Nucleus accumbens dopaminergic neurotransmission switches its modulatory action in chronification of inflammatory hyperalgesia.

Dopaminergic neurotransmission in the nucleus accumbens, a central component of the mesolimbic system, has been associated with acute pain modulation. As there is a transition from acute to chronic pain ('chronification'), modulatory structures may be involved in chronic pain development. Thus, this study aimed to elucidate the role of nucleus accumbens dopaminergic neurotransmission in chronification of pain. We used a rat model in which daily subcutaneous injection of prostaglandin E2 in the hindpaw for 14 days induces a long-lasting state of nociceptor sensitization that lasts for at least 30 days following the end of the treatment. Our findings demonstrated that the increase of dopamine in the nucleus accumbens by local administration of GBR12909 (0.5 nmol/0.25 µL), a dopamine reuptake inhibitor, blocked prostaglandin E2 -induced acute hyperalgesia. This blockade was prevented by a dopamine D2 receptor antagonist (raclopride, 10 nmol/0.25 µL) but not changed by a D1 receptor antagonist (SCH23390, 0.5, 3 or 10 nmol/0.25 µL), both co-administered with GBR12909 in the nucleus accumbens. In contrast, the induction of persistent hyperalgesia was facilitated by continuous infusion of GBR12909 in the nucleus accumbens (0.021 nmol/0.5 µL/h) over 7 days of prostaglandin E2 treatment. The development of persistent hyperalgesia was impaired by SCH23390 (0.125 nmol/0.5 µL/h) and raclopride (0.416 nmol/0.5 µL/h), both administered continuously in the nucleus accumbens over 7 days. Taken together, our data suggest that the chronification of pain involves the plasticity of dopaminergic neurotransmission in the nucleus accumbens, which switches its modulatory role from antinociceptive to pronociceptive.

Protocol on induction of TMJ articular disc degeneration in rats by utilization of botulinum toxin.

OBJECTIVE: To develop a model of experimental degeneration in the articular disc of the TMJ of rats through the use of botulinum toxin that can be used in future studies of degenerative diseases on fibrocartilage. METHODS: Aiming at the above-mentioned objective, 12 Lewis male rats were used and divided into two groups: CG, control group and DG, group of animals to which the botulinum toxin was administered (6 units/kg). The morphological analysis was carried out utilizing histological cuts stained with hematoxyline-eosine, toluidine blue and Picrosirius; the biochemical analysis was made by SDS-polyacrylamide gel electrophoresis. RESULTS: The DG showed peculiar characteristics regarding a degeneration joint disk, compatible with those described in literature as: reduction of cells number, general disorganization of cells direction and extracellular matrix, increase in glycosaminoglycans content and degradation of the tissue collagen. CONCLUSIONS: Based on the morphological and biochemical results, it was concluded that the proposed degeneration model showed to be satisfactory for futures studies of injuries and fibrocartilage regeneration processes.

Estimulacao eletrica neuromuscular do tibial anterior nao altera a morfologia dos musculos soleo(antagonista) e extensor digital longo(sinergista) do rato / Neuromuscular electrical stimulation of tibialis anterior do not change the morphology of soleus(antagonistic) and extensor digitorum longus(synergistic) muscles of rat

A estimulacao eletrica neuromuscular(EENM) e um recurso fisioterapico muito utilizado para produzir fortalecimento e hipertofia muscular. O objetivo deste trabalho foi analisar os efeitos morfologicos da EENM na musculatura sinergista e antagonista ao musculo diretamente estimulado. O musculo tibial anterior(TA) direito de seis ratos (Wistar)foi submetido a eletroestimulacao e os musculos extensor digital longo(EDL) e soleo, sinergista e antagonista ao TA, repectivamente, foram analisados. A EENM foi realizada em uma frequencia de 52 Hz., com ciclo ON-OFF na proporcao de 1/1, rampa de subida de trens de pulso de 2,2 seg. e intensidade de aproximadamente 0,5 mA. Foram produzidas 20 contracoes em cada sessao, 3 vezes por semana, durante 8 semanas. Posteriormente os animais foram anestesiados,e os musculos EDL e soleo direito e esquerdo foram removidos, pesados, congelados, seccionados e corados com Azul de Toluidina, para avaliacao morfologica das fibras musculares. Estudo previo, realizado no TA diretamente estimulado, nao revelou alteracoes morfologicas significativas no peso, area media das fibras e incidencia de sinais de lesao no EDL e no soleo, quando comparados com os musculos da pata controle nao estimulada. Esses resultados indicam que o protocolo utilizado para EENM, nao produziu alteracoes morfologicas significantes nos musculos EDL(sinergista) e soleo(antagonista) apos estimulacao do TA