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

Analysis of Postnatal Mutant Phenotypes in Mice

Viable homozygous mutant newborn mice may show effects of a mutation at any time during their development by exhibiting abnormal structure, function, or lethality. This overview guides the analysis of postnatal mice through gross anatomical assessment and the detection of visible phenotypes prior to weaning such as altered growth patterns, neurological problems, or abnormalities in movement or coordination. Advice on marking pups for identification purposes and providing adequate nutrition in the event of eating problems is given. After weaning and at the onset of puberty, different phenotypes may become manifest, including compromised growth and vigor and reproductive problems in males and/or females. Assessing infertility in each sex is addressed.

Behavioral evidence of the functional interaction between the main and accessory olfactory system suggests a large olfactory system with a high plastic capability

Olfaction is fundamental in many species of mammals. In rodents, the integrity of this system is required for the expression of parental and sexual behavior, mate recognition, identification of predators, and finding food. Different anatomical and physiological evidence initially indicated the existence of two anatomically distinct chemosensory systems: The main olfactory system (MOS) and the accessory olfactory system (AOS). It was originally conceived that the MOS detected volatile odorants related to food, giving the animal information about the environment. The AOS, on the other hand, detected non-volatile sexually relevant olfactory cues that influence reproductive behaviors and neuroendocrine functions such as intermale aggression, sexual preference, maternal aggression, pregnancy block (Bruce effect), puberty acceleration (Vandenbergh effect), induction of estrous (Whitten effect) and sexual behavior. Over the last decade, several lines of evidence have demonstrated that although these systems could be anatomically separated, there are neuronal areas in which they are interconnected. Moreover, it is now clear that both the MOS and the AOS process both volatile and no-volatile odorants, indicating that they are also functionally interconnected. In the first part of the review, we will describe the behavioral evidence. In the second part, we will summarize data from our laboratory and other research groups demonstrating that sexual behavior in male and female rodents induces the formation of new neurons that reach the main and accessory olfactory bulbs from the subventricular zone. Three factors are essential for the neurons to reach the AOS and the MOS: The stimulation frequency, the stimulus's temporal presentation, and the release of opioids induced by sexual behavior. We propose that the AOS and the MOS are part of a large olfactory system with a high plastic capability, which favors the adaptation of species to different environmental signals.

PA1 participates in the maintenance of blood-testis barrier integrity via cooperation with JUN in the Sertoli cells of mice

Background

The blood–testis barrier (BTB) is essential to the microenvironment of spermatogenesis, and Sertoli cells provide the cellular basis for BTB construction. Numerous nuclear transcription factors have been identified to be vital for the proper functioning of Sertoli cells. PA1 has been reported to play important roles during diverse biological processes, yet its potential function in male reproduction is still unknown.

Results

Here, we show that PA1 was highly expressed in human and mouse testis and predominantly localized in the nuclei of Sertoli cells. Sertoli cell-specific Pa1 knockout resulted in an azoospermia-like phenotype in mice. The knockout of this gene led to multiple defects in spermatogenesis, such as the disorganization of the cytoskeleton during basal and apical ectoplasmic specialization and the disruption of the BTB. Further transcriptomic analysis, together with Cut-Tag results of PA1 in Sertoli cells, revealed that PA1 could affect the expression of a subset of genes that are essential for the normal function of Sertoli cells, including those genes associated with actin organization and cellular junctions such as Connexin43 (Cx43). We further demonstrated that the expression of Cx43 depended on the interaction between JUN, one of the AP-1 complex transcription factors, and PA1.

Conclusion

Overall, our findings reveal that PA1 is essential for the maintenance of BTB integrity in Sertoli cells and regulates BTB construction-related gene expression via transcription factors. Thus, this newly discovered mechanism in Sertoli cells provides a potential diagnostic or even therapeutic target for some individuals with azoospermia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00773-y.

Transcription factor gene Pea3 regulates erectile function during copulation in mice

Male mice with homozygous loss of function mutations of the transcription factor gene Pea3 (Pea3 null) are infertile due to their inability to inseminate females, however the specific deficits in male sexual behaviors that drive this phenotype are unknown. Here, the copulatory behavior of male mice (Pea3 null and control) with hormonally primed ovariectomized females was monitored via high-speed and high-resolution digital videography to assess for differences in female-directed social behaviors, gross sexual behaviors (mounting, thrusting), and erectile and ejaculatory function. Pea3 null male mice exhibit greatly reduced erectile function, with 44% of males displaying no visible erections during copulation, and 0% achieving sustained erections. As such, Pea3 null males are incapable of intromission and copulatory plug deposition, despite displaying largely normal female-directed social behaviors, mounting behaviors, and ejaculatory grasping behavior. Additionally, the organization and timing of thrusting behaviors is impaired in Pea3 null males. Our results show that the transcription factor gene Pea3 regulates the ability to achieve and maintain erections during copulation in mice.

