Middle-aged female rats lack the dynamic changes in GAD(67) mRNA levels observed in young females on the day of a luteinising hormone surge

The hypothalamic decapeptide gonadotrophin-releasing hormone (GnRH), modulates gonadotrophin synthesis and secretion and is essential for the preovulatory luteinising hormone (LH) surge. As females age, there is a gradual attenuation and eventual loss of the preovulatory LH surge and oestrous cyclicity. Data from previous studies have demonstrated evidence of compromised GnRH neuronal function at this time. The present study begins to explore the hypothesis that the age-related attenuation of the LH surge and decline in GnRH neuronal function are due, in part, to increased inhibitory influences on GnRH neurones. In situ hybridisation (ISH) was used to assess relative levels of mRNA for one isoform of glutamic acid decarboxylase (GAD), the rate-limiting enzyme for GABA synthesis. Ovariectomised young and middle-aged rats were injected with oestradiol benzoate and progesterone in a regimen for LH surge induction. Animals were killed at time points prior to, during the ascending phase, and during the peak and early descending phase of the LH surge. Dynamic changes in GAD(67) mRNA levels were observed in young but not middle-aged females in two regions known to be important for LH surge induction, the rostral proeptic area in the region of the organum vasculosum of the lamina terminalis (OVLT) and in the ventral periventricular preoptic area. Furthermore, GAD(67) mRNA levels were elevated in middle-aged relative to young females in the region of the OVLT at the time of LH surge induction and in the ventral periventricular preoptic area prior to surge induction. Age-related differences were not observed in other brain regions analysed. These data suggest that GABA synthesis may be elevated in middle-aged relative to young females in specific brain regions at critical times in conjunction with the LH surge, and that the lack of dynamic changes in GABA levels in these regions may contribute to the attenuated LH surge observed in middle-aged females.

Dynamic changes in luteinizing hormone releasing hormone transcriptional activity are associated with the steroid-induced LH surge

Luteinizing hormone releasing hormone (LHRH) gene transcription was examined in ovariectomized female rats on the day of a steroid-induced LH surge using the RNase protection assay. LHRH mRNA levels were measured in cytosolic extracts, and LHRH primary transcript levels were measured in nuclear extracts prepared from tissue fragments that contained the organum vasculosum of the lamina terminalis (OVLT) and the preoptic area (POA). Measurements of both mature and primary transcript levels demonstrated modest but significant changes over time. Alterations in LHRH primary transcript levels preceded changes in levels of mature mRNA suggesting a delay in the detectable response of the cytoplasmic pool of LHRH mRNA to changes in gene transcription at this time. When viewed in relation to circulating LH titers, LHRH primary transcript levels were high prior to the start of the LH surge and after peak levels of LH were attained, and they declined during the ascending phase of the LH surge. These findings suggest a potential role for increased LHRH gene transcription in the accumulation of LHRH prior to the start of the LH surge and in the replenishment of LHRH stores depleted during the surge. Moreover, the decrease in LHRH gene transcription during the ascending phase of the LH surge may be important for limiting surge duration. The data presented are consistent with a role for dynamic changes in LHRH transcriptional activity in modulating parameters of the steroid-induced LH surge and in replenishing the releasable pool of this essential decapeptide.

Perinatal exposure to low doses of bisphenol A affects body weight, patterns of estrous cyclicity, and plasma LH levels

The nonsteroidal estrogenic compound bisphenol A (BPA) is a monomer used in the manufacture of polycarbonate plastics and resins. BPA may be ingested by humans as it reportedly leaches from the lining of tin cans into foods, from dental sealants into saliva, and from polycarbonate bottles into their contents. Because BPA is weakly estrogenic--approximately 10,000-fold less potent than 17beta-estradiol--current environmental exposure levels have been considered orders of magnitude below the dose required for adverse effects on health. Herein we demonstrate measurable effects on the offspring of Sprague-Dawley female rats that were exposed, via their drinking water, to approximately 0.1 mg BPA/kg body weight (bw)/day (low dose) or 1.2 mg BPA/kg bw/day (high dose) from day 6 of pregnancy through the period of lactation. Offspring exposed to BPA exhibited an increase in body weight that was apparent soon after birth and continued into adulthood. In addition, female offspring exposed perinatally to the high dose of BPA exhibited altered patterns of estrous cyclicity and decreased levels of plasma luteinizing hormone (LH) in adulthood. Administration of neither the doses of BPA that caused effects during perinatal exposure nor a 10-fold higher dose was able to evoke a uterotropic response in ovariectomized postpubertal females. These data indicate an increased sensitivity to BPA during the perinatal period and suggest the need for careful evaluation of the current levels of exposure to this compound.

Hypothalamic alterations and reproductive aging in female rats: evidence of altered luteinizing hormone-releasing hormone neuronal function

Prior to the age-related loss of regular estrous cycles, female rats exhibit an attenuated preovulatory LH surge, a sign that reproductive decline is imminent. Numerous studies have revealed an important role for the hypothalamus in aging of the reproductive axis in this species. Because LHRH represents the primary hypothalamic signal that regulates gonadotropin release, assessments of LHRH neuronal activity can provide a window into hypothalamic function during reproductive aging. Studies of the dynamic activity of LHRH neurons during times of enhanced secretion have revealed deficits in middle-aged females. Available data are consistent with a decline in LHRH synthesis, transport, and secretion in middle-aged females during times of increased demand for LHRH output. Moreover, the alterations noted in LHRH neuronal function could account, in part, for the attenuation and eventual loss of the preovulatory LH surge with age. Elements extrinsic to LHRH neurons undoubtedly contribute to the decline in the parameters of LHRH neuronal function observed in middle-aged females. Whether alterations intrinsic to LHRH neurons also play a role in the age-associated reduction in LHRH synthesis and secretion remains to be determined. Recent examinations of hormone profiles during the perimenopausal period suggest that a potential hypothalamic contribution to aging of the reproductive axis in women warrants further examination.

