N. Ando

Chapter 19 Synaptic organization of the vestibulo-collic pathways from six semicircular canals to motoneurons of different neck muscles

The pattern of inputs from six semicircular canals to neck motoneurons was investigated by stimulating six ampullary nerves electrically and recording intracellular potentials from motoneurons of the rectus capitis dorsalis (RD), the complexus (COMP) and the obliquus capitis caudalis (OCA) muscles at the upper cervical cord of the cat. RD and COMP motoneurons received disynaptic excitation from bilateral anterior and contralateral horizontal ampullary nerves and disynaptic inhibition from bilateral posterior and ipsilateral horizontal ampullary nerves. OCA motoneurons received excitation from ipsilateral vertical and contralateral horizontal ampullary nerves and inhibition from contralateral vertical and ipsilateral horizontal ampullary nerves. Ipsilateral disynaptic inhibitory postsynaptic potentials and contralateral disynaptic excitatory postsynaptic potentials to these motoneurons were mediated by the medial longitudinal fasciculus (MLF) and the other postsynaptic potentials by the extra-MLF pathways. The results indicated that motoneurons of a neck muscle have its own characteristic pattern of inputs from six semicircular canals.

Synaptic Organization of the Ventral Lateral Thalamus and the Reticular Nucleus in the Cerebello-Thalamo- Cortical System

To investigate the input-output organization of the ventrolateral nucleus and its related reticular nucleus, intracellular recordings were performed from thalamocortical neurons (TCNs) and reticular nucleus neurons (RNNs) in anesthetized cats, while stimulating the cerebellum and the motor cortex. Single TCNs in the VL receive monosynaptic excitatory and disynaptic inhibitory inputs from both the dentate and interpositus nucleus. They receive disynaptic inhibition from the motor cortex via thalamic RNNs and interneurons in addition to corticothalamic monosynaptic excitation. A TCN has the strongest excitatory and inhibitory input from the cortical area to which it projects. This inhibition is evoked from the wider cortical area than the excitation. RNNs receive disynaptic excitationoriz from the dentate and interpositus nuclei via axon collaterals of TCNs and monosynaptic excitation from the cortex. Terminal arbation of single HRP-labelled RNNs is very wide in the portion of the VL where cerebellar afferents terminate. Positive feedback loop between the VL and the motor cortex and wider negative feedback to the VL may be a neural substrate for dynamic focussing mechanisms for signal transmission from cerebellar output neurons to pyramidal tract neurons in the motor cortex.

1606 Myological classification of neck muscles and input patterns from six semicircular canal nerves to motoneurons of different muscle groups

1606 MYOLOGICAL CLASSIFICATION OF NECK MUSCLES AND INPUT PATTERNS FROM SIX SEMICIRCULAR CANAL NERVES TO MOTONEURONS OF DIFFERENT MUSCLE GROUPS. YURIKO SUGIUCHI’. TAKAHIRO FUTAMI*. NAOTO AND03. YOSHIKAZU SHINODA4a ‘Dent. of Otokwneol.. and 4DeDt of Phvsiol. Sch. of Med.. Tokvo Medical and Dental Univ.. Bunkyo-ku. Tokvo. 113. *Lab. for Neural Svstems. Riken. Wako. Saitama. 3Deot. of Neurosure.. Sch. of Med.. Hamamatsu Univ., Shizuoka. Janan.