The EFFECT OF ANAESTHETICS ON THE UPTAKE AND RELEASE OF Γ‐AMINOBUTYRATE AND D‐ASPARTATE IN RAT BRAIN SLICES

1 The synaptic concentrations of glutamate and g-aminobutyric acid (GABA) are modulated by their release and re-uptake. The e ects of general anaesthetics on these two processes remain unclear. This study evaluates the e ects of iso¯urane, a clinically important anaesthetic, on glutamate and GABA release and re-uptake in superfused mouse cerebrocortical slices. 2 Experiments consisted of two 1.5-min exposures to 40 mM KCl in 30 min intervals. During the second exposure, di erent concentrations of iso¯urane with and without 0.3 mM L-transpyrrolidine-2,4-dicarboxylic acid (PDC, a competitive inhibitor of glutamate uptake transporter) or 1 mM nipecotic acid (a competitive inhibitor of GABA uptake transporter) were introduced. The ratios of the second to ®rst KCl-evoked increases in glutamate and GABA were used to determine the iso¯urane concentration-response curves.3 The results can be described as a sum of two independent processes, corresponding to the inhibitions of release and re-uptake, respectively. The EC 50 values for the inhibitions of release and re-uptake were 295+16 and 805+43 mM for glutamate, and 229+13 and 520+25 mM for GABA, respectively. Addition of PDC did not signi®cantly a ect glutamate release but shifted the re-uptake curve to the left (EC 50 =315+20 mM). Nipecotic acid completely blocked GABA uptake, rendering iso¯urane inhibition of GABA re-uptake undetectable. 4 Our data suggest that iso¯urane inhibits both the release and re-uptake of neurotransmitters and that the inhibitions occur at di erent EC 50 's. For GABA, both EC 50 's are within the clinical concentration range. The net anaesthetic e ect on extracellular concentrations of neurotransmitters, particularly GABA, depends on the competition between inhibition of release and that of re-uptake.

Section: Discussionmentioning

confidence: 99%

Concentration‐dependent isoflurane effects on depolarization‐evoked glutamate and GABA outflows from mouse brain slices

Liachenko

Tang

Somogyi

et al. 1999

“…Other studies, e.g. Minchin (1981), suggest that this potentiation is not the re- sult-of altered GABA uptake mechanisms. We are unaware of any other studies using ketamine that are directly comparable with ours.…”

Section: Anaesthetics Differ In Theirpostsynaptic Effectsmentioning

confidence: 97%

“…Anaesthesia was assessed according to the criteria of McFarland (1981). Assumptions (Minchin, 1981) (1959). The anaesthetics were dissolved in river water to the same concentrations as were employed in the iontophoresis experiments and each drug was tested on a minimum of 6 ammocoetes.…”

Section: Appendixmentioning

confidence: 99%

“…The anaesthetics, chosen to represent four classes of compound used in clinical anaesthetic practice, were bath-applied to the preparation in concentrations similar to those likely to obtain in the brain during clinical anaesthesia (Richards, 1972;Minchin, 1981). Although anaesthetics could equally interfere with synaptic transmission by a presynaptic action, we have concentrated on postsynaptic mechanisms, applying the putative transmitters directly to the cells and taking steps to preclude transsynaptic effects.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dissimilar Influences of Some Injectable Anaesthetics on the Responses of Reticulospinal Neurones to Inhibitory Transmitters in the Lamprey

Cullen¹,

Martin²

1982

Intracellular recordings were made from identified bulbar reticulo‐spinal neurones in the medulla of lamprey ammocoetes. Responses to iontophoretically applied inhibitory transmitters were measured as changes in membrane potential and input resistance. Dose‐dependent alterations in the responses to γ‐aminobutyric acid (GABA) and glycine during bath application of injectable anaesthetic drugs were measured; the compounds used were pentobarbitone, ketamine, metomidate and the steroid mixture alphaxalone/alphadolone (Saffan). GABA responses were potentiated by pentobarbitone (1–3 × 10−4m) and prolonged by ketamine (3.7 × 10−5m); but depressed by high concentrations (10−3m) of all drugs, as well as by anaesthetic concentrations of alphaxalone (1–3 × 10−5m). Glycine responses were depressed by alphaxalone (1–3 × 10−5m) and by supra‐anaesthetic concentrations of ketamine (3.7 × 10−4 m) and metomidate (1.8 × 10−3m). No drug potentiated the glycine responses. In the absence of an effect common to the 4 anaesthetics, it is concluded that neither potentiation nor inhibition of all GABA or glycine responses is an essential feature of anaesthesia. However, effects comparable to those described here may contribute to the overall clinical picture during anaesthesia of higher vertebrates. The findings do not support the notion that all anaesthetic agents act on biological membranes by a single mechanism.

“…Electrophysiological analysis has demonstrated that concentrations of barbiturates within the anaesthetic range do not interfere significantly with the propagation of the nerve impulse, but they inhibit the release of putative neurotransmitters such as glutamate from synaptosomes and slices of brain tissue (see Collins, 1981;Minchin, 1981;Kendall & Minchin, 1982). Moreover, Blaustein & Ector (1974) have shown that concentrations of barbiturates within the anaesthetic range depress the K'-stimulated Ca2+ influx into synaptosomes, but these authors did not correlate this decrease in Ca2+ flux with changes in transmitter release.…”

Section: Implicationsfor Anaesthetic Action In the Cnsmentioning

confidence: 99%

The action of pentobarbitone on stimulus‐secretion coupling in adrenal chromaffin cells

Pocock

Richards

1987

1 The action ofpentobarbitone on stimulus-secretion coupling was studied in bovine isolated adrenal medullary cells. 2 Pentobarbitone inhibited catecholamine release evoked by 5001M carbachol with half maximal inhibition (IC50) around 50 pM. It also inhibited catecholamine release induced by depolarization with 77 mM potassium (IC50 100 gM). These effects of pentobarbitone were observed with concentrations that lie within the range encountered during general anaesthesia. 3 Evoked secretion required the presence of calcium in the extracellular medium and was associated with an influx of Ca2" through voltage-sensitive channels. Pentobarbitone inhibited 45Ca influx in response to both carbachol (IC50 50 gM) and K+-depolarization (IC50 150 pM).4 The action of pentobarbitone on the relationship between intracellular free Ca and exocytosis was examined using electropermeabilised cells which were suspended in solutions containing a range of concentrations ofionised calcium between 10-8 and 10-4 M. Catecholamine secretion was measured in the presence of 0, 50, 200 or 500 pM pentobarbitone. The anaesthetic had no effect on the activation of exocytosis by intracellular free calcium. 5 When catecholamine secretion in response to potassium or carbachol was modulated by varying extracellular calcium or by adding pentobarbitone to the incubation medium, the amount of catecholamine secretion for a given Ca2' entry was the same.6 Pentobarbitone inhibited the secretion and 45Ca uptake induced by carbachol in a non-competitive manner.7 The secretion evoked by nicotinic agonists was associated with an increase in 22Na influx.Pentobarbitone inhibited this influx with an ICm of IOO1M. 8 We concluded that: (a) Pentobarbitone inhibits the catecholamine secretion from bovine adrenal chromaffin cells induced by nicotinic agonists by non-competitive inhibition of the nicotinic receptor. (b) The decrease in Ca influx caused by pentobarbitone accounts fully for the decrease in secretion in response to depolarization with potassium.