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Fast non-cholinergic depolarizing postsynaptic potentials in neurons of rat superior cervical ganglia
Neuroscience Letters, 78 (1987) 51 56 Elsevier Scientific Publishers Ireland Ltd.
51
NSL 04592
Fast non-cholinergic depolarizing postsynaptic potentials in neurons of rat superior cervical ganglia Daniel E u g e n e Lahoratoire ¢k" Cytologic, Universitt; Pierre et Marie Curie, lnstitut des Neurosciences, UA C.N.R.S. 1/99. Paris (France) (Received 8 December 1986; Revised version received 2 February 1987: Accepted 3 February' I9871 Key word~'.
Non-cholinergic neurotransmission: Postsynaptic potential; Bicuculline: Sympathetic neuron: Superior cervical ganglion: Rat
After the blockade of cholinergic transmission, stimulation of the preganglionic sympathetic trunk elicited fast depolarizing postsynaptic potentials (PSPs) in rat superior cervical ganglia. At 50 min, their amplitude measured intracellularly was 6.9_+ 1.7 mV and their duration 25.9_+ 7.6 ms ( m e a n + S . D . , n 9 ganglia). The cxtracellular electrical activity recorded from the postganglionic internal carotid nerve was monophasic and equal to 4.0_+ 2.2% of the normal activity (mean _+S.D., n - 12 ganglia). The effects on Ihese PSPs of some postsynaptic receptor antagonists have been tested. Bicuculline decreased the amplitude of the PSPs as well as that of the monophasic extracellular activity, suggesting thai (}ABA could mediate these non-cholinergic synaptic potentials.
In mammalian sympathetic ganglia, acetylcholine is the excitatory neurotransmitter released from preganglionic nerve terminals. Acetylcholine produces two types of excitatory postsynaptic potentials (EPSPs) in sympathetic neurons: an initial fast EPSP mediated through the action ofacetylcholine on nicotinic receptors [12, 13] and a delayed slow EPSP generated via muscarinic receptors [7, 8]. In addition, an excitatory transmission not blocked by cholinergic antagonists has been demonstrated in prevertebral sympathetic ganglia. This non-cholinergic transmission induces late slow EPSPs. It was attributed to neuropeptide release (for a recent review, see ref. 14). While fast and slow EPSPs are recorded in response to single presynaptic stimulations, repetitive stimulations are necessary to produce late slow EPSPs. No late slow EPSP has been recorded in rat superior cervical ganglia (SCG), although neuropeptides related to substance P have been found within nerve terminals [9] and substance P receptors were recently identified [11]. Other neurotransmitters, such as },-aminobutyric acid (GABA) and serotonin, are known to depolarize the SCG sympathetic neuron membrane [1, 15], suggesting the existence of postsynaptic receptors for these compounds. Recently, the presence of neurons with GABACorrespondence: D. Eugene, Laboratoire de Cytologie, Universite Pierre et Marie Curie, lnstitul des Neurosciences, U A C.N.R.S. [ 199, 7 Quai Saint-Bernard, F-75252 Paris Cedex 05, France. 0 3 0 4 - 3 9 4 0 8 7 5 03.5(I (c) 1987 Elsevier Scientific Publishers Ireland Ltd.
