Effect of insulin and 2-deoxy-D-glucose on feeding and plasma glucose levels in the spiny mouse

Genetic variance contributes to ingestive processes: a survey of 2-deoxy-D-glucose-induced feeding in eleven inbred mouse strains

The feeding response following administration of the anti-metabolic glucose analogue, 2-deoxy-d-glucose (2DG), is conceptualized as an experimental model of glucoprivation, which may contribute to the understanding of inter-individual differences in glucose and carbohydrate intake and, ultimately, obesity. Although variation in the intake of several nutrients as well as food and water are known to be associated with genetic variation, it is not known whether 2DG-induced feeding is similarly genotype dependent. The present study therefore examined 2DG-induced feeding in mice of 11 inbred (A/J, AKR/J, BALB/cJ, CBA/J, C3H/HeJ, C57BL6/J, C57BL10/J, DBA/2J, SJL/J, SWR/J, 129P3/J) and one outbred (CD-1) strains across a wide range of previously determined effective 2-DG doses (200, 400, 600, 800 mg/kg) and test times (1-4 h). Orderly dose-dependent increases in 2DG-induced feeding occurred after all four doses in outbred CD-1 and inbred DBA/2J mice, across the three highest doses for BALB/cJ, SJL/J and 129P3/J mice, and across the two highest doses for CBA/J and AKR/J mice. Limited instances of 2DG-induced feeding were noted only at the highest dose in A/J and C3H/HeJ mice, or at a moderate dose in C57BL/6J mice. Further, the full 2DG dose range failed to alter food intake in C57BL/10J mice, and produced significant reductions in food intake in SWR/J mice. Food intake after 2DG doses of 200-600 mg/kg, but not 800 mg/kg, displayed significant cross-correlation, suggesting that large 2DG doses may recruit non-specific effects upon food intake. There was no correlation between food intake in the absence (vehicle baseline) of and presence of 2DG, suggesting that the regulation of glucose intake in non-challenged mice does not predict subsequent responses to glucoprivic challenge. The data demonstrate genotype-dependent variability in this glucoprivic response, and may provide the basis for the subsequent identification of trait-relevant genes.

Reproduction-related behaviors of Swiss-Webster female mice living in a cold environment

Based on a molecular neuroendocrine theory about cold environments, thyroid hormone levels, and liganded thyroid hormone receptor interference with estrogen receptor function, experiments were designed to test female mouse reproductive behaviors in the cold. Because natural seasonal temperature declines would usually be associated with decreased photoperiods and reduced food supplies, we combined cold temperatures with short days and metabolic challenge. The simplest hypothesis was that lordosis quotients would be significantly reduced as a result of cold temperatures. That hypothesis was denied. Instead, female approaches to the stud male declined. Because cold temperatures also led to significant reductions of activity in locomotor wheels, a straightforward reduction of activity could explain the female's behavior during mating tests. We suggest that cold temperatures accompanied by reduced photoperiod and reduced metabolic fuel can reduce overall activity in female mice, thus indirectly blocking untimely reproductive behaviors.

Reproduction-related behaviors of Swiss-Webster female mice living in a cold environment

Based on a molecular neuroendocrine theory about cold environments, thyroid hormone levels, and liganded thyroid hormone receptor interference with estrogen receptor function, experiments were designed to test female mouse reproductive behaviors in the cold. Because natural seasonal temperature declines would usually be associated with decreased photoperiods and reduced food supplies, we combined cold temperatures with short days and metabolic challenge. The simplest hypothesis was that lordosis quotients would be significantly reduced as a result of cold temperatures. That hypothesis was denied. Instead, female approaches to the stud male declined. Because cold temperatures also led to significant reductions of activity in locomotor wheels, a straightforward reduction of activity could explain the female's behavior during mating tests. We suggest that cold temperatures accompanied by reduced photoperiod and reduced metabolic fuel can reduce overall activity in female mice, thus indirectly blocking untimely reproductive behaviors.

