ABSTRACT Peripheral nerves are most commonly affected by pressure, traction, friction, anoxia or cutting and these injuries can easily cause allodynia of the limbs. Beta-endorphin is an endogenous pain inhibitor. It can produce profound and long-lasting analgesia for patients with intractable pain. Prominent endogenous opioid peptides are modulated by the hypothalamic-pituitary-adrenal axis. The expression of pro-opiomelanocortin (POMC) produces opioid peptides, including the beta-endorphins, other shorter endorphins, adrenocorticotropic hormones (ACTH), and melanocyte-stimulating hormones (MSH). The aim of this study is to evaluate the efficacy of POMC gene therapy for neuropathic pain that is caused by chronic constriction injury (CCI) in a rat model. Experimental painful peripheral neuropathy is induced by CCI of the sciatic nerve which results in allodynia of the hind limb. We used the method of conventional electrical stimulation to quantitatively analyze the efficacy of gene therapy. In addition, two nociceptive tests, including thermal-withdrawal latency and mechanical withdrawal threshold, were also conducted to evaluate the effect of treatment. Adult male Sprague Dawley rats (250-300 g, n = 24) were divided into three groups: (1) the control group (n = 8); (2) the sciatic nerve ligation group that received an injection of adenoviral vectors with green fluorescent protein (Ad-GFP) (n = 8); and (3) the sciatic nerve ligation group that received an injection of adenoviral vectors with POMC gene (Ad-POMC) (n = 8). The electrophysiological studies and nociceptive tests were carried out on day 3 before ligation and days 3, 7 and 14 after ligation. The POMC injection was performed on day 3 after ligation. We measured the amplitude and onset latency of maximal compound muscle action potential (CMAP) in braches of the sciatic nerve (nerves to the gastrocnemius, tibialis anterior), motor nerve conduction velocity, H-reflex and F-wave by electrical stimulation and denervation sign by electromyography (gastrocnemius, tibialis anterior). In addition, the latency of the thermal-withdrawal and threshold of mechanical withdrawal were also recorded. The results showed that prominent thermal-withdrawal latencies and mechanical withdrawal thresholds were elevated in the sciatic nerve ligation group with POMC gene therapy on days 14 and 21 after ligation. It also demonstrated that administrations of POMC gene therapy which produced the beta-endorphins to elevate the pain threshold and reduced the allodynia of the injured limbs. In conventional electrophysiological studies, no significant differences were noted between the Ad-GFP and Ad-POMC groups. The reduction of CMAP amplitude was recorded in rats of the sciatic nerve ligation groups. There was no significant difference in the mean onset latency of CMAP and nerve conduction velocity (NCV) within these three groups, except for the fact that the NCV of the tibial nerve was slowing in the Ad-GFP group on day 14. Electrophysiological analysis was revealed prolonged or absent H-reflex and F-wave in animals of the neuropathy groups by electrical stimulation. Electromyography showed prominent denervation potentials over the sampling muscles in the sciatic nerve ligation groups. In conclusion, POMC gene therapy for neuropathic pain is very efficacious. However, the influence of POMC gene therapy for nerve protection or minimizing the progress of nerve injury will require further investigations.

