1346 



HORMONAL REGULATION OF BEHAVIOR 



of the back. Lehrman concluded that the 

 prolactin injections had induced regurgita- 

 tion- feeding behavior through two main 

 effects: it had induced the crop to become 

 engorged by an accumulation of the de- 

 generating epithelial cells which the birds 

 regurgitate to their young (Beams and 

 Meyer, 1931) ; and, by suppressing gonadal 

 activity (Riddle and Bates, 1933; Nal- 

 bandov, 1953) it had eliminated sexual and 

 aggressive behavior which would interfere 

 with the parental behavior (Carpenter, 

 1933a, b). The fact that emetic responses 

 in the pigeon are easily conditioned to ex- 

 ternal stimuli (Riddle and Burns, 1931) 

 may be related to the fact that doves with 

 previous breeding experience direct their 

 behavior toward the head of the stimulus 

 squab in such a way as to stimulate it to 

 perform the movements which cause the 

 parents to regurgitate food to it, whereas 

 inexperienced birds show no such behavior. 



Now, this experiment does not demon- 

 strate conclusively that prolactin does not 

 have any direct effects on the central nerv- 

 ous system which might be relevant to the 

 elicitation of parental feeding behavior. It 

 does show, however, that some of its pe- 

 ripheral effects play an important role. 

 Prolactin has metabolic relations with some 

 other tissues, w-hich are not shared by nerve 

 tissue. Sgouris and Meites (1952) found 

 that prolactin is inactivated (rendered in- 

 capable of inducing the development of the 

 pigeon crop) by being incubated in vitro 

 with slices of mammary gland, pigeon crop, 

 ovary, or liver, all of which are known 

 to be affected by prolactin in vivo. Slices 

 of muscle (which is not known to be 

 changed by prolactin) did not inactivate 

 prolactin solutions. Further, brain slices had 

 no effect. 



It should be noted that the distinction 

 between "central" and "peripheral" effects 

 is not a rigid one, and that the behavioral 

 effect of the hormone is not conceivable 

 except in terms of a network of interre- 

 lationships between central and peripheral 

 influences. For example, it is not known 

 whether the antigonadotrophic effect of pro- 

 lactin is exerted directly on the pituitary 

 gland, or on the hypothalamus. Further, is 

 the disappearance of sexual behavior be- 



cause of the suppression of gonad secretion 

 caused by changes in peripheral structures, 

 or in central ones? Finally, even in cases 

 where peripheral effects are the most im- 

 portant ones, they can only act by altering 

 the activities of central structures. 



Nest-building behavior in rats. Hypo- 

 physectomy or thyroidectomy causes strik- 

 ing increases in the amount of nest-building 

 activity in rats (Richter, 1937, 1941), in 

 spite of the fact that these operations cause 

 decreased "general activity," as measured 

 in an activity wheel (Richter and Wislocki, 

 1930) . What is the basis of this effect? 



It will be recalled that Kinder (1927) 

 found that rats tended to do more nest- 

 building at lower temperatures than at 

 higher, and that similar results were ob- 

 tained in mice by Koller (1956). This, plus 

 the fact that thyroidectomy, which reduces 

 body temperature (Richter, 1941), also 

 causes increased nest-building, led Richter 

 and others to suggest that nest-building be- 

 havior is in part a thermoregulatory mech- 

 anism, and that its regulation is closely re- 

 lated to factors affecting body temperature. 

 There is a great deal of evidence in support 

 of this view. 



Richter (1941) found that thyroidecto- 

 mized or hypophysectomized rats would die 

 if the ambient temperature was kept only 

 a few degrees below normal room tempera- 

 tures, unless the rats had nesting material 

 available, and could build nests. Stone 

 and Mason (1955) tested hypophysecto- 

 mized and intact rats in an apparatus in 

 which the rats could rest in either of two 

 chambers, which were kept at different tem- 

 peratures. Temperatures varied from about 

 45°F. to about 95°F. The hypophysecto- 

 mized rats selected the warm box sig- 

 nificantly more often than did the controls. 



Koller (1956) shaved the hair from the 

 bodies of mice whose nest-building be- 

 havior had been measured. In all cases, the 

 amount of nest-building on the next night 

 after the shaving was higher than on the 

 preceding night. Here, too, the amount of 

 nest-building is apparently related to the 

 body's need for heat regulation. In this 

 connection, it may be noted that tempera- 

 ture preferences have been related to hair 

 density in a quite different experimental 



