title: Inhibitory control of ascending glutamatergic projections to the lamprey respiratory rhythm generator.
abstract: Neurons within the vagal motoneuron region of the lamprey have been shown to modulate respiratory activity via ascending excitatory projections to the paratrigeminal respiratory group (pTRG), the proposed respiratory rhythm generator. The present study was performed on in vitro brainstem preparations of the lamprey to provide a characterization of ascending projections within the whole respiratory motoneuron column with regard to the distribution of neurons projecting to the pTRG and related neurochemical markers. Injections of Neurobiotin were performed into the pTRG and the presence of glutamate, GABA and glycine immunoreactivity was investigated by double-labeling experiments. Interestingly, retrogradely labeled neurons were found not only in the vagal region, but also in the facial and glossopharyngeal motoneuron regions. They were also present within the sensory octavolateral area (OLA). The results show for the first time that neurons projecting to the pTRG are immunoreactive for glutamate, surrounded by GABA-immunoreactive structures and associated with the presence of glycinergic cells. Consistently, GABAA or glycine receptor blockade within the investigated regions increased the respiratory frequency. Furthermore, microinjections of agonists and antagonists of ionotropic glutamate receptors and of the GABAA receptor agonist muscimol showed that OLA neurons do not contribute to respiratory rhythm generation. The results provide evidence that glutamatergic ascending pathways to the pTRG are subject to a potent inhibitory control and suggest that disinhibition is one important mechanism subserving their function. The general characteristics of inhibitory control involved in rhythmic activities, such as respiration, appear to be highly conserved throughout vertebrate evolution.
authors.affiliation: Dipartimento di Medicina Sperimentale e Clinica, Sezione Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, 50134 Firenze, Italy.
authors.forename: Elenia
authors.initials: E
authors.lastname: Cinelli
authors.affiliation: Dipartimento di Medicina Sperimentale e Clinica, Sezione Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, 50134 Firenze, Italy.
authors.forename: Donatella
authors.initials: D
authors.lastname: Mutolo
authors.affiliation: Dipartimento di Medicina Sperimentale e Clinica, Sezione Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, 50134 Firenze, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Contini
authors.affiliation: Dipartimento di Medicina Sperimentale e Clinica, Sezione Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, 50134 Firenze, Italy.
authors.forename: Tito
authors.initials: T
authors.lastname: Pantaleo
authors.affiliation: Dipartimento di Medicina Sperimentale e Clinica, Sezione Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, 50134 Firenze, Italy. Electronic address: fulvia.bongianni@unifi.it.
authors.forename: Fulvia
authors.initials: F
authors.lastname: Bongianni
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001933:Brain Stem / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D005930:Glossopharyngeal Nerve / Q000187:drug effects; D018698:Glutamic Acid / Q000032:analysis; D005998:Glycine / Q000032:analysis; D018684:Glycine Agents / Q000494:pharmacology; D007798:Lampreys; D009046:Motor Neurons / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D011963:Receptors, GABA-A / Q000502:physiology*; D018009:Receptors, Glycine / Q000502:physiology*; D012119:Respiration; D013331:Strychnine / Q000494:pharmacology; D014630:Vagus Nerve / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000032:analysis
chemical_list: D058787:GABA-A Receptor Antagonists; D018684:Glycine Agents; D011963:Receptors, GABA-A; D018009:Receptors, Glycine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D013331:Strychnine; D005998:Glycine; D001640:Bicuculline
keywords: control of breathing; glutamatergic transmission; inhibitory amino acids