Biomedical subjects

M J Baum

Publications and source records attributed to M J Baum.

At least 55 records · Page 3Linked to original sources

PubMed1996

Neonatal inhibition of brain estrogen synthesis alters adult neural Fos responses to mating and pheromonal stimulation in the male rat.

Neonatal inhibition of brain estrogen formation in male rats by administration of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), permanently changes aspects of their mating behavior and partner preference in adulthood. The medial preoptic area receives chemosensory inputs via a sexually dimorphic vomeronasal projection circuit, which responds to reproductively relevant pheromonal cues. The medial preoptic area also receives genital somatosensory inputs via the midbrain central tegmental field and the medial amygdala. We used Fos immunoreactivity as a marker of neuronal activation to determine whether there is a correspondence between the behavioral profiles of neonatally ATD-treated male rats and their neuronal responses in the medial preoptic area and other brain regions to somatosensory and chemosensory stimuli. Achieving eight intromissions with an estrous female led to a greater neuronal Fos immunoreactivity in the medial preoptic area of neonatally ATD-treated male rats compared with neonatally cholesterol-treated male rats. Exposure for 1.5 h to chemosensory cues derived from soiled bedding of estrous females induced Fos immunoreactivity throughout the vomeronasal pathway (i.e. medial amygdala, bed nucleus of the stria terminalis and medial preoptic area) in both ATD and cholesterol males (Experiment 2a). By contrast, exposure for 1.5 h to chemosensory cues derived from soiled bedding of sexually active males revealed clear differences between ATD and cholesterol males in neuronal Fos immunoreactive (Experiment 2b). At peripheral portions of the vomeronasal pathway (i.e. the accessory olfactory bulb and the medial amygdala), there were no differences in the number of Fos immunoreactivity neurons between ATD and cholesterol males. However, neurons in the more central portions of the vomeronasal pathway (i.e. the bed nucleus of the stria terminalis and the medial preoptic area) showed increased Fos immunoreactivity after exposure to odors from sexually active males in ATD males as opposed to cholesterol males. Females, like ATD males, showed neuronal Fos immunoreactivity at each level of the vomeronasal pathway after being exposed to odors from sexually active males. These results suggest that the responsiveness of neurons in the central portion of the vomeronasal projection circuit to odors from sexually active males, but not estrous females, is sexually differentiated in male rats due to the neonatal action of estrogens.

Androstatrienes↗

PubMed1996

The temporal pattern of mating-induced immediate-early gene product immunoreactivity in LHRH and non-LHRH neurons of the estrous ferret forebrain.

