NMDA receptor NR1 and NR2A/B subunit expression in trigeminal neurons during early postnatal development

Trigeminal motoneurons (Mo5), mesencephalic trigeminal neurons (Me5), and supratrigeminal (Su5) and intertrigeminal (I5) neurons are important constituents of the neural circuitry responsible for jaw movements observed during ingestive behaviors. In addition, in adult animals, N-methyl-D- aspartate (NMDA) receptors are a critical component of the brainstem circuitry responsible for reflex- and centrally activated jaw movements. However, little is known about the expression of this receptor in circuitry used to produce neonatal jaw movements. Receptor immunohistochemistry was used to describe changes in the expression of NMDA NR1 and NR2A/B receptor subunits in Mo5, Me5, Su5, and I5 neurons during postnatal development. Rats at postnatal days (P) 1, 3, 8, 15-16, 21-24, and 28-35 were used. An affinity-purified polyclonal antibody against the NR1 subunit and an affinity-purified polyclonal antibody that recognizes both NR2A and 2B subunits were used to depict the expression of these subunits. In Mo5, immunoreactivity was noted for both antibodies throughout the time frame sampled. NR1 expression in Me5 neurons emerged at P1. NR2A/B expression emerged at P3 in caudal and middle regions of Me5 and at P8 for rostral regions of the nucleus. NR1 immunoreactivity was present at P1 for neurons in I5 and at P3 for neurons in the Su5 region. NR2A/B subunit expression in Su5 and I5 neurons emerged at P8. These results provide evidence for NMDA receptor subunits in neonatal trigeminal neurons used in oral-motor circuitry and suggest a role for the NMDA receptor in synaptogenesis associated with these neurons during postnatal development.