georgia, United States. Changes in saltwater flooding due to sea level rise have been credicted with pushing the coastal limit of cabbage palms inland, eliminating regeneration before causing death of mature trees. Localized freshwater discharge along the coast causes different forest stands to experience tidal flooding with waters that differ in salinity. To elucidate the effect of such variation on regeneration failure under tidal flooding, we examined relative effects of flooding and salinity on the performance of cabbage palm seedlings. We examined the relationship between seedling establishment and degree of tidal inundation in the field, compared the ability of seedlings to withstand tidal flooding at two coastal sites that differed in tidal water salinity, and investigated the physiological responses of cabbage palm seedlings to salinity and flooding in a factorial greenhouse experiment. Seedling survival was inversely correlated with depth and frequency of tidal flooding. Survival of seedlings at a coastal site flooded by waters low in salinity [c. 3 parts per thousand (ppt)] was greater than that at a site flooded by waters higher in salinity (up to 23 ppt). Greenhouse experiments revealed that leaves of seedlings in pots flushed twice daily with salt solutions of 0 ppt and 8 ppt exhibited little difference in midmorning net CO2 assimilation rates; those flushed with solutions of 15 ppt and 22 ppt, in contrast, had such low rates that they could not be detected. Net CO2 assimilation rates also declined with increasing salinity for seedlings in pots that were continuously inundated. Continuous root zone inundation appeared to ameliorate effects of salinity on photosynthesis, presumably due to increased salt concentrations and possibly water deficits in periodically flushed pots. Such problems associated with periodic flushing by salt water may play a role in the mortality of cabbage palm seedlings in the field. The salinity range in which plant performance plummeted in the greenhouse was consistent with the salinity difference found between our two coastal study sites, suggesting that variation in tidal water salinity along the coast plays an important role in the ability of cabbage palm seedlings to withstand tidal flooding.
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  • 3
    ISSN: 1432-1939
    Keywords: Key wordsSabal palmetto ; Cabbage palm ; Nonstructural carbohydrates ; Defoliation ; Seedling growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sabal palmetto (Walt.) Lodd. ex Schultes (cabbage palm) is an arborescent palm common in many plant communities throughout Florida, U.S.A., and the Caribbean. Although its seedlings grow very slowly in forest understories, they survive damage and defoliation well, and the species may increase in dominance following disturbances such as fire, logging, and hurricanes. We investigated the potential importance of total nonstructural carbohydrate (TNC) pools in the ability of cabbage palm seedlings to recover from the loss of aboveground tissue such as that caused by fire, grazing, or shallow burial by storm debris. TNC concentrations in belowground organs of seedlings from a forest understory were high, and TNC pools were sufficient to theoretically replace 〉50% of a seedling's canopy. The largest fraction of the belowground TNC pool was in stem tissue, where TNC in unclipped plants accounted for 26–54% of stem dry mass. Experimental reduction of TNC pools by repeated defoliation slowed seedling regrowth, and seedlings with inherently smaller pools (smaller seedlings) suffered higher mortality after repeated defoliation than did larger seedlings. Although regrowth and recovery after the loss of aboveground tissue was related to the size of the TNC pool in belowground organs, even the smallest seedlings with the smallest pools had sufficient stores to withstand at least two defoliations at frequent (7-week) intervals. Large belowground TNC pools in S. palmetto seedlings appear to enable them to survive all but the most frequent defoliations (e.g., frequent grazing or mowing). Allocation of resources to these stores, however, may contribute to the slow growth rates of S. palmetto seedlings in natural communities.
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