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NEUROSCIENCE |
7-containing nicotinic receptors on the vertebrate postsynaptic neurons1 Neurobiology Section, Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357, USA
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Abstract |
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7 gene product and has a high relative permeability to calcium. Both on rodent hippocampal interneurons and on chick ciliary ganglion neurons these 7-nAChRs are often closely juxtaposed to GABAA receptors. We show here that in both cases activation of 7-nAChRs on the postsynaptic neuron acutely down-regulates GABA-induced currents. Nicotine application to dissociated ciliary ganglion neurons diminished subsequent GABAA receptor responses to GABA. The effect was blocked by 7-nAChR antagonists, by chelation of intracellular Ca2+ with BAPTA, and by inhibition of both Ca2+–calmodulin-dependent protein kinase II and mitogen-activated protein kinase. A similar outcome was obtained in the hippocampus where electrical stimulation to activate cholinergic fibres reduced the amplitude of subsequent GABAA receptor-mediated inhibitory postsynaptic currents. The reduction showed the same calcium and kinase dependence seen in ciliary ganglion neurons and was absent in hippocampal slices from 7-nAChR knockout mice. Moreover, 7-nAChR blockade in hippocampal slices reduced rundown of GABAA receptor-mediated whole-cell responses, indicating ongoing endogenous modulation. The results demonstrate regulation of GABAA receptors by 7-nAChRs on the postsynaptic neuron and identify a new mechanism by which nicotinic cholinergic signalling influences nervous system function.
(Received 7 November 2006;
accepted after revision 3 January 2007;
first published online 4 January 2007)
Corresponding author D. K. Berg: Neurobiology Section, Division of Biological Sciences; University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA. Email: dberg{at}ucsd.edu
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Introduction |
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Nicotinic cholinergic transmission is mediated by the transmitter acetylcholine (ACh) acting on nicotinic acetylcholine receptors (nAChRs), which, in vertebrates, are cation-selective ligand-gated ion channels (McGehee & Role, 1995; Margiotta & Pugh, 2004). One of the most abundant is a species composed of 7 subunits which appears early in development and has a high calcium permeability relative to sodium (Bertrand et al. 1993; Seguela et al. 1993; Zhang et al. 1998; Drisdel & Green, 2000; Adams et al. 2002). Numerous studies have identified a presynaptic role for these receptors (7-nAChRs), showing that they enhance transmitter release at a variety of synapses (McGehee et al. 1995; Gray et al. 1996; Alkondon et al. 1997; Guo et al. 1998; Li et al. 1998; Radcliffe & Dani, 1998; Maggi et al. 2001, 2004; Mok & Kew, 2006). Much less is known about possible postsynaptic roles for 7-nAChRs though several studies have identified the receptors at postsynaptic sites (Fabian-Fine et al. 2001; Levy & Aoki, 2002) and have reported postsynaptic 7-nAChR responses (Alkondon et al. 1998; Frazier et al. 1998; Hefft et al. 1999; Hatton & Yang, 2002).
Relatively high levels of 7-nAChRs are found in the hippocampus early in postnatal life (Adams et al. 2002). The receptors cocluster in part with GABAA receptors on filopodia, dendritic shafts, and somatic surfaces of hippocampal interneurons (Liu et al. 2001; Kawai et al. 2002), and the sites appear to become dually innervated by cholinergic and GABAergic fibres (Zago et al. 2006). A similar juxtaposition of 7-nAChRs and GABAA receptors occurs on chick ciliary ganglion (CG) neurons where nicotinic receptors are concentrated on somatic spines (Wilson Horch & Sargent, 1995; Shoop et al. 1999). Recent evidence has identified clusters of GABAA receptors near nAChRs on the cells and has shown that GABAergic terminals contact the neurons, along with the cholinergic fibres (Liu et al. 2006).
We used patch-clamp recordings from dissociated CG neurons and from interneurons in mouse hippocampal slices to examine the acute interactions of 7-nAChRs and GABAA receptors. The results show that activation of 7-nAChRs diminishes subsequent responses from GABAA receptors and that the effect depends on intracellular calcium–calmodulin-dependent protein kinase II (CaMKII), and mitogen-activated protein kinase (MAPK) in the postsynaptic cell. Moreover, spontaneous activation of 7-nAChRs by endogenous cholinergic activity in hippocampal slices has an ongoing tonic effect on GABA responses. These results identify a new modulatory role for 7-nAChRs on the postsynaptic cell.
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Methods |
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C57/BL6 mice of both sexes were used, ranging in age from postnatal day 9–14 (P9–14). All animal procedures performed were in accordance with the institutional guidelines and approved by the UCSD Institutional Animal Care and Use Committee. The animals were anaesthetized with sodium pentobarbital (40 mg (kg body weight)–1). The brains were dissected rapidly, and 300 µm thick hippocampal slices were obtained in ice-cold artificial cerebrospinal fluid (ACSF) using a Vibratome (series 1000, Technical Products International Inc., St Louis, USA). The ACSF was saturated with 95% O2–5% CO2 and contained (mM): NaCl 119, KCl 2.5, CaCl2 2.5, MgSO4 1.3, NaH2PO4 1.0, NaHCO3 26.2 and glucose 11. Slices were maintained in the gas-saturated ACSF at room temperature for at least 1 h before use.
