PARENTAL BEHAVIOR 



1331 



wlu'thcr the milk pressure is res))()nsibl(' for 

 the amount of nursing or vice versa, or 

 whether there is a I'eciprocal relation be- 

 tween the two. Bartliolomew and Hoel 

 (1953), for ('xam})le, found that mother 

 Alaska fur seals stay at sea for 3 to 10 

 days, then ashore with their pups for 1 to 

 3 days. As the season progresses (after the 

 birth of the young), the females spend 

 about the same time ashore at each visit, 

 but the time spent at sea between visits in- 

 creases. Bartholomew and Hoel suggested 

 that the mothers may return when the 

 mammary glands are full, and the diminu- 

 tion of the rate of secretion, or the increase 

 in the pup's demands, could cause the fe- 

 male to stay at sea longer as the season pro- 

 gresses. Similar observations have been 

 made on many mammals (Krumbiegel, 

 1955) . 



In many cases a correspondence is ob- 

 served between the occurrence of lactation 

 and of nursing behavior in response to 

 physiologic stimulation. Allan and Wiles 

 (1932) found that cats hypophysectomized 

 during pregnancy (which, of course, pro- 

 duced no milk) paid no attention to the 

 young, and made no attempt to nurse them. 

 Cannon and his co-workers found that sym- 

 pathectomized dogs and cats, if they were 

 made pregnant very soon after sympathec- 

 tomy, might lactate normally after parturi- 

 tion, and in such cases would nurse their 

 young. On the other hand, if parturition did 

 not occur until some time after sympathec- 

 tomy {e.g., 6 months postoperatively) the 

 mammary glands failed to develop, lacta- 

 tion was not established, and no attempts 

 were made by the mothers to nurse their 

 young. In the case of a cat which had 3 kit- 

 tens 20 months after sympathectomy, the 

 animal withdrew from the kittens as soon as 

 possible, even after the kittens were forcibly 

 put to her nipples to suckle (Cannon, New- 

 ton and Bright, 1929; Cannon, 1930; Can- 

 non and Bright, 1931). Labate (1940) sym- 

 pathectomized rabbits, then allowed them 

 to mate and delivered the young by cesarian 

 section. In these animals, lactation was nor- 

 mal, as was nursing behavior. 



In other cases, however, it is clear that 

 nursing behavior does not necessarily de- 

 pend on a distended condition of the mam- 



mary gland, or on the presence of milk 

 secretion. Hain (1935) found that estrone 

 injected into lactating rats caused the ces- 

 sation of suckling behavior, although the 

 involution of the mammary glands did not 

 occur until after the suckling behavior had 

 stopped. Weichert and Kerrigan (1942) 

 similarly found that estrone injected into 

 rats caused parental care to become spo- 

 radic, the pups occasionally being scattered 

 over the cage and inadequately warmed. 

 Intervals between nursing episodes became 

 less and less frequent as the estrone injec- 

 tions continued. These authors also had the 

 impression that the decrease of lactation 

 was a secondary effect of the behavioral 

 disturbance in the mother. Obias (1957) 

 found that rats hypophysectomized during 

 gestation delivered young at the normal 

 time. All nursed their young, although all 

 the young died because no milk was pro- 

 duced. Collip, Selye and Thomson (1933) 

 hypophysectomized lactating rats and found 

 that, although the mammary glands re- 

 gressed, maternal behavior, including nurs- 

 ing, was not impaired and the young con- 

 tinued to attempt to suckle until they died. 

 Eayrs and Baddeley (1956), who anesthe- 

 tized the nipples by cutting the dorsal roots 

 of their spinal nerves, found that lactation 

 stojjped altogether, although the rats con- 

 tinued to attempt to nurse their young, and 

 the anesthetized nipples were vigorously 

 suckled. 



Nelson and Smelser (1933) induced lac- 

 tation in male guinea pigs by injecting es- 

 trone, followed by pituitary extracts. Ani- 

 mals lactating as a result of such treatment 

 refused to nurse young, even though the 

 young animals vigorously tried to suckle. 



Although there are many suggestive ob- 

 servations indicating a relationship between 

 mammary engorgement and the motivation 

 to nurse the young, it is apparent that this 

 cannot be the only factor, and, in some spe- 

 cies, may not even be an important factor. 

 The exact contribution, if any, which mam- 

 mary engorgement makes to the regulation 

 of nursing behavior, and the manner in which 

 it may interact with other physiologic fac- 

 tors and with previous experience, remain to 

 be investigated. 