The mating-induced preovulatory surge of luteinizing hormone (LH) lasts for at least 12 h in the female ferret. This prolonged increase in circulating LH is presumably accompanied by a corresponding elevation in the activity and output of luteinizing hormone-releasing hormone (LHRH) neurons projecting to the hypothalamic-hypophyseal portal blood vessels and adenohypophysis. We used the protein products of the immediate early genes (IEGs) c-fos, and c-jun as markers of neural activation in order to determine whether a sub-population of LHRH neurons is differentially activated by mating and whether non-LHRH neurons in specific forebrain regions are selectively activated at different times during the mating-induced preovulatory LH surge. In Experiment 1, estrous female ferrets were perfused 0.5, 1.5, 3.0, 6.0 or 12.0 h after receiving one 5-min intromission from a male or after being placed alone in a testing cage for 20 min. Fos-like immunoreactivity (Fos-IR; Oncogene Ab-2 antiserum) and LHRH-like immunoreactivity (LHRH-IR; LR-1 antiserum) were visualized. The percentage of Fos-IR LHRH neurons was significantly augmented 1.5 h after mating but had returned to basal levels by 3.0 h. The double-labeled LHRH neurons were concentrated in the caudal medio-basal hypothalamus. In non-LHRH neurons the number of Fos-IR neural nuclei was significantly increased by mating in the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MA), ventrolateral hypothalamus (VLH), and midbrain central tegmental field (CTF) 1.5 h after mating but, as in LHRH neurons, had returned to basal levels by 3.0 h. In Experiment 2, estrous females were perfused 1.5 h or 8.0 h after either receiving one 5-min intromission or being placed alone in a testing cage, and the brains were processed for LHRH and c-Fos-like (DCH-1, Dr Gerard Evan), c-Jun-like (Jun-IR; Oncogene Ab-2) or Egr-1-like (Egr-IR; Santa Cruz) immunoreactivity. The percentage of LHRH neurons colabeled with both Fos-IR and Jun-IR was significantly greater in the 1.5 h group than in the unpaired group. Again, the induction of these IEG products occurred in LHRH neurons in the caudal medio-basal hypothalamus. Mating significantly increased the number of Fos-IR non-LHRH neural nuclei in the MPOA, BNST, MA, VMH and CTF, as well as the number of Egr-IR nuclei in the MPOA, BNST and MA in the 1.5 h group. By contrast, the number of Jun-IR non-LHRH neurons was unaffected by mating. In these Experiments we have identified a sub-population of LHRH neurons which, using Fos and Jun as markers of neural activation, is activated by mating and may be differentially involved in the generation of the preovulatory LH surge. Although the LHRH system is presumably activated throughout the duration of the 12 h preovulatory LH surge, c-Fos and c-Jun immunoreactivity in LHRH neurons is augmented only transiently. Fos-IR and Egr-IR in non-LHRH neurons show a similar time-course. Together, these results suggest that the presence of augmented levels of these proteins is not required for the maintenance or termination of the preovulatory output of LHRH.

Animals↗

PubMed1996

Ferret mothers provide more anogenital licking to male offspring: possible contribution to psychosexual differentiation.

European ferret (Mustela putorius furo) mothers displayed significantly higher levels of anogenital licking (AGL) towards male as opposed to female kits in tests given on postpartum (P) days 6, 12, and 15. In these tests the entire litter was removed from the nestbox for 10 min, whereupon individual male and female kits were reintroduced to the mother in a counterbalanced order. In a second study an analysis of videotapes, sampled over the 24 h of several days, showed that mothers provided significantly more AGL to males than to females on P15, with a similar trend being observed on P1 and P8. This difference was no longer present on P22. In neither experiment was any sex difference observed in the amount of maternal licking of other (nonanogenital) body parts or in maternal carrying behavior received by kits. These results are comparable to those previously published for rat and gerbil, and further emphasize the possible contribution of sex differences in maternal stimulation, especially AGL, to the development of sexually dimorphic features of brain and behavioral development in different mammalian orders.

Aging↗

PubMed1995

Telencephalic and diencephalic origin of radial glial processes in the developing preoptic area/anterior hypothalamus.

Neuronal birth-dating studies using [3H] thymidine have indicated that neurons in the preoptic area/anterior hypothalamus (POA/AH) are derived primarily from progenitors in proliferative zones surrounding the third ventricle. Radial glial processes are potential guides for neuronal migration, and their presence and orientation during development may provide further information about the origin of cells in the POA/AH. In addition to determining the orientation of radial glial fibers, we examined the relationship of neurons with identified birth dates to radial glial processes in the developing POA/AH of ferrets. Neuronal birth dates were determined by injecting ferret fetuses with bromodeoxyuridine (BrdU) at several different gestational ages; brains were taken from ferret kits at subsequent prenatal ages. Sections were processed for immunocytochemistry to reveal vimentin or glial fibrillary acidic protein in radial glial, or BrdU-labeled cell nuclei. Numerous radial glial processes extended from the lateral ventricles through ventral portions of the septal region to the pial surface of the POA/AH. These fibers both encapsulated and coursed ventrally through and around the anterior commissure of ferret, rat, and mouse fetuses. These ventrally directed fibers were less evident at older ages. In double-labeled sections from ferrets, BrdU-labeled cells in the dorsal POA/AH were often aligned in the same dorsal-ventral orientation as adjacent radial glial fibers. We suggest that a subset of neurons, originating in telencephalic proliferative zones, migrates ventrally along radial glial guides into the dorsal POA/AH.

