Effect of gonadal hormones on enzyme activities in brain and pituitary of male and female rats

Expansion of mossy fibers and CA3 apical dendritic length accompanies the fall in dendritic spine density after gonadectomy in male, but not female, rats

Androgen loss is an important clinical concern because of its cognitive and behavioral effects. Changes in androgen levels are also suspected to contribute to neurological disease. However, the available data on the effects of androgen deprivation in areas of the brain that are central to cognition, like the hippocampus, are mixed. In this study, morphological analysis of pyramidal cells was used to investigate if structural changes could potentially contribute to the mixed cognitive effects that have been observed after androgen loss in males. Male Sprague-Dawley rats were orchidectomized or sham-operated. Two months later, their brains were Golgi-impregnated for morphological analysis. Morphological endpoints were studied in areas CA3 and CA1, with comparisons to females either intact or 2 months after ovariectomy. CA3 pyramidal neurons of orchidectomized rats exhibited marked increases in apical dendritic arborization. There were increases in mossy fiber afferent density in area CA3, as well as robust enhancements to dendritic structure in area CA3 of orchidectomized males, but not in CA1. Remarkably, apical dendritic length of CA3 pyramidal cells increased, while spine density declined. By contrast, in females overall dendritic structure was minimally affected by ovariectomy, while dendritic spine density was greatly reduced. Sex differences and subfield-specific effects of gonadal hormone deprivation on the hippocampal circuitry may help explain the different behavioral effects reported in males and females after gonadectomy, or other conditions associated with declining gonadal hormone secretion.

Direct, complex effects of estrogens on basal forebrain cholinergic neurons

Although controversial, estrogens remain one of the few agents purported to influence the incidence of Alzheimer's disease and one of their postulated mechanisms of action is their effects on basal forebrain cholinergic neurons. However, it is unclear whether the responses of cholinergic neurons to estrogens are direct or mediated via the retrograde influences of neurotrophins, known to be induced by estrogens in the hippocampus and neocortex. In the present study, we explore the issue of the primary site of action of estrogens by studying the regulation of expression of genes that characterize mature cholinergic neurons, i.e., choline acetyltransferase, trkA, and p75(NTR) in the medial septum and the nucleus basalis complex. In parallel, we study the hippocampal expression of NGF, BDNF, and NT-3, i.e., neurotrophins with known trophic roles on cholinergic neurons. Gene expression is studied by RT-PCR in ovariectomized female rats with and without estrogen supplementation within the physiological estradiol range and in rats with complete fimbria-fornix transactions treated with estrogen or vehicle. To clarify mechanisms of estrogen transduction in cholinergic neurons, we study the effects of estrogen treatment on fimbria-fornix-lesioned mice with genetic ablations of ER subtypes alpha and beta. The results of the present study suggest that, while estrogens do regulate BDNF expression in the hippocampus and neocortex, they also exert stimulatory non-trophic effects on basal forebrain cholinergic neurons, primarily on ChAT expression. Cholinergic neurons retain their ability to respond to estrogens after their complete separation from the hippocampus. The elimination of ERalpha alters significantly the phenotypic responsiveness of cholinergic neurons to estrogens, whereas elimination of ERbeta appears to have no effect. Our findings support the idea that estrogens directly enhance cholinergic neuron function and that ERalpha plays a significant role in transducing these regulatory effects.

Sex difference in the response of melanin-concentrating hormone neurons in the lateral hypothalamic area to glucose, as revealed by the expression of phosphorylated cyclic adenosine 3',5'-monophosphate response element-binding protein

Because there are sex differences in feeding behavior in rats, we looked for a possible sex difference in the response to glucose of melanin-concentrating hormone (MCH) neurons in the lateral hypothalamic area using phosphorylated cAMP response element-binding protein (pCREB) as a marker of neural activity. Intact male rats and female rats at diestrus 2, proestrus, or estrus were fed normally or fasted for 48 h and injected with saline or glucose (400 mg/kg). Thereafter, preparations were subjected to immunohistochemical processing for the double staining of MCH and pCREB. Fasting increased the ratio of MCH neurons with pCREB (double-stained cells) in both male and female rats. In fasted rats, glucose injection decreased the ratio of double-stained cells more promptly in females than in males. The magnitude of decrease caused by glucose was greater at proestrus and estrus than at diestrus 2. Gonadectomy in males enhanced and in females attenuated the response of MCH neurons to glucose. Testosterone and estrogen replacement in males and females, respectively, restored the response of MCH neurons to glucose. The demonstrated sex differences in the response of MCH neurons to glucose correlated well with the gonadal steroid milieu; thus, MCH neurons may play an important role in sex differences in feeding behavior.

Neuroendocrinology of female aging

BACKGROUND

Because the average human life span has increased, a greater part of more women's lives will be lived in a hypoestrogenic state.

