Connectivité fonctionnelle entre le noyau sensoriel principal du trijumeau et le noyau moteur du trijumeau
Masticatory movements are generated by a brainstem neuronal network known as the central pattern generator (CPG). Increasing evidence associate the trigeminal main sensory nucleus (NVsnpr) to the rhythmogenic heart of the masticatory CPG, despite the fact that it is conventionally seen as a sensory relay to the thalamus. The present study provides new evidence of a functional connectivity between NVsnpr and the trigeminal motor nucleus (NVmt), known to contain all the motoneurons (MNs) innervating jaw muscles. Our results indicate that neurons projecting to NVmt are located in the dorsal ¾ region of NVsnpr. Electrical stimulation of the dorsal NVsnpr induced multiphasic excitatory synaptic responses in trigeminal MNs while BAPTA application, which causes NVsnpr neurons to fire rhythmically, also induced rhythmic firing in some MNs, further emphasizing the functional relationship between these two nuclei in terms of rhythm transmission. In our calcium imaging experiments, electrical stimulation of NVsnpr evoked calcium responses in MNs located mainly in the jaw-closing region of NVmt and revealed a specific pattern of connectivity between the two nuclei. The organization of the projections seemed to depend critically on the dorsoventral location of the stimulation site within NVsnpr. The dorsolateral region of NVmt received mainly inputs from the dorsal NVsnpr (R1 and R2), whereas the ventromedial region of NVmt was found to receive inputs from R2 and R3 which account for the major part of the intermediate division of the NVsnpr. This study confirms and develops earlier experiments by exploring the physiological nature and functional topography of the connectivity between NVsnpr and NVmt that was demonstrated in the past with neuroanatomical techniques.
Mastication NVsnpr NVmt trigeminal motoneurons jaw muscles burst firing connectivity