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Vasoactive intestinal polypeptide elecits a discharge in chronically decentralized sympathetic ganglia
European Journal of Pharmacology, 129 (1986) 375-378
375
Elsevier EJP 448SC Short communication
Vasoactive intestinal polypeptide elicits a discharge in chronically decentralized sympathetic ganglia Michael J. Rutigliano, M a s a h i t o K a w a t a n i a n d William C. D e G r o a t * Department of Pharmacology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, U.S.A
Received7 August 1986,accepted 12 August 1986
Vasoactive intestinal polypeptide (VIP, 5-50 #g) injected intraarterially to the chronically decentralized cat superior cervical ganglion elicited a prolonged (2-5 min) postganlionic discharge which was resistant to cholinergic blocking agents but was blocked by [LeuS]enkephalin and GABA (10-200 /tg i.a.). VIP did not elicit a discharge in acutely decentralized ganglia. These findings indicate that VIP has direct excitatory effects on ganglion cells and that these excitatory effects are enhanced following degeneration of the preganglionic nerve terminals. Vasoactive intestinal polypeptide; Sympathetic ganglia; Denervation; Muscarinic excitation
1. Introduction
Recent studies (Voile and Patterson, 1982; Ip et al., 1982; Kawatani and De Groat, 1983a; Kawatani et al., 1985b, c, in press; Mo and Dun, 1984; De Groat et al., 1985) have shown that vasoactive intestinal polypeptide (VIP) elicits a number of effects at cholinergic synapses in autonomic ganglia. In sympathetic and parasympathetic ganglia of the cat the administration of VIP facilitated muscarinic excitatory transmission and enhanced the ganglionic depolarization and the postganglionic firing elicited by muscarinic agonists (Kawatani and De Groat, 1983a; Kawatani et al., 1985b, c, in press). These responses occurred over a wide range of VIP concentrations which did not alter nicotinic transmission. Similar results were obtained in the inferior mesenteric ganglion of the guinea-pig (Mo and Dun, 1984). VIP also evoked a depolarization of sympathetic ganglion cells (Kawatani et al., 1985c). This effect * To whom all correspondence should be addressed: 572 Scaife Hall, Department of Pharmacology,Medical School, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A. 0014-2999/86/$03.50 © 1986 Elsevier SciencePublishers B.V.
was not reduced by acetylcholine antagonists which blocked nicotinic or muscarinic transmission. The present study was undertaken to determine whether the ganglionic effects of VIP are dependent upon the presence of preganglionic nerve terminals. Experiments, conducted in chronically decentralized superior cervical ganglia (SCG) of the cat, indicate that intact preganglionic pathways are not essential for the muscarinic facilitatory effects of VIP. However, elimination of the preganglionic pathways did enhance the direct ganglionic excitatory effect of VIP, resulting in a prominent VIP-induced postganglionic discharge in the chronically decentralized preparations.
2. Materials and methods
Experiments were conducted on adult cats (1.83.5 kg) of either sex anesthetized with dial urethane. Decentralization of the SCG was performed two to three weeks prior to the experiments by transecting the cervical sympathetic trunk on one side under halothane anesthesia.
376
Following intubation of the trachea the SCG were exposed bilaterally and postganglionic nerves (external and internal carotid branches and spinal gray rami) were isolated for recording multiunit activity. Recordings were made bilaterally with silver wire electrodes in acutely (2-10 h) and chronically decentralized ganglia in the same animal. Drugs were dissolved in saline and administered via close arterial injection (0.1 ml) into the common carotid artery. Neural activity was photographed on 35 mm film or monitored with a ratemeter and displayed on a paper recorder.
