J Physiol Volume 509, Number 1, 211-219, May 15, 1998
The Journal of Physiology (1998), 509.1, pp. 211-219
© Copyright 1998 The Physiological Society
Ionotropic and metabotropic activation of a neuronal chloride channel by serotonin and dopamine in the leech Hirudo medicinalis
Declan W. Ali, Stefano Catarsi and Pierre Drapeau
Centre for Research in Neuroscience, McGill University and Montreal General Hospital, Research Institute, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4
Received 9 October 1997; accepted after revision 30 January 1998.
 |
ABSTRACT |
- Cl- channels on the pressure-sensitive (P) neuron in the leech are directly activated by synaptic release of serotonin (5-HT) and are indirectly stimulated by the cAMP second messenger pathway, suggesting an unusual dual regulation of the channels. We have investigated the mode of action of 5-HT and dopamine (DA) on a Cl- channel in adult P cells in culture by recording from cell-attached patches.
- 5-HT increased Cl- channel activity only when included in the recording pipette and not when applied in the bath.
- Pipette or, more effectively, bath application of DA led to an increase in Cl- channel activity. This effect was blocked by the potent and specific dopaminergic (DA1) receptor blocker, SCH-23390.
- The stimulation by DA, but not by 5-HT, was also blocked by the cAMP-dependent protein kinase A (PKA) inhibitor Rp-cAMP and was mimicked by the membrane-permeant cAMP analogue dibutyryl cAMP (db-cAMP).
- Our results show that 5-HT directly gates a Cl- channel that is also activated by DA via the cAMP pathway. This study demonstrates that a ligand-gated channel can be independently operated by another transmitter acting via a second messenger pathway.
|
INTRODUCTION |
The activity of ion channels can be gated by neuroactive substances in two different ways: ionotropically, by the binding of a ligand to a receptor-channel complex or metabotropically, via the production of second messengers. The same ion channel can also be gated by different substances and this also occurs by two different mechanisms. One way is by activation of two distinct modulatory pathways involving second messengers. An example is the S-K+ channel of Aplysia, which is inhibited by 5-HT acting via protein kinase A (PKA) and is activated by the peptide FMRFamide acting via the arachidonic acid cascade (Volterra & Siegelbaum, 1990). A channel can otherwise be affected by two different neuroactive substances when one binds as a ligand to activate a current directly, while the other indirectly alters this current by acting as a neuromodulator. This more common mechanism of neuronal plasticity can affect the postsynaptic responses of the target neurons. For example, glutamate responses can be enhanced by 5-HT (Blank, Zwart, Nijholt & Spiess, 1996), DA (Smith, Lowe, Temkin, Jensen & Hatt, 1995) or insulin (Liu, Brown, Webster, Morrisett & Monaghan, 1995), which act through a variety of second messengers. The modulators therefore change the amplitude of the transmitter-activated synaptic currents without altering channel activity in the absence of their ligand (Cheun & Yeh, 1992; Smith et al. 1995). So far, no examples have been found of an ion channel being regulated both ionotropically and metabotropically.
In P neurons of the leech, synaptic release of 5-HT activates Cl- channels in vivo (Fuchs, Henderson & Nicholls, 1982) and this effect is retained in culture (Drapeau & Sanchez-Armass, 1988). These channels have been reported to be directly activated by 5-HT in patches isolated from cultured, embryonic neurons; furthermore, dialysis of the cells, inhibition of G proteins or blocking of phosphorylation processes failed to reduce channel activation by 5-HT (Lessmann & Dietzel, 1995a). In contrast, voltage-clamp recordings from adult P cells have shown that activation of PKA mimics the actions of 5-HT on Cl- currents and non-specific inhibitors of PKA block the effects of 5-HT (Sanchez-Armass, Merz & Drapeau, 1991). These results have led to ambiguity concerning the mode of action of 5-HT but they also suggest the possibility of a novel, dual activation of the channels by PKA on the one hand and 5-HT on the other. Interestingly DA, another biogenic amine, is capable of hyperpolarizing the P cell (Sargent, King-Wai & Nicholls, 1977), possibly by the activation of Cl- channels. Moreover, both DA and 5-HT were speculated to bind to the same receptors in the leech (Leake & Walker, 1980). Here we investigated the dual actions of 5-HT and DA on single Cl- channels recorded from adult P cells in culture.
