The source of physiologically stimulated glutamate efflux from the striatum of conscious rats.

Abstract

1. Glutamate in the extracellular compartment of the striatum of freely moving rats was monitored at 5 min intervals using microdialysis and an enzyme-based assay. 2. Basal levels of dialysate glutamate were 3-6 + 05 1uM. Local infusion through the dialysis probe of tetrodotoxin (TTX), cadmium chloride or magnesium chloride produced no reduction in basal levels of glutamate; with the latter two there was, instead, an increase. 3. Neuronal activation stimulated by induced grooming was accompanied by an increase in total glutamate efflux of 47 5 + 25-0% above basal level; this increase was not reduced by local infusion of 'ITX. 4. We propose that the ITX-insensitive release of glutamate in response to physiological stimulation is derived from glial cells and is a Ca2+-dependent mechanism triggered by a receptor-mediated release of Ca2+ from internal stores that spreads through the network of astrocytes.Glutamate is the main central excitatory transmitter in the vertebrate nervous system. This function has been extensively investigated using electrophysiological techniques. However glutamate, as well as being a neurotransmitter, has an additional role in energy and nitrogen metabolism. As a result, it is present in relatively high concentration in the cytoplasm of all neurones, as well as glia.

N-methyl-D-aspartate receptor-mediated modulation of monoaminergic metabolites and amino acids in the chick forebrain: Anin vivo microdialysis and electrophysiology study

“…4), which confirms the idea that acute tissue damage has a great influence especially on extracellular glutamate levels. Similar observations have been reported from microdialysis experiments in mammals under different experimental conditions (Miele et al, 1996;Moghaddam et al, 1997); however, the reasons for this large variability are unknown.…”

Parabrachial Nucleus Induces Suppression of Baroreflex Bradycardia by the Release of Glutamate in the Rostral Ventrolateral Medulla of the Rat

“…The baseline concentration of glutamate we measured in the dialysate collected from the RVLM was in agreement with that reported by Caringi et al [2]. It was also in the same range as that detected in the brain of conscious rats [33]. Relevant to the present study, an increase in the extracellular glutamate concentration in the RVLM has been demonstrated to account for the attenuation of the BRR response to the central application of angiotensin II [49].…”

“…In support of the vesicular origin of glutamate in dialysate, basal or evoked levels of glutamate have been reported to be dereased in the presence of the fast sodium channel blocker, tetrodotoxin [9,36], or on infusion with calcium-free aCSF [9,34]. On the other hand, lack of a blunting effect by tetrodotoxin or calcium channel blocker on basal or evoked levels of glutamate in the brain has also been shown [33,41]. With our demonstration of site specificity in the PBN-induced increase in extracellular glutamate levels in the RVLM ( fig.…”

Oxygen tolerance of an implantable polymer/enzyme composite glutamate biosensor displaying polycation-enhanced substrate sensitivity

“…The task of detecting brain ECF Glu, however, is significantly more challenging than glucose monitoring, mainly because the baseline ECF concentration of Glu appears to be ≤5 M (Miele et al, 1996;Lada and Kennedy, 1996;Baker et al, 2002;Chen, 2005;Fillenz, 2005), although values as high as 15 M have been suggested (Kulagina et al, 1999), and compares to ∼500 M for ECF glucose (Boutelle et al, 1992;Lowry et al, 1998a). Thus, optimization of Glu sensitivity is critical for physiological applications, and we reported recently a significant enhancement of the linear region slope (LRS) for Glu, by incorporating the polycation polyethyleneimine (PEI) in these PPD-based biosensors (Pt/PEI/GluOx/PPD) (McMahon et al, 2006b The protein immobilizing agent (Tang et al, 1998) and stabilizer (Bryjak, 1995;Andersson and Hatti-Kaul, 1999), PEI, has been used previously in biosensors for a number of analytes, including Glu (Belay et al, 1999;Rahman et al, 2005;Varma et al, 2006).…”