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Cognitive dysfunction, dementia and Alzheimer's disease (AD) are increasing as the population worldwide ages. Therapeutics for these conditions is an unmet need. This review focuses on the role of the positive GABA-A receptor modulating steroid allopregnanolone (APa), it's role in underlying mechanisms for impaired cognition and of AD, and to determine options for therapy of AD. On one hand, APa given intermittently promotes neurogenesis, decreases AD-related pathology and improves cognition. On the other, continuous exposure of APa impairs cognition and deteriorates AD pathology. The disparity between these two outcomes led our groups to analyze the mechanisms underlying the difference. We conclude that the effects of APa depend on administration pattern and that chronic slightly increased APa exposure is harmful to cognitive function and worsens AD pathology whereas single administrations with longer intervals improve cognition and decrease AD pathology. These collaborative assessments provide insights for the therapeutic development of APa and APa antagonists for AD and provide a model for cross laboratory collaborations aimed at generating translatable data for human clinical trials.

ObjectiveSeveral studies have reported that -aminobutyric acid (GABA) ergic circuits are involved in the pathophysiology of polycystic ovary syndrome (PCOS). The progesterone metabolite allopregnanolone is a potent GABA(A)-receptor-modulating steroid, and patients may have increased concentrations of allopregnanolone or altered GABA(A) receptor sensitivity. We investigated both of these possibilities in this study. PatientsWe enrolled 9 women with PCOS and 24 age-matched eumenorrhoeic controls, who were divided into two groups by body mass index (BMI) (16 normal weight and 8 overweight). MeasurementsWe investigated the effects of allopregnanolone injection on GABA(A) receptor sensitivity in both groups of women. All women received a single intravenous dose of allopregnanolone (0050mg/kg). GABA(A) receptor sensitivity was assessed with the saccadic eye velocity (SEV) over 30 degrees (SEV30 degrees), the SEV30 degrees/allopregnanolone concentration ([Allo]) ratio, and sedation, which were measured together with serum allopregnanolone at intervals for 180min after injection. The controls were tested in the follicular phase of the menstrual cycle. ResultsBaseline allopregnanolone concentrations were higher in the PCOS women than in the normal-weight (P=0034) and overweight controls (P=0004). The allopregnanolone concentrations after injection were higher in the PCOS women (P=0006) and overweight controls (P=0037) than in the normal-weight controls. All groups showed a decline in the SEV30 degrees/[Allo] ratio after injection. Allopregnanolone had a smaller effect on the SEV30 degrees/[Allo] ratio in the overweight women (PCOS, P=0032; controls, P=0007) than in the normal-weight controls. The sedation score after allopregnanolone injection was lower in the PCOS patients than in the controls, but was not different between the two control groups. ConclusionsPCOS women had elevated baseline allopregnanolone concentrations compared with follicular-phase controls. All overweight women (PCOS and controls) were less sensitive to allopregnanolone than normal-weight controls.

Previously, we have shown that chronic treatment with allopregnanolone (ALLO) for three months impaired learning function in the Swe/PS1 mouse model. ALLO is a neurosteroid, produced in the CNS and a GABA(A) receptor agonist. ALLO modulates the general inhibitory system in the CNS by enhancing the effect of GABA. Chronic treatment with other GABA(A) receptor active compounds, such as benzodiazepines, ethanol and medroxy-progesterone acetate has been associated to cognitive decline and/or increased risk for dementia. In this study, we sufficed with a treatment period of one month for the Swe/PS1 mouse, and included another Alzheimer's disease mouse model; the Swe/Arc model. We found that one month of chronic treatment with elevated ALLO levels within physiological range impaired learning and memory function in the Swe/Arc female and male mice. Male Swe/PS1 mice also showed marginally impaired function, while the female mice did not. Furthermore, the chronic ALLO treatment caused increased levels of soluble A beta in the Swe/PS1 mouse model while the levels were unchanged in the Swe/Arc model. Therefore, both Swe/Arc and Swe/PS1 mice showed signs of accelerated disease progression. Still, further studies are required to determine the mechanisms behind the cognitive impairment and the increased A beta-levels caused by mildly elevated ALLO-levels.

