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M J Baum

Publications and source records attributed to M J Baum.

At least 37 records · Page 2Linked to original sources
PubMed2000

Steroidal modulation of scent investigation and marking behaviors in male and female ferrets (Mustela putorius furo).

Gonadectomized male and female ferrets (Mustela putorius furo) given either testosterone propionate (TP) or oil vehicle preferred to investigate the side of a test cage previously soiled by a breeding male or female as opposed to a clean side. Male and female ferrets receiving TP showed more urogenital wiping than oil-treated animals in either side of the test cage. In a 2nd experiment, ferrets treated sequentially with TP, oil, and estradiol benzoate (EB) were given simultaneous access to sides of a test cage previously soiled by either a breeding female or male. Either EB or TP treatment of females and TP treatment of males facilitated the investigation of odors of opposite-sex ferrets. Females given TP and males given either TP or EB showed increased urogenital wiping in both sides of the test cage. Sex steroids modulate scent investigation and marking in adult ferrets in a sexually differentiated fashion.

Animals↗
PubMed2000

Effect of gonadal steroids on pituitary LH secretion and mediobasal hypothalamic GnRH mRNA in ferrets.

In vitro release and content of GnRH in mediobasal hypothalamic slices are reduced by ovariectomy of female ferrets but are not affected by castration of male ferrets in breeding condition. The aim of the present study was to determine whether this sex difference reflects a sexually dimorphic effect of gonadal steroids on mediobasal hypothalamic GnRH mRNA content of male and female ferrets killed 4 weeks after gonadectomy, either with or without steroid hormone replacement. This time interval exceeds the 6-10 days needed for increments in plasma LH concentrations to stabilize after gonadectomy of ferrets of both sexes. In situ hybridization using an (35)S-labelled oligoprobe complementary to the human GnRH coding region showed that the number of mediobasal hypothalamic neurones and the cellular content of GnRH mRNA did not differ significantly among groups of male and female ferrets that were either in breeding condition or that had been gonadectomized and treated with sex steroids or oil vehicle. These results indicate that gonadal hormones regulate mediobasal hypothalamic GnRH biosynthesis and release in both sexes via post-transcriptional events that may include GnRH mRNA translation or the conversion of pre-pro GnRH precursor into mature GnRH.

Analysis of Variance↗
PubMed1999

Neuronal Fos activation in olfactory bulb and forebrain of male rats having erections in the presence of inaccessible estrous females.

Volatile odors from estrous female rats are necessary and sufficient to induce non-contact penile erections in male rats. It is not known whether these pheromones are detected by the accessory as opposed to the main olfactory system or whether they are processed by forebrain regions that receive olfactory inputs. Using nuclear Fos immunoreactivity as a marker of neuronal activation, we asked how the detection and processing of distal cues from inaccessible estrous females, which elicited non-contact penile erections, compared with the processing of sensory cues from soiled estrous bedding which did not elicit non-contact penile erections. In Experiment 1, groups of sexually experienced males were given one of five treatments. A control group was placed on clean bedding. A second group displayed non-contact penile erections when exposed to the smell, sight and sound of an estrous female restrained behind a permeable barrier. A third group was exposed to the same stimuli as the second (an estrous female) but failed to exhibit non-contact penile erections during the first hour of testing. A fourth group was placed on soiled estrous bedding, and a fifth group was allowed two ejaculations with an estrous female. All males were perfused with 4% paraformaldehyde 2 h after the onset of these respective treatments, and their brains were later processed for Fos immunoreactivity. Non-contact penile erections were observed in males that were exposed to distal cues from an estrous female but not in males exposed to soiled estrous bedding. Males that displayed non-contact penile erections or that were exposed to estrous bedding showed significantly more neuronal Fos immunoreactivity than clean-bedding controls in the nucleus accumbens core and shell, anterior and posterior medial amygdala, bed nucleus of the stria terminalis and the medial preoptic nucleus. Even greater neuronal Fos responses occurred in these regions in mated males. In Experiment 2 these same treatments were given to another cohort of sexually experienced males. Increased neuronal Fos immunoreactivity was observed in the granule and mitral cell layers of the accessory olfactory bulb of males that were either mated or exposed to estrous bedding, but not in males that displayed non-contact penile erections in response to distal cues from an estrous female. The volatile odors which presumably caused non-contact penile erections failed to stimulate significant neuronal Fos immunoreactivity in five main olfactory bulb sites examined. Even so, it seems likely that these pheromones are detected via the main olfactory system and are subsequently processed by the same projection circuit that responds to other pheromones present in estrous bedding that are incapable of eliciting non-contact penile erections.

