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M J Baum

Publications and source records attributed to M J Baum.

At least 73 records · Page 4Linked to original sources
PubMed1991

Estradiol binding in the sexually dimorphic nucleus of the preoptic/anterior hypothalamic area of adult male ferrets and in the equivalent region of females.

A large number of estradiol-concentrating cells were visualized by autoradiography in a subpopulation of large neurons located in and around the sexually dimorphic male nucleus of the preoptic/anterior hypothalamic area (MN-POA/AH) of castrated male ferrets and in a comparable dorsal portion of the POA/AH of ovariectomized females. Considerably fewer estradiol-labelled cells were seen in the non-dimorphic ventral POA/AH nucleus of both sexes. Estrogen binding in cells in or around the MN-POA/AH may contribute to the formation of this sexually dimorphic nucleus in fetal males and may mediate specific estrogen-dependent behavioral functions in adulthood.

Animals↗
PubMed1991

Reciprocal relationships between pulsatile androgen secretion and the expression of mating behavior in adult male ferrets.

The pulsatile secretion of androgen was similar over a 12-hr period in breeding male ferrets implanted with jugular catheters which either achieved an intromission with an estrous female or received no socio-sexual contact. This negative result contrasts with the previous demonstration (Carroll, Erskine, and Baum, 1987, Endocrinology 121, 1349-1359) of a significant, delayed rise in mean plasma androgen concentrations in breeding male ferrets 5-12 hr after mating. Males used in that previous study had lower initial mean plasma levels of androgen and smaller testis diameters than the present males. We therefore asked whether differences in circulating androgen levels, characteristic of males in different phases of the seasonal breeding cycle, might affect the expression of mating behavior. Castrated males given 0, 0.2, 2.0, or 5.0 mg/kg of testosterone propionate (TP) showed dose-related increases in the expression of different components of sexual behavior, including neck gripping, mounting, and intromitting. Surprisingly, intromissive performance was significantly better in intact breeding males than in castrates given even the highest dosage of TP. These results suggest that ferrets' mating performance may vary with seasonal variations in androgen availability, and that the ability of males to exhibit a postcoital increase in the testicular secretion of androgen may be limited to the beginning or end of the breeding season, when circulating levels of androgen are relatively low. Mating-induced increments in androgen secretion at these times may enhance subsequent reproductive success by facilitating males' intromissive capacity, which is required for the induction of ovulation and optimal sperm transport in female partners.

Animals↗
PubMed1991

Sex difference in whole-body androgen content in rats on fetal days 18 and 19 without evidence that androgen passes from males to females.

The whole-body content of androgen (testosterone + 5 alpha-dihydrotestosterone) was significantly higher on Fetal Days 18 and 19 in male than in female rats; androgen content was equivalent in the two sexes at other fetal ages, including Days 16, 17, 20, and 21, and prior to parturition on Fetal Day 22. These results partially corroborate previous data of Weisz and Ward (Endocrinology 1980; 106:306-316), who measured testosterone in pooled plasma from rat fetuses and suggest that androgens contribute to masculine brain sexual differentiation only briefly during fetal life. No significant differences in whole-body androgen content were observed among groups of females situated in utero between 0, 1, or 2 males on each side (contiguous male model) or among groups of females with 0, 1, or 2 or more males located caudally (on the cervical side) in the same uterine horn, regardless of whether combined data from Fetal Days 17-22 or only Fetal Days 18 and 19 were considered. These results provide no evidence that androgens from males reach female fetuses in the same uterine horn.

Androgens↗
PubMed1991

Differential regulation of brain aromatase by androgen in adult and fetal ferrets.

