FiODY TEMPERATURE AND FOOD AND WATER INTAKE 369 



may thus be concerned with the coordination ofahmentary motor activity. 

 Ascending tracts, on the other hand, may be thought to transmit the urges 

 to eat and to drink to higher organized parts of the central nervous system. 

 This could also explain why descrete lesions in the lateral hypothalamus 

 are often seen to cause not only aphagia but also adipsia (Teitelbaum, 

 1961 ; Morgane, 1961a) in spite of the fact that polydipsia as a conse- 

 quence of stimulation is obtained from a more medial part of the hypo- 

 thalamus, the perifornical region (Andersson and McCann, 1955b). The 

 importance of the hypothalamus for the regulation of food intake would 

 then be essentially to modify the hunger '' drive '' by determining the 

 degree of satiety. 



24 



8 



16 



24 



8 Tiny: of day 



Fig. 7. Diminished release of PBP^^ into plasma during preoptic warming, 



followed by an increased release and a rise of body temperature on cessation 



of preoptic warming. Sixty microcurie of carrier free P^^ given at the arrow. 



(From Andersson, Ekman, Gale, and Sundsten, 1962c.) 



Although stimulation and ablation experiments help to delimit regions or 

 " centres " in the hypothalamus of importance for the control of food and 

 water intake, such experiments generally do not reveal how changes in the 

 internal and external environments may influence the activity and reactivity 

 of these " centres ''. Since cellular dehydration seems to be a crucial 

 factor eliciting thirst, it is not unreasonable to suggest that the urge to 

 drink may originate from a similar " osmoreceptor " mechanism that is 

 regulating the release of antidiuretic hormone from the neurohypophysis 



