QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online November 1, 2006
Journal of Experimental Biology 209, 4429-4435 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02553

This Article Summary Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cheung, U. Articles by Woodin, M. A. Search for Related Content PubMed PubMed Citation Articles by Cheung, U. Articles by Woodin, M. A. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB OXYGEN Social Bookmarking                         What's this?

Excitatory actions of GABA mediate severe-hypoxia-induced depression of neuronal activity in the pond snail (Lymnaea stagnalis)

Una Cheung, Mehrnoush Moghaddasi, Hannah L. Hall, J. J. B. Smith, Leslie T. Buck and Melanie A. Woodin^*

Department of Cell and Systems Biology, University of Toronto, Ontario, Canada

^* Author for correspondence (e-mail: m.woodin{at}utoronto.ca)

Accepted 18 September 2006

	Summary

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 
To characterize the effect of severe hypoxia on neuronal activity, long-term intracellular recordings were made from neurones in the isolated central ring ganglia of Lymnaea stagnalis. When a neurone at rest in normoxia was subjected to severe hypoxia, action potential firing frequency decreased by 38% (from 2.4-1.5 spikes s^-1), and the resting membrane potential hyperpolarized from -70.3 to -75.1 mV. Blocking GABA_A receptor-mediated synaptic transmission with the antagonist bicuculline methiodide (100 µmol l^-1) decreased neuronal activity by 36%, and prevented any further changes in response to severe hypoxia, indicating that GABAergic neurotransmission mediates the severe hypoxia-induced decrease in neuronal activity. Puffing 100 µmol l^-1 GABA onto the cell body produced an excitatory response characterized by a transient increase in action potential (AP) firing, which was significantly decreased in severe hypoxia. Perturbing intracellular chloride concentrations with the Na⁺/K⁺/Cl^- (NKCC1) cotransporter antagonist bumetanide (100 µmol l^-1) decreased AP firing by 40%, consistent with GABA being an excitatory neurotransmitter in the adult Lymnaea CNS. Taken together, these studies indicate that severe hypoxia reduces the activity of NKCC1, leading to a reduction in excitatory GABAergic transmission, which results in a hyperpolarization of the resting membrane potential (V_m) and as a result decreased AP frequency.

Key words: GABA, Lymnaea stagnalis, hypoxia

	Introduction

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 
The cellular and physiological responses to a near lack of oxygen differ from those during more routine moderate hypoxia. For example, anoxia rapidly depresses neuronal activity and synaptic transmission in rat (Haddad and Jiang, 1997; Pena and Ramirez, 2005; Zhu and Krnjevic, 1994) and turtle brain (Feng et al., 1988; Lutz, 1992). These severe-hypoxia-induced decreases in neuronal activity and synaptic transmission are not surprising given the high metabolic cost of these processes (Attwell and Laughlin, 2001; Seisjo, 1978). For example, a detailed energy expenditure budget of grey matter in the rodent brain reveals that action potential generation and propagation consumes 47% of available ATP, while postsynaptic potentials consume an additional 34% (Attwell and Laughlin, 2001). GABAergic (-aminobutyric acid) neurones make widespread connections within neuronal networks and thus are capable of controlling network oscillations and patterns of activity in numerous systems and organisms. GABA modulates oscillatory networks in the olfactory system of the terrestrial slug Limax marginatus (Bazhenov et al., 2001; Ito et al., 2004), as well as suppressing the oscillatory activity of crustacean pyloric neurones (Cazalets et al., 1987). Thus GABAergic transmission in Lymnaea is well-positioned to regulate severe-hypoxia-induced decreases in neuronal activity that are required to preserve limited ATP stores.

GABAergic synaptic transmission itself is modulated by decreases in oxygen; extracellular levels of GABA rise in the anoxic brains of the shore crab Carcinus maenas (Nilsson and Winberg, 1993), Crucian carp (Hylland and Nilsson, 1999) and turtle Trachemys scripta (Nilsson and Lutz, 1991). The ability of oxygen to modulate GABAergic transmission, coupled with the ability of GABAergic transmission to regulate neuronal network activity, led to our hypothesis that modulation of GABAergic neurotransmission may be responsible for severe-hypoxia-induced decreases in neuronal activity.