We are still unable to effectively suppress neuropathic pain, therefore it remains a serious problem. Ghrelin, the orexigenic hormone released by enteroendocrine stomach cells, could contribute to alleviation of the neuropathic pain by its antinociceptive effect. Previous studies have shown that ghrelin prevents development of nociceptive symptoms of neuropathic pain. The aim of our study was to determine whether chronic administration of ghrelin will affect the already fully developed neuropathic pain and differentiate its antinociceptive and analgesic effect. We used a model of chronic constriction injury of the sciatic nerve. We have proven that ghrelin suppressed the already developed thermal and mechanical hyperalgesia, so ghrelin not only prevents the development, but also suppresses the already developed nociceptive symptoms. However analgesia test showed that ghrelin did not affect the temperature preference, neither did induce the place preference. We suppose that ghrelin does not cause analgesia in neuropathic pain and its antinociceptive effect could be caused by anti- inflammatory or neuroprotective action. Key words: Ghrelin, neuropathic pain, chronic constriction injury, preference methods

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Some forms of neuropathic pain are maintained by sympathetic fibers, but the underlying mechanisms are poorly understood. Thus, the aim of this study was to investigate the possible involvement of the TRPA1 receptor as well as the role of the sympathetic nervous system (involved in sympathetically maintained neuropathic pain) in a model of neuropathic pain induced by chronic sciatic nerve constriction injury (CCI) in mice. The systemic injection of the selective TRPA1 antagonist HC-030031 reversed both mechanical and cold allodynia induced by chronic sciatic nerve constriction injury. Nerve injury also sensitizes mice to the nociception induced by the intraplantar injection of a low dose of the TRPA1 agonist allyl isothiocyanate without changing TRPA1 immunoreactivity in the injected paw. Furthermore, the chemical sympathectomy produced by guanethidine largely prevented CCI-induced mechanical and cold allodynia. CCI also induced a norepinephrine-trigged nociception that was inhibited by α-adrenoceptor antagonism and norepinephrine transporter and monoamine oxidase inhibition. Finally, the peripheral injection of HC-030031 also largely reduced CCI-induced nociception by norepinephrine and mechanical or cold allodynia. Taken together, the present findings reveal the critical role of TRPA1 in mechanical and cold hypersensitivity as well as in hypersensitivity to norepinephrine following nerve injury. This article presents the role of TRPA1 receptor on the sympathetically-maintained nociception induced by nerve injury in mice. Our results suggest that TRPA1 antagonists may be useful to treat neuropathic patients that present sympathetically maintained pain. / Algumas formas de dor neuropática são mantidos por fibras simpáticas, contudo os mecanismos subjacentes são pouco compreendidos. Assim, o objetivo deste estudo foi investigar o possível envolvimento do receptor TRPA1, bem como o papel do sistema nervoso simpático num modelo de dor neuropática induzido pela constrição crônica do nervo ciático (CCI) em camundongos. A administração sistêmica do antagonista seletivo do receptor TRPA1, HC-030031, reverteu a alodinia mecânica e ao frio induzida pela CCI. A injeção de uma baixa dose do agonista do receptor TRPA1, isotiocianato de alila, induziu uma resposta nociceptiva nos animais que sofreram a lesão no nervo, sem alterar a imunorreatividade do TRPA1 na pata injetada. Além disso, a simpatectomia química produzida pela guanetidina amplamente previniu a alodínia mecânica e ao frio induzida pela CCI. Ainda, a injeção intraplantar de norepinefrina induziu nocicepção espontânea, a qual foi reduzida pelo antagonista α-adrenérgico, inibidor do transportador de norepinefrina e inibidor da enzima monoamina oxidase. Finalmente, a administração periférica do HC-030031 reduziu a nocicepção espontânea induzida pela norepinefrina e também a alodínia mecânica e térmica de animais neuropáticos. Assim, nossos resultados revelam o papel crítico do receptor TRPA1 na alodínia mecânica e ao frio, bem como na hipersensibilidade à norepinefrina após lesão do nervo em um modelo de dor neuropática mantida pelo simpático. Dessa forma, o receptor TRPA1 poderá ser um alvo para o desenvolvimento de novos tratamentos para esse tipo de dor.

Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-15T15:07:42Z No. of bitstreams: 1 DissEMFC.pdf: 1127581 bytes, checksum: a37fcb5548575f25ebe36ee92d664535 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:26:53Z (GMT) No. of bitstreams: 1 DissEMFC.pdf: 1127581 bytes, checksum: a37fcb5548575f25ebe36ee92d664535 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:27:10Z (GMT) No. of bitstreams: 1 DissEMFC.pdf: 1127581 bytes, checksum: a37fcb5548575f25ebe36ee92d664535 (MD5) / Made available in DSpace on 2016-09-16T19:27:21Z (GMT). No. of bitstreams: 1 DissEMFC.pdf: 1127581 bytes, checksum: a37fcb5548575f25ebe36ee92d664535 (MD5) Previous issue date: 2014-05-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neuropathic pain is a type of chronic pain that can causes comorbidities such as generalized anxiety and depression, and, consequently, it produces considerable damage to the quality of life of affected people. Despite it being refractory to most conventional pharmacological treatments, studies evidence that serotonergic drugs, like antidepressants, are effective in treatment of this type of pain. Serotonin is a neurotransmitter with an important role in the modulation of nociceptive stimuli as well as the behaviors related to fear and anxiety. There is evidence that aversive situations, such as predator exposure may cause antinociception as a defensive reaction. Thus, several studies have demonstrated that fear or anxiety stimulus can cause antinociception and the serotonin (5-HT) produces this antinociceptive effect in structures of the central nervous system, such as the periaqueductal gray matter (PAG). In this sense, studies from our group demonstrate that activation of 5-HT2C receptors in PAG is involved in anxiolytic effects and in fear and anxiety-induced antinociception in mice exposed to the elevated plus maze. However, it is unknown what the role of PAG serotonergic receptors in the modulation of antinociception induced by exposure to predator (rat). Thus, the objective of this study was to evaluate the effect of activation of 5-HT2C receptors of PAG on the antinociception and defensive behaviors in mice submitted to sciatic nerve constriction. For this, Swiss-albino male mice were submitted to sciatic nerve constriction on the first day of the experiment and, seven days later, they received implantation of guide cannula in the PAG. Four days after stereotactic surgery, mice received intra-PAG injection of vehicle or mK212 and were exposed to the predator. The test consisted of two phases: a) habituation to the apparatus for 10 minutes for 3 consecutive days, which started the next day after stereotactic surgery; b) exposure to predators or neutral stimulus for 10 minutes. The analysis of variance (ANOVA) of three factors (condition x stimulation x treatment) showed that chronic constrition injured (CCI) mice exhibited increased of scratching behavior, that is indicative of chronic pain. The exposure of these animals to the predator (rat) produced antinociception in CCI mice and increased behaviors related to fear and anxiety such as time spent in protected area and total number of stretched attend posture (SAP) and decreased time of contact with the grid, when compared to mice exposed to neutral stimulus (toy rat). Treatment with mK212 intra-PAG (0.21 and 0.63 nmol) produced no significant change in antinociception and fear and anxiety assessed during exposure to rat. However, the mK212 0.21nmol dose treatment increased scratching behavior, indicating hyperalgesia in CCI mice exposed to toy rat. Thus, we suggest that 5-HT2C receptors of PAG appear to modulate differently this type of antinociception and fear and anxiety in mice. However, further studies should be conducted using more selective subtypes of serotonergic receptors and perhaps other models of nociception to enlarge and clarify the role of 5-HT2C receptors in the processes that modulate antinociception induced by aversive stimuli. / A dor neuropática é um tipo de dor crônica que pode ocasionar comorbidades como a ansiedade e a depressão e, consequentemente, grandes prejuízos a qualidade de vida da população atingida. Apesar de ser refratária a maioria dos tratamentos farmacológicos convencionais, há estudos que descrevem a eficácia dos medicamentos que atuam na transmissão serotonérgica, como os antidepressivos, no tratamento da dor neuropática. A serotonina é um neurotransmissor com papel importante na modulação dos estímulos nociceptivos, assim como dos comportamentos relacionados ao medo e a ansiedade. Há evidências de que situações aversivas, como a exposição ao predador, podem causar antinocicepção como reação defensiva. Dessa forma, vários trabalhos têm demonstrado