Animals↗

PubMed1995

A sex comparison of increments in FOS immunoreactivity in forebrain neurons of gonadectomized, testosterone-treated rats after mounting an estrous female.

The protein product of the immediate-early gene, c-fos, was visualized immunocytochemically in forebrain neurons of gonadectomized male and female rats which were injected daily with testosterone propionate (TP) and either tested for mounting directed toward a sexually receptive female or left alone in a test arena. Lidocaine anesthetic paste was applied to the genital region of all subjects in an attempt to reduce the incidence of intromissive behavior patterns. In this way we hoped to compare the relative contribution in the two sexes of vomeronasal/olfactory, as opposed to genital/somatosensory, stimuli to mounting-induced forebrain Fos immunoreactivity (FOS-IR). Males displayed high levels of mounting, with very few intromissions; females displayed a similar level of mounting coupled with a significantly higher number of intromissive behavior patterns than males. Significant increments in the number of FOS-IR neurons were seen in the medial amygdala (mAMYG) and medial preoptic area (mPOA) of males and females killed 1 h after testing. In experiment 2, ovariectomized, TP-treated females were given a unilateral lesion of the olfactory peduncle and subsequently tested with an estrous female as in Experiment 1. Unilateral lesions significantly reduced the number of FOS-IR neurons counted in the ipsilateral piriform (primary olfactory) cortex, but failed to attenuate the ability of stimuli associated with mounting an estrous female to augment FOS-IR in ipsilateral mAMYG or mPOA neurons. The results suggest that vomeronasal/olfactory stimuli were primary determinants of the mounting-induced increments in neuronal FOS-IR observed in males, whereas in females a combination of genital/somatosensory and olfactory/vomeronasal stimuli account for the observed induction of forebrain FOS-IR.

Amygdala↗

PubMed1995

Altered sexual partner preference in male ferrets given excitotoxic lesions of the preoptic area/anterior hypothalamus.

Numerous experiments suggest that perinatal exposure of male vertebrates to testosterone (T), or its estrogenic metabolites, masculinizes aspects of coital function, including males' characteristic preference to seek out and mate with a female as opposed to another male conspecific. Other research has shown that this perinatal action of sex steroids also masculinizes aspects of neuronal morphology in the medial preoptic area/anterior hypothalamus (mPOA/AH). We asked whether neurons of the mPOA/AH contribute to males' preference to mate with a female. The ferret is an ideal species in which to ask this question. When tested in a T-maze after gonadectomy and treatment with estradiol benzoate (EB), female ferrets prefer to approach and receive neck grips from a stimulus male whereas males prefer to approach and neck grip an estrous female. In the minority of trials when EB-treated males approach a stimulus male, they occasionally receive a neck grip to which they display receptive postures as opposed to agonistic behaviors. In Experiment 1 castrated, EB-treated male ferrets which received bilateral infusions of the NMDA excitotoxin, quinolinic acid aimed at the dorsomedial POA/AH, preferred to approach a stimulus male significantly more often than groups of control males which either received a sham lesion, received a unilateral mPOA/AH lesion or in which bilateral infusions of quinolinic aci produced no histologically detectible excitotoxic damage to the mPOA/AH. Males with bilateral mPOA/AH lesions also displayed neck gripping on a significantly lower percentage of trials than control males when they approached the stimulus female. Ovariectomized, EB-treated female ferrets with bilateral mPOA/AH lesions, like control females, preferred to approach and receive neck grips from a stimulus male. The males used in Experiment 1 had never experienced circulating levels of T characteristic of the breeding season. Therefore, in Experiment 2 prepubertally gonadectomized males and females were treated chronically with a high dose of T propionate (TP) and tested several times with a receptive female prior to brain surgery. Males which received bilateral excitotoxic lesions of the mPOA/AH neck gripped and mounted stimulus females significantly less than control males. Again, when given EB followed by T-maze tests of partner preference, males with bilateral mPOA/AH lesions, like sham-operated female controls, preferred to approach the sexually active stimulus male significantly more often than control males, which preferred to approach the stimulus female. Our results suggest that neurons in the mPOA/AH play an important role in the integration of sensory cues which determine heterosexual partner preference in the male ferret, in addition to facilitating masculine coital performance.