Abstract: Previously, we have shown that chronic treatment with allopregnanolone (ALLO) for three months impaired learning function in the Swe/PS1 mouse model. ALLO is a neurosteroid, produced in the CNS and a GABA_A receptor agonist. ALLO modulates the general inhibitory system in the CNS by enhancing the effect of GABA. Chronic treatment with other GABA_A receptor active compounds, such as benzodiazepines, ethanol and medroxy-progesterone acetate has been associated to cognitive decline and/or increased risk for dementia. In this study, we sufficed with a treatment period of one month for the Swe/PS1 mouse, and included another Alzheimer’s disease mouse model; the Swe/Arc model. We found that one month of chronic treatment with elevated ALLO levels within physiological range impaired learning and memory function in the Swe/Arc female and male mice. Male Swe/PS1 mice also showed marginally impaired function, while the female mice did not. Furthermore, the chronic ALLO treatment caused increased levels of soluble Aβ in the Swe/PS1 mouse model while the levels were unchanged in the Swe/Arc model. Therefore, both Swe/Arc and Swe/PS1 mice showed signs of accelerated disease progression. Still, further studies are required to determine the mechanisms behind the cognitive impairment and the increased Aβ-levels caused by mildly elevated ALLO-levels. learning function in the Swe/PS1 mouse model. ALLO is a neurosteroid, produced in the CNS and a GABA_A receptor agonist. ALLO modulates the general inhibitory system in the CNS by enhancing the effect of GABA. Chronic treatment with other GABA_A receptor active compounds, such as benzodiazepines, ethanol and medroxy-progesterone acetate has been associated to cognitive decline and/or increased risk for dementia. In this study, we sufficed with a treatment period of one month for the Swe/PS1 mouse, and included another Alzheimer’s disease mouse model; the Swe/Arc model. We found that one month of chronic treatment with elevated ALLO levels within physiological range impaired learning and memory function in the Swe/Arc female and male mice. Male Swe/PS1 mice also showed marginally impaired function, while the female mice did not. Furthermore, the chronic ALLO treatment caused increased levels of soluble Ab in the Swe/PS1 mouse model while the levels were unchanged in the Swe/Arc model. Therefore, both Swe/Arc and Swe/PS1 mice showed signs of accelerated disease progression. Still, further studies are required to determine the mechanisms behind the cognitive impairment and the increased Aβ-levels caused by mildly elevated ALLO-levels.

Patients with Alzheimer's disease (AD) or dementia are increasing in numbers as the population worldwide ages. Mid-life psychological stress, psychosocial stress and posttraumatic stress disorder have been shown to cause cognitive dysfunction and lead to increased risk for dementia. The mechanisms behind stress-induced AD or dementia are not known. Solid amyloid plaques in the affected brain tissues characterize AD. However, over the last decade it has been concluded that the level of soluble beta-amyloid proteins (Aβ) are reliable diagnostic markers as they correlate to cognitive performance while plaques do not. The soluble Aβ accumulate intracellularly and disturb the synaptic function. In addition, it has been shown that the levels of intracellular Aβ depend on neuronal activity. Previous studies in animal models have shown that deceased neuronal activity cause increased levels of Aβ inside neurons and cognitive decline. Allopregnanolone is produced in the brain at stress. It enhances the activity of the GABAergic neurotransmission and affects neuronal activities. In a series of studies using in transgenic Alzheimer's disease model, we have shown that chronically elevated levels of allopregnanolone accelerated AD development. After a period of exposure to chronically elevated levels of allopregnanolone, impaired learning and memory pattern occurred in the AD mice. Accordingly, increased levels of β-amyloids were also observed in AD mice. We have also demonstrated that high levels of β-amyloids corresponded to dysfunction among brain synapses. This was seen after a period of chronically elevated levels of allopregnanolone, but not after placebo treatment. This effect of allopregnanolone treatment was identified early in the disease development when AD mice normally have intact memory function. This review covers a wide topic of neurosteroids and brain aging, and provides insight on the mechanisms behind stress-induced AD or dementia.

The endogenous neurosteroid allopregnanolone alters neuronal excitability via modulation of the GABA(A) receptor and causes decreased neurotransmission. In Alzheimer's disease (AD), neurotransmission seems to alter the levels of toxic intracellular amyloid-beta (A beta) oligomers, which are implicated in AD pathogenesis and cause cognitive decline. Inhibition of synaptic activity has been shown to increase levels of intracellular A beta. Allopregnanolone at endogenous stress levels inhibits synaptic activity and could have similar effects. By using a transgenic A beta PP(Swe)PSEN1(Delta E9) mouse model for AD, we observed that chronic allopregnanolone treatment for three months with stress levels of allopregnanolone impaired learning in the Morris water maze. The learning impairment was seen one month after the end of treatment. Chronic allopregnanolone treatment also led to increased levels of soluble A beta in the brain, which could be a sign of advanced pathogenesis. Since the learning and memory of wild-type mice was not affected by the treatment, we propose that chronic allopregnanolone treatment accelerates the pathogenesis of AD. However, further studies are required in order to determine the underlying mechanism.

