RESUMO
Because cholecystokinin (CCK) acts as a "functional" endogenous opioid antagonist, it has been proposed that changes in central CCKergic neurotransmission might account for the relative resistance of neuropathic pain to the analgesic action of morphine. This hypothesis was addressed by measuring CCK-related parameters 2 weeks after unilateral sciatic nerve section in rats. As expected, significant decreases (-25-38%) in the tissue concentrations and in vitro release of both substance P and calcitonin gene-related peptide were noted in the dorsal quadrant of the lumbar spinal cord on the lesioned side. In contrast, the tissue levels and in vitro release of CCK were unchanged in the same area in lesioned rats. Measurements in dorsal root ganglia at L4-L6 levels revealed no significant changes in proCCK mRNA after the lesion. However, sciatic nerve section was associated with a marked ipsilateral increase in both CCK-B receptor mRNA levels in these ganglia (+70%) and the autoradiographic labeling of CCK-B receptors by [3H]pBC 264 (+160%) in the superficial layers of the lumbar dorsal horn. Up-regulation of CCK-B receptors rather than CCK synthesis and release probably contributes to increased spinal CCKergic neurotransmission in neuropathic pain.
Assuntos
Colecistocinina/metabolismo , Receptores da Colecistocinina/metabolismo , Medula Espinal/química , Medula Espinal/metabolismo , Transmissão Sináptica/fisiologia , Animais , Autorradiografia , Axotomia , Peptídeo Relacionado com Gene de Calcitonina/análise , Peptídeo Relacionado com Gene de Calcitonina/genética , Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Gânglios Espinais/química , Expressão Gênica/fisiologia , Masculino , Potássio/farmacologia , Precursores de Proteínas/análise , Precursores de Proteínas/genética , RNA Mensageiro/análise , Ratos , Ratos Sprague-Dawley , Receptor de Colecistocinina B , Receptores de Peptídeo Relacionado com o Gene de Calcitonina/análise , Receptores de Peptídeo Relacionado com o Gene de Calcitonina/genética , Receptores da Colecistocinina/genética , Receptores da Neurocinina-1/análise , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Nervo Isquiático/cirurgia , Substância P/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Taquicininas/análise , Taquicininas/genéticaRESUMO
Recombinant herpes simplex virus-1 encoding the rat preproenkephalin A (HSVLatEnk1) was generated for driving the expression of preproenkephalin A-derived peptides in dorsal root ganglia of rats in vivo. Three weeks after infection via the hind footpads, quantitative RT-PCR and in situ hybridization experiments showed a strong expression of preproenkephalin A mRNA in lumbar dorsal root ganglia. In addition, a 40-160% increase in radioimmunoassayable Met-enkephalin-like material concentrations was found in the dorsal spinal cord and dorsal root ganglia, respectively, at the lumbar level in HSVLatEnk1-infected rats as compared with animals infected with beta-galactosidase-encoding recombinant herpes simplex virus-1 or control rats. These data demonstrate the efficacy of the preproenkephalin A encoding vector and suggest that it should help in elucidating the role of Met-enkephalin-containing primary afferent fibers in pain transmission and/or control.