Animals↗
PubMed1999

Intracerebroventricular infusion of the galanin antagonist M40 attenuates heterosexual partner preference in ferrets.

Gonadectomized, estradiol-treated male and female ferrets (Mustela furo) received intracerebroventricular (i.c.v.) infusions of 4 doses of the galanin receptor antagonist M40 or galanin and were allowed to approach breeding male or female ferrets that were placed behind wire mesh barriers in the goal boxes of a T maze. After i.c.v. infusion of saline, subjects strongly preferred to approach stimulus ferrets of the opposite sex. Male and female subjects approached these preferred stimulus animals on significantly fewer trials after i.c.v. infusion of the 2 highest doses of M40, whereas this drug failed to affect males' coital behavior in separate tests with an estrous female. Endogenous galanin may facilitate neural reward mechanisms that control heterosexual partner preference in both sexes.

Analysis of Variance↗
PubMed1999

Changes in mediobasal hypothalamic gonadotropin-releasing hormone messenger ribonucleic acid levels induced by mating or ovariectomy in a reflex ovulator, the ferret.

The ferret is a reflex-ovulating species in which receipt of an intromission induces a prolonged (+/- 12 h) preovulatory LH surge in the estrous female. This LH surge is probably stimulated by a large release of GnRH from the mediobasal hypothalamus (MBH). In Exp 1 we asked whether GnRH messenger RNA (mRNA) levels increase in response to mating so as to replenish the MBH GnRH stores needed to sustain the preovulatory LH surge. Estrous females were killed 0, 0.25, 0.5, 1, 3, 6, 14, or 24 h after the onset of a 10-min intromission from a male. Coronal brain sections ranging from the rostral preoptic area caudally to the posterior hypothalamus were processed for in situ hybridization using a 35S-labeled oligoprobe complementary to the human GnRH-coding region. We found no evidence of increased MBH GnRH mRNA levels during the ferret's mating-induced preovulatory LH surge. Instead, the number of GnRH mRNA-expressing cells dropped significantly in the arcuate region beginning 6 h after onset of intromission and remained low thereafter. Furthermore, cellular GnRH mRNA levels decreased in the arcuate region toward the end of the preovulatory LH surge. In Exp 2 we asked whether ovarian hormones regulate MBH GnRH mRNA levels in the female ferret. Ovariectomy of estrous females significantly reduced the number of GnRH mRNA-expressing cells in the arcuate region. This decrease was probably not due to the absence of circulating estradiol. Gonadally intact anestrous females had levels of MBH GnRH mRNA similar to those in estrous females even though plasma estradiol levels were equally low in anestrous females and ovariectomized females. Ovarian hormones other than estradiol may stimulate MBH GnRH mRNA levels in anestrous and estrous females.

Animals↗
PubMed1999

Vomeronasal neuroepithelium and forebrain Fos responses to male pheromones in male and female mice.

Male urinary pheromones modulate behavioral and neuroendocrine function in mice after being detected by sensory neurons in the vomeronasal organ (VNO) neuroepithelium. We used nuclear Fos protein immunoreactivity (Fos-IR) as a marker of changes in neuronal activity to examine the processing of male pheromones throughout the VNO projection pathway to the hypothalamus. Sexually naive male and female Balb/c mice were gonadectomized and treated daily with estradiol benzoate (EB) or oil vehicle for 3 weeks. Subjects were then exposed to soiled bedding from gonadally intact Balb/c males or to clean bedding for 90 min prior to sacrifice and processing of their VNOs and forebrains for Fos-IR. Male pheromones induced similar numbers of Fos-IR cells in the VNO neuroepithelium of oil-treated male and female subjects; however, EB-treated females had significantly more Fos-IR neurons in the VNO than any other group. There was an equivalent neuronal Fos response to male odors in the mitral and granule cells of the anterior and posterior accessory olfactory bulb of males and females, regardless of hormone treatment. In central portions of the VNO projection pathway (i.e., bed nucleus of the stria terminalis, medial preoptic area) neuronal Fos responses to male pheromones were present in female but absent in male subjects, regardless of hormone treatment. In a separate experiment, mating induced neuronal Fos-IR in these brain regions at levels in gonadally intact male subjects which were equal to or greater than those seen in ovariectomized females primed with estrogen and progesterone. This suggests that neurons in the central portions of the male's VNO pathway are capable of expressing Fos. Our results suggest that sexually dimorphic central responses to pheromones exist in mice that may begin in the VNO neuroepithelium.

