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Morphological and pharmacological evidence for the existence of brain regulatory circuits in the immune response
~
Pergamon
Int. J. lmmunopharmac., Vol. 19, No. 9/10, pp. 507 -510, 1997 ~S~1998 Published by ElsevierScienceLtd on behalf of the International Societyfor lmmunopharmacology Printed in Great Britain 0192~0561/98 $19.00+ .00
PII:S0192-0561(97)00049-~ MORPHOLOGICAL A N D PHARMACOLOGICAL EVIDENCE FOR THE EXISTENCE OF BRAIN R E G U L A T O R Y CIRCUITS IN THE I M M U N E RESPONSE K. MASEK *~ and P. PETROVICKY b Institute of Pharmacology, Academy of Sciences, Prague, Czech Republic and bInstitute of Anatomy, Medical Faculty, Charles University, Prague, Czech Republic (ReceivedJbr publication 19 Auyust 1997) Abstraet--Muramyl dipeptide (MDP) has a variety of biological effects including the effect on CNS, such a promotion of sleep, fever, analgesic effect or some behavioural changes and of course a very potent effect on immune system. The latter effect is at least partly mediated through the structure in CNS~ With the small electrolytic lesions which were placed in brain from the spinal cord through the brain stem up to the cerebral cortex we have identified a number of structures such as medial frontal cortex (area CgrCg3), subnucleus basomedialis and centralis of amygdala, subnucleus medialis and dorsolateralis of nucleus parabrachialis, lateral part of reticular formation (monoaminergic groups A~ 7) and the part of the reticular formation (serotonergic groups B6-B8) which are evidently involved in the immunomodulatory and immunoadjuvant effect of muramyl dipeptide. The results of experiments also suggest that the interaction between neuroendocrine and immune systems might take place on the level of some of above mentioned anatomical structures. ~) 1998 Published by Elsevier Science Ltd on behalf of the International Society for Immunopharmacology. Keywords: muramyl dipeptide, CNS, neuroimmunomodulation
The functional interaction of the immune and neuroendocrine systems is not only very well documented but also generally accepted (Besedovsky et al., 1985; Weigent et al., 1990; Ma~ek and Petrovick~, 1990). Both systems play an important role in adaptation and maintenance of homeostasis, and pharmacological as well as morphological evidence support the concept of a close interaction and bi-directional communication between both systems. Clinical data are much more difficult to interpret, however, they also appear to support such a concept. The list of clinically used drugs which might also influence the immune response is steadily increasing. Working with muramyl peptides and their analogues we observed that this class of compounds, with a very potent immunopharmacological activity, also has a significant neuropharmacological effect (Ma~ek, 1986). In this article we discuss some of the neuropharmacological activities such as the effect on body temperature, effect on sleep, effect on pain threshold and the effect on behaviour. Comparing the effectiveness of M D P after intravenous and intra-
cerebroventricular administration we observed that the minimal pyrogenic dose in the case of intravenous injection in rabbits is 25 ~g/kg, while after the intracerebroventricular administration this dose is 0.13 ng/kg. These findings together with the other observations, strongly suggest the direct effect of M D P on thermoregulatory structures (Riveau et al., 1980). Another M D P effect which we observed was the effect on sleep patterns, this however was dose-related. With low doses such as 25 ]tg/kg we observed enhancement of slow wave sleep (SWS) and rapid eye movement ( R E M ) sleep. With higher doses such as 500 /~g/kg a profound inhibition of R E M sleep was registered. Our results also indicate that at least a part of the effect is mediated through the serotonergic structures (Ma~ek, 1986). Using two different methods, hot plate test and acetic acid writhing test, we also observed that M D P is able to produce mild transient analgesia. Doses of M D P however, had to be increased to 1 or 2 mg/kg in order to observe such an effect (Hor~ik and Magek, 1988).
