Corresponding author: Hristina Nocheva ( hndimitrova@medfac.mu-sofia.bg ) Academic editor: Plamen Peikov
© 2021 Hristina Nocheva, Zafer Sabit, Dimitar Bakalov, Evgeni Grigorov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Nocheva H, Sabit Z, Bakalov D, Grigorov E (2021) Interactions between the cannabinoid and the serotonergic systems in modulation of pain perception. Pharmacia 68(1): 109-115. https://doi.org/10.3897/pharmacia.68.e49219
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The aim of our study was to evaluate the effects of cannabinoids and serotonergic system on nociception in intact rats and after heat stress. Cannabinoid receptor type 1 (CB1) and 5-hydroxytryptamine receptor (5НТ1А) agonists and antagonists have been administered according to different experimental designs (alone and in combinations) in intact male Wistar rats, as well in animals subjected to one hour of heat stress. Pain perception has been evaluated by Paw pressure test. Our results pointed out that cannabinoids and the serotonergic system interact in nociception in intact animals as well as after heat stress. Cannabinoids seemed to have less prominent role in such interaction in intact animals than after heat stress. The interplay between the two systems probably involves different mechanisms in intact animals and after heat stress with time-dependent effects. The interaction between the cannabinoid and the serotonergic systems exerts a modulating rather than mediating effect on h-SIA.
cannabinoids, nociception, Paw pressure test, stress induced analgesia, serotonergic system
In the last three decades the endogenous cannabinoid system (ECS) has received increasing research attention due to its implication in many physiological (emotion, memory, sleep, metabolic function, etc.) and pathological (pain and inflammation) processes (
The serotonergic system has been traditionally associated with mood disorders (
In vivo effects of interaction between the cannabinoids and the serotonergic system have been evaluated mainly in connection with their impact on memory, affective and cognitive disorders (
Our study was focused on in vivo effects of cannabinoids and serotonergic system interaction on pain perception. Experiments involved intact animals as well as animals subjected to heat stress, since possible differences in the effects of the mediators in physiologic and pathologic conditions were also expected.
Physical and psychological stress exposure triggers a broad spectrum of physiological responses designated to increase chances for escape, survival, and homeostasis restoration. Synchronization between the nervous, the endocrine and the immune systems characterizes the stress-reaction of the body with apposite behavioral, autonomic and cognitive responses. Along with the undeniable importance of the stress reaction for stress coping, it is also true that such a reaction could unleash pathologic conditions and diseases of nervous, cardiovascular, gastrointestinal, reproductive systems (
Several physiologic parameters, pain perception among them, change during acute stress exposure – a phenomenon known as stress-induced analgesia (SIA). Since SIA develops along with stress itself and is underlined by the same mechanisms engaged in the stress-response, it could be regarded as an indirect marker for the stress-reaction. On the other hand, SIA depends also on pathways that suppress pain perception. Understanding the mechanisms underlying SIA could give interesting clues for both stress- and pain-control.
The experiments were carried out on male Wistar rats (180–200g). Animals were housed individually in polypropylene boxes with free access to food and water. Constant temperature environment (22±2 °C) on a 12 h light/dark cycle (lights on at 6.00 a.m.) was provided. All experiments were carried out between 10:00 a.m. and 1:00 p.m.
All procedures were approved by the Animal Care and Use Committee of the Medical University of Sofia and BFSA.
Аnimals were placed in thermal chamber at 38 °C for 1 hour. During the time of stress free movements were allowed, but no food or water was provided.
СВ1-agonist N-arachidonoyl-ethanolamine (or anandamide, AEA, 1 mg/kg) and СВ1-antagonist N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carbox-amide (AМ251, 1,25 mg/kg) were purchased from Sigma Aldrigh; 5НТ1А– agonist (R)-(+)-8-Hydroxy-DPAT hydrobromide (DPAT, 1 mg/kg) and 5НТ1А– antagonist NAN-190 hydrobromide (NAN, 1mg/kg) were purchased from Tocris Bioscience (Bristol, UK). All substances were administered intraperitoneally (i.p.) dissolved in DMSO.
Ugo Basile analgesimeter was used in order to estimate changes in the mechanical nociceptive (PP-) thresholds of experimental animals -Paw pressure (PP, Randall-Selitto) test. Pressure was applied to the hind-paw and the value (in arbitrary units, AU) required to elicit a nociceptive response (such as squeak or struggle) was taken as the mechanical nociceptive threshold. A cut-off value of 500 g was observed to prevent damage of the paw.
The results were statistically assessed by one-way analysis of variance (ANOVA) followed by t-test comparison, and represented as mean ± S.E.M. Values of p < 0.05 were considered to indicate statistical significance.
Administration of CB1-agonist AEA and 5НТ1А-agonist DPAT in intact animals (int+AEA+DPAT, Fig. 1А) decreased PP-thresholds compared to controls during the first 30 min of the experiment; an increase in PP-thresholds was observed after that period. When AEA and DPAT were administered after CB1-antagonist AM251 (int+AM251+AEA+DPAT, Fig. 1А) PP-thresholds remained comparable to controls till the 40th min of the experiment with an increase following that period. Administration of 5НТ1А-antagonist NAN-190 (int+NAN+AEA+DPAT, Fig. 1А) instead increased PP-thresholds for the entire time of the experiments compared to controls and int+AM251+AEA+DPAT.int+NAN+AEA+DPAT-animals showed higher PP-thresholds compared to int+AEA+DPAT for the first 30 min of the experiment (Fig. 1А).
