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PubMed1982

Alpha-melanocyte-stimulating hormone and behavior.

Melanocyte-stimulating hormone (MSH) has putative adaptive significance in all forms of species where it is present. In mammals the polypeptide chain influences learning, memory and attention. Chemically MSH shares the first 13 (alpha-MSH) or the first 18 or 22 (beta-MSH) amino acids with adrenocorticotropic hormone (ACTH), even though the mechanisms of secretion and behavioral effects are often quite different. The still shorter peptide chain MSH/ACH4-10 demonstrates significant melanotropic and behavioral actions of alpha-MSH without showing any steroidogenic effect. Behaviorally, alpha-MSH and MSH/ACTH analogues (MSH/ACTH4-9 and MSH/ACTH4-10 influence the parameters of learning, attention and memory in both human and infrahuman subjects. Alpha-MSH has also been reported to increase sensitivity and augment arousal mechanisms in the CNS. Alpha-MSH has been observed to increase and sustain novelty-induced defecation, and this behavior was found to be accompanied by a concomitant decrease in whole brain DA and NE levels in both intact and hypophysectomized rats exposed daily to a test box. The behavioral effects of alpha-MSH may be partially modulated by the enhanced cyclic-AMP activity in the CNS observed after MSH administration. MSH also seems to be working in conjunction with the hypothalamic tripeptide MIF-1 and the pineal hormone melatonin, both of which can affect the release of MSH from the pituitary. Recent evidence suggests that MSH is counterbalancing against and complementing with the effects of endorphins, specifically beta-endorphin (61-91 chain of beta-LPH), in maintaining learning and attentive behaviors.

Adrenocorticotropic Hormone↗

PubMed1990

Problem solving ability of Octopus vulgaris Lamarck (Mollusca, Cephalopoda).

Experiments presented in this study show that Octopus vulgaris Lamarck is able to open transparent glass jars closed with a plastic plug and containing a live crab (Carcinus mediterraneus). The animals remove the plus (Operandum: O) and seize the crab (Predation :P) in one single attack. The number of unsuccessful attacks appears to decrease over a series of trials (p less than .01); during the same period exploration time remains unchanged. There is a statistically significant increase in performance over trials for O (p less than .01) and P (p less than .05) mean times analyzed by single factor ANOVA, suggesting that the learning process is accomplished either by stimulus-response association or by trial and error. We propose that Octopus vulgaris is capable of learning the solutions of both problems, Operandum and Predation, thus showing a highly developed ability of "integration" of the behavioral program.

Animals↗

PubMedDate not supplied

Facilitation of efficient search of an unbaited radial-arm maze in rats by D1, but not D2, dopamine receptors.

Dopamine (DA) agonists facilitate and antagonists inhibit conditioned preparatory behaviors in rats. We provide added evidence that increased D1 receptor activation facilitates unconditioned preparatory behavior as well, this time in the form of efficient search of an unbaited radial-arm maze. Administration of 0.1, but not 1.0, mg/kg sc SKF81297, a full D1 agonist, increased the number of novel arms chosen in the first eight arms entered. Treatment with 0.1 mg/kg sc D-amphetamine, an indirect DA agonist, also increased search efficiency when given on the first test day but not when given following a test day with a 1.0 mg/kg dose. The 0.1-mg/kg amphetamine-induced facilitation was blocked by coinjection of 0.005 mg/kg SCH23390, a D1 antagonist. Treatment with quinpirole, a D2 agonist, or eticlopride, a D2 antagonist, decreased amount of maze search, but did not affect efficiency. Collectively, our results support the possibility there is a general facilitatory effect of D1 activation on unconditioned preparatory behavior.

Animals↗

PubMed1982

Effects of chlordiazepoxide on acquisition and performance of a go-no go successive discrimination task, and on brain biogenic amines in cats.

1. Normal and chlordiazepoxide (0.4 mg/kg/day, per os) treated cats were trained on a symmetric go-no go successive discrimination task with positive reinforcement. 2. The treatment impaired the acquisition, but not the performance once the task was learned. 3. Serotonin, 5-hydroxyindoleacetic acid and noradrenaline were assayed in 12 brain areas in trained cats, and in normal and treated cats which did not undergo the training. 4. The treatment produced localized changes in the serotonin: 5-hydroxyindoleacetic acid ratio and the noradrenaline level; these effects were modified by the training. 5. The drug induced an acquisition deficit rather than a general behavioral disinhibition, and produced neurochemical effects which were dependent upon the brain area, the treatment duration and the behavioral state.

Animals↗

PubMed2004

Differential control over cocaine-seeking behavior by nucleus accumbens core and shell.

Nucleus accumbens (NAc) dopamine is widely implicated in mediating the reinforcing effects of drugs of abuse. However, the precise function of the NAc itself in drug self-administration has been difficult to establish. Here we show a neural double-dissociation of the behavioral processes that underlie cocaine self-administration in rats. Whereas selective excitotoxic lesions of the NAc core had only a minor effect on the acquisition of responding for cocaine under a standard schedule of continuous reinforcement, these lesions profoundly impaired the acquisition of drug-seeking behavior that was maintained by drug-associated conditioned reinforcers and assessed using a second-order schedule of cocaine reinforcement. In contrast, selective excitotoxic lesions of the NAc shell did not impair drug self-administration or the acquisition of cocaine-seeking, but they did attenuate the psychostimulant effects of cocaine. These results further our understanding of how the NAc controls drug-seeking and drug-taking behavior.

