Influence of mediopreoptic stimulation on temperature regulation in rats before and after serotonin injection]

The effects of electrical stimulation of the Area praceoptica medialis (APM) and intraventricular serotonine injection were investigated in thirty Wistar rats tested under normo-, hypo- and hyperthermic conditions. Temperature responses such as oxygen consumption and rectal temperature were measured and heat loss was calculated. The effects of the first stimulation before serotonine injection were compared with those of the second one after serotonine application in order to prove the influence of serotonine on temperature responses due to APM stimulation. On the other hand, the influence of stimulation on changes produced by serotonine injection should be shown by the recordings of the second serotonine responses with stimulation effects and by comparison of these with those of the first serotonine responses without stimulation effects. The first APM stimulation depending on the rectal temperature before stimulation resulted in decreasing oxygen consumption in hypothermic rats while increasing that of hyperthermic animals. There was a little decrease of rectal temperature under hyper- and normothermic conditions. while under hypothermic conditions animals showed marked depression. The increase in heat loss, however, was least in hyperthermic rats and most pronounced in hypothermic animals. The second APM stimulation did almost not affect the temperature responses after serotonine application in normothermic rats, while causing supercooling agin under hypothermic conditions and insignificant cooling at hyperthermic environment temperature. Comparison of the first and second stimulation effects revealed statistical significant differences at normo-, hypo- and hyperthermic temperatures. The results are discussed under consideration of the different starting conditions before the first and second stimulation. These findings do not indicate that serotonine would shift the sensibility of mediopraeoptic structures and thus unequivocally modifies stimulation effects.     

Comparative spinal analgesic action of dynorphin1-8, dynorphin1-13, and a kappa-receptor agonist U50,488

The effect of intrathecal injections of dynorphin1-8 (DYN1-8), dynorphin1-13 (DYN1-13), and a putative kappa agonist, U50,488 was tested in the rat tail-flick test. DYN1-8 and DYN1-13 (5, 10, 20 micrograms) produced a dose-related biphasic antinociceptive response consisting of an initial and a delayed response. Injection of U50,488 (20, 40 60 micrograms) produced a monophasic response. The antinociceptive effect of DYN1-8 (5, 10, 20 micrograms) and DYN1-13 (20 micrograms), was present 24 h postintrathecal injection. Pretreatment with systemic naloxone (2 mg/kg s.c.) attenuated the delayed response, but not the initial response induced by DYN1-8 and DYN1-13. The initial response was attenuated by pretreatment with intrathecal naloxone at a dose of 0.5 and 2.0 micrograms. The antinociceptive effect of U50,488 (20, 60 micrograms) was not affected by pretreatment with 2.0 micrograms intrathecal naloxone, but was significantly reduced by 4 micrograms of the antagonist. Both DYN1-8 and DYN1-13 (5 micrograms) augmented the antinociceptive effect of intrathecally administered morphine (5, 10 micrograms). Intrathecal injection of DYN1-8 (5, 10, 20 micrograms), DYN1-13 (5 micrograms), and morphine (10 micrograms) reduced the spontaneous output of urine measured at 2 and 24 h postintrathecal injection. A similar injection of U50,488 (20 micrograms) had no significant action on the urinary output. The results show that long and short dynorphin fragments have a comparable activity and the spinal antinociceptive actions of dynorphin are sensitive to low doses of intrathecal naloxone. The activity profile of spinally administered dynorphins differs from that of the kappa agonist U50,488.     

Modulation of morphine induced antinociception by intracerebroventricularly administered captopril

Captopril when administered intracerebroventricularly (icv) in doses of 100, 300, 500 and 1000 micrograms induced a dose dependent antinociceptive effect in rats. Naloxone pretreatment (10 mg/kg, ip) completely antagonised antinociceptive effect of captopril, suggesting thereby the involvement of brain enkephalinergic system. Captopril 300 micrograms, icv potentiated the antinociceptive effect of morphine in intact animals. The bilateral adrenalectomy did not have any effect on this potentiation as against the reported blockade of potentiation in adrenalectomized animals when captopril was administered by systemic route. Thus potentiation of morphine induced antinociception by icv captopril is unlikely to be exerted through an effect on adrenal function and is most likely due to increased brain enkephalin levels.     