Animals↗
PubMed1998

Cell death in the sexually dimorphic dorsal preoptic area/anterior hypothalamus of perinatal male and female ferrets.

A sexually dimorphic male nucleus (MN) is present in Nissl-stained sections through the dorsal (d) preoptic area/anterior hypothalamus (POA/AH) of male ferrets. The MN-POA/AH is composed of a cluster of large cells which is organized in males by the action of estradiol, formed via the neural aromatization of circulating testosterone (T), during the last quarter of a 41-day gestation. Several recent studies using rodent species have raised the possibility that the hormone-induced masculinization of POA/AH morphology is mediated at least in part by a perinatal modulation of cell death. We asked whether a perinatal reduction in cell death contributes to the differentiation of the MN-POA/AH in the male ferret, which is a carnivore species. The appearance of internucleosomal DNA fragmentation, detected by in situ end labeling (ISEL) using the ApopTag kit (Oncor Corp.) and of pyknotic cell nuclei in Nissl-stained sections were used to estimate the occurrence of cell death. Male and female ferret kits were killed at four different ages spanning the perinatal period during which the MN-POA/AH is organized and assumes an adult phenotype. A peak density of dying cells was present in both sexes at postnatal day (P) 2, which is nearly 1 week after the age, embryonic day (E) 37, when the MN-POA/AH is first visible in male ferrets using Nissl stains. The density of cells in the sexually dimorphic dPOA/AH which were either ISEL-positive or pyknotic was similar in males and females on E34, as well as on P2, 10, and 20. In the nondimorphic ventral POA/AH, the highest density of dying cells was present in both sexes at E34, and there were significantly more ISEL-positive cells present in males than females at this particular age. In contrast to previous studies using rodents, our results suggest that in fetal male ferrets a modulation of the incidence of cell death contributes little to estradiol's organizational action in the dPOA/AH.

Animals↗
PubMed1998

Testosterone augments neuronal Fos responses to estrous odors throughout the vomeronasal projection pathway of gonadectomized male and female rats.

Pheromonal signals emanating from female rats' soiled bedding have previously been shown to attract male conspecifics and to augment the number of Fos-immunoreactive neurons present in portions of the vomeronasal projection pathway, ranging from the accessory olfactory bulb (AOB) to the medial preoptic area (mPOA) of gonadectomized, testosterone-treated male as well as female subjects. In the present study we extended these findings by showing that these neuronal Fos responses to estrous odors occurred only in gonadectomized subjects which received testosterone propionate (TP), as opposed to oil vehicle, at the time of testing. Previously, when treated with TP, all subjects had displayed mounting with an estrous female. In subsequent tests, gonadectomized male and female subjects spent significantly more time investigating soiled estrous bedding as opposed to clean or anestrous bedding, again, provided they were receiving TP. We propose that testosterone facilitates odor-induced neuronal Fos expression either via its conversion to estradiol, and the subsequent action of this steroid at estrogen response elements on the c-fos gene, or via some indirect mechanism involving centrifugal control of AOB neurotransmission. The ability of female odors to stimulate equivalent numbers of Fos-IR cells in gonadectomized, TP-treated male and female rats indicates that the functional responsiveness of neurons throughout the vomeronasal projection pathway is made more male-like by the fetal actions of testosterone in female as well as in male rats. Previous studies established that males have more neurons than females in several segments of the vomeronasal pathway; however, this morphological sexual dimorphism does not account for the observed isomorphic neuronal Fos responses to female odors.

Animals↗
PubMed1998

Sex difference and testosterone modulation of pheromone-induced NeuronalFos in the Ferret's main olfactory bulb and hypothalamus.