52 like immunoreactivity has been found in rat SCG [17]. However, the GABA release after nerve stimulation has not been demonstrated. The present study was carried out in rat SCG. It shows that, in response to single sympathetic trunk stimulations, a neurotransmitter other than acetylcholine produces a fast depolarizing PSP: since this PSP is blocked by bicuculline (GABA receptor antagonist), the neurotransmitter might be GABA. SCG were excised from male Wistar rats weighing 150-180 g. The isolated ganglia were placed in a recording chamber, superfused at 3 ml/min with a physiological solution and carefully desheathed. The normal physiological solution (solution N) had the following composition (mM): NaC1 130, KCI 5, NaH2PO4 1, NaHCO3 12, CaCI2 2.2, MgCI2 1, glucose l l. A second solution (solution A) contained, in addition, 1 mM hexamethonium and 10 I~M atropine (added as nicotinic and muscarinic cholinergic receptor antagonists), and 5 pM propranoiol (a noradrenergic fl-receptor antagonist added in order to block the possible activation of sympathetic neurons by postganglionic axon collaterals). The solutions were gassed with 5% CO2-95% 02. All experiments were carried out at pH 7.4 and at about 30~C. The preganglionic sympathetic trunk was stimulated with a suction electrode at 0.1 Hz with supramaximal pulses of 0.3 ms. Another suction electrode recorded the extracellular activity from the postganglionic internal carotid nerve. Intracellular recording from sympathetic neurons was made with conventional glass microelectrodes containing 3 M KCI (impedance 60-80 Mg2). Intracellular data were collected from the cells in which the resting membrane potential was more negative than - 5 0 mV. Fig. 1 shows comparable extracellular and intracellular recordings from two different ganglia (a and b) at different times after changing solution N for solution A. The intracellular records indicate that after 10 min in solution A, stimulation of the preganglionic trunk stopped producing an action potential in the sympathetic neuron, showing that cholinergic ganglionic transmission was reduced. But even after 20 min (and 50 min in the ganglion b) a fast depolarizing PSP subsisted. Similarly, the amplitude of extracellular signals recorded from the internal carotid nerve next to the ganglion was reduced but not abolished, suggesting that fast depolarizing PSPs persisted in many sympathetic neurons. The amplitude and the duration of PSPs have been measured in some preparations at 10, 20 and 50 min after changing solution N for solution A (Table I). The results show that after 20 min, both of them were relatively stable and respectively equal to about 7 mv and 25 ms. On the contrary, the amplitude of extracellular monophasic potentials decreased continuously with time. But at 50 min, it seemed to stabilize and was equal to 4.0_ 2.2% of the positive phase amplitude of the diphasic potential elicited in solution N (mean_+ S.D., n = 12 ganglia). This difference between extracellular and intracellular potential may be due to the progressive diffusion of cholinergic antagonists into the SCG. Then, both the extracellular and intracellular activity could be recorded during several hours in the same ganglion immersed in solution A. These activities were not modified by 10 pM eserine or neostigmine (anticholinesterase agents) but disappeared if calcium was omitted and the magnesium concentration was increased (CaCI2 substituted by
53
B
I:,..... N
;..., 0
. 7
.
.
.
.
.
1~
2'0
rain
b
~ Sohzt ion
N
;"'I
~
20mY
"'"
Fig. 1. Effects of cholinergic receptor antagonists on two different SCG (a, b). For the two ganglia, there were extracellular recordings from the internal carotid nerve (upper traces) and intracellular recordings from a sympathetic neuron of the same ganglion (lower traces). On the right recordings, the middle trace is the lower trace with an increased calibration. In the ganglia a and b, the two types of electrical activity were recorded after changing solution N for solution A containing 1 mM hexamethonium, 10 #M atropine and 5 #M propranolol (time 0). At 10 mira cholinergic transmission was strongly reduced since the intracellular action potential threshold was not reached (lower traces). Then, a fast depolarizing PSP could be recorded during a long time. (Note that the PSP of neuron a was double.) The diphasic extracellular potential (upper traces) became monophasic and very small.
TABLE I EVOLUTION WITH TIME OF THE INTRACELLULAR ACTIVITY IN SOLUTION A The amplitude and the duration of depolarizing PSPs were measured in the same sympathetic neuron. 10 min. 20 min and 50 rain after changing solution N for solution A (antagonists added). Data are means _+S. D. and numbers of experiments are given in brackets. Time after changing solution
10rain 20min 50min
Intracellular potential Amplitude
Duration
6.7+2.4 mV (n-10) 7.3+2.8 mV (n=10) 6.9_4_1.7 mV (n=9)
23.3_+2.5 ms (n=10) 25.2_+3.4 ms ( n - 1 0 ) 25.9+7.6 ms ( n - 9 )
MgC12 in e q u i m o l a r a m o u n t s ) . T h e r e s u l t s w e r e s i m i l a r if c h l o r i s o n d a m i n e (10 # M ) was used instead of hexamethonium
(1 m M ) . T h e s e o b s e r v a t i o n s s u g g e s t t h a t t h e
p o s t s y n a p t i c a c t i v i t y r e c o r d e d in s o l u t i o n A m a y b e d u e t o a n o t h e r n e u r o t r a n s m i t t e r than acetylcholine.