The antinociceptive properties of dalargin as an agent of anesthesiologic protection

The antinociceptive properties of dalargin (D) under nembutal anesthesia and artificial ventilation were studied in hemodynamic response to mechanical algesic stimulation in rats. D was introduced i/v (20 micrograms/kg) against a background of myoplegia with Arduan (0.1 mg/kg) and without it. The naloxon (100 micrograms/kg) prevented the protective effects of D. It is considered that injection of D (20 micrograms/kg) on the background of total myoplegia and artificial ventilation prevented hemodynamic response on algesic stimulus. Subsequent dose increase of opium peptide up to 3500 micrograms/kg does not cause amplification of protective properties.     

Treatment with pertussis toxin does not prevent central effects of eel calcitonin.

To determine whether or not the CNS inhibitory activity of eel calcitonin (eCT) on adenylyl cyclase is the endocellular mechanism underlying the antinociceptive effect of the peptide, as shown for morphine analgesia, we administered Bordetella pertussis toxin (PTX) by intracerebroventricular (ICV) injection (0.5 microgram/rat) to block the receptor-mediated inhibition of adenylyl cyclase. In PTX-treated rats there was no change in eCT (2.5 micrograms/rat, ICV)-induced antinociceptive activity (hot-plate test) nor in eCT (100 ng/rat, ICV) inhibition of gastric acid secretion (Shay test) whereas morphine (5 micrograms/rat, ICV) analgesia was significantly reduced. In vitro studies showed no reduction of eCT binding in the CNS of rats treated with PTX in vivo. Moreover, PTX treatment did not change the inhibitory effect of eCT on adenylyl cyclase in isolated membranes from rat striatum in contrast with opiates (DAME and morphine) whose effects were lost. As PTX is known to inactivate the guanidine binding inhibitory protein Gi, these data suggest that a G protein, distinct from the Gi protein involved in the coupling of opiate receptors into a functional response, could be responsible for regulating the intracellular pathways resulting in eCT-induced antinociceptive effect and inhibition of gastric acid secretion.     

Antinociceptive effect of spinal cholinergic stimulation: interaction with substance P

Activation of central muscarinic receptors results in an antinociceptive response in experimental animals. Employing intrathecal (i.t.) injection and radiant heat applied to a rat's tail as the experimental paradigm, a spinally-mediated antinociceptive response was obtained following injection of cholinergic agonists. Since "cholinergic' analgesia is mediated independently of the opiate system, the possibility was considered that this response was mediated through inhibition of the local release of substance P. Rats were prepared with indwelling i.t. catheters which terminated in the L2-L3 region of the spinal cord. I.t. injection of carbachol (0.05-5 micrograms) or neostigmine (1-10 micrograms), but not nicotine (0.5-10 micrograms) produced dose-related increases in tail flick latencies. Pretreatment with i.t. injection of atropine or hemicholinium-3 significantly inhibited the antinociceptive response to neostigmine. Spinal substance P levels were measured 30 min following 0.5 micrograms carbachol. Levels in the dorsal horn were reduced by 30% compared with saline controls. Levels in the ventral horn were unchanged by carbachol. These results support the role of endogenous spinal acetylcholine in pain modification and suggest an interaction with substance P neurons of the dorsal spinal cord.     

Centrally-mediated antinociceptive action of RWJ-22757 (formerly McN-5195): involvement of spinal descending inhibitory pathways (an hypothesis)

