Detection of Minute Temperature Transients by Thermosensitive Neurons in Ants

The antennae of leaf-cutting ants are equipped with sensilla coeloconica that house three receptor neurons, one of which is thermosensitive. Using convective heat (air at different temperatures), we investigated the physiological characteristics of the thermosensitive neuron associated with the sensilla coeloconica in the leaf-cutting ant Atta vollenweideri. The thermosensitive neuron very quickly responds to a drop in temperature with a brief phasic increase (50 ms) in spike rate and thus classifies as cold receptor (ambient temperature = 24°C). The short latency and the brief phasic response enable the thermosensitive neuron to follow temperature transients up to an estimated frequency of around 5 Hz. Although the neuron responds as a cold receptor, it is extremely sensitive to warm stimuli. A temperature increase of only 0.005°C already leads to a pronounced decrease in the resting activity of the thermosensitive neuron. Through sensory adaptation, the sensitivity to temperature transients is maintained over a wide range of ambient temperatures (18–30°C). We conclude that the thermosensitive neuron of the sensilla coeloconica is adapted to detect minute temperature transients, providing the ants with thermal information of their microenvironment, which they may use for orientation.

Central action of acidic fibroblast growth factor in feeding regulation

A phasic increase in activity similar to that of acidic fibroblast growth factor (aFGF) was detected in the cerebrospinal fluid of rats after feeding or after an intraperitoneal injection of glucose. This FGF-like activity in the cerebrospinal fluid was bioassayed in two systems: depression of the feeding response of Hydra and DNA synthesis-stimulating activity in BALB/c 3T3 cells after fractionation on a heparin affinity column. Dynamic feeding-related changes in activity of aFGF, basic FGF, and other growth factors were detected by both bioassay systems. Intracerebroventricular microinfusion of aFGF suppressed food intake in rats. Central infusion of inactivated aFGF, or peripheral administration of aFGF, in doses equivalent to or higher than those administered centrally was without effect. Electrophoretically applied aFGF specifically suppressed the activity of glucose-sensitive neurons in the lateral hypothalamus. Glucose-insensitive neurons were only slightly affected. The results suggest that aFGF may participate in the regulation of feeding at the level of the central nervous system.

Variations in evaporation and body temperatures during sleep in man

The thermal balance in man was investigated during nocturnal sleep in neutral and warm environments (from 32 to 39.5 degrees C, 45%rh). Changes of body temperatures and skin evaporation were continuously monitored throughout the whole night. In neutral conditions (32 and 34 degrees C) body temperature and skin evaporation decreased during the night, following the circadian rhythm deltaT sk = -0.34 degrees C; deltaT re = -0.52 degrees C;deltaE = -12 W-m-2. In warm conditions, body temperatures and evaporation remained steady. Marked fluctuations of body temperatures and evaporation occurred synchronously with the rapid eye movement (REM) periods. Each REM period induced phasic increase of Tsk reaching +2 degrees C in some cases, with a cessation of evaporation. Tre showed upward and downward rhythmical waves synchronously with REM sleep occurrence. The nocturnal variations of thermal balance were characterized by two rhythms: a basal circadian rhythm and superimposed on it a rhythm conditioned by occurrence of REM sleep every 80–90 min. The phasic changes of body temperatures and evaporation only appeared with REM's. The results suggest that the nervous integrative function conditioning the patterns of sleep, conditions also the phasic cyclic changes of thermoregulatory function.