VGluT1- and GAD-immunoreactive terminals in synaptic contact with PAGimmunopositive 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 phosphateactivated
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.