OBJECTIVE

This article provides an overview of our current knowledge of the neuroendocrine processes in the aging female brain.

METHODS

Using the search terms cardiovascular disease, cognition, dementia, depression, estrogens, female aging, gonadotropins, immune function, mood, neuroendocrinology, neurotransmitters, osteoporosis, and ovarian steroids, a review of English-language literature on the MEDLINE database was conducted from 1970 through June 2004.

RESULTS

It is thought that the temporal patterns of neural signals are altered during middle age, leading to cessation of reproductive cycles, and that the complex interplay of ovarian and hypothalamic/pituitary pacemakers becomes increasingly dysfunctional with aging, ultimately resulting in menopause. Estrogen deficiency is associated with low mood, whereas estrogen therapy tends to be linked with improvements in measures of well-being and a decline in depression scores. It is likely that these effects of estrogens are mediated through changes in the metabolism of serotonin and nor epinephrine. Evidence exists to support the role of estrogens in specific effects on cognitive functioning in women, enhancing aspects of verbal memory, abstract reasoning, and information processing. Significant gender dimorphism is evident in both humoral and cell-mediated immune responses. The effects of estrogens on the cardiovascular system are complex; recent evidence suggests a negative role for oral estrogen in primary and secondary prevention of cardiovascular events. Additionally, estrogens increase the risk of stroke, and estrogen deficiency influences the pathogenesis of osteoporosis in both men and women.

CONCLUSIONS

Changes in the neuroendocrine system due to the loss of ovarian function at menopause have an important biological role in the control of reproductive and nonreproductive functions, and regulate mood, memory, cognition, behavior, immune function, the locomotor system, and cardiovascular functions. More detailed insights are needed into the complex mechanisms of neuroendocrine alterations with aging.

Sex and housing conditions affect the 24-h acetylcholine release profile in the hippocampus in rats

To examine the sex difference in the 24-h profile of the acetylcholine (ACh) release in the hippocampus, in addition to the effects of housing conditions on this profile, we performed an in vivo microdialysis study in intact male and cycling female rats that had been living in large (diameter=35 cm) or small (diameter=19 cm) cylindrical cages. Each rat was individually housed in a cage for 4 days. On the day of the experiment, the dialysate was collected from the dorsal hippocampus at 20-min intervals and sequential blood samples were simultaneously obtained at 2-h intervals, under the freely moving condition for more than 24 h. ACh in the dialysates was measured by the high performance liquid chromatography system, while the corticosterone concentration in the serum was measured by radiostereoassay. Although the ACh release showed a clear daily rhythm in both sexes of rats, the amount of ACh released in female rats was significantly lower than that in males. Furthermore, the housing in the small cage significantly attenuated the ACh release during the dark phase in male rats, but not in female rats. Conversely, the serum corticosterone concentration showed a clear daily rhythm and the mean concentration of serum corticosterone in female rats was significantly higher than that in male rats. Housing in the small cage did not affect the corticosterone rhythm in either sex. These results reveal a sex difference in the 24-h profile of the ACh release, which suggests vulnerability of the cholinergic system in male rats depending on its housing conditions.

Effects of estrogen replacement therapy on cholinergic basal forebrain neurons and cortical cholinergic innervation in young and aged ovariectomized rhesus monkeys

Estrogen modulates the function of cholinergic basal forebrain neurons in aged female rats. The present study tested the hypothesis that estrogen enhances the phenotype of cholinergic basal forebrain neurons and their cortical cholinergic innervation in young adult and aged ovariectomized rhesus monkeys. Sixteen monkeys (9 young and 7 aged) received two injections of estradiol cypionate or vehicle separated by 3 weeks. All monkeys were killed 1 day after the last injection. Quantitative immunofluorescence in the vertical limb of the diagonal band (VLDB) revealed enhanced optical density for choline acetyltransferase (ChAT) in both young and aged monkeys treated with estrogen. In contrast, optical density for low-affinity p75 neurotrophin receptor immunoreactivity in the VLDB did not change after estrogen treatment in either aged or young animals. Quantitative immunofluorescence for either ChAT or the low-affinity p75 neurotrophin receptor in the nucleus basalis Meynert failed to reveal differences between vehicle and estrogen treatment in either age group. Quantitative estimates of acetylcholinesterase (AChE) fiber density revealed that estrogen-treated aged monkeys but not their younger counterparts had decreased numbers of AChE-positive fibers in layer II of frontal, insular, and cingulate cortices. These data indicate that estrogen administered in a manner simulating natural hormonal cyclicity produces modest age-specific chemical phenotypic and regional changes in select neuronal subfields of the cholinergic basal forebrain and their cortical projection sites in nonhuman primates.

Estrogen replacement therapy for cognitive benefits: viable treatment or forgettable "senior moment"?

