GABAergic and glycinergic inhibitory mechanisms in the lamprey respiratory control.
The specific role of gamma-aminobutyric acid (GABA) and glycine receptors in respiratory rhythm generation and pattern formation was investigated in in vitro brainstem preparations from adult lampreys by analyzing the changes in respiratory activity induced by bath application of specific antagonists, agonists, and uptake blockers. GABAA receptor blockade by bicuculline or picrotoxin increased both the frequency and amplitude of respiratory bursts. Similar effects were observed after glycine receptor blockade by strychnine. Combined bath application of bicuculline and strychnine markedly increased the frequency and amplitude of respiratory activity. These responses were associated, especially at the higher concentrations of the two drugs, with the appearance of tonic activity and irregular, high-frequency bursts followed by transient depression of respiratory activity. GABAA and glycine receptor agonists suppressed respiratory activity. These effects were prevented by bath application of the corresponding specific antagonists. GABAB receptor blockade by 2-hydroxysaclofen reduced the respiratory frequency but increased the peak amplitude of respiratory bursts. Activation of GABAB receptors suppressed respiratory activity. These responses were prevented by 2-hydroxysaclofen. Neither GABAC receptor agonist nor antagonist had any effects on respiration. Depression of both the frequency and amplitude of respiratory bursts was induced by blockades of GABA and glycine uptake using, respectively, nipecotic acid and sarcosine. The results suggest that GABA- and glycine-mediated inhibition is not essential for respiratory rhythm generation in the adult lamprey, although it appears to exert potent influences on respiratory activity and to have a role in maintaining a stable and regular breathing pattern.
Bongianni
Fulvia
F
Dipartimento di Scienze Fisiologiche, Universita' degli Studi di Firenze, Viale G.B. Morgagni 63, I-50134 Firenze, Italy.
Mutolo
Donatella
D
Nardone
Furio
F
Pantaleo
Tito
T
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001933:Brain Stem / Q000187:drug effects / Q000378:metabolism*; D004525:Efferent Pathways / Q000187:drug effects / Q000378:metabolism; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005998:Glycine / Q000378:metabolism*; D018684:Glycine Agents; D009415:Nerve Net / Q000187:drug effects / Q000378:metabolism; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009557:Nipecotic Acids / Q000494:pharmacology; D048428:Petromyzon; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism; D018080:Receptors, GABA-B / Q000187:drug effects / Q000378:metabolism; D018009:Receptors, Glycine / Q000187:drug effects / Q000378:metabolism; D012125:Respiratory Center / Q000187:drug effects / Q000378:metabolism*; D012143:Respiratory Physiological Phenomena / Q000187:drug effects*; D012521:Sarcosine / Q000494:pharmacology; D013331:Strychnine / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018755:GABA Agonists; D018756:GABA Antagonists; D018684:Glycine Agents; D009557:Nipecotic Acids; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D018009:Receptors, Glycine; C030278:nipecotic acid; D005680:gamma-Aminobutyric Acid; D013331:Strychnine; D005998:Glycine; D012521:Sarcosine