PARENTAL BEHAVIOR 



1343 



3. Hormone Secretion as a Conditioned 

 Response 



It is possible for the secretion of a hor- 

 mone to occur as a response to a conditioned 

 stimulus. 



Grachev (1952) inserted a catheter into 

 one mammary gland of a goat, and found 

 that when he milked the other mammary 

 gland, milk was ejected through the cathe- 

 ter. He then arranged to have a bell ring 

 starting 15 seconds before the beginning 

 of milking, and continuing through the 

 milking session. After 18 such pairings of 

 the bell and of the milking stimulus, the 

 sound of the bell, without any accompany- 

 ing milking stimulus, elicited an ejection of 

 milk from the catheterized gland similar to 

 that usually caused by the milking of the 

 other gland. It is well known to dairy 

 workers that milk ejection can occur in 

 response to stimuli normally associated with 

 the preparations for milking, such as the 

 rattling of buckets, the washing of the 

 udders, etc. (Ely and Petersen, 1941). Clini- 

 cal reports indicate that lactating human 

 mothers may eject milk in response to 

 stimuli such as the sound of the baby's 

 crying (Newton and Newton, 1948j, the 

 sound of the nurse opening the door to 

 bring the baby into the mother's room 

 (Waller, 1938), and other stimuli associated 

 with the anticipation of putting the baby 

 to the breast (Newton and Newton, 1950; 

 Campbell and Petersen, 1953). 



The conditioning of anterior pituitary 

 secretions is more difficult to demonstrate, 

 and would not be expected to occur in the 

 same form as the conditioning of posterior 

 pituitary secretion, since the nature of the 

 neurohumoral link between the hypothala- 

 mus and the anterior pituitary is such that 

 the interval between external stimulus and 

 hormonal response might be on the order 

 of hours or fractions of an hour, rather 

 than, as in the elicitation of oxytocin se- 

 cretion from the posterior pituitary, on the 

 order of minutes or fractions of a minute. 

 Nevertheless, Freud and Uyldert (1948a) 

 suggest that the superiority of the ma- 

 ternal care given to adopted young rats, 

 and the higher survival rate of the young, 

 when the foster mothers had had suckling 

 experience, compared with those which had 



borne young without being allowed to suckle 

 them (Uyldert, 1943, 1946), is evidence of 

 a conditioned elicitation of lactation. As 

 I indicated earlier (see above p. 000), the 

 data as presented do not demand such an 

 interpretation, but the possibility is one 

 which should be investigated. Craig (1913) 

 and Whitman (1919) reported that doves 

 reared solely by human keepers, or by fos- 

 ter parents of other species, might, when 

 mature, lay eggs in response to stimulation 

 by a human hand, or by a courting male 

 of the foster species. In this case, we are 

 undoubtedly dealing with some form of 

 conditioning of the secretion of gonado- 

 trophic hormones to external stimuli, but 

 the nature of this conditioning and the 

 course of its development are entirely ob- 

 scure. 



4. Parental Behavior and Refleiiy Induced 

 Hormone Secretion 



It is clear from the preceding discussion 

 that there exists a well established anatomic 

 and physiologic basis for the control of 

 endocrine secretion by the nervous system, 

 that this control in fact exists, and that it 

 is therefore possible for an extensive variety 

 of external stimuli, including stimuli pro- 

 vided by other members of the animal's 

 species, to elicit different types of hormone 

 secretion. Many of these stimulus-response 

 relationships, involving the stimulation of 

 hormone secretion, are important features 

 of the physiologic basis of parental be- 

 havior and of the establishment of parent- 

 young relationships. 



We have pointed out that external stimuli 

 provided by the male may induce endocrine 

 changes in many female birds, which in 

 turn induce nest-building behavior. In some 

 cases, stimuli provided by the nest con- 

 tribute, in turn, to the stimulation of egg- 

 laying. Stimuli coming from the egg may 

 then elicit the secretion of the pituitary 

 hormone (s) W'hich maintain the bird in a 

 state of readiness to incubate. After the 

 eggs hatch, the presence of the young con- 

 tributes to the maintenance of the physio- 

 logic condition appropriate for parental 

 care of the young, and to the suppression of 

 the secretion of those pituitary hormones 