The perceived benefits of estrogen on cognitive function are one of the few remaining potential roles for estrogen replacement therapy. The justification for such a role has a strong biologic basis and is easily shown in animal models. Purported benefits for estrogen on cognitive function include neuroprotective, neurostimulating, and neurotrophic effects. The objective of this study was to review the literature and to evaluate the role of estrogen replacement therapy in improving cognition in Alzheimer disease, vascular dementia, premenopausal women, and postmenopausal women without dementia. Additionally, the authors separately looked at the neuroprotective effects of estrogen replacement therapy on the subsequent risk of dementia. The available data fail to show a therapeutic benefit of estrogen replacement therapy in Alzheimer disease. Surprisingly, limited data allow consideration of a possible role of estrogen in the management of vascular dementia. Additionally, younger females with low estrogen levels secondary to primary ovarian failure and Turner syndrome benefit from estrogen replacement therapy. Despite the limited role of estrogen replacement therapy in cognitive enhancement, neuroprotective properties are likely because several prospective studies indicate a reduced risk of Alzheimer disease. A critical window of opportunity seems to exist for this protective effect in Alzheimer disease because once established, the course of the disease is not affected by concomitant estrogen replacement therapy. The authors conclude that the use of estrogen replacement therapy is not substantiated for the treatment of patients with Alzheimer disease. Alternatively, because of the evidence for a possible neuroprotective effect, women at high risk for the development of Alzheimer disease may be appropriate candidates for estrogen replacement therapy. Such a decision should be made on a case-by-case basis, after careful consideration of the risks and benefits.

Hormonal regulation of hippocampal spine synapse density involves subcortical mediation

It is well established that estrogen has positive effects on the density of pyramidal cell spines in the hippocampal CA1 subfield. This study explored whether afferent connections of the hippocampus that come from estrogen-sensitive subcortical structures, including the septal complex, median raphe and supramammillary area, play a role in this estrogen-induced hippocampal synaptic plasticity. These particular subcortical structures have major influences on hippocampal activity, including theta rhythm and long-term potentiation. The latter also promotes the formation of new synapses. All of the rats were ovariectomized; the fimbria/fornix, which contains the majority of subcortical efferents to the hippocampus, was transected unilaterally in each, and half of the animals received estrogen replacement. Using unbiased electron microscopic stereological methods, the CA1 pyramidal cell spine synapse density was calculated. In the estrogen-treated rats, contralateral to the fimbria/fornix transection, the spine density of CA1 pyramidal cells increased dramatically, compared to the spine density values of both the ipsilateral and contralateral hippocampi of non-estrogen-treated animals and to that of the ipsilateral hippocampus of the estrogen replaced rats. These observations indicate that fimbria/fornix transection itself does not considerably influence CA1 area pyramidal cell spine density and, most importantly, that the estrogenic effect on hippocampal morphology, in addition to directly affecting the hippocampus, involves subcortical mediation.

Modulation of the pituitary and basomedial hypothalamic lysyl-aminopeptidase activities be beta-estradiol and/or an aqueous extract of Physalis alkekengi fruits

Injections of an aqueous extract of winter cherry fruits (Physalis alkekengi) to adult female cycling rats by an intraperitoneal route resulted in the diminution of the pituitary lysyl-aminopeptidase (Lys-AP) activity by 50% and that of the basomedial hypothalamus (BMH) by 45%. Administration of daily doses of 3.75, 7.5, and 15 micrograms beta-estradiol for a period of 5-8 days to such animals increased pituitary Lys-AP activity from 31% to 61.5% and that of BMH from 20% to 87%, respectively. Administration of the same doses of beta-estradiol along with a given dose of the aqueous extract for 7-8 days diminished Lys-AP inhibitory effect of the extract in both the pituitary and BMH and eventually, at the highest dose of beta-estradiol, increased the pituitary enzyme activity by 9% and that of BMH by 5%. It is concluded that Lys-AP enzymes of both tissues, being estrogen-induced proteins, are inhibited by the estrogen antagonistic principle of the winter cherry aqueous extract. It is further suggested that BMH Lys-AP activity may be used as an enzyme marker for the action of beta-estradiol in hypothalamus.

Early postnatal changes in sexual dimorphism of catecholamine and indoleamine content in the brain of prenatally stressed rats

Sexual dimorphism in catecholamine and indoleamine content in the brain preoptic area and mediobasal hypothalamus was studied in 10-day-old rat pups whose mothers had been exposed to the daily 1-h immobilization stress during the last week of pregnancy. Concentration of noradrenaline in the preoptic area and 5-hydroxyindoleacetic acid in the mediobasal hypothalamus of the prenatally stressed male offspring as well as dopamine content in the mediobasal hypothalamus and 5-hydroxyindoleacetic acid content in the preoptic area of the females were increased by 59%, 45%, 34%, 76%, respectively. Dopamine content in the preoptic area of the female pups was decreased. In addition, an increase of 5-hydroxytryptamine metabolism in the female preoptic area has been revealed. As a result of prenatal stress, sex-related differences in noradrenaline and 5-hydroxyindoleacetic acid concentrations in the preoptic area and those in dopamine concentration in the mediobasal hypothalamus disappeared. The suggestion is made that the early changes in sexual dimorphism of the brain catecholamines and 5-hydroxytryptamine metabolism in prenatally stressed rats may be responsible for the development of the long-term disorders of sexual differentiation of the neuroendocrine functions.