Dissociation of chick CG neurons
CG were isolated from White Leghorn chick embryos at embryonic day 14 (E14) and treated with 1.25 mg ml–1 collagenase in dissection buffer containing (mM): NaCl 136, KCl 3, Hepes 10, glucose 10 (PH 7.4), at 37°C for 8–12 min. After rinsing, ganglia were transferred to Minimum Essential Medium Eagle (MEM, Mediatech, Herndon, VA, USA) with 10% horse serum, 50 U ml–1 penicillin–streptomycin, and 3% embryonic eye extract. Individual neurons were obtained by gentle trituration and plated onto poly D-lysine treated coverslips (Liu & Berg, 1999a; Liu et al. 2006). Cells were used for recording 1–5 h after plating.
Electrophysiology
Whole-cell recordings were obtained from interneurons in the CA1 stratum radiatum (SR) of fresh hippocampal slices as previously described (Zhang et al. 2003). Slices were perfused with gas-saturated ACSF at 2–3 ml min–1 at room temperature. Pipettes were pulled from borosilicate glass capillaries (Sutter Instruments, Novato, CA, USA) with a P-97 pipette puller (Sutter Instruments), and were filled with solution containing (mM): potassium gluconate 120, KCl 30, Hepes 10, Na2-phosphocreatine 10, ATP 4, GTP 0.3 and EGTA 1, and had a resistance of 4–6 M
. In all experiments using hippocampal slices, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) (20 µM), 2-amino-5-phosphonovaleric acid (APV; 50 µM), atropine (2 µM), and edrophonium (100 µM) were included in the ACSF to block AMPA, NMDA, and muscarinic receptors, and acetylcholinesterase, respectively. Synaptic responses were evoked by concentric bipolar tungsten electrodes placed either in the SR or the stratum oriens (SO). GABA was delivered to neurons by positioning the tip of a glass pipette containing GABA over the dendritic fields of SR interneurons, and applying brief pulses of air pressure generated by a Picospritzer (Parker Hannifin Corp., Cleveland, OH, USA). Nicotine was applied similarly but separately. When the effects of gabazine were to be tested on the GABA response, gabazine was applied through the bath perfusion.
For experiments on CG neurons, recordings were performed in a solution containing (mM): NaCl 140, KCl 1, CaCl2 1, Hepes 10, MgCl2 1, glucose 10 and 10% horse serum with the pH adjusted to 7.4. Nicotine and GABA were delivered to the neuron by a large bore multibarrelled applicator (Zhang et al. 1994). Gabazine, when present, was first applied from a separate barrel of the multibarrelled applicator and then with GABA from a different barrel.
In all experiments, neurons were clamped at –70 mV by a MultiClamp 700A amplifier (Molecular Devices, Sunnyvale, CA, USA), and signals were recorded by pCLAMP 9.2 (Molecular Devices). Data were filtered at 2 kHz and sampled at 5 kHz; pipette capacitance and serial resistance were compensated.
Materials
White Leghorn chick embryos were obtained locally and maintained in a humidified incubator. C57/BL6 mice heterozygous for knockout of the 7-nAChR gene were purchased from Jackson Laboratories (Bar Harbor, ME, USA) and used to establish a colony. Wild-type and homozygous knockout pups (determined by PCR analysis of DNA samples) were taken for experiments. Methyllycaconitine (MLA) was purchased from Tocris (Ellisville, MO, USA). All other reagents were purchased from Sigma (St Louis, MO, USA) unless otherwise indicated.
Statistics
Statistical significance was assessed by Student's paired t test or by analysis of variance (ANOVA) as indicated. Data are presented as the mean ± S.E.M.
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Results |
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7-nAChRs
Freshly dissociated E14 chick CG neurons were examined with whole-cell patch-clamp recording techniques to identify acute effects of 7-nAChRs on GABAA receptors. Rapid application of GABA (100 µM) for 1 s induced a fast inward current, and the response could be reproducibly elicited at 1 min intervals (Fig. 1A). Blockade of the GABA-induced current by incubation in the GABAA receptor antagonist gabazine (10 µM) confirmed that the response was mediated by GABAA receptors. Rapid application of nicotine (20 µM) for 2–3 s prior to application of GABA caused a significant reduction in the amplitude of the GABA responses (Fig. 1B). The reduction reversed within 8 s following termination of the nicotine (Fig. 1C). Incubating the neurons in MLA (50 nM) throughout the test prevented the nicotine-induced reduction in the amplitude of GABA-induced currents (1.4 ± 0.3 nA for MLA alone and 1.4 ± 0.3 for MLA + nicotine; mean ±
S.E.M., n
= 8 in each case). MLA at this concentration is a specific inhibitor of 7-nAChRs, indicating that 7-nAChR activation was necessary for the nicotinic effect (Fig. 1D).