To test this hypothesis we took advantage of the anoxiatolerant pulmonate pond snail Lymnaea stagnalis, which survives about 40 h in a N₂-bubbled environment at 20°C (Wijsman et al., 1985). It has also been used extensively for studies on respiratory neurophysiology, mainly because of its well characterized respiratory system and behaviours (Inoue et al., 2001; Syed et al., 1990; Taylor and Lukowiak, 2000). In this study, we demonstrate that under normoxic conditions GABA acts as an excitatory neurotransmitter in neurones of the dorsal pedal ganglia, and that during severe hypoxia the excitatory actions of GABA are significantly decreased. The severe-hypoxia-induced decrease in excitatory GABAergic transmission occurs via a decrease in cation-chloride cotransporter (NKCC1) activity, and accounts for the severe-hypoxia-induced decrease in action potential firing and hyperpolarization of the resting membrane potential.

	Materials and methods

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 
Animals
Laboratory-raised stocks of the freshwater snail Lymnaea stagnalis L were maintained in aquaria filled with well-aerated filtered water at 22°C. Lymnaea were fed organic lettuce leaves and carrot shavings every 2 days. Experiments were performed on snails 20-30 mm in length (3 months old).

Solutions
Lymnaea saline solution included (in mmol l^-1): 10 glucose; 51.3 NaCl; 1.7 KCl; 4 CaCl₂; 1.5 MgCl₂; 10 Hepes; pH 7.9 using NaOH; 144 mOsm. The extracellular chloride concentration in this saline solution was based on previous measurements of Lymnaea haemolymph (de With and van der Schors, 1984). Normoxic Lymnaea saline solution was prepared by bubbling air directly into the solution for a minimum of 30 min. Severely hypoxic Lymnaea saline solution was prepared in an identical manner with 100% N₂ replacing air. Perfusion tubes for the hypoxic saline were double jacketed, and the outer jacket gassed with 100% N₂. A Clarktype oxygen electrode and computer based acquisition software (Qubit System, Kingston, Ontario, Canada) was used to measure the partial pressure of oxygen (P_O2) in the perfusion chamber. Following perfusion with anoxic saline, P_O2 in the recording chamber decreased from approximately 155 mmHg (1 mmHg=133.3 Pa) P_O2 (normoxia) to 7 Pa P_O2 (severe hypoxia) in less than 10 min. The recording chamber was open to room air making anoxia difficult to achieve.

Isolated brain preparations
Snails were anesthetized briefly in Lymnaea saline solution containing 30% Listerine, a standard anaesthetic used in Lymnaea studies (Spencer et al., 2002), then de-shelled with forceps. Lymnaea were pinned dorsal surface up to the bottom of a Sylgard-filled dissection dish, covered with Lymnaea saline solution, and a medial incision was made from the base of the mantle to the head. The central ring ganglia were removed with a pair of fine surgical scissors, and transferred immediately to a recording dish with 3 ml of fresh Lymnaea saline solution, and pinned out (Fig. 1A). The connective tissue sheath was removed from the left and right pedal ganglia (LPeDG and RPeDG, respectively) with a pair of fine forceps, prior to being immediately transferred to the microscope stage where they were perfused with normoxic Lymnaea saline solution at a rate of 3 ml m^-1 at 22°C.

View larger version (29K): [in this window] [in a new window]   Fig. 1. Electrophysiological recording from neurones of the Lymnaea pedal ganglia. (A) The central ring ganglia isolated from Lymnaea. Intracellular recordings were made from neurones in cluster F (white region) on the dorsal surface of either the left or right pedal ganglion (LPeDG or RPeDG). (B) Schematic of the Lymnaea central ring ganglia. Recordings were not obtained from the identified neurones L- or RPeD1. (C) An example trace of a recording from a cluster F neurone maintained entirely under normoxic conditions.

