- Email: [email protected]
Involvement of nitric oxide in antinociceptive effect of newly synthesized analogues of Kyotorphin in rats
B. Preclinical
S32
persistent and excessive increased firing rate of dopaminergic neurones and subsequent release of dopamine evoked indirectly by MK-801.
)8-321
Effects cortical
of 17fi-oestradiol neurons and
on kainate in neuronallv
toxicity in primary differentiated PC12
M. Kajta, W. Lason. Department of Endocrinology, Institute of Pharmacology, Polish Academy of Sciences, I2 Smetna Street, 31-343 Krakow, Poland It is generally accepted that oestrogens affect neuronal outgrowth, differentiation and survival. Apart from classical actions at nuclear receptor sites with ensuing genomic effects, oestrogens can alter responses of conventional neurotrsnsmitter receptors throughout the brain. It has been indicated that local administration of o&radio1 potentiates excitatory responses to glutamate in Purkinje cells, and to kainate - in hippocampal neurons. Such excitotoxic insults may contribute to neuronal degeneration. There is, however, a growing body of evidence that oestrogens may be beneficial in some neurological disorders. Since a little is known about direct protective effects of oestrogens on kainate neurotoxicity, we addressed this problem to primary cortical neurons as well as to neuronally differentiated PC12 cells. Cortical neurons were prepared from fetal rats at 1617 days gestation and cultured for 11 days prior to experimentation [I, 21. PC12 cells exit the cell cycle and differentiated into cells resembling sympathetic neurons when treated with NGF (50 rig/ml) for 6 days [3]. 24 h exposure to kainate (I 50 PM; KA) resulted in cell damage, as detected with cell lysis and lactate dehydrogenase (LDH) efflux into the culture media. In primary cortical neurons it was reflected by ca. 220% and in PC12 neuronal cells by 160% increase in LDH concentration, as compared with control. Pretreatement with 17S-oestradiol (100 nM) attenuated kainate toxicity in primary cortical neurons and NGFdifferentiated PC12 cells. In both cases the effects of KA were reduced for about 20%. These in vitro data support hypothesis on neuroprotective action of oestradiol. This work was supported by the Polish Research Committee Grant KBN 0624/PO5/98/14 References [I]
Koch J-Y., Choi D. W.: Vulnerability of cultured cortical neurons to damage by excitotoxins: differential suceptibility of neurons containing NADPHdiaphorase. J. Neurosci., 1988, 8, 215343. [2] Dawson V. L., Dawson T. M., London E. D., Bredt D. S., Snyder S. H.: Nitric oxide mediates glutamate neurotoxicity in primary cortical cultures. Proc. Natl. Acad. Sci. USA, 1991, 88,6368-71. [3] Park D. S., Morris E. .I., Stefanis L., Troy C. M., Shelanski M. L., Geller H. M., Greene L. A.: Multiple pathways of neuronal death induced by DNA-damaging agents, NGF deprivation, and oxidative stress. .I. Neurosci., 1998, 18, 830-40.
