Responses to Many Anti-Aging Interventions Are Sexually Dimorphic.

There is increasing appreciation that sex differences are not limited to reproductive organs or traits related to reproduction and that sex is an important biological variable in most characteristics of a living organism. The biological process of aging and aging-related traits are no exception and exhibit numerous, often major, sex differences. This article explores one aspect of these differences, namely sex differences in the responses to anti-aging interventions. Aging can be slowed down and/or postponed by a variety of environmental ( lifestyle ), genetic or pharmacological interventions. Although many, particularly older studies utilized only one sex of experimental animals, there is considerable evidence that responses to these interventions can be very different in females and males. Calorie restriction (CR), that is reducing food intake without malnutrition can extend longevity in both sexes, but specific metabolic alterations and health benefits induced by CR are not the same in women and men. In laboratory mice, several of the genetic alterations that reduce insulin-like growth factor I (IGF-1) signaling extend longevity more effectively in females or in females only. Beneficial effects of rapamycin, an inhibitor of mTOR signaling, on mouse longevity are greater in females. In contrast, several anti-aging compounds, including a weak estrogen, 17 alpha estradiol, extend longevity of male, but not female, mice. Apparently, fundamental mechanisms of aging are not identical in females and males and it is essential to use both sexes in studies aimed at identifying novel anti-aging interventions. Recommendations for lifestyle modifications, drugs, and dietary supplements to maintain good health and functionality into advanced age and to live longer will likely need to be tailored to the sex of the user

Electrochemical techniques for subsecond neurotransmitter detection in live rodents.

Alterations in neurotransmission have been implicated in numerous neurodegenerative and neuropsychiatric disorders, including Alzheimer disease, Parkinson disease, epilepsy, and schizophrenia. Unfortunately, few techniques support the measurement of real-time changes in neurotransmitter levels over multiple days, as is essential for ethologic and pharmacodynamic testing. Microdialysis is commonly used for these research paradigms, but its poor temporal and spatial resolution make this technique inadequate for measuring the rapid dynamics (milliseconds to seconds) of fast signaling neurotransmitters, such as glutamate and acetylcholine. Enzymatic microelectrode arrays (biosensors) coupled with electrochemical recording techniques have demonstrated fast temporal resolution (less than 1 s), excellent spatial resolution (micron-scale), low detection limits (≤200 nM), and minimal damage (50 to 100 μm) to surrounding brain tissue. Here we discuss the benefits, methods, and animal welfare considerations of using platinum microelectrodes on a ceramic substrate for enzyme-based electrochemical recording techniques for real-time in vivo neurotransmitter recordings in both anesthetized and awake, freely moving rodents

Altered Neurotransmission Prior to Cognitive Decline in AβPP/PS1 Mice, a Model of Alzheimer\u27s Disease

Indirect evidence supports altered glutamate signaling with Alzheimer\u27s disease, however, it is not known if glutamate neurotransmission is impacted prior to cognitive decline. We examined cognition and glutamate neurotransmission in 2-4 month AβPP/PS1, an Alzheimer\u27s disease model, and age-matched control mice. There were no differences in learning and memory as assessed by Morris water maze. However, in vivo electrochemical measures of potassium-evoked glutamate release in the CA1, but not the CA3 or dentate, was significantly elevated in AβPP/PS1 mice. These data support changes in the glutamatergic system that precedes cognitive decline in a mouse model of Alzheimer\u27s disease

Soluble Amyloid-β42 Stimulates Glutamate Release through Activation of the α7 Nicotinic Acetylcholine Receptor.

