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  • 1
    Electronic Resource
    Electronic Resource
    Development of groundwater modeling for the Azraq Basin, Jordan (2000)
    Springer
    Environmental geology 40 (2000), S. 11-18 
    Details
    ISSN: 1432-0495
    Keywords: Keywords Calibration and prediction ; Groundwater modeling ; Aquifer systems ; Jordan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The three-dimensional groundwater flow model MODFLOW was applied to simulate water level change in the complex multi-aquifer systems (the Upper and Middle Aquifers) of the Azraq basin. The model was calibrated by matching observed and simulated drawdown for steady and transient states over the period 1970–1992. Drawdown data for the period 1993–1997 were used to test the model's ability to predict the response of the aquifers. The model performed well in representing the water level contours of the Upper and Middle Aquifers for steady state calibration. Agreement between the observed and simulated drawdowns was obtained for transient state calibration. To predict the aquifer system responses for the period of 1997–2025, four different pumping schemes (scenarios) have been investigated. The first scenario (present pumping rate) reveals that there will be approximately a 25 m drop in the water level at the well-field area in 2025. However, the worst scenario (pumping rate at 1.5 times the present rate) reveals an approximate 39 m drop in the water level at the well-field area in 2025. The safe yield for the Upper Aquifer System was found to be about 25 million cubic meters (MCM) yearly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002549900105
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of substance P on excitability and ionic currents of normal and axotomized rat dorsal root ganglion neurons (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 13 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Substance P (SP) may act within dorsal root ganglia (DRG) to modulate the transmission of nociceptive information. Because peripheral nerve injury (axotomy) alters the peptide content of sensory neurons, we used whole-cell recording to examine the effects of sciatic nerve section on the sensitivity of rat lumbar DRG neurons to SP (0.3–1 µm). At 1 µm, SP increased the excitability of ‘small’, putative nociceptive neurons but had little effect on the excitability of ‘large’ neurons. Two-four weeks after sciatic nerve section, however, the effect of SP on ‘large’ axotomized neurons was increased and its effect on ‘small’ neurons was decreased. SP did not affect Ca2+ channel currents in control or axotomized neurons. The effects of SP on the current-voltage (I–V) relationship of 77% of neurons involved increased inward current at potentials below −30 mV and suppressed outward current at potentials above −20 mV. The effects of SP on the I–V relationship were similar in control and in axotomized neurons and the altered sensitivity of ‘small’ and ‘large’ cells could not be attributed to axotomy-induced changes in input resistance or membrane potential. The possible relevance of alterations in sensitivity, of ‘large’ DRG neurons to SP, to the generation of neuropathic pain is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0953-816x.2000.01429.x
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  • 3
    Electronic Resource
    Electronic Resource
    An iontophoretic study of the effects of α-amino-hydroxy-5-methyl-4-isoxazole propionic acid lesions of the nucleus basalis magnocellularis on cholinergic and GABAergic influences on frontal cortex neurones of rats (1994)
    Springer
    Experimental brain research 98 (1994), S. 441-456 
    Details
    ISSN: 1432-1106
    Keywords: α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid lesion ; Cholinergic ; GABAergic ; Nucleus basalis ; Iontophoresis ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Unilateral lesions of the nucleus basalis magnocellularis (NBM) produced by α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid in rats caused, 8–10 weeks after the lesion, a 94% reduction in cortical acetylcholinesterase fibres and reduced activities of acetylcholinesterase and choline acetyltransferase by 70–80% in the frontal cortex ipsilateral to the lesion. In anaesthetized unlesioned control rats, iontophoretic administration of acetylcholine and carbachol produced atropine-sensitive inhibition and excitation of frontal cortical neurones, effects similar to those produced by electrically stimulating the NBM. The lesion reduced cortical neuronal firing rates but increased the percentage and sensitivity of neurones responding to acetylcholine, the predominant response changing from inhibition to excitation; response duration increased but latency was unaffected. The size of the response of individual neurones to carbachol, but not the percentage of sensitive neurones, was also increased in lesioned animals. The proportion of neurones responding to bicuculline and their individual sensitivities were increased by the lesion, suggesting that the lesion increased GABAergic tone; responses