1308 



HORMONAL REGULATION OF BEHAVIOR 



mals eventually delivered young normally, 

 but did not build nests or i^luck any of their 

 fur. 



Richter (1937; Richter and Eckert, 1936) 

 reported that gonadectomy and adrenalec- 

 tomy both produced very small increases in 

 nest-building behavior in rats. On the other 

 hand, Roller (1956) reported that removal 

 of the gonads of male and nonpregnant 

 female mice caused no change in their nest- 

 building behavior: the low-level nest-build- 

 ing behavior ("sleeping nests") character- 

 istic of such animals before treatment con- 

 tinued unchanged. 



In contrast to the failure of gonadectomy 

 to affect the level of nest-building be- 

 havior in nonpregnant mice, the striking in- 

 crease in nest-building behavior during 

 pregnancy ("brood-nests") is definitely un- 

 der gonadal control (Roller, 1952, 1956). 

 Injection of progesterone into intact or 

 gonadectomized female mice very quickly 

 (after 2 or three daily injections of 1.5 I.U. 

 each) induced a marked increase in the 

 amount of nesting material used per night, 

 on the same order as the increase which oc- 

 curs naturally during pregnancy (from 

 about 10 to 15 gm. to about 50 to 60 gm. ) . 

 Note that this effect of progesterone did not 

 require previous priming with an estrogen. 

 Large doses of estrone (200 I.U. per animal 

 per day) caused no increase in nest-building 

 activity in spayed female mice ; on the con- 

 trary. Roller's graphs suggest a slight but 

 consistent depression of nest-building ac- 

 tivity. If the same treatment is given to 

 intact adult female mice, the same slight 

 depression of nest-building activity occurs, 

 but when the injections are discontinued 

 after a 10-day treatment period, a marked 

 increase in nest-building activity is seen 

 (from about 8 gm. to about 20 gm.). It 

 seems likely that this increase in nest-build- 

 ing activity is a result of the secretion of 

 endogenous progesterone stimulated by the 

 estrone injections. 



An important finding in Roller's work is 

 that male mice, whether intact or castrated, 

 cannot be made to build "brood nests" {i.e., 

 increase the amount of nest-building activ- 

 ity) by treatment with progesterone or with 

 an estrogen. This sex difference is in con- 

 trast to the effects of hypoiihysectomy or 



thyroidectomy in rats, which are the same 

 in males as in females. 



A relationship also exists in the do- 

 mestic rabbit between progesterone and 

 nest-building behavior, but it seems to be 

 quite different from that which Roller dem- 

 onstrated in the mouse. Rlein (1952, 1956) 

 found that removal of the corpus luteum 

 during pregnancy would induce rabbits to 

 show immediate nest-building behavior, in- 

 cluding plucking of fur. Removal of the 

 gravid uterus was followed by involution of 

 the corpus luteum, with subsequent nest- 

 building behavior (Zarrow, Sawin, Ross 

 and Denenberg, 1960). Hammond (in Rlein, 

 1952) found that pseudopregnant rabbits 

 often build a nest during the involution of 

 the corpus luteum (after about 16 days of 

 pseudoprcgnancy). If the uterus and cervix 

 of such a rabbit are removed, the corpus 

 luteum undergoes involution, and the nest is 

 built, after 24 to 29 days instead of after 16 

 days. These data seem to indicate that nest- 

 building behavior in the female rabbit oc- 

 curs as a result of, or in association with, the 

 cessation of progesterone secretion, rather 

 than being stimulated by progesterone, as in 

 the mouse. We may note here that, in a 

 normal breeding cycle, the characteristic 

 nest-building behavior of the pregnant 

 mouse starts suddenly about the 4th or 5th 

 day of pregnancy (Roller, 1956), whereas 

 in the rabbit nest-building occurs just be- 

 fore or just after parturition (Sawin and 

 Crary, 1953) . 



Fisher ( 1956) has induced nest-building 

 behavior (and other aspects of maternal be- 

 havior) in rats by local injection of minute 

 amounts of a testosterone salt (sodium tes- 

 tosterone sulfate) directly into the hypo- 

 thalamus. At the time of this writing, only 

 a preliminary report of Fisher's work is 

 available, in which he reports the occurrence 

 of nest-building behavior in 19 of 130 male 

 rats tested in this manner. Fisher's descrip- 

 tion leaves no doubt that strongly motivated 

 behavior of various types, normally ma- 

 ternal, was induced by these injections, but 

 since this hormone does not normally cause 

 such behavior on systemic injection, it is 

 not yet possible to state what contribution 

 these observations make to an understand- 

 ing of the normal relationships between 