The contribution of androgens to the regulation of aromatase activity (AA), measured by quantifying the in vitro formation of [3H]estrone from 19-[3H]hydroxyandrostenedione precursor, was studied in equivalent microdissected brain regions of adult and fetal ferrets. In adulthood, AA was similar in the bed nucleus of the stria terminalis, medial (M) and lateral (L) preoptic area (POA), medial (MA) and lateral amygdala (LA), ventromedial hypothalamus (VMH), and parietal cortex of gonadectomized males and females given no concurrent steroid treatment. Daily sc injections of the androgen dihydrotestosterone propionate significantly stimulated AA in MPOA, MA, and VMH of adult males and in MA of females; a similar trend was seen in MPOA and VMH of females. By contrast, no evidence of androgenic regulation of AA was obtained in these three brain regions microdissected from fetuses killed on embryonic day 35 (E35; 41-day gestation). Transplacental administration of the antiandrogen flutamide beginning on day E24 failed to affect AA in MPOA, LPOA, MA, LA, or parietal cortex, although this treatment significantly reduced AA in bed nucleus of the stria terminalis of fetal males. The results suggest that the responsiveness of aromatizing enzymes to androgenic induction is similar in several subcortical brain regions of adult ferrets of both sexes. In breeding males such an action of androgen may augment the neural production of estrogen, which has previously been implicated in the control of sexual behavior and the feedback regulation of LH secretion. By contrast, androgen apparently contributes minimally to the regulation of AA in brain regions of fetal ferrets, particularly in the MPOA, in which a sexually dimorphic nucleus differentiates in males around E37 in response to estrogen produced locally.

Androgens↗
PubMed1990

Effects of lesions of a sexually dimorphic nucleus in the preoptic/anterior hypothalamic area on the expression of androgen- and estrogen-dependent sexual behaviors in male ferrets.

The male nucleus of the preoptic/anterior hypothalamic area (MN-POA/AH) is a sexually dimorphic structure present in male, but not in female ferrets. Ovariectomized female ferrets given increasing dosages of estradiol benzoate (EB) normally run faster towards a stud male in an L-maze (i.e. become more proceptive). In two separate experiments, only gonadectomized males with bilateral damage to the MN-POA/AH following large or small electrolytic lesions approached stud males more quickly in response to EB. By contrast, males which received sham lesions, unilateral large POA/AH lesions, or bilateral lesions which missed the MN-POA/AH on at least one side failed to show EB-induced reductions in approach latencies in pre- or post-operative tests. Males with large POA/AH lesions also displayed significant post-operative decrements in masculine sexual behaviors during treatment with a high dose of testosterone propionate (TP). Less severe, but statistically significant deficits in masculine coital performance were also observed in males with small lesions which damaged the MN-POA/AH bilaterally; however, the ability of these males to achieve intromissions appeared normal. Together, these results suggest that the MN-POA/AH of the male ferret exerts an inhibitory influence on estrogen-dependent proceptive responsiveness, but play only a minor role in the control of masculine coital behavior.

Animals↗
PubMed1990

Ontogeny of the sexually dimorphic male nucleus in the preoptic/anterior hypothalamus of ferrets and its manipulation by gonadal steroids.

A sexually dimorphic nucleus exists in the dorsal region of the ferret preoptic/anterior hypothalamic area (POA/AH), and is called the male nucleus of the POA/AH (MN-POA/AH) because it is found only in males. Development of the MN-POA/AH was studied in male ferrets, and for comparison a sexually nondimorphic ventral POA/AH nucleus was studied in both sexes. The MN-POA/AH was conspicuous in males as early as embryonic day 37 (E37) of a 41-day gestation, and its volume increased until postnatal day 56 (P56). No nucleus was present in the dorsal POA/AH of females at any age. The densities and average somal areas of cells in the dorsal POA/AH were similar in males and females at E33, before the MN-POA/AH could be visualized. However, at E37 and E41 dorsal cells were greater in density and/or somal area in males than in females, accounting for the appearance of a nucleus in males at these ages. To insure that the dorsal POA/AH nucleus seen in males at E37 and E41 was the presumptive MN-POA/AH present in adult males, pregnant ferrets were given progesterone and either implanted subcutaneously (s.c.) with testosterone (T) or ovariectomized and implanted s.c. with the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), on day 30 of gestation. As predicted from previous studies in which subjects were sacrificed in adulthood, formation of a dorsal POA/AH nucleus was promoted in female ferrets by T, and blocked in males by maternal ovariectomy and ATD treatment for animals sacrificed at E41. Much evidence suggests that behavioral sexual differentiation is accomplished in the male ferret between age E28 and P20. The MN-POA/AH is present and potentially functional in males during a considerable portion of this perinatal period.

Androstatrienes↗
PubMed1990

Naloxone disrupts the expression but not the acquisition by male rats of a conditioned place preference response for an oestrous female.

