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Prostaglandin E1 raises the cAMP content of peripheral nerve tissue
Neuroscience Letters, 12 (1979) 361--364
361
© Elsevier/North-Holland Scientific Publishers Ltd.
PROSTAGLANDIN E1 RAISES THE cAMP CONTENT OF PERIPHERAL NERVE TISSUE
PETER KALIX Department of Pharmacology, University of Geneva, Geneva (Switzerland) (Received December 18th, 1978) (Revised version received January 18th, 1979) {Accepted January 23rd, 1979)
SUMMARY
Prostaglandins of the E type have been found to increase the cAMP content in peripheral nerve tissue of several species. In rabbit vagus nerve, for example, the effect is rapid (1--5 min), it can be elicited by 10 -6 M PGE1 and it is maximal at 10 -s M. In this preparation the increase of the cAMP content caused by PGE, is about 4-fold, whereas it is about 2-fold in the vagus of calf. PGE1 also causes an increase in cAMP level in the superior cervical ganglion of calf, rat and rabbit. In these tissues, however, the presence of a phosphodiesterase inhibitor is required for cAMP accumulation.
The effect of the prostaglandins on cAMP synthesis in the central nervous system is well documented [1--4] and it has been suggested that these substances interfere with the effect of noradrenaline on cerebellar Purkinje cells [14] and hippocampal pyramidal cells [13]. With regard to the peripheral nervous system there is evidence that a modification of the electrophysiological properties of frog sciatic nerve [5] and of the superior cervical ganglion (SCG) of rabbit [9] results from superfusion with solutions of PGE1 in vitro. The experiments described in the following demonstrate that, under similar conditions, the prostaglandins increase the concentration of cAMP in these and several other tissues from the peripheral nervous system of various species. The tissues under study were dissected from unanaesthetized animals immediately after death and the connective tissue sheath was carefully removed from all preparations except those of calf vagus and frog sciatic nerve. The individual tissue samples were incubated in 5 ml of a KrebsRinger solution (see legend of Table I), the prostaglandins and the corresponding acids were added in the form of ethanolic solutions. This resulted in a solvent concentration of 1% in the medium, the same amount of ethanol was added to the medium of the control samples. After the incubation
362
period the samples were denaturated, an extract was assayed for cAMP and the amount of protein determined. The details of these procedures have been described previously [6,11]. When sections of rabbit vagus nerve were incubated in solutions containing E-prostaglandins, a rapid accumulation of cAMP was seen to occur in the tissue. Fig. 1 shows time course (A) and concentration dependence (B) of this effect. Both PGE~ (Table I) and PGE2 caused an approximately 4-fold increase of the cAMP content, while PGF~a and PGF2a had no effect (not shown). These observations indicate that in peripheral nerve, as has been shown for a preparation from the central nervous system [2], the prostaglandins of the E t y p e affect the cAMP content in a relatively specific manner. The cAMP-accumulating effect of PGE~ in the rabbit vagus is more rapid than that in brain slices, where the maximal cAMP level is attained after 15--20 min [2]. Moreover, when compared to the latter preparation, the vagus nerve shows a sensitivity that is greater by approximately a factor of 10 [2]. In order to exclude the possibility that the observed increases in cAMP are an effect specific for rabbit tissue, samples of vagus nerve from several other species were tested for their responsiveness to PGE~. The results of these experiments (Table I) indicated that, although there were minor differences in the magnitude of the cAMP increase, the prostaglandin-induced cAMP accumulation is a general observation in vagus nerves regardless of species. A 3-fold increase of the cAMP concentration following incubation with PGE~ was also observed in frog sciatic nerve, a myelinated nerve from a non-mammalian species. Additionally, vagus nerve tissue from several species was also stimulated with PGE~ in media containing the phosphodiesterase inhibitor theophylline at a concentration that did not change the basal cAMP level," but no modification of the prostaglandin effect resulted from the addition of this substance (Table I). On the other hand in the SCG of various species a PGE~-induced cAMP accumulation could only be observed when theophylline was present in the medium (Table I). This requirement of phosphodiesterase inhibition for the detection of an increased rate of cAMP synthesis in the ganglion has already been observed in previous studies A
B
CAMP ~ccum~lO~n ~c~nr % ot control . . -
c AMP aCcumulot~n ~oo 1% ot cont,ol
~oo i
// ~
"
i/
22,0
30o t 20c
'/ ~ac r~,/
"
. . ~ _ _
I h ~ ol ~cubQt,~,
1oo: ~ / ' " " "
conce'~trat~ ot PGE,,
Fig. 1. Time course and concentration dependence of the PGErinduced c A M P accumulation in rabbit vagus nerve. T w o sections of desheathed rabbit vagus were incubated for a given period in 10 -5 M PGE~ (A) or for 7 min in a given PGE~ concentration (B), a third section served as unstimulated control. The c A M P content of the stimulated tissue is expressed as percent of the c A M P content of the corresponding control. Each circle represents one stimulated sample and the curve has been drawn to approximate the m e a n of the two experiments."
