Inhibition of airlicking in thirsty rats by cooling the preoptic area

Abstract

THIRSTY rats lick avidly and persistently at a stream of air flowing through a drinking tube¹, behaviour which is not dependent on the previous experience of drinking water through a drinking tube² or on olfactory cues³. The most plausible explanation for the rewarding property of airlicking is that it is a result of evaporative cooling of the orolingual region. Heating and humidifying the air so as to decrease its cooling power reduces airlicking⁴. In addition, tongue cooling alone is rewarding for thirsty rodents⁵, and cold water has a greater satiating effect on water intake than warm water⁶. These observations seem to indicate that because airlicking leads to tongue cooling, it thereby reduces thirst and the reduction of thirst reinforces airlicking. Airlicking cannot be mediated entirely by tongue temperature receptors, however, because lingual denervation by bilateral section of the lingual, chorda tympani and one branch of the glossopharyngeal nerves has no influence on airlicking⁷. It is not clear whether central stimuli that affect water drinking and satiation will similarly influence airlicking. Temperature-sensitive neurones are located in the preoptic area (POA) and hypothalamus⁸, and since cooling of the POA reduces water intake in thirsty animals⁹, we tried to determine if cooling of the POA reduced airlicking. We found that acquisition of airlicking behaviour was completely blocked by POA cooling in naive animals and reduced about 50% in experienced animals.