JB-331
Neuropeptide rat frontal receptors
Y inhibits epileptiform cortex and hippocampus
M. Bijak. Institute of Pharmacology, 12, 31-343 Krakdw, Poland
Polish Academy
activity in via different
of Sciences,
Smetna
A growing body of evidence suggests that neuropeptide Y (NPY) is involved in the regulation of epileptic seizures. Transgenic mice, lacking NPY display spontaneous seizures, moreover, intracerebral injection of NPY can suppress some types of experimentally-induced convulsive seizures. Seizures trigger an increase of NPY expression, mainly in the hippocampus and cortex. Several receptor subtypes of the NPY receptor superfamily have been identified in the central nervous system. A discrete localization of different NPY receptor subtypes suggests that each subtype may participate in separate central function, In the hippocampus NPY-2 receptor predominates and this receptor subtype is involved in suppression of convulsive seizures originating in the hippocampus
Studies as well as in the reduction of excitatory synaptic transmission and depression of epileptiform discharges in hippocampal slices. It has also been demonstrated that NPY inhibits epileptiform discharges induced in the rat frontal cortex slices. In the frontal cortex NPY-1, NPY-2 and NPY-5 receptors have been identified. In the present study, the type of NPY receptor responsible for the inhibition of epileptiform discharges in the cortex was assessed by examining the effects of different subtypeselective NPY agonists on epileptiform discharges induced in the rat frontal cortex slices. For comparison, the effects of the NPY agonists were also studied in the hippocampal CA1 area in vitro. Spontaneous paroxysmal, synchronized activity developed in cortical and hippocampal slices upon perfusion with Mg 2+ -free artificial cerebrospinal fluid, these discharges were recorded using extracellular and intracellular electrophysiological techniques. NPY (1 PM) decreased the frequency of epileptiform discharges in both preparations, however, the NPY-1 selective agonist [Leu 3’ Pro34] NPY was much more effective in the cortex than in the hippocampus. On the contrary, the NPY-2 selective agonist NPY 13-36 attenuated epileptiform discharges in the hippocampal slice but not in the cortex. The NPY-S/NPY-2 preferring agonist NPYs-3s had no effect in the cortex but it attenuated epileptiform discharges in the hippocampal CA1 area. In conclusion, the anti-epileptiform action of NPY is mediated by the NPY-1 receptor subtype in the frontal cortex and by the NPY-2 receptor subtype in the hippocampus. Supported by the KBN grant 4P05A05211.
IB-341
Involvement of nitric oxide in antinociceptive newly synthesized analogues of Kyotorphin
A. Bocheva’ of Sciences,
effect in rats
of
, M. Lazarova. ‘Institute of Physiology; Bulgarian Academy Acad. G. Boncheo Str, b1.23, 1113 Sofia, Bulgaria
Pain is frequently observed symptom of various diseases. The great achievements in medicine are conected with the research on pain and especially on the development of antinociceptive drugs. The synthesis of nonprotein amino acids and their incorporation into a variety of natural biological active peptides lead to analogues with significant theoretical and practical importance. There is considerable evidence now that nitric oxide (NO) plays a role in nociceptive processing in the central nervous system. Our previous data have shown that canavanine substitution 2 in a Kyotorphin (Kyo) molecule lead to analogue with more pronounced antinociceptive effect. This effect is naloxone-reversible (Bocheva et al., 1996). The aim of present study was to elucidate whether NO plays a role in the antinociceptive effect of Kyo (20 ug i.c.v.) and Tyr-Cav (20 pg i.c.v.). The antinociceptive neurodipeptide Kyo was isolated from bovine brain and acts as a potent [Met5]enkephalin-releaser in the brain and in the spinal cord (Takagi et al., 1979). It has a pronounced opioid-like effect in vivo. which is antagonized by naloxone. Kyo is synthesized from L-Tyr and L-Arg by specific enzyme, kyotorphin synthetase, in the presence of ATP and MgClz. Endogenously applied L-Arg acts as an effective precursor of Kyo and has an antinociceptive effect in rats and mice. The changes in the mechanical nociceptive threshold of the rats were measured by the Randall-Selitto paw pressure test using an analgesimeter (Ugo Basile). The pressure was applied to the hindpaw and the pressure (g) required to elicit nociceptive responses such as squeak and struggle was taken as mechanical nociceptive threshold. A cut-off value of 500 g was used to prevent damage of the paw. Nitric oxide (NO) donor (SIN-I, 100 pg i.c.v.) induced hyperalgesia in rats, while, in contrast, the inhibitor of nitric oxide synthase L-NAME (30 mg/kg i.p.) elicited antinociception. L-NAME potentiated the antinociceptive effect of both Kyotorphin and Tyr-Cav, which was reversed by SIN-l. These result suggest that endogenous NO is involved in the antinociceptive effects of Kyotorphin and Tyr-Cav. This study was supported by Grant L-439 of the NSF Sofia, Bulgaria. References [l]
Bocheva A., T. Pajpanova., E. Golovinsky and M. Lazarova (1996) Studies on pain modulation by newly-synthesized analogues of kyotorphin. Management of pain a world perspective II, 15-18.
