Sexual dimorphism for protein kinase c epsilon signaling in a rat model of vincristine-induced painful peripheral neuropathy

Painful peripheral neuropathy is a major dose-limiting adverse effect of many cancer chemotherapeutic agents, such as the vinca alkaloids and taxanes. Recent studies demonstrate sexual dimorphism in second-messenger signaling for primary afferent nociceptor sensitization, and a role of second messengers in the models of metabolic and toxic painful peripheral neuropathies. This study tested the hypothesis that sexual dimorphism alters the severity and second-messenger signaling pathways for enhanced nociception in an animal model of vincristine-induced painful peripheral neuropathy.I.V. injection of vincristine induced mechanical hyperalgesia that was greater in female rats. Gonadectomy in the females but not the males abolished the sex-dependent difference in mechanical hyperalgesia; this effect of gonadectomy in females was reversed by estrogen replacement. Inhibition of protein kinase C epsilon (PKC epsilon ) attenuated vincristine-induced hyperalgesia in males and ovariectomized females, but not in normal females or in estrogen-replaced ovariectomized females. Inhibitors of protein kinase A, protein kinase G, p42 / p44-mitogen activated protein kinase and nitric oxide synthase also attenuated vincristine-induced hyperalgesia, but to a similar degree in both sexes. These data demonstrate an estrogen-dependent sexual dimorphism in vincristine-induced hyperalgesia (female>male) and an unexpected opposite sexual dimorphism in the contribution of PKC epsilon to the severity of this hyperalgesia (male>female).     

Severity of alcohol-induced painful peripheral neuropathy in female rats: role of estrogen and protein kinase (A and Cepsilon)

Small-fiber painful peripheral neuropathy, a complication of chronic ethanol ingestion, is more severe in women. In the present study, we have replicated this clinical finding in the rat and evaluated for a role of estrogen and second messenger signaling pathways. The alcohol diet (6.5% ethanol volume:volume in Lieber-DeCarli formula) induced hyperalgesia with more rapid onset and severity in females. Following ovariectomy, alcohol failed to induce hyperalgesia in female rats, well past its time to onset in gonad intact males and females. Estrogen replacement reinstated alcohol neuropathy in the female rat. The protein kinase A (PKA) inhibitor (Walsh inhibitor peptide, WIPTIDE) only attenuated alcohol-induced hyperalgesia in female rats. Inhibitors of protein kinase Cepsilon (PKCepsilon-I) and extracellular-signal related kinase (ERK) 1/2 (2'-amino-3'-methoxyflavone (PD98059) and 1,4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (U0126)) attenuated hyperalgesia in males and females, however the degree of attenuation produced by PKCepsilon-I was much greater in females. In conclusion, estrogen plays an important role in the expression of pain associated with alcohol neuropathy in the female rat. In contrast to inflammatory hyperalgesia, in which only the contribution of PKCepsilon signaling is sexually dimorphic, in alcohol neuropathy PKA as well as PKCepsilon signaling is highly sexually dimorphic.     

Sex differences in the brain of goldfish: gonadotropin-releasing hormone and vasotocinergic neurons.

The differences between male and female behaviors are reflected in sexual dimorphism of brain structures and are found throughout the nervous system in a variety of vertebrates. The present study examined neurons immunolabeled for gonadotropin-releasing hormone and arginine vasotocin in the brain of the goldfish Carassius auratus to determine if these neurons are sexually dimorphic. There was no sex difference or influence of sex steroids on the neuronal volume and optical density of staining of arginine vasotocin neurons. Similarly, gonadotropin-releasing hormone neurons of the terminal nerve and midbrain tegmentum did not differ between sexually mature males, females and maturing females replaced with sex steroids with respect to distribution, numbers, optical density of staining, or gross morphology. In maturing females, testosterone specifically recruited additional preoptic gonadotropin-releasing hormone neurons to equal those in sexually mature individuals. Since estrogen had no effect, the influence of testosterone on gonadotropin-releasing hormone neuronal numbers appears to be independent of aromatization. Specifically, the preoptic gonadotropin-releasing hormone neuronal size was significantly larger in sexually mature males than females. 11-Ketotestosterone-replacement to ovariectomized maturing females induced male-typical secondary characters and male-type courtship behavior but did not masculinize the preoptic gonadotropin-releasing hormone neuronal size.Our results show that the sexually dimorphic preoptic gonadotropin-releasing hormone neuronal size is determined by factors (genetic) other than gonadal steroids. Further, we propose the hypothesis that phenotypic and behavioral sex differences need not be accompanied by structural differences in gonadotropin-releasing hormone and arginine vasotocin in the brain.     

