Brain reward circuitry and the regulation of energy balance

Abstract

Reward signals contribute to the regulation of energy balance by influencing switching between feeding and competing behaviors. Properties of natural rewards are mimicked by electrical stimulation of certain brain regions. The rewarding effect produced by stimulating the perifornical region of the hypothalamus is modulated by body weight and is attenuated both by leptin and insulin. Research is reviewed concerning the dependence of the rewarding effect of perifornical stimulation on longterm energy stores and the effects of two neuropeptides implicated in the regulation of energy balance, neuropeptide Y and corticotropin-releasing hormone. It is proposed that the potentiating effect of weight loss on perifornical self-stimulation is not tied to an increased propensity to eat or to an enhancement of food reward per se, but resembles the influence of long-term energy stores on non-ingestive behaviors that defend body weight, such as hoarding. International Journal of Obesity (2001) 25, Suppl 5, S17 -S21 Keywords: brain stimulation reward; lateral hypothalamus; perifornical region; leptin; insulin The role of reward in the regulation of energy balanceBehavior is both the sole source of energy input and a major channel for energy expenditure. Thus, the maintenance of energy balance depends critically on the allocation of behavior between feeding and competing activities on the one hand and between energetically expensive activities and sedentary ones on the other.Rewards, such as a food object encountered while hungry, play a fundamental role in behavioral allocation. In real time, rewarding stimuli and activities create behavioral dispositions that bias an animal to resist interruption of ongoing actions. Information about rewards, such as their intensity, kind, amount and spatiotemporal distribution, is stored in memory and is used in concert with information gleaned from current stimuli to influence switching between competing behaviors. 1 Thus, unraveling the neural circuitry that confers rewarding properties on stimuli has implications for understanding the regulation of energy balance. Brain stimulation rewardProperties of rewarding natural stimuli can be mimicked by electrical stimulation of certain brain sites. The resulting neural activation gives rise to a powerful disposition to reinitiate the stimulation and to resist breaking contact with the manipulandum that triggers the stimulator. The effect responsible for this disposition is called 'brain stimulation reward' (BSR). Information about the strength of the rewarding effect and its rate of availability are stored in memory. At least in the case of lateral hypothalamic (LH) stimulation, the rewarding effect can compete with, summate with, and substitute for the rewarding effect of natural stimuli such as food. 1 It has long been suspected that the neural system responsible for BSR is not uniform and is subdivided along functional lines. 2 In this view, the rewarding effect of stimulating some sites is related to energy balance, whereas at other sites BS...

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