Optogenetic Activation of Accessory Olfactory Bulb Input to the Forebrain Differentially Modulates Investigation of Opposite versus Same-Sex Urinary Chemosignals and Stimulates Mating in Male Mice

Surgical or genetic disruption of vomeronasal organ (VNO)-accessory olfactory bulb (AOB) function previously eliminated the ability of male mice to processes pheromones that elicit territorial behavior and aggression. By contrast, neither disruption significantly affected mating behaviors, although VNO lesions reduced males' investigation of nonvolatile female pheromones. We explored the contribution of VNO-AOB pheromonal processing to male courtship using optogenetic activation of AOB projections to the forebrain. Protocadherin-Cre male transgenic mice received bilateral AOB infections with channelrhodopsin2 (ChR2) viral vectors, and an optical fiber was implanted above the AOB. In olfactory choice tests, males preferred estrous female urine (EFU) over water; however, this preference was eliminated when diluted (5%) EFU was substituted for 100% EFU. Optogenetic AOB activation concurrent with nasal contact significantly augmented males' investigation compared to 5% EFU alone. Conversely, concurrent optogenetic AOB activation significantly reduced males' nasal investigation of diluted urine from gonadally intact males (5% IMU) compared to 5% IMU alone. These divergent effects of AOB optogenetic activation were lost when males were prevented from making direct nasal contact. Optogenetic AOB stimulation also failed to augment males' nasal investigation of deionized water or of food odors. Finally, during mating tests, optogenetic AOB stimulation delivered for 30 s when the male was in physical contact with an estrous female significantly facilitated the occurrence of penile intromission. Our results suggest that VNO-AOB signaling differentially modifies males' motivation to seek out female vs male urinary pheromones while augmenting males' sexual arousal leading to intromission and improved reproductive performance.

C-fos down-regulation inhibits testosterone-dependent male sexual behavior and the associated learning

Environmental stimulation results in an increased expression of transcription factors called immediate early genes (IEGs) in specific neuronal populations. In male Japanese quail, copulation with a female increases the expression of the IEGs zenk and c-fos in the medial pre-optic nucleus (POM), a key nucleus controlling male sexual behavior. The functional significance of this increased IEG expression that follows performance of copulatory behavior is unknown. We addressed this question by repeatedly quantifying the performance of appetitive (learned social proximity response) and consummatory (actual copulation) sexual behavior in castrated, testosterone-treated males that received daily intra-cerebroventricular injection of an antisense oligodeoxynucleotide targeting c-fos or control vehicle. Daily antisense injections significantly inhibited the expression of copulatory behavior as well as the acquisition of the learned social proximity response. A strong reduction of the proximity response was still observed in antisense-treated birds that copulated with a female, ruling out the indirect effect of the absence of interactions with females on the learning process. After a 2-day interruption of behavioral testing but not of antisense injections, birds were submitted to a final copulatory test that confirmed the behavioral inhibition in antisense-injected birds. Brains were collected at 90 min after the behavioral testing for quantification of c-fos-immunoreactive cells. A significant reduction of the number of c-fos-positive cells in the POM but not in other brain regions was observed following antisense injection. Taken together, the data suggest that c-fos expression in the POM modulates copulatory behavior and sexual learning in male quail.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Adult testosterone treatment but not surgical disruption of vomeronasal function augments male-typical sexual behavior in female mice

It was recently reported that female mice lacking a functional vomeronasal organ (VNO) displayed male-typical sexual behavior indiscriminately toward female and male conspecifics. These results have been cited as showing that a circuit controlling male-typical sex behavior exists in both sexes, with its activation in females being tonically inhibited by VNO signaling, independent of adult sex hormones. We further assessed this hypothesis while controlling the endocrine status of female mice in which VNO function was surgically disrupted. In experiment 1, VNO-lesioned (VNOx) female mice showed no more mounting or pelvic-thrusting behavior toward an estrous female or a castrated, urine-swabbed male (presented simultaneously) than sham-operated (VNOi) females. This was true when subjects were either ovary-intact or ovariectomized and treated with estradiol, estradiol plus progesterone, or testosterone. In experiment 2, female mice given accessory olfactory bulb lesions or a sham lesion displayed equivalent frequencies of male sex behaviors when given testosterone after ovariectomy. In experiment 3, VNOx and VNOi females displayed equivalent frequencies of male sex behaviors toward an estrous female or a castrated male (presented in separate tests), again, when given testosterone after ovariectomy. Our results confirm early reports that adult testosterone can stimulate appreciable male-typical sex behavior in female mice. However, we failed to corroborate the recent claim that VNO signaling normally inhibits the activity of neural circuitry controlling the expression of male-typical mating behavior by female mice.

Mating-induced neuroendocrine responses during pseudopregnancy in the female mouse

Pseudopregnancy (PSP) is a neuroendocrine reflex triggered by vaginocervical stimulation similar to the neuroendocrine response of early pregnancy and is characterised by short-term neural activity, resulting in long-term neuroendocrine responses that cause repeated release of pituitary prolactin (PRL) over many days. PSP is a useful model to study how somatosensory input is transduced in the brain into neuroendocrine responses, and has been extensively characterised in rats. With increasing use of mice as an experimental model, however, and to allow use of transgenic mice to investigate mechanisms of this sensory response, it is important to characterise the principal neuroendocrine response of pseudopregnancy in this species. The present study aimed to examine the induction and neuroendocrine responses of PSP in mice using vasectomised stud males, to investigate mating-induced changes in vaginal cytology, uterine growth, and PRL secretion, and to map certain aspects of somatosensory transduction by assessing the neural activity marker FOS. Unlike the induction of pseudopregnancy in rats, which can be induced simply by multiple intromissions from a male or artificial mechanical stimulation of the cervix, PSP induction in mice required the receipt of an ejaculation from a male. In mice that received PSP-inducible mating stimuli, FOS expression was observed in a slightly different range of brain regions than has been observed in rats, with increases in the bed nucleus of the stria terminalis, medial preoptic area, and ventromedial hypothalamus, but not in limbic areas examined. Moreover, PSP mice expressed a single diurnal PRL surge on day 6 of PSP. Thus, the data demonstrate important species differences in the neuroendocrine mechanisms activated in response to a mating stimulus in mice compared with rats. A clear understanding of the species-specific response will be required in interpreting research into the reproductive biology of this species.