* To whom all correspondence should be addressed: Dr K. Ma~ek, Institute of Pharmacology, Academy of Sciences, Prague, Czech Republic. 5O7
508
K. MASEK and P. PETROVICK'f
The behavioural effect of M D P was evaluated in a model of agonistic behaviour in singly-hosted mice. M D P in this model, at doses of 100 and 200 Hgincreased timid activities and inhibited aggressive activities of mice without changing sociable and locomotor behaviour. In these experiments we noticed behavioural effects of M DP which are similar to those of drugs which have some influence on serotonergic receptors. Since our results suggest that at least part of the M D P effect might also involve the central serotonin structures, we decided to investigate such a possibility. In these experiments we measured turnover rate of serotonin in different bram areas of animals with M D P induced fever, sleep changes or delayed hypersensitivity (Table I). We noticed, in these different experiments, a significant increase of turnover rate of serotonin in different brain regions, The effect is specific since the administration of M D P D-D, which did not show this activily, also had no effect on the turnover rate of serotonin. It is noteworthy that with a sleep-promoting dose of 25 Hg/kg we observed the changes in medulla oblongata + p o n s , but not in the other areas. Because our experiments indicate that at
I-
I,
least a part of the biological effects of M D P might be related to CNS structures we decided to search the anatomical substrate for such an effect. With the aid of small electrolytic lesions in the brain from brain stem to the cortex we studied whether and how such lesions might influence the M D P induced delayed skin hypersensitivity or the utilization of 3H thymidine for synthesis of D N A in spleen and thymus. Our results clearly indicate that the lesion placed in some regions of brain had a very significant effect on the delayed hypersensitivity reaction as well as on the proliferation processes in the thymus and spleen. The lesions placed in the other areas of the brain, on the other hand, had no effect at all. Our results also indicate that while the lesion in some structures increased the immune response, in the other specific areas the effect was the opposite. On the basis of our results, the structures we have found so far. that are involved in the immune response are as follows: t 1) Catecholaminergic cell groups A~ 7 and the lateral part of the reticular formation. (2) Serotonergic cell groups B~, s and the rapheal part of reticular formation. (3) Nucleus parabrachialis, a structure known to participate in the transmission of gustatory and visceral afferents as well as in emotional behaviour and sleep regulation. (4) Amygdala, particularly subnuclei centralis and basomedialis belonging to the limbic system, which regulate vegetative functions and emotions. (5) The septum, a medial part of tile telencephalon, which is connected with the limbic and olfactory systems. (6) Hippocampus held CA, ;. (7) Medial frontal cingulate cortex, particularly areas I and 2.
% %
so% ~I, 75%
,~
oo%
MS Fig. I. A schematic diagram demonstrating the connection between the structures lesioned in our experiments. The lesions effective on the immune response are depicted by shaded areas and are expressed as a percentage of controls.
On the basis of our studies we can suggest the existence of three circuits that seem to be involved in the immune response. One circuit represents the reticular formation and its catecholaminergic cell groups A~ 7, nucleus parabrachialis and central nucleus of amygdala. These structures are connected mainly with descending neuronal pathways. A lesion in this circuit decreases the immune response. The second circuit represents the rapheal reticular formation with its serotonergic cell groups B(, > hypothalamus and basomedial nucleus of amygdala. These structures are connected mainly with ascending neuronal pathways. Lesions in this circuit increase the immune response. The third circuit, which is the highest circuit, is represented by limbic telencephalic structures such as the
Morphological and Pharmacological Evidence
509
Table 1. Effect of MDP on 5-HT turnover in the brain Turnover rate of 5-HT, ~g/(g.h) Treatment
Hypothalamus
Midbrain
Medulla oblongata + pons
Temperature rise, C
Saline MDP, 25/zg/kg* MDP, 250 ~g/kg**
0.75 ± 0.15 0.87 ± 0.19 1.65 ± 0.42~
0.45 ± 0.08 0.65 + 0.16 0.97 ± 0.24~
0.52 ± 0.15 0.95 ± 0.20 a 1.05 ± 0.32"
0.42 ± 0.04 0.48 q- 0.05 1.75 ± 0.62"
FIA + Saline F I A + M D P 100 #g
0.68 + 0.18 1.47+0.25 ~
0.42 _+0.09 1.05+0.14"
0.56 + 0.12 1.22+_0.2&
* This dose enhanced slow-wave sleep and rapid eye movement sleep. ** This dose enhanced slow-wave sleep and inhibited rapid eye movement sleep and it is pyrogenic. Values are means + SEM "Statistically significant results P < 0.05. FIA + MDP in this group of animals developed delayed hypersensitivity. F I A - Freund's incomplete adjuvant. MDP - Muramyl dipeptide.
