Potentiation of the glycine response by serotonin on the substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice

Olfactory stimulation Inhibits Nociceptive Signal Processing at the Input Stage of the Central Trigeminal System

The spinal trigeminal nucleus caudalis (SpVc) in the mammalian brainstem serves a pivotal function in pain processing. As the main relay center for nociceptive signals, SpVc conducts pain-related signals from various regions of the head toward higher levels of central processing such as the thalamus. SpVc also receives modulatory signals from other brain areas, which can alleviate the perception of headache. We studied the impact of olfactory co-stimulation on pain-related behavior and SpVc neural activity in mice. Using the TRPA1 agonist allyl isothiocyanate (AITC) as noxious stimulus, we quantified the aversive response and the perceived pain intensity by evaluating explorative running and the mouse grimace scale, respectively. We found that the floral odorants phenylethyl alcohol (PEA) and lavender oil mitigated the aversive response to AITC. Consistent with this finding, a newly developed, automated quantification of c-Fos expression in SpVc revealed that co-stimulation with PEA or lavender profoundly reduced network activity in the presence of AITC. These results demonstrated a substantial analgesic potential of odor stimulation in the trigeminal system and provide an explanation for the palliative effect of odors in the treatment of headache.

Potentiation of the Glycine Response by Bisphenol A, an Endocrine Disrupter, on the Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Mice

Lamina II, also called the substantia gelatinosa (SG) of the medullary dorsal horn (the trigeminal subnucleus caudalis, Vc), is thought to play an essential role in the control of orofacial nociception because it receives the nociceptive signals from primary afferents, including thin myelinated Aδ- and unmyelinated C-fibers. Glycine, the main inhibitory neurotransmitter in the central nervous system, plays an essential role in the transference of nociceptive messages from the periphery to higher brain regions. Bisphenol A (BPA) is reported to alter the morphological and functional characteristics of neuronal cells and to be an effector of a great number of ion channels in the central nervous system. However, the electrophysiological effects of BPA on the glycine receptors of SG neurons in the Vc have not been well studied. Therefore, in this study, we used the whole-cell patch-clamp technique to determine the effect of BPA on the glycine response in SG neurons of the Vc in male mice. We demonstrated that in early neonatal mice (0-3 postnatal day mice), BPA did not affect the glycine-induced inward current. However, in the juvenile and adult groups, BPA enhanced the glycine-mediated responses. Heteromeric glycine receptors were involved in the modulation by BPA. The interaction between BPA and glycine appears to have a significant role in regulating transmission in the nociceptive pathway.