B. Preclinical [2] Takagi, H., H. Shiomi and H. Amano, (1979) A novel analgesic dipeptide from bovine brain is a possible Met-enkephalin releaser. Natore 282; 410-412; 1979
ElB-35
Effect of tramadol analgesia
and
clonidine
on stress-induced
I. Panocka, B. Antkowiak, M. Kowalczyk. Department Military
Institute
of Hygiene
and Epidemiology,
of Pharmacology, Warsaw, Poland
Tramadol is a centrally acting, synthetic analgesic with opioid agonist properties. Experimental data suggest that tramadol may exert part of its analgesic effect through the activation of central inhibitory rnonoaminergic pathways. Systemically administered antagonists of noradrenergic and serotonergic receptors block the antinociception of spinally administered tramadol, but not morphine in the rat tail-flick test. Clonidine is a selective alpha2 adrenergic agonist which shows marked analgesic activity after spinal administration. In our experiments, we studied analgesic properties of tramadol together with systemically administered clonidine before and after stress using tail-immersion test. The experiments were performed on adult male Wistar rats weighing 250-350 g with reversed light/dark cycle. The tail-withdrawal latency following immersion in hot water (55’ C) was measured before and 2, 30 and 60 minutes afier stress (3 min. swimming in water at 20” C). Rats received intraperitoneal injections of tramadol (20 mgkg) or clonidine (50 Kg/kg) or tramadol co-injected with clonidine at the same doses 30 min. before stress. The control group received aqua pro iniectione. The results were expressed as percentage of maximal possible effect (% MPE) according to the formula: (postdrug latency - baseline latency)/(cut-off time - baseline latency) x 100%. Statistically significant differences between the groups analysed were determined using t-test. Before the swimming stress,both tramadol and clonidine given separately and injected together revealed a statistically significant analgesic effect in comparison with the control group. The analgesic effect of tramadol co-injected with clonidine was significantly greater than in the case of the drugs given separately. After stress tramadol together with clonidine produced a significant analgesic effect at minute 2 and 30, tramadol given separately - only at min. 2 and clonidine had no significant effect. Just after the stress,there was no difference between the efficacy of tramadol alone and tramadol together with clonidine. In our experiment the activation of alphal-adrenergic receptors potentiated the analgesic effect of tramadol before and 30 min. after but not just after stress. References [l]
Raffa, R.B. et al., 1992. Opioid and non-opioid mechanisms of action of tramadol, an ‘atypical’ analgesic. J. Pharmacol. Exp. Ther. 260, 275-85. [2] Desmeules, J.A., Pigwt, V., Collart, L., Dayer, P, 1996. Contributin of monoaminergic modulation to the analgesic effect of tramadol. Br. J. Clin. Pharmacol. 41, 7-12.
18-361
Involvement antinociceptlve
of histamlnergic system effect of Tyr-MIF-1
in the
A. Bocheva’, R. Zamfirova’ , W. Scbunack’, S. Todorov’ *. ‘Institute
of Physiology Bulgarian Academy of Science, 23 Acad. G. Bonchev St., I I I3 Sofia. Bulgaria ‘Institut ftir Pharmazie, Freie Universitiit, Kiinigin-Luise-Spaye 2 + 4, I4195 Berlin, Germany
Tyr-MIF-1 is a representative of the MlF’s family of endogenous peptides. It has been isolated from bovine hypothalamus and human parietal cortex that suggests its involvement in nociception. Tyr-MIF- 1 can bind to the p-receptors as well as to its specific non-opiate receptors in the brain. Data in the literature rise the idea that histamine (HA), a well known nociceptive agent, and ‘I@MIF-1 might have a common pathway in their effects on nociception. We tested that possibility by investigating the combined action of FUB 94 (a precursor of the H3-agonist R-amethyl histamine) and Tyr-MIF-1 on nociception. The changes in the
s33
Studies
