Effects of orbital cortical stimulation on facial motoneurons in the cat

Mechanisms regulating the activity of facial nucleus motoneurons--III. Synaptic influences from the cerebral cortex and subcortical structures

Peculiarities of synaptic processes in facial motoneurons evoked by stimulation of various regions of the cerebral cortex and subcortical structures were studied in acute experiments on cats by intracellular recording technique. Stimulation of the motor cortex as well as gyrus proreus and pyramidal tract was shown to evoke polysynaptic excitatory and inhibitory postsynaptic potentials in facial motoneurons. Stimulation of the lateral hypothalamus produced exclusively excitatory polysynaptic effects. It was also found that stimulation of the head of nucleus caudatus and globus pallidus evokes a polysynaptic activation in facial motoneurons, while stimulation of nucleus amygdala centralis leads to mono- and polysynaptic excitation of these neurons. Convergence of the above effects on the same motoneurons is shown to exist. Possible pathways and mechanisms of descending influences on the activity of facial motoneurons is discussed.

Mechanisms regulating the activity of facial nucleus motoneurons--IV. Influences from the brainstem structures

Peculiarities of synaptic processes of facial motoneurons evoked by stimulation of brainstem structures were studied in acute experiments on anaesthetized and immobilized cats by intracellular recording technique. It was shown that stimulation of nucleus reticularis parvocellularis of the medulla oblongata as well as interstitial nucleus of Cajal, nucleus Darkschewitsch, periaqueductal gray and pretectal area evokes in facial motoneurons monosynaptic excitatory postsynaptic potentials accompanied by single action potentials. Somatic localization of synapses under study is supposed. Convergence of inputs is revealed. Functional role of the midbrain structures as intermediate relays transmitting descending signals to the facial nucleus is discussed.

Peculiarities of cerebellar excitation of facial nucleus motoneurons

Excitatory postsynaptic potentials (EPSPs) of facial nucleus motoneurons evoked by stimulation of the cerebellar nuclei, were studied in anesthetized cats. It is shown that the stimulation of nucleus interpositus and dentatus evoked mono-, oligo- and polysynaptic EPSPs in facial motoneurons. From the experiments with lesions in the red nucleus it is suggested that this structure is implicated in the mechanisms and pathways through which the cerebellar control over facial nucleus motoneurons is realized.