Impaled neurones were maintained under normoxic conditions until action potential (AP) frequency and resting membrane potential (V_m) stabilized (10 min). AP frequency and V_m were then recorded for a minimum of 20 min under normoxic conditions. Following a 10 min switch from normoxic to hypoxic saline, AP frequency and V_m were again recorded for another 20 min period. Following this hypoxic recording, neurones were returned to normoxia for the duration of the recording. AP frequency was determined by analyzing V_m for 8.8 s every 20 s, at a sampling rate of 5 kHz. There was significant variation in the AP frequency between neurones (minimum number of APs in 8.8 s: 2.72±0.24 or 0.31 spikes s^-1; maximum number of APs in 8.8 s: 47.12±2.05 or 5.35 spikes s^-1). Therefore, in order to compare AP frequency between neurones, data were normalized to a control period.

Chemicals
-Aminobutyric acid (GABA; A5838, Sigma, Oakville, Ontario, Canada) was dissolved in Lymnaea saline solution and applied to the pedal ganglia using a VC-6 perfusion valve control system (Warner Instruments, Handen, CT, USA) at a final concentration of 500 µmol l^-1. A 100 mmol l^-1 stock solution of bicuculline methiodide (B6889, Sigma) was prepared in dimethyl sulfoxide (DMSO; D5879, Sigma); the stock was diluted to a final concentration of 100 µmol l^-1 in either normoxic or hypoxic Lymnaea saline solution. A 100 mmol l^-1 stock solution of bumetanide (B3023, Sigma) was prepared in ethanol and diluted to a final concentration of 100 µmol l^-1 in normoxic saline solution.

Statistical analysis
All averages are reported as means ± standard error (s.e.m.). Statistical analysis was performed using SigmaStat software (Point Richmond, CA, USA).

	Results

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 
The effects of severe hypoxia on neuronal activity were determined by monitoring AP firing frequency and V_m. Intracellular recordings were obtained from visualized neurones in cluster F (with the exception of identified neurones L- and RPeD1) on the dorsal surface of the left or right pedal ganglion (L- or RPeDG) of the central ring ganglia isolated from L. stagnalis, as shown in Fig. 1A,B. Under control normoxic conditions there were no significant changes in AP frequency for over 100 min of recording [normoxia (first half of the recording) normoxia (second half of the recording) = 1.9±0.61.8±0.6 spikes s^-1; N=9, P=0.935 paired t-test; Fig. 2A]. Switching from normoxic saline to a severely hypoxic saline solution (100% N₂ bubbled) induced a sustained 38% decrease in AP frequency (normoxia hypoxia = 2.4±0.71.5±0.6 spikes s^-1; N=9, P=0.001 paired t-test; Fig. 2A,B). After a 40 min exposure to severe hypoxia, normoxic conditions were resumed, but no restoration to normoxia AP frequency was observed (in the 1 h following the return from hypoxia to normoxia).

View larger version (12K): [in this window] [in a new window]   Fig. 2. Severe hypoxia decreases neuronal activity. (A) No significant changes in the action potential (AP) frequency were observed in normoxic neurones throughout the entire recording period (black bars; N=9, P=0.935 paired t-test). After switching from normoxia to severe hypoxia, AP frequency decreased significantly (grey bars; N=9, P=0.001 paired t-test). (B) Example traces of AP frequency during normoxia and 10 min after the switch to severe hypoxia.

V_m was also determined under both normoxic and hypoxic conditions (Table 1). When neurones were kept entirely normoxic there was no significant difference between V_m in the first and second halves of the recordings (-69.3±2.9 -69.7±2.9; N=10, P=0.92 paired t-test). However, under hypoxic conditions V_m is significantly hyperpolarized, as compared with normoxia (-70.3±3.0-75.1±4.5; N=14, P=0.001 paired t-test). Thus, neurones in the isolated central ring ganglia of Lymnaea respond to severe decreases in oxygen with a significantly reduced AP frequency and hyperpolarized V_m.