nociceptive effects were examined in male Wistar rats by the RandallSellito paw-pressure (PP) test, using an analgesimeter (Ugo Basile). A pressure was applied to the hind paw and its magnitude (in g) required to elicit nociceptive responses (squeak and struggle) was taken as the mechanical nociceptive threshold. A cut-off value of 500 g was used to prevent damage of the paw. Tyr-MiF-1 in a dose of 1 mg/kg exerted a strong naloxone-reversible analgesic effect. FUB 94 (5 mg/kg, i.p.) had an antinociceptive action, too. The co-administration of Tyr-MIF1 and FUB 94 increased the antinociceptive effect of the H3-agonist precursor. This effect was reversed when methylene blue (MB, 500 pg/rat) was applied 1 hour before the combination. The results obtained confhmed the hypothesis that second messengers might be involved in the realization of the nociceptive effects of both HA and Tyr-MIF- 1. This study was supported by Grant B-601 of the NSF, Bulgaria. 16-371
Participation antinocicedive oxaprotilik mice
of opioid mechanism on the effect induced bv (+I- and I-)in two behavioural pain’ tests in-
A. WesoIowska, J. Borycz. Institute of Sciences,
12 Sm@na Street, Krakow,
of Pharmacology, Poland
Polish
Academy
Oxaprotiline (OXA), a hydroxy derivative of maprotiline, has two optic isomers which exert an antidepressant action in patients (Delini-Stola et al., 1988). (+)-OXA is a highly selective noradrenaline uptake inhibitor, while (-)-OXA is devoid of such an activity (Waldmeier et al., 1982). The mechanism of clinical action of (-)-OXA has not been elucidated, as yet. Irrespective of its antidepressant activity, (+)-Ox4 produces antinociceptive effects in mice (Gray et al., 1998), however no studies of this type have been conducted for (-)-OXA. The purpose of the present study was to assess the activity of both OXA enantiomers in two experimental models of pain in mice, a hot plate (HPL) test and a writhing syndrome (WS) induced by phenylbenzoquinone, and to determine whether the opioidergic system may be engaged in their antinociceptive effects. Both OXAs were administered intraperitoneally to mice 1 h before the test. Administration of (+)-OXA (0.31-20 m&g) and (-)-OXA (20 m&g) produced a statistically significant elevation of the nociceptive threshold, measured by the increased latencies in the HPL test. Moreover, (+)-OXA (0.62-20 mg/kg) and (-)-enantiomer (5-20 m&g) decreased the number of writhing episodes induced by phenylbenzoquinone in mice. The analgesic effect induced by (+)-OXA (0.31 mg/kg) in the HPL test in mice was abolished by naloxone (2 mgkg, subcutaneously), an opioid antagonist. In the WR test, naloxone (2 m&g) partially, but not significantly, reduced the antinociceptive responses induced by (+)-OXA (0.62 m&g). The antinociceptive action of (-)-OXA (20 mgikg in the HPL test, or 5 mgikg in the WS test) was practically blocked by naloxone
(2 NW.
Naloxone given alone (2 m&g) 10 min before the test did not affect the nociceptive responses in comparison with the effect observed in animals receiving saline in both the tests used. The obtained results show that both OXA enantiomers produce antinociception in the HPL and the WR tests in mice, (+)-enantiomer (a noradrenaline uptake inhibitor) being more effective than (-)-OXA in either test. The endogenous opioid system seems to be implicated, at least partially, in their antinociceptive action. Possible participation of other neurotransmitter systems in the antinociceptive responses induced by both OXA enantiomers will be fhe aim of our further studies. References [l]
Delini-Stala, A., Vassout, A., Hanser, K., Bittiger, H., Buch, O., Olpe, H.R. (1988) Oxaprotiline and its enantiomcrs: do they open new avenues in the research on the mode of action of antidepressants? In: Usdin, E., Goldstein, M., Friedhoff, A., Georgotal, A. (eds.) Frontiers in Neuropsychiatric Research, Macmillan, London, pp. 121-134. [2] Gray, A.M., Spencer, W.J., Sewll, R.D.E. (1998) The involvement of the opioidergic system in the antinociceptive mechanism of action of antidepressant compounds. Br. J. Pharmacol. 124,669-674.
