Nesfatin-1, a fragment of the nucleobindin 2 (NUCB2) protein was described as an agent reducing food intake. However, its wide distribution in the brain suggests additional functions. We assumed that nesfatin-1 may affect also the energy expenditure, therefore we measured duration of food intake, core body temperature, locomotor activity and heart rate of male rats (250-300g) for 48h by telemetry, after icv administration of 25 pmol nesfatin-1 (n=10-12) at the beginning of the dark phase. Body weight, food and water intake were measured daily. One week before the experiment, a cannula was inserted into the lateral ventricle under anesthesia with ketamine (50mg/kg) and xylazine (15mg/kg). At the same time, VitalView biotelemetry emitters were implanted into the abdominal cavity. Telemetric data were collected in every min and calculated as sum ±s.e.m, or mean±s.e.m. Statistics were performed using two way RM-ANOVA. Nesfatin-1 reduced the duration of nocturnal food intake at the beginning of the dark phases (effect of treatment: F(1,9)=4.63, P<0.05). Food intake had a circadian rhythm (effect of time: F(11,99)=10.5, P<0.01), but the amplitude was smaller in treated animals (treatment x time interaction: F(11,99)=3.06, P<0.01). There was a reduction in food and water consumption on the first day and a compensation on the second day (food intake: effect of time: F(1,21)=4.66, P<0.05, treatment x time interaction: F(1,21)=6.09, P<0.05, water intake: effect of treatment: F(1,9)=6.1, P<0.05, effect of time: F(1,21)=5.2, P<0.05, tendency for treatment x time interaction: F(1,21)=4.8, P<0.056). Nesfatin-1 treatment elevated core body temperature immediately after injections (effect of treatment: F(1,9)=7.85, P<0.05). The most marked difference between groups was observed during the light phases of the 48 h observation period, since the circadian curve has been flattened (effect of time: F(11,99)=10.4, P<0.01). Heart rate and locomotion did not change. To elucidate morphological base of effect of nesfatin-1 on temperature regulation, we tested if cold (4 °C for 2 h) induces neuronal activation (Fos immunoreactivity) in nesfatin-1/NUCB2 (nesfatin)-positive neurons in the brain. Control animals were kept at room temperature. Cold activated nesfatin-positive neurons were present in many thermoregulatory areas of the hypothalamus and the brainstem. In the hypothalamic paraventricular nucleus Fos-nesfatin double labeled neurons colocalised with prepro-thyrotropin-releasing hormone (pTRH). pTRH also colocalised with nesfatin in the nucleus raphe pallidus and obscurus. These nuclei are known to act as sympathetic premotor neurons regulating heat production in brown adipose tissue and vasoconstriction in the skin. In summary, nesfatin has a longer effect than it was known before, and it influences the energy homeostasis not only by reducing food intake, but also by increasing the body temperature.