Effects of androgens on body weight, feeding, and courtship behavior in the pigeon

HORMONES

AND BEHAVIOR,

Effects

5, 289-302 (1974)

of Androgens on Body Weight, Feeding, Courtship Behavior in the Pigeon

and

RICHARD J. PIETRAS and BERNICE M. WENZEL Department of Physiology and Brain ResearchInstitute, UCLA School of Medicine, Los Angeles, California 90024 Adult male pigeons, some intact and some castrated in adulthood, were housed in individual cages kept in an isolated room with temperature and lighting controlled. Weekly measurements were made of ad lib. food intake and body weight for 4 mo after surgery. Castration was followed by a significant depression in body weight and by initially depressed but then progressively enhanced feeding. Food deprivation elicited an increase in food intake proportional to body weight loss, but castrates consumed less food at IOO%, 90%, and 80% of ad lib. feeding weight than either intact birds or castrates treated daily with testosterone propionate (TP). Castrates gained weight and ate more than, controls in response to daily treatments (im) with TP (6 mg/400 g) or Sa-dihydrotestosterone (DHT, 6 mg/400 g), while androstenedione (15 mg/400 g) and androsterone (15 mg/400 g) were ineffective. Administration of 100 mg DHT (SC) to castrates produced a significant enhancement of body weight without elevating the level of food intake. The biological potency of these diverse androgens on male courtship behavior was reciprocal to that for weight-promoting potency. The results suggest that the structural requirements of the androgen molecule for promoting body weight differ from those for stimulating sexual behavior.

An influence of androgens upon body weight, feeding, and sexual behavior has been reported for the rat and a few other mammals(Anand, 1961; BelI and Zucker, 1971; Beyer and Komisaruk, 1971; Lisk, 1967). Because the digestive

and reproductive

systems of the pigeon

differ in various

respects from those of mammals, comparative studies on the influence of gonadal steroids upon its feeding and sexual behavior should prove useful in asessing the generality of the findings in the rat. The pigeon (CoZumbalivia) is an excellent subject for studiesof feeding behavior due to its pattern of brief feeding periods distributed throughout the daylight hours (Zeigler, Green, and Lehrer, 1971). Several features distinguish the avian digestive system and seemto be important in setting the pattern of food intake, Teeth are absent, and the gastric apparatus is subdivided into a glandular and muscular stomach. In addition, the pigeon has a crop which servesasa temporary food storageorgan (Farner, 1960). 289 Copyright @ 1914 by Academic Press, Inc. All rights of reproduction in any form reserved.

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The production and metabolism of gonadal hormones in the pigeon is not completely understood. As in the mammal, testosterone is the primary androgen in the male. The Leydig cells of the tests seem to be the principal site for the production of testosterone. It can be produced from the metabolism of cholesterol, progesterone, or androstenedione (Sturkie, 1965). The major biosynthetic pathway for testosterone in the Japanese Quail and in the White Leghorn chicken appears to be via progesterone, 17a-hydroxyprogesterone, and androstenedione (see Nakamura and Tanabe, 1972). The androgen metabolite, androsterone, has been isolated in the urine (Levi, 1963). In addition, the comb, wattles, coccygeal gland, and liver of chicks can readily transform testosterone to another metabolite, Sa-dihydrotestosterone (Gloyna and Wilson, 1969; Williams-Ashman and Reddi, 1971; Wilson and Gloyna, 1970). The present experiments sought to determine the role of these diverse gonadal androgens in the regulation of feeding behavior and body weight in the adult male pigeon. A parallel study to test the effect of these hormones upon the pattern of sexual behavior of the male was conducted to ascertain the biological specificity of the hormonal effects. METHODS Subjects Mature male pigeons (250-450 g) from an inbred colony of mixed stock (racing homers and public square pigeons) were kept in individual cages under controlled light and temperature (21°C) conditions. They were provided with a high protein, low-fat grain mixture containing milo, maise, peas, kaffu, corn, popcorn, wheat, vetch, and maple peas. An excess of food was provided and weighed out either daily or weekly to the nearest 0.1 g. Tap water was available ad lib. Thirty-six birds were adapted to laboratory conditions for at least 2 mo before the start of any experiments. Under Equithesin anesthesia (1 ml/400 g), 29 birds were gonadectomized while seven other birds were sham operated by exposing the testes. The day length was maintained on a winter light schedule of 10 hr to reduce the high levels of gonadotropin in plasma thought to result from castration (Nalbandov, 1967), and thereby to inhibit regeneration of gonadal tissue and any possible effects of high concentrations of gonadotropin. The general health of the birds was good throughout the experimental period. All birds were sacrificed at the conclusion of these experiments. Postmortem inspection revealed that no regeneration of testicular tissue had occurred. Injections activity