54 In an attempt to characterize this neurotransmitter, some postsynaptic receptor antagonists were tested. No effect was produced by 10/~M methiothepine and 50 IzM ~,fl-methylene A T P (respectively serotonin and ATP receptor antagonists). In contrast, bicuculline ( G A B A a receptor antagonist) decreased the amplitude of the noncholinergic depolarizing PSPs and of the extracellular recordings. This decrease was just detectable with 5/zM bicuculline, 25% with 20/tM bicuculline, 50% with 50/~M bicuculline (4 ganglia). N o activity persisted with 2 0 0 / t M bicuculline (Fig. 2). This result suggests that G A B A could be the neurotransmitter responsible for fast depolarizing PSPs recorded in the presence ofcholinergic receptor antagonists. In the rat SCG, the electrophysioiogical effects of G A B A applications are well documented and can account for the present recordings. On the one hand, the GABA-induced opening of chloride channels produces a membrane depolarization of the sympathetic neuron [1], since the chloride equilibrium potential is less negative than the resting membrane potential [2]. On the other hand, bicucuiline is a GABAA postsynaptic receptor antagonist known to decrease the GABAergic membrane depolarization [4]. In the present experiments, the bicuculline concentration required to depress the depolarizing PSPs by 50% (IC50) was about 50/tM. This value is in approximate agreement with the bicuculline ICs0 values obtained in other experimental conditions, either with G A B A applications (14/zM) [4], or after [3H]muscimol binding to SCG homogenates (30/zM) [6]. The present results and several other data suggest that G A B A could play a role in ganglionic transmission of the rat SCG. First, G A B A is present at a relatively high J
%ol
A
[B,c u] T, r. e
0
2 I'-', o 15
5
I.
. 310
.
.
.
I~ .
.
4'5
.
.
210
50 610
l o05mV
.a,--___5°...
,00
2°°
I,..
7u5
~...
I...
9UO
'OS
1;5
I...
~, "'~;0
min
Fig. 2. Effectof bicuculline on extracellular (top traces) and intracellular (bottom traces) recordings from the same ganglion immersed in solution A. The bicuculline concentration ([Bicu]) was increased from 2 to 200/tM. An extracellular monophasic potential and an intracellular depolarizing PSP were simultaneously recorded, 15 rain after each step increase of the bicuculline concentration. The bicucultine concentration was then changed. The two types of potential began to decrease with 5/zM bicuculline and no potential persisted with 200/~M bicuculline.
