Estrogen induces ultrastructural changes in progesterone receptor-containing GABA neurons of the primate hypothalamus

Estrogen affects gonadotrophin levels and sex behavior in monkeys. This action could be via inhibitory GABA-ergic neurons in the hypothalamus. We tested for direct estrogen actions on such neurons. Seven days after ovariectomy (OVX) or OVX + estrogen treatment (10 mg estradiol valerate in 1 ml sesame oil s.c. on the day of OVX), light- and electron-microscopic double immunostaining procedures were used for simultaneous visualization of immunoreactivity for progesterone receptors (PR) and glutamic acid decarboxylase (GAD), and to detect ultrastructural changes in PR-containing neurons in the arcuate and ventromedial hypothalamic nuclei of colchicine- and noncolchicine-treated African green monkeys (Cercopithecus aethiops). Immunoreactivity for PR was found only in cell nuclei, and estrogen treatment enhanced the intensity of the immunostaining: in estrogen-treated monkeys in the arcuate nucleus 62%, while in the ventromedial nucleus 42% of the neurons contained PR-immunoreactive nuclei. All of the PR-containing neurons were immunopositive for GAD in colchicine-pretreated monkeys. OVX induced whorl body formation, while estrogen treatment of OVX animals resulted in a large number of nematosomes. While all of the whorl bodies and the majority of nematosomes were observed in PR-immunopositive GAD neurons, nematosomes were also found in non-PR-containing GAD-immunoreactive cells.

Comparison of age- and sex-related changes in cell nuclear estrogen-binding capacity and progestin receptor induction in the rat brain

Previous studies have suggested parallels between the mechanisms underlying sexual differentiation and age-related loss of reproductive cyclicity in the female rat. Both appear to involve the actions of estrogen on the brain and are associated with a reduction in hypothalamic estrogen sensitivity. In this study the effects of sex and aging on cell nuclear estrogen receptor-binding capacity and cytosol progestin receptor induction in the pituitary gland, periventricular preoptic area (PVP), medial preoptic area (mPO), bed nucleus of the stria terminalis, arcuate median eminence region (ARC), ventromedial nucleus (VMN), and corticomedial amygdala were directly compared. Young (2.5 months old) and middle-aged (8-10 months old) male and female and old (19 months old) female rats were gonadectomized 14 days before adrenalectomy (ADX). For comparison of cell nuclear estrogen receptor-binding capacity, animals received a saturating dose of estradiol (36.0 micrograms/kg BW) 3 days after ADX and 1 h before death. Cell nuclear estrogen binding was measured by an in vitro exchange assay. For comparison of estrogen-induced progestin receptors, animals received a sc placed Silastic capsule containing 10% 17 beta-estradiol at the time of ADX and were killed 3 days later. Cytosol progestin binding was measured by an in vitro binding assay. Cell nuclear estrogen-binding capacities and cytosol progestin receptor induction were lower in the PVP, mPO, and VMN of the young male than in the young female. In the female, the level of progestin receptor induction in the pituitary and brain was unaffected by age; however, cell nuclear estrogen-binding capacity in the mPO, VMN, ARC, and pituitary gland was lower in old than in middle-aged females. These results demonstrate that the effects of sexual differentiation and aging on the hypothalamus involve similar, but not identical, region-specific reductions in cell nuclear estrogen receptor-binding capacity. The consequences of these reduced estrogen receptor binding levels in terms of the induction of progestin receptor in response to estrogen exposure are, however, very different in the male compared to those in old female rats.

Catecholaminergic innervation of luteinizing hormone-releasing hormone and glutamic acid decarboxylase immunopositive neurons in the rat medial preoptic area. An electron-microscopic double immunostaining and degeneration study