que situações de geram medo/ansiedade, podem inibir a nocicepção e a serotonina (5-HT) produz esse efeito antinociceptivo em estruturas do sistema nervoso central, tais como a substância cinzenta periaquedutal (SCP). Neste sentido, estudos do nosso grupo mostraram que a ativação dos receptores 5-HT2C da SCP está envolvida nos efeitos ansiolíticos e na antinocicepção induzida pelo medo/ansiedade observados em camundongos expostos ao labirinto em cruz elevado. Entretanto não se conhece qual o papel desses receptores da SCP na modulação da antinocicepção induzida pela exposição ao predador (rato) em camundongos. Assim, o objetivo deste trabalho foi avaliar o efeito da ativação dos receptores 5-HT2C da SCP, sobre a antinocicepção e as respostas defensivas em camundongos submetidos a constrição do nervo ciático. Para isso, camundongos machos Suiço-albinos foram submetidos a constrição do nervo ciático (CNC) no primeiro dia do experimento e, sete dias depois, receberam implantação de cânula guia na SCP. Quatro dias após a estereotaxia, os camundongos receberam microinjeção de veículo ou mK212 e foram expostos ao predador. O teste consistiu em duas fases: a) habituação ao aparato, durante 10 minutos, por 3 dias consecutivos, iniciado no dia seguinte após a estereotaxia; b) exposição ao predador ou ao estímulo neutro durante 10 minutos. Os resultados obtidos após passarem pela análise de variância (ANOVA) de três fatores (condição x estímulo x tratamento), mostraram que os camundongos que passaram por CNC exibiram aumento do reflexo de coçar, comportamento indicativo de dor crônica. A exposição desses animais ao predador (rato) produziu antinocicepção nos camundongos CNC e aumentou os comportamentos relacionados ao medo/ansiedade tais como, tempo de permanência na área protegida e em contato com a grade e frequência de esticar, quando comparados aos camundongos expostos ao estímulo neutro (rato de brinquedo). O tratamento intra-SCP com mK212 (0,21 e 0,63nmol) não produziu alterações significativas na antinocicepção e no medo/ansiedade avaliados durante a exposição ao rato. Entretanto, apenas a menor dose de mK212 (0,21nmol) foi capaz de aumentar o reflexo de coçar, produzindo hiperalgesia nos camundongos CNC expostos ao estímulo neutro. Desta forma, sugerimos que os receptores 5-HT2C da SCP parecem modular de forma diferenciada este tipo de antinocicepção e medo/ansiedade em camundongos. Porém novos estudos devem ser realizados, utilizando subtipos de receptores mais seletivos e talvez outros modelos de nocicepção para ampliar e esclarecer o papel dos receptores 5-HT2C nos processos que modulam a antinocicepção induzida por estímulos aversivos.

O peptídeo sintético idêntico ao C-terminal da proteína S100A9 murina (pS100A9m) possui efeito antinociceptivo em diferentes modelos de dor inflamatória aguda. No presente estudo, o efeito do pS100A9m foi avaliado sobre a dor neuropática induzida pela constrição crônica (CCI) do nervo ciático em ratos. Ainda, foram investigados os possíveis mecanismos envolvidos neste efeito. A nocicepção foi avaliada pelos testes de hiperalgesia, alodinia e dor espontânea. Os animais foram tratados com diferentes doses do pS100A9m pelas vias intraplantar, oral ou intratecal 14 dias após a CCI e a nocicepção avaliada após 1 hora. As três vias de administração bloquearam a hiperalgesia, a alodinia e a dor espontânea decorrentes da dor neuropática. A duração do efeito do pS100A9m varia de acordo com a via utilizada e com o fenômeno nociceptivo testado. Ainda, a injeção intraplantar do peptídeo, na pata contralateral à CCI, inibiu a hiperalgesia e a alodinia observadas após a constrição do nervo. Quando o pS100A9m foi administrado pela via intraplantar no 7° dia após a CCI, ele também induziu inibição da hiperalgesia inflamatória que é observada nesse período. Os prováveis mecanismos envolvidos no efeito antinociceptivo do pS100A9m foram investigados pela administração de antagonistas de receptores de serotonina, noradrenalina, GABA (A e B) e opióides. Os resultados obtidos demonstraram que apenas o antagonista de receptor GABAB reverteu completamente o efeito antinociceptivo do pS100A9m sobre a dor neuropática, detectada no 14º dia pós-cirúrgico. Além disso, foram avaliadas as expressões das proteínas Egr-1, Fos e TNFα na medula dos ratos submetidos à CCI e tratados com o peptídeo 7 ou 14 dias do procedimento cirúrgico. O aumento na expressão das proteínas Egr-1 e Fos foi evidenciado tanto no 7º como no 14º dia após a CCI, em animais que não receberam nenhum tratamento ou aqueles que foram tratados com o veículo do peptídeo. Por outro lado, o pS100A9m inibiu a expressão destas duas proteínas no lado ipsolateral à CCI no corno dorsal da