35
level since the GABA content is similar to that of dopamine or noradrenaline [3]. This study was recently confirmed by immunocytochemical evidence of GABA-like immunoreactivity in interneurons intrinsic to the SCG [17]. A comparable investigation carried out in our laboratory showed the presence of GABA-containing nerve fibers in the preganglionic sympathetic trunk and surrounding principal ganglion cells (to be published). These nerve fibers could be excited by preganglionic stimulation. Moreover, since ganglionic neuroglial cells take up extracellular GABA by a specific Na +-dependent saturable process [5], the extracellular GABA concentration may be effectively controlled. Finally, after in vivo prolonged infusion, GABA seems to have long-term biochemical and morphologic effects on the ganglion cells [10, 16]. All these observations reinforce the hypothesis that preganglionic sympathetic trunk excitations might induce a GABA release which could modulate cholinergic transmission as previously discussed [1, 6]. I thank Professor P. Ascher and Professor J. Taxi for helpful suggestions and critical reading of the manuscript. 1 Adams, P.R. and Brown, D.A., Actions of y-aminobutyric acid on sympathetic ganglion cells, J. Physiol. (London), 250 (1975) 85 120. 2 Ballanyi, K., Grafe, P., Reddy, M.M. and ten Bruggencate, G., Different types of potassium transport linked to carbachol and ),-aminobutyric acid actions in rat sympathetic neurons, Neuroscience, 12 (1984) 917 927. 3 Bertilsson, L., Suria, A. and Costa, E., )'-Aminobutyric acid in rat superior cervical ganglion, Nature (London), 260 (1976) 540 54[. 4 Bowery. N.G. and Brown, D.A., Depolarizing actions of gamma-Aminobutyric acid and related compounds on rat superior cervical ganglia in vitro, Br. J. Pharmacol., 50 (1974) 205 218. 5 Bowery, N.G., Brown, D.A., White, R.D. and Yamini, G., [3H]7-aminobutyric acid uptake into neuroglial cclls of rat superior cervical sympathetic ganglia, J. Physiol. (London), 293 (1979) 51 74. 6 Bowery, N.G. and Hill, D.R., GABA mechanisms in autonomic ganglia. In S.L. Erd6 and N.G. Bowcry (Ed.), GABAergic mechanisms in the mammalian periphery. Raven, New York, t986, pp. 135 152. 7 Brown, D.A. and Constanti, A., Intracellular observations on the effects of muscarinic agonists on rat sympathetic neuroncs, Br. J. Pharmacol., 70 (1980) 593 608. 8 Constanti, A. and Brown, D.A., M-currents in voltage-clamped mammalian sympathetic neurones, Ncurosci. Left., 24 (1981) 289 294. 9 H6kfelt, T., Elfvin, L.-G., Schultzberg, M.. Goldstein, M. and Nilsson, G., On the occurrence of substance P-containing fibers in sympathetic ganglia: immunohistochemical evidence, Brain Res., 132 (1977) 29 41. 10 K~'tsa, P., Dames, W., Rakonczay, Z., Gulya, K., Jo6, F. and Wolff\ J.R., Modulation of the acctylcholine system in the superior cervical ganglion of rat: effects of GABA and hypoglossal nerve implantation after in vivo GABA treatment, J. Neurochem., 44 (1985) 1363 1372. 1 I Niwa, M., Shigematsu, K., Plunkett, L. and Saavedra, J.M., High-affinity substance P binding sites in rat sympathetic ganglia, Am. J. Physiol., 249 (1985) H694 H697. 12 Selyanko, A.A., Derkach, V.A. and Skok, V.I., Fast excitatory postsynaptic currents in voltageclamped mammalian sympathetic ganglion neurones, J. Auton. Nerv. Syst., 1 (1979) 127 137. 13 Selyanko. A.A.. Derkach, V.A. and Skok, V.I., Effects of some ganglion-blocking agents on fast cxcitatory postsynaptic currents in mammalian sympathetic ganglion neurones. In J. Salanki (Ed.), Physiology of Excitable Membranes, Adv. Physiol. Sci., Vol. 4, Pergamon, New York, 1981, pp. 329 342. 14 Simmons, M.A., The complexity and diversity ofsynaptic transmission in the prevertebral sympathetic ganglia, Prog. Neurobiol., 24 (1985) 43 93.
15 Wallis, D.I. and North, R.A., The action of 5-hydroxytryptamine on single neurones of the rabbit superior cervical ganglion, Neuropharmacology, 17 (1978) 1023- 1028. 16 Wolff, J.R., Joo, F. and Dames, W., Plasticity in dendrites shown by continuous GABA administration in superior cervical ganglion of adult rat, Nature (London), 274 (1978) 72 74. 17 Wolff, J.R., Jo6, F., K~isa, P., Storm-Mathiesen, J., Toldi, J. and Balcar, V.J., Presence of neurons with GABA-like immunoreactivity in the superior cervical ganglion of the rat, Neurosci. Lett.. 71 (1986) 157 162.