Development of sex differences in the principal nucleus of the bed nucleus of the stria terminalis of mice: role of Bax-dependent cell death

Neuron number in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp) is greater in adult male mice than in females. Deletion of the proapoptotic gene, Bax, increases the number of BNSTp cells in adulthood and eliminates the sex difference in cell number. Here, we map the ontogeny of sex differences in nuclear volume and cell number in the BNSTp of neonatal mice, and evaluate the role of cell death in the development of these differences. We find that BNSTp volume and cell number do not differ between male and female wild-type mice on postnatal days P3, P5, or P7. Sex differences emerge after the first postnatal week and both measures are significantly greater in males than in females on P9 and P11. Cell death, assessed by TUNEL staining, was observed in the BNSTp of both sexes from P1-P8. Females had more TUNEL-positive cells than males from approximately P3-P6, with the maximum number of dying cells observed on P5/P6. To test whether the Bax gene is required for sexually dimorphic cell death in the BNSTp, TUNEL cells were counted on P6 in Bax -/- mice and their Bax +/+ siblings. Bax gene deletion nearly abolished TUNEL-positive cells in the BNSTp of both sexes. Together, these findings support the interpretation that the sex difference in BNSTp cell number seen in adulthood is due to Bax-dependent, sexually dimorphic cell death during the first week of life.

Olfactory preference and Fos expression in the accessory olfactory system of male rats with bilateral lesions of the medial preoptic area/anterior hypothalamus

In the present study we evaluated if a medial preoptic area/anterior hypothalamus lesion affects the olfactory preference toward soiled bedding from receptive females in comparison to bedding from anestrous females or clean bedding. In the second part of the study we evaluated the accessory olfactory system response to estrous bedding with Fos immunoreactivity to determine if the preoptic lesions modify the processing of sexually relevant olfactory cues. Before medial preoptic area/anterior hypothalamus lesions, male rats spent more time investigating estrous bedding as opposed to anestrous or clean bedding. After the lesion, subjects showed no preference between estrous and anestrous bedding; that is, males spent the same amount of time investigating both types of bedding. These two odors were investigated more than clean bedding. Increments in Fos immunoreactivity neurons were seen in structures of the accessory olfactory system after exposure to soiled estrous bedding [granular layer of the accessory olfactory bulb, anterior-dorsal medial amygdala, posterior-dorsal medial amygdala, bed nucleus of the stria terminalis]. These results suggest that bilateral destruction of the medial preoptic area/anterior hypothalamus modify male olfactory preference in such a way that subjects spend the same time smelling and investigating bedding from estrous and anestrous females. This change in olfactory preference is not associated with alterations in the processing of sexually relevant olfactory cues by the accessory olfactory system.

Olfactory sex discrimination persists, whereas the preference for urinary odorants from estrous females disappears in male mice after vomeronasal organ removal

Based on observed changes in the social context for the display of ultrasonic vocalizations, scent marking, aggression, and mounting behavior by male mice with a null mutation of the transient receptor potential 2 ion channel, it was proposed recently that a primary function of the mouse vomeronasal organ (VNO)/accessory olfactory system is sex discrimination. We tested this hypothesis directly by studying the ability of male mice to discriminate between urinary odors of conspecifics of the two sexes and in different endocrine states using habituation-dishabituation tests. Male mice from which the VNO had been surgically removed (VNOx) resembled sham-operated controls (VNOi) in their ability to discriminate between volatile urinary odors from estrous females versus gonadally intact males, as well as between urinary odors from estrous versus ovariectomized females and from gonadally intact versus castrated males. When physical access to stimuli was permitted, VNOi control males strongly preferred to investigate volatile and nonvolatile urinary odorants from estrous females as opposed to intact males, whereas VNOx males showed no such preference. Mating performance in tests with estrous females was equivalent in VNOi and VNOx subjects. Both groups of males preferred to mount an estrous female instead of a castrated male. Our results suggest that the VNO is not required for sex discrimination but instead detects the nonvolatile components of opposite-sex urine that may be used to help prolong contact with individuals that produce these chemosignals.