A carnivore, the ferret possesses a vomeronasal organ--accessory olfactory bulb (VNO-AOB) projection to the hypothalamus; however, little is known about its function. Pheromones in soiled bedding from estrous female ferrets or an artificial peppermint odor significantly augmented nuclear Fos protein immunoreactivity (Fos-IR), a marker of neural activation, in several main olfactory bulb (MOB) sites but not in the AOB of gonadectomized male and females. Testosterone propionate (TP) significantly augmented the MOB's neuronal Fos responses to estrous females' pheromones, but not to peppermint. Estrous odors, but not peppermint, also augmented neuronal Fos-IR in the medial preoptic area (mPOA) of female, but not male, subjects. Pheromones in soiled bedding from breeding male ferrets significantly augmented neuronal Fos-IR in the MOB and in the medial amygdala of gonadectomized, TP-treated male and female subjects. Again, male pheromones failed to influence neuronal Fos-IR in the AOB of either sex, and only females showed significant increases in neuronal Fos-IR in the lateral aspect of the ventromedial nucleus and mPOA. These results point to an essential role among higher mammals of the main olfactory epithelium-MOB projection to the hypothalamus in detecting and processing pheromones. Gonadectomized ferrets showed significant increases in sniffing behavior when placed on either female or male bedding. This occurred regardless of whether they had received TP or oil vehicle, suggesting that testosterone's facilitation of neuronal Fos responses to estrous females' odors in the MOB of both sexes cannot be attributed to increased scent gathering. Androgen receptor-IR was present in the MOB granule cell layer of male and female ferrets, raising the possibility that testosterone acts directly on these cells to augment their responsiveness to pheromones.

Animals↗
PubMed1998

Large somal size is associated with the expression of galanin but not with neuronal birthdate in the sexually dimorphic male nucleus of ferret's preoptic area/anterior hypothalamus.

Using Nissl and Golgi stains, a sexually dimorphic male nucleus (MN) comprised of a cluster of large cells with large dendritic arbors has been identified in the dorsal preoptic area/anterior hypothalamus (POA/AH) of male ferrets. The MN-POA/AH is formed only in males by the action of estradiol derived from the neural aromatization of testosterone during the last quarter of a 41-day gestation. The ferret's dorsal POA/AH is also characterized by a sex difference in the expression of the neuropeptide galanin which first arises in males around embryonic day (e) 34. We asked whether the male-typical phenotype of large somal size is related to birthdate and/or the capacity of dorsal POA/AH neurons to express galanin. In experiment 1 we labeled cohorts of cells born on E20, E24, or E28 by injecting the amniotic sacs of individual fetuses with the thymidine analogue bromodeoxyuridine (BrdU). On postnatal day 20, BrdU-immunoreactive cells were visualized immunohistochemically, counterstained with cresyl violet, and their somal sizes were measured. BrdU-immunoreactive cells were significantly larger in the males' MN-POA/AH than in a comparable region of females, regardless of when they were born between E20 and E28. In experiment 2 galanin-immunoreactive cells in the dorsal POA/AH of adult ferrets were visualized immunohistochemically, and their somal sizes were measured. Somal areas of galanin-immunoreactive cells were significantly larger in the MN-POA/AH of intact, breeding, or castrated and testosterone-treated males than in the corresponding area of females. Our results suggest that cells in the males' MN-POA/AH are more likely to be larger than cells in females' corresponding region, regardless of birthdate. Finally, in adulthood the male-typical phenotype of large Nissl-stained somal areas of MN-POA/AH cells may, in part, reflect their increased galanin expression.

Amnion↗
PubMed1997

Sex difference and steroidal stimulation of galanin immunoreactivity in the ferret's dorsal preoptic area/anterior hypothalamus.

A sexually dimorphic male nucleus (MN) is seen in Nissl-stained sections from the dorsal preoptic area/anterior hypothalamus (dPOA/AH) of male, but not female, ferrets. We used immunohistochemical methods to determine whether particular neuropeptides are found in cells of the MN. A sexually dimorphic cluster of galanin-immunoreactive (IR) cells was found in the dPOA/AH of ferrets killed either on embryonic day (E) 38 or in adulthood. Significantly more galanin-IR cells were distributed in the MN and in other subregions of the dPOA/AH of intact breeding males than estrous females. The density of galanin-IR cells in the dPOA/AH was significantly reduced in adult males by castration and restored to the level of intact breeding males by daily injections of testosterone propionate (TP) for 5 weeks. The same TP treatment failed to augment the density of galanin-IR cells in the dPOA/AH of adult, ovariectomized females. Computer-assisted image analysis and grid-crossing analysis showed that the area and the number of galanin-IR fibers in the dPOA/AH were significantly greater in adult females than in males, regardless of subjects' concurrent steroidal condition. A cluster of galanin-IR cells was present in the dPOA/AH of males, but not females, killed on either E34 or E38. Administration of TP between E28 and E37 significantly increased the density of galanin-IR cells in the dPOA/AH of females killed on E38, up to the level seen in control males. The results suggest that the capacity of cells located in the dPOA/AH to express galanin after adult steroid exposure is sexually differentiated by the fetal action of testosterone, or its metabolite, estradiol, in males.