3. Results
A marked difference was noted in the effects of VIP on chronically and acutely decentralized SCG. In chronically decentralized ganglia, VIP in doses between 2-50/~g i.a. produced a slow onset, prolonged discharge on postganglionic nerves (fig. 1). Large doses of VIP (5-100 /lg i.a.) did not elicit postganglionic firing in acutely decentralized preparations (five experiments). The threshold dose
A
of VIP to elicit a discharge ranged between 2-5/~g i.a. (four experiments). The discharge occurred after a latency of 15-30 s and persisted for 2-8 min. The magnitude and duration of the discharge were dose dependent, maximal responses occurring with doses of 20-50 /~g i.a. The excitatory effects of VIP were reproducible when the peptide was administered at 20-30 rain intervals. In contrast to the slow onset prolonged discharge elicited by VIP, the administration of ACh (10-20/Lg i.a.) or tetramethylammonium (5-20 #g i.a.) produced postganglionic firing with a more rapid onset (5-10 s) and a shorter duration (10-30 s). The VIP-induced firing was resistant to doses of the nicotinic antagonist, hexamethonium (1-5 mg i.a.) and the muscarinic antagonists, atropine (40-70 #g i.a.) and pirenzepine (5-200 /~g i.a.), which blocked the postganglionic firing elicited by cholinergic drugs (tetramethylammonium, acetylcholine or acetyl-/~-methylcholine). However, the VIP discharge was blocked by agents, such as y-aminobutyric acid (GABA, 10-200 /~g i.a.) and [LeuS]enkephalin (LENK, 10-50 /xg i.a.), that are known to have direct postsynaptic depressant ac-
NORMAL SIDE
DENERVATED SIDE
.....................
~v
soo
E
CONTROL
AFTE.
ATROPINE
o -5oo
l
:~o AFTER HEXAMETHONIUM
~
.o w t role
¢
Fig. 1. The effect of VIP on the acutely and chronically decentralized superior cervical ganglia (SCG) in the same animal. (A) Oscilloscope records of multiunit firing showing that VIP (20/~g) did not produce a discharge on the acutely decentralized SCG (3 h, normal side), but did elicit a prolonged discharge in the chronically (18 days) decentralized SCG (denervated side). (B) Ratemeter records of VIP-induced firing showing that the firing in chronically decentralized SCG was not affected by either the muscarinic blocking agent, atropine (40/~g i.a.) or the nicotinic antagonist, hexamethonium (5 mg i.a.). The arrows correspond to injection of the peptide.
377
A
B
~VIP
~GABA
30n
rSO00 a.
30s
3om
Fig. 2. The effect of ~,-aminobutyric acid (GABA) and [LeuS]enkephalin (LENK) on the VIP-induced discharge in chronically decentralized SCG of the cat. (A) An oscilloscope record, and (B) a ratemeter recording showing that GABA (100 ~g i.a.) completely blocked the VlP (20 ~g i.a.) induced discharge. (C) A ratemeter recording showing that LENK (50 /lg i.a.) completely blocked a discharge elicited by 20 /~g of VIP. The arrows indicate injections of the various agents. Horizontal calibration bars represent 30 s; vertical calibration bars represent 10 ~V in (A) and 0-500 spikes/s in (B,C).
tions. As shown in fig. 2 the administration of GABA or LENK produced a rapid onset suppression of the VIP-induced discharge. The effects of the blocking agents were reversible within 3-5 min. In both acutely and chronically decentralized ganglia, VIP (5-10 /~g i.a.) enhanced the late muscarinic discharge elicited by acetylcholine (10 #g i.a.). The enhanced discharges were blocked by atropine (2-10 /~g i.a.). This facilitatory effect of VIP was not altered by decentralization.