Animals↗

PubMed1994

Differential effects of the serotonin1A agonist, 8-OH-DPAT, on masculine and feminine sexual behavior of the ferret.

Administration of the serotonin (5-HT)1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) facilitates the expression of masculine sexual behavior in male and female rats as well as in male rhesus monkeys and inhibits lordosis behavior in female rats. In the present study the effects of 8-OH-DPAT on masculine coital and feminine proceptive and receptive behaviors were evaluated in the ferret, a carnivore. Doses of 8-OH-DPAT (0.1 or 0.2 mg/kg) that facilitate masculine sexual behavior in rats inhibited masculine sexual behavior in castrated, estradiol benzoate (EB)-treated male ferrets. Lower doses of 8-OH-DPAT (5 or 10 micrograms/kg) had no effect on the expression of masculine sexual behavior in either males or females. In contrast to the female rat, administration of 8-OH-DPAT significantly facilitated receptive behaviors in ovariectomized, EB-treated female ferrets. None of the doses of 8-OH-DPAT tested modified proceptive behaviors of gonadectomized, EB-treated male or female ferrets, as assessed in a T-maze in which the subjects could choose to approach either a castrated, sexually inactive male or a castrated, testosterone-primed stud male. Thus whereas the 5-HT1A receptor agonist 8-OH-DPAT facilitates masculine sexual behavior and inhibits lordosis in the rat, it inhibits masculine sexual behavior and facilitates receptivity in the ferret. The different effects of 8-OH-DPAT observed in these two species may reflect differences in the neural control of their masculine coital and feminine receptive responses, respectively.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1994

Effect of a null mutation of the c-fos proto-oncogene on sexual behavior of male mice.

Sexual behavior was observed in male mice that were homozygous for a null mutation of the c-fos proto-oncogene, as well as in heterozygous mutants and wild-type controls. The onset of mounting was slower and the subsequent mounting rate was significantly lower in homozygous mutants than in either group of controls. Even so, a similar percentage of males of each genotype achieved ejaculation, and ejaculation latencies were equivalent in these mice. Likewise, in males that intromitted, the intromission efficiency and the number of intravaginal thrusts/intromission were similar among the three genotypes. The nuclear protein product (Fos) of c-fos was visualized immunocytochemically in the brains of heterozygous male mice 1 h after they exhibited a series of mounts, with or without intromission, leading to an ejaculation. As in the male of several other rodent species, nuclear Fos immunoreactivity was augmented in neurons of limbic and midbrain regions thought to convey olfactory/vomeronasal and genital/somatosensory information, respectively, to the medial preoptic area following contact with an estrous female. One interpretation of our behavioral results is that in the absence of normal neuronal c-fos expression, sensory stimuli that impinge on the male brain during mating lose their ability to initiate a cascade of further gene transcription events that otherwise control the rate at which a male reorients towards and mounts an estrous female during an ejaculatory series. Alternatively, the c-fos null mutation may disrupt normal neural development, leading to a structural change that mediates the observed deficit in mounting capacity.

Amygdala↗

PubMed1993

Estrogen receptor immunoreactive neurons in the fetal ferret forebrain.