All neurones were initially spontaneously active at their resting membrane potential, showing APs, and excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs; Fig. 3A). Inhibitory neurotransmission regulates the overall level of network activity in numerous preparations (Whittington and Traub, 2003), and so we hypothesized that the hypoxia-induced decrease in AP frequency may result from a modulation of inhibitory neurotransmission. Because classic fast inhibitory neurotransmission is commonly mediated by GABA binding to a Cl^- permeant GABA_A receptor, we examined the role of GABA_A-mediated neurotransmission in the hypoxia-induced decrease of neuronal activity. We repeated the normoxia hypoxia experiments in the presence of the GABA_A receptor antagonist bicuculline methiodide (100 µmol l^-1). The addition of bicuculline to the perfusate induced a 36% decrease in AP frequency from neurones resting in normoxia (Fig. 3B; normoxia normoxia + bicuculline= 3.3±0.62.1±0.5 spikes s^-1, N=7, P=0.003 paired t-test). The decrease in AP frequency observed when GABA_A neurotransmission was blocked with bicuculline was not significantly different from the decrease in AP frequency elicited by severe hypoxia (Fig. 3B; P=0.84). Normoxic neurones exposed to bicuculline showed no further depression in AP frequency upon switching the perfusate to hypoxia + bicuculline (Fig. 3B; normoxia + bicuculline hypoxia + bicuculline=2.5±1.21.9±0.9 spikes s^-1, N=6, P=0.235 paired t-test). Likewise, blocking GABA_A neurotransmission prevented the V_m hyperpolarization that occurred during the antagonist-free normoxia hypoxia experiment (Table 1; V_m normoxia + bicuculline=-72.3±1.9, V_m hypoxia + bicuculline=-72.6±1.9; N=6, P=0.8 paired t-test). Thus GABAergic synaptic transmission appears to be required for both the hypoxia-induced decrease in neural activity and V_m hyperpolarization.

View larger version (9K): [in this window] [in a new window]   Fig. 3. GABAA receptors mediate hypoxia-induced neuronal depression. (A) When neurones were recorded at rest under normoxic conditions action potentials (APs) (at I), inhibitory postsynaptic potential (IPSPs; at II) and excitatory postsynaptic potential (EPSPs; at III) were observed. (B) Addition of 100 µmol l-1 bicuculline to the perfusate induced a significant decrease in AP frequency (grey bars; N=7, P=0.003 paired t-test). When neurones underwent a normoxic to hypoxic transition in the presence of 100 µmol l-1 bicuculline, there was no significant change in AP frequency (white bars; N=6, P=0.235 paired t-test). The hypoxia-mediated decrease in AP frequency is not significantly different from the decrease observed during the normoxic application of bicuculline (black hypoxia bars vs grey normoxia+bicuculline bars; P=0.844 unpaired t-test). Data sets denoted by a white triangle were taken from Fig. 2A for direct visual comparison.

View larger version (38K): [in this window] [in a new window]   Fig. 4. Severe hypoxia decreases excitatory GABAergic neurotransmission in the Lymnaea central ring ganglia. (A) Example traces demonstrating the change in action potential (AP) firing frequency produced by puffing 500 µmol l-1 GABA (at arrow) onto the central ring ganglia. In normoxia (top trace) GABA produced an increase in AP firing frequency. Switching from normoxia to hypoxia decreased the excitatory response to GABA (lower trace). (B) Bar graph summarizing the percentage change in AP firing frequency and postsynaptic potential amplitude induced by puffing 500 µmol l-1 GABA onto both normoxic and hypoxic central ring ganglia.