363 TABLE I E F F E C T OF PGE, ON THE CYCLIC AMP CONCENTRATION IN PERIPHERAL NERVE TISSUE OF VARIOUS SPECIES Individual samples consisting of sections of vagus or sciatic nerve, of SCG of rabbit divided longitudinally whole SCG of rat or small blocks of calf SCG tissue were equilibrated for approx. 30 rain in a medium containing (retool/l) NaCI 136; KC1 5.6; NaHCO 3 20.0; NaH2PO 4 1.2; ~aC12 2.2; MgCI 2 1.2 and glucose 5.5. The solution was continuously bubbled with a mixture of 5% CO2--95% O; and kept at 37°C (19°C for frog sciatic nerve). Subsequently the tissue samples were stimulated by incubation for 7 min in 10 -5 M PGE~ (column 2 and 4), some of them in media containing 10 -~ M t h e o p h y l l i n e (column 4). F o r the latter experiments the corresponding control tissue was incubated for 7 min in theophylline alone (column 3). Results are expressed as pmol cAMP/rag protein ± S.E.M. with the number of experiments in parenthesis.
Cervical
vagus
SCG Sciatic nerve
Rabbit
Rat Guinea pig Calf Rabbit Rat Calf Frog
Without theophylline
With theophylline
Control
Stimulated
Control
Stimulated
19.8 -+ 4.4 (49) 10.9 ± 3.7 (5) 6.8 ± 2.9 (4)
91.2 -+ 16.8 (28) 24.7 ± 6.1 (5) 30.4 ± 6.6 (4)
24.1 ~ 4.8 (12) 12.7 ± 4.3 (4) 8.1 ± 2.3 (4)
98.6 -+ 15.8 (9) 33.7 ± 7.1 (4) 28.9 ± 5.7 (4)
8.9 21.1 12.5 14.0 4.4
19.9 18.4 18.1 18.4 13.5
6.8 ± 3.1 24.5 ± 3.4 18.8-+ 3.5 16.9 ± 5.0 7.1 ± 2.2
21.4 63.7 50.1 43.2 16.3
± 3.2 ± 3.4 ± 2.6 ± 3.9 ± 1.7
(6) (8) (6) (5) (6)
+ ± ± -+ +
4.8 2.2 4.8 4.4 3.6
(6) (8) (6) (5) (5)
(4) (8) (5) (5) (6)
-+ ± ± ± ±
4.0 6.8 6.2 7.2 2.8
(4) (8) (5) (6) (6)
a n d i t h a s b e e n s u g g e s t e d t h a t in t h e a b s e n c e o f a p h o s p h o d i e s t e r a s e i n h i b i t o r , the increased production of cAMP triggers the activation of the cAMP metabolizing enzyme [10,11]. The compound 7-oxa-13°prostynoic acid has been found to competitively i n h i b i t c A M P s y n t h e s i s i n d u c e d in m o u s e o v a r i e s b y PGE~ a n d PGE~ [ 8 ] . I n rabbit vagus nerve, however, this substance was without effect on the cAMP increase caused by PGE1. Furthermore, the increase was also unaffected by t h e p r e s e n c e in t h e i n c u b a t i o n m e d i u m o f 1 0 - s M o f e i t h e r d i h o m o - 7 - 1 i n o l e n i c a c i d o r a r a c h i d o n i c a c i d , p r e c u r s o r s o f t h e 1 a n d 2 series o f p r o s t a g l a n dins. Although these compounds were found not to affect the accumulation o f c A M P i n d u c e d b y PGE~ in r a b b i t v a g u s n e r v e , i t s h o u l d b e b o r n e in m i n d t h a t t h e p r o s t a g l a n d i n e f f e c t in t h e v a g u s h a s a c