Morphological Study On The Connections Between The Projection Neurons With Parvalbumin-like Immunoreactivity And The Serotongergic Terminals On The Central Pathway Of The Trigeminal Proprioceptive Sensation Of The Rat

In the central nervous system, nearly all the somatosensory pathways have long since been found and were described in textbook. But only until late in 1980s and early in 1990s did the important findings on how the trigeminal proprioceptive information is relayed in the CNS from peripheral to the cortex was made. Combining the horseradish peroxidase (HRP) retrograde, anterograde and transganglionic labeling techniques, Li Ji-Shuo , Wang Bai-Ren and coworkers found that the central pathway of trigeminal proprioceptive sensation consists of four orders of neurons, and neurons from the first- to the fourth-order are located, respectively, in the mesencephalic trigeminal nucleus (Vme), the dorsomedial part of the subnucleus oralis of the spinal trigeminal nucleus and its adjacent reticular formation (Vodm-LRF). the "zone-shaped area"(including the caudolateral part of the supratrigeminal nucleus(Vsup-CL), the dorsomedial part of the principal sensory trigeminal nucleus(Vpdm). the area ventral to the motor trigeminal nucleus (AVM) and the area dorsal to the superior olivary nucleus (ADO) and the contralateral ventral posteromedial nucleus (VPM) of the thalamus. Because the pathway is a novel finding, there has been no systematic morphological data available so far regarding the neurotransmitters involved in this pathway.Pavalbumin (PV) and calbinding D-28k are intracellular proteins which have high affinity for binding Ca²⁺. They are expressed in particular population of neurons in different brain regions, respectively. It is not know whether they are distributed in the relay nuclei on this newly found central pathway of the trigeminal proprioceptive sensation, though some previous reports showed that Vme neurons express PV-like immunoreactivity (PV-LI). In addition, it is worth studying whether the neurons in the relay nuclei expressing PV-LI, if any, are projection neurons or interneurons.Serotonin (5-HT) is an important neuromodulator involved in the descending inhibitory system. It has been reported that terminals with 5-HT-like...