Dosages for all hormones were equated on the basis of their biological relative to testosterone in the capon’s comb response (see Dorfman

BEHAVIORAL

EFFECTS

OF DIVERSE

ANDROGENS

291

and Shipley, 1956). The dosage of testosterone used in most experiments here (6 mg/400 g) was beyond the normal physiological range, but was selected on the basis of observable behavioral effects in the pigeon in pilot studies (see the comparative biological effectiveness of various dosages of testosterone in expt. 3). Androsterone, 5a-dihydrotestosterone (DHT), and androstenedione (all from Sigma Chemical Co., St. Louis, MO) were dissolved in sesame oil after previous solution in a small volume of methylene chloride which was subsequently evaporated. Testosterone propionate (TP) and estradiol benzoate (EB) (both from Pfizer, New York) were also in sesame oil solution. Hormone solutions were injected alternately into right or left pectoral muscle, and the volume of administration varied from 0.5 ml for androsterone and androstenedione to 0.1 ml for all other injections. Equivalent volumes of sesame oil were injected into control birds. Data Analysis Since these animals varied considerably in body weight, amounts of food intake were also variable among individuals in the different groups. Standard errors of the arithmetic means of raw group data, therefore, were large. Representation of the raw data as such would mask significant differences between the groups. In order to depict average trends in a meaningful way, most of the data presented here were transformed to percentages as described below. The significance of differences among several means was ascertained by analysis of variance. The t test applied to the differences between experimental and control means. Linear regression analysis was used to determine the linear correlation between two sets of data (Campbell, 1967).

RESULTS Experiment

1

It has been reported that the basal metabolism of a castrated male chicken is lower than that of an intact male (Mitchell, Card, and Haines, 1927). This observation indicates that gonadal hormones may play an important role in the regulation of metabolism and, in turn, in the determination of body weight and feeding. To evaluate their importance, the food intake and body weights of 16 birds, nine castrates and seven sham controls, were monitored over a period of 16 wk after surgery. Each parameter was measured once per week. The results are presented in Fig. 1. For each bird, body weights during the postoperative weeks are expressed relative to mean body weight in the week preceding surgery; feed consumption during each

292

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POSTOPLRATIVE WEEKS

Fig. 1. Comparison of postoperative body weight/preoperative body weight ratio with food intake (g)/body weight ratio for castrate and control groups over a 16-wk postoperative period.

weekly period is expressedrelative to body weight recorded at the beginning of each weekly measurementperiod. The comparison of group mean body weights in the upper portion of Fig. 1 shows that gonadectomy induces a significant decreasein body weight relative to controls (P< 0.001). The variation in feeding after castration depicted in the lower portion of Fig. 1 is more diphasic. Over the entire postoperative observation period, the difference in food consumption between experimental and control birds was not significant, apparently due to the fact that the castrates consumed less food than controls during the first 7 wk (I’< 0.001) and then consumed more than controls from week 8 to week 16 (P< 0.05). During this latter period, the castrates ate more than the controls and the difference in their body weights was not significant (P< 0.10). These results indicate, therefore, that androgens secreted by the testes play a significant role in the regulation of body weight and feeding in the male pigeon.