Alzheimer\u27s disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss and hippocampal atrophy. Soluble amyloid-β (Aβ)42 and plaque accumulation is implicated as the neurotoxic species in this disorder; however, at physiological concentrations (pM-nM), Aβ42 contributes to neurogenesis, long-term potentiation, and neuromodulation. Because Aβ42 binds the α7 nicotinic acetylcholine receptors (α7nAChRs) located presynaptically on glutamatergic terminals, involved with hippocampal dependent learning and memory, we examined the effects of the human, monomeric isoform of Aβ42 on glutamate release in the dentate gyrus (DG), CA3, and CA1, of isoflurane anesthetized, 6-9 month old male C57BL/6J mice. We utilized an enzyme-based microelectrode array selective for L-glutamate measures with fast temporal (4 Hz), low spatial resolution (50×100μm) and minimal damage to the surrounding parenchyma (50-100μm). Local application of Aβ42 (0.01, 0.1, 1.0, and 10.0μM; ∼150 nl; 1-2 Seconds) elicited robust, reproducible glutamate signals in all hippocampal subfields studied. Local application of 0.1 and 1.0μM Aβ42 significantly increased the average maximal amplitude of glutamate release compared to saline in the DG and CA1. 10.0μM Aβ42 significantly elevated glutamate release in the DG and CA3, but not in the CA1. Glutamate release was completely attenuated with coapplication of 10.0μM α-Bungarotoxin, the potent α7nAChR antagonist. Coapplication of 10.0μM tetrodotoxin, indicates Aβ42 - induced glutamate release originates from neuronal rather than glial sources. This study demonstrates that the human, monomeric Aβ42 isoform evokes glutamate release through the α7nAChR and varies across hippocampal subfields

FUNCTIONAL PROPERTIES OF L-GLUTAMATE REGULATION IN ANESTHETIZED AND FREELY MOVING MICE

L-glutamate (Glu) is the predominant excitatory neurotransmitter in the mammalian central nervous system with involvement encompassing learning and memory, cognition, plasticity, and motor movement. Dysregulation of the glutamatergic system is implicated in several neurological disorders including Parkinson’s disease, Alzheimer’s disease, Huntington’s disease and amyotrophic lateral sclerosis. The mechanisms underlying these neurological disorders are not clear, but evidence suggests that abnormal Glu neurotransmission plays a role. Elevated levels of Glu in the synaptic cleft overstimulate the N-methyl-Daspartate receptor leading to excitotoxicity, which causes neuronal loss in chronic neurological diseases. What is less understood is the source for the elevated Glu levels. One hypothesis involves alterations in either activity or concentration of Glu metabolizing enzymes. To study this, two transgenic mouse models were developed that increase levels of Glu pyruvate transaminase (GPT), responsible for Glu degradation, and Glu dehydrogenase (GLUD1), responsible for Glu synthesis. Our laboratory is interested in studying stimulusevoked Glu release and re-uptake dynamics in these mice using an enzymebased multisite microelectrode array (MEA) capable of subsecond measurements with low detection limits. Our main finding indicates that GLUD1 mice have increased release of Glu. The GLUD1 mice show spontaneous motor neuron degeneration of the hind limbs that could be correlated to an excitotoxic effect from the increased release of Glu. We wanted to study these GLUD1, motor deficient mice without the affects of anesthesia. First, we needed to modify the current MEAs for use in the awake, freely moving mouse. In these studies we measured resting Glu levels as well as MEA viability with local application of 1 mM Glu in both the striatum and prefrontal cortex of C57BL/6 mice. No change in MEA sensitivity for Glu was observed on days 3 through 7 post-implantation. Resting Glu levels are examined in the striatum of the freely moving mouse by locally applying an uptake inhibitor or a sodium-channel blocker. Our studies indicate the resting Glu levels are partially neuronally derived and not from reversal of the high-affinity transporters. This characterization has laid the foundation to study behavioral alterations of Glu in the GLUD1 mice

Amyloid Beta-Related Alterations to Glutamate Signaling Dynamics During Alzheimer\u27s Disease Progression.

Alzheimer’s disease (AD) ranks sixth on the Centers for Disease Control and Prevention Top 10 Leading Causes of Death list for 2016, and the Alzheimer’s Association attributes 60% to 80% of dementia cases as AD related. AD pathology hallmarks include accumulation of senile plaques and neurofibrillary tangles; however, evidence supports that soluble amyloid beta (Aβ), rather than insoluble plaques, may instigate synaptic failure. Soluble Aβ accumulation results in depression of long-term potentiation leading to cognitive deficits commonly characterized in AD. The mechanisms through which Aβ incites cognitive decline have been extensively explored, with a growing body of evidence pointing to modulation of the glutamatergic system. The period of glutamatergic hypoactivation observed alongside long-term potentiation depression and cognitive deficits in later disease stages may be the consequence of a preceding period of increased glutamatergic activity. This review will explore the Aβ-related changes to the tripartite glutamate synapse resulting in altered cell signaling throughout disease progression, ultimately culminating in oxidative stress, synaptic dysfunction, and neuronal loss