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7-nAChR activation influences GABA responses was dissected by intracellular application of specific blockers. Calcium dependence was tested because 7-nAChRs have significant calcium permeability (Bertrand et al. 1993; Seguela et al. 1993). Introducing the calcium chelator BAPTA (11 mM) into the neuron via the recording pipette prevented nicotine application from affecting the GABA response (Fig. 2A). This focused attention on calcium-dependent pathways involving kinases. Infusion of the CaMKII antagonist KN-93 (10 µM) into the neuron via the recording pipette nominally produced partial blockade of the nicotine-induced reduction in GABA responses, but the effect did not reach statistical significance for the number of cells tested. The same was true for infusion of the MAPK antagonist U0126 (10 µM). Combining KN-93 and U0126, however, completely prevented the nicotine-induced effect (Fig. 2A and B). In contrast, KN-92, used as negative control for KN-93, had no effect. Infusing the protein kinase C blocker chelerythrine (10 µM) or the PI3K blocker wortmannin (100 nM) also had no effect, indicating that these kinases were not likely to be involved (Fig. 2B). The results show that activation of 7-nAChRs on CG neurons acts through calcium-dependent pathways involving CaMKII and MAPK to reversibly reduce GABAA receptor responses.
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Hippocampal interneurons have significant numbers of 7-nAChRs coclustered with GABAA receptors on dendrites and filopodia. Whole-cell patch-clamp recordings were performed on interneurons in the SR of the CA1 region of hippocampal slices from P9–14 mice (Fig. 3A). NBQX (20 µM) and APV (50 µM) were applied to block AMPA and NMDA receptors, respectively. Stimulation of the SR with an extracellular concentric bipolar electrode elicited IPSCs in the interneuron (Fig. 3B). The IPSCs were blocked by gabazine (10 µM) as expected for responses generated by GABAA receptors (data not shown). Application of nicotine from a pipette placed about 0.1 mm from the cell body prior to stimulation of the SR caused a reduction in the amplitude of IPSCs elicited subsequently (Fig. 3B). The pipette position was chosen to optimize nicotine application to the dendritic tree and to avoid pressure-induced displacement of the soma. The reduction in IPSC amplitude was reversible, and was completely prevented when the slice was perfused with 50 nM MLA (Fig. 3B and C). The results indicate that activation of 7-nAChRs can reversibly diminish the response of synaptic GABAA receptors that produce the IPSCs.
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Cholinergic projections from the septum reach the SR by projecting through the SO of the CA1. Extracellular stimulation in the SO therefore can be used to release not only GABA from intrinsic GABAergic fibres but also ACh from invading cholinergic fibres (Maggi et al. 2003). To test the effect of cholinergic input on GABA responses, we placed one stimulating electrode in the SR and a second in the SO (Fig. 4A). NBQX, APV, atropine, and edrophonium (100 µM) were included to block AMPA, NMDA and muscarinic receptors, and cholinesterases, respectively. Pairs of IPSCs were elicited in an SR interneuron by stimulating the SO and SR sites 200 ms apart. Gabazine (10 µM) completely blocked the IPSCs, confirming they were generated by activation of GABAA receptors (data not shown). The stimulation protocol routinely employed six sets of paired stimuli at 1 min intervals using one stimulation order (e.g. SO and then SR), followed by another six sets with the stimulation order reversed. This pattern was repeated and yielded consistent results within a set and among sets. When the SO stimulation preceded SR stimulation in the pair, the SR-induced IPSC was smaller than when stimulation was applied in the reverse order (Fig. 4B). No reduction was seen if a delay of 2 s was interposed between the SO and SR pulses, indicating that the effect was transient (data not shown). No reduction was seen in the SO-induced IPSC when SR stimulation preceded SO stimulation (Fig. 4B and C). The results indicate that stimulation in the SO transiently reduces the amplitude of GABAergic IPSCs induced subsequently in SR interneurons.
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7-nAChRs. The first made use of MLA to block 7-nAChRs. In the presence of MLA, SO stimulation had no effect on subsequent SR-elicited IPSCs (Fig. 5A). The second approach employed 7-nAChR knockout mice (Orr-Urtreger et al. 1997). Stimulating the CA1 SO region of hippocampal slices from the knockout mice had no effect on subsequent IPSCs elicited in SR interneurons by stimulation of the SR, in contrast to wild-type (Fig. 5B). The results are consistent with SO stimulation recruiting cholinergic fibres that activate 7-nAChRs on SR interneurons, causing these receptors to produce a transitory reduction in GABAergic IPSC amplitude in the neurons.
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7-nAChRs mediating reduction of hippocampal IPSCs
If activation of 7-nAChRs on the interneuron itself mediates the transient reduction of IPSC amplitude and utilizes the same mechanisms found in CG neurons, one would expect the process to be blocked by calcium chelators and inhibitors of CaMKII and MAPK. Indeed, infusing BAPTA (11 mM) through the recording electrode completely blocked the ability of SO stimulation to reduce the amplitude of IPSCs subsequently evoked in the SR interneuron (Fig. 6A). Similarly, infusing KN-93 (10 µM) plus U0126 (10 µM) completely blocked the effect (Fig. 6B). BAPTA infusion into SR interneurons had no effect in hippocampal slices from 7-nAChR knockout mice (data not shown), thereby excluding the possibility that the protection seen above resulted from a compensatory and independent enhancement of the GABAergic response. The results indicate that, as in CG neurons, a calcium-dependent process involving CaMKII and MAPK mediate the 7-nAChR-dependent reduction of IPSCs in hippocampal interneurons.