BEHAVIORAL

Experiment

EFFECTS

OF DIVERSE

ANDROGENS

293

2

Prolonged periods of food deprivation in the pigeon are known to be followed by an increased responsiveness to food manifested not only by readiness to eat (Megibow and Zeigler, 1968) but also in the increasing amounts of food consumed with increasing body weight loss (Zeigler, Green, and Lehrer, 1971). The present experiment examined the relationship between weight loss and consummatory response in the male pigeon in various hormonal states to obtain a measure of any motivational effect of androgen on food intake. Responsiveness to food was determined at three levels of body weight, viz., lOO%, 90%, and 80% of ad lib. feeding weight. Since order effects were found to be insignificant in previous studies (Megibow and Zeigler, 1968; Zeigler, Green, and Lehrer, 1971) the birds were tested at each of the deprivation levels in order of successively decreasing weight. Testing commenced after 12 hr of deprivation to insure sufficient emptying of the crop. With the exception of a 30-min food consumption period during the test session at each level of weight loss, food deprivation was complete. A period of total deprivation ranging from 2 to 3 wk was required to produce a 20% weight loss. Three groups of six birds each were tested: intact males, gonadectomized males and gonadectomized males treated with 6 mg TP/400 g body weight. Testing with the castrates began 30 days after surgery. The ad lib. feeding weight of both treated and untreated castrates was the same at the start of these experiments. Since the maximal effect of TP injections was found in pilot experiments to occur on the third day of administration and to decline thereafter with continued treatment, TP injections were given only at intervals of 2.5-3 days during the deprivation period. The termination of each treatment interval was timed to correspond with the day of testing. Figure 2 presents cumulative food consumption data for the three groups of birds at each of the three levels of weight loss. Food intake is expressed relative to body weight and is plotted against the loss in body weight. As reported previously (Zeigler, Green, and Lehrer, 1971) food consumption increases significantly with increasing body weight loss in all groups (P < 0.05). The castrate group increased consumption proportionately less than either the intact or the TP-treated castrate groups (I’< O.lO), and the latter groups did not differ from each other. The trend of these data suggests that castration reduces the consummatory response, and that the response returns to normal levels after the administration of TP. These data also serve to highlight the role of the crop sac in regulating the pattern of feeding behavior in the pigeon. Linear regression analysis of the relationship between the ratio food intake/body weight, and the percentage decrease in body weight shows that the relation is significantly linear in all

294

PIETRAS AND WENZEL 14-

I2 -

2I

I 100

I 90

I 80

% AD LIB FEEDING WEIGHT

Fig. 2. The relation of body weight loss to food intake (g)/body weight ratio in intact, castrate, and TP-treated castrate male pigeons. The points on the graph at lOO%, 90%, and 80% of ad lib. feeding weight are 4.3 f 0.3, 7.8 f 0.7, and 12.0 f 0.8 for the intact males, 4.3 f 0.9, 7.9 + 0.6, and 12.7 + 0.7 for castrate males treated with 6 mg/400 g TP, and 3.2 f 0.2, 6.6 f 0.3, and 10.7 f 0.5 for castrate males. Six birds were present in each test group.

groups, where r is 0.95 or greater for the intact, TP-treated castrate, and castrate groups, and the slopes are 0.39, 0.41, and 0.37, respectively. The pigeon’s compensatory response to food deprivation is considered to be related to the presenceof the crop (Zeigler, Green, and Lehrer, 1971). Under ad lib. feeding conditions, movement of food stored in the crop to the stomach is irregular and is predominantly determined by the condition of the remainder of the gastric apparatus (Farner, 1960). During deprivation, however, the crop empties and food intake becomesproportional to body-weight loss. Since this relationship is qualitatively the samebut quantitatively lessin the castrated bird, it appearsthat androgensmay influence the motivation for feeding in the pigeon. Experiment 3 Having established that androgens play a significant role in the regulation of body weight and feeding in the pigeon, we next investigated the biological potency of four natural androgens,viz., androsterone(15 mg/400 g), androstenedione (15 mg/400 g), DHT (6 mg/400 g), and TP (0.5 mg1400g,