The influence of gender in the evaluation of platelet and plasma catecholamines

The platelet and plasma levels of catecholamines (CA) were simultaneously studied in a group of normal subjects in order to find possible sex-related changes in the distribution of CA in these two compartments. No significant differences between males and females were observed, but a marked platelet noradrenaline increase was found in the luteal phase as compared to the follicular phase. Furthermore, the platelet and plasma CA levels were strongly correlated in the male group but not in the female group. These results, while confirming the existence of a menstrual-related variability in noradrenergic activity, suggest a sex-related difference in the dynamic balance between platelet and plasma CA levels. The simultaneous assay of platelet and plasma CA enabled this phenomenon to be revealed, whereas the separate evaluation of platelet or plasma CA levels would not have done so.

Actions of sex hormones on the brain

1. The brain is a target for sex steroid hormones. As a result of sex hormone actions on the brain various behavioral changes are observed in animal and man. This paper gives a brief overview over the multiple central nervous functions that are under modulatory control of sexual hormones and describes the complex sex steroid actions on the brain by giving an example for "activating" and "organizing" effects of estrogens on noradrenergic neurons in the brain of rats. 2. Estradiol-17 beta induced sex specific alterations in the turnover of noradrenaline in the preoptic area and mediobasal hypothalamus showing "female" or "male" responses. 3. Neonatal manipulations of female rat pups by testosterone, estradiol-17 beta or 4-hydroxyestradiol-17 beta defeminized the "female" response of the noradrenaline turnover in the preoptic area. 4. Defeminization was not observed when neonatal females received the non aromatizable sex steroid dihydrotestosterone. 5. Activating and organizing effects of sex steroids on animal brain as shown here for noradrenergic neurons are discussed in relation to the regulation of behavior in man. Special regard is given to psychic disorders that might be associated with abnormalities in the production or metabolism of or the response to gonadal hormones.

Rat brain glycolysis regulation by estradiol-17 beta

The effect of estradiol-17 beta on the activities of glycolytic enzymes from female rat brain was studied. The following enzymes were examined: hexokinase (HK, EC 2.7.1.1), phosphofructokinase (PFK, EC 2.7.1.11), aldolase (EC 4.1.2.13), glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12), phosphoglycerate kinase (EC 2.7.2.3), phosphoglycerate mutase (EC 2.7.5.3), enolase (EC 4.2.1.11) and pyruvate kinase (PK, EC 2.7.1.40). The activities of HK (soluble and membrane-bound), PFK and PK were increased after 4 h of hormone treatment, while the others remained constant. The changes in activity were not seen in the presence of actinomycin D. The significant rise of the activities of the key glycolytic enzymes was also observed in the cell culture of mouse neuroblastoma C1300 treated with hormone. Only three of the studied isozymes, namely, HKII, B4 and K4 were found to be estradiol-sensitive for HK, PFK and PK, respectively. The results obtained suggest that rat brain glycolysis regulation by estradiol is carried out in neurons due to definite isozymes induction.

Differential regulation of proenkephalin gene expression by estrogen in the ventromedial hypothalamus of male and female rats: implications for the molecular basis of a sexually differentiated behavior

The ventrolateral aspect of the ventromedial hypothalamic nucleus (VL-VM) contains many estrogen-concentrating neurons which mediate estrogen facilitation of reproductive behavior. Previous studies have shown that estrogen treatment increases proenkephalin (PE) gene expression in neurons of the VL-VM in ovariectomized female rats, and that enkephalin peptides may stimulate lordosis behavior. To determine whether there is a sex difference in steroid hormone regulation of PE gene expression we have examined the effects of estrogen and testosterone on PE mRNA levels in male rats. Slot blot hybridization analysis of RNA isolated from the ventromedial hypothalamus indicated that estrogen treatment increased PE mRNA levels in the VL-VM of ovariectomized female rats (2.2-fold), but had no measurable effect on PE mRNA levels in gonadectomized males. Testosterone treatment of gonadectomized males also had no effect on PE gene expression. To determine whether the sex difference in estrogen-inducibility of PE gene expression is due to the developmental effects of gonadal steroids, we have investigated the effect of estrogen on PE mRNA levels in the VL-VM of neonatally androgenized female rats. Unlike the genetic male, the androgenized females responded to estrogen treatment with a female-typical increase in PE mRNA levels (1.7-fold). Further, although the androgenized rats clearly exhibited signs of defeminization, they did exhibit estrogen-facilitated lordosis behavior when tested with manual stimulation. The PE mRNA induction in estrogen-treated androgenized rats correlated well with the lordosis scores obtained by manual stimulation testing. These results indicate that estrogen regulation of PE gene expression in the VL-VM is sexually differentiated and support the hypothesis that the enkephalinergic neurons of the VL-VM are involved in the regulation of female reproductive behavior.

