Abstract
The present study shows new evidence of functional connectivity between the trigeminal main sensory (NVsnpr) and motor (NVmt) nuclei in rats and mice. NVsnpr neurons projecting to NVmt are most highly concentrated in its dorsal half. Their electrical stimulation induced multiphasic excitatory synaptic responses in trigeminal MNs and evoked calcium responses mainly in the jaw-closing region of NVmt. Induction of rhythmic bursting in NVsnpr neurons by local applications of BAPTA also elicited rhythmic firing or clustering of postsynaptic potentials in trigeminal motoneurons, further emphasizing the functional relationship between these two nuclei in terms of rhythm transmission. Biocytin injections in both nuclei and calcium-imaging in one of the two nuclei during electrical stimulation of the other revealed a specific pattern of connectivity between the two nuclei, which organization seemed to critically depend on the dorsoventral location of the stimulation site within NVsnpr with the most dorsal areas of NVsnpr projecting to the dorsolateral region of NVmt and intermediate areas projecting to ventromedial NVmt. 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.
Highlights
Mastication is a vital behavior that allows the preparation of food for swallowing during feeding
Our results suggest that trigeminal main sensory nucleus (NVsnpr) and NVmt are topographically connected in both rats and mice and that rhythmic firing in NVsnpr neurons can drive rhythmic activation of trigeminal MNs
The emphasis was placed on the most dorsal third of NVsnpr because of earlier findings of Tsuboi et al (2003) in the rabbit showing that NVsnpr neurons firing in phase with trigeminal MNs during fictive mastication were mostly confined to the most dorsal and medial third
Summary
Mastication is a vital behavior that allows the preparation of food for swallowing during feeding. This rhythmic movement can be initiated by repetitive stimulation of either the cortical masticatory area (CMA) or the trigeminal sensory afferents while its pattern of activity is shaped by a neuronal network in the brainstem known as the masticatory central pattern generator (CPG; Bremer, 1923; Dellow and Lund, 1971). Motoneurons (MNs) innervating masticatory muscles are clustered in two distinct divisions in the NVmt, a large dorsolateral (DL) and a much smaller ventromedial (VM) containing respectively the jaw-closing and jaw opening MNs (Mizuno et al, 1975; Limwongse and DeSantis, 1977; Sasamoto, 1979; Jacquin et al, 1983; Lynch, 1985; Rokx and van Willigen, 1985).
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