Differential NMDA NR1 mRNA expression among spinal trigeminal neurons that project to different targets

The N-methyl-D-aspartate (NMDA) NR1 glutamate receptor subtype has been proposed to play an important role in the transmission of orofacial sensory information in the spinal trigeminal nucleus (STN). The distribution of NR1 mRNA expression in the STN and its relationship to STN projection neurons has not been investigated previously. Using neuroanatomical tract tracing with in situ hybridization techniques, we found that neurons in the STN that project to the thalamus, cerebellum and spinal cord expressed more mRNA for NR1 than do nonprojection neurons. Trigeminothalamic neurons were found to express more NR1 mRNA than trigeminospinal or trigeminocerebellar neurons. Thus, NMDA-specific excitatory amino acids may be more efficacious in the relay of orofacial information to the thalamus than to the spinal cord or cerebellum.