Lifespan of long-lived growth hormone receptor knockout mice was not normalized by housing at 30°C since weaning

Growth hormone receptor knockout (GHRKO) mice are remarkably long-lived and have improved glucose homeostasis along with altered energy metabolism which manifests through decreased respiratory quotient (RQ) and increased oxygen consumption (VO2 ). Short-term exposure of these animals to increased environmental temperature (eT) at 30°C can normalize their VO2 and RQ. We hypothesized that increased heat loss in the diminutive GHRKO mice housed at 23°C and the consequent metabolic adjustments to meet the increased energy demand for thermogenesis may promote extension of longevity, and preventing these adjustments by chronic exposure to increased eT will reduce or eliminate their longevity advantage. To test these hypotheses, GHRKO mice were housed at increased eT (30°C) since weaning. Here, we report that contrasting with the effects of short-term exposure of adult GHRKO mice to 30°C, transferring juvenile GHRKO mice to chronic housing at 30°C did not normalize the examined parameters of energy metabolism and glucose homeostasis. Moreover, despite decreased expression levels of thermogenic genes in brown adipose tissue (BAT) and elevated core body temperature, the lifespan of male GHRKO mice was not reduced, while the lifespan of female GHRKO mice was increased, along with improved glucose homeostasis. The results indicate that GHRKO mice have intrinsic features that help maintain their delayed, healthy aging, and extended longevity at both 23°C and 30°C

Hippocampal alterations in glutamatergic signaling during amyloid progression in AβPP/PS1 mice

Our previous research demonstrated that soluble amyloid-β (Aβ)42, elicits presynaptic glutamate release. We hypothesized that accumulation and deposition of Aβ altered glutamatergic neurotransmission in a temporally and spatially dependent manner. To test this hypothesis, a glutamate selective microelectrode array (MEA) was used to monitor dentate (DG), CA3, and CA1 hippocampal extracellular glutamate levels in 2–4, 6–8, and 18–20 month-old male AβPP/PS1 and age- matched C57BL/6J control mice. Starting at 6 months of age, AβPP/PS1 basal glutamate levels are elevated in all three hippocampal subregions that becomes more pronounced at the oldest age group. Evoked glutamate release was elevated in all three age groups in the DG, but temporally delayed to 18–20 months in the CA3 of AβPP/PS1 mice. However, CA1 evoked glutamate release in AβPP/PS1 mice was elevated at 2–4 months of age and declined with age. Plaque deposition was anatomically aligned (but temporally delayed) with elevated glutamate levels; whereby accumulation was first observed in the CA1 and DG starting at 6–8 months that progressed throughout all hippocampal subregions by 18–20 months of age. The temporal hippocampal glutamate changes observed in this study may serve as a biomarker allowing for time point specific therapeutic interventions in Alzheimer’s disease patients

Amyloid-B(42) stimulated hippocampal lactate release is coupled to glutamate uptake

Since brain glucose hypometabolism is a feature of Alzheimer’s disease (AD) progression, lactate utilization as an energy source may become critical to maintaining central bioenergetics. We have previously shown that soluble amyloid-β (Aβ) 42 stimulates glutamate release through the α7 nicotinic acetylcholine receptor (α7nAChR) and hippocampal glutamate levels are elevated in the APP/PS1 mouse model of AD. Accordingly, we hypothesized that increased glutamate clearance contributes to elevated extracellular lactate levels through activation of the astrocyte neuron lactate shuttle (ANLS). We utilized an enzyme-based microelectrode array (MEA) selective for measuring basal and phasic extracellular hippocampal lactate in male and female C57BL/6J mice. Although basal lactate was similar, transient lactate release varied across hippocampal subregions with the CA1 \u3e CA3 \u3e dentate for both sexes. Local application of Aβ 42 stimulated lactate release throughout the hippocampus of male mice, but was localized to the CA1 of female mice. Coapplication with a nonselective glutamate or lactate transport inhibitor blocked these responses. Expression levels of SLC16A1, lactate dehydrogenase (LDH) A, and B were elevated in female mice which may indicate compensatory mechanisms to upregulate lactate production, transport, and utilization. Enhancement of the ANLS by Aβ 42 -stimulated glutamate release during AD progression may contribute to bioenergetic dysfunction in AD