Animals↗
PubMed1997

Sexually dimorphic activation of midbrain tyrosine hydroxylase neurons after mating or exposure to chemosensory cues in the ferret.

Mating with intromission induces a prolonged preovulatory LH surge in the estrous female ferret but inhibits LH secretion in the male. We used the dual immunocytochemical localization of Fos (as a marker of neural activation) and tyrosine hydroxylase (TH) to determine whether neurons containing norepinephrine or other catecholamines are activated after mating. Breeding male ferrets were allowed to intromit with estrous females; both animals were perfused 90 min after the onset of intromission. Other male and female ferrets were perfused 90 min after being placed in a cage in which an opposite-sex ferret in breeding condition had previously been housed for 48 h. Control ferrets of each sex were perfused 90 min after being placed alone in a clean testing cage. Mating with intromission significantly augmented the percentage of TH-immunoreactive (TH-IR) neurons colabeled with nuclear Fos-like immunoreactivity (Fos-IR) in both the A6 and the rostral A2 midbrain catecholamine cell groups in females, but not males. Exposure to chemosensory cues alone also increased the percentage of Fos-IR TH neurons in the rostral A2, but not the A6, cell group in females. Chemosensory cues alone did not affect the percentage of double-labeled neurons in either cell group in males. These activated midbrain TH-IR neurons are most likely noradrenergic, and their activation in estrous females may facilitate the mediobasal hypothalamic release of LHRH required for the preovulatory LH surge. In both sexes, mating with intromission, but not chemosensory cues alone, augmented the percentage of periglomerular TH-IR neurons in the main olfactory bulb (MOB) that were colabeled with Fos-IR. These activated TH-IR neurons in the MOB are most likely dopaminergic. Their role in the neural response to mating is currently unknown.

Animals↗
PubMed1997

Sexually dimorphic processing of somatosensory and chemosensory inputs to forebrain luteinizing hormone-releasing hormone neurons in mated ferrets.

The ferret is a reflexively ovulating species in which mating induces a preovulatory LH surge in the estrous female but significantly decreases LH secretion in the breeding male. This sexually dimorphic hormonal response is reflected in a sex difference in Fos-like immunoreactivity (Fos-IR) in forebrain LHRH and non-LHRH neurons after mating. We used dual immunocytochemistry for Fos and LHRH to determine whether the sex dimorphism occurs in the initial detection and transmission or in the central processing of sensory stimuli associated with mating? We also assessed the ability of chemosensory cues alone to augment neuronal Fos-IR in the ferret forebrain. Breeding male and female ferrets were paired, whereupon the male partner achieved an intromission lasting for 16-90 min. Mated male and female subjects were always perfused 90 min after the onset of the male's intromission. Additional male and female subjects were placed alone in a cage in which an opposite sex ferret in breeding condition had been housed for 48 h. Other control ferrets were placed alone in a clean cage. Chemosensory-stimulated and unpaired control subjects were perfused 90 min after being placed in their respective cages. In both sexes mating augmented neuronal Fos-IR in the granular layer of the main olfactory bulb, the caudal thalamic central tegmental field, and the medial amygdala, regions situated early in the putative input pathway to mediobasal hypothalamic LHRH neurons. Neuronal Fos-IR was also increased in these same forebrain regions (the central tegmental field excluded) in both sexes after exposure to chemosensory cues alone. However, more central components of this input pathway, including the preoptic area, the bed nucleus of the stria terminalis, and the ventrolateral portion of the ventromedial hypothalamus as well as the mediobasal hypothalamic LHRH neurons themselves were activated by mating only in the female. In estrous females, exposure only to chemosensory stimuli from a breeding male augmented Fos-IR in the preoptic area and the ventrolateral portion of the ventromedial hypothalamus, but not in the bed nucleus of the stria terminalis or mediobasal hypothalamic LHRH neurons. In breeding males, exposure only to chemosensory cues from an estrous female failed to affect Fos-IR in any of these proximal components of the input pathway or in LHRH neurons themselves. These results suggest that the sex dimorphism in mating-induced LH secretion reflects a sex difference in the central processing of genital-somatosensory stimuli and possibly of chemosensory inputs as well.

