Effect of sex steroids on choline acetyltransferase and acetylcholinesterase of cerebral hemisphere of male rats of various ages

Altered expression of Alzheimer's disease-related proteins in male hypogonadal mice

Age-related depletion of estrogens and androgens is associated with an increase in Alzheimer's disease (AD) brain pathology and diminished cognitive function. Here we investigated AD-associated molecular and cellular changes in brains of aged hypogonadal (hpg) male and female mice. hpg Mice have a spontaneous, inactivating genetic mutation in the GnRH gene resulting in life-long deficiency of gonadotropins and gonadal sex hormones. Western blot analysis revealed low levels of amyloid precursor protein and high levels of presenilin 1, amyloid precursor protein C-terminal fragment, and β-amyloid 42 in brains of aged male, but not female, hpg mice. Changes were confined to the hippocampus and were not evident in the cerebellum or other brain tissues. Male hpg mice tended to have lower levels of IL-1β protein than male littermate controls. Immunohistochemical staining of the basal forebrain revealed that male hpg mice had lower choline acetyltransferase levels per neuron compared with controls. These AD-like changes specific to male hpg mice supports a link between androgen depletion and the development of AD pathology.

Gonadal hormones modulate the potency of the disruptive effects of donepezil in male rats responding under a nonspatial operant learning and performance task

In contrast to estrogen in female rats, testosterone in male rats may decrease cholinergic activity in the brain, thereby attenuating behaviors mediated by the cholinergic system. To investigate this possibility, the interactive effects of the gonadal hormones and donepezil, an acetylcholinesterase (AChE) inhibitor, on the responding of male rats were examined under a multiple schedule of repeated acquisition and performance of response sequences and on AChE activity in specific brain regions. Donepezil dose-effect curves (0.56-10 mg/kg) were determined in males that were gonadally intact, gonadectomized (GX), GX with testosterone replacement (GX+T) or GX with estradiol replacement (GX+E). In all four groups, donepezil produced dose-dependent rate-decreasing and error-increasing effects in the acquisition and performance components. However, disruptions of response rate and accuracy in both components occurred at lower doses in GX and GX+E males than in intact males. The GX+E males also had the highest percentage of errors under control (saline) conditions in the acquisition components. In terms of AChE activity, GX males had higher levels in the prefrontal cortex, striatum and hippocampus, but lower levels in the midbrain, compared with intact males; hypothalamic and cortical levels were comparable for the GX and intact groups. Together, these results in male rats indicate that the potency of donepezil's disruptive effects on the responding under a complex operant procedure requiring learning and performance of response sequences depends upon the gonadal hormone status, and that the effects of testosterone on cholinergic activity vary among brain regions.

Structure activity relationship of cholesterol and steroid hormones with respect to their effects on the Ca2+-stimulated ATPase and lipid fluidity of synaptosomal plasma membranes from dog and rabbit brain

1. Binding of liposomal-[14C]-cholesterol into dog brain synaptosomal plasma membranes (SPM) follows a sigmoid path (Hill coefficient h = 1.96 +/- 0.12). 2. Ca2+-stimulated ATPase activity increased (approx. 95%) at a concentration range (0.1-0.4 mM) of liposomal cholesterol and testosterone (up to 10 microM). While progesterone up to 10 microM decreased the enzyme activity (approx. 70%) in dog and rabbit brain SPM. 3. Fluorescence anisotropy, [(r0/r)-1]-1, of 1,6-diphenyl-1,3,5-hexatriene (DPH) was 1.04 +/- 0.04 in rabbit brain SPM and 1.72 +/- 0.09 in dog brain SPM. 4. Lipid phase separations at 23.5 +/- 1.2 degrees C in dog brain SPM and at 17.2 +/- 0.9 degrees C in rabbit brain SPM were observed. In dog brain SPM it increased to 33.4 +/- 1.8 degrees C, while in rabbit brain SPM was abolished after treatment with liposomal cholesterol. 5. The allosteric inhibition of Ca2+-stimulated ATPase by Na+ ions showed a Hill coefficient h = 1.72 +/- 0.15 and h = 1.48 +/- 0.08 for dog and rabbit brain SPM respectively, which increased to h = 2.83 +/- 0.55 and h = 2.34 +/- 0.35 after treatment with liposomal cholesterol.

