Does mating prevent monogamous males from seeking other females? A study in prairie voles (Microtus ochrogaster).

Male prairie voles form pair bonds under laboratory conditions, but show a variety of mating tactics in nature. We tested them in the laboratory to determine if their decision to reproduce with a single or multiple females is related to how they process sensory information from females. Three groups of mated males were tested for their attentiveness toward two females and their odors. Males given a choice to investigate a box holding their mate or a box holding a sexually receptive female spent more time with the box of the sexually receptive female than that of their mate. Similar results were found when females were removed and replaced by their odors. However, males did not attend preferentially to the sexually receptive female under all circumstances. When given a choice between a sexually unreceptive and a sexually receptive female, males did not display a difference in their attentiveness. Furthermore, males tested in presence of their mate were more attentive to the odor of the sexually receptive female than males tested in presence of a sexually unreceptive female. The data suggest that access to the mate's sensory cues may influence male's decision to seek females other than his mate.

Cafeteria diet increases fat mass and chronically elevates lumbar sympathetic nerve activity in rats.

Obesity causes sympathetic activation that promotes atherosclerosis, end-organ damage, and hypertension. Because high-fat induced weight gain in rats elevates plasma leptin at 1 to 3 days after the onset of calorie-dense diets, we hypothesized that diet-induced overfeeding will increase sympathetic activity within 1 week after the onset of the regimen. To test this, we continuously measured sympathetic activity and blood pressure before and during the onset of diet-induced obesity using a high-calorie, cafeteria-style diet. Female Wistar rats, in which radiotelemeters had been implanted for continuous monitoring of lumbar sympathetic activity, mean arterial pressure, and heart rate, were randomly assigned to groups that received regular chow (control) or a cafeteria diet for a period of 15 days. This short-term, cafeteria-feeding regimen caused modest but nonsignificant increases in body weight (P=0.07) and a doubling of brown and white adipose tissue (P<0.01). The increases in fat mass were accompanied by elevations in plasma leptin (P<0.001) but no change in glucose. Overall heart rates and blood pressure were higher in cafeteria rats compared with controls (P<0.05). Cafeteria diet-induced weight gain caused increases in lumbar sympathetic nerve activity that became significant by the 12th day of the diet (P<0.001). These data show, for the first time, that the high-fat, cafeteria-style diet stimulates sustained increases in lumbar sympathetic neural drive in rats.