Neurosteroids represent a class of endogenous steroids that are synthesized in the brain, the adrenals, and the gonads and have potent and selective effects on the GABAA-receptor. 3α-hydroxy A-ring reduced metabolites of progesterone, deoxycorticosterone, and testosterone are positive modulators of GABA_A-receptor in a non-genomic manner. Allopregnanolone (3α-OH-5α-pregnan-20-one), 5α-androstane-3α, 17α-diol (Adiol), and 3α5α-tetrahydrodeoxycorticosterone (3α5α-THDOC) enhance the GABA-mediated Cl^- currents acting on a site (or sites) distinct from the GABA, benzodiazepine, barbiturate, and picrotoxin binding sites. 3α5α-P and 3α5α-THDOC potentiate synaptic GABA_A-receptor function and activate δ-subunit containing extrasynaptic receptors that mediate tonic currents. On the contrary, 3β-OH pregnane steroids and pregnenolone sulfate (PS) are GABA_A-receptor antagonists and induce activation-dependent inhibition of the receptor. The activities of neurosteroid are dependent on brain regions and types of neurons. In addition to the slow genomic action of the parent steroids, the non-genomic, and rapid actions of neurosteroids play a significant role in the GABA_A-receptor function and shift in mood and memory function. This review describes molecular mechanisms underlying neurosteroid action on the GABA_A-receptor, mood changes, and cognitive functions.

1. It is known that the alpha(4)-subunit is likely to occur in the brain predominantly in alpha(4)beta(3)delta receptors at extrasynaptic sites. Recent studies have revealed that the alpha(1)-, alpha(4)-, gamma(2)- and delta-subunits may colocalize extrasynaptically in dentate granule cells of the hippocampus. In the present study, we characterized a series of recombinant GABA(A) receptors containing human (H) and rat (R) alpha(1)/alpha(4)-, beta(2)/beta(3)- and gamma(2S)/delta-subunits in Xenopus oocytes using the two-electrode voltage-clamp technique. 2. Both H alpha(1)beta(3)delta and H alpha(4)beta(3)gamma(2S) receptors were sensitive to activation by GABA and pentobarbital. Contrary to earlier findings that the alpha(4)beta(3)delta combination was more sensitive to agonist action than the alpha(4)beta(3)gamma(2S) receptor, we observed extremely small GABA- and pentobarbital-activated currents at the wild-type H alpha(4)beta(3)delta receptor. However, GABA and pentobarbital activated the wild-type R alpha(4)beta(3)delta receptor with high potency (EC(50) = 0.5 +/- 0.7 and 294 +/- 5 micromol/L, respectively). 3. Substituting the H alpha(4) subunit with R alpha(4) conferred a significant increase in activation on the GABA and pentobarbital site in terms of reduced EC(50) and increased I(max). When the H alpha(4) subunit was combined with the R beta(3) and R delta subunit in a heteropentameric form, the amplitude of GABA- and pentobarbital-activated currents increased significantly compared with the wild-type H alpha(4)beta(3)delta receptor. 4. Thus, the results indicate that the R alpha(4)beta(3)delta, H alpha(1)beta(3)delta and H alpha(4)beta(3)gamma(2S) combinations may contribute to functions of extrasynaptic GABA(A) receptors. The presence of the R alpha(4) subunit at recombinant GABA(A) receptors containing the delta-subunit is a strong determinant of agonist action. The recombinant H alpha(4)beta(3)delta receptor is a less sensitive subunit composition in terms of agonist activation.

The endogenous progesterone metabolite allopregnanolone has a number of properties including anesthetic, sedative, antiepileptic, anxiolytic, impaired memory function and negative mood symptoms. Allopregnanolone is a potent positive GABA(A) receptor function modulators. In contrast, 3beta-hydroxy-steroids (3beta-steroids) usually modulate the GABA(A) receptor negatively. They have attracted some interest for their possible use as therapeutic agents that could counteract the negative symptoms induced by allopregnanolone. Two hypotheses for the action of 3beta-steroids have been proposed: 1) 3beta-steroids act in a similar way to pregnenolone sulphate, which non-competitively reduces GABA(A) receptor activity. 2) 3beta-steroids specifically antagonize the effect of allopregnanolone. We have therefore tried to clarify this issue by comparing the effect of pregnenolone sulphate and 5beta-pregnane-3beta, 20(R)-diol on the GABA-evoked currents by the patch clamp technique on neurons from the medial preoptic nucleus. Both pregnenolone sulphate and 5beta-pregnane-3beta, 20(R)-diol increase the desensitization rate of the current response evoked by a 2 s GABA application. However, their effects on other parameters of the GABA evoked currents differed in degree and sometimes even in direction. The actions of pregnenolone sulphate and 5beta-pregnane-3beta, 20(R)-diol were not altered in the presence of allopregnanolone, which indicates that they do not directly interact with allopregnanolone. In addition, when 5beta-pregnane-3beta, 20(R)-diol was tested on spontaneous inhibitory postsynaptic currents (sIPSCs), it dramatically reduced the allopregnanolone-induced prolongation of the decay time constant but it had no effect on the decay under control conditions. In conclusion, the effect of 5beta-pregnane-3beta, 20(R)-diol on GABA-evoked currents is different to that of pregnenolone sulphate in medial preoptic nucleus neurons.