title: Somatostatin 2a receptors are not expressed on functionally identified respiratory neurons in the ventral respiratory column of the rat.
abstract: Microinjection of somatostatin (SST) causes site-specific effects on respiratory phase transition, frequency, and amplitude when microinjected into the ventrolateral medulla (VLM) of the anesthetized rat, suggesting selective expression of SST receptors on different functional classes of respiratory neurons. Of the six subtypes of SST receptor, somatostatin 2a (sst2a ) is the most prevalent in the VLM, and other investigators have suggested that glutamatergic neurons in the preBötzinger Complex (preBötC) that coexpress neurokinin-1 receptor (NK1R), SST, and sst2a are critical for the generation of respiratory rhythm. However, quantitative data describing the distribution of sst2a in respiratory compartments other than preBötC, or on functionally identified respiratory neurons, is absent. Here we examine the medullary expression of sst2a with particular reference to glycinergic/expiratory neurons in the Bötzinger Complex (BötC) and NK1R-immunoreactive/inspiratory neurons in the preBötC. We found robust sst2a expression at all rostrocaudal levels of the VLM, including a large proportion of catecholaminergic neurons, but no colocalization of sst2a and glycine transporter 2 mRNA in the BötC. In the preBötC 54% of sst2a -immunoreactive neurons were also positive for NK1R. sst2a was not observed in any of 52 dye-labeled respiratory interneurons, including seven BötC expiratory-decrementing and 11 preBötC preinspiratory neurons. We conclude that sst2a is not expressed on BötC respiratory neurons and that phasic respiratory activity is a poor predictor of sst2a expression in the preBötC. Therefore, sst2a is unlikely to underlie responses to BötC SST injection, and is sparse or absent on respiratory neurons identified by classical functional criteria. J. Comp. Neurol. 524:1384-1398, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Faculty of Medicine & Health Sciences, Macquarie University, NSW, Australia.
authors.forename: Sheng
authors.initials: S
authors.lastname: Le
authors.affiliation: Faculty of Medicine & Health Sciences, Macquarie University, NSW, Australia.
authors.forename: Anita J
authors.initials: AJ
authors.lastname: Turner
authors.affiliation: ARC Center of Excellence for Nanoscale BioPhotonics, Macquarie University, NSW, Australia.
authors.forename: Lindsay M
authors.initials: LM
authors.lastname: Parker
authors.affiliation: Neuroscience Research Australia, Randwick, NSW, Australia.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Burke
authors.affiliation: Department of Pharmacology, University of Virginia, Charlottesville, Virginia, USA.
authors.forename: Natasha N
authors.initials: NN
authors.lastname: Kumar
authors.affiliation: Faculty of Medicine & Health Sciences, Macquarie University, NSW, Australia.
authors.forename: Ann K
authors.initials: AK
authors.lastname: Goodchild
authors.affiliation: Faculty of Medicine & Health Sciences, Macquarie University, NSW, Australia.
authors.forename: Simon
authors.initials: S
authors.lastname: McMullan
mesh_terms: D000818:Animals; D001703:Biophysics; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D004558:Electric Stimulation; D050487:Glycine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008845:Microinjections; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000378:metabolism; D017481:Receptors, Somatostatin / Q000235:genetics / Q000378:metabolism*; D012125:Respiratory Center / Q000166:cytology* / Q000187:drug effects; D012235:Rhodamines / Q000378:metabolism; D013004:Somatostatin / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D003911:Dextrans; C067661:Fluoro-Ruby; D050487:Glycine Plasma Membrane Transport Proteins; D018040:Receptors, Neurokinin-1; D017481:Receptors, Somatostatin; D012235:Rhodamines; C106140:somatostatin receptor sst2A; D013004:Somatostatin; D014446:Tyrosine 3-Monooxygenase; D002795:Choline O-Acetyltransferase
keywords: preBötzinger Complex; respiratory neurons; somatostatin