BEHAVIORAL

295

EFFECTS OF DIVERSE ANDROGENS

1 mg1400g, and 6 mg1400g). Eighteen gonadectomized birds were divided randomly into three equal groups. For each hormone, injections were given daily over a period of 7 days. After each week of experimental treatments, sesameoil was administered to all groups to allow body weights and feeding to return to pretreatment levels (a period averaging 3 days) before starting the next experimental series. Since weight and feed parameters were recorded before and after each experimental series,each bird servedas its own control. Three experimental treatment series were given. Group 1 received androsterone and 6 mg/400 gTP; group 2 received androstenedione and 0.5 mg/400 gTP; and group 3 received DHT and 1 mg/400 g TP. The experiment was conducted over a period of 5 wk from postoperative day 28 to day 63. With all hormones tested, peak responseswere observed at or within 4 days subsequentto the start of the experimental series.Food intake and body weight for each bird were transformed as in expt. 1 and then expressed relative to control values on the same bird. In Fig. 3, the mean maximal percentagechange in body weight and the correspondingpercentagechangein food intake (transformed as indicated above) are plotted against each other for each experimental group. In terms of maximal changein body weight, only the 6-mg TP and DHT groups were significantly different from controls (P< 0.05). In addition, these

0

101 -

z g. .

cm.

l-l

100 -

i

-I 99

0.5

no

TP

ANDROSTERONE

I

I

1

SO

100

110

FEED:

TP

cw 1 4

zj p

J

ANDROSTENEDIONE

HORMONE/CONTROL

I

120

130

140 X 100

Fig. 3. Effects of androsterone, androstenedione, DHT, and various concentrations of TP on the relation between body weight and feeding (means f SE) in castrate birds.

296

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groups were not significantly different from each other. As for the maximal increase in feeding, these groups again differed significantly from controls (P< 0.02). There was a significant increase in food intake in the group given 1 mg TP (P < 0.05) but none of the other hormone treatments was effective. Among the diverse androgens used in these experiments, therefore, only TP and DHT produced significant increases in body weight and feeding at the dosage levels selected. Experiment

4

The stimulatory effect of DHT was investigated further in this experiment. A lOO-mg dose of DHT crystals (i.e., small fused pellets) suspended in oil was applied subcutaneously at the back of the neck in nine male pigeons 30-40 days after castration. Data from other studies (see Dorfman and Shipley, 1956) in which compacted androgen crystals were implanted subcutaneously suggest that the daily rate of absorption of hormone is low, and that the duration of action is long. A similar group of four castrates served as a control group and received applications of oil subcutaneously. The results over a 9-day postadministration period are displayed in Fig. 4. Post-DHT body weights are expressed as a percentage of pre-DHT weight, and food intake is shown relative to daily body weight. As the upper graph in Fig. 4 indicates, treatment with DHT induced a significant increase in body weight with respect to the control group (P< 0.001). Furthermore, daily means in the DHT group did not fluctuate significantly. DHT appears to facilitate an elevated steady state in body weight. Surprisingly, the results also show that food intake in the DHT group was not significantly different from that of controls indicating that DHT applied subcutaneously stimulates a significant increase in body weight without altering the level of food intake. This latter result, however, may be more attributable to the high degree of variability in food intake in both the DHT and the control groups than to a specific anabolic effect of the hormone. Experiment

5

The pattern of male courtship behavior which appears in most birds (Adkins and Adler, 1972; Barfield, 1965; Hutchison, 1967; Komisaruk, 1967; Levi, 1963; Marshall, 1955) offers another opportunity to examine the biological specificity of diverse androgens. In the present experiments, male courtship behavior was measured in terms of the number of bow-coo responses performed with respect to a specified stimulus during a lo-min period of observation. In each bow-coo response, the male is observed to stand erect and then bow to a horizontal position while emitting a cooing sound. Chasing the stimulus was also observed, and these observations were recorded in terms of the percentage of males displaying chasing behavior.