4. Discussion
The present results demonstrate a greater sensitivity of the chronically decentralized superior cervical ganglion to the direct excitatory effects of VIP. This change might be explained by a more prominent action of VIP due to supersensitivity of the VIP receptors or changes in the transduction mechanisms for VIP-induced depolarization. Alternatively, it could be due to a change in the excitability of the denervated ganglion cells such
that a low amplitude VIP depolarization which is insufficient to elicit action potentials in the normal ganglion, can elicit firing of the decentralized cells. It is known that chronic decentralization also facilitates muscarinic excitation in the cat superior cervical ganglion and substance P-induced excitation in parasympathetic ganglia of the urinary bladder (Kawatani and De Groat, 1983b). Thus, cholinergic and peptidergic slow ganglionic excitatory mechanisms are enhanced by decentralization; however, nicotine responses are not enhanced. Although the mechanism for VIP-induced excitation of ganglion cells is still unknown it seems reasonable to conclude that the excitation is due to direct action of VIP rather than the release of other transmitters, since it was resistant to cholinergic blocking agents and occurred following degeneration of preganglionic inputs. Similarly, the facilitation by VIP of muscarinic excitatory responses must also be due to a direct postsynaptic action of VIP since it was unchanged in the chronically decentralized ganglia. The physiological significance of VIP effects on autonomic ganglion cells is uncertain. VIP is present in axons and varicosities in ganglia of various species and exogenous VIP can mimic several noncholinergic-nonadrenergic responses elicited in the rat superior cervical ganglion by stimulation of the preganglionic nerves (Voile and Patterson, 1982; Ip et al., 1982). It is not known whether VIP is synthesized and released by sympathetic preganglionic neurons, however the peptide is present in: (1) afferent axons which arise from dorsal root ganglion cells and pass through autonomic ganglia (Kawatani et al., 1985a, b), (2) peripheral afferent pathways from the intestine to prevertebral ganglia and (3) some sympathetic and parasympathetic postganglionic neurons. Thus VIP may function as an excitatory transmitter in afferent pathways to certain ganglia or may function as a modulator of cholinergic transmission following release from neurons within ganglia (Kawatani et al., 1985b, c; in press). Further studies are necessary to determine the function of VIP in the cat superior cervical ganglion and the mechanisms underlying the enhancement of VIP excitatory effects following decentralization.
378
Acknowledgements This work was supported by NSF Grant BNS-8507113, NIH Grants AM 37241, AM 31788 and Clinical Research Grant MH 30915.
References De Groat, W.C., M. Kawatani and M. Rutigliano, 1985, Ganglionic depolarization and enhancement of muscarinic ganglionic excitatory mechanisms in the cat by vasoactive intestinal polypeptide, J. Physiol. (London) 346, 41P. Ip, N.Y., C.K. Ho and R.E. Zigmond, 1982, Secretin and vasoactive intestinal peptide acutely increase tyrosine-3monooxygenase activity in the rat superior cervical ganglion, Proc. Natl. Acad. Sci. U.S.A. 79, 7566. Kawatani, M. and W.C. De Groat, 1983a, Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat, Pharmacologist 25, 157. Kawatani, M. and W.C. De Groat, 1983b, Reorganization of sympathetic efferent and sacral afferent inputs to parasympathetic ganglia of the urinary bladder in response to
partial denervation produced by interruption of the sacral preganglionic outflow, Soc. Neurosci. Abstr. 9, 938. Kawatani, M., S. Erdman and W.C. De Groat, 1985a, Vasoactive intestinal polypeptide and substance P in afferent pathways to the sacral spinal cord of the cat, J. Comp. Neurol. 241,327. Kawatani, M., M. Rutigliano and W.C. De Groat, 1985b, Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat, Brain Res. 336, 223. Kawatani, M., M. Rutigliano and W.C. De Groat, 1985c, VIP elicits ganglionic depolarization and selectively facilitates muscarinic excitation in a sympathetic ganglion, Science 229, 879. Kawatani, M., M. Rutigliano and W.C. De Groat, Selective facilitatory effects of vasoactive intestinal polypeptide on muscarinic mechanisms in sympathetic and parasympathetic ganglia of the cat, in: Dynamics of Cholinergic Function, ed. I. Hanin (Plenum Press, New York) (in press). Mo., N. and N.J. Dun, 1984, Vasoactive intestinal polypeptide facilitates muscarinic transmission in mammilian sympathetic ganglia, Neurosci. Lett. 52, 19. Vollc, R.L. and B. Patterson, 1982, Regulation of cyclic AMP accumulation in rat sympathetic ganglion: effects of vasoactive intestinal polypeptide, J. Neurochcm. 39, 1195.
