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Altered motivation masks appetitive learning potential of obese mice.

Harb MR, Almeida OF - Front Behav Neurosci (2014)

Bottom Line: Eating depends strongly on learning processes which, in turn, depend on motivation.We found that (i) the rate of pavlovian conditioning to an appetitive reward develops as an inverse function of body weight; (ii) higher body weight associates with increased latency to collect food reward; and (iii) mice with lower body weights are more motivated to work for a food reward, as compared to animals with higher body weights.Notably, however, all groups adjusted their consumption of the different food types, such that their body weight-corrected daily intake of calories remained constant.

View Article: PubMed Central - PubMed

Affiliation: NeuroAdaptations Group, Max Planck Institute of Psychiatry Munich, Germany ; Neuroscience Domain, Institute of Life and Health Sciences (ICVS), University of Minho Braga, Portugal ; ICVS/3B's - PT Government Associate Laboratory Braga/Guimarães, Portugal.

ABSTRACT
Eating depends strongly on learning processes which, in turn, depend on motivation. Conditioned learning, where individuals associate environmental cues with receipt of a reward, forms an important part of hedonic mechanisms; the latter contribute to the development of human overweight and obesity by driving excessive eating in what may become a vicious cycle. Although mice are commonly used to explore the regulation of human appetite, it is not known whether their conditioned learning of food rewards varies as a function of body mass. To address this, groups of adult male mice of differing body weights were tested two appetitive conditioning paradigms (pavlovian and operant) as well as in food retrieval and hedonic preference tests in an attempt to dissect the respective roles of learning/motivation and energy state in the regulation of feeding behavior. We found that (i) the rate of pavlovian conditioning to an appetitive reward develops as an inverse function of body weight; (ii) higher body weight associates with increased latency to collect food reward; and (iii) mice with lower body weights are more motivated to work for a food reward, as compared to animals with higher body weights. Interestingly, as compared to controls, overweight and obese mice consumed smaller amounts of palatable foods (isocaloric milk or sucrose, in either the presence or absence of their respective maintenance diets: standard, low fat-high carbohydrate or high fat-high carbohydrate). Notably, however, all groups adjusted their consumption of the different food types, such that their body weight-corrected daily intake of calories remained constant. Thus, overeating in mice does not reflect a reward deficiency syndrome and, in contrast to humans, mice regulate their caloric intake according to metabolic status rather than to the hedonic properties of a particular food. Together, these observations demonstrate that excess weight masks the capacity for appetitive learning in the mouse.

No MeSH data available.


Related in: MedlinePlus

Overweight and obese mice show poor acquisition of food-rewarded pavlovian conditioned learning. (A) Body masses of control (CON; normal chow, n = 18), overweight (O/weight; low fat-high carbohydrate diet; n = 16) and obese mice (high fat-high carbohydrate diet, n = 16) at the start of experimentation. (B) Locomotor activity, measured in an open field arena, of CON, O/weight and Obese mice before behavioral testing commenced. (C) Relative number of CS+ approaches and CS- approaches (D) during each session; only CON mice displayed different conditioned responses (cf. Harb and Almeida, 2014), characterized as sign-tracking (ST, predominantly approached the CS+; n = 4), goal-tracking (GT, predominantly approached the US; n = 8), and intermediate-tracking (IT, alternated between CS+ and US with approximately equal frequency; n = 6). Autoshaping was monitored over 11 sessions; in each session, mice received 15 CS+ and 15 CS- presentations. (E) Time in min needed to complete successive autoshaping sessions. (F) Mean latency (s) to retrieve food reward during consecutive training sessions. Data are means ± s.e.m. ***In (A) denotes p < 0.001. *, **, ***In (E,F) indicate differences between CON and obese groups at p < 0.05, 0.01, and 0.001, respectively. †, ††, †††In (E,F) indicate differences between O/weight mice vs. CON and Obese mice at p < 0.05, 0.01, and 0.001, respectively.
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Figure 1: Overweight and obese mice show poor acquisition of food-rewarded pavlovian conditioned learning. (A) Body masses of control (CON; normal chow, n = 18), overweight (O/weight; low fat-high carbohydrate diet; n = 16) and obese mice (high fat-high carbohydrate diet, n = 16) at the start of experimentation. (B) Locomotor activity, measured in an open field arena, of CON, O/weight and Obese mice before behavioral testing commenced. (C) Relative number of CS+ approaches and CS- approaches (D) during each session; only CON mice displayed different conditioned responses (cf. Harb and Almeida, 2014), characterized as sign-tracking (ST, predominantly approached the CS+; n = 4), goal-tracking (GT, predominantly approached the US; n = 8), and intermediate-tracking (IT, alternated between CS+ and US with approximately equal frequency; n = 6). Autoshaping was monitored over 11 sessions; in each session, mice received 15 CS+ and 15 CS- presentations. (E) Time in min needed to complete successive autoshaping sessions. (F) Mean latency (s) to retrieve food reward during consecutive training sessions. Data are means ± s.e.m. ***In (A) denotes p < 0.001. *, **, ***In (E,F) indicate differences between CON and obese groups at p < 0.05, 0.01, and 0.001, respectively. †, ††, †††In (E,F) indicate differences between O/weight mice vs. CON and Obese mice at p < 0.05, 0.01, and 0.001, respectively.