Hormone-dependent aggression in female rats: testosterone implants attenuate the decline in aggression following ovariectomy

Female rats were individually housed with a sterile male for a 4- to 5-week period. Each female was then tested for aggression toward an unfamiliar female intruder at weekly intervals. Those females that displayed a high level of aggression on each of three weekly tests were ovariectomized and given subcutaneous implants of testosterone-filled tubes, ovariectomized and given subcutaneous implants of empty tubes, or sham-ovariectomized and implanted with empty tubes. These implants should produce a serum testosterone concentration of about 0.6 ng/ml, compared to 0.17 ng/ml in intact females. Beginning 1 week postoperatively, the aggression of each female was tested weekly for 4 weeks. Ovariectomized females with testosterone implants displayed a level of aggression significantly higher than that of ovariectomized females with empty implants on 3 of 4 weekly tests. The level of aggression by females with testosterone implants was not significantly different from that of sham-ovariectomized females on the first postoperative test. Additional observations showed that testosterone implants did not produce an increase in aggression in females whose preoperative level of aggression was low. Further, Silastic implants containing estrogen (1 to 2 mm long) sufficient to maintain a serum estrogen level of 20 to 30 pg/ml also attenuated the decline of aggression following ovariectomy. These results suggest that testosterone and estrogen may both contribute to the biological substrate of hormone-dependent aggression in female rats.     

Progesterone rapidly recruits female-typical opioid-induced hyperalgesic mechanisms

Continuous morphine treatment can paradoxically increase nociception (i.e. hyperalgesia) in male and female mice, but sex differences have been reported. Here, we studied progesterone modulation of these differences by assessing nociception on the tail-withdrawal test in male and female mice rendered hyperalgesic during continuous infusion of two different morphine doses (1.6 and 40.0 mg/kg/24 h). Although the lower morphine infusion dose increased nociception in both sexes by infusion Day 4, this hyperalgesia dissipated by Day 6 in males and ovariectomized females, but not gonadally intact females. A single subcutaneous progesterone (0.0016 mg/kg) injection to males and ovariectomized females on Day 6 caused hyperalgesia to recur within 30 min and to persist for a minimum of 120 min. The larger morphine infusion dose also increased nociception in both sexes on Days 4 and 6. However, the NMDA receptor antagonist MK-801 (0.05 mg/kg) reversed hyperalgesia in males and ovariectomized females but not gonadally intact females on infusion Day 6. Subcutaneous progesterone (0.0016 mg/kg) injection inhibited this reversal in male and ovariectomized female mice but had no effect on nociception in saline-infused mice of either sex. These data confirm our previous findings that male and female mice utilize distinct hyperalgesic mechanisms, and show for the first time that a single progesterone bolus dose can recruit female-typical hyperalgesia in ovariectomized females and males.     

Aggression by ovariectomized female rats: combined testosterone/estrogen implants support the development of hormone-dependent aggression

Female hooded rats were ovariectomized and implanted with a single estrogen-filled and a single testosterone-filled Silastic tube. Control animals were ovariectomized and implanted with empty tubes. The implants produced an estrogen concentration of 30 pg/ml and a testosterone concentration of 0.25 ng/ml, levels close to those found in intact females. Two weeks following surgery, all animals were housed in individual cages, placed on a 23-hr food-deprivation schedule, and adapted to a liquid food. They were then housed in hormone-implant/empty-implant pairs and given a series of 3 restricted-access competition tests and 3 free-access competition tests (1/day). The animals were then paired with new partners and given a second series of restricted-access and free-access competition tests. Ovariectomized females with hormone implants were more successful at maintaining access to the liquid food and more aggressive than their competitors without hormone replacement. The aggression was used to maintain access to food during free-access as well as restricted-access competition. Following the competition tests, animals with hormone implants were significantly more aggressive toward an unfamiliar conspecific than were their cagemates with empty implants. The level of success and aggression by females with testosterone + estrogen implants appears greater than that which occurs with either hormone alone and comparable to that observed in intact females.     