Animals↗
PubMed1996

Neurogenesis and cell migration into the sexually dimorphic preoptic area/anterior hypothalamus of the fetal ferret.

A sexually dimorphic male nucleus (MN) of the preoptic area/anterior hypothalamus (POA/AH), comprising large, estradiol-receptor containing neurons, is formed in male ferrets due to the action of estradiol, derived from the neural aromatization of circulating testosterone, during the last quarter of a 41-day gestation. Two experiments were conducted to compare the birthdates and the migration pattern of cells into the sexually dimorphic portion of the dorsomedial POA/AH as well as the nondimorphic ventral nucleus (VN) of the POA/AH of males and females. In experiment 1 the thymidine analog, bromodeoxyuridine (BrdU), was injected into the amniotic sacs of fetuses of different mothers between embryonic (E) days 18 and 30. Kits from all mothers were sacrificed on E38, and brains were processed to localize BrdU immunoreactivity (IR) for determining the birthdates of neurons in the POA/AH. Cells in the MN-POA/AH of males and in a comparable region of females were born between E22 and E28; cells in the nondimorphic VN-POA/AH of both sexes were born between these same ages. These results suggest that cells in the sexually dimorphic as well as the nondimorphic subdivision of the ferret POA/AH are born during the same embryonic period. This is well before the ages (E30-E41) when administering testosterone to females can stimulate, and blocking androgen aromatization in males can inhibit, MN-POA/AH differentiation. In experiment 2 BrdU was injected on E24, and kits from different litters were perfused on E30, E34, or E38. Brains were processed for BrdU-IR as well as glial fibrillary acidic protein (GFAP), which served as a marker for radial glial processes. The orientation of radial glial processes in fetal brains of both sexes suggested that cells migrate into the dorsomedial POA/AH from proliferative zones lining the lateral as well as the third ventricles. Quantitative, computer-assisted image analysis of BrdU-IR in groups of male and female brains supported this hypothesis. There were no significant sex differences in the distribution of BrdU-IR over the three ages studied, suggesting that formation of the MN-POA/AH in males cannot be attributed to an effect of estradiol on the migration of those cells born on E24 into this sexually dimorphic structure. Finally, total BrdU-IR did not change significantly in the POA/AH of male and female kits killed at E30, E34, or E38 while the area of the POA/AH increased more than 2.5-fold over this period, suggesting that few of the POA/AH cells born on E24 die during this period in either sex. In the absence of evidence that formation of the male ferret's MN-POA/AH depends on steroid-induced changes in neurogenesis, cell migration, or death, we suggest that the specification of a particular neuronal phenotype (e.g., large somal size; capacity to produce some undetermined neurotransmitter or neuropeptide) may be responsible.

Animals↗
PubMed1996

Medial preoptic/anterior hypothalamic lesions induce a female-typical profile of sexual partner preference in male ferrets.

In T-maze tests given to gonadectomized ferrets treated daily with estradiol benzoate (EB), females consistently prefer to approach and interact sexually with a stud male whereas male subjects, on average, prefer an estrous female. In the present experiment this sexually allomorphic pattern of partner preference was changed in males given lesions of the medial preoptic area/anterior hypothalamus (mPOA/AH). Electrolytic lesions, which caused extensive bilateral damage to the mPOA/AH, including the sexually dimorphic male nucleus (MN) of the POA/AH, led males to shift their mean preference away from the estrous female to the stud male. Their postoperative profile of partner preference more closely resembled that of sham-operated females than that of sham-operated males or of males which sustained either partial or minimal bilateral damage to the mPOA/AH so as to spare the MN-POA/AH in one or both hemispheres. Males with extensive bilateral mPOA/AH lesions, like sham-operated females, showed an even stronger preference to approach the stud male during T-maze tests in which the subjects could smell, see, and hear the stimulus animals without physically interacting with them. After receiving testosterone propionate, male ferrets with either extensive or partial lesions of the mPOA/AH showed significant deficits in neck gripping and mounting performance in tests with either female or male stimulus animals which were sexually receptive after gonadectomy and EB treatment. The present results, coupled with those of a previous study using excitotoxic mPOA/AH lesions, suggest that the male-typical profile of preference for an estrous female depends on the functional integrity of sexually dimorphic mPOA/AH neurons and the reward engendered by coital interaction with such a female. When these neurons either are destroyed experimentally (as in male ferrets with extensive bilateral mPOA/AH lesions) or are absent (as in sham-operated females), subjects are attracted by distal (possibly chemosensory) incentive cues from a stud male.

