Anat Biol Anthropol.  2024 Sep;37(3):161-171. 10.11637/aba.2024.37.3.161.

Expression Patterns of P2X3 and Vesicular Glutamate Transporters in Rat Trigeminal Ganglion Neurons and Their Changes during Peripheral Inflammation

• Kim YS
• Hong J
• Cho YS
• Bae YC

• KMID: 2562491
• DOI: http://doi.org/10.11637/aba.2024.37.3.161

Abstract

Activation of purinergic receptor P2X3 expressed on the primary sensory neurons, induces the release of glutamate from their central and peripheral afferents, which is involved in both acute and chronic pain. However, little is known about the type of vesicular glutamate transporter (VGLUT) that is involved in the glutamate release associated with P2X3 activation. To address this issue, we investigated the expression of P2X3, VGLUT1, and VGLUT2 in rat trigeminal ganglion neurons by immunofluorescence under the normal condition and following inflammation induced by Complete Freund’s Adjuvant (CFA)-injection into the rat vibrissa pad. In addition, we examined the ultrastructure of P2X3-immunopositive ( + ) central terminals by electron microscopy. P2X3 + neurons were mostly small to medium-sized and frequently coexpressed VGLUT2, but rarely VGLUT1. In the CFA group, which exhibited thermal hyperalgesia, there was a significant increase in the number of P2X3+ , VGLUT2 + , and VGLUT2 + /P2X3 + neurons compared with controls (P2X3 + neurons: 39.0% vs. 28.4%, VGLUT2 + neurons: 44.6% vs. 34.9%, VGLUT2 + /P2X3 + neurons: 33.8% vs. 22.5%, p<0.05). Conversely, the numbers of VGLUT1 + and VGLUT1 + /P2X3 + neurons did not significantly differ between the CFA group and controls (VGLUT1 + neurons: 28.8% vs. 28.4%, VGLUT1 + /P2X3 + neurons: 0.6% vs. 0.5%). Additionally, P2X3 + axon terminals in the trigeminal caudal nucleus frequently received an axoaxonic synapse from an axon terminal containing pleomorphic vesicles, suggesting presynaptic modulation of P2X3-mediated sensory signals before synaptic transmission. These results indicate that 1) VGLUT2, rather than VGLUT1, is involved in glutamate release associated with P2X3 activation under acute and inflammatory pain conditions, and 2) P2X3 + primary afferents in the trigeminal caudal nucleus are finely regulated by various presynaptic mechanisms.

Keyword

Inflammation; P2X3; Trigeminal ganglion neurons; VGLUT