Gonadotropin-releasing hormone immunoreactivity in the adult and fetal human olfactory system

Studies in fetal brain tissue of rodents, nonhuman primates and birds have demonstrated that cells containing gonadotropin-releasing hormone (GnRH) migrate from the olfactory placode across the nasal septum into the forebrain. The purpose of this study was to examine GnRH neurons in components of the adult and fetal human olfactory system. In the adult human brain (n=4), immunoreactive GnRH was evident within diffusely scattered cell bodies and processes in the olfactory bulb, olfactory nerve, olfactory cortex, and nervus terminalis located on the anterior surface of the gyrus rectus. GnRH-immunoreactive structures showed a similar distribution in 20-week human fetal brains (n=2), indicating that the migration of GnRH neurons is complete at this time. In 10-11-week fetal brains (n=2), more cells were noted in the nasal cavity than in the brain. Our data are consistent with observations made in other species, confirming olfactory derivation and migration of GnRH neurons into the brain from the olfactory placode.

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

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

Expression of Fos within luteinizing hormone-releasing hormone neurons, in relation to the steroid-induced luteinizing hormone surge in guinea pigs

The induction of Fos protein was examined within LHRH neurons of guinea pigs; the aim was to delineate relationships between subgroups of LHRH neurons during an LH surge in a laboratory rodent in which the distribution of LHRH neurons and the presence of a true luteal phase in the reproductive cycle resemble those in primates. Approximately one third of the forebrain population of LHRH neurons was examined in ovariectomized steroid-treated guinea pigs killed either before or during a steroid-induced LH surge. LHRH/Fos double-labeled neurons were more abundant in surging compared to presurge guinea pigs (p = 0.008) and were most abundant within the preoptic area and anterior hypothalamus. Nonetheless, double-labeled LHRH/Fos neurons were observed throughout the remainder of the population of LHRH neurons in surging guinea pigs. A relative loss of LHRH reaction product was detected by image analysis in the LHRH terminals in the median eminence of surging guinea pigs, consistent with augmented LHRH release. Thus, there appears to be a coordinated increase in Fos expression in subgroups of LHRH neurons, more pronounced in rostral, as compared to caudal, regions in guinea pigs killed after the peak of the steroid-induced LH surge.

Fos expression in luteinizing hormone-releasing hormone neurons of guinea pigs, with knife cuts separating the preoptic area and the hypothalamus, demonstrating luteinizing hormone surges

LHRH neurons in guinea pigs, as in primates and other non-rodent species, are broadly distributed in the basal forebrain. In this study, knife cuts were made in the anterior hypothalamus, effectively separating more caudally positioned hypothalamic LHRH neurons from those in rostral preoptic areas. Guinea pigs with knife cuts displayed an LH surge in response to steroid administration. There was no significant difference in the number of LHRH neurons that expressed Fos in conjunction with an LH surge, although fewer total LHRH neurons were detected in the forebrain of knife-cut versus sham-cut animals. Knife-cut animals displayed a larger percentage of LHRH/Fos neurons in one region of the caudal hypothalamus than sham-cut animals. The area and perimeter of the LHRH reaction product within the cytoplasm of LHRH/Fos neurons were smaller than those of single-labeled LHRH neurons in sham-cut animals and in the caudal hypothalamus, but not the rostral preoptic area, of knife-cut animals. We conclude that caudal hypothalamic LHRH neurons separated from rostral preoptic regions are capable of sustaining an LH surge in guinea pigs. This finding is important, as LHRH neurons are present in the caudal hypothalamus, as well as in preoptic areas, of a large number of mammalian species, including humans.

Luteinizing hormone-releasing hormone gene expression differs in young and middle-aged females on the day of a steroid-induced LH surge

LHRH mRNA levels were examined in young and middle-aged female rats at 4 times (10:00 h, 14:00 h, 18:00 h and 20:00 h) on the day of a steroid-induced LH surge by in situ hybridization with a digoxigenin-labeled riboprobe. Young, but not middle-aged females, exhibited dynamic temporal changes in the number of LHRH mRNA positive neurons detected in the organum vasculosum of the lamina terminalis-preoptic area (OVLT-POA) continuum. Specifically, fewer LHRH mRNA positive neurons were detected at 18:00 h compared with the number detected at 14:00 h and 20:00 h (P < 0.01) in the OVLT-POA of young females. All LHRH mRNA positive neurons present in 4 anatomically matched sections through the rostral POA of young and middle-aged animals were digitized for detailed computer-assisted analysis of the hybridization reaction product. The mean hybridization area (P < 0.00025) and integrated optical density per cell (P < 0.006) were reduced in middle-aged compared to young females consistent with a relative age-related decline in LHRH mRNA levels. Moreover, an age-related reduction in cellular and/or regional hybridization area was noted at each of the time points examined (P < 0.05-P < 0.001). These data confirm earlier reports of dynamic changes in LHRH mRNA levels on the day of an LH surge. Furthermore, they support a role for age-related alterations in LHRH gene expression in the disruption of regular estrous cyclicity in middle-aged females.

Examination of guinea pig luteinizing hormone-releasing hormone gene reveals a unique decapeptide and existence of two transcripts in the brain

We sequenced the complementary DNA (cDNA) encoding guinea pig LHRH from an expression library derived from the preoptic area-anterior hypothalamus. Data from in situ hybridization and RNase protection assays verified that the cloned cDNA was complementary to guinea pig LHRH messenger RNA. The architecture of the deduced precursor resembles that of LHRH precursors identified in other species. In contrast, the predicted sequence of the decapeptide differs from mammalian LHRH by two amino acid substitutions in positions 2 and 7. This is a novel finding, because the amino acid sequence that comprises LHRH decapeptide is identical in all mammals studied to date. Moreover, the predicted substitution in amino acid position 2 is unique among vertebrates. A second observation of potential significance is the existence of two subspecies of LHRH messenger RNA differing only in the length of their 3' untranslated regions. These two transcripts were verified by sequence analysis of positive clones from the cDNA library and by RNase protection analysis of preoptic area-anterior hypothalamus extracts, and their presence is consistent with the two polyadenylation signals identified in the untranslated regions of the LHRH gene. Future studies will examine LHRH gene expression in guinea pigs, which like primates but unlike rats, have a true luteal phase as a component of their reproductive cycle.