Animals↗
PubMed1996

Estrogenic control of preoptic area development in a carnivore, the ferret.

1. Evidence is reviewed which shows that a sexually dimorphic nucleus located in the dorsomedial portion of the male ferret's preoptic area/anterior hypothalamus (POA/AH), called the male nucleus of the POA/AH (Mn-POA/AH), develops during fetal life in response to the action of estradiol, which is formed directly in the nervous system from circulating testosterone over the final quarter of a 41-day gestation. 2. Results are summarized which establish that neurons which make up the Mn-POA/AH are born prior to the critical period of estradiol's action in the male brain. Other data show that some radial glial processes, visualized immunocytochemically using antibodies against GFAP, emanate from proliferative zones at the base of the lateral ventricles in a dorsal-ventral orientation, whereas other glial processes emanate laterally from proliferative zones lining the third ventricle. 3. We suggest that at least some neurons which constitute the dorsomedial POA/AH are born in proliferative zones surrounding the lateral ventricles, raising the question of whether estradiol acts in developing males to influence the migration of these neurons along radial glial guides into the Mn-POA/AH. 4. Finally, evidence is summarized showing that excitotoxic lesions of the dorsomedial POA/AH enhance males' preference to approach and interact with another sexually active male, as opposed to an estrous female, when adult subjects are castrated and treated with estradiol benzoate. These data suggest that the sexually dimorphic Mn-POA/AH is an essential part of a CNS circuit which determines heterosexual partner preference in the male ferret.

Animals↗
PubMed1996

Sex comparison of neuronal Fos immunoreactivity in the rat vomeronasal projection circuit after chemosensory stimulation.

In rodents, reproductively relevant pheromonal cues are detected by receptors in the vomeronasal organ, which in turn transmit this information centrally via the accessory olfactory bulb, the medial nucleus of the amygdala, the posterior medial bed nucleus of the stria terminalis and the medial preoptic area. In the rat, more neurons are present in males than in females at virtually every relay in this vomeronasal projection circuit. Using Fos immunoreactivity as a marker of neuronal activation, we compared the ability of pheromonal cues derived from the urine and feces of estrous or anestrous female rats to activate neurons in this vomeronasal projection circuit in sexually experienced, gonadectomized male and female rats which were chronically treated in adulthood with a high dose of testosterone propionate (5 mg/kg). When compared with rats killed after 2 h of exposure to clean bedding, male and female subjects exposed for 2 h to bedding from estrous females had similar and significant increments in the number of Fos-immunoreactive neurons at each level of the vomeronasal projection circuit, including the granular layer of the accessory olfactory bulb, the posterior dorsal portion of the medial amygdaloid nucleus, the posterior medial portion of the bed nucleus of the stria terminalis and the medial preoptic area. Exposure to bedding from anestrous females stimulated similar and significant increments in Fos immunoreactivity in most of these same brain regions. Chemosensory stimulation failed to augment Fos immunoreactivity in neurons located in the ventrolateral subregion of the ventromedial nucleus of the hypothalamus or in the midbrain central tegmental field, sites at which mating has previously been shown to augment Fos immunoreactivity in both sexes. Finally, chemosensory stimulation augmented Fos immunoreactivity in the nucleus accumbens shell and core, two regions receiving dopaminergic afferents which have been implicated in sexual reward. On two occasions all subjects were given simultaneous access to bowls containing bedding from estrous versus anestrous females. Both males and females spent significantly more time investigating the estrous bedding, although the total time spent investigating either type of bedding was significantly greater in males. The results suggest that the previously established sexual dimorphism in the morphology of the rat's vomeronasal projection circuit is not reflected in the functional responsiveness of neurons in this circuit to chemosensory cues emitted by female conspecifics.

Animals↗