|
METHODS |
Cultures
P cells were isolated from the leech Hirudo medicinalis (Ricarimpex, Audenge, France) and cultured as previously described (Dietzel, Drapeau & Nicholls, 1986). Briefly, desheathed ganglia were exposed to collagenase (1 mg ml-1, Type XI, Sigma Chemical Co.) and the cell bodies of the easily identifiable P neurons were removed by aspiration into a micropipette. P neurons were plated for 3-5 days in the wells of polylysine-coated microtest culture dishes containing Leibovitz-15 medium supplemented with 0·2 mg ml-1 gentamicin, 0·1 mg ml-1 ampicillin and 2 % heat-inactivated fetal bovine serum (Gibco Canada).
Solutions
For cell-attached patch-clamp recordings (Hamill, Marty, Neher, Sakmann & Sigworth, 1981), the culture medium was replaced with a 'normal recording solution' containing (mM): NaCl, 155; KCl, 5; MgCl2, 1; CaCl2, 1; glucose, 10; Hepes, 10; brought to pH 7·4 with NaOH, with a resultant osmolarity of 330 mosmol l-1. The recordings were performed in 10 µl wells of NUNC microtest dishes (Gibco Laboratories, USA). Test solutions were added by ejection of 1 µl of a 10-fold concentrated solution to give the final concentration described in the text. In order to isolate the Cl- current, the pipette solution contained (mM): MgSO4, 245; glucose, 10; Hepes, 10; brought to pH 7·4 with N-methyl-D-glucamine, with a resultant osmolarity of 330 mosmol l-1. In experiments designed to determine the current-voltage relationship, 8·25 mM MgSO4 was replaced with MgCl2. DA, 5-HT and, dibutyril cyclic AMP (db-cAMP) were obtained from Sigma, while Rp-cyclic AMP and SCH-23390 were obtained from Research Biochemicals Inc.
Recordings
Neurons were patch clamped using 5-10 M
electrodes coated to within 50 µm of the tip with dental wax and filled with pipette solution. Seal resistances were typically in the range of 5-10 G. Recordings were made using an Axopatch-1D patch clamp (Axon Instruments) and were low-pass filtered at 2 kHz (-3 dB). This was the minimal level of filtration that allowed us to resolve the events. The data were digitized at 10 kHz (Neuro Data Instruments Corp., New York) and stored on video tape for off-line analysis. Analysis of the experiments was performed using the pCLAMP 5 and 6 programs (Axon Instruments). Except for the lower trace in Fig. 1A, all traces shown were filtered further at 1 kHz.
Statistics
Data were reported as means ± S.E.M. The significance of the effects among different treatments was tested using a one-way ANOVA followed by the Fisher's least significance difference (LSD) post hoc test. Student's one-tailed paired t tests were used to determine the significance of channel open probability (Po) before and after application of a drug.
|
RESULTS |
In order to isolate the Cl- channel activity during our recordings, we used a pipette solution containing MgSO4 (see Methods) because under these conditions inward currents are carried only by Cl- flowing from the cell into the pipette. Figure 1A shows a typical recording at two different time scales of spontaneous Cl- channel activity (i.e. in the absence of ligands) consisting of infrequent, brief and small inward current transients. Because of the low rate of events and the limited duration (typically 10-15 min) of the recordings before rupturing of the patch, we were able to obtain enough spontaneous openings at only one potential for the analysis of channel amplitude and open time duration. A mean amplitude of 1·2 pA was determined from a single Gaussian fit to the amplitude distributions (Fig. 1B). As shown in Fig. 1C , the single-channel dwell-time distribution was fitted with a single exponential with a time constant of 0·2 ms. This value is at the limit of detection under our recording conditions and therefore many events have been missed due to filtering of the small current transients.
