Integration in trigeminal premotor interneurones in the cat

Summary The profile of integration in a sample of 183 interneurones localized in the subnucleus- of the oral nucleus of the spinal trigeminal tract (NVspo-) has been analyzed. 134 neurones were tested for inputs from primary afferents of the trigeminal, facial and cervical nerves as well as for inputs from the midbrain and from the cervical spinal cord. The remaining 49 neurones were tested for inputs from the primary afferents and for descending convergence from defined sites within the oro-facial primary projections of the cerebral cortex. It was found that the interneurones, mainly recorded in the dorsal and dorsomedial aspect of the NVspo-, receive short latency inputs from the low threshold oral and perioral afferents and longer latency inputs from the high threshold jaw and neck muscle afferents. There was evidence for convergence from the cervical segmental level (29%) and some of the neurones had axon terminals in the superior colliculus. However, the interneurones did not receive a descending tectal input. About 80% of the NVspo- interneurones were activated from the orofacial primary projection fields within cytoarchitectonic areas 3a and 3b of the coronal gyrus. This input was topographically organized and the neurones were activated from the same oral and perioral region of the periphery as the cortical region from which the descending projections themselves originated. Minimum latencies indicated a monosynaptic connection. The convergence profile onto the NVspo- interneurones appeared unique as compared with interneurones located in the intertrigeminal area. Aspects of the possible functional roles of the NVspo- neurones are discussed in relation to ongoing oro-facial (masticatory) movements. The properties of a selected sample of NVspo- interneurones, which were antidromically activated from the digastric subnucleus of the trigeminal motor nucleus, are reported in a companion paper (Olsson and Westberg 1991).Abbreviations AD Antidromic - Alv inf Inferior alveolar nerve - C2 2nd cervical spinal nerve - C2mt Motor nuclei of the 2nd cervical spinal segment - Co Contralateral - Coll sup Colliculus superior - cor Coronal sulcus - D Dorsal - Dig Digastric nerve - FTC Central tegmental field - HRP Horseradish peroxidase - Ip Ipsilateral - Ling Lingual nerve - M Medial - Mass Masseteric nerve - MGP Principal nucleus of the medial geniculate body - Mx Maxillary nerve - Mx-w Infraorbital nerve, branch to whiskers and lip - NintV Intertrigeminal area - NR Nucleus ruber - NVmt Trigeminal motor nucleus - NVsnpr Main sensory trigeminal nucleus - NVspo--- Subnucleus--- of the oral nucleus of the spinal trigeminal tract - OD Orthodromic - orb Orbital sulcus - prsyl Presylvian sulcus - SCS Superior colliculus, superficial layer - SCI Superior colliculus, intermediate layer - SCD Superior colliculus, deep layer - T Threshold stimulus - V Trigeminal nerve/ tract - VII Facial nerve - Vrm Trigeminal motor root - WGA-HRP Wheat germ agglutinin-conjugated horseradish peroxidase