The development of estrogen receptors was studied in the preoptic area/anterior hypothalamus (POA/AH) of fetal male and female ferrets. In males this region includes a nucleus (MN-POA/AH), delineated by Nissl stains, which is not discernible in females. The results reveal the distribution of estrogen receptor containing cells during the period when estrogen is known to induce the differentiation of the male ferret's MN-POA/AH. Brains were taken from ferret kits on days 30, 34, 37 and 40 of a 41-42 day gestation, and were processed utilizing the H222 monoclonal antibody to reveal estrogen receptors. At E30 there were numerous H222 immunoreactive (ir) cells in central regions of the POA/AH. From E30 to E40 there was a striking increase in the number of H222ir cells in the POA/AH. A broad sweep of H222ir cells extended from the ventral POA dorsally and laterally into the caudal POA and AH of both males and females. H222ir cells were not restricted to the region of the MN-POA/AH at any fetal age. H222 immunoreaction product at E30 was restricted to nuclear compartments. By E40, H222ir processes extended from some cells with H222ir nuclei in the medial and lateral POA/AH in both males and females. At the older fetal ages immunopositive cell numbers increased in lateral positions. At E34 and E37 (but not E30) selective ventricular zones, and regions between the hypothalamus and amygdala contained H222ir cells, suggesting the presence of estrogen receptors in cells during migration. Although the amygdala contained a few H222ir cells as early as E34, the cortex lacked H222ir cells even as late as E40. The appearance of H222ir cells in positions suggestive of migration is consistent with the hypothesis that estrogen receptors play some role in determining cell positions in certain regions of the developing nervous system.

Animals↗

PubMed1993

A sex comparison of serotonin immunoreactivity and content in the ferret preoptic area/anterior hypothalamus.

Previous studies with rats raised the possibility that sexually dimorphic features of the medial preoptic area/anterior hypothalamus (POA/AH) may result, in part, from a sex difference in the serotonergic innervation of this region. We asked whether a similar phenomenon may occur in a carnivore, the ferret. A sexually dimorphic male nucleus of the dorsal POA/AH (Mn-POA/AH) has previously been characterized in Nissl-stained sections of the male ferret forebrain; this nucleus is absent in females. A nondimorphic ventral nucleus of the POA/AH is found in both sexes. In the present study numerous serotonin (5-HT) immunoreactive (ir) fibers were observed in the dorsal POA/AH of gonadectomized adult ferrets of both sexes. By contrast, in both sexes the ventral nucleus of the POA/AH had many fewer 5-HTir fibers. A similar difference in the distribution of immunoreactivity between dorsal and ventral POA/AH was observed for tyrosine hydroxylase (TH) localized in cell bodies and in nerve fibers and for H222ir estrogen receptors localized in cell nuclei. Likewise, in both sexes the content of 5-HT and dopamine (DA), measured by high pressure liquid chromatography with electrochemical detection, were significantly higher in the dorsal than the ventral POA/AH, thereby corroborating observed regional differences in 5-HTir and THir fibers, respectively. The present findings provide no support for the notion that sexually dimorphic cytoarchitectonic features of the dorsal POA/AH in ferrets are associated with a sex difference in the serotonergic innervation of this region.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Equivalent levels of mating-induced neural c-fos immunoreactivity in castrated male rats given androgen, estrogen, or no steroid replacement.

The nuclear protein product (FOS) of the immediate-early gene, c-fos, was visualized immunocytochemically in the brains of male rats after they either achieved 8 intromissions with an estrous female or were left alone in a test arena. Mating induced equivalent increments in the number of FOS immunoreactive (IR) neurons present in the medial preoptic area (mPOA), the bed nucleus of the stria terminalis (BNST), and the medial amygdala in groups of males that were gonadally intact or had been castrated and treated for 7 days with either testosterone propionate, dihydrotestosterone propionate, estradiol benzoate (EB), or oil vehicle. Equivalent, low numbers of FOS-IR neurons were seen in these brain regions in additional groups of castrated males that received either EB or oil vehicle but were not paired with a female before being killed. Circulating sex steroids apparently contribute little to the mating-induced stimulation of c-fos gene expression, even in brain regions known to contain high levels of androgen and estrogen receptor.

