Behaviour reward

Anorexia nervosa (AN) and Binge-eating disorder (BED) 1. Increased blood levels of AEA in patients with AN and BED may participate in reward aspects of aberrant eating behaviours 1. None tested... 

Most of the motor effects of amphetamine, especially stereotypy, are due to the release of DA as are its psychotic effects such as hallucinations. Its ability to mimic the action of DA in reward and reinforcement behaviour may contribute to its abuse potential (see Chapter 22) but its arousal (stimulant) properties also involve NA release. 

Initiation of behaviour Mesolimbic pathway to nucleus accumbens from VTA (AIO) Mesocortical pathways to prefrontal cortex from VTA (AIO) Animals Increases locomotor activity and intracranial self-stimulation Humans Hallucinations, psychoses (reward, reinforcement) Animals Decreases activity and self-stimulation Humans Reduces positive symptoms of schizophrenia D2 ... 

As a result of these observations it has been suggested that DA released in the nucleus accumbens is important in motivation by linking reward (especially when it is food) with the motor activity required to achieve it (Mogenson, Jones and Yim 1980). It is difficult, however, to distinguish a pure behavioural role for DA in actually initiating the sense of reward and motivation from its undisputed part in facilitating the motor response necessary to obtain the reward, e.g. a lever press in rats. 

Mesolimbic dopamine pathways are thought to be involved in the rewarding effects of drugs of abuse and an imbalance of this pathway is thought to be causal in psychoses. Several studies have revealed that 5-HT3 receptor antagonists can correct such imbalances. Thus, ondansetron inhibits the behavioural hyperactivity resulting from direct stimulation of this... 

Fig. 4 Role of extracellular dopamine in responding for natural rewards (a) and for nicotine (b). This figure illustrates the way increased extracellular DA in the shell subdivision of the nucleus ac-cumbens is postulated to increase the pleasure associated with behaviours that generate rewards. It is proposed that the behavioural role of the process is to facilitate the acquisition of behaviours that result in reward. The hypothesis proposes that the powerful reinforcing properties of drugs of dependence, such as nicotine, reflect their ability to act directly on the dopamine neurones that project to this subdivision of the accumbens. Reproduced with permission from Balfour (2006)...

There is evidence that nicotine also stimulates the DA projections to the dorsal striatum (BenweU and Balfour 1997 Quick 2004). To date, relatively few studies have sought to directly link this response to the drug with behavioural changes associated with dependence. Nevertheless, a number of studies have implicated these projections in the responses to rewarding stimuli, particularly in expectation of reward (Schultz 2006). A failure to deliver an anticipated reinforcer results in transient reduction in the activity of these neurones. Rice and Cragg (2004) have reported that... 

Cannon CM, Palmiter RD (2003) Reward without dopamine, J Neurosci 23 10827-10831 Carboni E, Bortone L, Giua C, Di Chiara G (2000) Dissociation of physical abstinence signs from changes in extracellular dopamine in the nucleus accumbens and in the prefrontal cortex of nicotine dependent rats. Drug Alcohol Depend 58 93-102 Castane A, Valjent E, Ledent C, Parmentier M, Maldonado R, Valverde O (2002) Lack of CBl cannabinoid receptors modifies nicotine behavioural responses, but not nicotine abstinence. Neuropharmacology 43 857-867... 

Di Chiara G (2000b) Behavioural pharmacology and neurobiology of nicotine reward and dependence, In Clementi C, Fornasari D, Gotti C (eds) Handbook of Experimental Pharmacology, vol, 14, Berlin, Springer, Berlin, pp 603-750... 

Laviolette SR, van der Krooy D (2004) The neurobiology of nicotine addiction bridging the gap from molecules to behaviour. Nat Rev Neurosci 5 55-65 Laviolette SR, Alexson TO, van der Krooy D (2002) Lesions of the tegmental pedunculopontine nucleus block the rewarding effects and reveal the aversive effects of nicotine in the ventral tegmental area. J Neurosci 22 8653-8660... 

In humans, at least, reward and punishment systems are clearly involved in conscious thought and behaviour. For example, anticipated rewards may be consciously deferred and relatively aversive activities carried out with the prospect of a future pleasurable goal. Conversely, instant pleasure may sometimes be seized despite knowledge of future punishment. Clearly, a degree of consciousness is required to choose the options. Almost every conscious activity carries some affective tone (Edelman Tononi, 2000 Greenheld, 2000) without this, there would be no motivation to do anything at all. This situation is seen in the anhedonia and apathy which sometimes accompanies schizophre-... 

These results led to the suggestion that the functional unit of reward is a population of individual neurons ( hedonistic neurons ) scattered around reward areas of the brain which are specifically responsive to certain transmitters and are presumably connected to pathways controlling motivated behaviour. Phillips and Fibiger (1989) demonstrated an increase in dopamine metabolism, synthesis and release in the ventral tegmental area and nucleus accumbens during ICSS in rats, an increase proportional to the stimulation rate and intensity. 

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