Brain protein changes during development and sexual differentiation in the rat

Subcellular fractions were prepared from the hypothalamus-preoptic area and the 'remainder of the brain' of intact male and female rats at 0, 8, 25 and 72 days of age. Proteins associated with each fraction were subjected to SDS-PAGE chromatography and stained with Coomassie Brilliant Blue. Developmental changes were found to occur in proteins associated with the soluble (14,600, 15,000, 29,900, 38,900 and 49,000 mol. wt), nuclear (40,000-50,000 and 13,800-16,000 mol. wt.), mitochondrial-lysosomal (49,000-52,000 mol. wt.) and microsomal (14,400, 20,000, 50,100, 56,900 and 130,000 mol. wt.) fractions. In addition, soluble proteins were greater in males than in females at days 0 (53,000-56,000 mol. wt.; probably tubulin) and 25 (14,600 and 15,000 mol. wt.). These changes in brain proteins probably reflect important structural and functional changes that occur during maturation and sexual differentiation of the brain.

Calcium-induced membrane metabolic alterations modify the sex steroids binding into dog brain synaptosomal plasma membranes

The binding of 45Ca2+ into synaptosomal plasma membranes (SPM) of dog brain follows a sigmoid path. In graphical analysis of this binding the mean Hill coefficient (h) was 1.64 +/- 0.09 (r2 = 0.96 +/- 0.02). Binding of Ca2+ into SPM was saturable, with an apparent binding constant of 1.2 +/- 0.1 microM. At saturation, such calcium specific binding sites corresponded to 11.2 +/- 0.9 nmol/mg SPM protein. The Hill plot in combination with the biphasic nature of the curve to obtain the equilibrium constant, showed a moderate degree of positive cooperativity in the binding of calcium into SPM of at least one class of high affinity specific binding sites. [14C]estradiol, [14C]estrone and [14C]progesterone, when incubated with SPM up to a concentration of 10 microM for 2 hr at 37 degrees C, bind into SPM at nmolar concentrations. Ca2+ ions up to 5 mM considerably increase steroids binding into SPM. This effect of calcium was concentration-dependent, reached saturation at approx 4-5 mM. Once calcium has promoted steroids binding, the subsequent addition of 25 mM EGTA failed to displace bound steroids. Molecular interactions between calcium and SPM was assessed by measuring the steady-state fluorescence polarization (P) of 1,6-diphenyl-1,3,5-hexatriene (DPH), and by estimating the production of malondialdehyde (MDA) during 2 hr incubation of Ca2+ (5 mM) with SPM at 37 degrees C. The effect of Ca2+ on the SPM structure was to increase both the rigidity of the membrane and the MDA production. Chelation of Ca2+ (5 mM) with EGTA (25 mM) did not reverse the increase in the rigidity owing to metabolic alterations of SPM lipids (e.g. production of MDA).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of oestradiol, testosterone and medroxyprogesterone on subcellular fraction marker enzyme activities from rat liver and brain

The following enzymes have been studied (subcellular fractions are shown between parentheses): NAG and beta-glucuronidase (lysosomes); SDH (mitochondrial); glucose-6-phosphatase (endoplasmic reticulum); 5'-nucleotidase and (Na+, K+)Mg2+ ATPase (plasma membranes). Alterations on their activities were observed after subcutaneous injection of sex hormones, compared with controls. NAG activity from liver was always significantly decreased in lysosomal and microsomal fractions after the hormonal treatment. In the same conditions, NAG from brain was always increased. beta-Glucuronidase behaves like NAG in brain; in liver it was not modified by testosterone and it was slightly increased in lysosomal fraction after oestradiol treatment. SDH activity was not modified in mitochondrial fractions from liver, but this activity was always significantly increased in brain. Glucose-6-phosphatase activity was always significantly decreased in microsomal fractions from liver. It was increased in brain after oestradiol and testosterone injection, but medroxyprogesterone treatment caused a decreased activity. 5'-Nucleotidase and (Na+, K+)Mg2+ ATPase from brain were significantly increased in microsomal fractions by oestradiol and testosterone. Medroxyprogesterone, however, caused an increase in ATPase, but did not affect 5'-nucleotidase. Both activities in liver were decreased by oestradiol and increased by testosterone, but medroxyprogesterone caused (Na+, K+)Mg2+ ATPase to rise and 5'-nucleotidase to fall.

