1204 



HANDBOOK OF PHYSrOLCJGY 



NEUROPHYSIOLOGY II 



In the goats studied in Andersson's laboratory, 

 drinking was accompanied by antidiuresis which 

 combined to gi\e the animal a phenomenal excess of 

 water within the liody (g, lo). Their results suggest 

 the localization of a thirst mechanism in the rostro- 

 dorsomedial portion of the hypothalamus. Destruc- 

 tion of this region reduced or aljolished drinking in 

 dogs (ii). A more precise type of localization has 

 been reported by Stevenson et al. (8i) and Monte- 

 murro & Stevenson (64, 65) who find that discrete 

 bilateral lesions in the lateral hypothalamic area re- 

 duce or even abolish drinking in rats. They regard 

 this as a drinking "center' analogous to the lateral 

 feeding mechanisms described by Anand (6). A gen- 

 eral confirmation of their results was published by 

 Morrison & Mayer (67), with certain differences, 

 including lesions of a larger size than those of Monte- 

 murro. A report by Gilbert suggests a location out- 

 side the hypothalamus for the thirst mechanism, but 

 further study is needed since he has reported that 

 lesions of the subcommissural organ and the injection 

 of extracts of this organ both have the same effect in 

 reducing drinking, where one would suppose on 

 theoretical grounds that the two procedures should 

 give opposite results (36). 



A state of persistent drinking, analogous to hyper- 

 phagia and independent of diabetes insipidus, does 

 not appear to have been disco\'ered. If there are 

 inhibitory mechanisms for drinking, either they are 

 not localized well enough to be destroyed by experi- 

 mental lesions or else the lesions tiius tar created are 

 not in the critical regions. If the brain does, indeed, 

 contain osmoreceptors, one can imagine how they 

 might at one time inhibit urine production, induce 

 drinking and limit food intake because the body is 

 relati\'ely low on water. At another time they could 

 allow urine to flow without inhibition, prevent drink- 

 ing and facilitate feeding reflexes when bodily reser- 

 voirs of water are relatisely full and food is lacking 

 (37). The interaction of neurons responding to avail- 

 ability of water with those sensitive to conditions of 

 temperature regulation might offer the beginning of 

 simple discriminations which could ije refined and 

 made more specific h\ scn.sory input from other parts 

 of the body, including taste, distance receptors and 

 the innervation of the digestive tract. In other words, 

 the permutations and combinations possible among 

 only a half dozen different reactions and mechanisms 

 known to be related to feeding and drinking may 

 well include most of the conditions under which both 

 food and water intake are known to respond to 

 changes in the animal and its environment. Experi- 



mental data suggest both such an interrelationship 

 (67, 82), and also a certain degree of independence of 

 the appetite and thirst mechanisms (65, 67). 



LOCOMOTOR ACTIVITY 



Integration of feeding and drinking with regulation 

 of other factors in energy exchange was noted above. 

 In conclusion, acti\'ity should be mentioned also as 

 one of the mechanisms assisting with water and food 

 intake. Laboratory animals with food either present 

 or supplied at intervals may have little need for forag- 

 ing. This, of course, is an artificial situation, for under 

 natural conditions the higher animals all mo\e about 

 in the process of getting their day's rations. Activity 

 precedes eating (90), while partial starvation in- 

 creases spontaneous activity (80, 91). The observa- 

 tions that either an increase (57) or a decrease (43) 

 in activity may follow appropriate lesions of the 

 hypothalamus, therefore, seem to complete the chain 

 of reactions in which the body correlates the variables 

 of energy exchange and at the same time utilizes 

 each of the several variables to facilitate the regula- 

 tion of the others. For this purpose, at least, a regula- 

 tion can be defined as the end result of the integrative 

 actions of the nervous system in the control of a 

 physiological xariaiale — in particular, a variable ex- 

 changed between the organism and its environment. 



SUMM.-VRY 



Progress in this field within the past 15 years has 

 led to the following conclusions and hypotheses. 



a) Water and energy exchange can be measured 

 under conditions where rcliabilitv and accuracy are 

 possible, and where the regulation of these variables 

 by the body can be studied. 



/)) Lesions in the hypothalamus may alter the regu- 

 lation of water excretion, water intake, food intake, 

 body temperature, spontaneous activity or body 

 weight. 



f) Stimulation of the lupothalamus or perfusion 

 with certain solutions will activate at least some of the 

 mechanisms which ha\e been identified in animals 

 with experimental lesions. 



d) These observations suggest the hypothesis that 

 the hypothalamus is an integrator of regulations con- 

 cerned with water and with energy exchange. 



e) The integration is affected by sensory input into 

 the brain from the organs of special sensation and 