Differential proopiomelanocortin gene expression in the medial basal hypothalamus of rats during pregnancy and lactation

Hypothalamic proopiomelanocortin (POMC) gene expression was determined using in situ hybridization histochemistry (ISHH) during pregnancy and lactation in rats with and without prior reproduction experience. POMC mRNA levels in the arcuate nucleus were compared between primigravid (first pregnancy) and multigravid (second pregnancy) and primiparous and multiparous lactating rats, and between these groups and age-matched, regularly cycling, nulliparous females in diestrus. Hybridizations were performed using a digoxigenin-labeled riboprobe complementary to 837 bp of the POMC gene. The number of cells expressing POMC mRNA in the arcuate nucleus decreased in primiparous rats on day 12 of lactation when compared with the number of POMC cells in the arcuate nucleus of nulliparous rats in diestrus. In addition, the number of cells expressing POMC mRNA in multigravid animals was significantly less than in the primigravid group on days 7 and 21 of pregnancy, and on day 12 of lactation in primiparous animals. Repeated reproductive experience affected the number of POMC mRNA positive cells; there were fewer cells expressing POMC mRNA in the multigravid females on day 7 of pregnancy and an increase in the number of POMC cells in the multiparous group on day 12 of lactation compared to the primiparous animals. Optical density measurements revealed a significant increase in reaction product in the labeled cells on all days of pregnancy compared with virgin females in diestrus and a significant decrease in reaction product on day 12 of lactation in the multiparous group. The results of the present study indicate that POMC gene expression changes across pregnancy and lactation and that repeated reproductive experience has long-term, possibly permanent, effects on the endogenous opioid system.

Spontaneous multivessel cervical artery dissection in a patient with a substitution of alanine for glycine (G13A) in the alpha 1 (I) chain of type I collagen

Cervical artery dissection occurs spontaneously and in multiple vessels with surprising frequency. An underlying arteriopathy is frequently suspected, but specific causes of vascular fragility are rarely identified. We describe a 35-year-old woman who developed multiple cervical artery dissections after scuba diving. She had no stigmata of connective tissue disease apart from bluish sclerae, and no family history of arterial dissection or congenital musculoskeletal disease. Analysis of the COL1A1 gene that encodes the pro alpha 1(I) chains of type I procollagen revealed a point mutation in one allele, resulting in substitution of alanine for glycine (G13A) in about half the alpha 1(I) chains of type I collagen. Genetic disorders of collagen, such as the mild phenotypic variant of osteogenesis imperfecta identified in our patient, should be considered in the differential diagnosis of unexplained cervical artery dissection.

A relative depletion of luteinizing hormone-releasing hormone was observed in the median eminence of young but not middle-aged rats on the evening of proestrus

Computer-assisted analysis was used to examine LHRH reaction product in the median eminence of young and middle-aged rats prior to and after the expected peak of the LH surge on proestrus. The area of LHRH reaction product was analyzed in 5 rostral-caudal levels (A-E) of the median eminence. The relative depletion of LHRH in the median eminence of young females on the evening compared to the afternoon of proestrus suggested LHRH neurosecretion in conjunction with the preovulatory LH surge. The pattern of depletion observed further suggested that LHRH release may occur preferentially from restricted regions of the median eminence or in a coordinated wave-like pattern. Four of the five levels of the median eminence exhibited a relative decrease in LHRH on the evening of proestrus in young females, and this time-related difference in LHRH reaction product was statistically significant in median eminence levels B and C. In contrast, little evidence of a relative depletion in LHRH reaction product from early to late proestrus was observed in the median eminence of aging animals. Moreover, the concentration of the densest LHRH reaction product appeared diminished in the median eminence of middle-aged compared to young females at the time points examined in the present study. The age-related differences observed in LHRH reaction product in the median eminence may contribute to the attenuated LH surge documented in middle-aged female rats. Whether these changes in LHRH immunoreactivity can be attributed to age-related alterations in afferents received by LHRH neuronal cell bodies or terminals or to intrinsic deficits in signalling mechanisms within LHRH neurons remains to be determined. Computer-assisted analysis of the immunocytochemical data enabled the assessment of relative changes in reaction product within specific elements of LHRH neurons in precise regions of the median eminence.

Reconstructions of populations of luteinizing hormone releasing hormone neurons in young and middle-aged rats reveal progressive increases in subgroups expressing Fos protein on proestrus and age-related deficits

Fos expression has been used as a marker of activation of neuroendocrine cells including LHRH neurons. In this study, Fos protein was localized within LHRH neurons in young and middle-aged rats to trace the temporal and spatial pattern of LHRH neuronal activation associated with the preovulatory LH surge. Animals were killed during the late morning, afternoon, and evening of proestrus. Dual immunocytochemical protocols localized LHRH and LHRH/Fos neurons, and computer-assisted methods were used to reconstruct forebrain populations of single- and double-labeled LHRH neurons. Although a significant increase in the number of LHRH/Fos neurons was noted by evening in both age groups, a greater increase was observed in young (12% in morning, 28% in afternoon, and 62% by evening) compared with aging females (5% in morning, 10% in afternoon, and 40% by evening). Reconstructions of LHRH and LHRH/Fos neurons revealed time- and age-dependent differences in Fos expression within LHRH neurons. In young females, LHRH/Fos neurons were restricted to central regions of the population of LHRH neurons on the morning of proestrus. By evening, Fos expression was also observed in more peripheral and caudal LHRH neurons. In middle-aged females, Fos expression was restricted to ventral subgroups of LHRH neurons on the afternoon of proestrus. By evening, more LHRH neurons contained Fos protein, however, few were located in the dorsal aspect of the population. These data trace the progressive increase in activation of LHRH neurons during the preovulatory LH surge in young females and reveal deficits in this pattern of activation by middle age.