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 1. Spontaneous activity of a Cl- channel recorded in a P cell-attached patch
Top trace in A is a representative current trace (2 s duration) of the 20 pS Cl- channel. A potential of 60 mV was applied to the pipette. Shorter events appear smaller due to filtering at 1 kHz. Bottom trace in A is a 40-fold expansion of the above trace filtered at 2 kHz showing that the openings are now better resolved. The drawing in the inset of this and other figures represents the experimental configuration. B, amplitude histogram of single openings from the same patch. The smooth curve is the Gaussian fit to the data, assuming a mean amplitude of -1·2 pA and a standard deviation of 0·3 pA. C, dwell-time histogram of openings. The smooth curve is a single exponential fit to the data assuming an open time constant of 0·2 ms (filtered at 2 kHz).
|
5-HT activation of Cl- channels
5-HT was either bath applied or included in the recording pipette in cell-attached patches in order to investigate the mode of action of 5-HT on P cell Cl- channels. We found that bath application of 100 µM 5-HT resulted in only a 1·4 ± 0·2-fold increase in Cl- channel activity, which was not significantly different from the basal level of activity (P = 0·18, n = 7) (Figs 2A and 3). Outside-out patches from adult P cells were unstable and this prevented a direct demonstration of Cl- channel gating by 5-HT. When 5-HT was included in the recording pipette, the basal activity of the channels was significantly higher than that obtained without 5-HT in the pipette (4·2 ± 2·0, P = 0·002, n = 8; Figs 2B and 3). The channel had a similar current amplitude and mean open time to those seen in the absence of 5-HT, confirming a direct gating of the Cl- channel as described previously for outside-out patch recordings in embryonic neurons (Lessmann & Dietzel, 1995a). Sometimes a larger Cl- conductance was also detected, as shown by Lessmann & Dietzel (1995a), but because these channels were rarely seen in the absence of 5-HT and were reported to desensitize, we did not investigate their properties further.
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 2. Effect of 5-HT on Cl- channel activity
A, 5 s current traces recorded before (left) and after (right) bath application of 100 µM 5-HT indicated by the arrow. 5-HT did not significantly alter the mean open probability of the Cl- channel. The values for Po and mean open time were, respectively, 0·00039 and 0·90 ms for the control period and 0·00044 and 0·82 ms after application of 5-HT. B, 10 s current trace recorded in an experiment carried out with 100 µM 5-HT in the recording pipette. Note the high level of channel activity throughout the recording. The values for Po and mean open time were 0·02185 and 0·65 ms.
|
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 3. Effect of 100 µM 5-HT or 200 µM db-cAMP, in the presence and absence of 100 µM Rp-cAMP, on Cl- channel activity
Po/Po,control represents the mean ratio between the open probabilities calculated after and before the treatment for each experiment performed with bath application of the drugs (black columns). The number of experiments is indicated above each S.E.M. line. Note that 5-HT had an effect on Po/Po,control only when included in the recording pipette and this effect was not blocked by Rp-cAMP. Asterisks denote values that are significantly different (P < 0·05) from basal levels (indicated by the dashed line).
|
Previous studies (Drapeau & Sanchez-Armass, 1989; Sanchez-Armass et al. 1991) suggested that the cAMP signalling pathway may mediate the action of 5-HT on the Cl- channels. In order to test for a possible role for cAMP, 200 µM of the membrane-permeable cAMP analogue db-cAMP was bath applied to P cells. This resulted in a significant (P = 0·013) increase in Cl- channel activity of 12·4 ± 4·3-fold (n = 7) without a change in mean open time (Fig. 3). This large increase in activity permitted us to estimate the channel conductance by measuring the current amplitude over a range of voltages. As shown in Fig. 4, the slope conductance was approximately 20 pS. Also shown in Fig. 4 are currents measured under control conditions and in the presence of 5-HT in other patches, as described above. The low level of activity under these latter conditions prevented us from measuring the current amplitudes at more than one potential. These latter values resemble the current amplitude seen upon application of db-cAMP at the same potential, consistent with activation of the same Cl- channels. Pretreatment of the cells for at least 20 min with the specific PKA inhibitor Rp-cAMP (100 µM) (Botelho, Rothermel, Coombs & Jastorff, 1988; Wang, Salter & MacDonald, 1991; Trudeau, Emery & Haydon, 1996; Obrietan & van den Pol, 1997) in the bath blocked the effect of db-cAMP as shown in Fig. 3 but not the effect of 5-HT when it was applied in the recording pipette (P = 0·19, n = 7) (Fig. 3), confirming that 5-HT does not activate the cAMP second messenger pathway.