to glutamate were unchanged. The lesion did not affect the proportion of neurones in which acetylcholine modulated neuronal responses but reversed the nature of the modulation to predominantly excitatory; excitation was the predominant response to electrical forepaw stimulation in unlesioned control animals. This suggests a possible interaction between GABAergic and cholinergic mechanisms in selective attention and processing of cognitive information. Acute administration of di-isopropyl fluorophosphate to unlesioned animals significantly increased the number of frontal cortical neurones responding to acetylcholine, without affecting individual neuronal sensitivity or responses to carbachol and glutamate. The similarity of these effects to those of acetylcholine in lesioned animals suggests that the increased sensitivity to acetylcholine in the latter was due to loss of acetylcholinesterase, enabling diffusion of acetylcholine to more distant neurones. However, acetylcholinesterase does not hydrolyse carbachol and therefore it is necessary to postulate a different post-synaptic mechanism to explain the lesion-induced increases in the sensitivities of individual neurones to carbachol and to acetylcholine; interpretation of experimental findings should take these two mechanisms into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233982
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between up-regulation of nicotine binding sites in rat brain and delayed cognitive enhancement observed after chronic or acute nicotinic receptor stimulation (1996)
    Springer
    Psychopharmacology 124 (1996), S. 323-331 
    Details
    ISSN: 1432-2072
    Keywords: Nicotine ; Water maze ; Nicotinic receptor up-regulation ; Cognitive enhancement ; Delayed acute effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract (−)-Nicotine tartrate (2 mg/kg), and a nicotinic agonist, RJR 2403 (1.4 mg/kg), and antagonist, mecamylamine (1 mg/kg), were administered to separate groups of rats SC twice daily for 10 days. Two other groups received the same doses of nicotine or RJR 2403 for 1 day followed by saline for 9 days. Twenty-four hours after the final injection, the rats were compared to a 10-day saline-injected group on acquisition of a hidden platform position in the Morris water maze (20 trials, 30-min inter-trial interval). The rats were killed 48 h after the last drug injection and frontal, entorhinal and posterior cingulate cortex and dorsal and ventral hippocampus assayed for [3H]-nicotine binding density. Chronic nicotine significantly increased the number of frontal and entorhinal cortical and dorsal hippocampal, but not posterior cingulate cortical or ventral hippocampal, nicotinic receptors, and improved rate of learning. Chronic mecamylamine and RJR 2403 also significantly increased the number of nicotinic receptors in frontal cortex, though not other regions, but retarded rate of learning. Nicotine given for 1 day 11 days earlier marginally increased nicotinic receptors in entorhinal cortex (but not other regions) and significantly increased rate of learning, though significantly less than 10-day nicotine. Entorhinal cortical and dorsal hippocampal nicotinic receptor numbers were positively associated with rate of learning but not performance at asymptote. Thus cognitive enhancement after chronic nicotine is in part a delayed consequence of nicotine administration 11 days earlier, and may reflect regional changes in nicotinic receptor up-regulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02247437
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  • 5
    Electronic Resource
    Electronic Resource
    Chronic treatments with cholinoceptor drugs influence spatial learning in rats (1993)
    Springer
    Psychopharmacology 111 (1993), S. 508-511 
    Details
    ISSN: 1432-2072
    Keywords: Spatial learning ; Rat ; Muscarinic ; Nicotinic ; Receptors ; Chronic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Nicotine, scopolamine, oxotremorine, diisopropyl-fluorophosphate (DFP) and tetrahydroaminoacridine (THA) were administered chronically to different groups of rats in doses reported to alter central muscarinic and/or nicotinic receptro numbers. Beginning 24 h after final drug injection, the groups were compared to a vehicle control group on acquisition of a hidden platform position in the Morris water maze over 20 trials with a 30-min inter-trial interval. Chronic treatment with either nicotine or scopolamine significantly improved the rate of learning, but oxotremorine and DFP retarded learning and THA had no effect on learning. The chronic drug effects on behaviour were consistent with known effects of the injected drugs on muscarinic and nicotinic binding in the forebrain and on the sensitivity of frontal cortex neurones to iontophoretically applied cholinoceptor agonists. However, alternative explanations for the observed changes cannot be ruled out, since the drugs used are known to have a wide range of effects on other neurotransmitters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02253544
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