BEHAVIORAL

EFFECTS

OF DIVERSE

297

ANDROGENS

DHT

36

I

DAYS AFTER DHT TREATMENT

Fig. 4. The variation in body weight and feeding of castrate single subcutaneous application of 100 mg DHT/400 g in oil.

birds

subsequent

to a

All birds were tested in a testing cage 45 X 45 X 60 cm, visually isolated from other pigeons. Tests were given in the middle of the light portion of the daily cycle. The stimulus birds came from three groups, viz., intact receptive (i.e., egg-laying) females, gonadectomized males (SO-64 days postcastration), and gonadectomized males treated with 100 gg EB/400 g for 2-4 days before the test session. Each experimental bird interacted with each stimulus bird in the appropriate group on a different day. Nine experimental groups of birds were studied as listed in Table 1. The number of animals per group, the stimulus bird, and the respective response measurements are shown for each of the nine test groups. In test groups 3-7, castrated males (50-64 days post surgery) were treated for 2-4 days preceding the test session with the hormone indicated. Comparing the results of group 1 with group 2, it is obvious that castration initially produced a sharp decrease (P< 0.001 for week 1) and eventually a complete loss of the observed components of courtship behavior in response to a receptive female. These results are consistent with those of

298

PIETRAS

AND TABLE

Courtship

1 Intact

1

Responses of Intact, Castrate, and Hormone-treated Pigeons to Different Behavioral Stimuli.

No. of animals

Group

WENZEL

6

Stimulus Intact Female

Bow-coo Responses (Mean + SE(n) 60+

35 (18)

)

Male

Range 20-l 10

Chasing Responses (% display) 100

2 Castrates postoperative Week 1

6

4+

O-24

61

Week 4

6

0~0

(18)

o-4

11

Week

8

6

O+O

(18)

0

0

Week

16

6

OtO

(18)

0

0

lO(l8)

3 Castrates 6 mg/400

g TP

6

8 i- 4 (18)

O-26

4 Castrates 6 mg/400

g DHT

6

O+O

(18)

o-2

(12)

5-32

50

(21)

22-82

78

Ok0

(15)

0

20

0~0

(18)

o-3

11

30+5

(15)

5-47

47

5 Castrates 15 mg/400 androsterone

50 0

g 4

13+2

6 Castrates 15 mg/400 g androstenedione

I

51+

7 Castrates 100 j&400

5

g EB

8 Intact

6

Castrate male

9 Intact

5

Castrate male 100 rsl 400 g EB

5

Hutchison (1967) for the dove. Treatment of castrates with 6 mg TP (group 3) or 15 mg androsterone (group 5) engendered a partial recovery of the behavior which was not significantly different from that observed in the first postcastration week in group 2. Treatment with 6 mg DHT (group 4) was ineffective. Treatment with 1OOpg EB (group 7) had no effect on the bow-coo response but, as previously demonstrated in the quail (Adkins and Adler, 1972), it did bring about a recovery of the chasing response in some birds. The most striking effect was observed after the administration of 15 mg androstenedione (group 6), which induced a nearly complete recovery of courtship behavior comparable to group 1 (P < 0.70). Consistent with studies