51
NSL 04592
Fast non-cholinergic depolarizing postsynaptic potentials in neurons of rat superior cervical ganglia Daniel E u g e n e Lahoratoire ¢k" Cytologic, Universitt; Pierre et Marie Curie, lnstitut des Neurosciences, UA C.N.R.S. 1/99. Paris (France) (Received 8 December 1986; Revised version received 2 February 1987: Accepted 3 February' I9871 Key word~'.
Non-cholinergic neurotransmission: Postsynaptic potential; Bicuculline: Sympathetic neuron: Superior cervical ganglion: Rat
After the blockade of cholinergic transmission, stimulation of the preganglionic sympathetic trunk elicited fast depolarizing postsynaptic potentials (PSPs) in rat superior cervical ganglia. At 50 min, their amplitude measured intracellularly was 6.9_+ 1.7 mV and their duration 25.9_+ 7.6 ms ( m e a n + S . D . , n 9 ganglia). The cxtracellular electrical activity recorded from the postganglionic internal carotid nerve was monophasic and equal to 4.0_+ 2.2% of the normal activity (mean _+S.D., n - 12 ganglia). The effects on Ihese PSPs of some postsynaptic receptor antagonists have been tested. Bicuculline decreased the amplitude of the PSPs as well as that of the monophasic extracellular activity, suggesting thai (}ABA could mediate these non-cholinergic synaptic potentials.
In mammalian sympathetic ganglia, acetylcholine is the excitatory neurotransmitter released from preganglionic nerve terminals. Acetylcholine produces two types of excitatory postsynaptic potentials (EPSPs) in sympathetic neurons: an initial fast EPSP mediated through the action ofacetylcholine on nicotinic receptors [12, 13] and a delayed slow EPSP generated via muscarinic receptors [7, 8]. In addition, an excitatory transmission not blocked by cholinergic antagonists has been demonstrated in prevertebral sympathetic ganglia. This non-cholinergic transmission induces late slow EPSPs. It was attributed to neuropeptide release (for a recent review, see ref. 14). While fast and slow EPSPs are recorded in response to single presynaptic stimulations, repetitive stimulations are necessary to produce late slow EPSPs. No late slow EPSP has been recorded in rat superior cervical ganglia (SCG), although neuropeptides related to substance P have been found within nerve terminals [9] and substance P receptors were recently identified [11]. Other neurotransmitters, such as },-aminobutyric acid (GABA) and serotonin, are known to depolarize the SCG sympathetic neuron membrane [1, 15], suggesting the existence of postsynaptic receptors for these compounds. Recently, the presence of neurons with GABACorrespondence: D. Eugene, Laboratoire de Cytologie, Universite Pierre et Marie Curie, lnstitul des Neurosciences, U A C.N.R.S. [ 199, 7 Quai Saint-Bernard, F-75252 Paris Cedex 05, France. 0 3 0 4 - 3 9 4 0 8 7 5 03.5(I (c) 1987 Elsevier Scientific Publishers Ireland Ltd.
