POSTNATAL CHANGES IN THE ROLE OF NMDA IN THE ISOLATED SPINAL-CORD OF THE HAMSTER, MESOCRICETUS-AURATUS

The frequency of spontaneous activity recorded from lumbar dorsal root s and the lumbar dorsal horn of isolated spinal cord preparations take n from hamsters aged between 2 days to 8 weeks showed an age dependent sensitivity to 1 mM Mg2+ and 5 mu M AP5. Spontaneous dorsal root and dorsal horn activity in cords from animals less than 3 weeks of age wa s depressed by 1 mM Mg2+ and 5 mu M AP5. Cords taken from animals olde r than 3 weeks showed significantly less depression of spontaneous act ivity. The application of 10 mu M NMDA to the cord produced a small (3 3%) depression in spontaneous dorsal root and dorsal horn activity in cords from 4 to 6 week old animals. Cords from younger animals exhibit ed a complex response to NMDA, with an initial increase in spontaneous activity followed by a profound (77%) depression of the firing rate. These results indicate that there are substantial changes taking place in the pharmacology of the dorsal horn during the early weeks of life , and care must be exercised when extrapolating results obtained from neonatal preparations to adult animals.