S32
persistent and excessive increased firing rate of dopaminergic neurones and subsequent release of dopamine evoked indirectly by MK-801.
)8-321
Effects cortical
of 17fi-oestradiol neurons and
on kainate in neuronallv
toxicity in primary differentiated PC12
M. Kajta, W. Lason. Department of Endocrinology, Institute of Pharmacology, Polish Academy of Sciences, I2 Smetna Street, 31-343 Krakow, Poland It is generally accepted that oestrogens affect neuronal outgrowth, differentiation and survival. Apart from classical actions at nuclear receptor sites with ensuing genomic effects, oestrogens can alter responses of conventional neurotrsnsmitter receptors throughout the brain. It has been indicated that local administration of o&radio1 potentiates excitatory responses to glutamate in Purkinje cells, and to kainate - in hippocampal neurons. Such excitotoxic insults may contribute to neuronal degeneration. There is, however, a growing body of evidence that oestrogens may be beneficial in some neurological disorders. Since a little is known about direct protective effects of oestrogens on kainate neurotoxicity, we addressed this problem to primary cortical neurons as well as to neuronally differentiated PC12 cells. Cortical neurons were prepared from fetal rats at 1617 days gestation and cultured for 11 days prior to experimentation [I, 21. PC12 cells exit the cell cycle and differentiated into cells resembling sympathetic neurons when treated with NGF (50 rig/ml) for 6 days [3]. 24 h exposure to kainate (I 50 PM; KA) resulted in cell damage, as detected with cell lysis and lactate dehydrogenase (LDH) efflux into the culture media. In primary cortical neurons it was reflected by ca. 220% and in PC12 neuronal cells by 160% increase in LDH concentration, as compared with control. Pretreatement with 17S-oestradiol (100 nM) attenuated kainate toxicity in primary cortical neurons and NGFdifferentiated PC12 cells. In both cases the effects of KA were reduced for about 20%. These in vitro data support hypothesis on neuroprotective action of oestradiol. This work was supported by the Polish Research Committee Grant KBN 0624/PO5/98/14 References [I]
Koch J-Y., Choi D. W.: Vulnerability of cultured cortical neurons to damage by excitotoxins: differential suceptibility of neurons containing NADPHdiaphorase. J. Neurosci., 1988, 8, 215343. [2] Dawson V. L., Dawson T. M., London E. D., Bredt D. S., Snyder S. H.: Nitric oxide mediates glutamate neurotoxicity in primary cortical cultures. Proc. Natl. Acad. Sci. USA, 1991, 88,6368-71. [3] Park D. S., Morris E. .I., Stefanis L., Troy C. M., Shelanski M. L., Geller H. M., Greene L. A.: Multiple pathways of neuronal death induced by DNA-damaging agents, NGF deprivation, and oxidative stress. .I. Neurosci., 1998, 18, 830-40.