medula espinhal dos animais. Com relação ao TNFα, apenas no 7º dia após a CCI foi detectado o aumento na expressão desta proteína. Ainda, foi neste período que o pS100A9m acarretou inibição da expressão do TNFα no corno ventral de animais submetidos ao procedimento cirúrgico. Estes resultados demonstram que o C-terminal da S100A9 murina inibe a dor neuropática experimental por uma ação dependente de receptores GABAB, sugerindo que este peptídeo possivelmente promova uma ativação dos mecanismos inibitórios espinhais, acarretando em redução da ativação de neurônios na medula. Desta forma, o pS100A9m demonstra um potencial terapêutico para o tratamento de dores persistentes. / The synthetic peptide identical to the C-terminus of murine S100A9 protein (mS100A9p) has antinociceptive effect on different acute inflammatory pain models. In this study, the effect of mS100A9p was evaluated on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats, and the possible mechanisms involved in this effect were investigated. Hyperalgesia, allodynia, and spontaneous pain were assessed to evaluate nociception. Rats were treated with different doses of mS100A9p by intraplantar, oral, or intrathecal routes on day 14 after CCI, and nociception was evaluated 1 hour later. These three routes of administration blocked hyperalgesia, allodynia and spontaneous pain. The duration of mS100A9p effect depends on the route used and the phenomenon analyzed. Moreover, intraplantar injection of mS100A9p in the contralateral paw inhibited the hyperalgesia and allodynia induced by CCI. When mS100A9p was administered by intraplantar route on day 7 after CCI, it reversed the inflammatory hyperalgesia observed in this period. The mechanisms likely involved in the antinociceptive effect of mS100A9p were investigated by administration of antagonists of serotonin, norepinephrine, GABA (A and B) and opioid receptors. Only the GABAB receptor antagonist completely reversed the antinociceptive effect of mS100A9p on neuropathic pain on day 14 after CCI. Besides, the expression of Egr-1, Fos and TNFα proteins was evaluated in the spinal cord of rats submitted to CCI and treated with mS100A9p on days 7 or 14 after CCI. The expression of Egr-1 and Fos was increased in animals not treated or treated with vehicle on days 7 and 14 after CCI. On the other hand, mS100A9p inhibited the expression of these two proteins in the dorsal horn of spinal cord ipsilateral to CCI. The increase in TNFα expression was observed exclusively on day 7 after CCI. In the same time period, mS100A9p nhibited the expression of TNFα in the ventral horn of spinal cord of animals submitted to CCI. The results obtained herein demonstrate that the C-terminus of murine S100A9 protein inhibits the experimental neuropathic pain by a GABAB-dependent action, suggesting that this peptide promotes the activation of spinal inhibitory mechanisms leading to the reduction of activation of spinal neurons. Therefore, mS100A9p demonstrates a potential therapeutic use in persistent pain syndromes.

O peptídeo sintético idêntico ao C-terminal da proteína S100A9 murina (pS100A9m) possui efeito antinociceptivo em diferentes modelos de dor inflamatória aguda. No presente estudo, o efeito do pS100A9m foi avaliado sobre a dor neuropática induzida pela constrição crônica (CCI) do nervo ciático em ratos. Ainda, foram investigados os possíveis mecanismos envolvidos neste efeito. A nocicepção foi avaliada pelos testes de hiperalgesia, alodinia e dor espontânea. Os animais foram tratados com diferentes doses do pS100A9m pelas vias intraplantar, oral ou intratecal 14 dias após a CCI e a nocicepção avaliada após 1 hora. As três vias de administração bloquearam a hiperalgesia, a alodinia e a dor espontânea decorrentes da dor neuropática. A duração do efeito do pS100A9m varia de acordo com a via utilizada e com o fenômeno nociceptivo testado. Ainda, a injeção intraplantar do peptídeo, na pata contralateral à CCI, inibiu a hiperalgesia e a alodinia observadas após a constrição do nervo. Quando o pS100A9m foi administrado pela via intraplantar no 7° dia após a CCI, ele também induziu inibição da hiperalgesia inflamatória que é observada nesse período. Os prováveis mecanismos envolvidos no efeito antinociceptivo do pS100A9m foram investigados pela administração de antagonistas de receptores de serotonina, noradrenalina, GABA (A e B) e opióides. Os resultados obtidos demonstraram que apenas o antagonista de receptor GABAB reverteu completamente o efeito antinociceptivo do pS100A9m sobre a dor neuropática, detectada no 14º dia pós-cirúrgico. Além disso, foram avaliadas as expressões das proteínas Egr-1, Fos e TNFα na medula dos ratos submetidos à CCI e tratados com o