medial frontal cortex, hippocampus and the septum (Petrovick~ et al., 1994). The lesions in these mutually interconnected structures are much more difficult to interpret. The lesions in septum, a medial part of the telencephalon, which is connected with the limbic and olfactory systems, diminished the immune response if the lesions were located in the dorsal and posterior parts of the lateral septum-nucleus septalis lateralis pars intermedia and dorsalis and the nucleus septohippocampal. The lesions in the ventral and anterior parts of the medial septum-nucleus septalis medial±s, the nucleus of the diagonal band of Broca, had the opposite effect. A number of other lesions such as those in nucleus lateralis sept± pars ventral±s, nucleus septohypothalamicus had no effect at all. First results with electrolytic lesions in hippocampus also seem to be interesting. Small lesions in rostral parts of this structure (area CA1 and CA2) decreased the immune response measured by the uptake of thymidine in spleen as well as in thymus by up to 80%. The lesions in the posterior part of these areas (CA. and CA2), however, have a different effect in spleen and thymus. While in spleen, again a decrease of up to 80% was noted and in thymus an increase up to 150% was observed. Small lesions in area CA3 could, on the other hand, increase the uptake of thymidine in spleen up to 160%, whereas in thymus no effect was observed. On the basis of our results it seems to be evident that a c o m p o u n d with a very potent immunostimulatory and immunoadjuvant activity, such as muramyl peptide, has also, evidently, a number of neuropharmacological activities. It is, however, not completely clear how these activities are related to the
immune response. Our morphological studies have identified a number of C N S structures which might be important for the interaction between neuroendocrine and immune systems. Some of these structures are endowed with different types of neurotransmitters or even immunotransmitters. In evaluation of our morphological results we have strictly followed the principle of removing the entire field of a lesion that was not effective from the whole investigated field. With this approach we have minimized the extent of "effective" structures, on the other hand we could then determine more exactly the structures which might influence the measured immune response. It is also important to mention that with the neuroanatomical approach using the horseradish peroxidase or dextrafer (D-F) techniques we were also able to detect not only the neuronal pathways and connections between lesioned structures but also structures to be lesioned. F r o m the neurotransmitters so far studied in relation to the anatomical structures and also to the M D P effects which we have observed, it is certainly interesting that we have found 5HT to be involved in M D P induced neuropharmacological as well as immunomodulatory effects. We have studied the possible interactions in detail on peripheral smooth-muscle preparations and have reached the conclusion that the interaction of M D P with 5HT receptors might take place on the postsynaptic as well as the presynaptic levels with the possible involvement of 5HT~ and 5HT 3 receptors (Slfinsk~ et al., 1996). It has to be mentioned that the interaction between M D P and 5HT1 receptors have also been reported by Root-Bernstein and Westall (1990) and Silverman et al. (1989). Our conclusion that the effect of muramyl peptide on temperature, sleep, pain threshold and behaviour,
510
K. MA;SEK and P. PETROVICKY
as well as at least part of the i m m u n o p h a r m a c o l o g i c a l effect is mediated t h r o u g h the effect on the central nervous system, is supported by the results of electrophysiological experiments in which the effect of microiontophoretic application of m u r a m y l dipeptide u p o n single cortical neurons in different brain areas was evaluated. The results obtained from cortical, hip-
p o c a m p a l and h y p o t h a l a m i c neurons d e m o n s t r a t e d a direct effect o f M D P u p o n all three of these regions in the brain (Dougherty a n d Dafny, 1990). The results so far obtained thus support the role of muramyl peptide in the process of n e u r o i m m u n o m o d u l a t i o n and further d e m o n s t r a t e the i m p o r t a n t interaction between n e u r o e n d o c r i n e a n d i m m u n e systems in CNS.
