Windows into estradiol effects in Alzheimer's disease therapy

BACKGROUND AND OBJECTIVES

Alzheimer's disease (AD) is a neurological disorder associated with aging. The neuropathologic features of this disease are senile plaques and neurofibrillary tangles, which are present in memory structures and cerebral cortex. This study focuses on evaluation of estradiol administration in the management of neurological changes accompanied with AD in ovariectomized rats intoxicated with aluminum.

MATERIALS AND METHODS

Fifty adult female rats were classified into 5 main groups as follows: Group (1): gonad intact control, Group (2): ovariectomized control group, Group (3): ovariectomized rats were injected subcutaneously with estradiol for 18 weeks, Group (4): ovariectomized rats were injected intraperitoneally with aluminum chloride (AlCl3) daily for three months, Group (5): ovariectomized rats were injected intraperitoneally with AlCl3 for three months, then, they were injected subcutaneously with estradiol three times weekly for 18 weeks. Hydrogen peroxide (H2O2), malondialdehyde (MDA), total antioxidant capacity (TAC), superoxide dismutase (SOD), catalase (CAT), B cell lymphoma 2 (Bcl-2), brain derived neurotrophic factor (BDNF), acetylcholinesterase (AchE) and acetylcholine (Ach) were determined in brain tissue of all studied groups.

RESULTS

The results showed that brain TAC, SOD activity, Bcl-2 and BDNF levels were decreased significantly due to ovariectomy. Brain H2O2, MDA levels and AchE activity were increased significantly after AlCl3 administration to ovariectomized rats. Brain TAC, Bcl-2, BDNF and Ach levels were decreased significantly as a result of AlCl3 supplementation to ovariectomized rats. Treatment of rats with estradiol produced marked improvement in the most studied biomarkers and this finding was well documented by histological investigation of the brain which showed remarkable improvement in the feature of the neurons in addition to the disappearance of plaques.

CONCLUSIONS

We could conclude that estradiol administration significantly ameliorates the neurodegeneration characteristic of Alzheimer's disease in experimental rat model. This may be attributed to its powerful antioxidant, antiapoptotic, neurotrophic as well as its antiamyloidogenic activities.

Tinnitus and ECT

We report the case of a 69-year-old man with major depressive disorder and occupational tinnitus; both problems were refractory to several different treatment modalities, but were successfully treated with electroconvulsive therapy (ECT). The tinnitus was present for 15-20 years, but had worsened during the 3 years before treatment, causing him significant distress. Extensive organic workup did not identify a treatable etiology for his symptoms. To date, he has been hospitalized four times due to depressive symptoms associated with tinnitus. He has received ECT each time, and has responded well on each occasion.

Differential agonist profile of the enantiomers of 3-PPP at striatal dopamine autoreceptors: dependence on extracellular dopamine

The effects of the enantiomers of 3-hydroxyphenyl-N-n-propylpiperidine (3-PPP) at dopamine (DA) synthesis modulating autoreceptors, measured as DOPA accumulation after decarboxylase inhibition, were assessed in vivo and in rat striatal slices. In vivo, (+)-3-PPP inhibited DOPA accumulation in the striatum, nucleus accumbens, and medial prefrontal cortex, whereas (-)-3-PPP either increased (striatal) or had no effect (accumbens, prefrontal cortex), on DOPA accumulation. In vitro, both (+)- and (-)-3-PPP reduced basal DOPA accumulation with a similar order of potency (apparent EC50 = 2.1 and 1.0 microns, respectively) and maximal effect, although they were less potent than the D2 DA receptor agonist quinpirole (EC50 = 0.15 microM). The inhibition of tyrosine hydroxylation was also observed in slices obtained from reserpine-pretreated rats and was blocked by the selective D2 DA antagonist (-)-sulpiride. This suggests that 3-PPP inhibition of DOPA accumulation was mediated directly by stimulation of DA D2 receptors. Increasing the amount of extracellular DA by depolarizing slices with 30 mM K+ did not alter the qualitative effects of either quinpirole or (+)-3-PPP. However, the stimulation of DA autoreceptors by (-)-3-PPP was no longer apparent under conditions of elevated extracellular DA. Under these depolarizing conditions, (-)-3-PPP actually antagonized the inhibitory effect afforded by either quinpirole or pergolide. A similar switch in profile was observed with transdihydrolisuride (TDHL). The data support the notion that (-)-3-PPP and TDHL are partial agonists at synthesis modulating DA autoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine autoreceptors modulate the phosphorylation of tyrosine hydroxylase in rat striatal slices

The hypothesis that dopamine (DA) autoreceptors modulate the phosphorylation of tyrosine hydroxylase (TH; EC 1.14.16.2) was investigated in rat striatal slices. Tissue was prelabeled with 32P inorganic phosphate, and TH recovered by immunoprecipitation with anti-TH rabbit serum. The TH monomer was resolved on sodium dodecyl sulfate polyacrylamide gels, and the extent of phosphorylation was determined by scanning densitometry of autoradiographs. Depolarization of striatal slices with 55 mM K+ markedly increased the incorporation of 32P into several proteins, including the TH monomer (Mr = 60,000). A similar increase in TH phosphorylation occurred in response to the adenylate cyclase activator forskolin and the cyclic AMP analog dibutyryl cyclic AMP. An increase in TH phosphorylation was not observed in response to the D1-selective agonist SKF 38393. The D2-selective DA autoreceptor agonist pergolide decreased the phosphorylation of TH below basal levels and blocked the increase in phosphorylation elicited by 55 mM K+. The inhibitory effect of pergolide was antagonized by the D2-selective antagonist eticlopride. Changes observed in the phosphorylation of TH were mirrored by changes in tyrosine hydroxylation in situ. These observations support the hypothesis that a reduction in TH phosphorylation is the mechanism by which DA autoreceptors modulate tyrosine hydroxylation in nigrostriatal nerve terminals.

The effects of central injections of adenosine analogs on blood pressure and heart rate in the rat

Rats were implanted with chronic indwelling cannulae into the lateral cerebral ventricle. After recovery from surgery, acute experiments on blood pressure were conducted under methoxyflurane/nitrous oxide anesthesia. Rats were injected intracerebroventricularly with two adenosine analogs, 5'-N-ethylcarboxaminidoadenosine (NECA) and (-)-N-(1-methyl-2-phenylethyl)adenosine(L-phenylisopropyladenosine) (L-PIA), and the effects on blood pressure and heart rate recorded. Both analogs produced dose-related reductions in blood pressure and heart rate with L-PIA producing a more potent depression of heart rate than NECA. These effects on blood pressure and heart rate were antagonized by parenteral injections of caffeine. In separate experiments, the responses of blood pressure and heart rate to microinjection of NECA into the brainstem of rats anaesthetized with methoxyflurane/nitrous oxide were also examined. Microinjection of 2.7 nmol/kg into the fourth ventricle in the region of the area postrema produced a profound and long-lasting depression of blood pressure and heart rate. These results show that central injections of analogs of adenosine can influence the areas of the central nervous system involved in the control of cardiovascular function.