52 like immunoreactivity has been found in rat SCG [17]. However, the GABA release after nerve stimulation has not been demonstrated. The present study was carried out in rat SCG. It shows that, in response to single sympathetic trunk stimulations, a neurotransmitter other than acetylcholine produces a fast depolarizing PSP: since this PSP is blocked by bicuculline (GABA receptor antagonist), the neurotransmitter might be GABA. SCG were excised from male Wistar rats weighing 150-180 g. The isolated ganglia were placed in a recording chamber, superfused at 3 ml/min with a physiological solution and carefully desheathed. The normal physiological solution (solution N) had the following composition (mM): NaC1 130, KCI 5, NaH2PO4 1, NaHCO3 12, CaCI2 2.2, MgCI2 1, glucose l l. A second solution (solution A) contained, in addition, 1 mM hexamethonium and 10 I~M atropine (added as nicotinic and muscarinic cholinergic receptor antagonists), and 5 pM propranoiol (a noradrenergic fl-receptor antagonist added in order to block the possible activation of sympathetic neurons by postganglionic axon collaterals). The solutions were gassed with 5% CO2-95% 02. All experiments were carried out at pH 7.4 and at about 30~C. The preganglionic sympathetic trunk was stimulated with a suction electrode at 0.1 Hz with supramaximal pulses of 0.3 ms. Another suction electrode recorded the extracellular activity from the postganglionic internal carotid nerve. Intracellular recording from sympathetic neurons was made with conventional glass microelectrodes containing 3 M KCI (impedance 60-80 Mg2). Intracellular data were collected from the cells in which the resting membrane potential was more negative than - 5 0 mV. Fig. 1 shows comparable extracellular and intracellular recordings from two different ganglia (a and b) at different times after changing solution N for solution A. The intracellular records indicate that after 10 min in solution A, stimulation of the preganglionic trunk stopped producing an action potential in the sympathetic neuron, showing that cholinergic ganglionic transmission was reduced. But even after 20 min (and 50 min in the ganglion b) a fast depolarizing PSP subsisted. Similarly, the amplitude of extracellular signals recorded from the internal carotid nerve next to the ganglion was reduced but not abolished, suggesting that fast depolarizing PSPs persisted in many sympathetic neurons. The amplitude and the duration of PSPs have been measured in some preparations at 10, 20 and 50 min after changing solution N for solution A (Table I). The results show that after 20 min, both of them were relatively stable and respectively equal to about 7 mv and 25 ms. On the contrary, the amplitude of extracellular monophasic potentials decreased continuously with time. But at 50 min, it seemed to stabilize and was equal to 4.0_ 2.2% of the positive phase amplitude of the diphasic potential elicited in solution N (mean_+ S.D., n = 12 ganglia). This difference between extracellular and intracellular potential may be due to the progressive diffusion of cholinergic antagonists into the SCG. Then, both the extracellular and intracellular activity could be recorded during several hours in the same ganglion immersed in solution A. These activities were not modified by 10 pM eserine or neostigmine (anticholinesterase agents) but disappeared if calcium was omitted and the magnesium concentration was increased (CaCI2 substituted by
53
B
I:,..... N
;..., 0
. 7
.
.
.
.
.
1~
2'0
rain
b
~ Sohzt ion
N
;"'I
~
20mY
"'"
Fig. 1. Effects of cholinergic receptor antagonists on two different SCG (a, b). For the two ganglia, there were extracellular recordings from the internal carotid nerve (upper traces) and intracellular recordings from a sympathetic neuron of the same ganglion (lower traces). On the right recordings, the middle trace is the lower trace with an increased calibration. In the ganglia a and b, the two types of electrical activity were recorded after changing solution N for solution A containing 1 mM hexamethonium, 10 #M atropine and 5 #M propranolol (time 0). At 10 mira cholinergic transmission was strongly reduced since the intracellular action potential threshold was not reached (lower traces). Then, a fast depolarizing PSP could be recorded during a long time. (Note that the PSP of neuron a was double.) The diphasic extracellular potential (upper traces) became monophasic and very small.
TABLE I EVOLUTION WITH TIME OF THE INTRACELLULAR ACTIVITY IN SOLUTION A The amplitude and the duration of depolarizing PSPs were measured in the same sympathetic neuron. 10 min. 20 min and 50 rain after changing solution N for solution A (antagonists added). Data are means _+S. D. and numbers of experiments are given in brackets. Time after changing solution
10rain 20min 50min
Intracellular potential Amplitude
Duration
6.7+2.4 mV (n-10) 7.3+2.8 mV (n=10) 6.9_4_1.7 mV (n=9)
23.3_+2.5 ms (n=10) 25.2_+3.4 ms ( n - 1 0 ) 25.9+7.6 ms ( n - 9 )
MgC12 in e q u i m o l a r a m o u n t s ) . T h e r e s u l t s w e r e s i m i l a r if c h l o r i s o n d a m i n e (10 # M ) was used instead of hexamethonium
(1 m M ) . T h e s e o b s e r v a t i o n s s u g g e s t t h a t t h e
p o s t s y n a p t i c a c t i v i t y r e c o r d e d in s o l u t i o n A m a y b e d u e t o a n o t h e r n e u r o t r a n s m i t t e r than acetylcholine.