375
Elsevier EJP 448SC Short communication
Vasoactive intestinal polypeptide elicits a discharge in chronically decentralized sympathetic ganglia Michael J. Rutigliano, M a s a h i t o K a w a t a n i a n d William C. D e G r o a t * Department of Pharmacology and Center for Neuroscience, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, U.S.A
Received7 August 1986,accepted 12 August 1986
Vasoactive intestinal polypeptide (VIP, 5-50 #g) injected intraarterially to the chronically decentralized cat superior cervical ganglion elicited a prolonged (2-5 min) postganlionic discharge which was resistant to cholinergic blocking agents but was blocked by [LeuS]enkephalin and GABA (10-200 /tg i.a.). VIP did not elicit a discharge in acutely decentralized ganglia. These findings indicate that VIP has direct excitatory effects on ganglion cells and that these excitatory effects are enhanced following degeneration of the preganglionic nerve terminals. Vasoactive intestinal polypeptide; Sympathetic ganglia; Denervation; Muscarinic excitation
1. Introduction
Recent studies (Voile and Patterson, 1982; Ip et al., 1982; Kawatani and De Groat, 1983a; Kawatani et al., 1985b, c, in press; Mo and Dun, 1984; De Groat et al., 1985) have shown that vasoactive intestinal polypeptide (VIP) elicits a number of effects at cholinergic synapses in autonomic ganglia. In sympathetic and parasympathetic ganglia of the cat the administration of VIP facilitated muscarinic excitatory transmission and enhanced the ganglionic depolarization and the postganglionic firing elicited by muscarinic agonists (Kawatani and De Groat, 1983a; Kawatani et al., 1985b, c, in press). These responses occurred over a wide range of VIP concentrations which did not alter nicotinic transmission. Similar results were obtained in the inferior mesenteric ganglion of the guinea-pig (Mo and Dun, 1984). VIP also evoked a depolarization of sympathetic ganglion cells (Kawatani et al., 1985c). This effect * To whom all correspondence should be addressed: 572 Scaife Hall, Department of Pharmacology,Medical School, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A. 0014-2999/86/$03.50 © 1986 Elsevier SciencePublishers B.V.
was not reduced by acetylcholine antagonists which blocked nicotinic or muscarinic transmission. The present study was undertaken to determine whether the ganglionic effects of VIP are dependent upon the presence of preganglionic nerve terminals. Experiments, conducted in chronically decentralized superior cervical ganglia (SCG) of the cat, indicate that intact preganglionic pathways are not essential for the muscarinic facilitatory effects of VIP. However, elimination of the preganglionic pathways did enhance the direct ganglionic excitatory effect of VIP, resulting in a prominent VIP-induced postganglionic discharge in the chronically decentralized preparations.
2. Materials and methods
Experiments were conducted on adult cats (1.83.5 kg) of either sex anesthetized with dial urethane. Decentralization of the SCG was performed two to three weeks prior to the experiments by transecting the cervical sympathetic trunk on one side under halothane anesthesia.
376
Following intubation of the trachea the SCG were exposed bilaterally and postganglionic nerves (external and internal carotid branches and spinal gray rami) were isolated for recording multiunit activity. Recordings were made bilaterally with silver wire electrodes in acutely (2-10 h) and chronically decentralized ganglia in the same animal. Drugs were dissolved in saline and administered via close arterial injection (0.1 ml) into the common carotid artery. Neural activity was photographed on 35 mm film or monitored with a ratemeter and displayed on a paper recorder.
