Ascending projections of nociceptive neurons from trigeminal subnucleus caudalis: A population approach

• Published in: Experimental neurology Vol. 293; pp. 124 - 136
• Main Authors: Saito, Hiroto, Katagiri, Ayano, Okada, Shinji, Mikuzuki, Lou, Kubo, Asako, Suzuki, Tatsuro, Ohara, Kinuyo, Lee, Jun, Gionhaku, Nobuhito, Iinuma, Toshimitsu, Bereiter, David A., Iwata, Koichi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2017
• Subjects: Animals; Capsaicin - toxicity; Disease Models, Animal; Extracellular Signal-Regulated MAP Kinases - metabolism; Facial Pain - chemically induced; Facial Pain - pathology; Male; Mediodorsal Thalamic Nucleus - pathology; Medulla; Neural Pathways - pathology; Neural Pathways - physiology; Nociceptors - metabolism; Nociceptors - pathology; Parabrachial nucleus; Parabrachial Nucleus - pathology; pERK; Rats; Rats, Sprague-Dawley; Receptors, Neurokinin-1 - metabolism; Sensory System Agents - toxicity; Statistics, Nonparametric; Stilbamidines - metabolism; Thalamic nucleus; Trigeminal nerve; Trigeminal Nuclei - pathology; Upper cervical cord; Ventral Thalamic Nuclei - pathology; FG; mid-Vc; MTN; CNS; Gr; NTS; Vc; Thalamic nucleus; C1; dPa5; Parabrachial nucleus; Upper cervical cord; VPM; Cu; Vi; PoT; Trigeminal nerve; NK1; MD; KF; PBN; Po; IR; CL; Medulla; CM; TRPV1; MAPK; TG; PF; PAG; pERK
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2017.03.024

Second-order neurons in trigeminal subnucleus caudalis (Vc) and upper cervical spinal cord (C1) are critical for craniofacial pain processing and project rostrally to terminate in: ventral posteromedial thalamic nucleus (VPM), medial thalamic nuclei (MTN) and parabrachial nuclei (PBN). The contribution of each region to trigeminal nociception was assessed by the number of phosphorylated extracellular signal-regulated kinase-immunoreactive (pERK-IR) neurons co-labeled with fluorogold (FG). The phenotype of pERK-IR neurons was further defined by the expression of neurokinin 1 receptor (NK1). The retrograde tracer FG was injected into VPM, MTN or PBN of the right hemisphere and after seven days, capsaicin was injected into the left upper lip in male rats. Nearly all pERK-IR neurons were found in superficial laminae of Vc-C1 ipsilateral to the capsaicin injection. Nearly all VPM and MTN FG-labeled neurons in Vc-C1 were found contralateral to the injection site, whereas FG-labeled neurons were found bilaterally after PBN injection. The percentage of FG-pERK-NK1-IR neurons was significantly greater (>10%) for PBN projection neurons than for VPM and MTN projection neurons (<3%). pERK-NK1-IR VPM projection neurons were found mainly in the middle-Vc, while pERK-NK1-immunoreactive MTN or PBN projection neurons were found in the middle-Vc and caudal Vc-C1. These results suggest that a significant percentage of capsaicin-responsive neurons in superficial laminae of Vc-C1 project directly to PBN, while neurons that project to VPM and MTN are subject to greater modulation by pERK-IR local interneurons. Furthermore, the rostrocaudal distribution differences of FG-pERK-NK1-IR neurons in Vc-C1 may reflect functional differences between these projection areas regarding craniofacial pain. •Vc-C1 neurons project to contralateral VPM and MTN, and to PBN bilaterally.•More than of 10% FG-pERK-NK1-IR Vc-C1 neurons project to contralateral PBN.•Less than of 3% FG-pERK-NK1-IR Vc-C1 neurons project to contralateral VPM or MTN.•pERK-NK1-IR VPM projection neurons are found mainly in middle Vc.•pERK-NK1-IR MTN and PBN projection neurons are found in middle and caudal Vc.