Medical Hypotheses
ENTEROTOXINS
5: 707-710, 1979
OF ESCHERICHIA
COLI AND EPILEPSY
E.Elomaa, Pitlj;inm;ikiEpilepsy Research Centre Kylgkirkontie 23, 00370 Helsinki, Finland ABSTRACT Evidence exists that cyclic nucleotides play an important role in the stabilisation of developing synapses during the early postnatal period, and later on participate in the generation of the slow excitatory and inhibitory postsynaptic potentials. It is postulated that enterotoxins of Escherichia coli, due to their long-lasting and specific action on cyclic nucleotide-dependent processes , provide a unique mechanism for selective impairment of synaptogenesis in the abscence of cell loss. Therefore it seems possible that early enteritis, when caused by certain pathogenic strains of Escherichia coli, might be an aetiological factor in the genesis of idiopathic epilepsy. Key Words: E.coli; enterotoxins, CAMP; cGMP; epilepsy
heat-stable,
heat-labile,
INTRODUCTION Arguing from epidemiological EEG data it has been postulated that gastroenteritis during the first postnatal month might be associated with spontaneous epileptogenic activity in the adult EEG and a lowered seizure threshold (1). This hypothesis, although highly speculative as such, seems to be in accordance both with the current theory concerning the principles involved in synaptogenesis and with recent experimental findings on the mechanisms of action of enterotoxins. HYPOTHESIS The concept of selective stabilisation of developing synapses suggests that the mature synapse represents the end product of a continuous process of growth and degeneration of the terminal part of nerve fibers (2). In the mammalian nervous system there are two separate periods of degeneration. The first is characterized by a powerful reduction in the number of neurones during and immediately after neuroblast proliferation (2). The stabilisation in the number of neurones is followed by a rapid growth of axon collaterals and dendrites (2). This growth continues until birth, whereupon a considerable part of the extensions disappears (2). In the rat the adult picture in morphology is achieved at the age of two weeks (2). 707
In the light of present knowledge concerning the action of enterOtOXinS it seems possible that the later stage of degeneration might be blocked or delayed under certain conditions during the course of early enteritis. It is well established that enterotoxins, like glycoprotein hormones, activate adenylate cyclase by binding to gangliosides at the cell membrane (3). The structural effects of enterotoxins, characterized by the formation of neurite-like extensions (4), may by mimicked by 3; 5'- cyclic adenosine monophosphate (cyclic AMP) (5). However, the effects of enterotoxins are extremely long-lasting: the powerful hyperactivity following application of enterotoxins into the basal nuclei of the brain lasts for weeks (6,7) and it has been suggested that enterotoxins are irreversibly bound to the membrane receptors (4). Therefore, a transient contact between an immature brain and enterotoxins might well result in a growth-inducing effect extending over the whole postnatal period of degeneration. Furthermore, there is experimental data of very recent origin suggesting that the mode of the postulated affection might be decisively dependent on factors related to the heat-sensitivity of the enterotoxins. Evidence has been found that the excitability of the postsynaptic neurone is regulated by cyclic nucleotide-dependent processes in such a way that 3; 5'- cyclic guanosine monophosphate (cyclic GMP) is involved in the generation of slow excitatory postsynaptic potentials while cyclic AMP is needed for the generation of slow inhibitory postsynaptic potentials (8). On the other hand it is known that the effects of the heat-stable enterotoxin of E.coli are due to a rise in cyclic GMF levels (9). whereas the heat-labile enterotoxin of E.coli and cholera enterotoxin exert their action through activation of cyclic AMP (10). Adding together these findings from independent lines of investigation it can be concluded that the development of the excitatory and inhibitory synaptic systems may be selectively interfered with by enterotoxins secreted by different strains of E.coli. Moreover, this selectivity might also hold true for the localisation of the involvement: In cerebellar cell homogenates only the levels of cyclic GMP, and not those of cyclic AMP, display the dramatic postnatal modulation (11) typical for cyclic AMP of the cerebrum (12). In addition, for the present the only structure within the brain in which the presence of a cyclic W-dependent protein kinase has been demonstrated is the cerebellum (13). Against this background it is tempting to speculate that induction of dendrite growth by the cyclic GMP-dependent heat-stable enterotoxin of E.coli during the postnatal stage of degeneration might result in an increased excitability of the neuronal networks in the cerebellum. The plausibility of this kind of suggestion is indirectly supported by recent reports that diazepam (14), ethanol (15,16) and pentobarbital (17), which all have anticonvulsant action, depress cerebellar cyclic GMP without affecting cyclic AMP. Assuming now that withdrawal of ethanol after prolonged use is followed by a rebound increase in cyclic GMP, so the abstinence symptoms including epileptic seizures might well be related to a cyclic GMP-induced cerebellar hyperexcitability. CONCLUSIONS In conclusion it is suggested that enterotoxins of Escherichia coli, due to their long-lasting action on cyclic nucleotide-dependent processes provide a unique mechanism for selective impairment of either the excitatory or inhibitory synaptic system in the abscence of cell loss during the course of early development. Because the enterotoxins are rapidly neutralized by 708
IgA antibodies of human breast milk (18) the hypothesis in addition makes it possible to understand the clinical significance of low IgA levels observed in idiopathic epilepsy (19). Testing of the hypothesis should be possible by assessing the long-term effects of intraventricularly administered enterotoxins on the seizure threshold and EEG patterns in experimental animals at different stages of maturation. REFERENCES 1.
