Effects of injecting GABAergic agents into the medullary reticular formation upon swallowing induced by the superior laryngeal nerve stimulation in decerebrate cats

• Published in: Neuroscience research Vol. 51; no. 4; pp. 395 - 404
• Main Authors: Harada, Hirofumi, Takakusaki, Kaoru, Kita, Shinichi, Matsuda, Mitsuyoshi, Nonaka, Satoshi, Sakamoto, Takashi
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 01.04.2005
• Subjects: Animals; Bicuculline; Bicuculline - administration & dosage; Brain Mapping; Cats; Cough - physiopathology; Coughing; Decerebrate State; Deglutition - drug effects; Deglutition - physiology; Electric Stimulation; Electromyography; GABA Agents - administration & dosage; Gagging - drug effects; Gagging - physiology; Injections, Intraventricular; Laryngeal Nerves - physiology; Larynx - physiology; Microinjections; Muscimol - administration & dosage; Pharynx - innervation; Pharynx - physiology; Respiratory neurons; Reticular Formation - drug effects; Reticular Formation - physiology; Swallowing; Respiratory neurons; Swallowing; Coughing; Bicuculline
• ISSN: 0168-0102; 1872-8111
• DOI: 10.1016/j.neures.2004.12.007

The purpose of this study was to elucidate the role of the GABAergic system in the medullary reticular formation (MRF) in the control of swallowing. In acutely decerebrated cats ( n = 12), swallowing was induced by electrical stimulation (0.3–6 V at 10–20 Hz for 10–20 s every minute) applied to the superior laryngeal nerve (SLN). The stimulus intensity was adjusted so that swallowing was induced two or four times during the period of the stimulation. Bicuculline, a GABA A receptor antagonist, was then injected (0.10–0.15 μl, 5 mM) into the MRF through a stereotaxically placed glass micropipette. In a total of 62 injections, 19 injections (30.6%) increased the frequency of SLN-induced swallowing when it was injected into the lateral part of the MRF corresponding to the nucleus reticularis parvocellularis (NRPv). In eight of the effective injections (42.1%) which increased the frequency of SLN-induced swallowing, SLN stimulation also induced coughing. With two injections, stimulation of the SLN-induced coughing but not facilitation of swallowing. On the other hand, an injection of 0.10–0.15 μl of 5 mM muscimol, a GABA A receptor agonist, into the NRPv decreased the frequency of SLN-induced swallowing. These results suggest that the NRPv neurons which are responsible for evoking swallowing are under the tonic inhibitory control of the GABAergic system.