Mentions: To address the hypothesis that appetitive learning is altered in overweight and obese individuals, we here applied the classical pavlovian conditioning paradigm to mice that differed in body mass, reflecting their maintenance on normal chow (NC) (CON, hereinafter referred to as “control mice,” N = 18), low-fat/high-carbohydrate (overweight, N = 16) or high-fat/high-carbohydrate (obese, N = 16) diets. Body weights differed significantly between each of the experimental groups (P < 0.001, Figure 1A); none of the groups displayed motor or other behavioral impairments, as indicated by the results of testing in an open field arena (Figure 1B).


Altered motivation masks appetitive learning potential of obese mice.

Harb MR, Almeida OF - Front Behav Neurosci (2014)

Overweight and obese mice show poor acquisition of food-rewarded pavlovian conditioned learning. (A) Body masses of control (CON; normal chow, n = 18), overweight (O/weight; low fat-high carbohydrate diet; n = 16) and obese mice (high fat-high carbohydrate diet, n = 16) at the start of experimentation. (B) Locomotor activity, measured in an open field arena, of CON, O/weight and Obese mice before behavioral testing commenced. (C) Relative number of CS+ approaches and CS- approaches (D) during each session; only CON mice displayed different conditioned responses (cf. Harb and Almeida, 2014), characterized as sign-tracking (ST, predominantly approached the CS+; n = 4), goal-tracking (GT, predominantly approached the US; n = 8), and intermediate-tracking (IT, alternated between CS+ and US with approximately equal frequency; n = 6). Autoshaping was monitored over 11 sessions; in each session, mice received 15 CS+ and 15 CS- presentations. (E) Time in min needed to complete successive autoshaping sessions. (F) Mean latency (s) to retrieve food reward during consecutive training sessions. Data are means ± s.e.m. ***In (A) denotes p < 0.001. *, **, ***In (E,F) indicate differences between CON and obese groups at p < 0.05, 0.01, and 0.001, respectively. †, ††, †††In (E,F) indicate differences between O/weight mice vs. CON and Obese mice at p < 0.05, 0.01, and 0.001, respectively.
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Figure 1: Overweight and obese mice show poor acquisition of food-rewarded pavlovian conditioned learning. (A) Body masses of control (CON; normal chow, n = 18), overweight (O/weight; low fat-high carbohydrate diet; n = 16) and obese mice (high fat-high carbohydrate diet, n = 16) at the start of experimentation. (B) Locomotor activity, measured in an open field arena, of CON, O/weight and Obese mice before behavioral testing commenced. (C) Relative number of CS+ approaches and CS- approaches (D) during each session; only CON mice displayed different conditioned responses (cf. Harb and Almeida, 2014), characterized as sign-tracking (ST, predominantly approached the CS+; n = 4), goal-tracking (GT, predominantly approached the US; n = 8), and intermediate-tracking (IT, alternated between CS+ and US with approximately equal frequency; n = 6). Autoshaping was monitored over 11 sessions; in each session, mice received 15 CS+ and 15 CS- presentations. (E) Time in min needed to complete successive autoshaping sessions. (F) Mean latency (s) to retrieve food reward during consecutive training sessions. Data are means ± s.e.m. ***In (A) denotes p < 0.001. *, **, ***In (E,F) indicate differences between CON and obese groups at p < 0.05, 0.01, and 0.001, respectively. †, ††, †††In (E,F) indicate differences between O/weight mice vs. CON and Obese mice at p < 0.05, 0.01, and 0.001, respectively.
Mentions: To address the hypothesis that appetitive learning is altered in overweight and obese individuals, we here applied the classical pavlovian conditioning paradigm to mice that differed in body mass, reflecting their maintenance on normal chow (NC) (CON, hereinafter referred to as “control mice,” N = 18), low-fat/high-carbohydrate (overweight, N = 16) or high-fat/high-carbohydrate (obese, N = 16) diets. Body weights differed significantly between each of the experimental groups (P < 0.001, Figure 1A); none of the groups displayed motor or other behavioral impairments, as indicated by the results of testing in an open field arena (Figure 1B).