Two experiments were conducted to investigate the possible role of endogenous opioid peptides in the regulation of masculine sexual reward. In experiment 1 sexually experienced male rats, which had recently been castrated or left gonadally intact, were allowed to mate with an oestrous female in an initially "non-preferred" chamber of a test apparatus. On alternate days these males were placed alone in the initially "preferred" chamber of the same apparatus. After eight such conditioning sessions both intact and castrated males had acquired a conditioned place preference (CPP) for the initially "non-preferred" chamber whereas control males, which were never given access to an oestrous female, showed no evidence of a significant shift in their preference for either chamber. Administration of the opioid receptor antagonist, naloxone (1 or 5 mg/kg, SC) prior to each conditioning session had no significant influence on the acquisition of a CPP for an oestrous female. By contrast, in experiment 2 naloxone treatment significantly attenuated the expression of a previously established CPP for an oestrous female in both gonadally intact and castrated males. The results suggest that opioid components of neural reward circuits are normally activated in the male rat by conditioned incentive stimuli, but not by the primary rewarding stimuli associated with access to and mating with an oestrous female.

Animals↗
PubMed1990

Endocrine correlates of mating-induced reductions in estrous behaviour in an induced ovulator, the ferret.

Experiments were conducted to assess the time course of behavioral and endocrine changes which occur in female ferrets as they switch from estrus to the pseudopregnant state. Significant reductions in females' acceptance of neck gripping by a stimulus male (receptivity) and in their latency to approach a stimulus male in an L-maze (proceptivity) were first observed 3 days after receipt of an intromission; no such changes occurred in other females which were only neck gripped by stimulus males during the initial test session. Corpora lutea were later found only in the ovaries of females which received intromissions, confirming that ovulation had occurred in these animals. Plasma concentrations of prostaglandin E1, prostaglandin F2 alpha, and the 13,14-dihydro 15-keto metabolite of prostaglandin F2 alpha (PGFM) were unchanged in female ferrets for 4-5 days after receipt of an intromission. By contrast, plasma concentrations of progesterone were significantly elevated beginning 5 days after, whereas plasma estradiol was significantly reduced beginning 4 days after receipt of an intromission. Daily sc administration of the progesterone receptor antagonist. RU 38486, significantly retarded the lengthening in females' approach latencies to a stimulus male, suggesting that postcoital elevations in circulating progesterone normally contribute to the expected decline in proceptive responsiveness. By contrast, postcoital reductions in acceptance quotients occurred at equivalent rates in females treated with RU 38486 versus vehicle, leading us to infer that postcoital reductions in estrogenic stimulation may cause this decline in ferrets' receptive responsiveness.

Animals↗
PubMed1990

Frank Beach's research on the sexual differentiation of behavior and his struggle with the "organizational" hypothesis.

Highlights are described of Frank Beach's research contributions in the area of steroidal control of behavioral sexual differentiation in rats and beagle dogs. Beach's initial struggle with and his subsequent partial acceptance of the organizational hypothesis of steroidal action in the developing male nervous system as an explanation of these steroidal effects on behavior, advanced by W. C. Young and co-workers, is also chronicled.

Animals↗
PubMed1990

Prenatal and neonatal testosterone exposure interact to affect differentiation of sexual behavior and partner preference in female ferrets.

Implanting testosterone (T) subcutaneously over Postnatal Days 5-20 masculinized sexual behavior, reduced proceptive responsiveness, and shifted sexual preference more readily in male than in female ferrets gonadectomized on Day 5. This enhanced sensitivity of males to neonatal T was best duplicated in females exposed transplacentally to T over Embryonic Days (E) 27-39 (41-day gestation) and injected at birth with T (2.5 micrograms sc in oil: 10% ethanol). Extended exposure of male ferrets to high levels of T, beginning shortly after the onset of testicular steroidogenesis (E25) and continuing for several hours after birth (E41) normally sensitizes their brains to the subsequent organizational effects on coital performance and sexual motivation of the relatively low levels of T that circulate in male ferrets during the first 3 postnatal weeks.

Animals↗
PubMed1989

Evidence that oestrogen exerts an equivalent negative feedback action on LH secretion in male and female ferrets.