Event-related slow potentials and associated catecholamine function in migraine

Plasma norepinephrine and dopamine and event-related slow potentials were measured at menses and ovulation in migraine with and without aura relative to normal subjects. The results indicated that at menses, but not ovulation, plasma dopamine was increased and norepinephrine was decreased relative to normal. This catecholamine imbalance was greater in migraine without aura than in migraine with aura. Conversely, event-related slow potentials measured over the posterior cortex at ovulation but not at the menses was altered relative to normal. Early epoch negativity was reduced in migraine with aura, whereas late epoch negativity was reduced in migraine without aura. The results suggested that (a) migraine without aura may involve dynamic shifts in the function of both norepinephrine and dopamine responsive neurons; (b) pathophysiology of migraine with aura is less dependent on catecholamine imbalance (norepinephrine alone affected); (c) these pathophysiological mechanisms are most prevalent in or restricted to posterior cortical regions but may be modulated by brainstem mechanisms.

Isocitrate dehydrogenase activity and its regulation by estradiol in tissues of rats of various ages

The activity and hormonal regulation of NAD- and NADP-linked isocitrate dehydrogenase (EC.1.1.1.41 and EC.1.1.1.42, respectively) in the brain, liver and kidney cortex of female rats of various ages was investigated. The activity of NAD-ICDH of brain was greater than extramitochondrial (-c) or intramitochondrial (-m) NADP-ICDH. In contrast, liver c-NADP-ICDH was much higher than NAD- or m-NADP-ICDH, whereas in kidney cortex the activity of m-NADP-ICDH is dominant over both NAD- and c-NADP-ICDH in all the age group of rats studied. The activity of the NAD-ICDH of brain and all the enzymes of liver and kidney cortex increases until adulthood (33-weeks) and decreases thereafter in old rats (85-weeks). In brain c-NADP-ICDH was much higher in immature (6-weeks) rats and decreases with increasing age of the animal, whereas m-NADP-ICDH showed no significant change with the age of the rats. Bilateral ovariectomy decreases the level of all the three forms of enzyme in all the tissues of 6-, 13- and 33-week rats but failed to show any significant effect in 85-week old rats. Exogenous administration of estradiol induces all the three forms of enzyme in all the tissues of ovariectomized rats. The degree of response is tissue- and age-specific.

Estrogen formation in the mammalian brain: possible role of aromatase in sexual differentiation of the hippocampus and neocortex

Recent studies suggest that sex differences in cognitive function may involve effects of circulating androgens on the developing cerebral cortex and hippocampus. The mechanism of these effects is not understood. In rhesus monkeys, aromatase activity is present in the hippocampus and several areas of the cerebral cortex during late fetal and early postnatal life. Similarly, work in rats and mice indicates that the hippocampus and cerebral cortex may be capable of estrogen biosynthesis during early development. These results are consistent with the hypothesis that the actions of androgens on the developing cerebral cortex and hippocampus may involve local estrogen-mediated effects similar to those responsible for differentiation of the hypothalamic mechanisms controlling reproductive function.

Androgens stimulate preoptic area Na+,K+-ATPase activity in male rats

This paper describes the effects of castration and testosterone replacement on the Na+,K+-ATPase activity levels of the cerebral cortex (CC), preoptic-suprachiasmatic region (POSC) and mediobasal hypothalamus (MBH) in male rats. Na+,K+-ATPase activity was estimated as the ouabain-sensitive fraction of ADP and AMP generation rate, measured by high-pressure liquid chromatography (HPLC) with UV detection, from a standard incubation mixture containing 3 mM ATP. Orchidectomy, performed 4 weeks before sacrifice, decreased ATPase activity of MBH. Testosterone propionate treatment (50 micrograms/day X 2 days) to castrated animals resulted in a 4-fold increase in enzyme activity in the POSC, an effect that might be related to the behavioral effects of androgens. None of the treatments seemed to influence the enzyme activity of the cerebral cortex.