Presence of intact and gonadectomized juveniles and the reduction of fighting between adult male rats

Research is reported which investigated the aggressive interactions between adult male rats in the presence of 17-27 day old juvenile conspecifics. Following a brief exposure to an inaccessible juvenile male, juvenile female, estrous adult female, or empty compartment, the males of Experiment 1 were allowed to interact with another adult male. Results were that the presence of both genders of juveniles reduced fighting between the adult males, and pre-pubertal females were particularly effective as an aggression-inhibitor. The hormonal bases for those sex differences were examined in Experiment 2 using juveniles gonadectomized on Postnatal Day 10. Adult males were more aggressive following exposure to intact juvenile males than to castrated juvenile males; the latter males, intact juvenile females, and ovariectomized juvenile females provoked similar and low rates of fighting between adult males. These data suggest that the sexual dimorphism is a function of testicular hormones present during the juvenile stage which modify the stimulus characteristics of a pre-pubertal male rat.     

Androgens and reproductive behavior in ovariectomized ring doves

Eighteen ovariectomized ring doves (Streptopelia risoria) received subcutaneous silastic implants of either testosterone propionate (TP), 5 alpha-dihydrotestosterone propionate (DHTP) or cholesterol. Birds were paired daily for 1-hr with intact males. Eleven days after implantation the pairs were observed. Both TP and DHTP activated wingflipping behavior in the females. None of the females showed receptive crouching. Aromatization of testosterone to estrogen does not appear to be involved in wingflipping in female doves. The results suggest that wingflipping in females is not as hormone specific as it appears to be in male doves.     

Estrogen-dependent,sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia by orphanin FQ in the rat

Activation of opioid receptor-like 1 receptor (ORL₁) by intrathecal administration of orphanin FQ (OFQ), an endogenous ligand for the ORL₁ receptor, has been shown to produce antinociception. In addition, we have recently shown gonadal hormone-dependent, sex-specific modulation of acute spinal nociception such that estrogen attenuated OFQ-induced antinociception in the female whereas testosterone was required for the expression of antinociception in the male. However, sex-related differences in the role of OFQ under hyperalgesic conditions are unknown. Hence, we investigated whether OFQ produces sex-specific modulation of mustard oil-induced secondary thermal hyperalgesia in the rat. Mustard oil application to the hind limb significantly reduced the tail-flick latencies (TFL) in male, and ovariectomized (OVX), estradiol treated ovariectomized (OVX + E), proestrous (ProE) and diestrous (DiE) females. Intrathecal administration of OFQ not only attenuated mustard oil-induced decrease in TFLs, i.e. reversed hyperalgesia, but also led to a significant increase in TFLs above the baseline, i.e. produced antinociception in male, OVX, and diestrous rats. However, OFQ failed to alter TFLs in proestrous or OVX + E females, thus these two groups with elevated estrogen levels remained hyperalgesic following mustard oil treatment. These findings demonstrate that OFQ modulates mustard oil-induced secondary hyperalgesia in an estrogen-dependent, sex-specific manner.     

Effects of intracerebral implants of steroid hormones on scent marking in the ovariectomized female gerbil (Meriones unguiculatus)