Elomaa E, Lehtovaara R, Bardy A. Do the peptide hormones common to intestine and brain participate in the genesis of epilepsy? Medical Hypotheses, 4:189, 1978
2.
Changeux J-P, Danchin A. Selective stabilisation of developing synapses as a mechanism for the spesification of neuronal networks. Nature, 264:705, 1976
3.
Fishman P H, Brady R 0. Biosynthesis Science, 194:906, 1976
4.
Rappaport R S, Grant N H. Growth hormone releasing factor of microbial orgin. Nature, 248:73, 1974
5.
Waymire J C, Gilmer-Waymire K, Haycock J W. Cyclic-AMP-induced differentiation in neuroblastoma is independent of cell division rate. Nature, 276:194, 1978
6.
Quenzer L F, Galli C L, Neff N H. Activation of the nigrostrial dopaminergic pathway by injection of cholera enterotoxin into the substantia nigra. Science, 195:78, 1977
7.
Miller R J, Kelly P H. Dopamine-like effects of cholera toxin in the central nervous system. Nature, 255:233, 1975
8.
Greengard P. Possible role for cyclic nucleotides and phosphorylated membrane proteins in postsynaptic actions of neurotransmitters. Nature, 260:101, 1976
9.
Hughes J M, Murad F, Chang B, Guerrant R L. Role of cyclic GMl? in the action of heat-stable enterotoxin of Escherichia coli. Nature, 271:755, 1978
and function of gangliosides.
10.
Gill D M, Evans D J Jr, Evans D G. Mechanism of activation of adenylate cyclase in vitro by polymyxin-released, heat-labile enterotoxin of Escherichia coli. J. Infec. Dis., 133:S103, 1976
11.
Grathwaite J, Baldzs R. Supersensitivity to the cyclic GMP response to glutamate during cerebellar maturation. Nature, 275~328, 1978
12.
Cheney D L, Costa E, Racagni G, Zsilla G. Cholinergic and adenylate cyclase systems in rat brain nuclei during development. p. 41 in Brain Dysfunction in Infantile Febrile Convulsions. ( MAB Brazier, F Coceani, eds.) Raven Press, New York, 1976
13.
Schlichter D J, Casnellier J E, Greengard P. An endogenous substrate for cGMP-dependent protein kinase in mammalian cerebellum. Nature, 273:61, 1978
709
14.
Mao C C, Guidotti A, Costa E. Inhibition by diazepam of the tremor and the increase of cerebellar cGMP content elicited by harmaline. Brain Res., 83:516, 1975
15.
Redos J D, Catravas G N, Hunt W A. Ethanol-induced depletion of cerebellar guanosine 3',5'- cyclic monophosphate. Science, 193:58, 1976
16.
Mailman R B, Frye G D, Mueller R A, Breese G R. Thyrotropin-releasing hormone reversal of ethanol-induced decrease in cerebellar cGMP. Nature, 272:832, 1978
17.
Kimura H, Thomas E, Murad F. Effects of decapitation, ether and pentobarbital on guanosine 3' ,5'-phosphate and adenosine 3',5'-phosphate levels in rat tissues. Biochim. Biophys. Acta, 343:519, 1974
18.
Stoliar 0 A, Pelley R P, Kaniecki-Green E, Klaus M H, Carpenter C C J. Secretory IgA against enterotoxins in breast-milk. Lancet i:1258, 1976
19.
