Article

Rapid microelectrode measurements and the origin and regulation of extracellular glutamate in rat prefrontal cortex.

Department of Psychiatry, Douglas Mental Health University Institute, McGill University, Montreal, Canada.
Journal of Neurochemistry (Impact Factor: 4.24). 10/2010; 115(6):1608-20. DOI: 10.1111/j.1471-4159.2010.07066.x
Source: PubMed

ABSTRACT Glutamate in the prefrontal cortex (PFC) plays a significant role in several mental illnesses, including schizophrenia, addiction and anxiety. Previous studies on PFC glutamate-mediated function have used techniques that raise questions on the neuronal versus astrocytic origin of glutamate. The present studies used enzyme-based microelectrode arrays to monitor second-by-second resting glutamate levels in the PFC of awake rats. Locally applied drugs were employed in an attempt to discriminate between the neuronal or glial components of the resting glutamate signal. Local application of tetrodotoxin (sodium channel blocker), produced a significant (∼ 40%) decline in resting glutamate levels. In addition significant reductions in extracellular glutamate were seen with locally applied ω-conotoxin (MVIIC; ∼ 50%; calcium channel blocker), and the mGluR(2/3) agonist, LY379268 (∼ 20%), and a significant increase with the mGluR(2/3) antagonist LY341495 (∼ 40%), effects all consistent with a large neuronal contribution to the resting glutamate levels. Local administration of D,L-threo-β-benzyloxyaspartate (glutamate transporter inhibitor) produced an ∼ 120% increase in extracellular glutamate levels, supporting that excitatory amino acid transporters, which are largely located on glia, modulate clearance of extracellular glutamate. Interestingly, local application of (S)-4-carboxyphenylglycine (cystine/glutamate antiporter inhibitor), produced small, non-significant bi-phasic changes in extracellular glutamate versus vehicle control. Finally, pre-administration of tetrodotoxin completely blocked the glutamate response to tail pinch stress. Taken together, these results support that PFC resting glutamate levels in rats as measured by the microelectrode array technology are at least 40-50% derived from neurons. Furthermore, these data support that the impulse flow-dependent glutamate release from a physiologically -evoked event is entirely neuronally derived.

0 Followers
 · 
106 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Comparative medicine 08/2014; 64(4):249-255. · 0.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The 5-choice serial reaction time task (5CSRTT) has been widely used to study attention and impulse control in rodents. In order to mimic cognitive impairments in psychiatry, one approach has been to use acute administration of NMDA antagonists. This disruption in glutamatergic transmission leads to impairments in accuracy, omissions, and premature responses although findings have been inconsistent. In this study, we further investigated glutamatergic mechanisms using a novel version of the 5CSRTT, which we have previously shown to be more sensitive to cognitive enhancers. We first investigated the effects of systemic treatment with NMDA antagonists. We also carried out a preliminary investigation using targeted medial prefrontal cortex infusions of a NMDA antagonist (MK801), mGluR2/3 antagonist (LY341495), and mGluR7 negative allosteric modulator (MMPIP). Acute systemic administration of the different NMDA antagonists had no specific effects on accuracy. At higher doses PCP, ketamine, and memantine, increased omissions and affected other measures suggesting a general disruption in task performance. Only MK801 increased premature responses, and reduced omissions at lower doses suggesting stimulant like effects. None of the NMDA antagonists affected accuracy or any other measures when tested using a short stimulus challenge. Infusions of MK801 had no effect on accuracy but increased premature responses following infralimbic, but not prelimbic infusion. LY341495 had no effects in either brain region but a decrease in accuracy was observed following prelimbic infusion of MMPIP. Contrary to our hypothesis, disruptions to glutamate transmission using NMDA antagonists did not induce any clear deficits in accuracy in this modified version of the 5CSRTT. We also found that the profile of effects for MK801 differed from those observed with PCP, ketamine, and memantine. The effects of MK801 in the infralimbic cortex add to the literature indicating this brain region and glutamate play an important role in impulse control.
    PLoS ONE 12/2014; 9(12):e115374. DOI:10.1371/journal.pone.0115374 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Depression is a prevalent neuropsychiatric disorder that affects an estimated 350 million people worldwide. Currently available treatments for depression are lacking in both speed of onset and efficacy. Recent pharmacological efforts have targeted the glutamatergic neurotransmitter system using the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine to produce rapid and robust antidepressant effects, however the widespread clinical use of ketamine is limited due to side effects and abuse liability. More recently, work evaluating metabotropic mGluR2/3 receptor antagonists has demonstrated many similarities with ketamine. Male, Sprague-Dawley rats were exposed to a chronic unpredictable stress paradigm, which produces decreased sucrose preference, a measure of anhedonia. Rats were then treated with vehicle or a single injection of the mGluR2/3 antagonist LY341495 (3 mg/kg, i.p.) and tested at 24 hrs, 48 hrs or 10 days after a single treatment. We demonstrate that a single treatment with LY341495 produces a rapid (within 1-2 days) and long-lasting (10 days) reversal of anhedonia caused by chronic unpredictable stress in rats. This model provides a rigorous test of rapid-acting agents as typical antidepressants require several weeks of treatment to produce a response. These data suggest that LY341495 has the ability to produce rapid and robust antidepressant effects similar to ketamine. Together, the results highlight the potential for similar compounds to produce rapid and lasting efficacy for the treatment of depression.

Full-text

Download
63 Downloads
Available from
May 31, 2014