Dynamic alterations in luteinizing hormone-releasing hormone (LHRH) neuronal cell bodies and terminals of adult rats

1. The decapeptide lueteinizing hormone-releasing hormone (LHRH) is synthesized in neuronal cell bodies diffusely distributed across the basal forebrain and is secreted from neuronal terminals in the median eminence. Once secreted, LHRH enters the portal vessels and is then transported to the anterior pituitary, where it modulates the synthesis and secretion of gonadotropins, which are essential to gonadal function and reproduction. 2. Because of the difficulties encountered in studying these diffusely distributed neurons, we have developed strategies which combine immunocytochemistry and computer-assisted techniques to examine individual LHRH neuronal cell bodies, as well as the entire population of LHRH neurons from the diagonal band of Broca to the mammillary bodies. In addition, we have examined LHRH neuronal terminals in the median eminence using computer-assisted imaging techniques to examine individual terminals by electron microscopy or across all rostral-caudal regions of the median eminence by light microscopy. In our most recent studies using confocal microscopy, we have examined the relationships of LHRH terminals to glial processes. 3. These studies reveal a very dynamic system of LHRH neuronal cell bodies and terminals. The population of neurons in which LHRH can be detected varies as a function of time after gonadectomy, during the estrous cycle, and during the preovulatory surge of LH during the afternoon of proestrus. Dynamic changes are also observed in LHRH terminals in the median eminence as a function of time after gonadectomy and in specific rostral-caudal regions of the median eminence during the preovulatory surge of LH. Finally, confocal microscopy reveals that LHRH terminals are prevented from contacting the basal lamina of the brain by glial end-feet. 4. We are currently examining the hypothesis that these relationships change as a function of endocrine milieu and, therefore, participate in the modulation of LHRH secretion. Ongoing studies focus on defining the sites of action and synergy of multiple sources of regulation of LHRH secretion and their relative importance to ensuring reproductive success.

A reduced proportion of luteinizing hormone (LH)-releasing hormone neurons express Fos protein during the preovulatory or steroid-induced LH surge in middle-aged rats

Results of previous studies suggest that altered patterns of LHRH neurosecretion contribute to attenuated LH surges and the eventual cessation of ovulation in aging female rats. The present study compared evidence of LHRH neuronal activation in conjunction with the preovulatory and steroid-induced LH surge in young and middle-aged animals to determine whether age-related alterations could be detected. Double immunocytochemical protocols were used to colocalize LHRH and the protein product of the proto-oncogene c-fos, which increases within the nucleus of LHRH neurons in association with spontaneous or induced LH surges. The mean proportion of LHRH neurons containing immunoreactive Fos was higher in the brains of young compared to middle-aged females in association with both the preovulatory (p < 0.01) and the steroid-induced LH surge (p < 0.001). The time course of activation of LHRH neurons was delayed in the brains of aging females, and the proportion of double-labeled LHRH neurons remained elevated longer in the brains of young compared to middle-aged steroid-treated females. Moreover, regional differences in LHRH neuronal activation were observed both within and between age groups. The data presented suggest that reduced LHRH neuronal activation may contribute to the attenuation and eventual loss of preovulatory LH surges in middle-aged female rats.

Dynamic changes in LHRH neurovascular terminals with various endocrine conditions in adults

Luteinizing hormone-releasing hormone (LHRH) release is required for ovulation in mammals. Although evidence for the direct action of gonadal steroids on LHRH neurons has been minimal, their importance in inducing the preovulatory surge of LHRH is unequivocal. We have identified a subgroup of LHRH neurons with progestin receptors in guinea pigs. Given their central position, these neurons may constitute foci of initial activity, which are amplified throughout the population of LHRH neurons, resulting in increased LHRH neurosecretion on the afternoon of proestrus. Additionally, gonadal steroids may regulate LHRH secretion at the level of the terminals. Using immunoelectron microscopy and image analysis, we have illustrated the dramatic influence of gonadal steroids on individual LHRH terminals in the median eminence of rats. Indirectly, gonadal steroids may modulate LHRH release by modulating glial elements. Using double-label fluorescence confocal microscopy, we illustrate that LHRH terminals in the median eminence are encased by end-feet of tanycytes. Acting on glial elements, gonadal steroids may regulate access of LHRH terminals to the basal lamina and influence the amount of the neuropeptide reaching the portal vessels. We propose that during the preovulatory surge, LHRH release is coordinated by synergistic mechanisms operating at the level of particular subgroups of neuronal perikarya and/or discrete regions of the median eminence. These synergistic actions may ensure that LHRH is released in a precipitous fashion, to induce the surge of LH from the pituitary, required for ovulation.

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.

The number and distribution of detectable luteinizing hormone (LH)-releasing hormone cell bodies changes in association with the preovulatory LH surge in the brains of young but not middle-aged female rats

The population of LHRH neurons was examined in young and middle-aged female rats at two different time points associated with the LH surge on proestrus. More immunopositive LHRH neurons were detected in the brains of young but not middle-aged females killed on the evening of proestrus (1830-2030 h) compared with those killed earlier in the afternoon (1300-1430 h). To facilitate the investigation of potential regional differences within the population, sections through the basal forebrain were divided into four areas based upon their rostral-caudal position. Whereas no change in detectability was observed in the most rostral subset of LHRH neurons, more LHRH perikarya were observed at the later compared to the earlier time point in the other three areas surveyed in the brains of young females. Only the increase observed in sections through the preoptic area, however, reached statistical significance. Computer assisted three-dimensional reconstruction of all LHRH neurons in sections through the preoptic area revealed a marked increase in a subgroup of LHRH neurons in the dorsomedial aspect of this region of the population. Changes in detectability of LHRH neurons in association with the LH surge suggest that these neurons may be involved in regulating preovulatory LH release. Examination of additional time points could reveal changes in other subgroups of LHRH neurons as well as significant changes in detectability of LHRH neurons in aging brains.

Asphyxial deaths due to physical restraint. A case series

OBJECTIVE

To assess the common factors and the pattern of deaths related to the use of physical restraints.

DESIGN

Case series.

PARTICIPANTS

The chief death investigators of 37 large jurisdictions were sent questionnaires for all cases of restraint-related deaths. Sixty-three questionnaires from 23 jurisdictions were returned.

MEASURES

The questionnaires allowed us to determine the restraint type used, the age and sex of the deceased, the furniture type with which restraints were used, the type of facility where the deceased was restrained, and whether the application of restraints was incorrect.

RESULTS

We report 63 cases of asphyxial deaths from the use of physical restraints. Ages of decedents ranged from 26 weeks to 98 years. The greatest number of deaths occurred in the 80- to 89-year-old patients. There is a higher frequency for females of all ages, but the distribution for males and females is roughly the same for all age groups. Deaths occurred while the patient was restrained in a chair (wheelchair or geriatric recliner) or a bed. Most chair-related deaths (six of 19) and bed-related deaths (16 of 42) involved the use of vest restraints. Thirteen of the 42 bed-related deaths involved bedrails. The majority of deaths (61%) occurred in nursing homes and 57 of these 63 cases occurred while restraints were properly applied.