REFERENCES
Besedovsky, H. O., Del Rey A. and Sorkin, E. (I 985) Immune neuroendocrine interactions. J. lmmunol. 135, 750 754. Dougherty, P. M. and Dafny, N. (1990) Microintophoretic application of muramyl dipeptide upon single cortical hippocampal and hypothalamic neurons in rats. Neuropharmacolo#y 29, 973 981. Horfik, P. and Ma~ek, K. (1988) Analgesic activity of two synthetic immunomodulators, muramyl dipeptide and adamantylamid dipeptide in mice and rats. Meth. and k)'nd. Exptl C/in. Pharmacol. 10, 569-574. Ma~ek, K. (1986) Immunopharmacology of muramyl peptides. Federation Proc. 45, 2549 2551. Magek, K. and Petrovick), P. (1990) A mutual role of CNS and immune system in host defence. In lmmunotherapeutic Prospects q/'h~/i~rtious Diseases, ed. K. N. Masihi and N. W. Lange, pp. 153 162. Springer, Berlin. Petrovick~, P., Magek. K. and Seifert, .1. (1994) Brain regulatory system for the immune response: immunopharmacotogy and morphology, Neuroimmunomodulation 1, 165 173. Riveau, G., Magek, K., Parant, M. and Chedid, k. (1980) Central pyrogenic activity of muramyl dipeptide..I. Exp. Med. 152, 869 877. Root-Bernstein, R. S. and Westall, F. C. (1990) Serotonin binding sites. 11. Muramyl dipeptide binds on myelin basic protein, LHRH and MSH-ACTH 4-10. Brain Res. Bull. 25, 827 841. Silverman D. H. S., Imam, I. and Karnovsky, M. L. (1989) Muramylpeptide/serotonin receptors in brain-derived preparations. Peptide Res. 2, 338344. Slfinsk~;', J., Kadlec, O.. ~ev6ik, J. and Ma~ek, K. t1996) Further evidence on the interaction of muramyl dipeptide with the serotonergic system. Int. J. lmmunopharmac. 18, 23 29. Weigent, D. A., Carr, D. J. J. and Blalock, J. E. (1990) Bi-directional communication between the neuroendocrine and immune systems, Common hormones and hormone receptors. In A Decade of Neuropeptides Past, Present and Future, eds. G. Koob, S. Sandman and F. Strand, pp. 17 27. Acad. Sci., Ann. N.Y.
Pergamon
Int. J. lmmunopharmac., Vol. 19, No. 9/10, pp. 507 -510, 1997 ~S~1998 Published by ElsevierScienceLtd on behalf of the International Societyfor lmmunopharmacology Printed in Great Britain 0192~0561/98 $19.00+ .00
PII:S0192-0561(97)00049-~ MORPHOLOGICAL A N D PHARMACOLOGICAL EVIDENCE FOR THE EXISTENCE OF BRAIN R E G U L A T O R Y CIRCUITS IN THE I M M U N E RESPONSE K. MASEK *~ and P. PETROVICKY b Institute of Pharmacology, Academy of Sciences, Prague, Czech Republic and bInstitute of Anatomy, Medical Faculty, Charles University, Prague, Czech Republic (ReceivedJbr publication 19 Auyust 1997) Abstraet--Muramyl dipeptide (MDP) has a variety of biological effects including the effect on CNS, such a promotion of sleep, fever, analgesic effect or some behavioural changes and of course a very potent effect on immune system. The latter effect is at least partly mediated through the structure in CNS~ With the small electrolytic lesions which were placed in brain from the spinal cord through the brain stem up to the cerebral cortex we have identified a number of structures such as medial frontal cortex (area CgrCg3), subnucleus basomedialis and centralis of amygdala, subnucleus medialis and dorsolateralis of nucleus parabrachialis, lateral part of reticular formation (monoaminergic groups A~ 7) and the part of the reticular formation (serotonergic groups B6-B8) which are evidently involved in the immunomodulatory and immunoadjuvant effect of muramyl dipeptide. The results of experiments also suggest that the interaction between neuroendocrine and immune systems might take place on the level of some of above mentioned anatomical structures. ~) 1998 Published by Elsevier Science Ltd on behalf of the International Society for Immunopharmacology. Keywords: muramyl dipeptide, CNS, neuroimmunomodulation
The functional interaction of the immune and neuroendocrine systems is not only very well documented but also generally accepted (Besedovsky et al., 1985; Weigent et al., 1990; Ma~ek and Petrovick~, 1990). Both systems play an important role in adaptation and maintenance of homeostasis, and pharmacological as well as morphological evidence support the concept of a close interaction and bi-directional communication between both systems. Clinical data are much more difficult to interpret, however, they also appear to support such a concept. The list of clinically used drugs which might also influence the immune response is steadily increasing. Working with muramyl peptides and their analogues we observed that this class of compounds, with a very potent immunopharmacological activity, also has a significant neuropharmacological effect (Ma~ek, 1986). In this article we discuss some of the neuropharmacological activities such as the effect on body temperature, effect on sleep, effect on pain threshold and the effect on behaviour. Comparing the effectiveness of M D P after intravenous and intra-