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7-nAChRs on the postsynaptic cell was the finding that SO stimulation had no detectable presynaptic effects on GABA release. This was assessed by comparing the paired-pulse ratio for IPSCs in an interneuron elicited by two consecutive stimuli applied to the SR both before and after SO stimulation. Though SO stimulation reduced the amplitude of subsequent SR-elicited IPSCs, it did not change the paired-pulse ratio (Fig. 6C). It should be noted that the experiment would not detect all-or-none effects presynaptically, e.g. blockade of conduction in the presynaptic fibre. The results are clearly consistent, however, with the postsynaptic effect advanced above, namely that stimulation of cholinergic fibres in the SO activates 7-nAChRs on interneurons, turning on calcium-dependent kinase pathways to transiently reduce GABAA receptor responses.
Spontaneous 7-nAChR activity in hippocampal slices
The stimulation experiments described above demonstrate that activation of 7-nAChRs can regulate GABAergic responses. The experiments reported here suggest that spontaneous agonist-induced activation of 7-nAChRs occurs in hippocampal slices and can provide ongoing regulation of GABAA receptor function.
GABA (100 µM) was applied to hippocampal slices from a glass pipette while perfusing the preparation with blockers for AMPA, NMDA and muscarinic receptors, as well as acetylcholinesterase (see above). This procedure elicited GABA-induced responses of consistent amplitude in SR interneurons when spaced at 1 min intervals. In contrast, application of GABA at 10 s intervals produced responses of decreasing amplitude (Fig. 7A). The time course of rundown had a 
-value (decay to 50%) of 10.3 ± 0.6 s (mean ±
S.E.M.; n
= 12 neurons). In the presence of 50 nM MLA to block 7-nAChRs, the -value increased to 14.8 ± 0.9 s (n
= 11; Fig. 7B). The rundown completely reversed within 3–5 min (not shown). Pre-incubation of the slices with 100 nM
-bungarotoxin (Bgt), a slowly reversing antagonist of 7-nAChRs, prevented MLA from altering the time course of inactivation (Fig. 7C). MLA also had no effect on the time course in slices prepared from 7-nAChR knockout mice (Fig. 7C). Lastly, MLA had no detectable effect on isolated single GABA responses (not shown). The results are consistent with spontaneous activation of 7-nAChRs in the slice preparation exerting a low level of GABAA receptor regulation to cause greater use-dependent reversible rundown.
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Discussion |
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7-nAChRs on the postsynaptic cell reversibly inhibit GABAA receptors and do so via calcium influx and activation of CaMKII and MAPK. The inhibition can be seen in autonomic neurons where 7-nAChRs are concentrated on the soma along with GABAA receptors, and on hippocampal interneurons where 7-nAChRs often cocluster with GABAA receptors on dendrites and filopodia. Activation of 7-nAChRs either by application of nicotine or by stimulation of cholinergic fibres reversibly decreases GABAergic IPSC amplitude in hippocampal interneurons. Chronic activation of 7-nAChRs by endogenous agonists appears to depress the ability of the neuron to sustain repeated GABAergic responses. These results identify a new mechanism by which nicotinic cholinergic pathways influence GABAergic signalling and thereby help shape the output of the system.
Freshly dissociated CG neurons provided a useful preparation for studying postsynaptic 7-nAChR effects on GABAA receptors because both receptor types are expressed in relative abundance on the soma and because presynaptic structures can be removed (McEachern et al. 1985; Engisch & Fischbach, 1990; Wilson Horch & Sargent, 1995; Shoop et al. 1999). Synaptic activation of 7-nAChRs is known to produce pronounced calcium influx in CG neurons (Shoop et al. 2001) and activation of both CaMKII and MAPK to drive downstream signalling (Liu & Berg, 1999b; Chang & Berg, 2001). The finding that inhibitors for both CaMKII and MAPK were required to block completely the 7-nAChR effects on GABA-induced currents raises the possibility that the two pathways operate in parallel. Alternatively, the inhibitors may not have had sufficient access to exert complete blockade individually.
The effects of 7-nAChRs on GABAergic IPSCs in hippocampal interneurons were shown both by applying nicotine directly to the cells and by stimulating endogenous cholinergic inputs to the cells. Both procedures reduced the amplitude of the evoked GABAergic IPSCs in SR interneurons. The latter paradigm provided a convenient system for examining mechanism, and revealed that the same components identified in the CG – calcium influx, CaMKII, and MAPK – were operative here, enabling 7-nAChRs to acutely and reversibly diminish the responsiveness of synaptic GABAA receptors. Blockade by the compounds also made unlikely an alternative explanation for the nicotinic effect on IPSCs, namely that activation of 7-nAChRs on distal dendrites might provide a local current shunt reducing the IPSC amplitude recorded in the soma. The blocking agents were effective when applied to the soma, and, moreover, would not themselves be expected to diminish 7-nAChR currents: in other systems these blockers preserve 7-nAChR responses (Liu & Berg, 1999b).