CONCLUSIONS

Our report of 63 cases is an underrepresentation of the true number of restraint deaths. Our finding that the vast majority of restraint deaths occurred while restraints were correctly applied implies an inherent danger in the use of physical restraints. The safety of restraining patients and the efficacy of physical restraint needs to be examined and alternate means of assuring the safety of patients need to be developed.

Naloxone stimulates comparable release of luteinizing hormone-releasing hormone from tissue fragments from ovariectomized, estrogen-treated young and middle-aged female rats

Endogenous opioids play a role in the regulation of LH-RH neurosecretion throughout the estrous cycle and during the preovulatory LH surge on proestrus. Experimental evidence suggests that opioid influence may be altered with age, and it has been hypothesized that these alterations may contribute to the loss of regular estrous cyclicity in aging female rats. The present study utilizes an in vitro perifusion paradigm to compare the ability of opiate receptor blockade with naloxone to stimulate LH-RH release from tissue fragments from ovariectomized, estrogen-treated young and middle-aged females. Naloxone stimulated a greater than 50% increase in LH-RH release from most fragments that contained primarily LH-RH axons and terminals and from all tissue fragments that contained the majority of LH-RH cell bodies as well as axons and terminals. The LH-RH response to naloxone administration was qualitatively, quantitatively and temporally comparable in tissue fragments from young and middle-aged animals. These data suggest that LH-RH neurosecretion in ovx, estrogen-primed middle-aged female rats remains under the inhibitory influence of endogenous opioid peptides. Although in vitro LH-RH release did not differ in response to naloxone, age-related differences in naloxone's ability to increase serum LH levels in vivo were observed. The data are discussed with regard to potential age-related differences in pituitary responsiveness to LH-RH and in other systems that enhance pituitary responsiveness to LH-RH as well as alterations in excitatory or inhibitory influences that may have been eliminated in the in vitro protocol.

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.

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.

Isolated hypothalami from aging female rats do not exhibit reduced basal or potassium-stimulated secretion of luteinizing hormone-releasing hormone

Serum LH levels are diminished in middle-aged rats during spontaneous or steroid-induced LH surges and following ovariectomy (ovx). The compromised LH responses are presumed to reflect age-related alterations in LHRH neurosecretion. Direct measurements of LHRH output in middle-aged females are, however, limited. The present study utilizes an in vitro perifusion paradigm to assess basal and stimulated secretory capacity of LHRH neurons in isolated hypothalamic preparations from aging female rats. Individual hypothalamic fragments from middle-aged and young proestrous, ovx, and ovx, estradiol-treated females were perifused for 6 h and effluents were collected continuously at 10-min intervals. After 4 h of unstimulated output, two 10-min depolarizing pulses of KCl were administered. Although stimulated LHRH secretion was comparable in the two age groups, basal LHRH release from aging hypothalami was significantly elevated (pbasal less than 0.001). Furthermore, endocrine influences on LHRH output from aging hypothalami were less pronounced when compared to endocrine influences on LHRH output from young hypothalami, suggesting that steroidal regulation of LHRH secretion may be impaired in middle-aged females. These data demonstrate that LHRH neurons maintain the capacity to respond to a depolarizing stimulus at the time when regular estrous cycles cease and consequently suggest the importance of altered modulation of LHRH neurosecretion to the development of reproductive senescence.

Corticotropin releasing hormone mRNA is elevated on the afternoon of proestrus in the parvocellular paraventricular nuclei of the female rat

We investigated changes during the estrous cycle in cellular levels of corticotropin-releasing hormone (CRH) mRNA in parvocellular neurons of the hypothalamic paraventricular nucleus, using in situ hybridization. Intact female rats with 4 day cycles were sacrificed at 11 different times during the cycle at 09.00 h and 16.00 h on each day, with additional collection times at 14.00 h, 18.00 h, and 20.00 h on the day of proestrus. Twelve microns coronal sections of fresh-frozen brains were made through the paraventricular nuclei (PVN) and placed on gelatin-coated slides. A 48 base oligodeoxynucleotide probe complementary to the coding region for rat CRH was used to measure CRH mRNA. There was a sharp increase (P less than 0.01) in CRH mRNA in the ventral PVN between 14.00 and 16.00 h on the day of proestrus, at the approximate time of the ovulatory surge. Following this rise, there was an even larger decline (P less than 0.01) between P 16.00 h and P 20.00 h. Levels of CRH mRNA did not change greatly on other days of the cycle, nor were there significant changes in the dorsal PVN. Given the known effects of CRH on GnRH secretion, these changes occur at a time when they could serve to modulate the midcycle luteinizing hormone (LH) surge.

Computed tomographic study of cervical carotid calcification

Contrast-enhanced computed tomography of the neck permits low-risk evaluation of morphologic complications of carotid plaque, including (and foremost) calcification. To investigate the patterns and clinical significance of calcified deposits in the cervical carotid arteries using computed tomography we studied 40 patients with unilateral symptoms of hemispheric ischemia. Calcium deposits observed in the external, internal, and common carotid arteries were oriented in space and individually scored. We found calcified deposits in 39 patients. Stepwise multiple regression of the data provided evidence strongly suggesting a correlation between advancing age and calcium scores. Calcium was more heavily concentrated in the posterior half of arteries (p less than 0.01), in particular of the internal and common carotid arteries, and always in relation to an atheromatous plaque, suggesting a causative link to hemodynamic forces within the arteries. There was no difference in calcification scores between symptomatic and asymptomatic sides, indicating that calcium deposits do not contribute to the development of symptoms.