e r t a i n d e g r e e o f s p e c i f i c i t y in t h a t i t is i n d u c e d p r i m a r i l y b y p r o s t a g l a n d i n s o f t h e E t y p e . I n t h i s r e s p e c t i t is o f i n t e r e s t t h a t t h e a c i d s m e n t i o n e d a b o v e h a d n o a g o n i s t i c e f f e c t o n t h e c A M P l e v e l in r a b b i t v a g u s n e r v e . From the results described above no conclusion can be drawn with regard t o t h e m e c h a n s i m o f t h e P G E ~ - i n d u c e d c A M P a c c u m u l a t i o n in p e r i p h e r a l n e r v o u s t i s s u e . I n t h e S C G , t h e s y n t h e s i s o f c A M P c a n b e s t i m u l a t e d b y inc u b a t i o n in d e p o l a r i z i n g m e d i a [ 7 ] , b u t t h i s is n o t t h e c a s e f o r r a b b i t v a g u s [12]. Thus, release of an intermediate might account for the prostaglandin e f f e c t in t h e S C G , b u t is m u c h less l i k e l y t o o c c u r in v a g u s n e r v e . I n c o n c e n -
364 t r a t i o n s similar t o t h o s e used in the present s t u d y for the same tissues, PGE, alters a m p l i t u d e and c o n d u c t i o n v e l o c i t y o f t h e c o m p o u n d action p o t e n t i a l in frog sciatic nerve [ 5] and it decreases the a m p l i t u d e o f the slow i n h i b i t o r y p o s t s y n a p t i c p o t e n t i a l in r a b b i t SCG [ 9 ] . The results o f the present experim e n t s raise t h e possibility t h a t these e l e c t r o p h y s i o l o g i c a l effects of the Eprostaglandins involve a m o d i f i c a t i o n o f the cAMP level. However, f u r t h e r investigation is n e e d e d t o s u b s t a n t i a t e such an interrelationship. ACKNOWLEDGEMENTS I t h a n k Dr. J. Pike, U p j o h n Co., K a l a m a z o o / M i c h i g a n for the prostaglandins and Professor J. Fried, D e p a r t m e n t o f B i o c h e m i s t r y , University o f Chicago, f o r 7 - o x a - 1 3 - p r o s t y n o i c acid. REFERENCES 1 Collier, H.O.J. and Roy, A.C., Morphine like drugs inhibit the stimulation by Eprostaglandins of cyclic AMP formation by rat brain homogenate, Nature (Lond.), 248 (1974) 24--27. 2 Dismukes, K. and Daly, J.W., Accumulation of adenosine 3',5'-monophosphate in rat brain slices: effects of prostaglandins, Life Sci., 17 (1975) 199--210. 3 Duffy, M.J. and Powell, D., Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion, Biochim. biophys. Acta (Amst.), 385 (1975) 275--280. 4 Gilman, A.G. and Schrier, B., Adenosine 3',5'-monophosphate in fetal rat brain cell cultures: effect of catecholamines, Mol. Pharmacol., 8 (1972) 410--416. 