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. 2019 May 1:7:e6877.
doi: 10.7717/peerj.6877. eCollection 2019.

Distribution and colocalization of melatonin 1a-receptor and NADPH-d in the trigeminal system of rat

Yifan He  1   2 , Wenguo Fan  1   2 , Yue Xu  1   2 , Yong Liang Liu  1 , Hongwen He  1   2 , Fang Huang  1   2
Affiliations

Distribution and colocalization of melatonin 1a-receptor and NADPH-d in the trigeminal system of rat

Yifan He et al. PeerJ. .

Abstract

Melatonin and nitric oxide (NO) are involved in orofacial signal processing in the trigeminal sensory system. The aim of the present study was to examine the distribution of melatonin 1a-receptor (MT1) and its colocalization with nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the spinal trigeminal nucleus (STN), the trigeminal ganglion (TG), and the mesencephalic trigeminal nucleus (MTN) in the rat, using histochemistry and immunohistochemistry. Our results show that MT1-positive neurons are widely distributed in the TG and the subnucleus caudalis of the STN. Furthermore, we found that MT1 colocalizes with NADPH-d throughout the TG and MTN, most extensively in the TG. The distribution pattern of MT1 and its colocalization with NADPH-d indicate that melatonin might play an important role in the trigeminal sensory system, which could be responsible for the regulation of NO levels.

Keywords: Melatonin 1a-receptor; Mesencephalic trieminal nucleus; NADPH-diaphorase; Spinal trigeminal nucleus; Trigeminal ganglion.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. MT1 distribution and colocalization with NADPH-d in TG neurons.
(A) and (B) Histochemical staining showing NADPH-positive cells. Neurons of varying sizes (arrows). (C) and (D) Immunofluorescent labeling of MT1-positive neurons. Neurons of varying sizes (arrows). (E) and (F) Coexpression of MT1 and NADPH-d in TG neurons. Double-labeled neurons are distributed widely throughout the TG (arrows). Scale bar: 100 μm (A, C, E, and F); 50 μm (B and D). NAS, small cell of NADPH-positive cell; NAM, medium cell of NADPH-positive cell; NAL, large cell of NADPH-positive cell; MTS, small cell of MT1-positive cell; MTM, medium cell of MT1-positive cell; MTL, large cell of MT1-positive cell; MNN, MT1-positive neurons were double-labeled with NADPH-d; SNN, single NADPH-d-stained cell; SC, small cell; MC, medium cell; LC, large cell.
Figure 2
Figure 2. MT1 distribution and colocalization with NADPH-d in MTN neurons.
(A) and (B) Histochemical staining showing NADPH-positive cells (arrows). (C) and (D) Immunofluorescent labeling of MT1-positive neurons (arrows). (E) and (F) Coexpression of MT1 and NADPH-d in MTN neurons. Most NADPH-d-positive neurons in the MTN coexpressed MT1 (arrows). Scale bar: 100 μm (B, D, E, and F); 50 μm (A and C). MT1, MT1-positive cell; NAC, NADPH-positive cell; MNC, MT1-positive neurons were double-labeled with NADPH-d.
Figure 3
Figure 3. The proportion of coexisting neurons MT1 and NADPH-d in TG and MTN.
TG, The proportion of TG neurons coexpressing MT1 and NADPH-d; MTN, The proportion of MTN neurons coexpressing MT1 and NADPH-d.
Figure 4
Figure 4. MT1 distribution and colocalization with NADPH-d in STN neurons.
(A) and (B) Histochemical staining showing NADPH-d-positive cells (arrows). (C) and (D) Immunohistochemical staining showing MT1-positive neurons (arrows). (E) and (F) Coexpression of MT1 and NADPH-d in Vc neurons. Most MT1-expressing neurons in the Vc were not coexpressed NADPH-d, a few of ones were weakly double-stained cells for MT1 and NADPH-d. Scale bar: 100 μm (A, C, and E); 50 μm (B, D, and F). MT1, MT1-positive cell; NAC, NADPH-d-positive cell; WDC, weakly double-stained cell for MT1 and NADPH-d; SNC, single NADPH-d-stained cell; SMC, single MT1-positive cell.
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