Neurological and stress related effects of shifting obese rats from a palatable diet to chow and lean rats from chow to a palatable diet.
ABSTRACT Rats exposed to an energy rich, cafeteria diet overeat and become obese. The present experiment examined the neural and behavioural effects of shifting obese rats from this diet to chow and lean rats from chow to the cafeteria diet. Two groups of male Sprague Dawley rats (n=24) were fed either highly palatable cafeteria diet or regular chow (30% vs. 12% energy as fat) for 16 weeks. Half of each group (n=12) was then switched to the opposing diet while the remainder continued on their original diet. The effects of diet switch on the response to restraint stress were assessed and rats were euthanised nine days after diet reversal. After 16 weeks of cafeteria diet, rats were 27% heavier than controls. Rats switched from chow to cafeteria diet (Ch-Caf) became hyperphagic and had increased dopamine D1, D2 and tyrosine hydroxylase mRNA expression in the ventral tegmental area (VTA) compared to rats switched from cafeteria to chow (Caf-Ch). Caf-Ch rats were hypophagic with significant reductions in white (16%) and brown (32%) adipose tissue mass, plasma leptin (34%) and fasting glucose (22%) compared to rats remaining on the cafeteria diet (Caf-Caf). Caf-Caf rats had an elevated plasma corticosterone response to restraint stress compared to Ch-Caf rats indicating that acute but not chronic consumption of palatable cafeteria diet may protect against stress. Caf-Ch rats had increased corticotropin releasing hormone mRNA expression in the dorsal hypothalamus compared to Ch-Ch rats implying that removal of the palatable diet activated the HPA axis. The results were discussed in terms of the links between palatability of diet, obesity and stress.
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ABSTRACT: 1. Adult male hooded rats which were offered a mixed, high energy diet for 90 days were hyperphagic and became significantly obese compared to chow-fed control rats. Fasting plasma insulin and glucose levels were initially elevated in the experimental rats, but later in the 90 day period were similar to control levels. 2. When the high energy foods were withdrawn after 90 days and just chow was available, the obese rats maintained the elevated body weights. The obese rats were initially hypophagic, but chow intakes rapidly reached control levels. Plasma insulin and glucose levels were similar in both groups, suggesting that the persisting obesity may not be associated with altered insulin resistance. 3. Five weeks after withdrawal of the 'fattening' diet, half of the experimental rats were offered restricted access to chow for 27 days to reduce their weights to control levels. When the rats were again given free access to chow, they returned to the previously elevated weight. 4. Eighteen weeks after withdrawal of the 'fattening' diet, the experimental rats had significantly elevated body weights and fat stores. The elevated body weight was not simply due to increased growth because, although the experimental rats had slightly more lean body mass than the control rats, the increase in fat was not related to body size.The Journal of Physiology 02/1980; 298:415-27. · 4.38 Impact Factor
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ABSTRACT: Thirty-three percent of the adult American population over the age of 20 is obese. Many attempts to treat this increasingly occurring problem have had poor results. Both achieving weight loss and maintaining weight loss are difficult; however, current treatments appear more effective in achieving weight loss than in maintaining weight loss. The current study followed a cohort of patients to analyze weight maintenance and predictors of weight maintenance in a 26-week, formula-based, very low calorie diet program. The study population consisted of a consecutive sample of 145 overweight patients who entered a very low calorie diet program and were contacted at 54 months after program entry. For men, the average initial weight loss at program termination was 27.2 kg (22% of original weight) and for women, 19.3 kg (18.8% of original weight). At 54 months after program entry, the average maintained loss was 5.1 kg (4.3% of original weight), at a cost of $630 per kg of long-term weight loss. There was no significant difference in maintained weight loss between men and women. Twenty-six percent of patients maintained a medically significant weight loss of 10% of entry weight. Subjects who exercised regularly maintained an average of 9.6 kg compared with 1.3 kg for nonexercisers. Those who attended the program for a longer period, and exercised more, maintained their weight better. The 54-month weight loss was similar to that seen at 30 months but markedly less than that at 18 months. Very low calorie diet programs have limited long-term success that may not justify the risk of adverse effects and high costs. Longer program attendance and continued exercise are associated with improved weight maintenance. Evaluation of dietary programs should be based on a sample of consecutive patients followed for a minimum of 2 years after program completion.The Journal of family practice 10/1995; 41(3):231-6. · 0.67 Impact Factor
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ABSTRACT: The mesocorticolimbic dopamine (DA) system is thought to comprise part of a neural substrate participating in behavioral reinforcement. While much emphasis has been placed on mesolimbic terminal field activity, the existence of somatodendritic DA release has also been established. In the present study, the release of endogenous DA from the ventral tegmental DA cell body region of freely moving rats was measured, using in vivo chronoamperometry after presentation of several environmental stimuli. While presentation of a 9-s moderately intense light stimulus did not significantly modify DA release, palatable food presentation (FD), 3 min of social interaction (SI) with another male rat and a 3-min tail-pinch (TP) produced an increase in electrochemical signal, suggesting an increase in somatodendritic DA release. Mean peak signal increases (calibrated in nM DA concentration) were 104, 135 and 161 nM after FD, SI and TP stimulus, respectively. After daily presentation of all four stimuli, one of four DA active drugs was given s.c. When compared with preinjection baseline, apomorphine (APO) caused a decrease while nomifensine (NOMI), cocaine (COC) and haloperidol (HALO) caused an increase in electrochemical signal. When TP was given 30 min after drug injection, APO, NOMI and COC suppressed the TP-induced signal increase compared with the predrug response. HALO, on the other hand, did not alter TP-induced DA release. These data support the hypothesis that the cells of origin of the mesocorticolimbic system release dendritic DA after physiologically relevant stimuli.Brain Research 10/1994; 656(1):59-70. · 2.88 Impact Factor