Though a significant fraction of 7-nAChRs on hippocampal interneurons are colocalized with GABAA receptors, the reverse is less true. Some populations of interneurons have few visible 7-nAChR clusters or express an excess of GABAA receptors compared to 7-nAChRs (Zago et al. 2006; Massey et al. 2006). Accordingly, nicotinic stimulation might be expected to have little effect on the whole-cell GABA-induced currents, which combine contributions from synaptic and extrasynaptic receptors. Nonetheless, spontaneous endogenous activation of 7-nAChRs measurably influenced the rate of inactivation observed for a series of closely spaced GABA-induced whole-cell currents. The effect was reversible and not large enough to be apparent when examining isolated single responses. That 7-nAChRs were responsible was demonstrated by showing blockade of the effect with low concentrations of MLA and confirming that MLA had no effect in hippocampal slices pretreated with Bgt to block 7-nAChRs or in slices from 7-nAChR knockout mice. The spontaneous activation of 7-nAChRs could have resulted either from the accumulation of ACh released from cholinergic fibres or from basal levels of choline in the preparation since both serve as agonists for the receptors (Alkondon et al. 1999).
Previous studies have emphasized the importance of presynaptic nicotinic receptors, particularly 7-nAChRs, in modulating GABAergic and glutamatergic transmission in the hippocampus (McGehee et al. 1995; Gray et al. 1996; Alkondon et al. 1997; Guo et al. 1998; Li et al. 1998; Radcliffe & Dani, 1998; Maggi et al. 2001, 2004; Mok & Kew, 2006). It is also clear that 7-nAChRs can contribute directly to postsynaptic responses and elevate intracellular calcium (Alkondon et al. 1998; Frazier et al. 1998; Hefft et al. 1999; Hatton & Yang, 2002; Khiroug et al. 2003). Together these 7-nAChRs can have complex effects, depending on the cell type affected (Ji & Dani, 2000). Globally, spontaneous nicotinic activity can drive giant depolarizing potentials, dependent on excitatory GABA in the developing hippocampus (Maggi et al. 2001; Le Magueresse et al. 2006), and recently it has been found that spontaneous nicotinic activity, via 7-nAChRs in part, drives the conversion of GABA excitation to inhibition during development with consequences for neuronal maturation (Liu et al. 2006).
The effects of 7-nAChRs on GABAergic signalling reported here are different from past reports in constituting a local and acute postsynaptic action that modulates GABAA receptors in a reversible manner. A recent study has demonstrated 7-nAChR responses from SR interneurons using slices from slightly older animals (Chang & Fischbach, 2006). The younger neurons examined here may have even higher levels of 7-nAChRs (Adams et al. 2002). Nicotine application did not induce visible currents in the present experiments presumably because the relatively distal and prolonged application of agonist would have induced little, if any, current in the soma, given the distance and susceptibility of 7-nAChRs to desensitization (Alkondon & Albuquerque, 1993; Zhang et al. 1994). Strong evidence for a postsynaptic site of action for 7-nAChRs in the present experiments came from infusion of blocking agents into the postsynaptic cell, which specifically blocked the 7-nAChR effects elicited by SO stimulation. Though the 7-nAChR-generated currents were too small to detect in the soma, the blockers were apparently able to diffuse into the dendrites and reach the sites where the calcium- and CaMKII/MAPK-dependent modifications of GABA responses would otherwise have occurred. Also supporting a postsynaptic site of 7-nAChR action was the observation that SO stimulation was unable to change the paired-pulse ratio of SR-elicited synaptic responses in the cell, as anticipated for most presynaptic effects. Notably, single SO stimuli were most effective at inducing 7-nAChR-dependent attenuation of SR-elicited IPSC amplitude. High frequency SO stimulation had no effect (data not shown), perhaps because of desensitization or because of a compensatory increase in GABA release mediated by presynaptic 7-nAChRs (Maggi et al. 2003).
The hippocampal experiments reported here were performed on slices from P9–14 animals. Activation of 7-nAChRs by endogenous agonist in P21–35 animals increases IPSC frequencies in SR interneurons (Mok & Kew, 2006). No effect on IPSC frequency was seen in the younger animals (Mok & Kew, 2006), and conversely, we saw no postsynaptic 7-nAChR effect on IPSC amplitude in the older animals (data not shown). The reasons for this are not clear but may reflect differences in the relative weighting of cholinergic input to pre- and postsynaptic 7-nAChRs as a function of age. Nicotine application to hippocampal slices from older animals has been reported to decrease the responsiveness of CA1 pyramidal neurons to GABA application, but the effect was thought to be indirect because no nicotine-induced currents were observed (Yamazaki et al. 2005). As noted above, however, nicotine application may activate nAChRs on pyramidal dendritic projections, which work through local calcium-dependent processes to regulate GABA responses, even though the nicotine-induced currents are not sufficient to be detected in the soma.