cerebroventricular administration we observed that the minimal pyrogenic dose in the case of intravenous injection in rabbits is 25 ~g/kg, while after the intracerebroventricular administration this dose is 0.13 ng/kg. These findings together with the other observations, strongly suggest the direct effect of M D P on thermoregulatory structures (Riveau et al., 1980). Another M D P effect which we observed was the effect on sleep patterns, this however was dose-related. With low doses such as 25 ]tg/kg we observed enhancement of slow wave sleep (SWS) and rapid eye movement ( R E M ) sleep. With higher doses such as 500 /~g/kg a profound inhibition of R E M sleep was registered. Our results also indicate that at least a part of the effect is mediated through the serotonergic structures (Ma~ek, 1986). Using two different methods, hot plate test and acetic acid writhing test, we also observed that M D P is able to produce mild transient analgesia. Doses of M D P however, had to be increased to 1 or 2 mg/kg in order to observe such an effect (Hor~ik and Magek, 1988).
* To whom all correspondence should be addressed: Dr K. Ma~ek, Institute of Pharmacology, Academy of Sciences, Prague, Czech Republic. 5O7
508
K. MASEK and P. PETROVICK'f
The behavioural effect of M D P was evaluated in a model of agonistic behaviour in singly-hosted mice. M D P in this model, at doses of 100 and 200 Hgincreased timid activities and inhibited aggressive activities of mice without changing sociable and locomotor behaviour. In these experiments we noticed behavioural effects of M DP which are similar to those of drugs which have some influence on serotonergic receptors. Since our results suggest that at least part of the M D P effect might also involve the central serotonin structures, we decided to investigate such a possibility. In these experiments we measured turnover rate of serotonin in different bram areas of animals with M D P induced fever, sleep changes or delayed hypersensitivity (Table I). We noticed, in these different experiments, a significant increase of turnover rate of serotonin in different brain regions, The effect is specific since the administration of M D P D-D, which did not show this activily, also had no effect on the turnover rate of serotonin. It is noteworthy that with a sleep-promoting dose of 25 Hg/kg we observed the changes in medulla oblongata + p o n s , but not in the other areas. Because our experiments indicate that at
I-
I,
least a part of the biological effects of M D P might be related to CNS structures we decided to search the anatomical substrate for such an effect. With the aid of small electrolytic lesions in the brain from brain stem to the cortex we studied whether and how such lesions might influence the M D P induced delayed skin hypersensitivity or the utilization of 3H thymidine for synthesis of D N A in spleen and thymus. Our results clearly indicate that the lesion placed in some regions of brain had a very significant effect on the delayed hypersensitivity reaction as well as on the proliferation processes in the thymus and spleen. The lesions placed in the other areas of the brain, on the other hand, had no effect at all. Our results also indicate that while the lesion in some structures increased the immune response, in the other specific areas the effect was the opposite. On the basis of our results, the structures we have found so far. that are involved in the immune response are as follows: t 1) Catecholaminergic cell groups A~ 7 and the lateral part of the reticular formation. (2) Serotonergic cell groups B~, s and the rapheal part of reticular formation. (3) Nucleus parabrachialis, a structure known to participate in the transmission of gustatory and visceral afferents as well as in emotional behaviour and sleep regulation. (4) Amygdala, particularly subnuclei centralis and basomedialis belonging to the limbic system, which regulate vegetative functions and emotions. (5) The septum, a medial part of tile telencephalon, which is connected with the limbic and olfactory systems. (6) Hippocampus held CA, ;. (7) Medial frontal cingulate cortex, particularly areas I and 2.
