Ventral tegmental area reward

In 1954, experiments by Olds and Milner revealed that the brain has specialized centers for reward functions. In these studies electrical stimulation of certain brain sites was found to be highly rewarding in the sense that rats operantly respond for electrical stimulation of these brain sites, often to the exclusion of any other activity. A neurotransmitter system that is particularly sensitive to electrical self-stimulation is the mesolimbic dopamine projection that originates in the ventral tegmental area and projects to structures closely... 

The neuroehemical sites for psyehomotor stimulant reward are likely to be the presynaptic dopamine terminals located in the region of the nucleus aeeumbens, frontal cortex, and other forebrain structures that originate in the ventral tegmental area. Note, however, that intraeranial self-administration of eoeaine is elicited from the frontal cortex, but not from the nucleus aeeumbens (Goeders and Smith 1983). Thus, eoneomitant activation of structures other than the nucleus accumbens may be an important part of the circuitry involved in initiation of cocaine intravenous self-administration, as has been hypothesized for the opiates (Smith and Lane 1983 Smith et al. 1982). 

O Virtually all abused substances appear to activate the same brain reward pathway. Key components of the reward pathway are the dopamine (DA) mesocorticolimbic system that projects from the ventral tegmental area (VTA) and the nucleus accumbens (NA) to the prefrontal cortex, the amygdala, and the olfactory tubercle (Figs. 33-3 and 33-4).5 Animal studies... 

A10 Ventral tegmental area Nucleus accumbens Reward... 

Tzschentke T., Schmidt W. (2000). Functional relationship among medial prefrontal cortex, nucleus accumbens, and ventral tegmental area in locomotion and reward. Crit. Rev. Neurobiol. 14, 131-42. 

Laviolette, S.R., van der Kooy, D. The motivational valence of nicotine in the rat ventral tegmental area is switched from rewarding to aversive following blockade of the alpha7-subunit-containing nicotinic acetylcholine receptor. Psychopharmacology (Berlin). 166 306, 2003. 

Laviolette, S.R., Alexson, T.O., van der Kooy, D. 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, 2002. 

Fiorino DF, Coury A, Fibiger HC and Phillips AG (1993). Electrical stimulation of reward sites in the ventral tegmental area increases dopamine release in the nucleus accumbens of the rat. Behavioral Brain Research, 55, 131-141. 

Laviolette SR, Gallegos RA, Henriksen SJ, Kooy van der D. 2004. Opiate state controls bi-directional reward signaling via GABAa. receptors in the ventral tegmental area. Nat Neurosci 7(2) 160-169. 

Laviolette SR, Van Der Kooy D (2003) Blockade of mesolimbic dopamine transmission dramatically increases sensitivity to the rewarding effects of nicotine in the ventral tegmental area. Mol Psychiatry 8 50-59... 

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. 

Figure 2.3 Many drugs of abuse act on the brain s reward center, which is illustrated above. The drugs cause neurons in the ventral tegmental area to release dopamine. The dopamine, in turn, initiates a chain of events that results in feelings of enjoyment and pleasure.

---