VGluT1- and GAD-immunoreactive terminals in synaptic contact with PAG-immunopositive neurons in principal sensory trigeminal nucleus of rat.

AIM

To trace the origin of abundant vesicular glutamate transporter 1-like immunoreactive (VGluT1-LI) axon terminals in the dorsal division of the principal sensory trigeminal nucleus (Vpd) and the relationships between VGluT1-LI, as well as the glutamic acid decarboxylase (GAD)-LI axon terminals, and phosphate- activated glutaminase (PAG)-LI thalamic projecting neurons in the Vpd.

METHODS

Following unilateral trigeminal rhizotomy, triple-immunofluorescence histochemistry for VGluT1, GAD and PAG and the immunogold-silver method for VGluT1 or GAD, combined with the immunoperoxidase method for PAG were performed, respectively.

RESULTS

After unilateral trigeminal rhizotomy, the density of VGluT1-like immunoreactivity (IR) in the Vpd on the lesion side was reduced compared to its contralateral counterpart. Under the confocal laser-scanning microscope, the VGluT1-LI or GAD-LI axon terminals were observed to be in close apposition to the PAG-LI thalamic projecting neuronal profiles, and further electron microscope immunocytochemistry confirmed that VGluT1- and GAD-LI axon terminals made asymmetrical and symmetrical synapses upon the PAG-LI neuronal structures.

CONCLUSION

The present results suggest that the VGluT1-LI axon terminals, which mainly arise from the primary afferents of the trigeminal ganglion, along with the PAG-LI neuronal profiles, form the key synaptic connection involved in sensory signaling.