3. Results
A marked difference was noted in the effects of VIP on chronically and acutely decentralized SCG. In chronically decentralized ganglia, VIP in doses between 2-50/~g i.a. produced a slow onset, prolonged discharge on postganglionic nerves (fig. 1). Large doses of VIP (5-100 /lg i.a.) did not elicit postganglionic firing in acutely decentralized preparations (five experiments). The threshold dose
A
of VIP to elicit a discharge ranged between 2-5/~g i.a. (four experiments). The discharge occurred after a latency of 15-30 s and persisted for 2-8 min. The magnitude and duration of the discharge were dose dependent, maximal responses occurring with doses of 20-50 /~g i.a. The excitatory effects of VIP were reproducible when the peptide was administered at 20-30 rain intervals. In contrast to the slow onset prolonged discharge elicited by VIP, the administration of ACh (10-20/Lg i.a.) or tetramethylammonium (5-20 #g i.a.) produced postganglionic firing with a more rapid onset (5-10 s) and a shorter duration (10-30 s). The VIP-induced firing was resistant to doses of the nicotinic antagonist, hexamethonium (1-5 mg i.a.) and the muscarinic antagonists, atropine (40-70 #g i.a.) and pirenzepine (5-200 /~g i.a.), which blocked the postganglionic firing elicited by cholinergic drugs (tetramethylammonium, acetylcholine or acetyl-/~-methylcholine). However, the VIP discharge was blocked by agents, such as y-aminobutyric acid (GABA, 10-200 /~g i.a.) and [LeuS]enkephalin (LENK, 10-50 /xg i.a.), that are known to have direct postsynaptic depressant ac-
NORMAL SIDE
DENERVATED SIDE
.....................
~v
soo
E
CONTROL
AFTE.
ATROPINE
o -5oo
l
:~o AFTER HEXAMETHONIUM
~
.o w t role
¢
Fig. 1. The effect of VIP on the acutely and chronically decentralized superior cervical ganglia (SCG) in the same animal. (A) Oscilloscope records of multiunit firing showing that VIP (20/~g) did not produce a discharge on the acutely decentralized SCG (3 h, normal side), but did elicit a prolonged discharge in the chronically (18 days) decentralized SCG (denervated side). (B) Ratemeter records of VIP-induced firing showing that the firing in chronically decentralized SCG was not affected by either the muscarinic blocking agent, atropine (40/~g i.a.) or the nicotinic antagonist, hexamethonium (5 mg i.a.). The arrows correspond to injection of the peptide.
377
A
B
~VIP
~GABA
30n
rSO00 a.
30s
3om
Fig. 2. The effect of ~,-aminobutyric acid (GABA) and [LeuS]enkephalin (LENK) on the VIP-induced discharge in chronically decentralized SCG of the cat. (A) An oscilloscope record, and (B) a ratemeter recording showing that GABA (100 ~g i.a.) completely blocked the VlP (20 ~g i.a.) induced discharge. (C) A ratemeter recording showing that LENK (50 /lg i.a.) completely blocked a discharge elicited by 20 /~g of VIP. The arrows indicate injections of the various agents. Horizontal calibration bars represent 30 s; vertical calibration bars represent 10 ~V in (A) and 0-500 spikes/s in (B,C).
tions. As shown in fig. 2 the administration of GABA or LENK produced a rapid onset suppression of the VIP-induced discharge. The effects of the blocking agents were reversible within 3-5 min. In both acutely and chronically decentralized ganglia, VIP (5-10 /~g i.a.) enhanced the late muscarinic discharge elicited by acetylcholine (10 #g i.a.). The enhanced discharges were blocked by atropine (2-10 /~g i.a.). This facilitatory effect of VIP was not altered by decentralization.