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 4. Current-voltage relationship for the Cl- channel
The channel current amplitudes for recordings in the absence of drug (control) and under different treatments were plotted as a function of the holding potential. Depolarization represents hyperpolarization of the pipette potential, and downward current steps are inward currents relative to the membrane. Current amplitudes were measured from the means of Gaussian distributions for event histograms obtained at each potential. The fit was a linear regression for a slope conductance of 19·6 pS (correlation coefficient of 0·99).
|
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 5. Effect of bath application of DA on Cl- channel activity
A, 5 s current traces recorded before (left) and after (right) bath application of 100 µM DA indicated by the arrow. DA significantly increased the mean open probability of the Cl- channel. B, continuous time histogram of the experiment depicted in A showing Po calculated in bins of 1 s duration. The values for Po and mean open time were, respectively, 0·00072 and 0·62 ms for the control period and 0·00860 and 0·50 ms after application of DA.
|
DA activation of Cl- channels
Because DA hyperpolarizes the P cell (Sargent et al. 1977), possibly by increasing a Cl- conductance, and since 5-HT and DA may bind to the same receptor (Leake & Walker, 1980), we tested the effect of bath application of DA on Cl- channel activity in cell attached patches. Interestingly, we found that bath application of 100 µM DA (n = 8) resulted in a 12·0 ± 5·6-fold increase in channel activity (P = 0·03, n = 8; Figs 5 and 7) of a channel with similar conductance (Fig. 4) and mean open time to the Cl- channel described above. The effect of DA was dependent upon the concentration because a lower concentration (50 µM) led to only a 4·3 ± 1·5-fold increase in channel activity (n = 6; Fig. 7). In order to examine whether DA bound to a dopaminergic receptor, 50 µM of the specific DA1 receptor blocker SCH-23390 (Sidhu, van Oene, Dandridge, Kaiser & Kebabian, 1986; Ali & Orchard, 1994) was tested for its ability to block the effects of 100 µM DA (Fig. 7). In the presence of SCH-23390, DA elicited only a 2·0 ± 0·5-fold increase in activity, a result significantly different from the one obtained when DA was applied alone (P = 0·046, n = 5). Furthermore, 100 µM Rp-cAMP significantly blocked the effect of bath application of 100 µM DA (P = 0·039, n = 5; Fig. 7).
When 100 µM DA was included in the recording pipette there was a gradual increase in channel activity of 4·1 ± 2·1-fold (P = 0·014, n = 9; Fig. 6), which was blocked by bath application of 100 µM Rp-cAMP (P = 0·031, n = 5; Fig. 7). Interestingly this suggests that Cl- channels can be activated via cAMP upon DA binding to nearby receptors.
In a few cases (n = 3) we included 5-HT in the pipette and waited until the increased activity was stable: then we bath applied DA and obtained an additional 2·7 ± 0·4-fold increase of the activity. This effect rather than being additive is much smaller than that obtained when DA was bath applied alone (12·0 ± 5·6). This suggests that 5-HT and DA operate on the same Cl- channels rather than activating two distinct populations of Cl- channels.
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 6. Effect of DA in the pipette on Cl- channel activity
A, 5 s current traces recorded in the first 60 s (left) and afterwards (right) in an experiment carried out with 100 µM DA in the recording pipette. Note the higher level of channel activity in the current trace on the right. B, continuous time histogram of the experiment depicted in A showing Po calculated in bins of 1 s duration. The values for Po and mean open time were 0·00039 and 0·68 ms for the first 60 s and 0·00127 and 0·76 ms after the first 60 s.
|
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 7. Effect of DA in the presence or absence of the D1 receptor blocker SCH-23390 (50 µM) or Rp-cAMP (100 µM) on Cl- channel activity
Note that, in contrast to 5-HT, DA increased Po/Po,control when applied to the bath and in the recording pipette. Its effect was blocked by both SCH-23390 and Rp-cAMP. Asterisks denote values that are significantly different from basal levels (indicated by the dashed line).