Sexual dimorphism in the response of the GABAergic system to estrogen administration

Administration of estradiol benzoate to gonadectomized female rats results in up-regulation of CNS gamma-aminobutyric acid (GABA) receptors. The increase of [3H]muscimol binding activity is observed in six of the seven brain areas examined. The same treatment, performed in castrated male or androgenized female rats, induced an increase of [3H]muscimol binding only in the striatum. Evidence is provided suggesting that the dimorphic sensitivity of GABA receptor is not correlated with the difference in spontaneous motor activity reported between male and female rats.

Decreased nuclear binding of estrogen receptors in the pituitary of mice: correlation with biological effects throughout aging

We have determined the biological impact of our previously reported decreased activation of pituitary E2 receptors (PER) in mice. Young (4-8 months), middle-aged (10-14 months) and aged (15-18 months) female mice were studied either intact (metestrous) or gonadectomized (ovx) for 2 weeks prior to decapitation. Recombination studies using heat-treated cytosolic PER and enriched nuclear fractions of various age groups showed a markedly reduced ability for nuclear binding with advancing age, despite unchanged affinity of activated PER for nuclear acceptor sites. Cross incubation studies of heat-activated cytosolic PER with nuclei from mice of various age groups suggested that the activation defect followed the onset of anestrous whereas a reduced nuclear ability to support receptor binding preceded this manifestation. In parallel with these endocrine changes we observed a decrease in baseline cytosolic progesterone receptor (RcP) concentration and in the activity of the enzyme G6PDH in intact aging mice. Ovx induced a further decrease of both markers in young and middle-aged, but not in old mice, while E2 administration induced a decreased pituitary response in RcP but not in G6PDH in aged mice. Our results suggest functional changes in cytosolic nuclear interactions in the pituitary of aging female mice.

Age and sex-dependent decreases in ChAT in basal forebrain nuclei

Microdissection techniques were utilized to measure the activity of choline acetyltransferase (ChAT) (enzyme responsible for synthesis of acetylcholine) in individual basal forebrain nuclei of aged (24 month) and young (4 month) male and female rats. Small but consistent decreases in the activity of ChAT in aged rats were found, and the location of the changes was dependent on the sex of the rat. Aged female rats showed approximately 30% lower ChAT and 40% lower acetylcholinesterase (AChE) activity in the ventral globus pallidus (vGP). Aged males did not show decreased ChAT in the vGP but activity in the medial aspect of the horizontal diagonal band nucleus was 50% lower than in the young males. ChAT activity in four other closely aligned basal forebrain nuclei was not different between the young and aged rats. Analysis of cell number, density and area in the vGP by AChE histochemistry showed no significant differences between aged and young females. In addition, age and sex-dependent changes were measured in pituitary glucose-6-phosphate dehydrogenase activity. The relationship of the changes to age-dependent decrements in memory, the possible influence of gonadal hormones on aging, and the mechanisms responsible for age-related declines in ChAT activity are discussed.

The role of estrogen in migraine: a review and hypothesis

The epidemiological, clinical and basic science evidence for a role of estrogen in migraine is reviewed. The hypothesis is put forward that estrogen exerts its influence by modulating sympathetic control of the cerebral vasculature.

Lack of an effect of estrogen on endogenous RNA polymerase II in guinea pig brain

An early action of estrogen in peripheral target tissues is to increase endogenous RNA polymerase II activity which precedes changes in protein synthesis. Previous reports have indicated that estrogen causes a similar increase in polymerase activity in rat brain regions containing high affinity receptors for this hormone. The present series of experiments was designed to test whether a similar action of estrogen on polymerase activity occurs in guinea pig brain, with the expectation being that this enzyme might prove to be a useful marker for the early actions of estrogen. Injections of 25 or 100 micrograms estradiol-17 beta in an ethanol-saline vehicle failed to induce significant changes in polymerase II activity in the basal hypothalamus, preoptic area-septum or cortex 1, 2, 6, 13 or 24 h after hormone administration. It is concluded that the modification of RNA polymerase II activity by estrogen is not a good marker for estrogen action in the brain. This may be due to the intrinsic heterogeneity of the tissue resulting possibly in (1) increased activity in some cells and decreased activity in other cells with no net change in overall polymerase activity after estrogen treatment (2) only a small percentage of the cells responding to the steroid with altered polymerase activity with this change not detectable when whole tissue is measured or (3) only a few genes within the cells being altered in transcription by the steroid.

Responsiveness of hypoglossal neurons to testosterone in pre-pubertal rats

We have shown previously that administration of testosterone propionate (TP) to adult rats accelerated regeneration of the hypoglossal nerve. This study was made to determine whether TP had a similar effect in pre-pubertal rats, in order to establish the ontogeny of the responsiveness of the hypoglossal neurons to androgenic stimulation. It was found that TP significantly shortened the time course of the regeneration of the hypoglossal nerve in the 4-weeks old but not in the 2- and 3-weeks old rats; and that males of 4-weeks of age responded to TP a few days earlier than females of the same age. The possible causes of the failure of the hypoglossal neurons of younger ages to respond to TP were discussed.