Insulin affects dopamine overflow in the nucleus accumbens and the striatum

To better characterize the central nervous system response to peripheral insulin administration, male Sprague-Dawley rats were fitted with microdialysis probes in the nucleus accumbens (NAC; n = 23) and striatum (STR; n = 22). Awake intact rats were injected with either 0, 200, 400, or 600 mU regular insulin i.p. Dopamine overflow was measured for at least 2 h postinjection. In the NAC, four postinjection samples were collected once every 30 min. In the STR, eight postinjection samples were collected, once every 20 min. Dopamine baselines in the NAC and STR were 9.22 pg +/- 2.02 and 10.33 pg +/- 2.22 per sample, respectively. In the nucleus accumbens, dopamine release was significantly greater in the group treated with 600 mU insulin (203 +/- 38% of baseline at 30 min). In the STR, increased dopamine release was observed in the groups treated with 200 and 400 mU insulin, whereas a suppression of a dopamine release was observed in the group treated with 600 mU. These data demonstrate that the metabolic state induced by peripheral insulin injection causes dopamine metabolism to change in both the NAC and STR, and at least in part support the hypothesis that insulin may have reinforcing properties in its effect on NAC dopamine release.

Biotransformation in Egyptian spiny mouse Acomys cahirinus

The activities of several representative biotransformation enzymes were determined in male and female spiny mouse tissues. Cytochrome P450 monooxygenase activity toward benzo(a)pyrene was significantly greater in female spiny mouse intestine than in males. Activity toward benzphetamine in both sexes was high in the liver, with little activity in the kidney and intestine. Sulfotransferase activity was high in kidney and intestine of female spiny mice but undetectable in the same tissues in males. Hepatic glutathione S-transferase activity towards 1-chloro-2,4-dinitrobenzene in females was significantly higher than in males. UDP-Glucuronosyltransferase activity toward 1-naphthol in both sexes in the kidney was significantly higher than hepatic and intestinal activity. Intestinal N-acetyltransferase activity towards 2-aminofluorene and beta-naphthylamine was significantly greater in females than males. No consistent relation appeared to exist between biotransformation activities in spiny mouse and those in other related rodent species.

Drinking behavior in the spiny mouse (Acomys cahirinus) following putative dipsogenic challenges

Male spiny mice (Acomys cahirinus) were challenged with several putative dipsogenic stimulus conditions: hypertonic sodium chloride (NaCl), 24-h water deprivation, d,l-isoproterenol HCl, angiotensin II (AII) and polyethylene glycol (PEG), or control conditions, in within-subjects designs. Water intake and drinking pattern were monitored electronically in the home cage over a 2--6-h test period without food present, during the light portion of the L/D cycle. In addition, hematocrits were measured following several treatments and mean arterial blood pressure was monitored in response to several doses of AII. As expected, both water deprivation and hypertonic NaCl led to robust drinking with short latencies. PEG was also an effective dipsogen; while quite variable, latencies were often shorter than are typically reported for the rat. Isoproterenol induced a modest, but significant, dose-related drinking. Interference by AII's prominent pressor action might account, at least in part, for its relative ineffectiveness as a dipsogen. Comparisons are made with other rodent species similarly challenged.

Effect of exogenous insulin on meal patterns and stomach emptying in the spiny mouse

Male adult spiny mice (Acomys cahirinus) were acutely challenged with a single dose of regular insulin or saline vehicle SC; either food intake, meal frequency and meal duration, or stomach emptying were then measured. Meal frequency, as well as amount eaten, was significantly higher over a 6-hr period following both 10 and 30 U/kg of insulin than following vehicle injection. Meal duration remained essentially the same across all conditions. When 30 U/kg of insulin was administered either 15 min prior to, or immediately after, a solid food meal, stomach emptying (as measured by dry weight of recovered stomach contents) was accelerated relative to vehicle controls. These data are generally consistent with and extend the comparative literature suggesting a possible link between rate of stomach emptying and insulin-induced hyperphagia in some species.