CONNECTIONS BETWEEN SEROTONERGIC, ENKEPHALINERGIC,GABAERGIC, GLYCINERGIC, SUBSTANCE P-ERGIC TERMINALS AND CALCIUM BINDING PROTEINS-CONTAINING NOCICEPTIVE NEURONS IN RAT MEDULLARY DORSAL HORN / 神经解剖学杂志

ABSTRACT

Calbindin-D28k (CB), calretinin (CR) and parvalbumin (PV) are the most common calcium-binding proteins (CaBPs). In the present study, FOS immunoreactivity was first induced in neurons of the medullary dorsal horn (MDH) of the rat by noxious orofacial stimulation; CaBPs (CB, CR and PV) in these neurons were then identified by imumunofluorescence histochemistry, and then, in addition, afferents to CaBPs/FOS double-labeled neurons were showed by immunofluorescence histochemical staining for the γ-aminobutyric acid (GABA) , glycine transporter 2 (GlyT2) , enkephalin (ENK) , serotonin (5-HT) or substance P (SP). Under the light microscope,we observed that (1) neuronal cell bodies exhibiting FOS-immunoreactivity were present throughout all laminae of the MOH, with the highest concentration in lamina Ⅱ; (2) most CB-, CR- and PV-immunoreactive (IR) neurons were located in lamina Ⅱ , but some were also encountered in laminae Ⅰ and Ⅲ; (3) 5-HT-, GABA-, GlyT2-, ENK- and SP-IR fibers and terminals were also chiefly located in laminae Ⅰ and Ⅱ of the MDH; (4) some FOS-IR neurons showed CB-, CR-, or PV-immunoreactivity; (5) 5-HT-, GABA-, GlyT2- and ENK-IR terminals made close contacts with FOS/CB, FOS/CR or FOS/PV double-labeled neurons; (6) SP-IR terminals, as well as 5-HT-, GABA-, GlyT2- or ENK-IR terminals, closely contacted CB-, CR- or PV-containing neurons. Under the electron microscope, 5-HT-, GABA-, GlyT2- and ENK-IR terminals principally made symmetric (inhibitory) synaptic connections with CB-, CR- and PV-containing neurons were observed. These results suggest that 5-HT, GABA, glycine (Gly) and ENK may modulate transmission of orofacial noxious information by inhibiting nociceptive neurons that contain CaBPs in the rat MDH.