Activation of choline acetyltransferase by vasoactive intestinal peptide

Addition of vasoactive intestinal peptide (VIP) to brain homogenates increased the activity of choline acetyltransferase (ChAT) but not that of acetylcholinesterase or glucose-6-phosphate dehydrogenase. Activity of ChAT was increased in the anterior hypothalamus and in the dorsal and ventral hippocampus, but not in the parietal cortex or posterior hypothalamus. Increased activity occurred rapidly after VIP addition to homogenates and was maximal at 10(-7)M concentration. Kinetic analysis indicates that the Vmax of the enzyme is increased and the Km for choline, but not acetyl-coenzyme A, is decreased in the presence of VIP. Results support a possible VIP-cholinergic interaction in the CNS.

Pathways of hydrogen utilization from NADPH generated by glucose-6-phosphate dehydrogenase in circumventricular organs and the hypothalamo-neurohypophysial system: a cytochemical study

Cytochemistry was used to examine the distribution of two pathways of utilization of hydrogen (Type I and Type II H) generated by glucose-6-phosphate dehydrogenase (G6PD) in circumventricular organs (CVOs) and the hypothalamo-neurohypophysial system in cryostat sections of rat brain. Type I H is defined as that portion of the total reducing equivalents (Total H) that is passed, in the intact cells, along the cytochrome chain (NADPH-diaphorase system). In the liver, energy from Type I H is used for cytochrome P-450-dependent oxidation of steroids, as well as xenobiotics. We proposed that mixed function oxidation, and therefore Type I H, would be preferentially localized in brain regions lacking a blood-brain barrier, such as CVOs and magnocellular cells with terminals in such brain regions. Type I H was identified in tissue sections using neotetrazolium. This reagent, when reduced, precipitates as formazan granules that can be quantified. The large difference in redox potential between NADPH and neotetrazolium ensures that only hydrogen (Type I H) passed in the intact cell along the cytochrome chain, can reduce the tetrazole. Total NADPH generation (Total H) from glucose-6-phosphate, was identified using medium containing phenazine methosulphate, a hydrogen acceptor that transfers all reducing equivalents from NADPH to the tetrazole. Type II H, the difference between Total and Type I H, is presumed to be used for NADPH-dependent biosynthetic functions such as lipid synthesis, or reduction of glutathione. In CVOs formazan granules indicative of Type I H were selectively concentrated and localized within cells throughout the SFO, organum vasculosum of the lamina terminalis, pineal gland and in the apical cytoplasm of columnar ependymocytes in the subcommissural organ. Formazan granules attributable to Type I H were also prominent throughout the hypothalamo-neurohypophysial system. Reaction product was present in the cytoplasm of some magnocellular neurons in both the supraoptic and paraventricular nuclei, in the median eminence, including the zona interna, and in and between cells in the neurohypophysis. The distribution of NADPH-diaphorase in sections incubated with NADPH instead of glucose-6-phosphate was similar to that of Type I H. These findings are consistent with the hypothesis that mixed function oxidation involving NADPH and the cytochrome chain occur in these brain regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of orchidectomy and dihydrotestosterone on the choline acetyltransferase activity of specific rat brain areas

1. The choline acetyltransferase (ChAT) activity of specific brain areas was determined in adult intact, orchidectomized and dihydrotestosterone (DHT)-treated orchidectomized rats. 2. Results show that orchidectomy decreased ChAT activity in most brain areas studied. 3. However, DHT treatment of orchidectomized animals increased ChAT activity only in the cerebral cortex.

Estrogen-dependent changes in the functional interrelationships among neurons, ependymal cells and glial cells of the arcuate nucleus. Cytometric studies in the female albino mouse

The synchronizing effect of ethinylestradiol (4 micrograms/g b.w.) on neurons of the arcuate nucleus 700-950 micrometers caudal to the posterior edge of the optic chiasma was studied by karyometry in 6-week-old albino mice during proestrus. The caudal portion of the arcuate nucleus was identified as the most estrogen-sensitive subdivision; all neurons showed an increase in their nuclear area (mean transect, profile area of the nucleus) 1 h following administration of ethinylestradiol. This hypothalamic region was selected for the subsequent electron-microscopic cytometric study to analyze functional interrelationships among neurons, ependymal cells and glial cells. Six and 12 days after ovariectomy no significant change in the nuclear area of neurons and ependymal cells was found 850-950 micrometers behind the posterior slope of the optic chiasma, but the neurons exhibited a decrease in the number of polyribosomes, the volume fraction (Vvmi) and the surface density of the inner membrane of mitochondria (Svmi). A similar decrease in Vvmi and Svmi was measured in the apical part of ependymal cells and in the pericapillary profiles of ependymal and glial cells, which was accompanied by a reduction in the surface density of ependymal processes extending into the ventricular lumen. In addition, no change of Vvmi and Svmi was seen in the basal subnuclear part of ependymal cells. This bipolar functional reaction of ependymal cells after ovariectomy is discussed as an indicator of ependymal control of neuronal activity by sequestering biologically active agents, e.g., transmitters of neurohormones, in their apical and basal extensions facing the ventricular surface or the pericapillary space.

