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  • 1
    Electronic Resource
    Electronic Resource
    Differential behavioral effects following microinjection of an NMDA antagonist into nucleus accumbens subregions (1994)
    Springer
    Psychopharmacology 116 (1994), S. 65-72 
    Details
    ISSN: 1432-2072
    Keywords: Nucleus accumbens ; Glutamate ; NMDA receptors ; Exploration ; Open field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recent studies have demonstrated the existence of two distinct regions within the nucleus accumbens (N.Acc) known as “core” and “shell”. In order to investigate whether the behavioral functions of excitatory amino acid receptors differed between these two subregions, rats were administered microinjections of 2-amino-5-phosphonovaleric acid (AP-5), a competitive NMDA antagonist (0, 0.05, 0.2, 0.5, 1.0 µg/0.5 µl) into selected central and medial regions of the accumbens. The central and medial sites were assumed to correspond approximately to core and shell subregions, respectively. The animals were tested in two exploratory tasks: the open field and a novel object test. In the open field test, AP-5 significantly decreased peripheral locomotion and center rearing frequency in the central but not the medial group. Locomotion and rearing were not affected by AP5 infusion into a control site, the anterior dorsal striatum (ADS). In the novel object test, animals were tested in the same open field, with prior habituation, and with several novel objects placed within it. In this test, infusions of AP-5 (0, 1.0 µg/0.5 µl) decreased the number and duration of contacts with the novel objects in the central but not the medial group. In addition, peripheral and center locomotion were decreased by AP-5 infusions into the central site, whether objects were present or not. In contrast, AP-5 infusions into the medial site elicited an increase in peripheral locomotion in both stimulus conditions. These findings provide behavioral-pharmacological evidence that the central and medial subregions of the nucleus accumbens can be differentiated. Moreover, the results suggest that exploratory motor responses may be dependent on glutamate-coded input to the nucleus accumbens area corresponding to the core region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02244872
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  • 2
    Electronic Resource
    Electronic Resource
    Microinfusion of corticotropin-releasing factor into the nucleus accumbens shell results in increased behavioral arousal and oral motor activity (1997)
    Springer
    Psychopharmacology 130 (1997), S. 189-196 
    Details
    ISSN: 1432-2072
    Keywords: Key words CRF ; Nucleus accumbens ; Locomotor activity ; Oral stereotypy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Corticotropin-releasing factor (CRF) is a 41 amino acid peptide postulated to be involved in integrating the physiological and behavioral responses to stress. The purpose of this experiment was to determine the effects of CRF microinfused into the nucleus accumbens core (AcbC) and shell (AcbSh) subregions. Rats were tested for general motor activity, cage crossings, and rearing following CRF (0, 125, 250, or 500 ng). Behavioral observations were also made to determine the profile of activity caused by CRF infusion into the Acb. CRF in the AcbSh but not the AcbC regions elicited an increase in general motor activity that lasted approximately 2 h. When compared with ventricular injections, CRF in the AcbSh had greater activating effects. The CRF-induced behavioral profile consisted of increases in grooming, sniffing, and oral behavior. Results are discussed as they pertain to the involvement of the AcbSh in stress, motivated behavior, and drug sensitization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050228
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  • 3
    Electronic Resource
    Electronic Resource
    Dopamine and conditioned reinforcement (1991)
    Springer
    Psychopharmacology 103 (1991), S. 197-203 
    Details
    ISSN: 1432-2072
    Keywords: Conditioned reinforcement ; Ventral tegmental area ; Nucleus accumbens ; Amphetamine ; Neuropeptides ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has been shown that infusion of certain neuropeptides into the ventral tegmental area (VTA) results in increased motor activity and enhanced dopamine turnover in the nucleus accumbens. In the present experiments, substance P (SP), neurotensin (NT),d-ala-metenkephalin (DALA) and morphine sulfate (MS) were injected bilaterally into the VTA and their effects on conditioned reinforcement were assessed. These effects were compared with infusion of amphetamine into the nucleus accumbens, which has previously been shown to strongly enhance responding for conditioned reinforcers. For these experiments, hungry rats were trained to associate a compound stimulus (light and click) with the presentation of food. In the test phase, responding on one lever (CR lever) resulted in the presentation of the stimulus but no food. Responding on the other (NCR lever) had no consequences. Different groups of animals received microinjections (0.5 µl, bilaterally) of SP (0, 0.03, 0.3, 3.0 µg), NT (0, 0.025, 0.25, 0.5 µg), DALA (0, 0.01, 0.1, 1.0 µg) or morphine (0, 0.025, 0.25, 2.5 µg) into the VTA. SP infusion into the VTA resulted in a small increase in responding which was not selective for the CR lever. NT, DALA and morphine had no effect on responding for conditioned reward. In contrast, amphetamine (0, 0.2, 2.0, 20 µg) injected into the nucleus accumbens markedly enhanced responding for conditioned reward. These findings suggest that stimulation of the mesolimbic system at the level of the DA cell bodies, which induces a small increase in DA turnover, is not sufficient to potentiate responding for conditioned reward. On the other hand, an important requirement for potentiation may be excessive release of dopamine in the nucleus accumbens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02244203
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Striatal regulation of morphine-induced hyperphagia: an anatomical mapping study (1993)
    Springer
    Psychopharmacology 111 (1993), S. 207-214 
    Details
    ISSN: 1432-2072