Fontana A, Grob P J, Sauter R, Joller H. IgA deficiency, epilepsy, and hydantoin medication. Lancet ii:228, 1976
710
ENTEROTOXINS
5: 707-710, 1979
OF ESCHERICHIA
COLI AND EPILEPSY
E.Elomaa, Pitlj;inm;ikiEpilepsy Research Centre Kylgkirkontie 23, 00370 Helsinki, Finland ABSTRACT Evidence exists that cyclic nucleotides play an important role in the stabilisation of developing synapses during the early postnatal period, and later on participate in the generation of the slow excitatory and inhibitory postsynaptic potentials. It is postulated that enterotoxins of Escherichia coli, due to their long-lasting and specific action on cyclic nucleotide-dependent processes , provide a unique mechanism for selective impairment of synaptogenesis in the abscence of cell loss. Therefore it seems possible that early enteritis, when caused by certain pathogenic strains of Escherichia coli, might be an aetiological factor in the genesis of idiopathic epilepsy. Key Words: E.coli; enterotoxins, CAMP; cGMP; epilepsy
heat-stable,
heat-labile,
INTRODUCTION Arguing from epidemiological EEG data it has been postulated that gastroenteritis during the first postnatal month might be associated with spontaneous epileptogenic activity in the adult EEG and a lowered seizure threshold (1). This hypothesis, although highly speculative as such, seems to be in accordance both with the current theory concerning the principles involved in synaptogenesis and with recent experimental findings on the mechanisms of action of enterotoxins. HYPOTHESIS The concept of selective stabilisation of developing synapses suggests that the mature synapse represents the end product of a continuous process of growth and degeneration of the terminal part of nerve fibers (2). In the mammalian nervous system there are two separate periods of degeneration. The first is characterized by a powerful reduction in the number of neurones during and immediately after neuroblast proliferation (2). The stabilisation in the number of neurones is followed by a rapid growth of axon collaterals and dendrites (2). This growth continues until birth, whereupon a considerable part of the extensions disappears (2). In the rat the adult picture in morphology is achieved at the age of two weeks (2). 707
In the light of present knowledge concerning the action of enterOtOXinS it seems possible that the later stage of degeneration might be blocked or delayed under certain conditions during the course of early enteritis. It is well established that enterotoxins, like glycoprotein hormones, activate adenylate cyclase by binding to gangliosides at the cell membrane (3). The structural effects of enterotoxins, characterized by the formation of neurite-like extensions (4), may by mimicked by 3; 5'- cyclic adenosine monophosphate (cyclic AMP) (5). However, the effects of enterotoxins are extremely long-lasting: the powerful hyperactivity following application of enterotoxins into the basal nuclei of the brain lasts for weeks (6,7) and it has been suggested that enterotoxins are irreversibly bound to the membrane receptors (4). Therefore, a transient contact between an immature brain and enterotoxins might well result in a growth-inducing effect extending over the whole postnatal period of degeneration. Furthermore, there is experimental data of very recent origin suggesting that the mode of the postulated affection might be decisively dependent on factors related to the heat-sensitivity of the enterotoxins. Evidence has been found that the excitability of the postsynaptic neurone is regulated by cyclic nucleotide-dependent processes in such a way that 3; 5'- cyclic guanosine monophosphate (cyclic GMP) is involved in the generation of slow excitatory postsynaptic potentials while cyclic AMP is needed for the generation of slow inhibitory postsynaptic potentials (8). On the other hand it is known that the effects of the heat-stable enterotoxin of E.coli are due to a rise in cyclic GMF levels (9). whereas the heat-labile enterotoxin of E.coli and cholera enterotoxin exert their action through activation of cyclic AMP (10). Adding together these findings from independent lines of investigation it can be concluded that the development of the excitatory and inhibitory synaptic systems may be selectively interfered with by enterotoxins secreted by different strains of E.coli. Moreover, this selectivity might also hold true for the localisation of the involvement: In cerebellar cell homogenates only the levels of cyclic GMP, and not those of cyclic AMP, display the dramatic postnatal modulation (11) typical for cyclic AMP of the cerebrum (12). In addition, for the present the only structure within the brain in which the presence of a cyclic W-dependent protein kinase has been demonstrated is the cerebellum (13). Against this background it is tempting to speculate that induction of dendrite growth by the cyclic GMP-dependent heat-stable enterotoxin of E.coli during the postnatal stage of degeneration might result in an increased excitability of the neuronal networks in the cerebellum. The plausibility of this kind of suggestion is indirectly supported by recent reports that diazepam (14), ethanol (15,16) and pentobarbital (17), which all have anticonvulsant action, depress cerebellar cyclic GMP without affecting cyclic AMP. Assuming now that withdrawal of ethanol after prolonged use is followed by a rebound increase in cyclic GMP, so the abstinence symptoms including epileptic seizures might well be related to a cyclic GMP-induced cerebellar hyperexcitability. CONCLUSIONS In conclusion it is suggested that enterotoxins of Escherichia coli, due to their long-lasting action on cyclic nucleotide-dependent processes provide a unique mechanism for selective impairment of either the excitatory or inhibitory synaptic system in the abscence of cell loss during the course of early development. Because the enterotoxins are rapidly neutralized by 708
IgA antibodies of human breast milk (18) the hypothesis in addition makes it possible to understand the clinical significance of low IgA levels observed in idiopathic epilepsy (19). Testing of the hypothesis should be possible by assessing the long-term effects of intraventricularly administered enterotoxins on the seizure threshold and EEG patterns in experimental animals at different stages of maturation. REFERENCES 1.