The effects of intracerebral implants of steroid hormones on scent marking in the female gerbil (Meriones unguiculatus) were studied in two experiments. In Experiment 1 various steroids were implanted alone or in combination into the preoptic and anterior hypothalamic area of ovariectomized females. Unilateral implants of testosterone + estrogen, estrogen, estrogen + progesterone, testosterone and testosterone + progesterone stimulated a significant level of marking when compared to controls. Experiment 2 utilized bilateral implants of estrogen dissolved in paraffin in order to explore the distribution hormone sensitive areas in the brain which might be important in the regulation of scent marking in the female gerbil. Pellets of estrogen-paraffin were implanted stereotaxically into either the anterior hypothalamus, preoptic area, septum, hippocampus, thalamus, amygdala or anterior olfactory nucleus of ovariectomized females. Total dosage of hormone implanted was 8.2–8.4 μg. A significant level of marking resulted in animals receiving implants into the anterior hypothalamus, preoptic area and septum when compared to controls. Marking appeared at about the same rate in each of these groups; however, the level of marking attained differed. By the last trial, anterior hypothalamic implanted animals were marking significantly more often than animals in either the preoptic or septum groups. Although there was no evidence of ieakage from the brain, the data suggested that some rapid diffusion of hormone, largely restricted to the brain, was taking place or that the three areas were differentially responsive to the hormone. The data do indicate that some localization of function does exist with respect to regulation of scent marking in the female.     

Effects of sustained-release testosterone on marking behavior in the Mongolian gerbil

Utilizing subcutaneous silastic implants containing testosterone the effect of sustained low-level release of testosterone on marking behavior in castrated Mongolian gerbils was determined. Castration resulted in a decrease in marking frequency from 38 +/- 4 to 4 +/- 1. Sustained release of 6 micrograms testosterone per day from implants did not stimulate marking behavior. Daily release of 11 micrograms increased marking 550% after one week. Release of 17 micrograms per day was required to restore marking to intact levels. Similar release rates of cholesterol did not increase marking. Release rates which increased marking in males did not increase marking in females. The minimum effective sustained-release dose of testosterone necessary to stimulate marking in females was five times greater than that in males. This difference is not due to a sex difference in plasma testosterone removal rates, since the circulating half-life of 3H-testosterone measured by testosterone-specific radioassay was not different in castrated males (72 +/- 5 min) and females (66 +/- 4 min). The present data are consistent with the hypothesis that there is a sexual dimorphism in the testosterone responsiveness of the neural substrate regulating territorial marking behavior.     

A competitive effect of androgen signaling on male mouse attraction to volatile female mouse odors

Olfaction plays an important role in animal communication. We hypothesized that males recognize the attractive volatile odors attributed to female reproductive ability. We measured the period during which a male mouse spent sniffing volatile odors from a sham-operated female mouse or an ovariectomized mouse without visual or tactile contact. Intact male mice spent more time sniffing volatile odors from proestrous, estrous or metestrous females than from ovariectomized females. There was no difference in castrated male mice. To investigate the involvement of sexual hormone in this behavior, castrated male mice were treated with 17 alpha-estradiol (E), dihydrotestosterone (DHT), or both. E-treatment did not affect sniffing behavior. Regardless of the estrous stages, DHT-treated castrated males spent less time sniffing the volatile odors from sham-operated than from ovariectomized female mice. Both E- and DHT-treated castrated males spent less time sniffing the volatile odors from proestrous or estrous females than from ovariectomized females. These results suggest that neither androgen nor estrogen is sufficient for reproducing male attraction to volatile female mouse odors, and that androgen signaling has a competitive effect against the attraction.     

Influence of neonatal androgen on the display of territorial marking behavior in the gerbil.

The effect of the presence or absence of androgen during the neonatal period on territorial marking behavior in the Mongolian gerbil was studied. Scent marking frequency was 20-40 fold greater in males than in females. Gonadectomy depressed marking in males but not in females. Testosterone propionate (TP) therapy completely restored marking in male but increased marking in intact and ovariectomized females to only one fourth that in males. Genetic males castrated within 2 days postpartum did not mark more frequently than TP-treated females after TP treatment in adulthood. Genetic females given a single TP injection within 6 days postpartum marked at male levels after TP treatment in adulthood. Males castrated after Day 2 and females given TP after Day 6 displayed marking frequencies intermediate between normal male and female levels after TP treatment in adulthood. This study suggests that sexual dimorphism in territorial marking behavior is due to a sex difference in the competency to respond to androgen, and it appears that development of this competency occurs during the neonatal period and is regulated, at least in part, by androgen. The onset of this differentiation process occurs earlier in the male than in the female.     