Energy-metabolizing enzymes in brain regions of adult and aging rats

The regional enzyme activities of glucose metabolism in the rat brain were investigated. Hexokinase (EC 2.7.1.1) and pyruvate dehydrogenase (EC 1.2.4.1), key enzymes for glucose metabolism, showed no changes in activity in all the regions studied of the aging brain as compared with the adult brain. However, the activity of D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) is low throughout the adult brain and, in contrast with hexokinase and pyruvate dehydrogenase, its activity decreases significantly during aging. Other enzymes that showed significant decreases during aging are aldolase (EC 4.1.2.13), lactate dehydrogenase (EC 1.1.1.27), citrate synthase (EC 4.1.3.7), and NAD+-linked isocitrate dehydrogenase (EC 1.1.1.41). The catabolic enzyme in cholinergic metabolism, acetylcholinesterase (EC 3.1.1.7), selected as an example of a non-energy-metabolising enzyme, also showed significant decreases in all regions of the brain in aging, although its highest activity remained in the striatum. These results are discussed with respect to the energy metabolism in various brain regions and their status with aging.

Neural gonadal steroid actions

Neurons sensitive to gonadal steroids are located strategically within neural circuits that mediate behaviors broadly related to the reproductive process. Some neuronal events and properties are regulated by these hormones. Variability in the occurrence and distribution of particular neural hormonal sensitivities across species may be related to variations in the hormonal requirements for sexual differentiation and for activation of reproductive behaviors.

Stimulatory effect of dihydrotestosterone on the acetylcholinesterase activity of rat adenohypophysis

Acetylcholinesterase (AChE) activity in the adenohypophysis of adult orchidectomized rats, and of orchidectomized rats treated with 100 microgram/100 g b.w. of dihydrotestosterone (DHT), was determined by a spectrophotometric method. Our result shows a significant increase in AChE activity of the adenohypophysis of orchidectomized rats treated with DHT.

Some biochemical characteristics of hormone-secreting pituitary tumors and of the host's anterior pituitary gland

The activity of some glycolytic, oxidative, and degradative enzymes was studied in transplanted rat hormone-secreting pituitary tumors MtTW15 and 7315a and in the host pituitary gland. The elevated serum-hormone concentrations produced by 7315a tumor decreased the size of the host's pituitary gland, its hormone content, and G6P-DH, LDH, PK, and ICDH, but produced no changes in MDH, acid phosphatase, cathepsin-D, and LYSAR enzyme activities (mU/mg tissue). LDH and PK activities were greater in unit weight of pituitary tumors than in pituitary glands. Although more G6P-DH was found in MtTW15 tumor than in normal pituitary tissue, less of the enzyme was detected in 7315a pituitary tumor. It is concluded that elevated serum pituitary hormones selectively decrease hormone production and the activity of some enzymes in the pituitary gland, presumably through a feedback mechanism.

Effect of gonadal steroids on activities of monoamine oxidase and choline acetylase in rat brain

Gonadectomized male and female rats were treated with equimolar doses of estradiol benzoate (EB) and testosterone propionate (TP) daily for periods of 3 days to 1 week and activities of monoamine oxidase (MAO) and choline acetyltransferase (ChAc) were measured in the cortex, hippocampus, basomedial hypothalamus, corticomedial amygdala and medial preoptic areas. After hormone treatment, changes in enzyme activities were found in those brain regions where gonadal hormones are known to affect sexual behavior and/or gonadotropin release and which contain putative hormone receptor sites. More specifically, EB administration to females resulted in decreased activity of MAO in the corticomedial amygdala and basomedial hypothalamus and an elevation of ChAc activity in the medial preoptic area and corticomedial amygdala while TP administration did not alter enzyme levels in any brain region. In contrast, EB administration to castrated males was without significant effect on enzyme activities while TP administration resulted in increased activity of MAO and ChAc in the medial-preoptic area. The estrogen antagonist, MER-25, given concomitantly with EB, effectively blocked EB-dependent changes in both enzymes in ovariectomized female rats. EB treatment to hypophysectomized females led to similar enzymatic changes as in ovariectomized females in all areas except the basomedial hypothalamus. Estradiol added directly to the enzyme incubation medium did not result in altered enzyme activities. Results obtained are discussed in relation to sexual differentiation of the brain, metabolism of gonadal hormones, and possible mechanism of gonadal hormone regulation of enzyme activities.