The neural basis of drug craving: An incentive-sensitization theory of addiction

New information regarding neuronal circuits that control food intake and their hormonal regulation has extended our understanding of energy homeostasis, the process whereby energy intake is matched to energy expenditure over time. The profound obesity that results in rodents (and in the rare human case as well) from mutation of key signalling molecules involved in this regulatory system highlights its importance to human health. Although each new signalling pathway discovered in the hypothalamus is a potential target for drug development in the treatment of obesity, the growing number of such signalling molecules indicates that food intake is controlled by a highly complex process. To better understand how energy homeostasis can be achieved, we describe a model that delineates the roles of individual hormonal and neuropeptide signalling pathways in the control of food intake and the means by which obesity can arise from inherited or acquired defects in their function.

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Central nervous system control of food intake

Well-being : the foundations of hedonic psychology

As humans, we perceive feelings from our bodies that relate our state of well-being, our energy and stress levels, our mood and disposition. How do we have these feelings? What neural processes do they represent? Recent functional anatomical work has detailed an afferent neural system in primates and in humans that represents all aspects of the physiological condition of the physical body. This system constitutes a representation of 'the material me', and might provide a foundation for subjective feelings, emotion and self-awareness.

How do you feel? Interoception: the sense of the physiological condition of the body.

https://lsa.umich.edu/psych/research&labs/berridge/publications/Berridge&RobinsonBrResRev1998.pdf

What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience?

1. A total of 51 single neurons was recorded from the pontine parabrachial nuclei of three rats being given sapid stimuli either via intraoral infusions or during spontaneous licking behavior. In 46 neurons, sapid stimuli elicited significant taste responses; of these, 28 responded best to NaCl, 15 to sucrose, 2 to citric acid, and 1 to quinine HCl. The remaining five neurons responded significantly only to water. The mean spontaneous rate of taste neurons during the intraoral infusion and licking sessions was 11.1 +/- 1.1 and 10.8 +/- 1.2 (SE) spikes/s, respectively. 2. Of the 39 neurons tested during both licking and intraoral infusions, four responded significantly only to water via either route. The remaining 35 neurons responded significantly to at least some sapid stimuli. The best-stimulus categories remained the same regardless of the route of fluid delivery (24 NaCl best, 10 sucrose best, 1 citric acid best). When the rats were licking the stimuli, nine taste neurons responded significantly to only one sapid chemical [6 Na specific (Ns) and 3 sucrose specific (Ss)] but were more broadly tuned during intraoral infusions. Conversely, three taste neurons that responded specifically during intraoral infusions (3 Na specific) were not as specific when the animal licked the same fluids. 3. Thirty-five taste neurons were tested via both stimulus routes. These data were compared in three ways. First, for each neuron, the responses elicited during licking and intraoral infusions were compared for each of the four standard sapid stimuli. The Pearson correlation coefficients for the 35 taste neurons ranged from 0.9997 to 0.6785, with a mean at 0.953 +/- 0.012 (SE). The second comparison was between stimulus routes across chemicals. With the use of raw responses, the correlation coefficients for NaCl, sucrose, citric acid, and QHCl ranged from 0.925 to 0.778 (t test, P less than 0.0001). With the activity elicited by water subtracted (corrected responses), the correlation coefficients for NaCl, sucrose, citric acid, and QHCl were 0.900, 0.795, 0.369, and 0.211, respectively. The coefficient for QHCl was not significant (t test, P greater than 0.05). Finally, the mean responses to NaCl, sucrose, and citric acid delivered by both routes were compared and found not to differ (paired t test, P greater than 0.05). 4. In separate hierarchical cluster analyses for the licking and infusion data, the largest cluster in each contained all of the Na-best neurons and the next largest, all of the sucrose-best cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Parabrachial gustatory neural activity during licking by rats

1. Fifty-seven taste neurons were isolated in the nucleus solitary tract (NST) and tested with 15 sapid chemicals. On average, NST neurons responded well to NaCl, sucrose, monosodium L-glutamate (M...

Taste responses of neurons in the nucleus of the solitary tract of awake rats: An extended stimulus array

Concentration-dependent licking of sucrose and sodium chloride in rats with parabrachial gustatory lesions

Microstructural analysis of successive negative contrast in free-feeding and deprived rats

Rats with ibotenic acid lesions of the parabrachial nucleus (PBN) failed to learn a taste aversion induced by lithium chloride (LiCI) toxicosis. The same rats also did not learn to prefer a taste that was paired with intragastric (IG) carbohydrate infusions during 22 hr/day trials. The PBN-lesioned rats did learn to prefer a flavor (odor + taste) paired with the IG carbohydrate infusions over a different flavor paired with IG water. The PBN-lesioned rats also learned to avoid a flavor paired with IG LiCI infusions during 22 hr/day trials. The flavor preference and aversion, however, were less pronounced than those displayed by control rats. These data indicate that the PBN is essential for forming orosensory-viscerosensory associations when taste is the primary cue but is less critical when more complex flavor cues are available.

Ralph Norgren

Papers

Parabrachial gustatory neural activity during licking by rats

Taste responses of neurons in the nucleus of the solitary tract of awake rats: An extended stimulus array

Concentration-dependent licking of sucrose and sodium chloride in rats with parabrachial gustatory lesions

Microstructural analysis of successive negative contrast in free-feeding and deprived rats

Parabrachial nucleus lesions block taste and attenuate flavor preference and aversion conditioning in rats.