Ovarian influences on the development of sexual behavior in neonatally androgenized rats

Female sexual behavior was studied in male and female rats. Males were castrated on the day of birth (Day 1); some received ovarian implants at that time; others were injected on Day 3 with oil, 5 μg testosterone propionate (TP), or 50 μg TP. Females were ovariectomized at birth, 20, or 60 days of age; on Day 3 all were injected with oil, 5 μg, TP, or 50 μg TP. Prepuberal ovarian tenancy in females tended to counteract the effects on sexual receptivity of TP administered during neonatal life. In males ovarian implants facilitated female sexual behavior at adulthood in oil-injected animals, but did not significantly influence the effect on neonatally injected TP.     

Dual progesterone action in diencephalon facilitates the induction of sexual receptivity in estrogen-primed golden hamsters

In order to identify and characterize the progesterone (P) sensitive neural system that regulates feminine sexual behavior, 28-gauge P-filled cannulae were implanted in the medial preoptic area (MPO), ventromedial hypothalamus (VMH), and central gray (CG) of ovariectomized estrogen-primed golden hamsters. Dual implants of P were placed either ipsilaterally or contralaterally in brain sites consisting of MPO-VMH, MPO-CG, or VMH-CG combinations. Tests for sexual receptivity commenced 44 hr after estrogen priming and consisted of a preimplantation test followed 4.5 to 5.5 hr later by a postimplantation test. In the preimplantation test, stimulus males were attacked when placed into the female's home cage which indicated that the subsequent display of sexual receptivity occurring in the postimplantation test was due to the action of P. Dual implants of P placed either ipsilaterally or contralaterally in MPO-VMH regions were significantly more effective in facilitating lordosis behavior than dual P implants placed in MPO-CG or VMH-CG regions. However, the duration of lordotic responsiveness produced by dual P implants in MPO and VMH regions appears to be shorter than the duration of lordosis typically observed in intact females on proestrus. Results suggest that MPO and VMH regions are sensitive to the lordosis facilitating actions of small dual implants of P.     

3D analysis of sexual dimorphism in size,shape and breathing kinematics of human lungs

Sexual dimorphism in the human respiratory system has been previously reported at the skeletal (cranial and thoracic) level, but also at the pulmonary level. Regarding lungs, foregoing studies have yielded sex‐related differences in pulmonary size as well as lung shape details, but different methodological approaches have led to discrepant results on differences in respiratory patterns between males and females. The purpose of this study is to analyse sexual dimorphism in human lungs during forced respiration using 3D geometric morphometrics. Eighty computed tomographies (19 males and 21 females) were taken in maximal forced inspiration (FI) and expiration (FE), and 415 (semi)landmarks were digitized on 80 virtual lung models for the 3D quantification of pulmonary size, shape and kinematic differences. We found that males showed larger lungs than females (P < 0.05), and significantly greater size and shape differences between FI and FE. Morphologically, males have pyramidal lung geometry, with greater lower lung width when comparing with the apices, in contrast to the prismatic lung shape and similar widths at upper and lower lungs of females. Multivariate regression analyses confirmed the effect of sex on lung size (36.26%; P < 0.05) and on lung shape (7.23%; P < 0.05), and yielded two kinematic vectors with a small but statistically significant angle between them (13.22°; P < 0.05) that confirms sex‐related differences in the respiratory patterns. Our 3D approach shows sexual dimorphism in human lungs likely due to a greater diaphragmatic action in males and a predominant intercostal muscle action in females during breathing. These size and shape differences would lead to different respiratory patterns between sexes, whose physiological implications need to be studied in future research.     

