Influence of solitary tract nucleus stimulation on activity of thalamic reticular nucleus and mesencephalic reticular formation of the brain

Elucidation of interrelations between the brainstem (BSN) and diencephalic structures of the brain is an important problem of neurophysiology, solution of which might allow revealing mechanisms of the workings of certain structures of the brain, on the one hand, and an overall activity of the central nervous system, on the other. The goal of present investigation was examination of the mechanism of interrelations between the mesencephalic reticular formation (MRF), solitary tract nucleus (STN), and the thalamic reticular nucleus (TRN). Activity of the TRN and MRF neurons was recorded with the tungsten microelectrodes, with tip diameter of 4-8 microm and a resistance of 4-15 MOhm. In some experiments a simultaneous (coupled) recording of the TRN and MRF neurons was made with an aid of two separate microelectrodes. Our experiments have shown that threshold stimulation of the MRF exerted an inhibitory influence on activity of the TRN neurons, while supra-threshold stimulation induced their activation. Stimulation of the STN induced inhibition of the MRF neurons and activation of the TRN. Meanwhile, during activation of the TRN neurons, in the MRF neurons inhibitory postsynaptic potentials did occur. Whatever mechanisms may underlie inhibition of the TRN neurons in response to the STN stimulation, it seems an important fact that synchronizing structure of the brainstem, which exerted a blocking impact on the MRF, facilitated activity of the TNR neurons. This is even more important because for revealing the neurophysiologic mechanisms of activity of the whole central nervous system in both norm and disorder.