The Distribution Of VGluT1 And VGluT2 In The Spinal Cord In Different Species And The Coexistence Of VGluT2 And NT Or Leu-ENK In The MDH In The Rats

Glutamate is the major excitatory neurotransmitter in the central nervous system and plays important roles in many neuronal process such as fast synaptic transmission and neuronal plasticity. It is synthesized in the excitatory neuronal soma and transported to the nerve terminals, packaged in synaptic vesicles. When depolarization takes place, glutamate will be released from the neuron to the synaptic cleft through a Ca2+-dependence manner, then bind to the different glutamate receptors in the postsynaptic membrane to exert a multiple influence on the postsynaptic neuron. Like other neurotransmitters such as acetylcholine and monoamines, glutamate is stored in synaptic vesicles before exocytosis. Vesicular glutamate transporters(VGluTs) are responsible for the storage of glutamate. Three specific VGluTs named VGluTl, VGluT2 and VGluT3 have been identified by molecular biology method, which belong to the SLC17 type I phosphate transporter family, and seem to be 12 transmembranous proteins with both amino- and carboxyl terminals facing the cytoplasm. Researches have shown that VGluTs, espicailly VGluTl and VGluT2 are located only in the glutamatergic axonal terminals, which have been used extensively as markers of glutamatergic axonal terminals. Appearance of VGluTs has solved the big problem of labeling the glutamatergic axonal terminals in the neuroscience field. Nowadays, the researches on the distribution of VGluTs, especially VGluTl andVGluT2 in the central nervous system come mainly from the rat, no researches from other species exist. On the other hand, the distribution pattern of VGluT1 is different from that of VGluT2 in the same region of the central nervous system of the rat. Therefore, it is not certain whether the distribution pattern of VGluTl and VGluT2 in the spinal cord in the other species is the same as that in the rat or not.MDH, especially lamina II is the primary gateway for peripheral nociceptive information from the orofacial region, where exist many neuropeptide-containing fibers and terminals, such as NT- and ENK-containing nerve terminals. Although physiological studies have showed that parts of NTergic or ENKergic nerve terminals may be excitatory, which play important roles in the transmission and modulation of nociceptive information, but no direct morphological evidences exist in the previous studies.To answer these questions, in the present study, an attempt was made to examine: (1) the distribution of VGluTl and VGluT2 in the spinal cord, especially the superficial layers in multiple species, including rat, cat and monkey by using the immunohistochemical technique; (2) whether axonal varicosities with NT- or ENK-like immunoreactivity might show VGluT2-like immunoreactivity by using the double immunofluorescence histochemical and pre-embedding electron microscopic double-labeled immunohistochemical techniques.Part oneDistribution of VGluTl and VGluT2 in the spinal cord in three different species: rat, cat and monkeyIn this study, an immunohistochemical technique was used to investigate the distribution of VGluTl and VGluT2 in the spinal cord in multiple species, including rat, cat and monkey. The results are the following: (1) VGluTl and VGluT2 were observed mainly in the nerveterminals, not in the neuronal bodies of the spinal cord of rat, cat and monkey. VGluT1-like immunoreactive(VGluTl-LI) terminals were most intense in the inner part of lamina II (IIi) and the medial parts of laminae III-VI of the spinal dorsal horn; weak in lamina I and outer part of lamina II (IIo); moderate in other parts in the rat and cat. The laminar distribution of VGluT1-LI terminals in the spinal cord in the monkey is different from those in the rat and cat. The VGluTl-immunopositive product was intense in laminae I, Hi, III and the medial parts of laminae IV-VI of the spinal dorsal horn; weak to absent in lamina IIo and the lateral parts of laminae IV-VI of the dorsal horn. In the spinal anterior horn of monkey, the VGluTl-LI profiles were observed sparsely just in lamina IX, not in oth...