JB-331
Neuropeptide rat frontal receptors
Y inhibits epileptiform cortex and hippocampus
M. Bijak. Institute of Pharmacology, 12, 31-343 Krakdw, Poland
Polish Academy
activity in via different
of Sciences,
Smetna
A growing body of evidence suggests that neuropeptide Y (NPY) is involved in the regulation of epileptic seizures. Transgenic mice, lacking NPY display spontaneous seizures, moreover, intracerebral injection of NPY can suppress some types of experimentally-induced convulsive seizures. Seizures trigger an increase of NPY expression, mainly in the hippocampus and cortex. Several receptor subtypes of the NPY receptor superfamily have been identified in the central nervous system. A discrete localization of different NPY receptor subtypes suggests that each subtype may participate in separate central function, In the hippocampus NPY-2 receptor predominates and this receptor subtype is involved in suppression of convulsive seizures originating in the hippocampus
Studies as well as in the reduction of excitatory synaptic transmission and depression of epileptiform discharges in hippocampal slices. It has also been demonstrated that NPY inhibits epileptiform discharges induced in the rat frontal cortex slices. In the frontal cortex NPY-1, NPY-2 and NPY-5 receptors have been identified. In the present study, the type of NPY receptor responsible for the inhibition of epileptiform discharges in the cortex was assessed by examining the effects of different subtypeselective NPY agonists on epileptiform discharges induced in the rat frontal cortex slices. For comparison, the effects of the NPY agonists were also studied in the hippocampal CA1 area in vitro. Spontaneous paroxysmal, synchronized activity developed in cortical and hippocampal slices upon perfusion with Mg 2+ -free artificial cerebrospinal fluid, these discharges were recorded using extracellular and intracellular electrophysiological techniques. NPY (1 PM) decreased the frequency of epileptiform discharges in both preparations, however, the NPY-1 selective agonist [Leu 3’ Pro34] NPY was much more effective in the cortex than in the hippocampus. On the contrary, the NPY-2 selective agonist NPY 13-36 attenuated epileptiform discharges in the hippocampal slice but not in the cortex. The NPY-S/NPY-2 preferring agonist NPYs-3s had no effect in the cortex but it attenuated epileptiform discharges in the hippocampal CA1 area. In conclusion, the anti-epileptiform action of NPY is mediated by the NPY-1 receptor subtype in the frontal cortex and by the NPY-2 receptor subtype in the hippocampus. Supported by the KBN grant 4P05A05211.
IB-341
Involvement of nitric oxide in antinociceptive newly synthesized analogues of Kyotorphin
A. Bocheva’ of Sciences,
effect in rats
of
, M. Lazarova. ‘Institute of Physiology; Bulgarian Academy Acad. G. Boncheo Str, b1.23, 1113 Sofia, Bulgaria
Pain is frequently observed symptom of various diseases. The great achievements in medicine are conected with the research on pain and especially on the development of antinociceptive drugs. The synthesis of nonprotein amino acids and their incorporation into a variety of natural biological active peptides lead to analogues with significant theoretical and practical importance. There is considerable evidence now that nitric oxide (NO) plays a role in nociceptive processing in the central nervous system. Our previous data have shown that canavanine substitution 2 in a Kyotorphin (Kyo) molecule lead to analogue with more pronounced antinociceptive effect. This effect is naloxone-reversible (Bocheva et al., 1996). The aim of present study was to elucidate whether NO plays a role in the antinociceptive effect of Kyo (20 ug i.c.v.) and Tyr-Cav (20 pg i.c.v.). The antinociceptive neurodipeptide Kyo was isolated from bovine brain and acts as a potent [Met5]enkephalin-releaser in the brain and in the spinal cord (Takagi et al., 1979). It has a pronounced opioid-like effect in vivo. which is antagonized by naloxone. Kyo is synthesized from L-Tyr and L-Arg by specific enzyme, kyotorphin synthetase, in the presence of ATP and MgClz. Endogenously applied L-Arg acts as an effective precursor of Kyo and has an antinociceptive effect in rats and mice. The changes in the mechanical nociceptive threshold of the rats were measured by the Randall-Selitto paw pressure test using an analgesimeter (Ugo Basile). The pressure was applied to the hindpaw and the pressure (g) required to elicit nociceptive responses such as squeak and struggle was taken as mechanical nociceptive threshold. A cut-off value of 500 g was used to prevent damage of the paw. Nitric oxide (NO) donor (SIN-I, 100 pg i.c.v.) induced hyperalgesia in rats, while, in contrast, the inhibitor of nitric oxide synthase L-NAME (30 mg/kg i.p.) elicited antinociception. L-NAME potentiated the antinociceptive effect of both Kyotorphin and Tyr-Cav, which was reversed by SIN-l. These result suggest that endogenous NO is involved in the antinociceptive effects of Kyotorphin and Tyr-Cav. This study was supported by Grant L-439 of the NSF Sofia, Bulgaria. References [l]
Bocheva A., T. Pajpanova., E. Golovinsky and M. Lazarova (1996) Studies on pain modulation by newly-synthesized analogues of kyotorphin. Management of pain a world perspective II, 15-18.