5 Horrobin, D.F., Durand, L.G. and Manku, M.S., Prostaglandin E 1 modifies nerve conduction and interferes with local anaesthetic action, Prostaglandins, 14 (1977) 103--108. 6 Kalix, P., Effect of decentralization and glucose withdrawal on the potassium-induced cAMP-increase in the rabbit superior cervical ganglion, Europ. J. Pharmacol., 39 (1976) 313--321. 7 Kalix, P. and Roch, Ph., Evidence of depolarization-induced cAMP increase in the superior cervical ganglion of several mammalian species, Gen. Pharmacol., 7 (1976) 267--270. 8 Kuehl, F. Jr., Humes, J.L., Tarnoff, J., Cirillo, V.J. and Ham E.A., Prostaglandin receptor site: evidence for an essential role in the action of luteinizing hormone, Science, 169 (1970) 883--886. 9 McAfee, D. and Greengard, P, Adenosine 3',5'-monophosphate: electrophysiological evidence for a role in synaptic transmission, Science, 178 (1972) 310--312. 10 Pawlson, L.G., Lovell-Smith, C.J., Manganiello, V.C. and Vaughan, M., Effects of epinephrine, adrenocorticotropic hormone and theophylline on adenosine 3',5'monophosphate phosphodiesterase activity in fat cells, Proc. Nat. Acad. Sci. (Wash.), 71 (1974) 1639--1642. 11 Roch, Ph. and Kalix, P., Adenosine 3',5'-monophosphate in bovine superior cervical ganglion: effect of high extracellular potassium, Biochem. Pharmacol., 24 (1975) 1293--1296. 12 Roch, Ph. and Salamin A., Effect of beta-adrenergic drugs on the adenosine 3'-5'monophosphate content in rabbit vagus. J. Neurochem., 28 (1977) 947--950. 13 Segal, M. and Bloom, F., The action of norepinephrine on the rat hippocampus: iontophoretic studies, Brain Res., 72 (1974) 79--97. 14 Siggins, G.R., Hoffer, B.J. and Bloom, F., Prostaglandin-norepinephrine interactions in brain: microelectrophoretic and histochemical correlates, Ann. N.Y. Acad. Sci., 180 (1971) 302N323.
361
© Elsevier/North-Holland Scientific Publishers Ltd.
PROSTAGLANDIN E1 RAISES THE cAMP CONTENT OF PERIPHERAL NERVE TISSUE
PETER KALIX Department of Pharmacology, University of Geneva, Geneva (Switzerland) (Received December 18th, 1978) (Revised version received January 18th, 1979) {Accepted January 23rd, 1979)
SUMMARY
Prostaglandins of the E type have been found to increase the cAMP content in peripheral nerve tissue of several species. In rabbit vagus nerve, for example, the effect is rapid (1--5 min), it can be elicited by 10 -6 M PGE1 and it is maximal at 10 -s M. In this preparation the increase of the cAMP content caused by PGE, is about 4-fold, whereas it is about 2-fold in the vagus of calf. PGE1 also causes an increase in cAMP level in the superior cervical ganglion of calf, rat and rabbit. In these tissues, however, the presence of a phosphodiesterase inhibitor is required for cAMP accumulation.