% %
so% ~I, 75%
,~
oo%
MS Fig. I. A schematic diagram demonstrating the connection between the structures lesioned in our experiments. The lesions effective on the immune response are depicted by shaded areas and are expressed as a percentage of controls.
On the basis of our studies we can suggest the existence of three circuits that seem to be involved in the immune response. One circuit represents the reticular formation and its catecholaminergic cell groups A~ 7, nucleus parabrachialis and central nucleus of amygdala. These structures are connected mainly with descending neuronal pathways. A lesion in this circuit decreases the immune response. The second circuit represents the rapheal reticular formation with its serotonergic cell groups B(, > hypothalamus and basomedial nucleus of amygdala. These structures are connected mainly with ascending neuronal pathways. Lesions in this circuit increase the immune response. The third circuit, which is the highest circuit, is represented by limbic telencephalic structures such as the
Morphological and Pharmacological Evidence
509
Table 1. Effect of MDP on 5-HT turnover in the brain Turnover rate of 5-HT, ~g/(g.h) Treatment
Hypothalamus
Midbrain
Medulla oblongata + pons
Temperature rise, C
Saline MDP, 25/zg/kg* MDP, 250 ~g/kg**
0.75 ± 0.15 0.87 ± 0.19 1.65 ± 0.42~
0.45 ± 0.08 0.65 + 0.16 0.97 ± 0.24~
0.52 ± 0.15 0.95 ± 0.20 a 1.05 ± 0.32"
0.42 ± 0.04 0.48 q- 0.05 1.75 ± 0.62"
FIA + Saline F I A + M D P 100 #g
0.68 + 0.18 1.47+0.25 ~
0.42 _+0.09 1.05+0.14"
0.56 + 0.12 1.22+_0.2&
* This dose enhanced slow-wave sleep and rapid eye movement sleep. ** This dose enhanced slow-wave sleep and inhibited rapid eye movement sleep and it is pyrogenic. Values are means + SEM "Statistically significant results P < 0.05. FIA + MDP in this group of animals developed delayed hypersensitivity. F I A - Freund's incomplete adjuvant. MDP - Muramyl dipeptide.
medial frontal cortex, hippocampus and the septum (Petrovick~ et al., 1994). The lesions in these mutually interconnected structures are much more difficult to interpret. The lesions in septum, a medial part of the telencephalon, which is connected with the limbic and olfactory systems, diminished the immune response if the lesions were located in the dorsal and posterior parts of the lateral septum-nucleus septalis lateralis pars intermedia and dorsalis and the nucleus septohippocampal. The lesions in the ventral and anterior parts of the medial septum-nucleus septalis medial±s, the nucleus of the diagonal band of Broca, had the opposite effect. A number of other lesions such as those in nucleus lateralis sept± pars ventral±s, nucleus septohypothalamicus had no effect at all. First results with electrolytic lesions in hippocampus also seem to be interesting. Small lesions in rostral parts of this structure (area CA1 and CA2) decreased the immune response measured by the uptake of thymidine in spleen as well as in thymus by up to 80%. The lesions in the posterior part of these areas (CA. and CA2), however, have a different effect in spleen and thymus. While in spleen, again a decrease of up to 80% was noted and in thymus an increase up to 150% was observed. Small lesions in area CA3 could, on the other hand, increase the uptake of thymidine in spleen up to 160%, whereas in thymus no effect was observed. On the basis of our results it seems to be evident that a c o m p o u n d with a very potent immunostimulatory and immunoadjuvant activity, such as muramyl peptide, has also, evidently, a number of neuropharmacological activities. It is, however, not completely clear how these activities are related to the