B. Preclinical [2] Takagi, H., H. Shiomi and H. Amano, (1979) A novel analgesic dipeptide from bovine brain is a possible Met-enkephalin releaser. Natore 282; 410-412; 1979
ElB-35
Effect of tramadol analgesia
and
clonidine
on stress-induced
I. Panocka, B. Antkowiak, M. Kowalczyk. Department Military
Institute
of Hygiene
and Epidemiology,
of Pharmacology, Warsaw, Poland
Tramadol is a centrally acting, synthetic analgesic with opioid agonist properties. Experimental data suggest that tramadol may exert part of its analgesic effect through the activation of central inhibitory rnonoaminergic pathways. Systemically administered antagonists of noradrenergic and serotonergic receptors block the antinociception of spinally administered tramadol, but not morphine in the rat tail-flick test. Clonidine is a selective alpha2 adrenergic agonist which shows marked analgesic activity after spinal administration. In our experiments, we studied analgesic properties of tramadol together with systemically administered clonidine before and after stress using tail-immersion test. The experiments were performed on adult male Wistar rats weighing 250-350 g with reversed light/dark cycle. The tail-withdrawal latency following immersion in hot water (55’ C) was measured before and 2, 30 and 60 minutes afier stress (3 min. swimming in water at 20” C). Rats received intraperitoneal injections of tramadol (20 mgkg) or clonidine (50 Kg/kg) or tramadol co-injected with clonidine at the same doses 30 min. before stress. The control group received aqua pro iniectione. The results were expressed as percentage of maximal possible effect (% MPE) according to the formula: (postdrug latency - baseline latency)/(cut-off time - baseline latency) x 100%. Statistically significant differences between the groups analysed were determined using t-test. Before the swimming stress,both tramadol and clonidine given separately and injected together revealed a statistically significant analgesic effect in comparison with the control group. The analgesic effect of tramadol co-injected with clonidine was significantly greater than in the case of the drugs given separately. After stress tramadol together with clonidine produced a significant analgesic effect at minute 2 and 30, tramadol given separately - only at min. 2 and clonidine had no significant effect. Just after the stress,there was no difference between the efficacy of tramadol alone and tramadol together with clonidine. In our experiment the activation of alphal-adrenergic receptors potentiated the analgesic effect of tramadol before and 30 min. after but not just after stress. References [l]
Raffa, R.B. et al., 1992. Opioid and non-opioid mechanisms of action of tramadol, an ‘atypical’ analgesic. J. Pharmacol. Exp. Ther. 260, 275-85. [2] Desmeules, J.A., Pigwt, V., Collart, L., Dayer, P, 1996. Contributin of monoaminergic modulation to the analgesic effect of tramadol. Br. J. Clin. Pharmacol. 41, 7-12.
18-361
Involvement antinociceptlve
of histamlnergic system effect of Tyr-MIF-1
in the
A. Bocheva’, R. Zamfirova’ , W. Scbunack’, S. Todorov’ *. ‘Institute
of Physiology Bulgarian Academy of Science, 23 Acad. G. Bonchev St., I I I3 Sofia. Bulgaria ‘Institut ftir Pharmazie, Freie Universitiit, Kiinigin-Luise-Spaye 2 + 4, I4195 Berlin, Germany
Tyr-MIF-1 is a representative of the MlF’s family of endogenous peptides. It has been isolated from bovine hypothalamus and human parietal cortex that suggests its involvement in nociception. Tyr-MIF- 1 can bind to the p-receptors as well as to its specific non-opiate receptors in the brain. Data in the literature rise the idea that histamine (HA), a well known nociceptive agent, and ‘I@MIF-1 might have a common pathway in their effects on nociception. We tested that possibility by investigating the combined action of FUB 94 (a precursor of the H3-agonist R-amethyl histamine) and Tyr-MIF-1 on nociception. The changes in the
s33
Studies
