Functional significance of inhibitory interneurons in the neuronal mechanisms of mastication - the intracellular recording and labeling and immuno-gold labeling techniques.

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Is has been reported that rostrodorsomedial oralis (Vo.r) neurons synapsing on trigeminal motoneurons use inhibitory neurotransmitters. At first, therefore, injections of Nb and HRP were made into a Vo.r neuron and an α-motoneuron in the jaw-closing (JC) and jaw-opening (JO) motor nucleus, respectively, in cats in order to determine the number and spatial distribution of contacts between the Vo.r neuron and motoneuron. Single Vo.r neurons terminating in the JC nucleus (Vo.r-dl neurons) issued on average 10 times more boutons than Vo.r neurons terminating in the JO nucleus (Vo.r-vm neurons). The Vo.r-dl neuron-JC α-mosoneuron pairs and the Vo.r-vm neuron-JO motoneuron pairs made on average 5 and 4 contacts, respectively, on the soma or dendrites of the motoneurons. These results suggest that the overall inhibitory effect exerted by Vo.r neurons is much greater within JC than JO motoneuron pool.It is also very important to determine geometrical similarities and differences of the dendrit … More ic tree between the JC and JO α-motoneurons, which receive the inhibitory contacts. Thus, JC and JO α-motoneurons were intracellulary labeled with HRP and quantitatively analyzed using a computer-assisted three-dimensional system. The dendritic tree of JC α-motoneurons was confined within the JC motor nucleus, despite locations of the cell body. Whereas, JO α-motoneurons generated extensive extranuclear dendrites in the reticular formation. The branching pattern of proximal dendritic segments was simpler in the JC than JO α-motoneurons. Despite these differences, the mean values of dendritic parameters examined per neuron were not different between the two kinds of α-motoneurons, and the stem dendrite diameter was positively correlated with several dendritic parameters in a linear manner. These results suggest that underlying design principles of the geometry of dendritic tree are not concerned with the differences in configuration and branching pattern of the dendritic tree of trigeminal α-motoneurons innervating antagonistic muscles. Less