The present studies were an attempt to examine the mechanism of action of the novel antinociceptive compound RWJ-22757, (+/-)-trans-3-(2-bromophenyl)-octahydroindolizine (McN-5195). Intracerebroventricular (i.c.v.) administration of RWJ-22757 produced dose-related antinociception in the mouse tail-flick (48 degrees C) and rat hot-plate (51 degrees C) tests (ED50 = 243.3 and 261.3 micrograms, respectively). In contrast, intrathecal (i.t.) administration was without effect. The antinociception produced by peripherally (i.p.) or centrally (i.c.v.) administered RWJ-22757 was attenuated by i.t. administration of 2 micrograms phentolamine, 5 micrograms yohimbine, or 10 micrograms methysergide. I.t. administration of naloxone, at a dose (0.5 micrograms) that significantly attenuated the antinociceptive effects of peripherally or centrally administered morphine, had no effect on RWJ-22757-induced antinociception. We conclude from these results, coupled with the overall pharmacological and neurochemical profile of RWJ-22757, that the data are consistent with the hypothesis that RWJ-22757 produces antinociception predominantly at a site or sites located supraspinally with little or no activity at the spinal level and that RWJ-22757 activates adrenergic and serotonergic descending inhibitory pathways, increasing the tonic activity of endogenous antinociceptive systems.     

The structural dynamics of vagus influence on the heart rhythm in exposures directed at altering the acting acetylcholine concentration]

In 29 experiments on anaesthetized cats burst stimulation of peripheral cut end of right vagus nerve leads to synchronization of heart and vagus rhythm. Influence of proserine, pilocarpine and prolonged vagus stimulation upon extent of vagus chronotropic effect and its components--tonic and synchronizing--was investigated. In all cases changes of vagus chronotropic effect during this actions were caused by unidirectional shifts of tonic component. Extent of synchronizing vagus chronotropic influences did not depend on the changes of acetylcholine concentration.     

The role of dopamine and serotonin in modulating the defensive behavior of the edible snail

Dopamine application in concentration of 10(-5)-10(-6) M into saline around the snail CNS leads to decrease of excitability of LPa7 neurone which is presynaptic in relation to defensive behaviour command neurones, and to decrease of amplitude of monosynaptic excitatory postsynaptic potential (EPSP) in the command neurones elicited by intracellular stimulation of LPa7 neurone. Besides, the dopamine causes a decrease of summated EPSP amplitude in the studied neurones in response to intestinal nerve stimulation (70% in average), a change of rest potential towards hyperpolarization for 6-8 mV, a reduction of the command neurones input resistance (20% in average). The described influences can lead to a general increase of the threshold of defensive system reaction to stimulation. Dopamine action on the defensive behaviour command neurones is significantly weakened in serotonine presence. Against the dopamine background, the efficiency of serotonine influence on the value of EPSP in command neurones in response to testing stimulus is reduced. According to the obtained data, a conclusion is made that interrelation of dopamine and serotonine concentrations can be a base for formation of behaviour choice in snail.     

Role of KATP channels in reduced antinociceptive effect of morphine in streptozotocin-induced diabetic mice

The nociceptive effect was measured using withdrawal latency in tail flick test in mice rendered diabetic by administering streptozotocin (200 mg/kg, i.p.). The antinociceptive effect of morphine (4 and 8 mg/kg, s.c.) and cromakalim, a KATP channel opener, (0.3, 1 and 2 micrograms, i.c.v.) was significantly reduced in diabetic mice. Moreover, co-administration of cromakalim(0.3 microgram) did not alter the reduced antinociceptive effect of morphine(4 mg/kg) in diabetic mice. Spleenectomy in diabetic mice restored the decrease in antinociceptive effect of morphine and cromakalim. Multiple dose treatment with insulin to maintain euglycaemia for 3 days in diabetic mice prevented the decrease in antinociceptive effect of morphine and cromakalim. However, hyperglycaemic tyrode's buffer did not alter the pD2 value of morphine in isolated guinea pig ileum suggesting that hyperglycaemia does not interfere with mu receptor mediated responses in vitro. The results suggest that hyperglycaemia induced decrease in antinociceptive effect of morphine and cromakalim may be due to alteration in KATP channels. Some unknown factor from spleen in diabetic mice may be responsible for this alteration in KATP channels in diabetic mice.     

The effect of substance P on the neuronal activity of the antinociceptive system

The experiments on rats showed that the 1 micrograms substance P injection to dorsal raphe nucleus caused prolonged (24 hours of study) analgetic effect--it enhances the reaction latent period to thermal nociceptive stimulation, intensifies the background impulse activity, rises the middle frequency of neuron discharges and creates high-frequency neurons as well as the neurons with burst impulse activity. The supposition is being confirmed that the mechanism of antinociceptive structures activation leads to analgesia caused by substance P.     