As described earlier, the polarity of GABAergic neurotransmission is dependent upon the concentration of [Cl^-]_i, which in neurones is mainly determined by the differential expression of two cation-chloride cotransporters (Payne et al., 2003): NKCC1 (Na⁺/K⁺/2Cl^-), a cotransporter that actively accumulates Cl^- into the cell (Delpire, 2000); and the neuronespecific KCC2 (K⁺/Cl^-), which extrudes Cl^-. To examine if the cotransporter NKCC1 was largely responsible for maintaining relatively high [Cl^-]_i rendering GABA excitatory in our preparation, we observed the effect of the NKCC1 antagonist bumetanide (100 µmol l^-1) on AP frequency and V_m. When 100 µmol l^-1 bumetanide was added to the bath, neurones resting in normoxic solution showed a significant decrease in their AP frequency (Fig. 5A,B; normoxia normoxia + bumetanide=3±0.81.8±0.5 spikes s^-1, N=6, P=0.01 paired t-test). In three out of 15 recordings, APs were absent following bumetanide or hypoxia, such as in Fig. 5B. This decrease was not significantly different from the decrease observed when neurones underwent the normoxia hypoxia switch. The significant decrease in AP frequency induced by bumetanide is readily observed in Fig. 5B, which shows an abolishment of APs. When bumetanide blocks the inward movement of Cl^-, [Cl^-]_i decreases resulting in less excitatory GABAergic transmission, causing a hyperpolarizing of V_m (Table 1; V_m normoxia=-64.5±3.63, V_m normoxia + bumetanide=-72.3±1.9; N=6, P=0.03 paired t-test), thus decreasing AP frequency.

View larger version (12K): [in this window] [in a new window]   Fig. 5. NKCC1 renders GABA excitatory in the Lymnaea CNS. (A) Addition of the NKCC1 antagonist bumetanide (100 µmol l-1) to the perfusate significantly decreases action potential (AP) firing frequency (grey bars; N=6, P=0.01 paired t-test). The normoxic decrease in AP frequency caused by bumetanide is not significantly different from the decrease observed in the normoxia to hypoxia switch (black bars vs grey bars; P=0.844 unpaired t-test). (B) Spontaneous firing of APs was prevented by the addition of 100 µmol l-1 bumetanide (at bar).

	Discussion

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

Experiments were restricted to neurones in cluster F of the dorsal pedal ganglia in order to take advantage of their similar electrophysiological properties (Kyriakides et al., 1989) and proximity to GABAergic neurones (Hatakeyama and Ito, 2000). The dorsal pedal ganglia each have three pairs of GABA-like immunoreactive cell clusters that make widespread connections in the CNS of adult Lymnaea stagnalis. GABA binds to the Lymnaea GABA_A receptor, a multi-subunit membrane-spanning complex containing an integral chloride ion channel, which shares 30-50% similarity with the vertebrate GABA_A receptor (Barnard et al., 1988; Harvey et al., 1991). The excitatory actions of GABA in this study are consistent with those previously reported, where GABA evoked a depolarization of the membrane potential on the majority of Lymnaea neurones studied (Rubakhin et al., 1996). In fact, GABA acts as both an excitatory and inhibitory neurotransmitter in the CNS of several gastropods (Alkon et al., 1992; Kim and Takeuchi, 1990; Yarowsky and Carpenter, 1977; Zhang et al., 1997). It will be interesting to know whether hypoxia has a similar depressive effect on excitatory GABA inputs in other organisms that are routinely challenged by hypoxia.

One also has to consider the possibility that in our study GABA may also be activating the K⁺-permeable GABA_B receptor. In fact, GABA is known to exert excitatory effects through GABA_BRs in the Lymnaea osphradium (Kamardin et al., 1999). However, the involvement of excitatory GABA_B in our study is unlikely based on the fact that the GABA_AR antagonist bicuculline entirely abolished the hypoxia-induced decrease in neuronal activity.

The present results are consistent with those previous published by Inoue et al. (Inoue et al., 2001) who demonstrated that perfusion with anoxic saline decreases the action potential firing frequency of respiratory pattern-generating neurones in Lymnaea (Inoue et al., 2001). Inoue et al. also report an inability to rescue baseline neuronal activity (Inoue et al., 2001). In our study, the inability to rescue was not due to a glycolytic substrate limitation, as glucose was included in the extracellular recording solution. It is also important to note that the decrease in AP activity and hyperpolarization of V_m did not appear to adversely affect neuronal health, as APs were still present. Interestingly, the hypoxia-induced changes in GABA neurotransmission reported in turtle CNS, in particular the rise in GABA_A receptor number, are maintained for at least 24 h (Lutz and Leone-Kabler, 1995). Thus, the inability of normoxia to rescue the membrane potential and spontaneous action potential firing probably results from the activation of mechanisms that are maintained significantly longer than the hypoxic exposure.