Sex differences in Fos protein expression in the neonatal rat brain

Sex differences in the brain and behaviour are mostly a result of transient increases in testosterone during the perinatal period. Testosterone influences brain development primarily through aromatization to oestradiol and subsequent binding to oestrogen receptors. Although some studies report that steroid hormones regulate the expression of the inducible transcription factor, Fos, in developing brain, it is not known if there is a sex difference in Fos expression. Changes in Fos protein can be used as an indicator of neuronal/genomic activity. Thus, it provides a useful tool to identify brain regions responding directly or indirectly to steroid hormones. In a first experiment, we examined Fos protein expression in the developing male and female rat brain using western immunoblotting. Dissections were taken from male and female rat pups on the day of birth (postnatal day 0; PN 0), PN1, PN5, PN11 or PN20. Although there was no difference on PN 0, males expressed significantly greater levels of Fos protein on PN1, PN5 and PN20. In a second experiment, we localized the sex difference in Fos protein expression using immunocytochemistry. We found that males expressed significantly higher levels of Fos within a variety of brain regions. These data indicate a sex difference in Fos protein expression during brain development, suggesting a potential role for Fos in differentiating male from female rat brain.

Sexual incentive motivation, olfactory preference, and activation of the vomeronasal projection pathway by sexually relevant cues in non-copulating and naive male rats

There are some apparently healthy male rats that fail to mate after repeated testing with receptive females. We have previously shown that these "non-copulator (NC)" males show no partner preference for a receptive female when given the opportunity to physically interact with a sexually receptive female or a sexually active male. We also demonstrated that although NC males prefer odors from estrous females to odors from anestrous females, this preference is significantly reduced in comparison to the preference displayed by copulating (C) males. The aim of the present study was to evaluate in NC males sexual incentive motivation, that is, the approach behavior of male rats to either a sexually receptive female or a sexually active male in a test where the subjects can smell, hear, and see the stimulus animal but prevents their physical interaction. In addition, we determined whether NC rats have alterations in their ability to detect odors from conspecifics or odors related to food. In the detection of odors from conspecifics, we determined if these NC males are sexually attracted toward odors from receptive females or sexually active males. For food-related odors, we quantified the time it took the subjects to locate a hidden a piece of apple. Finally, using the induction of Fos-immunoreactivity (Fos-IR) as an index of neuronal activation, we compared the response of the vomeronasal projection pathway (VN pathway) of C and NC male rats exposed to estrous bedding. Males without sexual experience (WSE) were included in all experiments to determine the importance of previous heterosexual experience in the different behavioral tests and in the activity of the VN pathway. In the sexual incentive motivation test, we found that C and WSE male rats have a clear preference for estrous females over sexually active males, whereas NC male rats showed no preference. In odor tests, our results showed that C males had a clear preference for odors from estrous females as opposed to odors from sexually active males. Although NC and WSE male rats showed a preference for estrous female odors, this preference was significantly reduced compared to that shown by C males. No differences were found between WSE, C, and NC males in the detection of stimuli associated with food-related odors. A significant increase in Fos-IR was observed in the mitral cell layer of the accessory olfactory bulb in all groups when exposed to estrous bedding. However, only the C male rats exposed to estrous female bedding showed an increase Fos-IR in all structures of the VN pathway. An increase in Fos-IR was observed in the medial preoptic area (MPOA) of WSE males exposed to estrous bedding. No increases in Fos-IR were detected along the VN pathway in NC male rats. We proposed that NC male rats do not display sexual behavior due to a reduced sexual motivation that could be caused by alterations in the neuronal activity of the VN pathway during the processing of estrous odors.

Medial preoptic area/anterior hypothalamus and sexual motivation

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a brain site derived from proliferative zones from the diencephalon and telencephalon. It is probably this characteristic that makes this brain region participate in different physiological and behavioral functions. The present review addresses the role of the MPOA/AH in the control of male sexual behavior. It is clear that the MPOA/AH is a crucial site in the control of sexual behavior in males of all species studied to date. But although many different publications have followed the contribution of Heimer and Larsson there is no agreement as to what is specifically the role of the MPOA/AH in sexual behavior. At least three hypotheses have been presented. The first one suggests that this brain region is involved in the consummatory aspects (execution) of sexual behavior. The second indicates that the MPOA/AH is involved in the appetitive components (motivation) of masculine sexual behavior. The third hypothesis considers that MPOA/AH neurons are involved in the regulation of consummatory and appetitive aspects of sexual behavior. From the literature reviewed, it will become evident that the evidence supporting a role of the MPOA/AH in the execution of sexual behavior is based on a number of limited studies not easy to interpret. On the other hand, several lines of evidence using a variety of methodologies support the notion that the MPOA/AH is involved in the motivational aspects of male sexual behavior.

Anatomical markers of activity in neuroendocrine systems: are we all 'fos-ed out'?

It has now been nearly 15 years since the immediate early gene, c-fos, and its protein product, Fos, were introduced as tools for determining activity changes within neurones of the nervous system. In the ensuing years, this approach was applied to neuroendocrine study with success. With it have come advances in our understanding of which neuroendocrine neurones respond to various stimuli and how other central nervous system components interact with neuroendocrine neurones. Use of combined tract-tracing approaches, as well as double-labelling for Fos and transmitter markers, have added to characterization of neuroendocrine circuits. The delineation of the signal transduction cascades that induce Fos expression has led to establishment of the relationship between neurone firing and Fos expression. Importantly, we can now appreciate that Fos expression is often, but not always, associated with increased neuronal firing and vice versa. There are remaining gaps in our understanding of Fos in the nervous system. To date, knowledge of what Fos does after it is expressed is still limited. The transience of Fos expression after stimulation (especially if the stimulus is persistent) complicates design of experiments to assess the function of Fos and makes Fos of little value as a marker for long-term changes in neurone activity. In this regard, alternative approaches must be sought. Useful alternative approaches employed to date to monitor neuronal changes in activity include examination of (i) signal transduction intermediates (e.g. phosphorylated CREB); (ii) transcriptional/translational intermediates (e.g. heteronuclear RNA, messenger RNA (mRNA), prohormones); and (iii) receptor translocation. Another capitalizes on the fact that many neuroendocrine systems show striking stimulus-transcription coupling in the regulation of their transmitter or its synthetic enzymes. Together, as we move into the 21st Century, the use of multiple approach to study activity within neuroendocrine systems will further our understanding of these important systems.