peptídeo 7 ou 14 dias do procedimento cirúrgico. O aumento na expressão das proteínas Egr-1 e Fos foi evidenciado tanto no 7º como no 14º dia após a CCI, em animais que não receberam nenhum tratamento ou aqueles que foram tratados com o veículo do peptídeo. Por outro lado, o pS100A9m inibiu a expressão destas duas proteínas no lado ipsolateral à CCI no corno dorsal da medula espinhal dos animais. Com relação ao TNFα, apenas no 7º dia após a CCI foi detectado o aumento na expressão desta proteína. Ainda, foi neste período que o pS100A9m acarretou inibição da expressão do TNFα no corno ventral de animais submetidos ao procedimento cirúrgico. Estes resultados demonstram que o C-terminal da S100A9 murina inibe a dor neuropática experimental por uma ação dependente de receptores GABAB, sugerindo que este peptídeo possivelmente promova uma ativação dos mecanismos inibitórios espinhais, acarretando em redução da ativação de neurônios na medula. Desta forma, o pS100A9m demonstra um potencial terapêutico para o tratamento de dores persistentes. / The synthetic peptide identical to the C-terminus of murine S100A9 protein (mS100A9p) has antinociceptive effect on different acute inflammatory pain models. In this study, the effect of mS100A9p was evaluated on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats, and the possible mechanisms involved in this effect were investigated. Hyperalgesia, allodynia, and spontaneous pain were assessed to evaluate nociception. Rats were treated with different doses of mS100A9p by intraplantar, oral, or intrathecal routes on day 14 after CCI, and nociception was evaluated 1 hour later. These three routes of administration blocked hyperalgesia, allodynia and spontaneous pain. The duration of mS100A9p effect depends on the route used and the phenomenon analyzed. Moreover, intraplantar injection of mS100A9p in the contralateral paw inhibited the hyperalgesia and allodynia induced by CCI. When mS100A9p was administered by intraplantar route on day 7 after CCI, it reversed the inflammatory hyperalgesia observed in this period. The mechanisms likely involved in the antinociceptive effect of mS100A9p were investigated by administration of antagonists of serotonin, norepinephrine, GABA (A and B) and opioid receptors. Only the GABAB receptor antagonist completely reversed the antinociceptive effect of mS100A9p on neuropathic pain on day 14 after CCI. Besides, the expression of Egr-1, Fos and TNFα proteins was evaluated in the spinal cord of rats submitted to CCI and treated with mS100A9p on days 7 or 14 after CCI. The expression of Egr-1 and Fos was increased in animals not treated or treated with vehicle on days 7 and 14 after CCI. On the other hand, mS100A9p inhibited the expression of these two proteins in the dorsal horn of spinal cord ipsilateral to CCI. The increase in TNFα expression was observed exclusively on day 7 after CCI. In the same time period, mS100A9p nhibited the expression of TNFα in the ventral horn of spinal cord of animals submitted to CCI. The results obtained herein demonstrate that the C-terminus of murine S100A9 protein inhibits the experimental neuropathic pain by a GABAB-dependent action, suggesting that this peptide promotes the activation of spinal inhibitory mechanisms leading to the reduction of activation of spinal neurons. Therefore, mS100A9p demonstrates a potential therapeutic use in persistent pain syndromes.

Pharmacological treatment of neuropathic pain is still insufficient. Methylphenidate, a psychostimulant that increases the dopamine and noradrenaline levels, is commonly used for treating ADHD. There have been reports of changes in patients pain thresholds by ADHD patients treated with methylphenidate. The aim of the study is to examine if methylphenidate can affect peripheral neuropathic pain. Neuropathic pain has been modelled on laboratory rats by chronic constriction of the ischiatic nerve. The effect of methylphenidate on the evoked pain component was evaluated on control animals and on animals with neuropathic pain using reflex (plantar test, vonFrey test) and operanting test (thermal place preference). The effect of methylphenidate on the spontaneous components of pain was evaluated using the methods of conditioned place preference. This study has proven that methylphenidate in an applicable dose of 1 mg/kg has an antialodynic effect but does not act antinociceptively. This study further confirms that methylphenidate in low doses does not act as attractant and has no effect on spontaneous pain. The last part of the study compares the different methods for pain measurement and comes to the conclusion that the plantar test is not an adequate method for evaluating the effect of analgesics...