Ecdysterone induces acetylcholinesterase in mammalian brain

The effects of ecdysterone on brain acetylcholinesterase (AChE) in immature and adult rats of both sexes have been studied in in vitro conditions. Ecdysterone produced an increase of AChE in rat brain slices. The most remarkable effect was found in immature male rats. In vitro assay using a purified AChE from electric eel showed no effect. Pretreatment with cycloheximide or actinomycin D abolished the ecdysterone action on brain AChE. These results support the idea that induction of AChE may be involved in the heterophilic action of ecdysterone.

Effect of hemagglutinin extracts on acetylcholinesterase activity in some brain areas of weanling rats

Two trials involving male and female weanling albino rats (Wistar strain) were conducted to investigate the effects of cowpea and limabean hemagglutinin extracts on acetylcholinesterase (AChE) activity in different parts of the brain. The results show that AChE activity varies with brain region. Cowpea hemagglutinin significantly inhibited AChE activity in the pons of male and female rats, while limabean hemagglutinin significantly inhibited AChE activities in the pons of both male and female rats, in the hippocampus of female rats and in the medulla, cerebellum and midbrain of male rats. Inhibition of AChE activities was more pronounced in male or female rats inoculated with a mean lethal dose of either phytohemagglutinin, than in those inoculated with a sublethal dose.

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.

A new type of lesion-induced synaptogenesis: II. The effect of aging on synaptic turnover in non-denervated zones

Partial denervation of the dentate molecular layer causes sprouting and reinnervation by undamaged afferents within the denervated zones of young adult animals and to a lesser extent in aged animals. We have previously reported a non-degenerative remodeling of the dentate molecular layer in areas outside the primary denervated zone of young adult rats after a unilateral entorhinal lesion. In this study, we evaluate the response of aged rats under the same conditions, to see if aged animals also respond to injury in non-denervated zones. After a unilateral entorhinal lesion, the outer two-thirds of the ipsilateral dentate molecular layer loses about 85% of its input, while the outer two-thirds of the contralateral molecular layer loses less than 5% of its input (crossed temporo-dentate path). Denervation does not occur in the inner one-third of the molecular layer on either side. Within the ipsilateral inner molecular layer, the synaptic density rapidly drops 21% in the absence of degeneration and then recovers by 10 days post-lesion, as is the case in young adult animals. On the contralateral side, young adult animals show synapse turnover similar to the ipsilateral inner molecular layer. In contrast, no significant response in the total synaptic density was observed in the non-denervated contralateral inner molecular layer or the partially denervated outer two-thirds of the contralateral molecular layer. Thus, in aged animals, synaptic turnover is restricted to the massively denervated ipsilateral side. The small loss of input to the contralateral side apparently is not sufficient to initiate quantifiable turnover of synaptic contacts. This steady-state situation may be the result of an on-going stabilization of neuronal circuitry, which may limit restoration of function after injury in aged animals.

Acetylcholinesterase activity in seven brain areas and adenohypophysis during the estrous cycle

Acetylcholinesterase activity was investigated in the adenohypophysis and 7 brain areas during the rat estrous cycle. In comparison with diestrous II, enzyme activity levels were significantly higher at proestrous in the adenohypophysis, amygdala and cerebral cortex. It is thought that endogenous estradiol and progesterone, acting independently and/or synergistically through their receptor systems, induce central acetylcholinesterase activity levels in the intact female rat.

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.

Effect of orchidectomy and estradiol on acetylcholinesterase activity in rat brain areas and adenohypophysis

Orchidectomy plus estradiol administration decreased acetylcholinesterase activity in the rat cerebral cortex and mesencephalon, while in the amygdala it was increased. In the adenohypophysis, orchidectomy increased enzyme activity, but subsequent estradiol treatment decreased it. The hypothalamus did not respond to either manipulation.