Estrogen in the medial preoptic area of male rats facilitates copulatory behavior

Mating was studied in sexually experienced, gonadally intact male rats assigned to two surgical groups matched on the basis of mean mounting frequency during behavioral screening trials conducted prior to the study. Estradiol (E(2)) was delivered bilaterally into the medial preoptic area (MPO) of experimental males by means of hormone-coated implants, and fadrozole was given sc (0.25 mg/kg/day) via osmotic minipumps to block E(2) formation from testicular testosterone throughout the brain. Control males received blank bilateral implants in the MPO and sc fadrozole. After the completion of behavioral testing, immunocytochemical comparisons of the brains from experimental and control rats were made using the H222 antiestrogen receptor (ER) antibody, whose labeling is inhibited by the presence of E(2). The histology demonstrated that E(2) was confined exclusively to the MPO of experimental males but was absent throughout the brains of controls. In controls, mounting decreased significantly by the 7th day after surgery compared with presurgical levels and did not recover. In contrast, on all postsurgical days, the mounting frequency of the experimental group was significantly higher than that of controls. Although experimental males also showed an initial, significant postsurgical decline in mounting frequency, it recovered completely by the 28th postoperative day. Ejaculations declined significantly after surgery in both groups but, unlike in controls whose performance remained low, ejaculations in experimental males partially recovered and were significantly higher than in controls during the postoperative period. Results showed that ER-containing neurons in the MPO influence male rat copulatory behavior.

Targeted disruption of the murine junD gene results in multiple defects in male reproductive function

JunD is one of three mammalian Jun proteins that contribute to the AP-1 transcription factor complex. Distinct regulation and functions have been proposed for each Jun member, but less is known about the biological functions of each of these proteins in vivo. To investigate the role of JunD, we have inactivated the murine gene by replacement with a bacterial lacZ reporter gene. Embryonic JunD expression was initially detected in the developing heart and cardiovascular system. Subsequent broadening phases of JunD expression were observed during embryonic development and expression in the adult was widespread in many tissues and cell lineages. Mutant animals lack JunD mRNA and protein and showed no evidence of upregulation of c-Jun and JunB mRNA levels. In contrast to the other two Jun members, homozygous JunD−/− mutant animals were viable and appeared healthy. However, homozygous JunD−/− animals showed a reduced postnatal growth. Furthermore, JunD−/− males exhibited multiple age-dependent defects in reproduction, hormone imbalance and impaired spermatogenesis with abnormalities in head and flagellum sperm structures. No defects in fertility were observed in JunD−/− female animals. These results provide evidence for redundant functions for members of the Jun family during development and specific functions for JunD in male reproductive function.

Effects of mating on c-fos expression in the brains of male macaques

The c-fos polyclonal anti-c-fos antibody was used to examine the effects of mating on Fos expression in brain neurons of 11 male macaques. Behavior tests were for 30 min, five males were unmated, four were mated, and two were social controls. Mated males were killed 60 min after ejaculation. Social controls were paired with females, but mating did not occur. Fos immunoreactive (Fos-ir) neuronal nuclei were counted in nine brain regions extending from the medial preoptic to the mammillary body area of all males. In contrast to previous reports on nonprimate laboratory species, overall there was as much Fos-ir in unmated as in mated males. Moreover, there was significantly less Fos expression in four brain regions (known to contain steroid receptors), namely, ventromedial hypothalamus, arcuate nucleus, lateral mammillary area, and bed nucleus of stria terminalis, of mated than of unmated males. There were no significant differences between mated and unmated males in the 5 other brain regions studied. These findings may reflect taxonomic differences between primates and nonprimates, or result from greater neural activation in feral animals maintained in a laboratory than in domesticated, inbred laboratory species. The simplest interpretation would be that neural activity in the male primate is turned off by mating in some brain sites but not in others.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Fos-immunoreactivity within the extended amygdala is correlated with the onset of sexual satiety

