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  • 1
    Electronic Resource
    Electronic Resource
    Sensory and associative effects of morphine and naloxone in classical conditioning of the rabbit nictitating membrane response (1984)
    Springer
    Psychopharmacology 83 (1984), S. 114-121 
    Details
    ISSN: 1432-2072
    Keywords: Morphine ; Naloxone ; Classical conditioning ; Acquisition ; Rabbit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In Experiment I, classical conditioning of the rabbit's nictitating membrane response was accomplished by the pairing of tone and light conditioned stimuli with a shock unconditioned stimulus applied to the paraorbital region of the head. Morphine (5 mg/kg) significantly retarded the acquisition of conditioned responses to both conditioned stimuli. Moreover, morphine had no effect on nonassociative responding (baseline responding or responding to tone and light stimuli) or on the latency and amplitude of the unconditioned response elicited by shock during the explicitly unpaired presentations of tone, light and shock stimuli. The retardant effect of morphine on acquisition of conditioned responses was blocked by naloxone (1 mg/kg). In Experiment II, morphine (0.2–10 mg/kg) had no effect on the intensity threshold of the shock unconditioned stimulus for elicitation of unconditioned responses or on the latencies of the elicited responses. However, morphine (5 and 10 mg/kg) did produce a small but significant decrease in the amplitude of unconditioned responses elicited by the two highest shock intensities employed (3 and 4 mA). This latter effect of morphine was completely blocked by naloxone (1 mg/kg). In Experiment III, morphine (5 mg/kg) blocked the sensory processing of a tone conditioned stimulus, in previously trained animals, as measured by a significant (24 dB) elevation in the intensity threshold of the conditioned stimulus for elicitation of conditioned responses and an increase in the latency of the elicited response. Naloxone (1 mg/kg) completely blocked the effects of morphine on the sensory processing of the tone-conditioned stimulus. The retardant effect of morphine on the acquisition of conditioned responses appears to be primarily due to an action on opioid receptors that produces a decrease in the sensory processing of the conditioned stimulus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00427434
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  • 2
    Electronic Resource
    Electronic Resource
    Behavioural and neurochemical characteristics of phentermine and fenfluramine administered separately and as a mixture in rats (1997)
    Springer
    Psychopharmacology 131 (1997), S. 296-306 
    Details
    ISSN: 1432-2072
    Keywords: Key words Drug discrimination ; Microdialysis ; Dopamine ; Serotonin ; Phentermine ; Fenfluramine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Clinical case studies suggest that combined administration of the serotonergic agent fenfluramine (FEN) and the weak amphetamine-like anorexic agent phentermine (PHEN) may be useful in the treatment of alcohol and cocaine addictions. The present experiment examined the nature of the interaction between the two agonists using the drug discrimination paradigm. In vivo microdialysis served to examine the neurochemical profile of dopamine and serotonin release in the nucleus accumbens. In conscious rats, acute injections of FEN (1.0–2.0 mg/kg IP) or PHEN (1.0–2.0 mg/kg IP) selectively elevated levels of serotonin and dopamine in the nucleus accumbens, respectively. A mixture (1 mg/kg of each) increased levels of both amines by similar magnitudes to those observed with each individually. Three groups of Sprague-Dawley rats were trained to discriminate (1) FEN (1.0 mg/kg IP) alone, (2) PHEN (1.0 mg/kg IP) alone or a mixture (3) PHEN+FEN (1 mg/kg of each, IP) from saline under a fixed ratio (FR-10) schedule of food reinforcement. Rats acquired the mixture discrimination rapidly, while for the other groups the training dose had to be increased to 2.0 mg/kg to attain stimulus control. The individual components of the mixture at the training dose generalized partially to the mixture, and complete generalisation was observed following 3.0 mg/kg FEN or PHEN. Rats trained to discriminate the individual components showed respective cross-generalisation profiles. Generalisation to cocaine (0.3–10.0 mg/kg IP), amphetamine (0.1–3.0 mg/kg IP) and nicotine (0.1–0.8 mg/kg SC) was greatest in the MIX-trained rats, while partial or no generalisation was observed in rats trained to discriminate the individual compounds. From the present results, it may be concluded that the two drugs given as a mixture do not produce a novel cue. Rather, these aminergics appear to interact additively. Furthermore, the dual stimulation of the amines by the mixture may be the basis for the cueing effects of the FEN+PHEN drug mixture, and its effectiveness in treating drug addictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050296
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  • 3
    Electronic Resource
    Electronic Resource
    Behavioural and biochemical adaptations to nicotine in rats: influence of MK801, an NMDA receptor antagonist (1997)
    Springer
    Psychopharmacology 134 (1997), S. 121-130 
    Details
    ISSN: 1432-2072
    Keywords: Key words Nicotine ; Rats ; MK801 ; NMDA receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Chronic exposure of rats to nicotine can result in sensitization to the stimulant effects of nicotine on locomotor activity. At a biochemical level, chronic exposure to nicotine increases the number of CNS nicotinic binding sites, and this has been suggested as the basis for sensitization to nicotine. The present experiment was conducted to examine the effects of MK801, an NMDA receptor antagonist, on sensitization to nicotine. In addition, the hypothesis that MK801 may block behavioural sensitization by preventing the up-regulation of nicotinic receptors was tested by measuring receptor numbers in the same individuals using quantitative autoradiography with [3H]-cytisine and [3H]-MK801. Male Sprague-Dawley rats were chronically treated with nicotine (0.4 mg/kg SC) or saline daily for 7 days. Over the next 2 days, in a counterbalanced order, rats were challenged with nicotine (0.4 mg/kg SC) or saline and locomotor activity was monitored. In saline-pretreated rats, nicotine produced a small increase in activity. Nicotine-pretreated rats exhibited higher levels of activity following a nicotine challenge. This sensitized response was attenuated in rats administered MK801 (0.3 mg/kg IP) 30 min before each daily nicotine injection. Rats pretreated with MK801 alone showed activity scores no different from saline pretreated control groups. Biochemical studies revealed increased [3H]-cytisine binding following chronic nicotine treatment; however, receptor increases were significantly attenuated by MK801 pretreatment. Binding of [3H]-MK801 remained unchanged across the four groups. The results suggest that MK801 prevents behavioural sensitization to nicotine via the prevention of receptor up-regulation. Although the findings support the notion that receptor up-regulation may be the basis for the increased responsiveness to nicotine, other interpretations are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050433
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    Paper (German National Licenses)
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