Catecholaminergic innervation of luteinizing hormone-releasing hormone (LHRH) and glutamic acid decarboxylase (GAD) immunoreactive neurons in the rat medial preoptic area (MPO) was studied using electron-microscopic (EM) double-label immunostaining and combinations of single- and double-label immunostaining with acute axonal degeneration. The EM double-immunostaining experiments included double staining for either tyrosine hydroxylase (TH) and LHRH, or TH and GAD. Analysis of TH and LHRH double-immunostained material revealed synaptic connections between TH immunoreactive axons and LHRH immunopositive neurons. The TH and GAD double-staining experiments also demonstrated synaptic connections between axons immunoreactive for TH and GAD immunopositive neurons. Two days following unilateral surgical transection of the ventral and dorsal noradrenergic bundles, synaptic connections were found between degenerated boutons and GAD immunoreactive neurons in the ipsilateral MPO. However, no synapses could be observed in the same area between degenerated axons and the LHRH immunopositive neurons. Following the same operation and immunostaining for TH, a moderate number of degenerating TH axons as well as a large number of nondegenerated TH immunoreactive boutons were observed. Double immunostaining for TH and GAD in MPO sections ipsilateral to the operation revealed synaptic connections between the degenerating TH immunopositive axons and GAD immunoreactive neurons. These results suggest that there are direct synaptic connections between catecholaminergic axons and GAD and LHRH immunoreactive neurons in the medial preoptic area of the rat. Some of the connections between TH immunopositive afferents and GAD immunoreactive neurons may represent connections from noradrenergic neurons in the brain stem, while the majority of TH-GAD and TH-LHRH connections may represent innervation of GABA and LHRH neurons from local dopamine-containing cells.

Immunohistochemical evidence for synaptic connections between pro-opiomelanocortin-immunoreactive axons and LH-RH neurons in the preoptic area of the rat

Connections between adrenocorticotropic hormone (ACTH)-immunoreactive neurons in the arcuate nucleus and the preoptic area were studied in the female rat. ACTH-immunopositive terminals were observed in the medial preoptic area in contact with dendritic shafts, while in the ventrolateral preoptic area the majority of ACTH-immunoreactive synapses were found on dendritic spines. Double-label electron microscopic immunocytochemistry using peroxidase and avidin-ferritin as contrasting electron-dense markers revealed numerous synaptic contacts between ACTH-immunopositive boutons and luteinizing hormone-releasing hormone (LH-RH)-immunoreactive dendritic shafts in the medial preoptic area. Following injection of horseradish peroxidase (HRP) into the medial preoptic area, retrogradely HRP-labeled perikarya were observed throughout the arcuate nucleus. Double-staining experiments revealed that a proportion of these retrogradely labeled cells, in the ventromedial arcuate nucleus, are also immunoreactive for ACTH. These results suggest that pro-opiomelanocortin peptide-producing neurons in the ventromedial arcuate nucleus project to the medial preoptic area. Some of these neurons establish direct synaptic contacts with LH-RH-immunoreactive cells.

Metabolism and binding of androgens in the spinal cord of the rat

The binding of [3H]androgens and estrogens, and the metabolism of [3H]androgens, were studied in the spinal cord of the adult rat. High-affinity, specific binding sites for [3H]testosterone and [3H]estradiol were detected in cytosol fractions from the spinal cords of castrate animals. Equilibrium dissociation constants for reaction of these sites with their respective ligands were similar to those of androgen and estrogen receptors from other regions of the central nervous system. Nuclear binding of [3H]estradiol was observed in the spinal cord 1 h after intravenous administration of the isotope. Likewise, exchange assay demonstrated the presence of high-affinity androgen binding sites in spinal cord nuclei from orchidectomized, testosterone propionate treated animals. 5 alpha-Reductase activity in homogenates of the spinal cord was relatively high, approximately 3 times that in the pooled hypothalamus, preoptic area, septum and amygdala. However, in contrast to the latter brain regions, estrogen formation was not detectable in spinal cord tissue. No sex differences were observed in the metabolism of [3H]testosterone by spinal cord homogenates. These results confirm the presence of androgen and estrogen receptors in the rat spinal cord. The lack of detectable aromatase activity in the spinal cord is consistent with the hypothesis that the effects of circulating testosterone on spinal reflex function are mediated primarily through the androgen receptor system.

Preservation of steroid receptors in frozen brain and pituitary tissue: use of the cryoprotective agent, dimethylsulfoxide

This paper examines the effects of freezing and thawing on steroid receptor concentrations in the brain and pituitary of the rat. Storage at -70 degrees C for 1-2 weeks had no detectable effect on levels of cytoplasmic estrogen receptors. However, freezing and thawing resulted in measurable losses of cytoplasmic androgen, progestin and glucocorticoid receptors. Cell nuclear receptors were measured by exchange assay after in vivo administration of non-radioactive steroids. Nuclear estrogen, androgen and progestin receptor concentrations were all reduced by freezing compared to the levels in fresh tissue. In all cases except that of cytoplasmic glucocorticoid receptors, these losses could be prevented by freezing the tissue in 10% aqueous dimethylsulfoxide.