We hypothesized that c-fos expression in the medial amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the male Syrian hamster brain correlated with sexual satiety. To address this hypothesis, males were mated for 4 consecutive days. Experiment 1 determined whether the number of Fos-immunoreactive (Fos-ir) nuclei was equivalent in two groups of males mated to sexual satiety, one group of rested males (9.67 +/- 0.80 ejaculations) and a second group mated for 4 consecutive days (3.50 +/- 0.56 ejaculations). Fos-ir was increased within the caudal posterodorsal Me (cMePD), the anterodorsal and posteroventral subdivisions of the posteromedial BNST [BNSTpm(ad) and BNSTpm(pv)], the dorsolateral MPOA, and the medial preoptic nucleus of all males mated to sexual satiety compared to nonmated controls. In addition, Fos-ir "clusters" within the cMePD and BNSTpm(ad) were present in males mated to satiety regardless of the number of ejaculations. However, all males achieved multiple ejaculations. Therefore, Experiment 2 examined whether two groups of males stopped at one ejaculation exhibit different patterns of Fos-ir depending on proximity to sexual satiety. Brains of consecutively mated males, closer to satiety than rested males, showed greater BNSTpm(pv) Fos-ir and 5/6 males, but no rested male, exhibited cMePD Fos-ir clusters. These results support the hypothesis that cMePD and BNSTpm(pv) neuronal activation is associated with satiety and may constitute a discrete circuit to terminate mating.

Behavior in mice with targeted disruption of single genes

The use of mice with targeted deletion, or knockout, of specific genes provides a relatively new approach to establish the molecular bases of behavior. As with all ablation studies, the interpretation of behavioral data may be limited by the technique. For example, indirect effects of the missing gene may affect behavior, rather than the missing gene per se. Also, because the missing gene might affect many developmental processes throughout ontogeny and because up-regulation or compensatory mechanisms may be activated in knockouts, behavioral data from mice with targeted gene deletions should be interpreted with caution. The development of conditional knockouts, in which a specific gene can be inactivated any time during ontogeny, should allow investigators to avoid these conceptual shortcomings associated with behavioral data from knockouts in the near future. The behavioral alterations reported in knockout mice are reviewed here. Many dramatic changes in complex motivated behaviors including aggression, sexual, ingestive, and parental behaviors, have been reported for knockouts. There have also been many reports of alterations in sensorimotor abilities and spontaneous activity, as well as impairments in balance, coordination, and gait. Impaired learning and memory have also been reported for mice with targeted disruption of specific genes. Taken together, the use of knockouts will provide an important new tool to understand the mechanisms underlying behavior.

Masculine sexual behavior is disrupted in male and female mice lacking a functional estrogen receptor alpha gene

Masculine sexual behavior is regulated by testosterone (T). However, T can be metabolized to form estrogens or other androgens, which then activate their own receptors. We used knockout mice lacking a functional estrogen receptor alpha (ER alpha) gene to test the hypothesis that, following aromatization, T acts via the ER alpha to activate normal masculine sexual behavior. After gonadectomy and T replacement, wild-type (WT) male and female mice displayed masculine behavior. However, given the same T treatment, little masculine behavior was displayed by mice of either sex that lack a normal copy of the ER alpha gene. In particular, the latency to display masculine sex behavior and the number of mount attempts per trial were significantly reduced in the ER alpha- mice compared to WT littermates (P < 0.05). In addition, we found that in both sexes, ER alpha- mice have a smaller cluster of androgen receptor immunoreactivity in the bed nucleus of the stria terminalis. Using adult ER alpha- mice we were unable to determine whether these genotypic differences are due to organizational or activational effects. However, it is clear that the ER alpha plays a key role in the expression of masculine sexual behavior and in the regulation of androgen receptors in a neuronal cell population involved in the display of motivated behaviors.

Sex differences in function of a pheromonally stimulated pathway: role of steroids and the main olfactory system

Exposure to the pheromones contained in female hamster vaginal secretions (FHVS) produces stereotypic, sex-specific behaviors in Syrian hamsters. Using Fos as a marker of neuronal stimulation we have found that (1) FHVS stimulates neurons in the posterior subdivision of the medial nucleus of the amygdala (MeP), the posterior medial subdivision of the bed nucleus of the stria terminalis (BNSTpm), and the magnocellular subdivision of the medial preoptic nucleus (MPN mag); (2) this stimulation is mediated by the main olfactory system; (3) stimulation of the MPN mag is regulated by testosterone in males; (4) stimulation of the BNSTpm and MeP is regulated by testosterone in females; and (5) FHVS does not induce Fos production in the MPN mag in females regardless of the hormonal state. These results support the hypothesis that the main olfactory system plays an important role in the regulation of pheromonally driven behaviors, identifies functional sex differences in pathways that regulate these behaviors, and emphasizes the different roles of the BNSTpm, MeP, and MPN mag in the regulation of male copulatory behavior.

Sexual and social experience is associated with different patterns of behavior and neural activation in male prairie voles