|
|
DISCUSSION |
The 20 pS channel that we have studied resembles the 13 pS Cl- channel described by Lessmann & Dietzel (1995a). The discrepancy between the two conductances is possibly due to the fact that those authors studied embryonic neurons while we have recorded from adult identified P cells. In addition, differences in recording solutions (saline in their study and MgSO4 here) would also have led to slightly different results. We found that 5-HT was able to rapidly increase the activity of single Cl- channels when included in the recording pipette but not when applied in the bath. This confirms a direct gating of the channel as reported previously by Lessmann & Dietzel (1995a) and is consistent with the observation of spontaneous miniature synaptic events at the synapse between serotonergic Retzius neurons and the P cell (Henderson, Kuffler, Nicholls & Zhang, 1983). 5-HT is a common neuromodulator which binds to an ionotropic receptor and to several types of metabotropic receptors (Peroutka, 1993). The latter include 5-HT1A receptors which activate the cAMP signalling pathway.
Our results also confirmed a role for cAMP in mimicking the effect of 5-HT. Although Rp-cAMP blocked the effect of db-cAMP, it was unable to block the effect induced by 5-HT included in the recording pipette. An activation of the 5-HT-induced Cl- current by PKA was suggested by previous voltage-clamp experiments performed on adult P cells in culture (Drapeau & Sanchez-Armass, 1989; Sanchez-Armass et al. 1991). This assumption was based on the fact that db-cAMP and forskolin activated a Cl- current while tolbutamide and H8, poorly selective antagonists of PKA, were able to block the effect of 5-HT. More recently whole-cell and outside-out recordings on embryonic leech neurons confirmed a role for cAMP in the activation of Cl- channels but 5-HT did not appear to act through second messengers; 5-HT-activated Cl- currents were in fact observed in outside-out patches for more than half an hour and after dialysing the cell for up to 2 h with GDP-
-S, a G protein inhibitor, or with AMP-PNP, a non-hydrolysable analogue of ATP (Lessmann & Dietzel, 1995a). The lack of effect of these more specific antagonists of phosphorylation processes rule out an indirect effect of 5-HT on the channels. Thus we have investigated the possibility that other endogenous neurotransmitters might modulate the activity of the Cl- channels via cAMP. Similar to glutamate and GABA receptors, the 5-HT3 receptor, which is a ligand-gated channel, is also regulated by intracellular signals. For example manipulations that are known to elevate cAMP levels lead to an accelerated rate of desensitization in mouse hippocampal cultures (Yakel & Jackson, 1988) and activation of PKC decreases the current amplitude of a 5-HT-induced current in a mouse hippocampus neuroblastoma cell line (Glitsch, Wischmeyer & Karschin, 1996).
We found that DA was able to induce an increase in Cl- channel activity when either bath applied or included in the recording pipette. Several lines of evidence suggest that DA is capable of modulating the activity of these Cl- channels via cAMP. First, application of 100 µM and, to a lesser extent, 50 µM DA outside the recording pipette led to an enhanced level of channel activity in cell-attached patches, suggesting the role of a cytoplasmic messenger. Secondly, the selective, membrane-permeable inhibitor of PKA Rp-cAMP (Botelho et al. 1988; Wang et al. 1991; Trudeau et al. 1996; Obrietan & van den Pol, 1997) blocked the increase of Cl- channel activity induced by DA. Thirdly, the specific DA1 receptor blocker SCH-23390 was capable of blocking the effects of DA on the Cl- channel, and in both vertebrates and invertebrates the DA1 receptor appears to activate the cAMP second messenger system (Sidhu et al. 1986; O'Boyle & Waddington, 1987; Ali & Orchard, 1994). Finally, the significant gradual increase in Cl- channel activity due to DA included in the pipette was also blocked by bath application of Rp-cAMP.
Although increased levels of cAMP result in an increase in channel activity, we have not determined the final components of the transduction mechanism. It is possible that PKA acts directly on the Cl- channels or on other proteins which in turn activate the channel. The functional significance of this type of mechanism in the leech is yet to be determined, although dopaminergic neurons have been described in leech ganglia (Stuart, Hudspeth & Hall, 1974).