nociceptive effects were examined in male Wistar rats by the RandallSellito paw-pressure (PP) test, using an analgesimeter (Ugo Basile). A pressure was applied to the hind paw and its magnitude (in g) required to elicit nociceptive responses (squeak and struggle) was taken as the mechanical nociceptive threshold. A cut-off value of 500 g was used to prevent damage of the paw. Tyr-MiF-1 in a dose of 1 mg/kg exerted a strong naloxone-reversible analgesic effect. FUB 94 (5 mg/kg, i.p.) had an antinociceptive action, too. The co-administration of Tyr-MIF1 and FUB 94 increased the antinociceptive effect of the H3-agonist precursor. This effect was reversed when methylene blue (MB, 500 pg/rat) was applied 1 hour before the combination. The results obtained confhmed the hypothesis that second messengers might be involved in the realization of the nociceptive effects of both HA and Tyr-MIF- 1. This study was supported by Grant B-601 of the NSF, Bulgaria. 16-371
Participation antinocicedive oxaprotilik mice
of opioid mechanism on the effect induced bv (+I- and I-)in two behavioural pain’ tests in-
A. WesoIowska, J. Borycz. Institute of Sciences,
12 Sm@na Street, Krakow,
of Pharmacology, Poland
Polish
Academy
Oxaprotiline (OXA), a hydroxy derivative of maprotiline, has two optic isomers which exert an antidepressant action in patients (Delini-Stola et al., 1988). (+)-OXA is a highly selective noradrenaline uptake inhibitor, while (-)-OXA is devoid of such an activity (Waldmeier et al., 1982). The mechanism of clinical action of (-)-OXA has not been elucidated, as yet. Irrespective of its antidepressant activity, (+)-Ox4 produces antinociceptive effects in mice (Gray et al., 1998), however no studies of this type have been conducted for (-)-OXA. The purpose of the present study was to assess the activity of both OXA enantiomers in two experimental models of pain in mice, a hot plate (HPL) test and a writhing syndrome (WS) induced by phenylbenzoquinone, and to determine whether the opioidergic system may be engaged in their antinociceptive effects. Both OXAs were administered intraperitoneally to mice 1 h before the test. Administration of (+)-OXA (0.31-20 m&g) and (-)-OXA (20 m&g) produced a statistically significant elevation of the nociceptive threshold, measured by the increased latencies in the HPL test. Moreover, (+)-OXA (0.62-20 mg/kg) and (-)-enantiomer (5-20 m&g) decreased the number of writhing episodes induced by phenylbenzoquinone in mice. The analgesic effect induced by (+)-OXA (0.31 mg/kg) in the HPL test in mice was abolished by naloxone (2 mgkg, subcutaneously), an opioid antagonist. In the WR test, naloxone (2 m&g) partially, but not significantly, reduced the antinociceptive responses induced by (+)-OXA (0.62 m&g). The antinociceptive action of (-)-OXA (20 mgikg in the HPL test, or 5 mgikg in the WS test) was practically blocked by naloxone
(2 NW.
Naloxone given alone (2 m&g) 10 min before the test did not affect the nociceptive responses in comparison with the effect observed in animals receiving saline in both the tests used. The obtained results show that both OXA enantiomers produce antinociception in the HPL and the WR tests in mice, (+)-enantiomer (a noradrenaline uptake inhibitor) being more effective than (-)-OXA in either test. The endogenous opioid system seems to be implicated, at least partially, in their antinociceptive action. Possible participation of other neurotransmitter systems in the antinociceptive responses induced by both OXA enantiomers will be fhe aim of our further studies. References [l]
Delini-Stala, A., Vassout, A., Hanser, K., Bittiger, H., Buch, O., Olpe, H.R. (1988) Oxaprotiline and its enantiomcrs: do they open new avenues in the research on the mode of action of antidepressants? In: Usdin, E., Goldstein, M., Friedhoff, A., Georgotal, A. (eds.) Frontiers in Neuropsychiatric Research, Macmillan, London, pp. 121-134. [2] Gray, A.M., Spencer, W.J., Sewll, R.D.E. (1998) The involvement of the opioidergic system in the antinociceptive mechanism of action of antidepressant compounds. Br. J. Pharmacol. 124,669-674.