4. Discussion
The present results demonstrate a greater sensitivity of the chronically decentralized superior cervical ganglion to the direct excitatory effects of VIP. This change might be explained by a more prominent action of VIP due to supersensitivity of the VIP receptors or changes in the transduction mechanisms for VIP-induced depolarization. Alternatively, it could be due to a change in the excitability of the denervated ganglion cells such
that a low amplitude VIP depolarization which is insufficient to elicit action potentials in the normal ganglion, can elicit firing of the decentralized cells. It is known that chronic decentralization also facilitates muscarinic excitation in the cat superior cervical ganglion and substance P-induced excitation in parasympathetic ganglia of the urinary bladder (Kawatani and De Groat, 1983b). Thus, cholinergic and peptidergic slow ganglionic excitatory mechanisms are enhanced by decentralization; however, nicotine responses are not enhanced. Although the mechanism for VIP-induced excitation of ganglion cells is still unknown it seems reasonable to conclude that the excitation is due to direct action of VIP rather than the release of other transmitters, since it was resistant to cholinergic blocking agents and occurred following degeneration of preganglionic inputs. Similarly, the facilitation by VIP of muscarinic excitatory responses must also be due to a direct postsynaptic action of VIP since it was unchanged in the chronically decentralized ganglia. The physiological significance of VIP effects on autonomic ganglion cells is uncertain. VIP is present in axons and varicosities in ganglia of various species and exogenous VIP can mimic several noncholinergic-nonadrenergic responses elicited in the rat superior cervical ganglion by stimulation of the preganglionic nerves (Voile and Patterson, 1982; Ip et al., 1982). It is not known whether VIP is synthesized and released by sympathetic preganglionic neurons, however the peptide is present in: (1) afferent axons which arise from dorsal root ganglion cells and pass through autonomic ganglia (Kawatani et al., 1985a, b), (2) peripheral afferent pathways from the intestine to prevertebral ganglia and (3) some sympathetic and parasympathetic postganglionic neurons. Thus VIP may function as an excitatory transmitter in afferent pathways to certain ganglia or may function as a modulator of cholinergic transmission following release from neurons within ganglia (Kawatani et al., 1985b, c; in press). Further studies are necessary to determine the function of VIP in the cat superior cervical ganglion and the mechanisms underlying the enhancement of VIP excitatory effects following decentralization.
378
Acknowledgements This work was supported by NSF Grant BNS-8507113, NIH Grants AM 37241, AM 31788 and Clinical Research Grant MH 30915.
References De Groat, W.C., M. Kawatani and M. Rutigliano, 1985, Ganglionic depolarization and enhancement of muscarinic ganglionic excitatory mechanisms in the cat by vasoactive intestinal polypeptide, J. Physiol. (London) 346, 41P. Ip, N.Y., C.K. Ho and R.E. Zigmond, 1982, Secretin and vasoactive intestinal peptide acutely increase tyrosine-3monooxygenase activity in the rat superior cervical ganglion, Proc. Natl. Acad. Sci. U.S.A. 79, 7566. Kawatani, M. and W.C. De Groat, 1983a, Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat, Pharmacologist 25, 157. Kawatani, M. and W.C. De Groat, 1983b, Reorganization of sympathetic efferent and sacral afferent inputs to parasympathetic ganglia of the urinary bladder in response to
partial denervation produced by interruption of the sacral preganglionic outflow, Soc. Neurosci. Abstr. 9, 938. Kawatani, M., S. Erdman and W.C. De Groat, 1985a, Vasoactive intestinal polypeptide and substance P in afferent pathways to the sacral spinal cord of the cat, J. Comp. Neurol. 241,327. Kawatani, M., M. Rutigliano and W.C. De Groat, 1985b, Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat, Brain Res. 336, 223. Kawatani, M., M. Rutigliano and W.C. De Groat, 1985c, VIP elicits ganglionic depolarization and selectively facilitates muscarinic excitation in a sympathetic ganglion, Science 229, 879. Kawatani, M., M. Rutigliano and W.C. De Groat, Selective facilitatory effects of vasoactive intestinal polypeptide on muscarinic mechanisms in sympathetic and parasympathetic ganglia of the cat, in: Dynamics of Cholinergic Function, ed. I. Hanin (Plenum Press, New York) (in press). Mo., N. and N.J. Dun, 1984, Vasoactive intestinal polypeptide facilitates muscarinic transmission in mammilian sympathetic ganglia, Neurosci. Lett. 52, 19. Vollc, R.L. and B. Patterson, 1982, Regulation of cyclic AMP accumulation in rat sympathetic ganglion: effects of vasoactive intestinal polypeptide, J. Neurochcm. 39, 1195.