Several lines of evidence suggest that the same Cl- channel is present throughout all our experiments: (a) the conductance was approximately 20 pS (Fig. 4); (b) the mean open time did not appear to vary; and (c) the effect of bath application of DA was much smaller when 5-HT was included in the pipette (
3-fold compared with 12-fold). Together these results suggest an activation of the same channels by the two transmitters rather than the activation of two different populations of channels.
Our results suggest that, in the absence of 5-HT, DA increases the activity of an ionotropic Cl- channel, which can be directly-gated by 5-HT, in adult leech P neurons in culture (Fig. 8). The dopaminergic receptors, the transduction mechanism and the Cl- channels appear to be in very close proximity since DA in the recording pipette resulted in an increase in Cl- channel activity. PKA is known to be anchored to the membrane in mammalian neurons by A-kinase-anchoring proteins (Scott & McCartney, 1994). If this also occurs in the P cell, we hypothesize that dopaminergic signalling may occur by activation of a macromolecular complex containing the receptor, PKA and the channel. Interestingly, a non-synaptic cation channel in the P cell is thought to be tightly associated with a tyrosine phosphatase (Catarsi & Drapeau, 1997) and tyrosine phosphatases are also thought to be tightly associated with Aplysia bag cell neuron cation channels (Wilson & Kaczmarek, 1993) and NMDA receptors in mammalian neurons (Wang, Yu & Salter, 1996). These observations raise the interesting possibility that second messenger signalling may commonly occur in macromolecular assemblies that include the channel as an efficient means for spatial and temporal regulation of channel activity. To confirm that PKA is associated with the Cl- channels, cAMP should increase their activity when applied in excised, inside-out patches. Unfortunately, we were unable to record from patches in these conditions since the large voltage that had to be applied to resolve the small openings in the absence of the resting potential rendered the patches unstable.
|
 |
View larger version
[in this window]
[in a new window] |
|
|
Figure 8. A model for the mode of action of 5-HT and DA on the Cl- channel
5-HT directly gates the Cl- channel while DA binds to receptors that activate adenylate cyclase. Production of cAMP activates in turn PKA, which then leads to an increase in Cl- channel activity.
|
For the P cell we propose a mechanism through which a neuromodulator (DA), acting via a second messenger (cAMP), activates a channel which is also directly operated by another neurotransmitter (5-HT). Our observation of a dual activation of the Cl- channel suggests a novel regulatory mechanism for the convergence of neurotransmitter actions. In addition to being the target for neuromodulatory and synaptic actions of DA and 5-HT, respectively, the Cl- channels may be regulated by additional mechanisms. Our observation that tolbutamide and H8 can suppress the Cl- current activated by 5-HT (Sanchez-Armass et al. 1991) suggests that a basal level of Cl- channel phosphorylation (in the absence of DA) may be necessary for its normal functioning, and perhaps also for spontaneous activity. Moreover, intracellular calcium has been reported to potentiate the actions of 5-HT (Lessmann & Dietzel, 1995b), suggesting yet another level of regulation. The Cl- channels thus appear to be the target for diverse modulatory mechanisms as well as for the synaptic actions of 5-HT and may be a crucial locus for the regulation of activity in the P cell.
|
REFERENCES |
Ali, D. W. & Orchard, I. (1994). Characterization of dopamine and 5-HT receptors on the salivary glands of the locust, Locusta migratoria. Biogenic Amines 10, 195-212.
Blank, T., Zwart, R., Nijholt, I. & Spiess, J. (1996). 5-HT2 receptor activation potentiates N-methyl-D-aspartate receptor-mediated ion currents by a protein kinase C-dependent mechanism. Journal of Neuroscience Research 45, 153-160.
[Medline]
Botelho, L. H., Rothermel, J. D., Coombs, R. V. & Jastorff, B. (1988). cAMP analog antagonists of cAMP action. Methods in Enzymology 159, 159-172.
[Medline]
Catarsi, S. & Drapeau, P. (1997). Requirement for tyrosine phosphatase during serotonergic neuromodulation by protein kinase C. Journal of Neuroscience 17, 5792-5797.