The juxtaposition of 7-nAChR clusters and GABAA receptors on developing hippocampal interneurons clearly positions 7-nAChRs for calcium-dependent regulation of GABAergic responses (Kawai et al. 2002; Zago et al. 2006). Finding discrete cholinergic terminals abutting the 7-nAChR clusters suggests focal transmission (Zago et al. 2006), though volume transmission may also contribute to activation (Descarries, 1998; Zoli et al. 1999a). It is striking that this positioning of 7-nAChRs and the potential for GABAA receptor regulation by nicotinic signalling is prominent at a time in postnatal development when spontaneous nicotinic activity drives conversion of GABAergic signalling from excitatory to inhibitory (Liu et al. 2006). The contribution of 7-nAChRs to the GABAergic conversion is qualitatively different and clearly distinct from the effects described here, but the capacity for acute, local regulation of GABAA receptors by 7-nAChRs may be particularly important for constraining GABAergic signalling during such a critical period.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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7 nicotinic cholinergic receptor in rat hippocampal formation. Dev Brain Res 139, 175–187.[Medline]Alkondon M & Albuquerque EX (1993). Diversity of nicotinic acetylcholine receptors in rat hippocampal neurons. I. Pharmacological and functional evidence for distinct structural subtypes. J Pharmacol Exp Ther 265, 1455–1473.
Alkondon M, Pereira EFR & Albuquerque EX (1998). -Bungarotoxin- and methyllycaconitine-sensitive nicotinic receptors mediate fast synaptic transmission in interneurons of rat hippocampal slices. Brain Res 810, 257–263.[CrossRef][Medline]
Alkondon M, Pereira EFR, Barbosa CTF & Albuquerque EX (1997). Neuronal nicotinic acetylcholine receptor activation modulates 
-aminobutyric acid release from CA1 neurons of rat hippocampal slices. J Pharmacol Exp Ther 283, 1396–1411.
Alkondon M, Pereira EFR, Eisenberg HM & Albuquerque EX (1999). Choline and selective antagonists identify two subtypes of nicotinic acetylcholine receptors that modulate GABA release from CA1 interneurons in rat hippocampal slices. J Neurosci 19, 2693–2705.
Bannon AW, Decker MW, Holladay MW, Curzon P, Donnelly-Roberts D, Puttfarcken PS, Bitner RS, Diaz A, Dickenson AH, Porsolt RD, Williams M & Arneric SP (1998). Broad-spectrum, non-opioid analgesic activity by selective modulation of neuronal nicotinic acetylcholine receptors. Science 279, 77–81.
Bertrand D, Galzi JL, Devillers-Thiery A, Bertrand S & Changeux J-P (1993). Mutations at two distinct sites within the channel domain M2 alter calcium permeability of neuronal 7 nicotinic receptor. Proc Natl Acad Sci U S A 90, 6971–6975.
Chang K & Berg DK (2001). Voltage-gated channels block nicotinic regulation of CREB phosphorylation and gene expression in neurons. Neuron 32, 855–865.[CrossRef][Medline]
Chang Q & Fischbach GD (2006). An acute effect of neuregulin 1
to suppress 7-containing nicotinic acetylcholine receptors in hippocampal interneurons. J Neurosci 26, 11295–11303.
Cui C, Booker TK, Allen RS, Grady SR, Whiteaker P, Marks MJ, Salminen O, Tritto T, Butt CM, Allen WR, Stitzel JA, McIntosh JM, Boulter J, Collins AC & Heinemann SF (2003). The 3 nicotinic receptor subunit: a component of -conotoxin MII-binding nicotinic acetylcholine receptors that modulate dopamine release and related behaviors. J Neurosci 23, 11045–11053.
Dani JA (2001). Overview of nicotinic receptors and their roles in the central nervous system. Bio Psychiatry 49, 166–174.[CrossRef]
Descarries L (1998). The hypothesis of an ambient level of acetylcholine in the central nervous system. J Physiol (Paris) 92, 215–220.[CrossRef][Medline]
Drisdel RC & Green WN (2000). Neuronal -bungarotoxin receptors are 7 subunit homomers. J Neurosci 20, 133–139.
Engisch KL & Fischbach GD (1990). The development of ACh- and GABA-activated currents in normal and target-deprived embryonic chick ciliary ganglia. Dev Biol 139, 417–426.[CrossRef][Medline]
Fabian-Fine R, Skehel P, Errington ML, Davies HA, Sher E, Stewart MG & Fine A (2001). Ultrastructural distribution of the 7 nicotinic acetylcholine receptor subunit in rat hippocampus. J Neurosci 21, 7993–8003.
Frazier CJ, Buhler AV, Weiner JL & Dunwiddie TV (1998). Synaptic potentials mediated via -bungarotoxin-sensitive nicotinic acetylcholine receptors in rat hippocampal interneurons. J Neurosci 18, 8228–8235.
Gray R, Rajan AS, Radcliffe KA, Yakehiro M & Dani JA (1996). Hippocampal synaptic transmission enhanced by low concentrations of nicotine. Nature 383, 713–716.[CrossRef][Medline]
Guo J-Z, Tredway TL & Chiappinelli VA (1998). Glutamate and GABA release are enhanced by different subtypes of presynaptic nicotinic receptors in the lateral geniculate nucleus. J Neurosci 18, 1963–1969.
Hatton GI & Yang QZ (2002). Synaptic potentials mediated by 7 nicotinic acetylcholine receptors in supraoptic nucleus. J Neurosci 22, 29–37.
Hefft S, Hulo S, Bertrand D & Muller D (1999). Synaptic transmission at nicotinic acetylcholine receptors in rat hippocampal organotypic cultures and slices. J Physiol 510, 709–716.
Ji D & Dani JA (2000). Inhibition and disinhibition of pyramidal neurons by activation of nicotinic receptors on hippocampal interneurons. J Neurophysiol 83, 2682–2690.