Gonadally intact male ferrets in breeding condition, which received an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD) s.c. in Silastic capsules, had significantly more LH pulses and higher mean LH concentrations in plasma than did control males implanted with empty capsules. Aromatase activity in the hypothalamus + preoptic area and temporal lobe was strongly suppressed by ATD treatment whereas circulating concentrations of testosterone and oestradiol were not affected. These results suggest that oestradiol, formed via neural aromatization of circulating testosterone, contributes to the feedback regulation of LH secretion in breeding male ferrets just as oestradiol of ovarian origin controls LH secretion in females. No sex difference was observed in the rate at which mean plasma LH concentrations rose after the removal from gonadectomized ferrets of s.c. Silastic capsules containing oestradiol. Daily s.c. injections of oestradiol in oil caused an equivalent, dose-dependent inhibition of LH pulse frequency and mean LH concentrations in plasma of male and female ferrets. These findings suggest that the negative feedback control of pulsatile LH secretion by oestrogen is not sexually differentiated in this reflexly ovulating species. The ferret appears to differ from spontaneously ovulating mammalian species in which the female is generally more sensitive than the male to the inhibitory feedback action of oestradiol on LH secretion.

Androstatrienes↗
PubMed1988

Evidence implicating aromatization of testosterone in the regulation of male ferret sexual behavior.

We compared the effects of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD) and castration on the expression of mating behavior in adult male ferrets which were in breeding condition. Males implanted SC with Silastic capsules containing ATD displayed significantly less neck gripping, mounting and intromittive behavior than intact males which received empty capsules, although the ATD-induced reductions in behavior were not as large as those seen after castration. ATD had no effect on mating behavior in castrated males. As reported in another publication, brain aromatase activity was significantly reduced in both the intact and castrated males treated with ATD in the present study. Plasma estradiol (E2) levels were uniformly low in intact and castrated males, regardless of whether they received ATD or no steroid. As expected, plasma testosterone (T) levels were significantly lower in castrated than in intact males, and ATD treatment did not affect these values. These results suggest that E2 formed via the neural aromatization of T contributes to the activation of masculine sexual behavior in intact male ferrets in breeding condition.

Androstatrienes↗
PubMed1988

Immediate postnatal rise in whole body androgen content in male rats: correlation with increased testicular content and reduced body clearance of testosterone.

Whole body content of androgen (testosterone + 5 alpha-dihydrotestosterone) was invariably higher in male than in female rat pups killed 1 or 3 h after natural delivery, whereas androgen content was equivalent in males and females killed immediately or 6, 12, and 24 h after birth. Testicular content of androgen was significantly elevated in males killed 1 and 24 h after birth, compared with levels in males killed immediately, or 3, 6, and 12 h after birth. Thus, heightened testicular androgen content was only initially associated with increased systemic levels of androgen in males during the immediate postpartum period. A second study assessed the possibility that the body's clearance (i.e., metabolism plus excretion) of testosterone is lower in newborn rats upon separation from the placental circulation than in slightly older pups. Rats of both sexes killed 1 and 3 h after s.c. injection of [3H] testosterone had significantly higher plasma concentrations of [3H] testosterone as well as several 5 alpha-reduced androgens (5 alpha-dihydrotestosterone, 3 alpha-androstanediol, and androsterone) when injections were given within minutes as opposed to 24 h after birth. This suggests that in both sexes the clearance of testosterone is slower immediately after birth than at later ages. This phenomenon together with a brief postnatal elevation in the testicular synthesis and secretion of testosterone may explain the temporary rise in circulating androgen concentrations that occurs in the newborn male rat.

Age Factors↗
PubMed1988

Effect of birth on plasma testosterone, brain aromatase activity, and hypothalamic estradiol in male and female ferrets.