[Abstract/Full Text]
Cheun, J. E. & Yeh, H. H. (1992). Modulation of GABAA receptor-activated current by norepinephrine in cerebellar Purkinje cells. Neuroscience 51, 951-960.
[Medline]
Dietzel, I. D., Drapeau, P. & Nicholls, J. G. (1986). Voltage dependence of 5-hydroxytryptamine release at a synapse between identified leech neurons in culture. The Journal of Physiology 372, 191-205.
[Abstract]
Drapeau, P. & Sanchez-Armass, S. (1988). Selection of postsynaptic 5-HT receptors during reinnervation of an identified leech neuron in culture. Journal of Neuroscience 8, 4718-4727.
[Abstract]
Drapeau, P. & Sanchez-Armass, S. (1989). Parallel processing and selection of the responses to 5-HT during innervation of an identified leech neuron. Journal of Neurobiology 20, 312-325.
[Medline]
Fuchs, P. A., Henderson, L. P. & Nicholls, J. G. (1982). Chemical transmission between individual Retzius and sensory neurones of the leech in culture. The Journal of Physiology 323, 195-210.
[Abstract]
Glitsch, M., Wischmeyer, E. & Karschin, A. (1996). Functional characterization of two 5-HT3 receptor splice variants isolated from a mouse hippocampal cell line. Pflügers Archiv 432, 134-143.
[Medline]
Hamill, O. P., Marty, A., Neher, E., Sakmann, B. & Sigworth, F. J. (1981). Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflügers Archiv 391, 85-100.
[Medline]
Henderson, L. P., Kuffler, D. P., Nicholls, J. G. & Zhang, R. J. (1983). Structural and functional analysis of synaptic transmission between identified leech neurones in culture. The Journal of Physiology 340, 347-358.
[Abstract]
Leake, L. D. & Walker, R. J. (1980). Invertebrate Neuropharmacology, pp. 172-174. Halsted Press (John Wiley & Sons), New York.
Lessmann, V. & Dietzel, I. D. (1995a). Two kinetically distinct 5-hydroxytryptamine-activated Cl- conductances at Retzius P-cell synapses of the medicinal leech. Journal of Neuroscience 15, 1496-1505.
[Abstract]
Lessmann, V. & Dietzel, I. D. (1995b). Enhancement of postsynaptic serotonin-activated Cl- currents by depolarization-induced Ca2+ entry into leech neurons. Neuroscience 67, 525-529.
[Medline]
Liu, L., Brown, J. C. III, Webster, W. W., Morrisett, R. A. & Monaghan, D. T. (1995). Insulin potentiates N-methyl-D-aspartate receptor activity in Xenopus oocytes and rat hippocampus. Neuroscience Letters 192, 5-8.
[Medline]
O'Boyle, K. M. & Waddington, J. L. (1987). [3H]SCH-23390 binding to human putamen D1 dopamine receptors: Stereochemical and structure affinity relationships among 1-phenyl-1H-3-benzapine derivatives as a guide to D1 receptor topography. Journal of Neurochemistry 48, 1039-1042.
[Abstract]
Obrietan, K. & van den Pol, A. N. (1997). GABA activity mediating cytosolic Ca2+ rises in developing neurons is modulated by cAMP-dependent signal transduction. Journal of Neuroscience 17, 4785-4799.
[Abstract/Full Text]
Peroutka, S. J. (1993). 5-Hydroxytryptamine receptors. Journal of Neurochemistry 60, 408-416.
[Medline]
Sanchez-Armass, S., Merz, D. C. & Drapeau, P. (1991). Distinct receptors, second messengers and conductances underlying the dual responses to 5-HT in an identified leech neurone. Journal of Experimental Biology 155, 531-547.
[Abstract]
Sargent, P. B., King-Wai, Y. & Nicholls, J. G. (1977). Extrasynaptic receptors on cell bodies of neurons in central nervous system of the leech. Journal of Neurophysiology 40, 446-452.
[Medline]
Scott, J. D. & McCartney, S. (1994). Localization of A-kinase through anchoring proteins. Molecular Endocrinology 8, 5-11.