Reversal of normal cerebral sexual dimorphism in schizophrenia: evidence and speculations

Sex differences in epidemiology, clinical course and symptomatology of schizophrenia have been widely documented, but still relatively little is known about the brain sexual dimorphism in this psychiatric disorder. While some neuroanatomical and neuropsychological studies have reported existence of differences between male and female patients in a direction of normal sexual dimorphism, others did not find any effect. A few recent reports point to a peculiar disturbance of normal sexual dimorphism in brain regions implicated in the processing of emotions, including amygdala, orbitofrontal cortex and anterior cingulate. Prompted by these findings we compared cerebral activations between the sexes during performance of two emotion processing tasks and found overall much more extensive and intense cerebral activations in men than in women with schizophrenia. Moreover, the pattern of obtained sex differences in cerebral activation in patients differed significantly from what has been observed in the general population. Based on these preliminary structural and functional neuroimaging data, as well as some clinical reports, it is hypothesized in the present paper that schizophrenia is characterized by a reversed (or at least seriously disturbed) cerebral sexual dimorphism. It is further argued that this phenomenon stems from masculinization and/or un-feminization of females and feminizations and/or un-masculinization of males by sex steroid hormones, such as estrogen and testosterone, during both organizational and activational stages of neurodevelopment.     

Sexual receptivity: Brain sites of estrogen action in female hamsters

In order to investigate the brain sites of estrogen action, ovariectomized hamsters were stereotaxically implanted with unilateral 27 gauge cannulae containing estradiol. Groups of females received implants into either the lateral septum, bed nucleus of the stria terminalis, preoptic area, anterior hypothalamus, ventromedial hypothalamus, arcuate nucleus, corticomedial amygdala or mesencephalic central gray. Another set of animals received implants containing cholesterol. One week later the animals were injected with progesterone and 4–5 hours later tested for sexual receptivity. The most receptivity and the most consistent response was seen in females with estradiol implants in the ventromedial hypothalamus. Only a few scattered animals in the other anatomical groups showed any receptivity. Only in animals with implants in the anterior hypothalamus was there any evidence of leakage of estrogen into peripheral circulation as measured by uterine weight. There was no response in females with cholesterol implants. Our results suggest that the ventromedial hypothalamus is the most sensitive brain area for the estrogenic induction of female sexual receptivity in hamsters.     

Sex differences in electrophysiological and behavioral responses to NaCl taste

We tested the hypothesis that sex differences in preference for NaCl are attributable to estrogen-mediated alterations in gustatory processing. Electrophysiological responses of the chorda tympani nerve to NaCl were blunted by estrogen treatment in ovariectomized female rats, suggesting that females are less sensitive to concentrated NaCl solutions during high estrogen conditions. In contrast, after a taste aversion was conditioned to 150-mM NaCl, estrogen- and oil-treated ovariectomized rats generalized the aversion to a lower concentration of NaCl than did males, suggesting that females are more sensitive to the taste of dilute NaCl solutions regardless of estrogen. Thus, sex differences in NaCl preferences may be attributable to differences in NaCl taste processing that involve both acute and developmental effects of estrogen.     

Behavioral insensitivity to progesterone during lactation in female rats

Lactating female rats failed to display sexual receptivity after receiving 50 μg of estradiol benzoate followed by 1 mg of progesterone. Lactating rats appear to be insensitive to progesterone, based on several experiments. In ovariectomized control rats receiving moderate estrogen priming (1 μg EB for 3 days), progesterone greatly facilitated sexual receptivity; similarly estrogen-primed lactating females showed no responsiveness to progesterone injections, even at a high dose of progesterone (10 mg). Consistent with this reduced behavioral responsiveness to progesterone, lactating females had significantly reduced nuclear progestin receptor levels after an injection of 1 mg progesterone compared to ovariectomized controls. On the other hand, both ovariectomized controls and lactating rats responded with high levels of receptivity to 3 days of priming with 10 μg of estradiol benzoate (without progesterone). Lactating females treated for 3 days with a moderate dose (1 μg) of estradiol benzoate showed slightly reduced receptivity compared to ovariectomized controls; this result could reflect a reduced sensitivity to estrogen but is more likely related to the somewhat lower serum levels of estradiol and consequently lower nuclear estrogen receptors in lactating females compared to ovariectomized controls. The possibility of reduced sensitivity to estrogen leading to a reduced sensitivity to progesterone cannot be eliminated (since animals respond to progesterone only after estrogen priming); however, the reported results favor the idea that lactating females are primarily refractory to progesterone and do not have a generalized insensitivity to estrogen.