BEHAVIORAL

EFFECTS

OF DIVERSE

ANDROGENS

299

in other avian species (Adkins and Adler, 1972; Hutchison, 1967; Komisaruk, 1967), these results confirm that male courtship behavior involving stereotyped visual displays is androgen dependent. The courtship displays disappear within 30 days of castration, are partially restored with daily injections of TP or androsterone, and are nearly completely restored to normal levels with androstenedione at the dosage levels indicated. The ineffectiveness of DHT, however, suggests that the behavior is also specific to specific androgens. Groups 8 and 9 were designed to investigate the specificity of the stimulus. The intact male showed little response to a castrate but did display considerable courtship behavior in response to a castrate treated with 100 pg EB. Frequency of the bow-coo response to the latter stimulus was significantly less than in group 1 (P< 0.05) but did not differ from groups 3, 5, or 6. The basis for these observations is not clear. Recent studies with the quail (Adkins and Adler, 1972) show that functionally castrated males treated with EB display both male and female copulatory patterns but none of the appetitive sexual behavior (i.e., breast rubbing and gentle pecking) seen in females. In our stimulus group, however, the EB-treated castrates were both hostile and evasive to the courtship of the intact male. It is also possible that male courtship in the pigeon, as in male mammals (Michael and Keverne, 1968; Signoret, 1970), may be initiated by pheromones secreted by the female or, as in group 9, pheromones secreted by the EB-treated male castrate. With regard to this possibility, it is pertinent to note that olfactory acuity in the pigeon is greater than has been previously assumed (Wenzel, 197 1).

DISCUSSION The results of these studies are consistent with reports of the stimulatory action of androgens on body weight and food consumption in the adult rat (Bell and Zucker, 1971). Furthermore, the effect in the pigeon appears to be specific to specific androgens. At selected dosages, DHT and TP are equally effective in enhancing body weight while androsterone and androstenedione are ineffective. In terms of structure-function relationships, it is worthwhile to note that the biological potency of these four androgen metabolites varies with the group substitution at position 17 of the steroid structure. Both DHT and TP have a polar /3-hydroxy group at this position while androsterone and androstenedione have the less polar ketone group. There are other notable structural differences but none consistent with weight-promoting potency. Castrated pigeons treated with testosterone propionate eat more than controls (expt. 2). Recent experiments in the rat suggest that hormonal modulation of food intake may occur in the brain (Wade and Zucker, 1970). Our experiments, however, indicate that enhancement of body weight by

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PIETRAS

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androgen is not solely dependent upon the level of food intake since subcutaneously applied DHT at a selected dosagelevel induces a considerable increment in body weight without altering food intake. Androgens have, in fact, been reported to increase basal metabolism in mammalian and avian species without changing the respiratory quotient (Kenyon et al., 1940; Mitchell, Card, and Haines, 1927). Androgen-dependent enhancement of the transport of inorganic phosphate, amino acids, and sugarsinto various tissues (Riggs, 1970) may well account for these changesin metabolism. In the mammal, androgensmay also be associatedwith cell proliferation and growth in androgen-sensitivetissues(Williams-Ashman and Reddi, 197l), generalized muscular hypertrophy (Papanicolaou and Falk, 1938), and vascular bed distribution (Edwards et al., 1941). Although androgensmay have specific neural effects on the regulation of food consumption, our data and the other available evidence suggests that actions on the peripheral utilization of foodstuffs and on energy utilization must be given equal consideration. The androgen-dependentcourtship behavior of the male pigeon is also characterized by wide variations in the responseto different androgens at selected dosages.The biological potency, however, is reciprocal to that for weight-promoting potency. Androstenedione (15 mg/400 g) was found to be most effective in restoring male courtship behavior in castrates while androsterone (15 mg/400 g), TP (6 mg/400 g), EB (100 pg/400 g), and DHT (6 mg/400 g) were progressively lesseffective. Several recent reports strongly suggestthat hormonal effects on sexual behavior are directly mediated at the neural level in both mammalian and avian species(Barfield, 1965; Hutchison, 1971; Komisaruk, 1967; Lisk, 1967; Ross et al., 1971). It is necessary, therefore, that peripherally administered androgensfirst crossthe blood-brain barrier before functional expression at the neural level can occur. Limited available evidence on the characteristics of membrane permeation of steroids shows that the introduction of polar groups to the primary steroid structure progressively and drastically lowers the rate of membrane transport (Scheuplein and Blank, 1971; Scheuplein et al., 1969). In consideration of these findings, we would expect the least polar androgen of those tested, androstenedione,to have the highest rate of transport into the brain. Our data show that it is also the most potent stimulator of courtship behavior. In those hormone pairs where equal dosagelevels were used(i.e., androstenedioneand androsterone; DHT and TP), it appearsthat the order of biological potency may be more reflective of neural accessthan neural effect. Further experiments with equal dosagelevels of all hormones are needed to determine if this is a more general characteristic of androgen effectivenessat the neural level. Our experiments show that androgens play an important role in the pigeon in the regulation of body weight, feeding, and sexual behavior. It is clear that the structural characteristicsof the androgen molecule important for stimulating body weight and feeding responsesdiffer from those determining