Neuronal intracellular chloride is regulated by the opposing actions of two electroneutral cation-chloride cotransporters: NKCC1 and KCC2. Under physiological conditions NKCC1 transports 1Na⁺:1K⁺:2Cl^- into cells, while KCC2 transports 1K⁺:1Cl^- out. The differential expression of these two transporters is what sets the reversal potential for Cl^- in neurones: when KCC2 dominates [Cl^-]_i is low and GABA is inhibitory, when NKCC1 is dominant [Cl^-]_i is high and GABA is excitatory. Based on the excitatory effects of GABA in these neurones we examined the effects of antagonizing NKCC1 with bumetanide and found a significant decrease in AP firing. This result is consistent with the previous observation that bumetanide rapidly inhibited the spontaneous bursts of individual pyramidal cells from rat hippocampus (Sipila et al., 2006).

Based on the results from the present study we suggest the following mechanism to account for how severe hypoxia depresses neuronal activity: in normoxia NKCC1 maintains high [Cl^-]_i, which renders GABA an excitatory neurotransmitter, since Cl^- would excite the cell when the GABA_A receptor is activated. Severe hypoxia reduces the activity of NKCC1, which results in a decrease in [Cl^-]_i, which in turn decreases the magnitude of the excitatory GABAergic neurotransmission; decreasing excitation through GABA_A receptors would decrease the excitatory drive to the recorded neurones resulting in a hyperpolarization of the resting V_m and, as a result, decreased AP frequency. This proposed mechanism can be tested in the future by: (1) examining the response of isolated Lymnaea neurones in cell culture to severe hypoxia; and (2) demonstrating directly the relationship between GABAergic neurotransmission and NKCC1 regulation of [Cl^-]_i.

	List of abbreviations

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 

GABA

-amino butyric acid

ATP

adenosine triphosphate

P_O2

partial pressure of oxygen

mOsm

milliOsmol

PeDG

pedal ganglia

AP

action potential

V_m

membrane potential

EPSP and IPSP

excitatory and inhibitory synaptic potential

	Acknowledgments

 
This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grants to M.A.W. and L.T.B. We thank Z. P. Feng for providing a seed stock of L. stagnalis.

	References

TOP Summary Introduction Materials and methods Results Discussion List of abbreviations References

 

Alkon, D. L., Sanchez-Andres, J. V., Ito, E., Oka, K., Yoshioka, T. and Collin, C. (1992). Long-term transformation of an inhibitory into an excitatory GABAergic synaptic response. Proc. Natl. Acad. Sci. USA 89,11862 -11866.[Abstract/Free Full Text]

Attwell, D. and Laughlin, S. B. (2001). An energy budget for signaling in the grey matter of the brain. J. Cereb. Blood Flow Metab. 21,1133 -1145.[Medline]

Barnard, E. A., Darlison, M. G., Fujita, N., Glencorse, T. A., Levitan, E. S., Reale, V., Schofield, P. R., Seeburg, P. H., Squire, M. D. and Stephenson, F. A. (1988). Molecular biology of the GABAA receptor. Adv. Exp. Med. Biol. 236, 31-45.[Medline]

Bazhenov, M., Stopfer, M., Rabinovich, M., Abarbanel, H. D., Sejnowski, T. J. and Laurent, G. (2001). Model of cellular and network mechanisms for odor-evoked temporal patterning in the locust antennal lobe. Neuron 30,569 -581.[CrossRef][Medline]

Ben-Ari, Y. (2002). Excitatory actions of gaba during development: the nature of the nurture. Nat. Rev. Neurosci. 3,728 -739.[CrossRef][Medline]

Cazalets, J. R., Cournil, I., Geffard, M. and Moulins, M. (1987). Suppression of oscillatory activity in crustacean pyloric neurons: implication of GABAergic inputs. J. Neurosci. 7,2884 -2893.[Abstract]

de With, N. D. and van der Schors, R. C. (1984). Urine composition and kidney function in the pulmonate freshwater snail Lymnaea stagnalis. Comp. Biochem. Physiol. 79,99 -103.

