Lippincott, Williams & Wilkins, PAIN, 1(111), p. 38-50, 2004
DOI: 10.1016/j.pain.2004.05.025
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Opioid requirements in neonatal patients are reported to be lower than older infants and this may be a reflection of the developmental regulation of opioid receptors. In this study we have investigated the postnatal regulation of Mu opioid receptor (MOR) function in both rat lumbar dorsal root ganglion (DRG) cultures and behavioural mechanical and thermal reflex tests in rat pups. Immunostaining with MOR and selective neurofilament (NF200) antibodies was combined with calcium imaging of MOR function in cultured neonatal and adult rat dorsal root ganglion cells. Calcium imaging showed that a significantly greater number of neonatal DRG neurons expressed functional MOR compared to adult (56.5 +/- 3.4 versus 39.9 +/- 1.5%, n = 8, mean +/- SEM, P