[Medline]
Sidhu, A., van Oene, J. C., Dandridge, P., Kaiser, C. & Kebabian, J. W. (1986). [125I]SCH-23390: The ligand of choice for identifying the D1 dopamine receptor. European Journal of Pharmacology 128, 213-220.
[Medline]
Smith, D. O., Lowe, D., Temkin, R., Jensen, P. & Hatt, H. (1995). Dopamine enhances glutamate-activated currents in spinal motoneurons. Journal of Neuroscience 15, 3905-3912.
[Abstract]
Stuart, A. E., Hudspeth, A. J. & Hall, Z. W. (1974). Vital staining of specific monoamine-containing cells in the leech nervous system. Cell and Tissue Research 153, 55-61.
[Medline]
Trudeau, L., Emery, D. G. & Haydon, P. G. (1996). Direct modulation of the secretory machinery underlies PKA-dependent synaptic facilitation in hippocampal neurons. Neuron 17, 789-797.
[Medline]
Volterra, A. & Siegelbaum, S. A. (1990). Opposing modulation of S-K+ channel activity by cyclic AMP and arachidonic acid metabolites. Progress in Clinical and Biological Research 334, 323-338.
[Medline]
Wang, L. Y., Salter, M. W. & MacDonald, J. F. (1991). Regulation of kainate receptors by cAMP-dependent protein kinase and phosphatases. Science 253, 1132-1135.
[Medline]
Wang, Y. T., Yu, X.-M. & Salter, M. W. (1996). Ca2+-independent reduction of NMDA channel activity by protein tyrosine phosphatase. Proceedings of the National Academy of Sciences of the USA 93, 1721-1725.
[Abstract]
Wilson, G. F. & Kaczmarek, L. K. (1993). Mode-switching of a voltage-gated cation channel is mediated by a protein kinase A-regulated tyrosine phosphatase. Nature 366, 433-438.
[Medline]
Yakel, J. L. & Jackson, M. B. B (1988). 5-HT3 receptors mediate rapid responses in cultured hippocampus and a clonal cell line. Neuron 1, 615-621.
[Medline]
Acknowledgements
This research was supported by Postdoctoral Fellowships from NSERC (D. W. A), the MRC of Canada (S. C.), an FRSQ Senior Research Scholarship and an MRC Operating Grant (P. D.).
Corresponding author
P. Drapeau: Department of Neurology, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4.
Email: mcpd{at}musica.mcgill.ca
D. W. Ali and S. Catarsi contributed equally to this work.
This article has been cited by other articles:
|
|
|
|
 
K. M. Crisp and K. A. Mesce
Beyond the central pattern generator: amine modulation of decision-making neural pathways descending from the brain of the medicinal leech
J. Exp. Biol.,
May 1, 2006;
209(9):
1746 - 1756.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. T. Mukai, L. Kiehn, and A. S. M. Saleuddin
Dopamine stimulates snail albumen gland glycoprotein secretion through the activation of a D1-like receptor
J. Exp. Biol.,
June 15, 2004;
207(14):
2507 - 2518.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Scuri, R. Mozzachiodi, and M. Brunelli
Activity-Dependent Increase of the AHP Amplitude in T Sensory Neurons of the Leech
J Neurophysiol,
November 1, 2002;
88(5):
2490 - 2500.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. A. Mesce, K. M. Crisp, and L. S. Gilchrist
Mixtures of Octopamine and Serotonin Have Nonadditive Effects on the CNS of the Medicinal Leech
J Neurophysiol,
May 1, 2001;
85(5):
2039 - 2046.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. D. Burrell, C. L. Sahley, and K. J. Muller
Non-Associative Learning and Serotonin Induce Similar Bi-Directional Changes in Excitability of a Neuron Critical for Learning in the Medicinal Leech
J. Neurosci.,
February 15, 2001;
21(4):
1401 - 1412.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Eghbali, P. W. Gage, and B. Birnir
Pentobarbital Modulates gamma -Aminobutyric Acid-Activated Single-Channel Conductance in Rat Cultured Hippocampal Neurons
Mol. Pharmacol.,
September 1, 2000;
58(3):
463 - 469.
[Abstract]
[Full Text]
|
|
|
Top
Introduction