Kawai H, Zago W & Berg DK (2002). Nicotinic 7 receptor clusters on hippocampal GABAergic neurons: regulation by synaptic activity and neurotrophins. J Neurosci 22, 7903–7912.
Khiroug L, Giniatullin R, Klein RC, Fayuk D & Yakel JL (2003). Functional mapping and Ca2+ regulation of nicotinic acetylcholine receptor channels in rat hippocampal CA1 neurons. J Neurosci 23, 9024–9031.
Lambe EK, Olausson P, Horst N, Taylor JR & Aghajanian GK (2005). Hypocretin and nicotine excite the same thalamocortical synapses in prefrontal cortex: correlation with improved attention in rat. J Neurosci 25, 5225–5229.
Laviolette SR & van der Kooy D (2004). The neurobiology of nicotine addiction: bridging the gap from molecules to behaviour. Nat Rev Neurosci 5, 55–65.[CrossRef][Medline]
Le Magueresse C, Safiulina V, Changeux JP & Cherubini E (2006). Nicotine modulation of network and synaptic transmission in the immature hippocampus investigated with genetically modified mice. J Physiol 576, 533–546.
Levin ED, McClernon FJ & Rezvani AH (2006). Nicotinic effects on cognitive function: behavioral characterization, pharmacological specification, and anatomic localization. Psychopharmacol 184, 523–539.[CrossRef][Medline]
Levy RB & Aoki C (2002). 7 nicotinic acetylcholine receptors occur at postsynaptic densities of AMPA receptor-positive and -negative excitatory synapses in rat sensory cortex. J Neurosci 22, 5001–5015.
Li X, Rainnie DG, McCarley RW & Greene RW (1998). Presynaptic nicotinic receptors facilitate monoaminergic transmission. J Neurosci 18, 1904–1912.
Liu QS & Berg DK (1999a). Extracellular calcium regulates responses of both 3- and 7-containing nicotinic receptors on chick ciliary ganglion neurons. J Neurophysiol 82, 1124–1132.
Liu Q-S & Berg DK (1999b). Actin filaments and the opposing actions of CaM kinase II and calcineurin in regulating 7-containing nicotinic receptors on chick ciliary ganglion neurons. J Neurosci 19, 10280–10288.
Liu Y, Ford B, Mann MA & Fischbach GD (2001). Neuregulins increase 7 nicotinic acetylcholine receptors and enhance excitatory synaptic transmission in GABAergic interneurons of the hippocampus. J Neurosci 21, 5660–5669.
Liu Z, Neff RA & Berg DK (2006). Sequential interplay of nicotinic and GABAergic signaling guides neuronal development. Science 314, 1610–1613.
Maggi L, Le Magueresse C, Changeux J-P & Cherubini E (2003). Nicotine activates immature ‘silent’ connections in the developing hippocampus. Proc Natl Acad Sci U S A 100, 2059–2064.
Maggi L, Sher E & Cherubini E (2001). Regulation of GABA release by nicotinic acetylcholine receptors in the neonatal rat hippocampus. J Physiol 536, 89–100.
Maggi L, Sola E, Minneci F, Le Magueresse C, Changeux JP & Cherubini E (2004). Persistent decrease in synaptic efficacy induced by nicotine at Schaffer collateral-CA1 synapses in the immature rat hippocampus. J Physiol 559, 863–874.
Mansvelder HD & McGehee DS (2002). Cellular and synaptic mechanisms of nicotine addiction. J Neurobiol 53, 606–617.[CrossRef][Medline]
Margiotta J & Pugh P (2004). Nicotinic acetylcholine receptors in the nervous system. In Molecular and Cellular Insights to Ion Channel Biology, ed. Maue RA, pp. 269–302. Elsevier, Amsterdam.
Marubio LM, del Mar Arroyo-Jimenez M, Cordero-Erausquin M, Lena C & Le Novere N, de Kerchove d'Exaerde A, Huchet M, Damaj MI, Changeux J-P (1999). Reduced antinociception in mice lacking neuronal nicotinic receptor subunits. Nature 398, 805–810.[CrossRef][Medline]
Massey KA, Zago WM & Berg DK (2006). BDNF up-regulates nicotinic receptor levels on subpopulations of hippocampal interneurons. Mol Cell Neurosci 33, 381–338.[CrossRef][Medline]
McEachern AE, Margiotta JF & Berg DK (1985). GABA receptors on chick ciliary ganglion neurons in vivo and in cell culture. J Neurosci 5, 2690–2695.[Abstract]
McGehee D, Heath MJ, Gelber S & Role LW (1995). Nicotine enhancement of fast excitatory synaptic transmission in CNS by presynaptic receptors. Science 269, 1692–1696.
McGehee DS & Role LW (1995). Physiological diversity of nicotinic acetylcholine receptors expressed by vertebrate neurons. Ann Rev Physiol 57, 521–546.[CrossRef][Medline]
Mok MH & Kew JNC (2006). Excitation of rat hippocampal interneurons via modulation of endogenous agonist activity at the 7 nicotinic ACh receptor. J Physiol 574, 699–710.