54 In an attempt to characterize this neurotransmitter, some postsynaptic receptor antagonists were tested. No effect was produced by 10/~M methiothepine and 50 IzM ~,fl-methylene A T P (respectively serotonin and ATP receptor antagonists). In contrast, bicuculline ( G A B A a receptor antagonist) decreased the amplitude of the noncholinergic depolarizing PSPs and of the extracellular recordings. This decrease was just detectable with 5/zM bicuculline, 25% with 20/tM bicuculline, 50% with 50/~M bicuculline (4 ganglia). N o activity persisted with 2 0 0 / t M bicuculline (Fig. 2). This result suggests that G A B A could be the neurotransmitter responsible for fast depolarizing PSPs recorded in the presence ofcholinergic receptor antagonists. In the rat SCG, the electrophysioiogical effects of G A B A applications are well documented and can account for the present recordings. On the one hand, the GABA-induced opening of chloride channels produces a membrane depolarization of the sympathetic neuron [1], since the chloride equilibrium potential is less negative than the resting membrane potential [2]. On the other hand, bicucuiline is a GABAA postsynaptic receptor antagonist known to decrease the GABAergic membrane depolarization [4]. In the present experiments, the bicuculline concentration required to depress the depolarizing PSPs by 50% (IC50) was about 50/tM. This value is in approximate agreement with the bicuculline ICs0 values obtained in other experimental conditions, either with G A B A applications (14/zM) [4], or after [3H]muscimol binding to SCG homogenates (30/zM) [6]. The present results and several other data suggest that G A B A could play a role in ganglionic transmission of the rat SCG. First, G A B A is present at a relatively high J
%ol
A
[B,c u] T, r. e
0
2 I'-', o 15
5
I.
. 310
.
.
.
I~ .
.
4'5
.
.
210
50 610
l o05mV
.a,--___5°...
,00
2°°
I,..
7u5
~...
I...
9UO
'OS
1;5
I...
~, "'~;0
min
Fig. 2. Effectof bicuculline on extracellular (top traces) and intracellular (bottom traces) recordings from the same ganglion immersed in solution A. The bicuculline concentration ([Bicu]) was increased from 2 to 200/tM. An extracellular monophasic potential and an intracellular depolarizing PSP were simultaneously recorded, 15 rain after each step increase of the bicuculline concentration. The bicucultine concentration was then changed. The two types of potential began to decrease with 5/zM bicuculline and no potential persisted with 200/~M bicuculline.
