Pavlovian conditioning of gentoo penguins (Pygoscelis papua) to underwater sound.

Penguins are known to react to underwater noise, but it is unknown if they make use of sound cues while diving. We tested whether captive gentoo penguins (Pygoscelis papua) can pair underwater sounds with food through Pavlovian conditioning. Two seconds after an underwater sound (a 1-4 kHz sweep with a received level of 130 dB re 1 µPa RMS) was played back to one or two unidentifiable penguins, a dead fish was flushed into the water close to the underwater sound source. After 8 weeks of conditioning, one or more individual penguins approached the sound source after sound emission in 78.3% out of 230 trials. In 43 intermixed control trials with no sound preceding the fish, the penguins did not show any reaction in the pre-flush period. In an additional experiment, three identified penguins reacted to the sound in 66.7-100% out of 30 trials, with 0% reactions in five intermixed control trials. Our experiments demonstrate that gentoo penguins can be conditioned to underwater sound and that they associate underwater sounds with food. It is possible that gentoos, as well as other species of penguins, use sound cues while foraging. This may explain why penguins have been observed to react negatively to anthropogenic noise.

Adiponectin receptors in human adipose tissue: effects of obesity, weight loss, and fat depots.

OBJECTIVE: To investigate the presence and regulatory properties of the adiponectin receptors, AdipoR1 and AdipoR2, in human adipose tissue (AT) and in isolated human adipocytes. RESEARCH METHODS AND PROCEDURES: The effect of obesity, weight loss, and gender on expression of AdipoR1 and AdipoR2 was investigated in subcutaneous AT. The influence of fat distribution on these receptors was investigated in paired samples of subcutaneous and omental AT. Gene expression of these receptors was quantified by reverse transcriptase-polymerase chain reaction. RESULTS: AdipoR1 mRNA levels were approximately 10-fold higher than adipoR2 in both AT fragments and in isolated adipocytes. AdipoR1 expression was lower in AT from obese subjects (p < 0.05) compared with that from normal-weight subjects, and AdipoR1 displayed a negative correlation with BMI (r = -0.53, p < 0.01). In obese subjects, weight loss (approximately 12 kg) increased AdipoR1 expression by 80% in AT (p < 0.01). Concerning regional differences, AdipoR1 showed significantly lower expression in omental AT than in subcutaneous AT (p < 0.01). No gender difference was observed in the expression of these receptors. In human preadipocyte cultures, AdipoR1 expression was not induced during the differentiation process, whereas AdipoR2 was induced by 5-fold (p < 0.05). DISCUSSION: AdipoR1 is highly expressed in human AT, indicating that adiponectin may have biological effects in AT in an autocrine/paracrine manner. AdipoR1 expression in AT is reduced in obese subjects and is increased after weight loss. Thus, it can be suggested that adiponectin might have reduced biological effects in AT due to low levels of adiponectin receptors in obese subjects and in omental adipocytes, which may further aggravate the negative metabolic effect of low levels of adiponectin characterizing the obese state.