The present studies examined the patterns of circulating testosterone (T) within 0-24 h after birth in male and female ferrets along with concomitant changes in neural aromatase activity and hypothalamic concentrations of estradiol (E2). Plasma and brain samples were obtained 0 and 2 h (cesarean delivery) or 0, 2, 12, and 24 h (natural delivery) after birth. Plasma T levels were significantly higher in male neonates 2 h after birth than at 0 h in both cesarean-delivered (9.48 +/- 1.25 vs. 3.37 +/- 0.60 ng/ml) and naturally delivered (19.28 +/- 2.94 vs. 5.13 +/- 1.93 ng/ml) ferrets, while female neonates showed no significant changes in T over these sampling times. T levels had returned to 0 h levels by 12 h in naturally delivered males. T was significantly lower in females than in males 0, 2, and 24 h after natural delivery, whereas T levels were equivalent in males and females immediately after cesarean delivery. Male kits kept on a heating pad for 2 h after natural delivery had lower plasma T levels than males that were left with their mothers over this same period. Brain aromatase activity in anterior hypothalamus-preoptic area, medial basal hypothalamus (MBH), temporal lobe, and cerebral cortex was equivalent in males and females at all postpartum ages, regardless of whether delivery occurred by cesarean section or naturally. However, in naturally delivered kits of both sexes significant elevations in aromatase activity occurred in MBH and temporal lobe 24 h postpartum. Finally, E2 concentrations in anterior hypothalamus-preoptic area and MBH were equivalent 0 and 2 h postpartum in males and females, regardless of whether they were delivered naturally or by cesarean section. The observed postnatal elevation in T may contribute to brain and behavioral sexual differentiation of male ferrets. It is unclear, however, whether such an effect of T depends on its neural aromatization to E2.

Animals↗
PubMed1987

Role for prenatal estrogen in the development of masculine sexual behavior in the male ferret.

Previous studies have shown that neonatal exposure to testosterone is essential for coital masculinization in male ferrets. In the present experiments, masculine sexual behavior was diminished in male ferrets by prenatal exposure to drugs which inhibited estrogenic stimulation of the brain. Similarly timed prenatal treatments with testosterone failed to masculinize the behavior of female offspring. We hypothesize that prenatal exposure of the male ferret to estrogen, derived from the neural aromatization of circulating androgen, may sensitize the developing brain to the subsequent masculinizing action of testosterone shortly after birth.

Androstatrienes↗
PubMed1987

Naloxone inhibits mating and conditioned place preference for an estrous female in male rats soon after castration.

Three experiments were conducted to assess the role of endogenous opioids in controlling mating behavior and sexual reward in the male rat. In Experiment 1 SC administration of naloxone (0.5, 1.0, 5.0, or 10.0 mg/kg) significantly reduced mounting and ejaculation in male rats tested 14, but not 7 days, after castration. In Experiment 2 naloxone (5.0 mg/kg) administered SC to gonadally intact males, which had ejaculated repeatedly with one female until they were sexually sated, significantly inhibited the resumption of mating after the reintroduction of a female partner. One interpretation of these results is that naloxone attenuated the reward experienced by castrated and sexually sated males in the presence of an estrous female, thereby disrupting males' coital performance. This hypothesis was tested in Experiment 3 using a conditioned place preference paradigm in which males copulated with an estrous female in an initially "non-preferred" (white) compartment, whereas on alternate days they remained alone in an initially "preferred" (black) compartment. After 10 such conditioning sessions, males were either castrated or sham-operated. They later were given free access to both compartments in the absence of an estrous female. Seven days after conditioning and surgery, sham-operated, naloxone-injected males and both groups of castrates spent significantly less time than sham-operated, saline-injected controls in the initially "non-preferred" compartment. Fourteen days after conditioning and surgery castrated, naloxone-treated males spent significantly less time in the "non-preferred" compartment than males in the other three groups. Endogenous opioids may play an important role in the interpretation by males of the incentive motivational stimuli which emanate from an estrous female.

Animals↗
PubMed1987

Alpha-melanocyte-stimulating hormone infusions during pregnancy in the rat: effects on offspring weight, pain reactivity and sexual behavior.

Pregnant rats treated during the last third of pregnancy with a continuous infusion of alpha-melanocyte-stimulating hormone (alpha-MSH) produced offspring that weighed less at birth and in adulthood. These offspring of the alpha-MSH treated mothers were less sensitive to pain and as adults showed a reduced analgesic response to morphine. Male offspring of alpha-MSH treated mothers and of control animals responded similarly in sexual performance tests, except that the treated animals significantly shifted their pattern of responding when they encountered a new testing arena or experienced defeat. The offspring of alpha-MSH treated mothers were influenced more by changes in their environment than were control offspring. These effects are similar to those reported following perinatal treatment with opiate drugs or peptides.

Aging↗