Delpire, E. (2000). Cation-chloride cotransporters in neuronal communication. News Physiol. Sci. 15,309 -312.[Abstract/Free Full Text]

Feng, Z. C., Sick, T. J. and Rosenthal, M. (1988). Orthodromic field potentials and recurrent inhibition during anoxia in turtle brain. Am. J. Physiol. 255,R485 -R491.[Medline]

Haddad, G. G. and Jiang, C. (1997). O₂-sensing mechanisms in excitable cells: role of plasma membrane K⁺ channels. Annu. Rev. Physiol. 59, 23-42.[CrossRef][Medline]

Harvey, R. J., Vreugdenhil, E., Zaman, S. H., Bhandal, N. S., Usherwood, P. N., Barnard, E. A. and Darlison, M. G. (1991). Sequence of a functional invertebrate GABAA receptor subunit which can form a chimeric receptor with a vertebrate alpha subunit. EMBO J. 10,3239 -3245.[Medline]

Hatakeyama, D. and Ito, E. (2000). Distribution and developmental changes in GABA-like immunoreactive neurons in the central nervous system of pond snail, Lymnaea stagnalis. J. Comp. Neurol. 418,310 -322.[CrossRef][Medline]

Hylland, P. and Nilsson, G. E. (1999). Extracellular levels of amino acid neurotransmitters during anoxia and forced energy deficiency in crucian carp brain. Brain Res. 823, 49-58.[CrossRef][Medline]

Inoue, T., Haque, Z., Lukowiak, K. and Syed, N. I. (2001). Hypoxia-induced respiratory patterned activity in Lymnaea originates at the periphery. J. Neurophysiol. 86,156 -163.[Abstract/Free Full Text]

Ito, I., Kimura, T., Watanabe, S., Kirino, Y. and Ito, E. (2004). Modulation of two oscillatory networks in the peripheral olfactory system by gamma-aminobutyric acid, glutamate, and acetylcholine in the terrestrial slug Limax marginatus. J. Neurobiol. 59,304 -318.[CrossRef][Medline]

Kamardin, N., Szucs, A. and Rozsa, K. S. (1999). Distinct responses of osphradial neurons to chemical stimuli and neurotransmitters in Lymnaea stagnalis L. Cell. Mol. Neurobiol. 19,235 -247.[CrossRef][Medline]

Kim, K. H. and Takeuchi, H. (1990). Pharmacological characteristics of two different types of inhibitory GABA receptors on Achatina fulica neurones. Eur. J. Pharmacol. 182,49 -62.[CrossRef][Medline]

Kyriakides, M., McCrohan, C. R., Slade, C. T., Syed, N. I. and Winlow, W. (1989). The morphology and electrophysiology of the neurones of the paired pedal ganglia of Lymnaea stagnalis (L.). Comp. Biochem. Physiol. 93A,861 -876.[Medline]

Lutz, P. L. (1992). Mechanisms for anoxic survival in the vertebrate brain. Annu. Rev. Physiol. 54,601 -618.[CrossRef][Medline]

Lutz, P. L. and Leone-Kabler, S. L. (1995). Upregulation of the GABAA/benzodiazepine receptor during anoxia in the freshwater turtle brain. Am. J. Physiol. 268,R1332 -R1335.[Medline]

Nilsson, G. E. and Lutz, P. L. (1991). Release of inhibitory neurotransmitters in response to anoxia in turtle brain. Am. J. Physiol. 261,R32 -R37.[Medline]