Immunoreactive Prolactin in the Cerebrospinal Fluid of Estrogen-Treated and Lactating Rats as Determined by Push-pull Perfusion of the Lateral Ventricles

Abstract Immunoreactive (ir) prolactin levels in the cerebrospinal fluid were measured in push-pull perfusion samples collected from the lateral cerebral ventricles in freely-moving ovariectomized rats prior to and after estrogen treatment, and in rats during pregnancy and lactation. Ir-prolactin levels in cerebrospinal fluid were elevated throughout the perfusion period in ovariectomized animals given estrogen and in Day 8 lactating females following the onset of nursing by their young. Cerebrospinal fluid perfusates collected from ovariectomized animals prior to estradiol treatment and from females on Days 18 and 22 of gestation contained levels of ir-prolactin that were below the limit of detectability of the prolactin radioimmunoassay. Data from previous studies in our laboratory suggest that pituitary prolactin is involved in the mediation of maternal responsiveness. Where and how prolactin exerts its actions in this regard remains to be determined. Results of the present study indicate that detectable levels of ir-prolactin are present in the cerebrospinal fluid of nulliparous females after exposure to an estradiol regimen known to shorten their latency to display maternal responsiveness and in lactating females actively exhibiting maternal behavior. Once in the cerebrospinal fluid, prolactin should have access to neural target sites behind the blood-brain barrier. The presence of ir-prolactin in the cerebrospinal fluid of females in the present study is consistent with a role for this protein hormone, acting at the level of the central nervous system, in the facilitation of maternal responsiveness as well as in the regulation of other neural and neuroendocrine processes.

Alterations in luteinizing hormone-releasing hormone release from the mediobasal hypothalamus of ovariectomized, steroid-primed middle-aged rats as measured by push-pull perfusion

The spontaneous luteinizing hormone (LH) surge on proestrus as well as the steroid-induced LH surge and hypersecretion of LH following ovariectomy are attenuated in middle-aged female rats when compared to their young counterparts. It is generally assumed that the lower titers of serum LH measured in aging animals result, in part, from age-related alterations in luteinizing hormone-releasing hormone (LHRH) neurosecretion, yet no direct measurements of LHRH release from the hypothalamus of aging females are currently available. The present study utilized the push-pull perfusion technique to characterize and compare in vivo LHRH output from the mediobasal hypothalamus of ovariectomized middle-aged and young females during a steroid-induced LH surge. Twelve-minute perfusates were collected for a period of 6 h from middle-aged and young animals outfitted with push-pull cannulae resting in the mediobasal hypothalamus in close proximity to the median eminence. The overall pattern of LHRH release differed in the two age groups. Mean levels of LHRH measured in brain perfusates from middle-aged females were significantly lower than mean levels measured in young animals. Moreover, mean levels of LHRH detected in perfusates during the 1- and 2-hour intervals prior to and the 1-hour interval after the time of maximal LHRH output were lower in middle-aged animals, and a larger percentage of samples from middle-aged females contained levels of LHRH below the detectability of the assay. The mean amplitude of identified LHRH pulses and maximal LHRH output, however, did not differ in the two age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Processing of luteinizing hormone-releasing hormone precursor in rat neurons

Results of previous immunocytochemical studies indicate that in the rat brain proteolytic cleaving of LHRH precursors to generate the physiologically active decapeptide takes place within neuronal fibers and terminals and not within perikarya. A 69-amino acid (aa) LHRH precursor comprised of the decapeptide, a 3-aa cleavage and amidation site, and a 56-aa C-terminal extension has recently been characterized. Two antisera generated to specific aa sequences of the C-terminal extension (RM 8/5, anti aa 14-26; PS 39A, anti aa 40-53) and two directed to specific regions of the LHRH decapeptide (RM 1076, anti aa 4-8; A 422 generated to the N-terminal pGlu and C-terminal amidated Gly) were used to further examine intraneuronal sites of precursor processing. Patterns of immunoreactivity revealed with antisera directed to non-LHRH sequences of LHRH precursor paralleled those observed with antisera to the decapeptide. Immunopositive perikarya, processes, and neurovascular terminals were observed with PS 39A. Antiserum PS 39A binds to an internal aa sequence of the C-terminal extension and would, therefore, be expected to detect intact precursor LHRH as well as products of proteolytic cleavage. In contrast, only immunopositive processes and neurovascular terminals were observed with RM 8/5, an antiserum directed to an initial aa sequence of the C-terminal extension. The pattern of immunoreactivity revealed with RM 8/5 resembled that observed with an antiserum that binds the fully processed decapeptide (A 422), indicating that proteolytic cleavage of the decapeptide from the C-terminal extension is required for binding by this antiserum. Furthermore, the restricted distribution of reaction product observed with RM 8/5 relative to A 422 suggests that additional processing of the C-terminal extension may be required for binding. Such additional processing appears to occur in neurovascular terminals of the median eminence.

Estrogen binding in nuclear and cytosolic extracts from brain and pituitary of middle-aged female rats

Estrogen binding was compared in brain and pituitary of long-term ovariectomized young and middle-aged (MA) female rats. Binding was quantified in both cytosolic and nuclear extracts to ascertain whether fractions of estrogen binding are altered in MA females. Estrogen binding detected in nuclear extracts from hypothalamus/preoptic area and anterior pituitary of MA females was significantly lower than levels detected in young females. In each case where an age-related decrease in nuclear estrogen binding was observed, an increased number of putative estrogen receptors was detected in the cytosolic extract. Therefore, the age-related decrease in nuclear estrogen binding did not appear to result from a simple decrease in total available cellular estrogen receptors. Rather these results suggest a decrease in the ability of putative estrogen receptors in aging females to remain tightly bound to nuclei after their isolation. The ability of estrogen receptor complexes from aging animals to bind to DNA was evaluated by DNA-cellulose chromatography in order to examine possible quantitative or qualitative differences in estrogen binding proteins with age. The data did not indicate that the properties of estrogen receptors themselves changed with age. It is possible, therefore, that age-related alterations may interfere with the interaction between the estrogen receptor complex and the nucleus.

Hypothalamic LHRH in aging rats: effects of ovariectomy and steroid replacement

Hypothalamic LHRH was measured by RIA in young and middle-aged (MA) female rats in several endocrine conditions. Temporal alterations in LHRH content associated with the steroid induced gonadotropin surge were compared in medial basal hypothalamic and anterior hypothalamic-preoptic area fragments of ovariectomized young and MA subjects. LHRH content was also compared in ovariectomized, untreated subjects from the two age groups. Finally, LHRH content in MA constant estrous females was compared with content in young females on the morning of proestrus. In all conditions, LHRH levels in both brain regions of MA females were similar to, or significantly elevated above levels measured in young females, yet both the steroid induced surge and the castration induced hypersecretion of gonadotropins were markedly attenuated in aging females. Because studies have verified the responsiveness of the pituitary of MA rats to LHRH, the data suggest that adequate amounts of hypothalamic LHRH do not reach the pituitary. Rather, high levels of hypothalamic LHRH measured in MA subjects may represent accumulation of the peptide in LHRH neurons due to an age-related impairment in release.