Effects of transcranial laser irradiation in near infrared range on antinociceptive reactions in mice after administration of diazepam, clopheline and morphine]

The experiments were carried out on white mice whose brain was irradiated transcranially with laser light in infrared range. Exposure to irradiation was 20 min. In one group of animals only laser light was used, in others laser was combined with morphine (3mg/kg), clonidine (0.5 mg/kg), and diazepam (1 mg/kg) injected intraperitoneally. The nociceptive reactions were studied with the help of "tail-flick" and "hot-plate" tests. It was found that laser light did not modify significantly the results of both tests. Moreover, it didn't influence the antinociceptive properties of morphine, clonidine and diazepam in the "hot-plate" test. In the "tail-flick" test laser light did not affect the action of clonidine, but provided naloxone-independent antinociceptive reaction with diazepam and increased the antinociceptive effect of morphine. Laser irradiation of the brain did not cause any significant morphological changes. These results suggest the possibility of modulating antinociceptive actions of morphine and diazepam by laser irradiation of the brain.     

L-NAME causes antinociception by stimulation of the arginine-NO-cGMP pathway

NG-nitro-L-arginine methyl ester (L-NAME) has been used extensively as a paradigmatic inhibitor of NO synthase and has been shown to cause antinociception in several experimental models. We describe here how L-NAME produced a dose-dependent antinociceptive effect when injected intraperitoneally in the mouse after acetic acid induced writhings, or intraplantarly in the rat paw pressure hyperalgesia induced by carrageenin or prostaglandin E2. In contrast another NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), had no significant effect per se but inhibited L-NAME systemic induced antinociception in mice and local induced antinociception in the rat paw hyperalgesia test. D-NAME had no antinociceptive effect upon carrageenin-induced hyperalgesia. Pretreatment of the paws with two inhibitors of guanylate cyclase, methylene blue (MB) and 1H-:[1,2,4]-oxadiazolo-:[4,3-a] quinoxalin-1-one (ODQ) abolished the antinociceptive effect of L-NAME. L-Arginine and the cGMP phosphodiesterase inhibitor, MY 5445 significantly enhanced the L-NAME antinociceptive effect. The central antinociceptive effect of L-NAME was blocked by co-administration of L-NMMA, ODQ and MB. The present series of experiments shows that L-NAME, but not L-NMMA, has an antinociceptive effect. It can be suggested that L-NAME causes the antinociceptive effect by stimulation of the arginine/ NO/ cGMP pathway, since the antinociceptive effect of L-NAME can be antagonized by L-NMMA and abolished by the guanylate cyclase inhibitors (MB and ODQ). In addition, the NO synthase substrate, L-arginine and the cGMP phosphodiesterase inhibitor, MY5445 were seen to potentiate the effects of L-NAME. Thus, L-NAME used alone, has limitations as a specific inhibitor of the arginine-NO-cGMP pathway and may therefore be a poor pharmacological tool for use in characterising participation in pathophysiological processes.     

Effects of the removal of the orbito-frontal cortex on the development of reflex analgesia

The authors studied the effect of electric acupuncture stimulation (EAP) on the changes in pain thresholds prior to and after removal of the orbito-frontal cortex (OFC) of the brain in behavioral experiments on adult cats. Removal of OFC increased the thresholds of pain response at the 4th and the 5th levels of the conventional scale, reflecting emotionally-affective manifestations of pain, and intensified the effect of antinociceptive EAP. The results obtained are analysed in relation to the inhibitory tonic effect of OFC on antinociceptive structures of the brain. Different effects of OFC and somatosensory cortex on the antinociceptive structures of the brain are discussed.     