Amygdala↗

PubMed1993

Mating-induced FOS-like immunoreactivity in the rat forebrain: a sex comparison and a dimorphic effect of pelvic nerve transection.

Previous research has shown that mating induces the expression of the immediate-early gene, c-fos, as detected by the increased presence of nuclear FOS-like immunoreactivity (FOS-IR), in specific forebrain regions of both male and female rats. In the male both olfactory-vomeronasal (O/V) and genital/somatosensory (G/S) inputs appear to contribute to the neural FOS response to mating whereas in the female G/S input carried by the pelvic nerves appears to mediate the forebrain FOS response. To date, however, no direct sex comparison of the mating-induced forebrain FOS response has been made in rats maintained under the same steroidal conditions nor has the contribution of afferent sensory input from the pelvic nerves been assessed in males. We first compared the level of FOS-IR in brain regions of mated and unpaired gonadectomized male and female rats given 5 micrograms/kg estradiol benzoate (EB) for 7 days and 500 micrograms progesterone (P) 4 h prior to testing. One h after experiencing 1 ejaculation, both sexes showed increased FOS-IR in the medial preoptic a (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala, the ventro-lateral portion of the ventromedial nucleus of the hypothalamus (VMN), and the midbrain central tegmental field (CTF). This increase was significantly greater in the MPOA and medial amygdala of mated females than of males. Bilateral transection of the pelvic nerves significantly attenuated the increase in FOS-IR after mating in the CTF of male rats and in the MPOA, BNST, VMN, medial amygdala and CTF of females. Thus, following mating there is no sex difference in the brain regions which express c-fos, but there is a dimorphism in the contribution of afferent information conveyed by the pelvic nerves to the mating-induced FOS response. The neural FOS response of the female to mating is heavily dependent upon the G/S afferent inputs carried by the pelvic nerves whereas the male's neural c-fos response may depend on O/V input plus G/S input conveyed via other efferent pathways such as the pudendal nerves.

Animals↗

PubMed1993

Sex and regional differences in intracellular localization of estrogen receptor immunoreactivity in adult ferret forebrain.

Estrogen receptors were visualized in adult ferret brains using the H222 estrogen receptor antibody and immunocytochemical techniques. H222 immunoreactive (H222ir) cell nuclei were present in many forebrain regions in gonadectomized ferrets of both sexes. In many instances, H222ir cells also had immunoreaction product in their processes. All cells with H222ir processes also contained H222ir nuclei. More H222ir processes were observed in females in the medial and lateral preoptic area/anterior hypothalamus, and at the level of the descending fornix and caudal anterior commissure. Quantitative image analysis confirmed that females had significantly more (approximately 50%) extranuclear H222 immunoreaction product than males in cells in the magnocellular or preoptic subnuclei of the bed nucleus of the stria terminalis. Cells in the principal subnucleus of the bed nucleus of the stria terminalis and ventrolateral septum were notable for the relative paucity of H222ir processes. Sex differences in the intracellular extranuclear distribution of estrogen receptor protein in particular brain regions might contribute to the differential regulation of estrogen-dependent functions in the two sexes.

Animals↗

PubMed1992

Effects of sex and androgen treatment on dendritic dimensions of neurons in the sexually dimorphic preoptic/anterior hypothalamic area of male and female ferrets.