Newhouse PA, Potter A & Levin ED (1997). Nicotinic system involvement in Alzheimer's and Parkinson's diseases. Implications for therapeutics. Drugs Aging 11, 206–228.[Medline]
Orr-Urtreger A, Goldner FM, Saeki M, Lorenzo I, Goldberg L, De Biasi M, Dani JA, Patrick JW & Beaudet AL (1997). Mice deficient in the 7 neuronal nicotinic acetylcholine receptor lack -bungarotoxin binding sites and hippocampal fast nicotinic currents. J Neurosci 17, 9165–9171.
Picciotto MR & Zoli M (2002). Nicotinic receptors in aging and dementia. J Neurobiol 53, 641–655.[CrossRef][Medline]
Picciotto MR, Zoli M, Lena C, Bessis A, Lallemand Y, Le Novere N, Vincent P, Pich EM, Brulet P & Changeux J-P (1995). Abnormal avoidance learning in mice lacking functional high-affinity nicotine receptor in the brain. Nature 374, 65–67.[CrossRef][Medline]
Radcliffe KA & Dani JA (1998). Nicotinic stimulation produces multiple forms of increased glutamatergic synaptic transmission. J Neurosci 18, 7075–7083.
Raggenbass M & Bertrand D (2002). Nicotinic receptors in circuit excitability and epilepsy. J Neurobiol 53, 580–589.[CrossRef][Medline]
Saint-Mleux B, Eggermann E, Bisetti A, Bayer L, Machard D, Jones BE, Muhlethaler M & Serafin M (2004). Nicotinic enhancement of the noradrenergic inhibition of sleep-promoting neurons in the ventrolateral preoptic area. J Neurosci 24, 63–67.
Seguela P, Wadiche J, Dineley-Miller K, Dani JA & Patrick JW (1993). Molecular cloning, functional properties, and distribution of rat brain 7: a nicotinic cation channel highly permeable to calcium. J Neurosci 13, 596–604.[Abstract]
Shoop RD, Chang KT, Ellisman MH & Berg DK (2001). Synaptically-driven calcium transients via nicotinic receptors on somatic spines. J Neurosci 21, 771–781.
Shoop RD, Martone ME, Yamada N, Ellisman MH & Berg DK (1999). Neuronal acetylcholine receptors with 7 subunits are concentrated on somatic spines for synaptic signaling in embryonic chick ciliary ganglia. J Neurosci 19, 692–704.
Vernallis AB, Conroy WG & Berg DK (1993). Neurons assemble acetylcholine receptors with as many as three kinds of subunits while maintaining subunit segregation among receptor subtypes. Neuron 10, 451–464.[CrossRef][Medline]
Wilson Horch HL & Sargent PB (1995). Perisynaptic surface distribution of multiple classes of nicotinic acetylcholine receptors on neurons in the chicken ciliary ganglion. J Neurosci 15, 7778–7795.[Abstract]
Yamazaki Y, Jia Y, Hamaue N & Sumikawa K (2005). Nicotine-induced switch in the nicotinic cholinergic mechanisms of facilitation of long-term potentiation induction. Eur J Neurosci 22, 845–860.[CrossRef][Medline]
Zago WM, Massey KA & Berg DK (2006). Nicotinic activity stabilizes convergence of nicotinic and GABAergic synapses on filopodia of hippocampal interneurons. Mol Cell Neurosci 31, 549–559.[CrossRef][Medline]
Zhang X, Liu C, Miao H, Gong Z-H & Nordberg A (1998). Postnatal changes in nicotinic acetylcholine receptor 2, 3, 4, 7 and 2 subunits genes expression in rat brain. Int J Devl Neurosci 16, 507–518.[CrossRef][Medline]
Zhang ZW, Vijayaraghavan S & Berg DK (1994). Neuronal acetylcholine receptors that bind -bungarotoxin with high affinity function as ligand-gated ion channels. Neuron 12, 167–177.[CrossRef][Medline]
Zhang J, Wang HK, Ye CQ, Ge W, Chen Y, Jiang ZL, Wu CP, Poo MM & Duan S (2003). ATP released by astrocytes mediates glutamatergic activity-dependent heterosynaptic suppression. Neuron 40, 971–982.[CrossRef][Medline]
Zoli M, Jansson A, Sykova E, Agnati LF & Fuxe K (1999a). Volume transmission in the CNS and its relevance for neuropsychopharmacology. Trends Pharmacol Sci 20, 142–150.[CrossRef][Medline]
Zoli M, Picciotto MR, Ferrari R, Cocchi D & Changeux J-P (1999b). Increased neurodegeneration during ageing in mice lacking high-affinity nicotine receptors. EMBO J 18, 1235–1244.[CrossRef][Medline]
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2 s *P < 0.05, one-way ANOVA, Dunnett's post hoc test. D, nicotine-induced depression of GABA responses (control) was abolished by the 
SR-IPSC) nicotine application in the absence (top traces) or presence (bottom traces) of 50 nM MLA. C, compiled results (mean ±
S.E.M., n
= 10 neurons) of IPSCs elicited in the presence of nicotine (± MLA) expressed as a fraction of the response in the absence of nicotine. *P < 0.01, Student's t test.
) and absence (
) of 50 nM MLA. Time to 50% depression (