The effect of the prostaglandins on cAMP synthesis in the central nervous system is well documented [1--4] and it has been suggested that these substances interfere with the effect of noradrenaline on cerebellar Purkinje cells [14] and hippocampal pyramidal cells [13]. With regard to the peripheral nervous system there is evidence that a modification of the electrophysiological properties of frog sciatic nerve [5] and of the superior cervical ganglion (SCG) of rabbit [9] results from superfusion with solutions of PGE1 in vitro. The experiments described in the following demonstrate that, under similar conditions, the prostaglandins increase the concentration of cAMP in these and several other tissues from the peripheral nervous system of various species. The tissues under study were dissected from unanaesthetized animals immediately after death and the connective tissue sheath was carefully removed from all preparations except those of calf vagus and frog sciatic nerve. The individual tissue samples were incubated in 5 ml of a KrebsRinger solution (see legend of Table I), the prostaglandins and the corresponding acids were added in the form of ethanolic solutions. This resulted in a solvent concentration of 1% in the medium, the same amount of ethanol was added to the medium of the control samples. After the incubation
362
period the samples were denaturated, an extract was assayed for cAMP and the amount of protein determined. The details of these procedures have been described previously [6,11]. When sections of rabbit vagus nerve were incubated in solutions containing E-prostaglandins, a rapid accumulation of cAMP was seen to occur in the tissue. Fig. 1 shows time course (A) and concentration dependence (B) of this effect. Both PGE~ (Table I) and PGE2 caused an approximately 4-fold increase of the cAMP content, while PGF~a and PGF2a had no effect (not shown). These observations indicate that in peripheral nerve, as has been shown for a preparation from the central nervous system [2], the prostaglandins of the E t y p e affect the cAMP content in a relatively specific manner. The cAMP-accumulating effect of PGE~ in the rabbit vagus is more rapid than that in brain slices, where the maximal cAMP level is attained after 15--20 min [2]. Moreover, when compared to the latter preparation, the vagus nerve shows a sensitivity that is greater by approximately a factor of 10 [2]. In order to exclude the possibility that the observed increases in cAMP are an effect specific for rabbit tissue, samples of vagus nerve from several other species were tested for their responsiveness to PGE~. The results of these experiments (Table I) indicated that, although there were minor differences in the magnitude of the cAMP increase, the prostaglandin-induced cAMP accumulation is a general observation in vagus nerves regardless of species. A 3-fold increase of the cAMP concentration following incubation with PGE~ was also observed in frog sciatic nerve, a myelinated nerve from a non-mammalian species. Additionally, vagus nerve tissue from several species was also stimulated with PGE~ in media containing the phosphodiesterase inhibitor theophylline at a concentration that did not change the basal cAMP level," but no modification of the prostaglandin effect resulted from the addition of this substance (Table I). On the other hand in the SCG of various species a PGE~-induced cAMP accumulation could only be observed when theophylline was present in the medium (Table I). This requirement of phosphodiesterase inhibition for the detection of an increased rate of cAMP synthesis in the ganglion has already been observed in previous studies A
B
CAMP ~ccum~lO~n ~c~nr % ot control . . -
c AMP aCcumulot~n ~oo 1% ot cont,ol
~oo i
// ~
"
i/
22,0
30o t 20c
'/ ~ac r~,/
"
. . ~ _ _
I h ~ ol ~cubQt,~,
1oo: ~ / ' " " "
conce'~trat~ ot PGE,,
Fig. 1. Time course and concentration dependence of the PGErinduced c A M P accumulation in rabbit vagus nerve. T w o sections of desheathed rabbit vagus were incubated for a given period in 10 -5 M PGE~ (A) or for 7 min in a given PGE~ concentration (B), a third section served as unstimulated control. The c A M P content of the stimulated tissue is expressed as percent of the c A M P content of the corresponding control. Each circle represents one stimulated sample and the curve has been drawn to approximate the m e a n of the two experiments."
363 TABLE I E F F E C T OF PGE, ON THE CYCLIC AMP CONCENTRATION IN PERIPHERAL NERVE TISSUE OF VARIOUS SPECIES Individual samples consisting of sections of vagus or sciatic nerve, of SCG of rabbit divided longitudinally whole SCG of rat or small blocks of calf SCG tissue were equilibrated for approx. 30 rain in a medium containing (retool/l) NaCI 136; KC1 5.6; NaHCO 3 20.0; NaH2PO 4 1.2; ~aC12 2.2; MgCI 2 1.2 and glucose 5.5. The solution was continuously bubbled with a mixture of 5% CO2--95% O; and kept at 37°C (19°C for frog sciatic nerve). Subsequently the tissue samples were stimulated by incubation for 7 min in 10 -5 M PGE~ (column 2 and 4), some of them in media containing 10 -~ M t h e o p h y l l i n e (column 4). F o r the latter experiments the corresponding control tissue was incubated for 7 min in theophylline alone (column 3). Results are expressed as pmol cAMP/rag protein ± S.E.M. with the number of experiments in parenthesis.