Nilsson, G. E. and Winberg, S. (1993). Changes in the brain levels of GABA and related amino acids in anoxic shore crab (Carcinus maenas). Am. J. Physiol. 264,R733 -R737.[Medline]

Payne, J. A., Rivera, C., Voipio, J. and Kaila, K. (2003). Cation-chloride co-transporters in neuronal communication, development and trauma. Trends Neurosci. 26,199 -206.[CrossRef][Medline]

Pena, F. and Ramirez, J. M. (2005). Hypoxia-induced changes in neuronal network properties. Mol. Neurobiol. 32,251 -283.[CrossRef][Medline]

Rubakhin, S. S., Szucs, A. and Rozsa, K. S. (1996). Characterization of the GABA response on identified dialysed Lymnaea neurons. Gen. Pharmacol. 27,731 -739.[Medline]

Seisjo, B. K. (1978). Brain Energy Metabolism. New York: Wiley & Sons.

Sipila, S. T., Schuchmann, S., Voipio, J., Yamada, J. and Kaila, K. (2006). The cation-chloride cotransporter NKCC1 promotes sharp waves in the neonatal rat hippocampus. J. Physiol. 573,765 -773.[Abstract/Free Full Text]

Spencer, G. E., Kazmi, M. H., Syed, N. I. and Lukowiak, K. (2002). Changes in the activity of a CpG neuron after the reinforcement of an operantly conditioned behavior in Lymnaea. J. Neurophysiol. 88,1915 -1923.[Abstract/Free Full Text]

Syed, N. I., Bulloch, A. G. and Lukowiak, K. (1990). In vitro reconstruction of the respiratory central pattern generator of the mollusk Lymnaea. Science 250,282 -285.[Abstract/Free Full Text]

Taylor, B. E. and Lukowiak, K. (2000). The respiratory central pattern generator of Lymnaea: a model, measured and malleable. Respir. Physiol. 122,197 -207.[CrossRef][Medline]

Whittington, M. A. and Traub, R. D. (2003). Interneuron diversity series: inhibitory interneurons and network oscillations in vitro. Trends Neurosci. 26,676 -682.[CrossRef][Medline]

Wijsman, T. C. M., van der Lugt, H. C. and Hoogland, H. P. (1985). Anaerobic metabolism in the freshwater snail Lymnaea stagnalis: haemolymph as a reservoir of D-lactate and succinate. Comp. Biochem. Physiol. 81,889 -895.[CrossRef][Medline]

Yarowsky, P. J. and Carpenter, D. O. (1977). GABA mediated excitatory responses on Aplysia neurons. Life Sci. 20,1441 -1448.[CrossRef][Medline]

Zhang, W., Han, X. Y., Wong, S. M. and Takeuchi, H. (1997). Pharmacologic characteristics of excitatory gamma-amino-butyric acid (GABA) receptors in a snail neuron. Gen. Pharmacol. 28,45 -53.[Medline]

Zhu, P. J. and Krnjevic, K. (1994). Anoxia selectively depresses excitatory synaptic transmission in hippocampal slices. Neurosci. Lett. 166,27 -30.[CrossRef][Medline]

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				K. Pfeiffer, I. Panek, U. Hoger, A. S. French, and P. H. Torkkeli Random Stimulation of Spider Mechanosensory Neurons Reveals Long-Lasting Excitation by GABA and Muscimol J Neurophysiol, January 1, 2009; 101(1): 54 - 66. [Abstract] [Full Text] [PDF]

				J. E. Podrabsky, J. P. Lopez, T. W. M. Fan, R. Higashi, and G. N. Somero Extreme anoxia tolerance in embryos of the annual killifish Austrofundulus limnaeus: insights from a metabolomics analysis J. Exp. Biol., July 1, 2007; 210(13): 2253 - 2266. [Abstract] [Full Text] [PDF]

This Article Summary Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cheung, U. Articles by Woodin, M. A. Search for Related Content PubMed PubMed Citation Articles by Cheung, U. Articles by Woodin, M. A. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB OXYGEN Social Bookmarking                         What's this?