Elomaa E, Lehtovaara R, Bardy A. Do the peptide hormones common to intestine and brain participate in the genesis of epilepsy? Medical Hypotheses, 4:189, 1978
2.
Changeux J-P, Danchin A. Selective stabilisation of developing synapses as a mechanism for the spesification of neuronal networks. Nature, 264:705, 1976
3.
Fishman P H, Brady R 0. Biosynthesis Science, 194:906, 1976
4.
Rappaport R S, Grant N H. Growth hormone releasing factor of microbial orgin. Nature, 248:73, 1974
5.
Waymire J C, Gilmer-Waymire K, Haycock J W. Cyclic-AMP-induced differentiation in neuroblastoma is independent of cell division rate. Nature, 276:194, 1978
6.
Quenzer L F, Galli C L, Neff N H. Activation of the nigrostrial dopaminergic pathway by injection of cholera enterotoxin into the substantia nigra. Science, 195:78, 1977
7.
Miller R J, Kelly P H. Dopamine-like effects of cholera toxin in the central nervous system. Nature, 255:233, 1975
8.
Greengard P. Possible role for cyclic nucleotides and phosphorylated membrane proteins in postsynaptic actions of neurotransmitters. Nature, 260:101, 1976
9.
Hughes J M, Murad F, Chang B, Guerrant R L. Role of cyclic GMl? in the action of heat-stable enterotoxin of Escherichia coli. Nature, 271:755, 1978
and function of gangliosides.
10.
Gill D M, Evans D J Jr, Evans D G. Mechanism of activation of adenylate cyclase in vitro by polymyxin-released, heat-labile enterotoxin of Escherichia coli. J. Infec. Dis., 133:S103, 1976
11.
Grathwaite J, Baldzs R. Supersensitivity to the cyclic GMP response to glutamate during cerebellar maturation. Nature, 275~328, 1978
12.
Cheney D L, Costa E, Racagni G, Zsilla G. Cholinergic and adenylate cyclase systems in rat brain nuclei during development. p. 41 in Brain Dysfunction in Infantile Febrile Convulsions. ( MAB Brazier, F Coceani, eds.) Raven Press, New York, 1976
13.
Schlichter D J, Casnellier J E, Greengard P. An endogenous substrate for cGMP-dependent protein kinase in mammalian cerebellum. Nature, 273:61, 1978
709
14.
Mao C C, Guidotti A, Costa E. Inhibition by diazepam of the tremor and the increase of cerebellar cGMP content elicited by harmaline. Brain Res., 83:516, 1975
15.
Redos J D, Catravas G N, Hunt W A. Ethanol-induced depletion of cerebellar guanosine 3',5'- cyclic monophosphate. Science, 193:58, 1976
16.
Mailman R B, Frye G D, Mueller R A, Breese G R. Thyrotropin-releasing hormone reversal of ethanol-induced decrease in cerebellar cGMP. Nature, 272:832, 1978
17.
Kimura H, Thomas E, Murad F. Effects of decapitation, ether and pentobarbital on guanosine 3' ,5'-phosphate and adenosine 3',5'-phosphate levels in rat tissues. Biochim. Biophys. Acta, 343:519, 1974
18.
Stoliar 0 A, Pelley R P, Kaniecki-Green E, Klaus M H, Carpenter C C J. Secretory IgA against enterotoxins in breast-milk. Lancet i:1258, 1976
19.
Fontana A, Grob P J, Sauter R, Joller H. IgA deficiency, epilepsy, and hydantoin medication. Lancet ii:228, 1976
710