Cervical
vagus
SCG Sciatic nerve
Rabbit
Rat Guinea pig Calf Rabbit Rat Calf Frog
Without theophylline
With theophylline
Control
Stimulated
Control
Stimulated
19.8 -+ 4.4 (49) 10.9 ± 3.7 (5) 6.8 ± 2.9 (4)
91.2 -+ 16.8 (28) 24.7 ± 6.1 (5) 30.4 ± 6.6 (4)
24.1 ~ 4.8 (12) 12.7 ± 4.3 (4) 8.1 ± 2.3 (4)
98.6 -+ 15.8 (9) 33.7 ± 7.1 (4) 28.9 ± 5.7 (4)
8.9 21.1 12.5 14.0 4.4
19.9 18.4 18.1 18.4 13.5
6.8 ± 3.1 24.5 ± 3.4 18.8-+ 3.5 16.9 ± 5.0 7.1 ± 2.2
21.4 63.7 50.1 43.2 16.3
± 3.2 ± 3.4 ± 2.6 ± 3.9 ± 1.7
(6) (8) (6) (5) (6)
+ ± ± -+ +
4.8 2.2 4.8 4.4 3.6
(6) (8) (6) (5) (5)
(4) (8) (5) (5) (6)
-+ ± ± ± ±
4.0 6.8 6.2 7.2 2.8
(4) (8) (5) (6) (6)
a n d i t h a s b e e n s u g g e s t e d t h a t in t h e a b s e n c e o f a p h o s p h o d i e s t e r a s e i n h i b i t o r , the increased production of cAMP triggers the activation of the cAMP metabolizing enzyme [10,11]. The compound 7-oxa-13°prostynoic acid has been found to competitively i n h i b i t c A M P s y n t h e s i s i n d u c e d in m o u s e o v a r i e s b y PGE~ a n d PGE~ [ 8 ] . I n rabbit vagus nerve, however, this substance was without effect on the cAMP increase caused by PGE1. Furthermore, the increase was also unaffected by t h e p r e s e n c e in t h e i n c u b a t i o n m e d i u m o f 1 0 - s M o f e i t h e r d i h o m o - 7 - 1 i n o l e n i c a c i d o r a r a c h i d o n i c a c i d , p r e c u r s o r s o f t h e 1 a n d 2 series o f p r o s t a g l a n dins. Although these compounds were found not to affect the accumulation o f c A M P i n d u c e d b y PGE~ in r a b b i t v a g u s n e r v e , i t s h o u l d b e b o r n e in m i n d t h a t t h e p r o s t a g l a n d i n e f f e c t in t h e v a g u s h a s a c e r t a i n d e g r e e o f s p e c i f i c i t y in t h a t i t is i n d u c e d p r i m a r i l y b y p r o s t a g l a n d i n s o f t h e E t y p e . I n t h i s r e s p e c t i t is o f i n t e r e s t t h a t t h e a c i d s m e n t i o n e d a b o v e h a d n o a g o n i s t i c e f f e c t o n t h e c A M P l e v e l in r a b b i t v a g u s n e r v e . From the results described above no conclusion can be drawn with regard t o t h e m e c h a n s i m o f t h e P G E ~ - i n d u c e d c A M P a c c u m u l a t i o n in p e r i p h e r a l n e r v o u s t i s s u e . I n t h e S C G , t h e s y n t h e s i s o f c A M P c a n b e s t i m u l a t e d b y inc u b a t i o n in d e p o l a r i z i n g m e d i a [ 7 ] , b u t t h i s is n o t t h e c a s e f o r r a b b i t v a g u s [12]. Thus, release of an intermediate might account for the prostaglandin e f f e c t in t h e S C G , b u t is m u c h less l i k e l y t o o c c u r in v a g u s n e r v e . I n c o n c e n -
