Comparison of NMDA modulation of breathing and NR1 expression in medullary nuclei of weanling male and female rats

We investigated effects of dextromethophan (DXM), an NMDA receptor antagonist, on ventilation and metabolism in unanesthetized male and female weanling rats, and densities of neurons positive for the NR1 subunit in four medullary nuclei. Relative to saline, DXM treatment decreased oxygen consumption 12% in males and increased it 9% in females (interaction, P < 0.05). DXM compared to saline decreased frequency of breathing significantly more in females than males when exposed to hypercapnia. During hypoxia, DXM relative to saline significantly decreased frequency and minute ventilation in males and increased these variables in females. NR1 positive neuron densities were significantly greater in females than males in the nucleus tractus solitarius (NTS), commissural nucleus of the NTS and hypoglossal nucleus due to higher counts. Few sex differences were noted in the dorsal vagal motor nucleus. Thus, in weanling rats NMDA receptor modulation of breathing is sex specific, as are the densities of NR1 positive neurons in medullary nuclei associated with control of breathing.