POSTNATAL ONTOGENY OF GLUTAMATE RECEPTORS IN THE RAT NUCLEUS-TRACTUS-SOLITARII AND VENTROLATERAL MEDULLA

The nucleus tractus solitarii and the ventrolateral medulla are two br ainstem regions involved in regulation of autonomic functions. Glutama te (Glu) receptors localized within these two regions play a key role in neural control of swallowing and breathing and in blood pressure re gulation. In the present study, postnatal changes in global [H-3]Glu b inding and in [H-3]Glu binding to N-methyl-D-aspartate (NMDA) receptor s were analyzed in the nucleus tractus solitarii and the ventrolateral medulla using in vitro receptor autoradiography. Similar results were obtained in both regions. When expressed as density Values (fmol/mg t issue), both global and NMDA-sensitive Glu binding increased by approx imately 50-70% between birth and postnatal day 9 (P9) and then decreas ed until P30. When expressed as binding per nucleus (i.e., after corre ction for tissue growth), global Glu binding still increased between b irth and P9 and decreased between P9 and P30 whereas NMDA-sensitive bi nding increased until P9 and remained stable thereafter. Saturation st udies showed a postnatal increase in Glu receptor number per nucleus, which occurred mainly between birth and P9, and a decrease in Glu rece ptor affinity between P9 and adulthood. These results indicate that dr amatic changes in glutamatergic neurotransmission occur in the nucleus tractus solitarii and the ventrolateral medulla during the first mont h of postnatal life. They suggest that both neonates and young animals may not be fully mature as regard to central regulation of autonomic functions. (C) 1997 Elsevier Science B.V.