A sexually dimorphic group of cells at the dorsal border of the preoptic/anterior hypothalamic area (POA/AH) of ferrets has been previously identified in Nissl-stained tissue. In this study, Golgi-stained tissue was examined in order 1) to determine whether sex differences exist in dendritic dimensions of neurons from this region, and 2) to assess the effects of adult androgen treatment on dendritic morphology in ferrets of both sexes. Brains from adult ferrets given daily injections of testosterone propionate (5 mg/kg body weight) or oil vehicle for 5 weeks after gonadectomy were impregnated by Golgi-Cox procedures. After sectioning at 120 microns, 78 multipolar neurons were selected from the sexually dimorphic POA/AH of 12 ferrets and reconstructed in three dimensions with the aid of a computer-assisted neuron tracing system. Large sex differences were observed in somal area and most aspects of dendritic morphology, including total length, number of branches, and total dendritic surface area. Androgen also appeared to accentuate dendritic arborization in both sexes, but this effect was weaker than the sex effect, more apparent in males than females, and restricted to fewer variables. The most statistically significant effects of adult androgen treatment in males were found for total dendritic surface area and percentage of fourth order dendrites, and in females, average dendritic thickness. These data show that strong sex differences exist in dendritic structure of neurons in the POA/AH, and suggest that alterations in levels of gonadal steroids in adulthood may promote synaptic remodeling in a region of the brain involved in the control of sexually dimorphic behaviors.

Animals↗

PubMed1992

Sexual dimorphism in the effects of mating on the in vitro release of LHRH from the ferret mediobasal hypothalamus.

A sexually dimorphic pattern in the secretion of luteinizing hormone (LH) has previously been shown to occur in response to mating in an induced ovulating species, the ferret, with mating augmenting the secretion of LH in females but not in males. The aim of this study was to determine whether this dimorphic pattern in the postcoital secretion of LH reflects a dimorphic effect of mating on the neural release of luteinizing hormone releasing hormone (LHRH). The effect of mating on the in vitro release of LHRH from mediobasal hypothalami (MBH) collected from breeding male and female ferrets was studied. Luteinizing hormone releasing hormone release and content were significantly reduced in tissues from estrous females sacrificed 0.25 h after mating compared to unpaired estrous females and estrous females sacrificed 1 or 2.6 h after the mating stimulus. By contrast, the release of LHRH from MBH fragments and LHRH tissue content were equivalent in breeding males that were sacrificed 0.25 h after mating and in breeding males that were left unpaired. These data suggest that the postcoital surge of LH in the female ferret is preceded by a release of LHRH that initially depletes neuronal terminals within the MBH, whereas LHRH release, like pituitary LH secretion, is minimally affected by mating in males.

Animals↗

PubMed1992

Increased expression of c-fos in the medial preoptic area after mating in male rats: role of afferent inputs from the medial amygdala and midbrain central tegmental field.

Immunocytochemical methods were used to localize the protein product of the immediate-early gene, c-fos, in male rats after exposure to, or direct physical interaction with, oestrous females. Increasing amounts of physical contact with a female, with resultant olfactory-vomeronasal and/or genital-somatosensory inputs, caused corresponding increments in c-fos expression in the medial preoptic area, the caudal part of the bed nucleus of the stria terminalis, the medial amygdala, and the midbrain central tegmental field. Males bearing unilateral electrothermal lesions of the olfactory peduncle showed a significant reduction in c-fos expression in the ipsilateral medial amygdala, but not in other structures, provided their coital interaction with oestrous females was restricted to mount-thrust and occasional intromissive patterns due to repeated application of lidocaine anaesthetic to the penis. No such lateralization of c-fos expression occurred in other males with unilateral olfactory lesions which were allowed to intromit and ejaculate with a female. These results suggest that olfactory inputs, possibly of vomeronasal origin, contribute to the activation of c-fos in the medial amygdala. However, lesion-induced deficits in this type of afferent input to the nervous system appear to be readily compensated for by the genital somatosensory input derived from repeated intromissions. Unilateral excitotoxic lesions of the medial preoptic area, made by infusing quinolinic acid, failed to reduce c-fos expression in the ipsilateral or contralateral medial amygdala or central tegmental field following ejaculation. By contrast, combined, unilateral excitotoxic lesions of the medial amygdala and the central tegmental field significantly reduced c-fos expression in the ipsilateral bed nucleus of the stria terminalis and medial preoptic area after mating; no such asymmetry in c-fos expression occurred when lesions were restricted to either the medial amygdala or central tegmental field. This suggests that afferent inputs from the central tegmental field (probably of genital-somatosensory origin) and from the medial amygdala (probably of olfactory-vomeronasal origin) interact to promote cellular activity, and the resultant induction of c-fos, in the ipsilateral bed nucleus of the stria terminalis and medial preoptic area. The monitoring of neuronal c-fos expression provides an effective means of studying the role of sensory factors in governing the activity of integrated neural structures which control the expression of a complex social behaviour.

