Functional Role of the Substantia Nigra Pars Reticulate on Electrically Induced Vocalization in Ketamine Anesthetized Cats

概要

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The midbrain periaqueductal gray (PAG) region where electrical stimulation induces vocalization receives both excitatory inputs from the motor cortex and the limbic structures and inhibitory in-puts which contain GABA as a transmitter substance. To know whether the substantia nigra pars reticulata (SNr) is one of origin of the GABA inhibitory system, effects of GABA antagonist (bicuculline methiodide (BIC)), agonist (muscimol) or local anesthetics (lidocaine) into the SNr on the PAG threshold for vocalization were investigated in ketamine anesthetized cats.<BR>After injection of BIC into the SNr, the PAG threshold for vocalization increased by about 20 to 100% for 60 to 90 min. With the higher stimulus intensity, vocalization was induced with similar motor pattern to that was observed before the injection, although the spontaneous respiratory cycle tended to be longer after BIC injection. This suggests that the BIC injection altered the vocalization threshold not at medulla but at midbrain.<BR>While, injection of GABA A agonist, muscimol, or local anesthetics decreased the PAG threshold for vocalization.<BR>These results indicate that the SNr is a plausible origin of the GABA A inhibitory system which regulates the motor outflow for vocalization, which comes from the limbic structures to the lower brain structures via the PAG area.
The Japan Laryngological Associationの論文