Disruption of ongoing maternal responsiveness in rats by central administration of morphine sulfate

The ability of central morphine administration to disrupt established maternal responsiveness in rats was examined. Studies focused on the direct administration of morphine sulfate (M) to the preoptic area (POA), a region known to be involved in the expression of maternal behavior in this species. In the first experiment, crystalline M was administered via bilateral 28 g cannulae to the POA or ventromedial hypothalamus (VMH) of 31 ovariectomized, estrogen-primed, nulliparous, pup-induced, maternal females. All subjects were tested twice for maternal responsiveness; once after M-filled cannulae and once after blank inserts were lowered into place. Behavioral tests lasted for 1 h after foster young were introduced into the test cage, and retrieval, grouping and crouching responses were recorded. Thirteen of 14 females with cannulae placements in the POA showed disruption of maternal responsiveness following morphine treatment. In contrast, only 4 of 17 females with VMH implants showed some deficit in maternal behavior following opiate administration. Results of a second experiment established that M-filled implants placed in the POA of lactating females were capable of disrupting the responsiveness of nursing females toward their own young. Finally, the specificity of morphine's central effects were examined in a third experiment in which lactating females received bilateral POA infusions of morphine (0.5 microgram, n = 7), dextrorphan (an inactive stereoisomer of an active opioid compound; 1.0 microgram, n = 7) or saline alone (n = 6). Whereas maternal behavior was disrupted in all morphine-treated subjects, infusions of dextrorphan or saline had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoreactive forms of luteinizing hormone-releasing hormone in the brains of aging rats exhibiting persistent vaginal estrus

The luteinizing hormone-releasing hormone (LHRH) system in middle-aged female rats exhibiting persistent vaginal estrus (PVE) was examined using immunocytochemical (ICC) techniques. Three LHRH antisera (A-R419, A-R744, A-R422; generously supplied by Dr. A. Arimura) directed toward different portions of the LHRH molecule were utilized to compare the immunoreactive molecular moieties of this hypothalamic peptide present in neurons of aging and young female rats. The immunoreactive forms of the decapeptide detected within neurons of young cycling animals were present within the same regions of the LHRH neurons of PVE females. Immunoreactive LHRH perikarya and fibers in the middle-aged anovulatory females did not differ in their distribution in the basal forebrain from those of young cycling females. Furthermore, no gross morphological differences were apparent at the light microscopic level in LHRH neurons from young and aging females. Of particular importance was the apparent presence of the physiologically active form of the mature decapeptide in terminal regions of the median eminence. These data lead us to propose that failure to release adequate amounts of LHRH from neurovascular terminals and not the lack of availability of this hypothalamic decapeptide contributes to reproductive decline in aging female rats.

Progesterone in the ventromedial hypothalamus of ovariectomized, estrogen-primed rats inhibits subsequent facilitation of estrous behavior by systemic progesterone

The putative neural target sites of progesterone's (P) inhibitory influence on estrous behavior were re-examined utilizing intracranial hormone implants. Subjects were estrogen-primed ovariectomized, Long-Evans rats, and all were outfitted with permanent indwelling guide cannulae aimed for the ventromedial hypothalamus (VMH), preoptic area (POA), or midbrain. In a series of 4 weekly testing paradigms, the ability of blank or P-filled implants to both facilitate estrous responsiveness and to interfere with an animal's ability to exhibit estrous behavior following a systemic injection of P 24 hours later was assessed. P-filled implants placed bilaterally into the VMH inhibited the subsequent facilitation of estrous behavior by systemic P administration. Neither P-filled implants in other brain regions nor blank implants lowered into the VMH had this same effect. Seven of the females that exhibited progesterone-induced behavioral refractoriness 24 h after P stimulation of the VMH exhibited facilitation of estrous responsiveness in behavioral tests given 4.5 h after cannulae placement suggesting that progesterone may exert its facilitative and inhibitory actions on estrous responsiveness at the same neuroanatomical locus.

Behavioral effects of progestin in the brain

In this article we review research on the role of progestins in the regulation of estrous responsiveness in female rats. Estrous responsiveness normally results from a synergistic action of estradiol (E2) and progesterone (P). E2 primes the system but normally does not result in estrous behavior. The full expression of estrous responsiveness results from the action of P on the E2-primed system. It has been demonstrated with implants of dilute E2 (1 part E2: 250 parts cholesterol) that the site of E2 priming is the ventromedial nucleus of the hypothalamus (VMN). In females primed with systemically administered E2, P also acts on the VMN to facilitate full estrous responsiveness. It has been shown in addition that estrous responsiveness results from sequential application of E2 and P to the VMN but not to other areas of the brain. The VMN is also the site at which P produces sequential inhibition of estrous responsiveness. The time course of P action in facilitating full estrous responsiveness is about two hours, regardless of whether the hormone is administered intracerebrally or intravenously. The duration of estrous responsiveness is directly correlated with the length of time P is in contact with brain tissue. Experiments with the protein synthesis inhibitor anisomycin are consistent with the view that P acts in the VMN by way of a protein synthetic mechanism to facilitate estrous behavior; however, other mechanisms must be considered as alternatives. Finally, we address the question of whether estrogenic priming depends upon induction of progestin receptors in the VMN. Results indicate that estrogenic priming of estrous responsiveness may occur without concomitant induction of progestin receptors.