364 t r a t i o n s similar t o t h o s e used in the present s t u d y for the same tissues, PGE, alters a m p l i t u d e and c o n d u c t i o n v e l o c i t y o f t h e c o m p o u n d action p o t e n t i a l in frog sciatic nerve [ 5] and it decreases the a m p l i t u d e o f the slow i n h i b i t o r y p o s t s y n a p t i c p o t e n t i a l in r a b b i t SCG [ 9 ] . The results o f the present experim e n t s raise t h e possibility t h a t these e l e c t r o p h y s i o l o g i c a l effects of the Eprostaglandins involve a m o d i f i c a t i o n o f the cAMP level. However, f u r t h e r investigation is n e e d e d t o s u b s t a n t i a t e such an interrelationship. ACKNOWLEDGEMENTS I t h a n k Dr. J. Pike, U p j o h n Co., K a l a m a z o o / M i c h i g a n for the prostaglandins and Professor J. Fried, D e p a r t m e n t o f B i o c h e m i s t r y , University o f Chicago, f o r 7 - o x a - 1 3 - p r o s t y n o i c acid. REFERENCES 1 Collier, H.O.J. and Roy, A.C., Morphine like drugs inhibit the stimulation by Eprostaglandins of cyclic AMP formation by rat brain homogenate, Nature (Lond.), 248 (1974) 24--27. 2 Dismukes, K. and Daly, J.W., Accumulation of adenosine 3',5'-monophosphate in rat brain slices: effects of prostaglandins, Life Sci., 17 (1975) 199--210. 3 Duffy, M.J. and Powell, D., Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion, Biochim. biophys. Acta (Amst.), 385 (1975) 275--280. 4 Gilman, A.G. and Schrier, B., Adenosine 3',5'-monophosphate in fetal rat brain cell cultures: effect of catecholamines, Mol. Pharmacol., 8 (1972) 410--416. 5 Horrobin, D.F., Durand, L.G. and Manku, M.S., Prostaglandin E 1 modifies nerve conduction and interferes with local anaesthetic action, Prostaglandins, 14 (1977) 103--108. 6 Kalix, P., Effect of decentralization and glucose withdrawal on the potassium-induced cAMP-increase in the rabbit superior cervical ganglion, Europ. J. Pharmacol., 39 (1976) 313--321. 7 Kalix, P. and Roch, Ph., Evidence of depolarization-induced cAMP increase in the superior cervical ganglion of several mammalian species, Gen. Pharmacol., 7 (1976) 267--270. 8 Kuehl, F. Jr., Humes, J.L., Tarnoff, J., Cirillo, V.J. and Ham E.A., Prostaglandin receptor site: evidence for an essential role in the action of luteinizing hormone, Science, 169 (1970) 883--886. 9 McAfee, D. and Greengard, P, Adenosine 3',5'-monophosphate: electrophysiological evidence for a role in synaptic transmission, Science, 178 (1972) 310--312. 10 Pawlson, L.G., Lovell-Smith, C.J., Manganiello, V.C. and Vaughan, M., Effects of epinephrine, adrenocorticotropic hormone and theophylline on adenosine 3',5'monophosphate phosphodiesterase activity in fat cells, Proc. Nat. Acad. Sci. (Wash.), 71 (1974) 1639--1642. 11 Roch, Ph. and Kalix, P., Adenosine 3',5'-monophosphate in bovine superior cervical ganglion: effect of high extracellular potassium, Biochem. Pharmacol., 24 (1975) 1293--1296. 12 Roch, Ph. and Salamin A., Effect of beta-adrenergic drugs on the adenosine 3'-5'monophosphate content in rabbit vagus. J. Neurochem., 28 (1977) 947--950. 13 Segal, M. and Bloom, F., The action of norepinephrine on the rat hippocampus: iontophoretic studies, Brain Res., 72 (1974) 79--97. 14 Siggins, G.R., Hoffer, B.J. and Bloom, F., Prostaglandin-norepinephrine interactions in brain: microelectrophoretic and histochemical correlates, Ann. N.Y. Acad. Sci., 180 (1971) 302N323.