| 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-order and four-order neurons, respectively, located between the mesencephalic trigeminal nucleus (Vme) and the ventral posteromedial nucleus (VPM) of thalamus. In this pathway, glutamate (Glu) as the main excitatory neurotransmitter and parvalbumin (PV) as the main calcium-binding protein play important role in the transmission of the orofacial region proprioceptive sensory information.Phosphate activated glutaminase (PAG) can catalyze the hydrolysis of glutamine into glutamate and ammonia. It is the dominating resource of glutamate in the central nervous system (CNS), so PAG can be used as the specific marker of the glutamatergic neurons. PV, a member of the family of calcium-binding proteins, is shown high immunoreactivity in both the central pathway of somatic and the trigeminal proprioceptive sensation. Although the function of PV is still controversial up to now, many studies have disclosed that its appearance in neurons during development stage is consistent withfunctional maturation of the neurons. Brain-specific Na+-dependent inorganic phosphate transporter (BNPI) is one of vesicular glutamate transporters, and has been named as vesicle glutamate transporter of type 1 (VGluTl). Some recent researches have indicated that VGluTl was distributed not in the presynaptic vesicular membrane of symmetrical synapses but in the presynaptic vesicular membrane of most asymmetrical synapses. Therefore, VGluTl can be used as the specific marker of the brain glutamatergic terminals.The central pathway of trigeminal proprioceptive sensation conveys information about the spatial position of the orafacial region and the movement of the jaw-closing muscles. It is involved in regulating the activities of sucking, chewing, swallowing, voicing, and so on. It is well known that these activities change with each passing day during development stage. One of the key hidden events is the establishment of the perfect pattern for movement regulation. Certainly, the maturation of the central pathway of trigeminal proprioceptive sensation is crucial. Morphological and physiological studies have proved that glutamatergic neurons play a great role in this pathway. The central pathway of trigeminal proprioceptive sensation was found recently, so the functional maturation course of the neurons, especially the glutamatergic neurons in this pathway, is unknown now.In the present study, an attempt was made to examine the distribution and development of PAG- or PV-like immunoreactive (PV-LI) neurons and VGluTl-like immunoreactive (VGluTl-LI) terminals and the connections between VGluTl-LI terminals and PAG - or PV -LI neurons in the central pathway of trigeminal proprioceptive sensation by means ofimmunohistochemistry and immunofluorescence histochemical double-staining methods.Part IDevelopment and distribution of PV-positive neurons in thecentral pathway of the trigeminal proprioceptionof the rat brainstemImmunohistochemical techniques were used to investigate the development and distribution of PV-LI neurons in the central pathway of the trigeminal proprioception of the rat brainstem. The results showed: (1)At embryonic day 13 (El3), PV-LI neurons were observed initially in the Vme. Most PV-LI neurons were large pseudounipolar neurons with moderate immunostaining. At postnatal day 3 (P3), more neurons were labeled with intense immunostaining in the Vme. (2)At P10, moderately PV-LI neurons appeared both in the Vodm and Vpdm. At PI4, PV-LI neurons were seen in the LRF, Vsup-CL, AVM, and ADO. (3)At P21, PV-LI neurons and fibers attained the adult-like pattern in the Vodm-LRF, and "zone-shaped area" which includes the Vpdm, Vsup-CL, AVM, and ADO.The present results indicated that the PV-LI neurons in the Vme achieved functional maturation during the stage from El3 to P3, and in the Vodm-LRF and "zone shaped... |
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