Antinociceptive effects in mice after intrathecal injection of a substance P receptor antagonist, Spantide: lack of 'neurotoxic' action

The present investigation was undertaken to determine the antinociceptive potency and possible neurotoxic effects of a substance P (SP) receptor antagonist, [D-Arg,D-Trp,Leu]SP (Spantide), after intrathecal injection in mice. After the nociceptive tests had been carried out, the animals were sacrificed and the spinal cords were investigated for histopathological changes, since such have been reported previously to occur in rats. It was found that the reaction latency in the tail-flick test increased in the dose range 0-10 micrograms. The effect was maximal at 10 and 45 min after 10 micrograms Spantide, and somewhat lower when 5 micrograms was used. None of the animals showed the complete motor impairment reported previously to occur after intrathecal administration in rats. In some of the mice we observed a slight rigidity in the hind-legs. At histopathological examination, it was found that Spantide produced no histological changes indicative of 'neurotoxic' effects. In agreement with this, the immunohistochemical evaluation, using calcitonin gene-related peptide (CGRP) as a marker for motoneurons and central branches of primary sensory neurons, did not provide evidence that the intrathecal injection of 10 micrograms Spantide produced any effects when compared to vehicle-injected animals. In conclusion, the present results demonstrate an antinociceptive effect of Spantide when injected intrathecally in mice, and that this occurred without any signs of toxic reactions in spinal cord as previously has been reported for the rat.     

Change in the nociceptive reactions caused by dental pulp stimulation during excitation of the midbrain]

It was demonstrated in chronic experiments on cats that stimulation of certain midbrain regions decreased or fully depressed the pain reaction evoked by dental pulp stimulation. The antinociceptive effect depending on the parameters of the brain stimulation was shown in differential change of the separate motor and vegetative and emotional - behaviour components, forming a general pain reaction. A poststimulation analgesia was revealed and the dynamic of restoration of different pain manifestations after the cessation of brain stimulation was traced. Possible mechanism of the realization of the antinociceptive effect are discussed.     

Electroacupuncture analgesia could be mediated by at least two pain-relieving mechanisms; endorphin and non-endorphin systems.

This present paper shows different levels of electroacupuncture analgesia (antinociceptive effect) induced by three different frequencies of stimulation (i.e. 0.2, 4 and 200 Hz); highest analgesia is induced at 200 Hz and lowest at 0.2 Hz. Naloxone (1 mg/kg) completely reverses the electroacupuncture effects at low frequency stimulation (4 Hz) but produces no inhibition at high frequency stimulation (200 Hz). Conversely, parachlorophenylalanine (320 mg/kg) partially blocks the high-frequency (200 Hz) analgesia but produces no effect on the low-frequency (4 Hz) electroacupuncture analgesia. This suggests that electroacupuncture analgesia induced by low frequency stimulation may be mediated by endorphins while high frequency stimulation is not endorphinergic but may be partly due to serotonin.     

Change in the antinociceptive effect occurring on stimulation of the midbrain under the action of analgesics and tranquilizers

It was shown in chronic experiments on cats that analgetics in subanalgetic doses not only revealed the antinociceptive effect under subthreshold stimulation of the midbrain, but also enhanced the analgetic effect of the central stimulation. The tranquilizers promoted only the analgetic action under the subthreshold stimulation of the midbrain. Possible causes of different effect of the drugs under study are discussed.     

Effect of repeated serotonin injections on temperature regulation in the rat]

The effect of repeated serotonine injections was investigated in thirty Wistar rats tested under normo-, hypo- und hyperthermic conditions. 7 mul of a 0.5% serotonine solution (5HT) were injected into the third ventricle at 1-hr intervals. Temperature responses such as oxygen consumption and rectal temperature were measured and the heat loss was calculated. Intraventricular serotonine produced cooling in all animals. The central mechanisms of heat production were inhibited and those of heat loss were activated. The serotonine responses were most pronounced in hypothermic rats and least effective in hyperthermic animals.     

Interaction between tryptophanyl-tRNA synthetase and tryptophan analogs with modified alpha-amino group

Analogs of L-tryptophane with modified alpha-amino groups (substituted for hydrogen or keto-group, or acylated) are competitive reversible inhibitors of the aminoacylation of tRNNATrp catalyzed by tryptophanyl-tRNA synthetase from beef pancreas. Compounds lacking alpha-amino group are weakly bound to the enzyme, whereas the Ki values for N-acylated L-tryptophane derivates and for beta-indolylpyruvic acid are similar and approximately two orders of magnitude higher than the KM value for L-tryptophane.