MITRAL TUFTED CELL-ACTIVITY IS ATTENUATED AND BECOMES UNCOUPLED FROM RESPIRATION FOLLOWING NARIS CLOSURE/

Patterned neural activity helps to establish neuronal connectivity, pr oduce coding of sensory information, and shape synaptic strengths. Wer e we demonstrate that normal olfactory bulb development might rely on spatial and temporal patterns of afferent neural activity. Neonatal na ris occlusion profoundly impacts the development of the ipsilateral ol factory bulb, including reduced bulb volume, decreased protein synthes is, and increased cell death. Relatively few morphologic changes occur if closure is performed postweaning. We examined the immediate electr ophysiological consequences of occlusion across this developmentally s ensitive period by recording spontaneous and odor-driven mitral/tufted cell responses while the naris was open, closed, and then reopened. I n 1-week-old animals, occlusion severely attenuated spontaneous activi ty, and presentation of the broad-spectrum odorant amyl acetate failed to evoke responses. In 2- and 4-week old rats, spontaneous activity w as also reduced by naris closure. However, some cells remained respons ive to concentrated odors, even in animals with transected anterior co mmissures, suggesting passage of odors across the septal window or ret ronasal pathways, In all age groups, cellular activity became uncouple d from the respiratory cycle. Approximately 47% (18 of 38) of the mitr al/tufted cells exhibited activity that was correlated with respiratio n in the open-naris state, while only 5% (2 of 38) were coupled during naris closure. These data (a) indicate that naris closure reduces bot h spontaneous and odor-evoked responses, and (b) provide an electrophy siological correlate to a sensitive period in bulb development. The lo ss of respiration-related synchrony and the reduced activity of mitral /tufted cells may synergistically contribute to the diverse consequenc es of naris closure on bulb development. (C) 1997 John Wiley & Sons, I nc.