    Keywords: Feeding ; Striatum ; Nucleus accumbens ; Morphine ; Opiates ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Both systemic and intracranial administration of morphine can result in spontaneous feeding in nondeprived rats. The present investigation was conducted to examine the involvement of the striatum in this phenomenon. Morphine sulfate (0, 0.5, 1.0, 5.0, 10.0, and 20.0 µg/0.5 µl) was microinjected into five discrete striatal subregions in non-deprived rats: the nucleus accumbens, the ventromedial striatum, the ventrolateral striatum, the anterior dorsal striatum, and the posterior dorsal striatum. Feeding, drinking, locomotion, rearing, and food intake were measured over 4 h after infusion. Results indicate that the striatum is a heterogeneous structure with regard to the regulation of opiate-induced feeding behavior and locomotor activity. Morphine infusion into anteroventromedial regions including the nucleus accumbens resulted in a marked hyperphagia that was generally delayed in onset; much smaller increases or no change in feeding occurred after administration into more dorsal, lateral and posterior areas. It is hypothesized that there may exist within the striatum an anatomical gradient that is most sensitive to opiate-induced feeding within the anteroventromedial sector. Since this area has extensive connections with other brain sites sensitive to opiate-induced feeding, it may be a critical part of an opiatergic feeding system within the brain. In addition, a possible role for the anteroventromedial striatum in compulsive feeding and bulimia is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02245525
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Opiate agonists microinjected into the nucleus accumbens enhance sucrose drinking in rats (1997)
    Springer
    Psychopharmacology 132 (1997), S. 350-360 
    Details
    ISSN: 1432-2072
    Keywords: Key words Opioids ; Nucleus accumbens ; Sucrose intake ; Morphine ; DAMGO ; DPEN ; U50488H ; Dynorphin ; Food reward ; Palatability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have indicated that central opioid peptides and opiate receptors play an important role in the modulation of ingestive behaviors. The nucleus accumbens (Acb), a forebrain region involved in reinforcement, contains high levels of opiate receptors. The present investigation was undertaken to determine the relative involvement of opiate receptor subtypes in sucrose drinking. Morphine (0, 0.5, 5 μg/0.5 μl), the mu agonist D-Ala2,NMe-Phe4,Glyo15-enkephalin (DAMGO; 0, 0.025, 0.25 and 2.5 μg/0.5 μl), the delta agonist D-Pen2,5-enkephalin (DPEN; 0, 0.031, 0.31,3.1 μg/0.5 μl), and the kappa agonists U50488H (0, 0.0186, 0.186, 1.86 μg/0.5 μl), and dynorphin (0, 0.05, 0.5, 5 μg/0.5 μl) were microinfused into Acb. Intake of 5% sucrose, drinking duration, locomotion, rearing, and grooming were measured in a 30-min session in rats previously adapted to sucrose. After microinjection into Acb, morphine induced a robust increase in both sucrose intake and drinking duration at the low dose. DAMGO enhanced sucrose drinking at lower doses, and suppressed drinking at the highest dose. DPEN also increased sucrose intake in a dose-dependent manner. U50488H and dynorphin had no effect on sucrose drinking. In addition, it was demonstrated that intra-Acb administration of DAMGO specifically enhanced palatable sweet solution drinking, leaving water intake unchanged. Although mu and delta agonists tended to increase spontaneous motor activity, the pattern of effects indicated that increases in ingestion could not be simply attributed to general arousal. These findings demonstrate that both mu and delta receptors within the accumbens may have an important modulatory role in ingestion of palatable substances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050355
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  • 6
    Electronic Resource
    Electronic Resource
    Dopamine and conditioned reinforcement (1991)
    Springer
    Psychopharmacology 103 (1991), S. 187-196 
    Details
    ISSN: 1432-2072
    Keywords: Conditioned reinforcement ; Striatum ; Dopamine ; Amphetamine ; Nucleus accumbens ; Reward ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the conditioned reinforcement paradigm, animals learn a new instrumental response reinforced solely by conditioned reward (a stimulus that has previously been associated with primary reward). It has been shown that psychostimulants potentiate responding for conditioned reward and there is evidence that the nucleus accumbens is involved in this effect. The present experiments extend this work and examine the roles of various striatal subregions in the enhancement of responding for conditioned reward. In the conditioning phase, hungry rats were trained to associate a light/click stimulus with food delivery, with no levers present in the operant chamber. In the test phase, two levers were present and responding on one provided conditioned reward (presentation of the compound stimulus but no food). During this phase, microinjections ofd-amphetamine (0, 0.2, 2.0, 20.0 µg/0.5 µl) were made into seven striatal subregions in separate groups of rats. Injection of amphetamine into the nucleus accumbens elicited a dose-dependent, selective increase in responding for CR. Injections into posterior regions of the striatum had no effect. Significant and selective increases in CR responding were noted after injections into two regions neighboring the nucleus accumbens, the anterior dorsal and the ventromedial striatum, although the magnitude of these effects was considerably less than that following accumbens injections. Injections into ventrolateral regions increased responding in some rats, but this effect was very variable and not selective for the CR lever. These results are interpreted as evidence for functional heterogeneity of the striatum with regard to enhancement of conditioned reinforcement. The findings are discussed in relation to the theory that increased dopaminergic activity in the nucleus accumbens results in amplification of the response to a previously learned reward-related signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02244202
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