Bottom Line: Eating depends strongly on learning processes which, in turn, depend on motivation.We found that (i) the rate of pavlovian conditioning to an appetitive reward develops as an inverse function of body weight; (ii) higher body weight associates with increased latency to collect food reward; and (iii) mice with lower body weights are more motivated to work for a food reward, as compared to animals with higher body weights.Notably, however, all groups adjusted their consumption of the different food types, such that their body weight-corrected daily intake of calories remained constant.

View Article: PubMed Central - PubMed

Affiliation: NeuroAdaptations Group, Max Planck Institute of Psychiatry Munich, Germany ; Neuroscience Domain, Institute of Life and Health Sciences (ICVS), University of Minho Braga, Portugal ; ICVS/3B's - PT Government Associate Laboratory Braga/Guimarães, Portugal.

ABSTRACT
Eating depends strongly on learning processes which, in turn, depend on motivation. Conditioned learning, where individuals associate environmental cues with receipt of a reward, forms an important part of hedonic mechanisms; the latter contribute to the development of human overweight and obesity by driving excessive eating in what may become a vicious cycle. Although mice are commonly used to explore the regulation of human appetite, it is not known whether their conditioned learning of food rewards varies as a function of body mass. To address this, groups of adult male mice of differing body weights were tested two appetitive conditioning paradigms (pavlovian and operant) as well as in food retrieval and hedonic preference tests in an attempt to dissect the respective roles of learning/motivation and energy state in the regulation of feeding behavior. We found that (i) the rate of pavlovian conditioning to an appetitive reward develops as an inverse function of body weight; (ii) higher body weight associates with increased latency to collect food reward; and (iii) mice with lower body weights are more motivated to work for a food reward, as compared to animals with higher body weights. Interestingly, as compared to controls, overweight and obese mice consumed smaller amounts of palatable foods (isocaloric milk or sucrose, in either the presence or absence of their respective maintenance diets: standard, low fat-high carbohydrate or high fat-high carbohydrate). Notably, however, all groups adjusted their consumption of the different food types, such that their body weight-corrected daily intake of calories remained constant. Thus, overeating in mice does not reflect a reward deficiency syndrome and, in contrast to humans, mice regulate their caloric intake according to metabolic status rather than to the hedonic properties of a particular food. Together, these observations demonstrate that excess weight masks the capacity for appetitive learning in the mouse.

No MeSH data available.


Related in: MedlinePlus