PERINATAL DEVELOPMENTAL-CHANGES IN RESPIRATORY ACTIVITY OF MEDULLARY AND SPINAL NEURONS - AN IN-VITRO STUDY ON FETAL AND NEWBORN RATS

Experiments were performed in vitro on fetal and newborn rat brainstem -spinal cord preparations to analyse the perinatal developmental chang es in inspiratory motor output. The amplitude of the inspiratory burst s of the whole C-4 ventral root (global extracellular recording), the firing patterns of 80 medullary inspiratory neurons (unitary extracell ular recording) and the firing and membrane properties of 71 respirato ry neurons in the C-4 ventral horn (whole-cell recording) were analyse d at embryonic day 18 (E18), 21 (E21) and post natal days 0 to 3 (P0-3 ). At E18, the amplitude of the C-4 bursts was weak and variable from one respiratory cycle to the next, as well as the discharge pattern of most of the medullary inspiratory neurons. C-4 motoneurons were immat ure, very excitable and displaying variable inspiratory discharges, bu t already able to deliver sustained bursts of potentials when depolari sed. At E21 and P0-3, the amplitude of the C-4 bursts was increased an d stable, most of the medullary inspiratory neurons already were able to generate a stable firing pattern and C-4 motoneurons showed maturat ional changes in terms of the resting potential, spike amplitude and i nput membrane resistance. This work suggests that the short period ext ending from E18 to E21 is a critical maturational period for the medul lary respiratory network which becomes able to elaborate a stable resp iratory motor output.