35
level since the GABA content is similar to that of dopamine or noradrenaline [3]. This study was recently confirmed by immunocytochemical evidence of GABA-like immunoreactivity in interneurons intrinsic to the SCG [17]. A comparable investigation carried out in our laboratory showed the presence of GABA-containing nerve fibers in the preganglionic sympathetic trunk and surrounding principal ganglion cells (to be published). These nerve fibers could be excited by preganglionic stimulation. Moreover, since ganglionic neuroglial cells take up extracellular GABA by a specific Na +-dependent saturable process [5], the extracellular GABA concentration may be effectively controlled. Finally, after in vivo prolonged infusion, GABA seems to have long-term biochemical and morphologic effects on the ganglion cells [10, 16]. All these observations reinforce the hypothesis that preganglionic sympathetic trunk excitations might induce a GABA release which could modulate cholinergic transmission as previously discussed [1, 6]. I thank Professor P. Ascher and Professor J. Taxi for helpful suggestions and critical reading of the manuscript. 1 Adams, P.R. and Brown, D.A., Actions of y-aminobutyric acid on sympathetic ganglion cells, J. Physiol. (London), 250 (1975) 85 120. 2 Ballanyi, K., Grafe, P., Reddy, M.M. and ten Bruggencate, G., Different types of potassium transport linked to carbachol and ),-aminobutyric acid actions in rat sympathetic neurons, Neuroscience, 12 (1984) 917 927. 3 Bertilsson, L., Suria, A. and Costa, E., )'-Aminobutyric acid in rat superior cervical ganglion, Nature (London), 260 (1976) 540 54[. 4 Bowery. N.G. and Brown, D.A., Depolarizing actions of gamma-Aminobutyric acid and related compounds on rat superior cervical ganglia in vitro, Br. J. Pharmacol., 50 (1974) 205 218. 5 Bowery, N.G., Brown, D.A., White, R.D. and Yamini, G., [3H]7-aminobutyric acid uptake into neuroglial cclls of rat superior cervical sympathetic ganglia, J. Physiol. (London), 293 (1979) 51 74. 6 Bowery, N.G. and Hill, D.R., GABA mechanisms in autonomic ganglia. In S.L. Erd6 and N.G. Bowcry (Ed.), GABAergic mechanisms in the mammalian periphery. Raven, New York, t986, pp. 135 152. 7 Brown, D.A. and Constanti, A., Intracellular observations on the effects of muscarinic agonists on rat sympathetic neuroncs, Br. J. Pharmacol., 70 (1980) 593 608. 8 Constanti, A. and Brown, D.A., M-currents in voltage-clamped mammalian sympathetic neurones, Ncurosci. Left., 24 (1981) 289 294. 9 H6kfelt, T., Elfvin, L.-G., Schultzberg, M.. Goldstein, M. and Nilsson, G., On the occurrence of substance P-containing fibers in sympathetic ganglia: immunohistochemical evidence, Brain Res., 132 (1977) 29 41. 10 K~'tsa, P., Dames, W., Rakonczay, Z., Gulya, K., Jo6, F. and Wolff\ J.R., Modulation of the acctylcholine system in the superior cervical ganglion of rat: effects of GABA and hypoglossal nerve implantation after in vivo GABA treatment, J. Neurochem., 44 (1985) 1363 1372. 1 I Niwa, M., Shigematsu, K., Plunkett, L. and Saavedra, J.M., High-affinity substance P binding sites in rat sympathetic ganglia, Am. J. Physiol., 249 (1985) H694 H697. 12 Selyanko, A.A., Derkach, V.A. and Skok, V.I., Fast excitatory postsynaptic currents in voltageclamped mammalian sympathetic ganglion neurones, J. Auton. Nerv. Syst., 1 (1979) 127 137. 13 Selyanko. A.A.. Derkach, V.A. and Skok, V.I., Effects of some ganglion-blocking agents on fast cxcitatory postsynaptic currents in mammalian sympathetic ganglion neurones. In J. Salanki (Ed.), Physiology of Excitable Membranes, Adv. Physiol. Sci., Vol. 4, Pergamon, New York, 1981, pp. 329 342. 14 Simmons, M.A., The complexity and diversity ofsynaptic transmission in the prevertebral sympathetic ganglia, Prog. Neurobiol., 24 (1985) 43 93.
15 Wallis, D.I. and North, R.A., The action of 5-hydroxytryptamine on single neurones of the rabbit superior cervical ganglion, Neuropharmacology, 17 (1978) 1023- 1028. 16 Wolff, J.R., Joo, F. and Dames, W., Plasticity in dendrites shown by continuous GABA administration in superior cervical ganglion of adult rat, Nature (London), 274 (1978) 72 74. 17 Wolff, J.R., Jo6, F., K~isa, P., Storm-Mathiesen, J., Toldi, J. and Balcar, V.J., Presence of neurons with GABA-like immunoreactivity in the superior cervical ganglion of the rat, Neurosci. Lett.. 71 (1986) 157 162.