Induction of estrous behavior in ovariectomized rats by sequential replacement of estrogen and progesterone to the ventromedial hypothalamus

The present experiment was designed to determine whether sequential replacement of estrogen and progesterone to the ventromedial hypothalamus (VMH) would be sufficient to induce estrous behavior in ovariectomized rats. Bilateral cannulae containing 17 beta-estradiol (E2) diluted with cholesterol (1:250) were lowered into the VMH, preoptic area or midbrain and left in place for 4 days. On day 5, the E2 inserts were removed and P-filled cannulae were lowered into half of the subjects. The remaining females received systemic progesterone (500 micrograms). This steroid regimen was repeated 2 weeks later with the mode of progesterone administration reversed. All subjects were tested for estrous behavior twice after progesterone treatment. In a second experiment, 3H-P:P-filled cannulae were lowered into the VMH of estrogen-primed females in order to estimate the extent of hormone spread from full-strength P-filled cannulae. Results indicated that estrogen and progesterone stimulation of the VMH is sufficient to activate estrous behavior in spayed female rats, however, precise localization of the hormone implants within the VMH is essential. 9 of the 11 females with both cannulae located within or at the border of the ventromedial nucleus (VMN) exhibited estrous behavior whereas only half of the females with only one implant resting in the VMN exhibited estrous responsiveness. Subjects with neither cannula located within or at the border of the VMN did not exhibit the behavior. The facilitative effects of P appeared to result from hormonal stimulation of the VMH and not from leakage of the steroid into other brain regions or into the systemic circulation. Following placement of tritiated progesterone implants into the VMH, high levels of radioactivity were recovered only from the mediobasal hypothalamus. The low levels of radioactivity measured in other brain regions, pituitary, uterus and blood indicate that relatively little if any hormone reached these tissues.

Progesterone in the ventromedial hypothalamus facilitates estrous behavior in ovariectomized, estrogen-primed rats

The putative neural target sites of progesterone (P) action for the facilitation of estrous behavior in female rats were reexamined using the hormone implant technique. Subjects were ovariectomized, estrogen-primed Long-Evans females. All were outfitted with bilateral double barreled cannulae assemblies consisting of 23-gauge guide cannulae and 28-gauge inserts. Subjects in Exp 1 received sc injections of individually determined threshold priming doses of estradiol benzoate. Estrogenic priming for subjects in Exp 2 was provided by sc placed Silastic capsules (5 mm) filled with 17 beta-estradiol-cholesterol (1:20). Each subject was tested for estrous behavior with a male after P-filled cannulae and after blank inserts were lowered into the brain. Behavioral tests were conducted 1 and 4.5 h postcannulae placement. Thirty-five of 40 females with P in the ventromedial hypothalamus exhibited high levels of lordosis behavior during the 4.5-h test. Moreover, 29 of the 35 exhibited solicitation behavior as well. Estrous behavior was not exhibited by these animals during the 1-h test. Implants in other regions of the brain (i.e. mesencephalic reticular formation, preoptic area, central grey, caudate putamen, and hippocampus; n = 80) did not consistently facilitate estrous responsiveness. In Exp 3, levels of estrous responsiveness were similar before and after adrenalectomy (n = 10); thus, facilitation of estrous behavior by P-filled implants in the ventromedial hypothalamus was not dependent upon activation of the hypothalamic-pituitary-adrenal axis.

Onset of the receptive and proceptive components of feminine sexual behavior in rats following the intravenous administration of progesterone

The present study was carried out in order to assess the time course of action of progesterone (P) in the facilitation of complete feminine sexual behavior. Female rats (estrogen primed via 5% E2 Silastic capsules) were given 200 micrograms of P either intravenously (iv) or subcutaneously (sc), and tested for estrous behavior at 1/4, 1/2, 1, 2, and 4 hr after treatment. Among iv-treated animals, significant amounts of lordosis behavior were seen as early as 1/2 hr, and a dramatic rise in solicitation behavior was observed at 2 hr. Although sc-treated animals displayed significant amounts of lordosis and solicitation behavior at 2 hr, the behavior was not maximal until 4 hr. Intravenous administration of 400 micrograms P was equipotent to 200 micrograms P, whereas 50 micrograms of iv P was relatively ineffective. A dual mechanism hypothesis pertaining to progesterone's actions in the facilitation of both the receptive and proceptive components of feminine sexual behavior in rats is discussed.

Intracerebroventricular administration of oxytocin and maternal behavior in rats after prolonged and acute steroid pretreatment

The role of oxytocin in the initiation of maternal responsiveness in rats was reexamined. Oxytocin (400 ng in 4 microliters saline) or saline alone was infused into the cerebral ventricular system of ovariectomized steroid-primed virgin females. Subjects received 2 weeks of exposure to ovarian steroids via subcutaneously implanted Silastic capsules (Experiment 1) filled with 17 beta-estradiol (1 mm; from Day 1) and progesterone (15 mm; Days 3-13), or they received a single injection of estradiol benzoate (100 micrograms/kg) 48 hr before intracerebral infusion (Experiment 2). Behavioral testing began immediately after oxytocin or saline administration. Latencies to retrieve, group, and crouch over foster young were scored. Contrary to previous reports, oxytocin did not stimulate a rapid onset of maternal responsiveness. The mean latencies to exhibit pup-oriented behaviors ranged from 2.8 to 5.1 days in all groups, regardless of treatment.

Priming of estrous responsiveness by implants of 17 beta-estradiol in the ventromedial hypothalamic nucleus of female rats

In an attempt to obtain a more precise localization of the neural target site(s) of estrogen-priming action in the activation of estrous behavior, 30-gauge cannulae containing a preparation of 17 beta-estradiol diluted 1:250 with cholesterol were implanted bilaterally into the brains of ovariectomized rats. Subjects were tested for sexual behavior with intact males at 4-day intervals for 3 weeks beginning 2-3 days after stereotaxic surgery. Animals received a systemic injection of 0.5 mg progesterone 4-6 h before all but 1 test. After this treatment, estrous behavior was observed in 19 of the 20 animals judged to have both cannulae resting in or within 0.25 mm of the ventromedial nucleus of the hypothalamus (VMN). Virtually no estrous behavior was observed without the administration of progesterone. Behavioral scores decreased as a function of the distance of the cannulae tips from the VMN. Cholesterol implants in the same region (n = 8) were without effect. Implants in other regions of the brain (e.g. preoptic area, diagonal band of Broca, lateral habenula, amygdala, or cortex; n = 52) were ineffective. These results indicate that estrogenic stimulation of the region of the VMN alone is sufficient to prime the activation of estrous behavior in the ovariectomized rat.