Monogamous prairie voles (Microtus ochrogaster) show mating-induced aggression towards conspecific strangers. This behavior is both selective and enduring. The present study was designed to investigate the behavioral conditions for the emergence of selective aggression (by varying prior experience with a female and identity of intruders) and the limbic activation in response to an intruder (by mapping regional staining for c-fos) in male prairie voles. In a first experiment, males that mated with a female for 24 h exhibited aggression towards a male intruder and had more Fos-immunoreactive (Fos-ir) cells in the medial amygdala (AMYGme) and medial preoptic area (MPO) relative to males that cohabited with a female without mating or that had no prior exposure to a female. Cohabited males did not become aggressive. However, these males along with mated males had an increased number of Fos-ir cells in the lateral septum (LS) and the bed nucleus of the stria terminalis (BST) relative to males without prior exposure to a female. In a second experiment, mated males exhibited more offensive aggression to a male intruder but more defensive aggression to a female intruder. Both types of aggression, however, induced an increase in the number of Fos-ir cells in the AMYGme. In addition, Fos-ir staining in the BST was induced selectively in response to a male intruder and a similar trend was found in the LS. Exposure to a male or female intruder did not increase Fos-ir staining in the MPO. Taken together, our data suggest the neural substrates activated by social/sexual activity and involved in response to intruders. The AMYGme was involved in processing intruder-related cues and/or in the regulation of aggressive response to both male and female intruders. The BST and LS were modulated by social experience with a female (mating or cohabitation) and were responsive to male-related cues even in the absence of aggression. Finally, the MPO was activated at different magnitudes by social or sexual experience but did not respond to intruder-related cues as measured by Fos-ir.

Haloperidol regulates neurotensin gene expression in striatum of c-fos-deficient mice

The immediate-early gene c-fos has been proposed to play a role in induction of neurotensin/neuromedin N (NT/N) gene expression in the striatum following acute haloperidol (HAL) treatment. We utilized mice with targeted disruption of the c-fos gene to directly test this hypothesis. A robust increase in NT/N gene expression was observed in the dorsolateral striatum (DLSt) in both wild-type (WT) and c-fos-deficient mice 4-6 h after a single injection of HAL (1 or 4 mg/kg) indicating that products of the c-fos gene are not absolutely required for induction of NT/N mRNA. The basal expression of preprotachykinin, preproenkephalin and preprocholecystokinin mRNAs did not differ between WT and c-fos knockout mice. HAL treatment first increased striatal NT/N mRNA on postnatal day (PD) 10. HAL-induced NT/N mRNA levels were significantly lower in c-fos knockout mice than in WT mice on PD 10 and 15. These findings indicate that reliance on c-fos may be greater earlier in development and that redundant molecular pathways can lead to induction of NT/N mRNA in mouse striatum.

Mating-induced expression of c-fos in the male Syrian hamster brain: role of experience, pheromones, and ejaculations

This study was designed to investigate the effects of pheromonal cues and specific behaviors within the male copulatory sequence on c-fos expression in the medial nucleus of the amygdala (Me), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA) of the Syrian hamster brain. Sexually experienced male hamsters were placed into clean testing arenas and were either: 1) left alone as handled controls; 2) exposed to female hamster vaginal secretion (FHVS) on cotton swabs; or mated to various end points of copulation with a sexually receptive female: 3) five intromissions, 4) one ejaculation, 5) five ejaculations, or 6) long intromissions, A seventh group of sexually naive control males 7) was left alone in the arena. The brains of these males were compared to those of the sexually experienced controls to determine whether exposure to cues associated with prior sexual experience could alter c-fos expression. In males exposed only to FHVS, Fos immunoreactivity (Fos-ir) increased within the posterodorsal Me, the anterodorsal part of the posteromedial BNST, and the magnocellular medial preoptic nucleus (MPNmag). Following one ejaculation, Fos-ir increased within the caudal posterodorsal Me, the dorsolateral MPOA, and the paraventricular nucleus of the hypothalamus. After multiple ejaculations, additional labeling was observed within the posteroventral part of the posteromedial BNST, the medial preoptic nucleus (MPN), the central tegmental field, and in cell clusters of the caudal posterodorsal Me and rostral posteromedial BNST. Fos-ir also increased within the posterodorsal Me, MPN, and MPNmag in sexually experienced control males exposed to the empty test chamber compared to sexually naive males exposed to an identical chamber. These results demonstrate that the mating-induced pattern of neuronal activation in sexually experienced males is dependent upon multiple factors, including prior sexual experience in the testing environment, investigation of FHVS, and the number of ejaculations achieved.

Altered hematopoiesis, behavior, and sexual function in mu opioid receptor-deficient mice

The mu opioid receptor is thought to be the cellular target of opioid narcotics such as morphine and heroin, mediating their effects in both pain relief and euphoria. Its involvement is also implicated in a range of diverse biological processes. Using a mouse model in which the receptor gene was disrupted by targeted homologous recombination, we explored the involvement of this receptor in a number of physiological functions. Mice homozygous for the disrupted gene developed normally, but their motor function was altered. Drug-naive homozygotes displayed reduced locomotor activity, and morphine did not induce changes in locomotor activity observed in wild-type mice. Unexpectedly, lack of a functional receptor resulted in changes in both the host defense system and the reproductive system. We observed increased proliferation of granulocyte-macrophage, erythroid, and multipotential progenitor cells in both bone marrow and spleen, indicating a link between hematopoiesis and the opioid system, both of which are stress-responsive systems. Unexpected changes in sexual function in male homozygotes were also observed, as shown by reduced mating activity, a decrease in sperm count and motility, and smaller litter size. Taken together, these results suggest a novel role of the mu opioid receptor in hematopoiesis and reproductive physiology, in addition to its known involvement in pain relief.

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.