Reproductive failure due to experimentally induced constant estrus does not alter the LH-RH fiber density in the median eminence of the rat

The effects of anterior hypothalamic deafferentation on luteinizing hormone releasing hormone (LH-RH) fiber density in the mediobasal hypothalamus (MBH) were compared to those of a number of nonsurgical treatments which give rise to anovulatory sterility (injections of estradiol valerate, exposure to constant light, or neonatal androgen administration) in the female rat. All of the treatments used (surgical and nonsurgical) disrupted the normal 4-day pattern of estrous cyclicity. Bilateral anterior hypothalamic deafferentation markedly reduced the packing density of LH-RH fibers in the MBH. Unilateral deafferentation reduced the number of fibers on the ipsilateral side of the MBH by 31-64% and on the contralateral side by 15-40%. In contrast, none of the three nonsurgical treatments had any significant effect on the LH-RH fiber density. Electron microscopic examination revealed no morphologic, or distribution differences in MBH LH-RH fibers between control females and animals rendered anovulatory by the nonsurgical experimental procedures. These results demonstrate that estrogen, androgen, and constant light induced anovulatory sterility are not associated with any overt change in the number or morphology of LH-RH immunoreactive fibers in the MBH, suggesting that the primary lesion responsible for the failure of normal estrous cyclicity in such animals resides in the systems responsible for regulating the activity of the LH-RH neurons rather than in the LH-RH neurons themselves.

The LH-RH-containing neuronal network in the preoptic area of the rat: demonstration of LH-RH-containing nerve terminals in synaptic contact with LH-RH neurons

The existence of a luteinizing hormone-releasing hormone (LH-RH)-containing local neuronal network in the preoptic area of the rat was demonstrated by electron microscopic immunocytochemistry. LH-RH-immunostained presynaptic boutons were observed in synaptic contact with LH-RH-immunoreactive dendrites and perikarya.

Glutamic acid decarboxylase-containing axons synapse on LHRH neurons in the rat medial preoptic area

A double-label electron microscopic immunostaining procedure was employed to examine the interconnections of glutamic acid decarboxylase(GAD)- and LHRH-immunoreactive neurons in the medial preoptic area of the rat. The results provide ultrastructural evidence that GABA-ergic neurons establish symmetric (Gray II) synapses on LHRH neurons.

Intrinsic tyrosine hydroxylase (TH) immunoreactive axons synapse with TH immunopositive neurons in the rat arcuate nucleus

Synaptic connections were demonstrated between tyrosine hydroxylase (TH) immunoreactive axons and dendrites in the arcuate nucleus of the rat, by electron microscopic immunocytochemistry. These connections were primarily found in the lateral part of the nucleus. The results of two types of medial-dorsal-lateral surgical de-afferentation suggest that the TH-TH contacts represent intrinsic connections.

Estrogen responsive cells in the arcuate nucleus of the rat contain glutamic acid decarboxylase (GAD): an electron microscopic immunocytochemical study

Twenty-one days after ovariectomy (OVX) an increased frequency of lamellar cytoplasmic organelles, termed 'whorl' bodies (WB), was observed in neurons of the rat arcuate nucleus (AN). When estradiol valerate (2 mg s.c.) was injected either at the time of OVX or one week later, the frequency of WB at 21 days was reduced. The estrogen treatment resulted in a concomitant rise in the frequency of 'nematosomes' (NS), filamentous electron-dense cytoplasmic structures. In the medial part of the AN glutamic acid decarboxylase (GAD) immunopositive symmetric (Gray II) synapses were observed in contact with WB- and NS-containing cells. After colchicine treatment, GAD immunoreactivity was observed in the WB- and NS-containing perikarya in the medial AN. Some of the NS-containing cells in the lateral AN of the colchicine-pretreated animals remained immunonegative for GAD.

Application of avidin-ferritin and peroxidase as contrasting electron-dense markers for simultaneous electron microscopic immunocytochemical labelling of glutamic acid decarboxylase and tyrosine hydroxylase in the rat arcuate nucleus

A pre-embedding immunostaining procedure was developed using ferritin and peroxidase to enable simultaneous electron microscopic localization of two antigens in the same tissue section. This method was used to study the anatomic relationship between glutamic acid decarboxylase (GAD) immunoreactive axons and tyrosine hydroxylase (TH) - containing neurons of the rat arcuate nucleus. The findings provide ultrastructural evidence that GAD-immunoreactive terminals establish symmetric (Gray II) synapses on TH-reactive neurons.