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male courtship behavior. The diversity of the predominant weight-promoting action of DHT and the predominant courtship-promoting action of androstenedione with subtle variations in steroid structure cannot be fully elucidated from these experiments. The findings, however, point to the potential value of natural androgenic hormones in the area of poultry meat production and reproduction and indicate the need for further study of the avian endocrine system.

ACKNOWLEDGMENTS This research was supported by U.S.P.H.S. Mental Health 5 TO1 MH06415-17. We thank Drs. C. M. Szego and L. J. Rausch for and discussions in the preparation of this manuscript.

Training Grant useful comments

REFERENCES Adkins,

E. K., and Adler, N. T. (1972). Hormonal control of behavior in the Japanese Quail. J. Comp. Physiol. Psychol. 81, 27-36. Anand, B. K. (1961). The nervous control of food and water intake. Physiol. Rev. 41, 677-708. Barfield, R. J. (1965). Induction of aggressive and courtship behavior by intracerebral implants of androgen in capons. Amer. Zool. 5, 203. Bell, D. B., and Zucker, 1. (1971). Sex differences in body weight and eating: organization and activation by gonadal hormones in the rat. Physiol. Behav. 7, 27-34. Beyer, C., and Komisaruk, B. (1971). Effects of diverse androgens on estrus behavior, lordosis reflex and genital tract morphology in the rat. Horm. Behav. 2, 217-225. Campbell, R. C. (1967). Statistics for Biologists. Cambridge Univ. Press, London. Dorfman, R. I., and Shipley, R. A. (1956). Androgens, Biochemistry, Physiology, and Clinical Significance. Wiley, New York. Edwards, E. A., Hamilton, J. B., Dutley, S. Q., and Hubert, G. (1941). Cutaneous vascular and pigmentary changes in castrate and eunuchoid men. Endocrinology 28, 119-124. Farner, D. S. (1960). Digestion and the digestive system. In A. J. Marshall (Ed.), Biology and Comparative Physiology of Birds. Vol. 1. New York, Academic Press. Gloyna, R. E., and Wilson, J. D. (1969). Comparative study of the conversion of testosterone to 17p-OH-5a-androstan-3-one (dihydrotestosterone) by prostate and epididymis. J. Clin. Endocrinol. Metab. 29, 970-976. Hutchison, J. B. (1967). The initiation of courtship behavior by hypothalamic implants of testosterone propionate in castrated doves. Nature (London) 216, 591-592. Hutchison, J. B. (1971). Effects of hypothalamic implants of gonadal steroids on courtship behavior in barbary doves. J. Endocrinol. 50, 97-l 13. Kenyon, A. T., Knowlton, K., Sandiford, I., Koch, F. C., and Lotwin, G. (1940). A comparative study of the metabolic effects of testosterone propionate in normal men and women and in eunuchoidism. Endocrinology 26, 26-32. Komisaruk, B. R. (1967). Effects of local brain implants of progesterone on reproductive behavior in doves. J. Comp. Physiol. Psychol. 64, 219-224. Levi, W. (1963). The Pigeon. Levi Publ. Sumter, S.C.

302 Lisk,

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