Amygdala↗

PubMed1992

Sex difference in the effect of mating on c-fos expression in luteinizing hormone-releasing hormone neurons of the ferret forebrain.

The pulsatile secretion of LH was previously found to rise in female ferrets after receipt of an intromission, whereas in males that achieved an intromission, both LH and testosterone secretion were either reduced or unchanged. We sought to determine whether this sexually dimorphic pattern of LH secretion reflects a sex difference in the effect of mating on the activity of forebrain neurons that secrete LHRH. Immunocytochemical methods were used to localize the nuclear protein product of the immediate early gene, c-fos, as an index of increased neuronal activity after mating. Nuclear FOS immunoreactivity (FOS-IR) was monitored in LHRH-IR neurons as well as other non-LHRH forebrain neurons. In confirmation of previous reports, LHRH-IR perikarya in ferrets of both sexes were located medially along the base of the brain at rostral, medial, and caudal levels of the preoptic-hypothalamic continuum. In each of these regions a significantly higher percentage of LHRH-IR neurons was colabeled with nuclear FOS-IR in mated than in unpaired females. By contrast, an equivalent low percentage of LHRH-IR neurons was colabeled with FOS-IR in mated and unpaired male ferrets. Significantly more FOS-IR neurons (not colabeled with LHRH) were detected in the bed nucleus of the stria terminalis, the medial preoptic area, the dorsal-medial hypothalamus, and the medial amygdala (MA) of mated vs. unpaired females. By contrast, mating significantly augmented FOS-IR only in the MA of male ferrets. The results suggest that the sexually dimorphic pattern of LH secretion that occurs in ferrets after mating reflects a selective activation of LHRH neurons in the female forebrain. This sex-specific increase in the responsiveness of LHRH neurons to mating may depend on input from a limbic circuit which includes the medial amygdala, bed nucleus of the stria terminalis, and medial preoptic area.

Animals↗

PubMed1991

Neonatal testosterone masculinizes sexual behavior without affecting the morphology of the dorsal preoptic/anterior hypothalamic area of female ferrets.

We examined whether testosterone (T) administered to female ferrets neonatally--a treatment known to enhance masculine coital capacity--induces formation of the sexually dimorphic male nucleus in the dorsal preoptic/anterior hypothalamic area (MN-POA/AH), and/or sensitizes dorsal POA/AH neurons to the stimulatory effect of later androgen treatment on somal dimensions. In males, the MN-POA/AH was present in all subjects, and exposure to androgen following castration at postnatal day 56 (P56) increased both MN-POA/AH volume as well as mean somal areas of MN-POA/AH neurons relative to oil-treated controls. Females given androgen from P5 to P20 and for one month beginning after ovariectomy on P56 failed to develop the MN-POA/AH, but displayed high levels of masculine sexual behavior. Somal areas of dorsal POA/AH neurons in females that received either T or a control neonatally did not increase following androgen treatment at P56. Thus, the correlation that exists between somal enlargement of dorsal POA/AH neurons and masculine sexual behavior in androgen-treated males is not found in behaviorally masculinized females. Masculine coital ability does not appear related to aspects of dorsal POA/AH morphology, supporting data from a previous study in which lesions of the MN-POA/AH caused negligible deficits in masculine sexual behavior of adult male ferrets.

Animals↗