Steroid regulation of sexual behavior

Investigation into the hormonal control of sexual behavior has a rich and extensive history. For many researchers currently active in the field, the physiological psychologist Frank A. Beach is recognized as the modern father of the study of hormones and behavior. His publication of the seminal book Hormones and Behavior-A Survey of Interrelationships Between Endocrine Secretions and Patterns of Overt Response, published in 1948, was a compilation of the previous 20 years of research establishing that gonadal secretions acted in the brain and modulated behavior. The question of precisely how hormones can alter brain functioning in a coordinated fashion and profoundly influence the patterns of behavioral responsiveness remains unanswered. As with many research areas, application of new techniques and approaches to the problem reveals additional layers of complexity and previously unimagined relationships between hormones, brain, and behavior. In addition, with the increasing understanding that the brain is a target organ for steroids, the implications of the ramifications of this steroid sensitivity have broadened. The hormonal regulation of sexual behavior is not an isolated aspect of steroid action in the brain; rather, it is one component of a host of physiological responses influenced by steroids. These include such diverse responses as anxiety, aggression, feeding, and learning and memory. An appreciation of the diverse effects of steroids has emerged from studies on sexual behavior, and a mutually beneficial relationship between this and other aspects of behavioral neuroscience has flourished and endured. As with all of neuroscience, this research area has been dynamic and progressive and has additionally benefited from a long history of comparative and integrative approaches to animal behavior.

c-Fos immunoreactivity in the sexually dimorphic area of the hypothalamus and related brain regions of male gerbils after exposure to sex-related stimuli or performance of specific sexual behaviors

The sexually dimorphic area of the gerbil hypothalamus is essential for male sex behavior. To determine which aspects of mating activate its cells, or cells near or connected to it, we visualized c-Fos in the brains of male gerbils that had been exposed to various types of sex-related stimuli or that had displayed various aspects of sex behavior. Five groups of males were placed in familiar arenas containing sex-related odors. All subjects had previously mated in these arenas. For four groups, a female was introduced and remained with the male until he ejaculated, intromitted, mounted or sniffed her. Males in the fifth group remained in the arena alone. Males in a sixth group were placed in a clean arena in another room. These males were also familiar with this arena but had never encountered a female there. The seventh group remained in their home cages. The posterodorsal preoptic nucleus, the lateral part of the posterodorsal medial amygdala, the medial part of the sexually dimorphic area and the parvicellular part of the subparafascicular nucleus of the thalamus expressed c-Fos after ejaculation. Whether these cells triggered ejaculation or responded to it is not clear. The latter two areas also expressed c-Fos whenever males were exposed to the sex arena, but the sexually dimorphic area pars compacta did not express c-Fos under any condition. The medial core of the nucleus accumbens, the ventrolateral septum, the caudomedial bed nucleus of the stria terminalis, the medial/central part of the posterodorsal medial amygdala and the lateral part of the sexually dimorphic area also expressed c-Fos when males entered the sex arena. The ventrolateral part of the ventromedial nucleus of the hypothalamus expressed c-Fos whenever males were with females. None of the 31 areas studied responded to mounting or intromission, but the zona incerta, the amygdalohippocampal area, the lateral part of the sexually dimorphic area and the area lateral to the medial part of the sexually dimorphic area showed progressive increases in c-Fos expression as mating progressed. The area dorsal to the medial part of the sexually dimorphic area, the paraventricular nucleus of the hypothalamus, the ventral premammillary nucleus and the retrorubral field showed the same level of c-Fos expression when males were exposed to the non-sexual context as when they were exposed to the sexual one. While a projection to the retrorubral field from the sexually dimorphic area is critical for male sex behavior, the retrorubral field did not show a sex-related c-Fos response. The data suggest that brain regions involved in male sex behavior are involved in different aspects of it and that this can also apply to different subsets of cells in each area. The data also indicate that cells involved in mating do not necessarily show mating-related patterns of c-Fos expression. Thus, while c-Fos is useful for identifying areas involved in mating, or other behaviors, its characteristics could cause relevant areas to be overlooked.

c-fos antisense DNA inhibits proliferation of osteoclast progenitors in osteoclast development but not macrophage differentiation in vitro

We previously reported that osteoclast formation in vitro, by coculture of mouse bone marrow and primary osteoblastic cells, occurs in two phases: proliferation of osteoclast progenitors followed by terminal differentiation into mature osteoclasts. Using this coculture system, we examined the effects of c-fos antisense and sense phosphorothioate oligonucleotides on osteoclast development and macrophage differentiation. Treatment with c-fos antisense for the first 4 days of coculture inhibited osteoclast formation in a dose-dependent fashion. However, when c-fos antisense was added during the second phase of coculture (4-6 days), osteoclast formation was unaffected. In contrast, c-fos antisense treatment had no effect on the appearance of F4/80 antigen-positive cells of the macrophage lineage in these cultures or on the induction by colony stimulating factor-1 of macrophage colony formation in cultures of mouse bone marrow cells in agar. Neither osteoclast differentiation nor macrophage appearance was inhibited by adding control c-fos sense in the cocultures. When c-fos antisense was added into an assay of bone resorption by mature osteoclasts, pit formation on dentine slices was unaffected. These results indicate that c-fos plays an important role in the proliferative phase of osteoclast progenitors in osteoclast development, but not in the terminal differentiation phase or in the bone resorbing activity of mature osteoclasts. c-fos antisense specifically inhibited osteoclast formation but had no effect on macrophage development.