immune response. Our morphological studies have identified a number of C N S structures which might be important for the interaction between neuroendocrine and immune systems. Some of these structures are endowed with different types of neurotransmitters or even immunotransmitters. In evaluation of our morphological results we have strictly followed the principle of removing the entire field of a lesion that was not effective from the whole investigated field. With this approach we have minimized the extent of "effective" structures, on the other hand we could then determine more exactly the structures which might influence the measured immune response. It is also important to mention that with the neuroanatomical approach using the horseradish peroxidase or dextrafer (D-F) techniques we were also able to detect not only the neuronal pathways and connections between lesioned structures but also structures to be lesioned. F r o m the neurotransmitters so far studied in relation to the anatomical structures and also to the M D P effects which we have observed, it is certainly interesting that we have found 5HT to be involved in M D P induced neuropharmacological as well as immunomodulatory effects. We have studied the possible interactions in detail on peripheral smooth-muscle preparations and have reached the conclusion that the interaction of M D P with 5HT receptors might take place on the postsynaptic as well as the presynaptic levels with the possible involvement of 5HT~ and 5HT 3 receptors (Slfinsk~ et al., 1996). It has to be mentioned that the interaction between M D P and 5HT1 receptors have also been reported by Root-Bernstein and Westall (1990) and Silverman et al. (1989). Our conclusion that the effect of muramyl peptide on temperature, sleep, pain threshold and behaviour,
510
K. MA;SEK and P. PETROVICKY
as well as at least part of the i m m u n o p h a r m a c o l o g i c a l effect is mediated t h r o u g h the effect on the central nervous system, is supported by the results of electrophysiological experiments in which the effect of microiontophoretic application of m u r a m y l dipeptide u p o n single cortical neurons in different brain areas was evaluated. The results obtained from cortical, hip-
p o c a m p a l and h y p o t h a l a m i c neurons d e m o n s t r a t e d a direct effect o f M D P u p o n all three of these regions in the brain (Dougherty a n d Dafny, 1990). The results so far obtained thus support the role of muramyl peptide in the process of n e u r o i m m u n o m o d u l a t i o n and further d e m o n s t r a t e the i m p o r t a n t interaction between n e u r o e n d o c r i n e a n d i m m u n e systems in CNS.
REFERENCES
Besedovsky, H. O., Del Rey A. and Sorkin, E. (I 985) Immune neuroendocrine interactions. J. lmmunol. 135, 750 754. Dougherty, P. M. and Dafny, N. (1990) Microintophoretic application of muramyl dipeptide upon single cortical hippocampal and hypothalamic neurons in rats. Neuropharmacolo#y 29, 973 981. Horfik, P. and Ma~ek, K. (1988) Analgesic activity of two synthetic immunomodulators, muramyl dipeptide and adamantylamid dipeptide in mice and rats. Meth. and k)'nd. Exptl C/in. Pharmacol. 10, 569-574. Ma~ek, K. (1986) Immunopharmacology of muramyl peptides. Federation Proc. 45, 2549 2551. Magek, K. and Petrovick), P. (1990) A mutual role of CNS and immune system in host defence. In lmmunotherapeutic Prospects q/'h~/i~rtious Diseases, ed. K. N. Masihi and N. W. Lange, pp. 153 162. Springer, Berlin. Petrovick~, P., Magek. K. and Seifert, .1. (1994) Brain regulatory system for the immune response: immunopharmacotogy and morphology, Neuroimmunomodulation 1, 165 173. Riveau, G., Magek, K., Parant, M. and Chedid, k. (1980) Central pyrogenic activity of muramyl dipeptide..I. Exp. Med. 152, 869 877. Root-Bernstein, R. S. and Westall, F. C. (1990) Serotonin binding sites. 11. Muramyl dipeptide binds on myelin basic protein, LHRH and MSH-ACTH 4-10. Brain Res. Bull. 25, 827 841. Silverman D. H. S., Imam, I. and Karnovsky, M. L. (1989) Muramylpeptide/serotonin receptors in brain-derived preparations. Peptide Res. 2, 338344. Slfinsk~;', J., Kadlec, O.. ~ev6ik, J. and Ma~ek, K. t1996) Further evidence on the interaction of muramyl dipeptide with the serotonergic system. Int. J. lmmunopharmac. 18, 23 29. Weigent, D. A., Carr, D. J. J. and Blalock, J. E. (1990) Bi-directional communication between the neuroendocrine and immune systems, Common hormones and hormone receptors. In A Decade of Neuropeptides Past, Present and Future, eds. G. Koob, S. Sandman and F. Strand, pp. 17 27. Acad. Sci., Ann. N.Y.