Effects of CB1- and 5НТ1А-agonists (AEA+DPAT) administration on nociceptive (PP) thresholds in (A) intact animals (int) and (B) animals subjected to 1 hour of heat stress (1 h HS) without and after pretreatment with CB1- and 5НТ1А-antagonists (AM and NAN, respectively). PP-thresholds are represented as mean values ± S.E.M. in arbitrary units (AU). ***p < 0.001, **p < 0.01 vs. controls. A. +++p < 0.001, ++p < 0.01 vs. int+AEA+DPAT. B. +++p < 0.001 vs. 1 h HS; xxxp < 0.001, xxp < 0.01 vs. 1 h HS+AEA+DPAT.
Serotonin and endogenous cannabinoids have been both demonstrated to take part in pain perception modulation. The spinal 5НТ1А-receptor has most commonly been reported to promote antinociception (
The interplay between the serotonergic system and the ECS may involve changes in the release of eCB and/or 5-HT, common second messengers, as well as other mediatory systems. Data exist that endocannabinoids (eCBs) may influence the firing rate of 5-HT neurons (
In our experiments the PP-curve of int+AEA+DPAT indeed resembled the one for int+DPAT (Fig.
Effects of CB1-agonist (AEA) and 5НТ1А-agonists (DPAT) alone administration on nociceptive (PP) thresholds in (A) intact animals (int) and (B) animals subjected to 1 hour of heat stress (1h HS) without and after pretreatment with CB1- and 5НТ1А-antagonists (AM and NAN, respectively). PP-thresholds are represented as mean values ± S.E.M. in arbitrary units (AU). ***p < 0.001, **p < 0.01, *p < 0.05 vs. controls. A. +++p < 0.001, ++p < 0.01 vs. int+AEA+DPAT. int+NAN+DPAT were compared to int+DPAT – xxxp < 0.001, xxp < 0.01; int+AM+AEA were compared to int+AEA – $$$ p < 0.001. B. +++p < 0.001, ++p < 0.01 vs. 1h HS; xxxp < 0.001, xxp < 0.01 vs. 1h HS+AEA+DPAT. 1h HS+NAN+DPAT were compared to 1h HS+DPAT – $$$p < 0.001, $$p < 0.01; 1h HS+AM+AEA were compared to 1h HS+AEA – &&&p < 0.001.
1 hour of heat stress (Fig.
Administration of AEA and DPAT after the end of 1h HS (1h HS+AEA+DPAT, Fig.
Both CB1- and 5НТ1А-receptor antagonist’s administration before the agonists (1h HS+AM+AEA+DPAT; 1h HS+NAN+AEA+DPAT, Fig.
In an additional experimental trial, DPAT and AEA were administered each one alone in intact animals and after 1h HS. DPAT administration in intact animals (int+DPAT, Fig. 2А) increased pain perception during the first 30 min compared to controls. Instead, an increase in h-SIA was observed after 1h HS on the 10th min, with 1h HS+DPAT-animals- PP-thresholds higher than control levels for the first 20 min of the experiment (Fig.
NAN-pretreatment before DPAT-administration in intact animals (int+NAN+DPAT, Fig.
CB1- and 5НТ1А-receptor agonists administration in animals after 1h HS had a modulator type effect on h-SIA. Contemporal administration of AEA and DPAT after the end of heat stress was characterized by different PP-thresholds than the ones after each one of the substances applied alone (Fig.
The ECS participates in mediation of stress (
The serotonergic system is also engaged during stress, and some authors retain 5НТ1А-receptor’s role pivotal for regulation of the stress-response (
Our experiments revealed that cannabinoids and 5-HT exerted opposite and time-dependent effects on nociception in intact animals and after stress. DPAT and the combination DPAT+AEA increased nociception during the first 30 min in intact animals, while decreased nociception was observed during the same period in animals after stress. A marked change in pro-/ anti- nociceptive activity of DPAT and AEA was also detected on the 30th min (Fig.
The role of 5НТ1А-receptors is essential in the mechanism ofaction of various drugs (
Cannabinoid and serotonergic systems will attract even more future scientific attention given new emerging data about their participation in heteroreceptor complexes (5-HT1A-CB2, orexin1receptor-CB1) implicated in morbidity and mortality (
The endogenous cannabinoid and the serotonergic systems interact in nociception in intact animals as well as after heat stress. The ECS seems to have less prominent role in such interaction in intact animals than after heat stress. The interplay between the two systems seems to involve different mechanisms in intact animals and after heat stress with time-dependent effects. The interaction between the endogenous cannabinoid and the serotonergic systems exerts a modulating rather than mediating effect on h-SIA.
The present work was supported by a Grant D-61/03.05.2018 from the Medical Science Council of Medical University of Sofia.