| The nucleus of the solitary tract (NTS) innervates the visceral primary afferents of most organs in the neck, chest and abdomen. The rostral part of NTS receives the special visceral, gustatory afferents, while the mid-caudal part receives the respiratory, gastrointestinal and cardiovascular afferents. There are reciprocal projections between NTS and dorsal motor nucleus of vagus nerve (DMV), ventrolateral medulla (VLM), ambiguus nucleus (Amb), interstitial nucleus of the spinal trigeminal tract (INV), locus ceruleus (LC), lateral parabrachial nucleus (LPB), ventrolateral midbrain periaqueductal gray (vlPAG), central nucleus of the amgydala (CeA) and bed nucleus of stria terminalis (BST), which are involved in the visceral reflexion and the transmission of visceral, including nociceptive information. Calbindin D-28K (CB) is an important member of calcium-binding protein family and has a high affinity for binding Ca-", one of the important intracellular messengers. The CB has been regarded as a selective marker of some neuronal populations especially of projection neurons in various regions of the central nervous system. Recent study has proved that CB occurs in some pathways of transmitting somatic nociceptive information. It is suggested that CB might be involved in processing somatic nociceptive information. But, so far, there is little study with the relationship between CB and visceral nociceptive stimulation. Morphological study of the distribution of CB-immunoreactive neurons involved in modulating visceral nociceptive signal in the related nuclei in brainstem and the projection of those neurons from NTS to BST was investigated in the present study.Using the double-labeled methods of visceral nociceptive stimulation induced by formalin combined with immunocytochemistry, it was observed that the CB positive neurons expressing Fos protein distributed in the related nuclei of brainstem in the rat. Under microscope it was showed that there were a various numbers of Fos/CB double-labeled neurons, besides Fos and CB single-labeled neurons, in NTS, VLM, LC, LPB and vlPAG. About 12.8%, 42.7%, 48.1%,14.0% and 13.9% of Fos immunoreactive neurons showed CB immunoreactivity; while 14.3%, 24.3%, 38.4%, 6.8% and 8.9% of CB immunoreactive neurons expressed Fos protein in NTS, VLM, LC, LPB and vlPAG, respectively. The results suggest that the neurons containing CB might involve in the transmission and/or modulation of visceral nociceptive information in the brainstem.Using the methods of fluoro-gold (FG) retrograde tracing combined with immuno-fluorescence histochemistry, CB-immunoreactive neurons expressed immunoreactivity for Fos protein in NTS which send their axons to BST were investigated. After injecting FG into BST mainly in lateral part, the FG retrogradely labeled neurons were found in the mid-caudal part of NTS bilaterally with ipsilateral side predominance. CB- and Fos-immunoreactive neurons were distributed equally in both sides of NTS. The three types of single-labeled neurons (FG, CB and Fos), FG/CB, FG/Fos and Fos/CB double-labeled neurons, and FG/CB/Fos triple-labeled neurons were found to overlap in the same region in NTS. Except the Fos/CB double-labeled neurons distributed bilaterally, the rest of double-labeled and triple-labeled neurons were found in the ipsilateral injection side predominantly. The proportions of FG/CB, Fos/CB double-labeled and FG/CB/Fos triple-labeled neurons in NTS were about 2.79%, 15.3% and 2.56% to total numbers of the CB immunoreactive neurons, respectively. The proportions of FG/CB/Fos triple-labeled neurons were aparoximately 47.8% to total numbers of the FG/CB double-labeled neurons in NTS. The results of the present study suggest that CB might be involved in the transmission of visceral nociceptive information from NTS to BST. |
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