TY - JOUR
T1 - The expression of GABA(A) beta subunit isoforms in synaptic and extrasynaptic receptor populations of mouse dentate gyrus granule cells
AU - Herd, Murray B.
AU - Haythornthwaite, Alison R.
AU - Rosahl, Thomas W.
AU - Wafford, Keith A.
AU - Homanics, Gregg E.
AU - Lambert, Jeremy J.
AU - Belelli, Delia
PY - 2008/2/15
Y1 - 2008/2/15
N2 - The subunit composition of GABA(A) receptors influences their biophysical and pharmacological properties, dictates neuronal location and the interaction with associated proteins, and markedly influences the impact of intracellular biochemistry. The focus has been on alpha and gamma subunits, with little attention given to beta subunits. Dentate gyrus granule cells (DGGCs) express all three beta subunit isoforms and exhibit both synaptic and extrasynaptic receptors that mediate 'phasic' and 'tonic' transmission, respectively. To investigate the subcellular distribution of the beta subunits we have utilized the patch-clamp technique to compare the properties of 'tonic' and miniature inhibitory postsynaptic currents (mIPSCs) recorded from DGGCs of hippocampal slices of P20-26 wild-type (WT), beta(-/-)(2), beta(2N265S) (etomidate-insensitive), alpha(-/-)(1) and delta(-/-) mice. Deletion of either the beta(2) or the delta subunit produced a significant reduction of the tonic current and attenuated the increase of this current induced by the delta subunit-preferring agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). By contrast, mIPSCs were not influenced by deletion of these genes. Enhancement of the tonic current by the beta(2/3) subunit-selective agent etomidate was significantly reduced for DGGCs derived from beta(2N265S) mice, whereas this manipulation had no effect on the prolongation of mIPSCs produced by this anaesthetic. Collectively, these observations, together with previous studies on alpha(-/-)(4) mice, identify a population of extrasynaptic alpha(4)beta(2)delta receptors, whereas synaptic GABA(A) receptors appear to primarily incorporate the beta(3) subunit. A component of the tonic current is diazepam sensitive and is mediated by extrasynaptic receptors incorporating alpha(5) and gamma(2) subunits. Deletion of the beta(2) subunit had no effect on the diazepam-induced current and therefore these extrasynaptic receptors do not contain this subunit. The unambiguous identification of these distinct pools of synaptic and extrasynaptic GABA(A) receptors should aid our understanding of how they act in harmony, to regulate hippocampal signalling in health and disease.
AB - The subunit composition of GABA(A) receptors influences their biophysical and pharmacological properties, dictates neuronal location and the interaction with associated proteins, and markedly influences the impact of intracellular biochemistry. The focus has been on alpha and gamma subunits, with little attention given to beta subunits. Dentate gyrus granule cells (DGGCs) express all three beta subunit isoforms and exhibit both synaptic and extrasynaptic receptors that mediate 'phasic' and 'tonic' transmission, respectively. To investigate the subcellular distribution of the beta subunits we have utilized the patch-clamp technique to compare the properties of 'tonic' and miniature inhibitory postsynaptic currents (mIPSCs) recorded from DGGCs of hippocampal slices of P20-26 wild-type (WT), beta(-/-)(2), beta(2N265S) (etomidate-insensitive), alpha(-/-)(1) and delta(-/-) mice. Deletion of either the beta(2) or the delta subunit produced a significant reduction of the tonic current and attenuated the increase of this current induced by the delta subunit-preferring agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). By contrast, mIPSCs were not influenced by deletion of these genes. Enhancement of the tonic current by the beta(2/3) subunit-selective agent etomidate was significantly reduced for DGGCs derived from beta(2N265S) mice, whereas this manipulation had no effect on the prolongation of mIPSCs produced by this anaesthetic. Collectively, these observations, together with previous studies on alpha(-/-)(4) mice, identify a population of extrasynaptic alpha(4)beta(2)delta receptors, whereas synaptic GABA(A) receptors appear to primarily incorporate the beta(3) subunit. A component of the tonic current is diazepam sensitive and is mediated by extrasynaptic receptors incorporating alpha(5) and gamma(2) subunits. Deletion of the beta(2) subunit had no effect on the diazepam-induced current and therefore these extrasynaptic receptors do not contain this subunit. The unambiguous identification of these distinct pools of synaptic and extrasynaptic GABA(A) receptors should aid our understanding of how they act in harmony, to regulate hippocampal signalling in health and disease.
KW - GENERAL ANESTHETIC ETOMIDATE
KW - AMINOBUTYRIC ACID(A) RECEPTOR
KW - ADULT-RAT BRAIN
KW - A RECEPTOR
KW - TONIC INHIBITION
KW - PHARMACOLOGICAL CHARACTERIZATION
KW - IMMUNOCYTOCHEMICAL DISTRIBUTION
KW - NEUROSTEROID MODULATION
KW - NEURONAL EXCITABILITY
KW - NEUROACTIVE STEROIDS
UR - http://www.scopus.com/inward/record.url?scp=39449099627&partnerID=8YFLogxK
U2 - 10.1113/jphysiol.2007.146746
DO - 10.1113/jphysiol.2007.146746
M3 - Article
C2 - 18079158
SN - 0022-3751
VL - 586
SP - 989
EP - 1004
JO - Journal of Physiology
JF - Journal of Physiology
IS - 4
ER -