A local GABAergic system within rat trigeminal ganglion cells

Abstract

We investigated the GABAergic system within the Sprague-Dawley rat (2-3-weeks old) trigeminal ganglion (TG). Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed expression of glutamate decarboxylase (GAD) 65 and GAD67 mRNAs and mRNAs encoding GABA(A) receptor subunits alpha1-6, beta1-3, gamma1-3, and delta. In situ hybridization revealed that GAD65 and GAD67 mRNAs were expressed in neuronal cell bodies but not satellite cells. Immunohistochemical analysis showed that only GAD65 was expressed in all neuronal cell bodies, and approximately 70% of all neurons exhibited GABA immunoreactivity. Satellite cells were strongly immunopositive for GABA. GABA(A) receptor alpha1, alpha5, beta2/3 and gamma1/2/3 subunit immunoreactivities were observed in the majority of neurons, but no immunoreactivity for alpha2 was observed. Two types of cells were identified in TG based on cell size and morphology, type A and B. The percentage of cells expressing alpha3, alpha4, alpha6, and delta subunits appeared to be dependent on cell size, as delta and alpha6 expression were only observed in small (B-type) neurons. In whole-cell patch clamp experiments, GABA application induced inward Cl- currents in all neurons examined. The EC50 for GABA varied from 5.3 to 240 microm, and the Hill Coefficient (nH) varied between 0.98 and 2.6 at -60 mV. We found that GABA was released from TG cells by increasing extracellular K+ concentration to 100 mm. We speculate that GABA acts as a nonsynaptically released diffusible neurotransmitter, which may modulate somatic inhibition of neurons within the TG.

Properties and mechanisms of spontaneous activity in the embryonic chick hindbrain

“…It is possible that the fibers in the more lateral areas of the hindbrain mediate the lateral activity that is synchronized with the midline activity, and that sensory input from caudal hindbrain or spinal cord influences SA in the hindbrain. GAD expression is observed in early postnatal trigeminal motor neurons (Turman et al, 2001) and trigeminal ganglion cells (Hayasaki et al, 2006). The presence of both GABAergic and serotonergic axons within the hindbrain midline commissural region suggests that either or both may mediate excitation of the hindbrain initiation.…”

Glutamate- and GABA-mediated neuron–satellite cell interaction in nodose ganglia as revealed by intracellular calcium imaging

“…Furthermore, GABA, that is released in Ca 2? -independent manner as suggested in TG (Hayasaki et al 2006), may regulate basal threshold levels of the nodose ganglion cells. In conclusion, the satellite cells may regulate threshold level of ganglion neurons via glutamate and GABA mediated systems.…”

“…Hayasaki et al (2006) demonstrated that TG neuronal cell bodies express GABA, GAD, and functional GABA A receptors, and that satellite cells express GABA, suggesting the existence of a local GABAergic system within TG. Furthermore, it has been reported that GABA has an analgesic effect via GABA A receptors in TG neurons in mice that undergo injection of the GAD65 gene into satellite cells (Vit et al 2009) and that GABA inhibits the excitatory effects of ATP via GABA A receptors in DRG neurons (Sokolova et al 2001).…”

GABA Receptor Activation in the Lumbosacral Spinal Cord Decreases Detrusor Overactivity in Spinal Cord Injured Rats

“…One and 5 μg of RNA (DRG and spinal cord, respectively) was reverse-transcribed into cDNA using Superscript II (Invitrogen). Primers for GAD67 8 and β-actin (Ambion, Austin, Texas) were used: GAD67 forward primer, 5′-GCTGGAAGGCATGGAAGGTTTTAA-3′; reverse primer, 5′-AATATCCCATCACCATCTTTATTTGACC-3′. The GAD67 and β-actin mRNA level was quantified with an MX3000P real-time PCR system (Stratagene, La Jolla, California) in a 25 μl volume using SYBR Green PCR Master Mix (QIAGEN, Valencia, California).…”