| It has been proved by our previous studies that the central pathway of trigeminal proprioceptive sensation consists of two parallel pathways which are composed of three orders and four orders neurons located between the mesencephalic trigeminal nucleus (Vine) and the ventral posteromedial nucleus of the thalamus (VPM). As the collection of primary sensory neurons in this pathway, Vine plays an important role in the transmission and regulation of the orofacial region proprioceptive sensory signals. Glutamate (Glu) is the main excitatory neurotransmitter in the mammals. Glu is widely distributed not only in various brain regions of central nervous system (CNS), but also in primary afferent fibers, ganglia and Vine neurons, and it seems to be closely related to the transmission of exteroceptive or proprioceptive sensory signals. Phosphate-activated glutaminase (PAG) can catalyze the hydrolysis of glutamine into glutamate and amonia, so PAG can be used as a marker of the glutamatergic neurons. Parvalbumin (PV), a member of the family of calcium-binding proteins, has a widespread distribution in the CNS. The neurons of both the central pathway of somatic and the trigeminal proprioceptive 4 sensation express PV-like immunoreactivity (PV-LI). Although previous studies have demonstrated that Vine neurons showed PAG- or PV-LI, so far it is still not clear whether PAG and PV coexist in Vine neuronal cell bodies and what the proportion is. It is generally accepted that Vine neurons belong to sensory ganglion cells, however, Vine neurons are quite distinct from other ganglion cells because they migrate from the periphery to center and are accumulated in the brainstem during embryo development. The main distinction is the presence of some axon terminals that were in close apposition to the cell bodies of Vine neurons. Morphological studies have indicated that these terminals show iminunoreactivity for sertonin, dopamine, GABA, noradrenaline, substance P, chlecystokinin, vasoactive interstinal polypeptide and neuropeptide Y GABA is an important inhibitory neurotransmitter in the brain. Glutamate acid decarboxylase (GAD), a necessary enzyme in the synthesis of GABA, is known as a marker enzyme of GABAergic neurons. However, no systematic morphological evidence exists to show that GABAergic terminals make direct synaptic contact with cell bodies of Vine neurons, which kind of GABA receptor is expressed on Vine neurons and the relationship between them. Dynorphin (DYN) and enkephalin (ENK) are two kinds of opioids and involved in the modulation of neuronal activities. Preprodynorphin (PPD) and preproenkephalin (PPE) are precursors of DYN and ENK, therefore, can be used as markers for them. It is still unclear whether the axonal terminals in the Vine show DYN-LI and what is the relationship between DYNergic or ENKergic terminals and PAG-, PV-LI neurons, although it was reported that some ENK-LI fibers and terminals are distributed in Vine. Therefore, in the present study, an attempt was made to examine the association of PAG-, PV-, GABAB receptor-LI neurons in Vine, and the 5 connections of GABAergic, DYNergic, ENKergic terminals with those neurons showing PAG-, PV-, GABAB receptor-LI by means of immunohistochemistry, immunofluorescence histochemical double- and triple-staining methods, tract-... |
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