Animals↗

PubMed2004

Drug seeking becomes compulsive after prolonged cocaine self-administration.

Compulsive drug use in the face of adverse consequences is a hallmark feature of addiction, yet there is little preclinical evidence demonstrating the actual progression from casual to compulsive drug use. Presentation of an aversive conditioned stimulus suppressed drug seeking in rats with limited cocaine self-administration experience, but no longer did so after an extended cocaine-taking history. In contrast, after equivalent extended sucrose experience, sucrose seeking was still suppressed by an aversive conditioned stimulus. Persistent cocaine seeking in the presence of signals of environmental adversity after a prolonged cocaine-taking history was not due to impaired fear conditioning, nor to an increase in the incentive value of cocaine, and may reflect the establishment of compulsive behavior.

Animals↗

PubMed1997

Neurobiological constraints on behavioral models of motivation.

The application of neurobiological tools to behavioral questions has produced a number of working models of the mechanisms mediating the rewarding and aversive properties of stimuli. The authors review and compare three models that differ in the nature and number of the processes identified. The dopamine hypothesis, a single system model, posits that the neurotransmitter dopamine plays a fundamental role in mediating the rewarding properties of all classes of stimuli. In contrast, both nondeprived/deprived and saliency attribution models claim that separate systems make independent contributions to reward. The former identifies the psychological boundary defined by the two systems as being between states of nondeprivation (e.g. food sated) and deprivation (e.g. hunger). The latter identifies a boundary between liking and wanting systems. Neurobiological dissociations provide tests of and explanatory power for behavioral theories of goal-directed behavior.

Animals↗

PubMed1989

Behavioral effects of yohimbine and chlordiazepoxide: dependence on the rat's previous familiarization with the test conditions.

The effects of yohimbine and chlordiazepoxide on locomotor activity in an open field were found to depend on the rat's previous habituation to the test environment: chlordiazepoxide induced a locomotor activation in nonhabituated, but not in habituated rats; yohimbine activated in habituated rats only. In a further study, carried out in the rat's homecage (habituated conditions), the effect of both drugs on competition for sucrose pellets was assessed: yohimbine, but not chlordiazepoxide, helped so-called poor-performing rats to temporarily overcome their typical abstention from competition. The presence or absence of drug effects, obviously depending on the rat's previous familiarization with the test environment, are discussed with view to Gray's concept of the behavioral inhibition system.

Animals↗

PubMed1991

Analysis of fixed-ratio behavior maintained by drug reinforcers.

Behavior maintained by intravenously delivered alfentanil, cocaine, or ketamine was assessed using a fixed-ratio schedule of reinforcement. As the dose of each drug was increased, rate of responding also increased up to a maximum. Further increases in dose resulted in decreased response rates (inverted U-shaped curve). An analysis of postreinforcement-pause-time and run-time measures for the ascending limb of the inverted U-shaped functions revealed that behavior was characterized by systematic decreases in both pause time and run time as dose and rate increased. An examination of the descending limb of the dose-response functions revealed that lowered response rates for cocaine and ketamine were correlated with increases in run time and small and inconsistent effects on postreinforcement pause time. Behavior maintained by rate-reducing doses of alfentanil was characterized by lengthened postreinforcement pauses with small increases in run time. These data suggest that at larger doses, drug reinforcers may have unconditioned or direct effects on the behavior that the drug is maintaining, and more important, that the nature of these unconditioned effects depends on the drug that is maintaining behavior.

Alfentanil↗

PubMed2003

Dynamical concurrent schedules.

Previous work on the matching law has predominantly focused on the molar effects of the contingency by examining only one reinforcer ratio for extended periods. Responses are distributed as a function of reinforcer ratios under these static conditions. But the outcome under a dynamic condition in which reinforcer ratios change continuously has not been determined. The present study implemented concurrent variable-interval schedules that changed continuously across a fixed 5-min trial. The schedules were reciprocally interlocked. The variable interval for one key changed continuously from a variable-interval 15-s to a variable-interval 480-s, while the schedule for the other key changed from a variable-interval 480-s to a variable-interval 15-s. This dynamical concurrent schedule shifted behavior in the direction of matching response ratios to reinforcer ratios. Sensitivities derived from the generalized matching law were approximately 0.62, the mean absolute bias was approximately 0.11, and r2s were approximately 0.86. It was concluded that choice behavior can come to adapt to reinforcer ratios that change continuously over a relatively short time and that this change does not require extensive experience with a fixed reinforcer ratio. The results were seen as supportive of the view that all behavior constitutes choice.

Animals↗

PubMed1990

Effect of reinforcer devaluation on discriminative control of instrumental behavior.

Two experiments examined the effect of reinforcer devaluation on the ability of a discriminative stimulus (Sd) to control instrumental behavior in Sprague-Dawley rats. In Experiment 1 reinforcer devaluation reduced, but did not eliminate, the ability of the Sd to control performance of the original response and to transfer its control to a new response trained with the same reinforcer. The effect of devaluation was more complete in Experiment 2, in which the reinforcer was delivered directly into the oral cavity. However, retraining the response with a different reinforcer partially restored the ability of the Sd to control performance of that response. These results suggest that an Sd may not augment its trained responses when the reinforcer has been completely devalued but may promote responses with which it shares a reinforcer, as long as those responses are associated with some reinforcer that retains its value. The implications of these results for the way that discriminative stimuli control instrumental behavior are discussed.

Animals↗

PubMed1972